Cell Structure & Function

Subtopic: Types of Cell Junctions and Their Functions

Keyword Definitions:

• Adhering Junctions: Also called desmosomes, these junctions fasten cells together into strong sheets, maintaining tissue structure under mechanical stress.

• Tight Junctions: Form impermeable barriers that prevent leakage of extracellular molecules across layers of cells.

• Gap Junctions: Channels connecting the cytoplasm of adjacent cells, allowing passage of ions and small molecules for cell-to-cell communication.

• Synaptic Junctions: Specialized junctions in neurons where neurotransmitters transmit signals from one neuron to another across synapses.

• Cell Communication: The process by which cells exchange information via chemical or electrical signals.

• Extracellular Matrix: Network of molecules surrounding cells providing structural and biochemical support.

• Neurotransmitters: Chemical messengers released by neurons to transmit signals across synaptic junctions.

Lead Question – 2022 (Abroad)
Match List-I with List-II
List-I
(a) Adhering junctions
(b) Tight junction
(c) Gap junctions
(d) Synaptic junctions
List-II
(i) Establish a barrier that prevents leakage of extracellular fluid across a layer of cells
(ii) Functions like rivets and fasten cells junctions together into strong sheets
(iii) Pass information through neurotransmitters from one cell to another
(iv) Provide cytoplasmic channels from one cell to an adjacent cell for communication
Choose the correct answer from the options given below:
1. (iv), (iii), (ii), (i)
2. (i), (iii), (ii), (iv)
3. (ii), (i), (iv), (iii)
4. (i), (ii), (iii), (iv)

Explanation:
Correct answer is option 3. Adhering junctions act like rivets, fastening cells together into strong sheets to maintain tissue integrity. Tight junctions establish impermeable barriers, preventing leakage of extracellular fluid. Gap junctions provide cytoplasmic channels for communication between adjacent cells. Synaptic junctions transmit signals using neurotransmitters from one neuron to another. These four types of junctions are essential for tissue structure, intercellular communication, and signal transduction. Understanding their distinct roles helps explain how cells coordinate function in multicellular organisms. The correct matching ensures each junction type is paired with its precise function, as demonstrated in option 3.

1. Which junction type allows direct cytoplasmic exchange between adjacent cells?
1. Adhering junction
2. Tight junction
3. Gap junction
4. Synaptic junction
Explanation: Correct answer is gap junction. Gap junctions provide cytoplasmic channels connecting adjacent cells, enabling passage of ions, nutrients, and signaling molecules for rapid communication. They are crucial for synchronized activity in cardiac and smooth muscle tissues, and other cellular networks.

2. Which junction prevents leakage of molecules across epithelial layers?
1. Gap junction
2. Tight junction
3. Adhering junction
4. Synaptic junction
Explanation: Correct answer is tight junction. Tight junctions seal adjacent epithelial cells, creating a barrier to prevent the movement of ions, water, and other molecules between cells. This is vital for tissue compartmentalization and maintaining homeostasis across epithelial layers.

3. Which junction provides mechanical strength by linking cells into sheets?
1. Tight junction
2. Synaptic junction
3. Adhering junction
4. Gap junction
Explanation: Correct answer is adhering junction. Adhering junctions, also called desmosomes, act like rivets fastening cells together, distributing mechanical stress across tissue sheets. They are particularly important in epithelial tissues and cardiac muscle where structural stability is required.

4. Which junction is specialized for neuron-to-neuron signaling?
1. Gap junction
2. Adhering junction
3. Tight junction
4. Synaptic junction
Explanation: Correct answer is synaptic junction. Synaptic junctions are chemical synapses where neurotransmitters are released from the presynaptic neuron and received by postsynaptic receptors. This allows rapid, directional communication essential for neural network function and signal propagation.

5. Which junction type is critical for synchronized contraction in cardiac tissue?
1. Adhering junction
2. Gap junction
3. Tight junction
4. Synaptic junction
Explanation: Correct answer is gap junction. Gap junctions in cardiac muscle allow ions to flow directly between cells, facilitating synchronized contraction of the heart muscle. This electrical coupling ensures efficient and coordinated heartbeat.

6. Which junction is also called desmosome?
1. Tight junction
2. Adhering junction
3. Gap junction
4. Synaptic junction
Explanation: Correct answer is adhering junction. Desmosomes are specialized adhering junctions that link the cytoskeletons of adjacent cells via cadherin proteins, providing mechanical strength and resistance to tissue stress.

7. Assertion-Reason:
Assertion (A): Tight junctions are crucial for maintaining compartmentalization in tissues.
Reason (R): They prevent leakage of extracellular fluid between cells.
1. Both A and R are true, R explains A
2. Both A and R are true, R does not explain A
3. A true, R false
4. A false, R true
Explanation: Correct answer is option 1. Tight junctions prevent extracellular leakage, thereby maintaining distinct compartments across epithelial and endothelial layers. This explains why they are crucial for tissue integrity and functional compartmentalization.

8. Matching Type:
Match the junction with its main component:
A. Adhering junction – (i) Cadherins
B. Tight junction – (ii) Claudins and Occludins
C. Gap junction – (iii) Connexins
D. Synaptic junction – (iv) Neurotransmitters
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–i, D–ii
4. A–iv, B–iii, C–ii, D–i
Explanation: Correct answer is option 1. Adhering junctions use cadherins for adhesion, tight junctions use claudins/occludins for sealing, gap junctions are formed by connexins, and synaptic junctions rely on neurotransmitters for signal transmission.

9. Fill in the Blanks:
________ junctions function as rivets to fasten cells into strong sheets.
1. Gap
2. Tight
3. Adhering
4. Synaptic
Explanation: Correct answer is adhering. Adhering junctions mechanically link adjacent cells via cadherins and cytoskeletal elements, forming strong cellular sheets, especially in epithelial and cardiac tissues. They help maintain tissue integrity under mechanical stress.

10. Choose the correct statements:
Statement I: Gap junctions allow direct communication between cells.

Chapter: Cell Organelles; Topic: Plastids and Their Functions; Subtopic: Types of Plastids

Keyword Definitions:

• Chromoplasts: Plastids containing pigments like carotenoids, responsible for red, orange, or yellow colors in fruits and flowers.

• Amyloplasts: Non-pigmented plastids that store starch granules in roots and tubers.

• Elaioplasts: Colorless plastids specialized for storing oils and fats.

• Aleuroplasts: Protein-storing plastids found in seeds.

• Starch: Polysaccharide used as energy storage in plants.

• Carotene: Orange pigment found in chromoplasts.

• Oil and Fats: Lipid molecules stored in elaioplasts for energy.

• Proteins: Macromolecules stored in aleuroplasts, providing nutrients for seed germination.

Lead Question – 2022 (Abroad)
Match List-I with List-II:
List-I
(a) Chromoplasts
(b) Amyloplasts
(c) Elaioplasts
(d) Aleuroplasts
List-II
(i) Proteins
(ii) Oil and fats
(iii) Starch
(iv) Carotene
Choose the correct answer from the options below:
1. (iv) (i) (iii) (ii)
2. (iv) (iii) (ii) (i)
3. (iv) (ii) (iii) (i)
4. (iv) (iii) (i) (ii)

Explanation:
Correct answer is option 4. Chromoplasts contain pigments like carotene (iv), responsible for red, orange, or yellow coloration in fruits and flowers. Amyloplasts store starch granules (iii) as energy reserves in roots and tubers. Elaioplasts are specialized for storing oils and fats (ii). Aleuroplasts store proteins (i), providing nutrients for seed germination. This classification of plastids demonstrates functional specialization, with different types of plastids contributing to storage, coloration, or metabolism in plants. Matching List-I to List-II helps in understanding plastid roles in plant physiology and adaptation to ecological functions.

1. Which plastid is responsible for storing starch in plants?
1. Chromoplasts
2. Amyloplasts
3. Elaioplasts
4. Aleuroplasts
Explanation: Correct answer is Amyloplasts. Amyloplasts are non-pigmented plastids specialized for storing starch granules in roots, tubers, and seeds. They play a key role in energy storage and metabolism, providing a source of glucose for plant growth and germination. Unlike chromoplasts, they do not contain pigments, and unlike elaioplasts or aleuroplasts, they store carbohydrates rather than lipids or proteins.

2. Which plastid contains carotenoid pigments for coloration?
1. Amyloplasts
2. Chromoplasts
3. Elaioplasts
4. Aleuroplasts
Explanation: Correct answer is Chromoplasts. Chromoplasts are plastids containing carotenoid pigments such as carotene, giving yellow, orange, or red coloration to fruits and flowers. These pigments attract pollinators and aid in seed dispersal. Chromoplasts differ from chloroplasts, which contain chlorophyll for photosynthesis, and from storage plastids like amyloplasts or elaioplasts that store starch or lipids.

3. Elaioplasts primarily store:
1. Carotenoids
2. Proteins
3. Starch
4. Oils and fats
Explanation: Correct answer is Oils and fats. Elaioplasts are colorless plastids specialized in lipid storage, providing energy for seed germination and metabolic processes. They are abundant in oil-rich seeds. Unlike amyloplasts storing starch or aleuroplasts storing proteins, elaioplasts focus on lipid accumulation, highlighting plastid functional specialization in plants.

4. Aleuroplasts are specialized for storing:
1. Carotenoids
2. Proteins
3. Starch
4. Lipids
Explanation: Correct answer is Proteins. Aleuroplasts are protein-storing plastids found in seeds, providing nutrients during germination. They are distinct from amyloplasts (starch), chromoplasts (pigments), and elaioplasts (lipids). Their stored proteins supply amino acids for early growth of seedlings, ensuring proper development.

5. Which of the following plastids contributes to fruit coloration?
1. Aleuroplasts
2. Elaioplasts
3. Chromoplasts
4. Amyloplasts
Explanation: Correct answer is Chromoplasts. Chromoplasts contain pigments such as carotene that impart yellow, orange, or red colors to fruits and flowers. This coloration aids in attracting pollinators and seed dispersers. Unlike storage plastids (amyloplasts, elaioplasts, aleuroplasts), chromoplasts function primarily in pigmentation rather than nutrient storage.

6. Which plastid is colorless and stores starch?
1. Chromoplast
2. Amyloplast
3. Elaioplast
4. Aleuroplast
Explanation: Correct answer is Amyloplast. Amyloplasts are non-pigmented plastids storing starch granules. They provide an energy reserve for plants, especially in roots and tubers. Being colorless distinguishes them from chromoplasts and chloroplasts. Their specialization exemplifies plastid diversity for specific plant functions.

7. Assertion-Reason:
Assertion (A): Chromoplasts are responsible for coloration in fruits and flowers.
Reason (R): Chromoplasts contain carotenoid pigments like carotene.
1. Both A and R are true, R is correct explanation of A
2. Both A and R are true, R is not correct explanation
3. A is true, R is false
4. A is false, R is true
Explanation: Correct answer is option 1. Chromoplasts contain carotenoids such as carotene, responsible for red, orange, and yellow colors in fruits and flowers. This pigmentation attracts pollinators and aids in seed dispersal. The reason explains the function stated in the assertion, demonstrating the link between pigment content and coloration.

8. Matching Type:
Match List-I (Plastids) with List-II (Contents):
A. Chromoplast – (i) Carotene
B. Amyloplast – (ii) Starch
C. Elaioplast – (iii) Oil and fats
D. Aleuroplast – (iv) Proteins
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–i, B–iii, C–ii, D–iv
4. A–iv, B–ii, C–i, D–iii
Explanation: Correct answer is option 1. Chromoplasts store carotene, amyloplasts store starch, elaioplasts store oils and fats, and aleuroplasts store proteins. This matching clarifies the functional diversity of plastids and their role in storage and pigmentation in plant tissues.

9. Fill in the Blanks:
Plastids that store __________ are called elaioplasts.
1. Starch
2. Carotenoids
3. Oils and fats
4. Proteins
Explanation: Correct answer is Oils and fats. Elaioplasts are colorless plastids specialized in lipid storage, providing energy for seed germination. They are distinct from amyloplasts (starch), chromoplasts (pigments), and aleuroplasts (proteins). Their presence in seeds and fruits ensures energy availability for early growth.

10. Choose the correct statements:
Statement I: Amyloplasts are non-pigmented plastids storing starch.
Statement II:</

Topic: Endomembrane System; Subtopic: Membrane-bound Organelles

Keyword Definitions:

• Endomembrane System: Network of membrane-bound organelles including ER, Golgi apparatus, lysosomes, and vesicles, coordinating cellular functions.

• Membrane-bound Organelles: Cellular structures surrounded by lipid bilayers that compartmentalize different biochemical processes.

• Mitochondria: Double-membrane organelle responsible for ATP production through oxidative phosphorylation, not part of the endomembrane system.

• Chloroplasts: Double-membrane organelle in plants and algae that performs photosynthesis, also not part of the endomembrane system.

• Endoplasmic Reticulum (ER): Organelle of the endomembrane system involved in protein and lipid synthesis.

• Golgi Apparatus: Organelle modifying, sorting, and packaging proteins and lipids from the ER.

• Lysosomes: Vesicles containing hydrolytic enzymes for intracellular digestion, part of the endomembrane system.

• Vesicles: Membrane-bound sacs transporting materials between organelles and plasma membrane.

Lead Question - 2022 (Abroad)
Given below are two statements :
Statement - I : Membrane-bound organelles of the endomembrane system coordinate cellular functions.
Statement - II : Mitochondria and chloroplasts are not considered a part of the endomembrane system.
In the light of the above statements, choose the most appropriate answer from the options given below:
1. Statement - I is correct but Statement - II is incorrect
2. Statement - I is incorrect but Statement - II is correct
3. Both Statement - I and Statement - II are correct
4. Both Statement - I and Statement - II are incorrect
Explanation: The correct answer is Both Statement - I and Statement - II are correct. The endomembrane system includes ER, Golgi apparatus, lysosomes, and vesicles, which coordinate cellular processes such as protein and lipid trafficking, and intracellular digestion. Mitochondria and chloroplasts are double-membrane organelles with independent DNA and ribosomes, carrying out energy conversion and photosynthesis. They are functionally and structurally distinct from the endomembrane system. Therefore, Statement I correctly describes the coordination role of the endomembrane system, and Statement II correctly identifies that mitochondria and chloroplasts are excluded from this system, highlighting key organizational principles of eukaryotic cells.

1. Single Correct Answer Type:
Which organelle modifies and packages proteins synthesized in the ER?
1. Lysosome
2. Golgi Apparatus
3. Mitochondria
4. Chloroplast
Explanation: The correct answer is Golgi Apparatus. Proteins synthesized in the endoplasmic reticulum are transported to the Golgi apparatus in vesicles, where they undergo modification, sorting, and packaging for secretion or delivery to other organelles. Lysosomes degrade macromolecules, mitochondria produce ATP, and chloroplasts perform photosynthesis. This system ensures proper trafficking and functionality of proteins and lipids, essential for maintaining cellular organization and endomembrane system efficiency in eukaryotic cells.

2. Single Correct Answer Type:
Which of the following organelles is part of the endomembrane system?
1. Mitochondria
2. Chloroplast
3. Lysosome
4. Peroxisome
Explanation: The correct answer is Lysosome. Lysosomes are membrane-bound organelles containing hydrolytic enzymes and are integral to the endomembrane system, receiving proteins and lipids from the ER and Golgi apparatus for intracellular digestion. Mitochondria and chloroplasts are double-membrane organelles with their own DNA and ribosomes, performing energy conversion and photosynthesis. Peroxisomes are not classically part of the endomembrane system. Lysosomes play a central role in cellular homeostasis, recycling macromolecules, and coordinating with other endomembrane components.

3. Single Correct Answer Type:
Which organelle stores calcium and participates in lipid synthesis as part of the endomembrane system?
1. Rough ER
2. Smooth ER
3. Mitochondria
4. Chloroplast
Explanation: The correct answer is Smooth ER. Smooth endoplasmic reticulum is a membrane-bound organelle of the endomembrane system involved in lipid synthesis, detoxification, and calcium storage. Rough ER is associated with protein synthesis. Mitochondria and chloroplasts are energy-related organelles with their own DNA and ribosomes, not part of the endomembrane system. Smooth ER interacts with other organelles like Golgi and vesicles, facilitating coordinated cellular functions and maintaining the biochemical compartmentalization characteristic of the endomembrane system.

4. Single Correct Answer Type:
Which statement correctly describes mitochondria and chloroplasts?
1. Part of endomembrane system
2. Double-membrane organelles with independent DNA
3. Synthesize proteins for lysosomes
4. Store digestive enzymes
Explanation: The correct answer is Double-membrane organelles with independent DNA. Mitochondria and chloroplasts contain their own circular DNA and ribosomes, enabling semi-autonomous protein synthesis. They are not part of the endomembrane system. Their double-membrane structure distinguishes them from ER, Golgi, and lysosomes. They are responsible for energy conversion, ATP production in mitochondria, and photosynthesis in chloroplasts. Their unique features support endosymbiotic theory, explaining the evolutionary origin of eukaryotic cells and their compartmentalized organelles.

5. Single Correct Answer Type:
Which vesicles transport proteins from ER to Golgi apparatus?
1. Lysosomes
2. Transport Vesicles
3. Peroxisomes
4. Endosomes
Explanation: The correct answer is Transport Vesicles. Transport vesicles are membrane-bound sacs that bud off from the endoplasmic reticulum and carry newly synthesized proteins to the Golgi apparatus for modification and sorting. Lysosomes degrade macromolecules, peroxisomes metabolize fatty acids, and endosomes mediate endocytosis. Transport vesicles are central to the endomembrane system, ensuring proper delivery of proteins, maintaining cellular homeostasis, and coordinating inter-organelle communication essential for eukaryotic cell functionality.

6. Single Correct Answer Type:
Which organelle receives and digests macromolecules in the endomembrane system?
1. Lysosome
2. Smooth ER
3. Mitochondria
4. Chloroplast
Explanation: The correct answer is Lysosome. Lysosomes contain hydrolytic enzymes to digest macromolecules delivered via endocytosis or from intracellular organelles. They are part of the endomembrane system, interacting with Golgi-derived vesicles. Smooth ER participates in lipid synthesis and calcium storage, mitochondria in ATP production, and chloroplasts in photosynthesis. Lysosomes maintain cellular homeostasis, recycle biomolecules, and enable coordinated intracellular processes with other endomembrane organelles.

7. Assertion-Reason Type:
Assertion (A): The endomembrane system coordinates intracellular transport.
Reason (R): Mitochondria and chloroplasts are independent and not included in the endomembrane system.
1. Both A and R are correct, and R is the correct explanation of A
2. Both A and R are correct, but R is not the correct explanation of A
3. A is correct, R is false
4. A is false, R is true
Explanation: Correct answer is Both A and R are correct, and R is the correct explanation of A. The endomembrane system, comprising ER, Golgi, lysosomes, and vesicles, coordinates protein and lipid transport. Mitochondria and chloroplasts are double-membrane organelles with their own DNA and ribosomes, functioning independently in energy conversion, and thus are excluded. Their independence highlights the specialization of the endomembrane system in intracellular trafficking and compartmentalization of biochemical processes in eukaryotic cells.

8. Matching Type:
Match the organelle with its function:
A. Rough ER → (i) Lipid synthesis
B. Smooth ER → (ii) Protein synthesis
C. Golgi apparatus → (iii) Modification and sorting of proteins
D. Lysosome → (iv) Intracellular digestion
1. A-(ii), B-(i), C-(iii), D-(iv)
2. A-(i), B-(ii), C-(iv), D-(iii)
3. A-(iii), B-(ii), C-(i), D-(iv)
4. A-(ii), B-(iii), C-(iv), D-(i)
Explanation: Correct answer is A-(ii), B-(i), C-(iii), D-(iv). Rough ER has ribosomes for protein synthesis; smooth ER synthesizes lip

Topic: Endoplasmic Reticulum (ER)
Subtopic: Types and Functions of ER

Keyword Definitions:
• Endoplasmic Reticulum (ER): A membranous organelle in eukaryotic cells forming a network of tubules and sacs.
• Smooth ER (SER): ER lacking ribosomes, involved in lipid synthesis, detoxification, and calcium storage.
• Rough ER (RER): ER with ribosomes on its surface, site of protein synthesis and modification.
• Ribosomes: Cellular structures that synthesize proteins using mRNA template.
• Lipid Synthesis: Biochemical process of producing fats and phospholipids in SER.
• Prokaryotes: Organisms lacking nucleus and membrane-bound organelles.
• Eukaryotes: Cells with nucleus and membrane-bound organelles including ER.
• Detoxification: Removal or modification of toxic substances in cells.
• Protein Modification: Post-translational processes in RER for proper folding and transport.
• Calcium Storage: SER stores calcium ions important for cellular signaling.

Lead Question (2022):
Which of the following statements with respect to Endoplasmic Reticulum is incorrect ?
(1) SER is devoid of ribosomes
(2) In prokaryotes only RER are present
(3) SER are the sites for lipid synthesis
(4) RER has ribosomes attached to ER

Explanation: The correct answer is (2). Prokaryotic cells lack membrane-bound organelles including both SER and RER. Only eukaryotic cells contain ER. SER lacks ribosomes and is involved in lipid synthesis, whereas RER has ribosomes attached for protein synthesis, making option (2) factually incorrect.

Guessed MCQs:

1. Single Correct Answer:
Which ER is responsible for detoxification and carbohydrate metabolism?
(a) RER
(b) SER
(c) Both RER and SER
(d) Golgi apparatus
Explanation: The correct answer is (b). Smooth ER (SER) detoxifies drugs and harmful substances and participates in carbohydrate metabolism. Its lack of ribosomes differentiates it from RER, which is primarily responsible for protein synthesis and processing.

2. Single Correct Answer:
Which ER has ribosomes attached to it for protein synthesis?
(a) SER
(b) RER
(c) Golgi apparatus
(d) Lysosome
Explanation: The correct answer is (b). Rough ER (RER) has ribosomes attached to its cytoplasmic surface. These ribosomes translate mRNA into proteins, which are folded and modified in RER before transport to Golgi or other destinations.

3. Single Correct Answer:
Lipid synthesis mainly occurs in:
(a) SER
(b) RER
(c) Mitochondria
(d) Nucleus
Explanation: The correct answer is (a). Smooth ER (SER) is the main site of lipid synthesis, including phospholipids and steroids, essential for cell membrane formation, hormone production, and storage, distinguishing its function from RER.

4. Assertion-Reason MCQ:
Assertion (A): RER is studded with ribosomes.
Reason (R): RER is primarily involved in lipid synthesis.
(a) Both A and R are correct and R explains A
(b) Both A and R are correct but R does not explain A
(c) A is correct, R is false
(d) A is false, R is true
Explanation: The correct answer is (c). RER is correctly studded with ribosomes; however, its primary function is protein synthesis, not lipid synthesis, which occurs in SER. Hence, the reason is incorrect.

5. Single Correct Answer:
Which statement is true regarding SER?
(a) Contains ribosomes
(b) Participates in lipid synthesis
(c) Present in prokaryotes
(d) Synthesizes proteins
Explanation: The correct answer is (b). Smooth ER (SER) lacks ribosomes, is absent in prokaryotes, and primarily participates in lipid synthesis, detoxification, and calcium storage, distinguishing it from RER.

6. Single Correct Answer:
Which type of cell contains ER?
(a) Prokaryotic cells
(b) Eukaryotic cells
(c) Bacterial cells
(d) Archaeal cells
Explanation: The correct answer is (b). Only eukaryotic cells contain membrane-bound organelles including ER. Prokaryotic cells lack ER and other organelles such as mitochondria and Golgi apparatus.

7. Fill in the Blanks:
The _______ is involved in synthesis of steroid hormones and detoxification.
(a) SER
(b) RER
(c) Lysosome
(d) Nucleus
Explanation: The correct answer is (a). Smooth ER (SER) synthesizes lipids including steroid hormones and detoxifies xenobiotics, playing a crucial role in cellular metabolism.

8. Single Correct Answer:
Which ER is more prominent in cells producing large amounts of protein?
(a) RER
(b) SER
(c) Golgi apparatus
(d) Mitochondria
Explanation: The correct answer is (a). Cells that synthesize large amounts of protein, such as pancreatic cells, have extensive RER. The ribosomes attached to RER enable high protein production and secretion.

9. Single Correct Answer:
Which feature differentiates RER from SER?
(a) Presence of ribosomes
(b) Lipid synthesis
(c) Calcium storage
(d) Detoxification
Explanation: The correct answer is (a). The presence of ribosomes on the cytoplasmic surface is the primary structural feature distinguishing RER from SER. SER lacks ribosomes and has different functions like lipid synthesis and detoxification.

10. Choose the correct statements:
(a) SER lacks ribosomes
(b) RER is studded with ribosomes
(c) SER is site of protein synthesis
(d) RER is absent in prokaryotes
Options:
1. a, b, d only
2. a and c only
3. b and c only
4. All statements
Explanation: The correct answer is (1). SER lacks ribosomes (a), RER has ribosomes (b), and RER is absent in prokaryotes (d). Statement (c) is incorrect because protein synthesis occurs in RER, not SER.

Topic: Structure of Chromosomes
Subtopic: Types of Chromosomes Based on Centromere Position

Keyword Definitions:

• Chromosome: Thread-like structure made of DNA and proteins carrying genetic information.

• Centromere: The constricted region of a chromosome where spindle fibers attach during cell division.

• Metacentric Chromosome: Centromere lies in the middle forming two equal arms.

• Sub-metacentric Chromosome: Centromere slightly away from the center forming unequal arms.

• Acrocentric Chromosome: Centromere near one end forming one long and one short arm.

• Telocentric Chromosome: Centromere located at the terminal end, forming a single arm.

Lead Question (2022):
Match List–I with List–II.
List – I           List – II
(a) Metacentric           (i) Centromere situated close to the end forming one extremely short and one very long arm
(b) Acrocentric           (ii) Centromere at the terminal end
(c) Sub-metacentric           (iii) Centromere in the middle forming equal arms
(d) Telocentric           (iv) Centromere slightly away from the middle forming unequal arms
(1) (a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
(2) (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
(3) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
(4) (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation: Metacentric chromosomes have centromere in the middle, sub-metacentric slightly away from the center, acrocentric near the end, and telocentric at the terminal end. Hence, the correct answer is (3) (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii).

1. Guessed Question:
The centromere is located exactly in the middle in:
(1) Acrocentric chromosome
(2) Metacentric chromosome
(3) Sub-metacentric chromosome
(4) Telocentric chromosome

Explanation: In metacentric chromosomes, the centromere lies in the center forming two equal arms, giving a ‘V’ shape during anaphase. Hence, the correct answer is (2) Metacentric chromosome.

2. Guessed Question:
Which type of chromosome has the centromere near one end, producing one short and one long arm?
(1) Telocentric
(2) Metacentric
(3) Sub-metacentric
(4) Acrocentric

Explanation: Acrocentric chromosomes have the centromere near one end, resulting in one extremely short and one long arm, forming a ‘J’ shape. Hence, the correct answer is (4) Acrocentric.

3. Guessed Question:
Sub-metacentric chromosomes have arms that are:
(1) Equal in length
(2) Unequal in length
(3) Without arms
(4) Circular in structure

Explanation: Sub-metacentric chromosomes have the centromere slightly away from the center, forming one shorter and one longer arm. Hence, the correct answer is (2) Unequal in length.

4. Guessed Question:
Telocentric chromosomes are found in:
(1) Humans
(2) Mice
(3) Plants only
(4) Bacteria

Explanation: Telocentric chromosomes have centromeres at the terminal end, forming only one arm. They are common in mice but not in humans. Hence, the correct answer is (2) Mice.

5. Guessed Question:
Which chromosome type appears ‘V’-shaped during anaphase?
(1) Metacentric
(2) Sub-metacentric
(3) Acrocentric
(4) Telocentric

Explanation: Metacentric chromosomes have centromeres in the middle, resulting in a V-shape during anaphase movement as both arms are equal. Hence, the correct answer is (1) Metacentric.

6. Guessed Question:
The term “centromere” refers to:
(1) End region of chromosome
(2) Primary constriction region
(3) Tip of the chromatid
(4) Region where crossing over occurs

Explanation: Centromere is the primary constriction on a chromosome that holds sister chromatids together and attaches to spindle fibers during cell division. Hence, the correct answer is (2) Primary constriction region.

7. Assertion-Reason Question:
Assertion (A): The shape of a chromosome during anaphase depends on centromere position.
Reason (R): The centromere attaches to spindle fibers, pulling chromatids apart.
(1) Both A and R are true, and R explains A.
(2) Both A and R are true, but R does not explain A.
(3) A is true, R is false.
(4) A is false, R is true.

Explanation: Chromosome shape at anaphase (V, L, J, or I) is determined by centromere position. Centromeres connect spindle fibers for separation. Hence, both statements are true, and R explains A. The correct answer is (1).

8. Matching Type Question:
Match chromosome type with its shape at anaphase:
A. Metacentric — (i) V-shaped
B. Sub-metacentric — (ii) L-shaped
C. Acrocentric — (iii) J-shaped
D. Telocentric — (iv) I-shaped
(1) A–i, B–ii, C–iii, D–iv
(2) A–ii, B–i, C–iv, D–iii
(3) A–iii, B–iv, C–i, D–ii
(4) A–iv, B–iii, C–ii, D–i

Explanation: Metacentric chromosomes are V-shaped, sub-metacentric L-shaped, acrocentric J-shaped, and telocentric I-shaped. Hence, the correct answer is (1) A–i, B–ii, C–iii, D–iv.

9. Fill in the Blanks:
The position of the ______ determines the shape of chromosomes during ______.
(1) Nucleolus, prophase
(2) Centromere, anaphase
(3) Spindle fiber, metaphase
(4) Chromatid, telophase

Explanation: Centromere position decides the shape of chromosomes at anaphase. V, L, J, or I shapes appear based on centromere location. Hence, the correct answer is (2) Centromere, anaphase.

10. Choose the Correct Statements:
(a) Centromere position determines chromosome type.
(b) Metacentric chromosomes form equal arms.
(c) Telocentric chromosomes have no short arm.
(d) Acrocentric chromosomes form equal arms.
(1) (a), (b), and (c) only
(2) (b) and (d) only
(3) (a), (c), and (d) only
(4) (a), (b), and (d) only

Explanation: Centromere position defines chromosome type. Metacentric chromosomes have equal arms, telocentric lack short arm, while acrocentric have unequal arms. Hence, the correct answer is (1) (a), (b), and (c) only.

Topic: Molecular Genetics
Subtopic: Chromatin Structure and Nucleosome

Keyword Definitions:

• Euchromatin: Loosely packed chromatin that is transcriptionally active and accessible for RNA synthesis.

• Heterochromatin: Densely packed chromatin that is usually transcriptionally inactive.

• Histone octamer: Protein complex of eight histone molecules around which DNA wraps to form a nucleosome.

• DNA: Negatively charged nucleic acid that wraps around histones to form chromatin.

• Histones: Positively charged proteins rich in lysine and arginine that help package DNA.

• Nucleosome: Basic structural unit of chromatin, consisting of DNA wrapped around a histone octamer.

• Base pairs (bp): Pair of complementary nucleotides in DNA; 1 bp ≈ 0.34 nm in length.

• Transcriptionally active: Regions of DNA being actively transcribed into RNA.

• Transcriptionally inactive: DNA regions that are tightly packed and not transcribed.

• Chromatin: Complex of DNA and protein found in eukaryotic cells.

Lead Question (2022)
Read the following statements and choose the set of correct statements:
(a) Euchromatin is loosely packed chromatin
(b) Heterochromatin is transcriptionally active
(c) Histone octomer is wrapped by negatively charged DNA in nucleosome
(d) Histones are rich in lysine and arginine
(e) A typical nucleosome contains 400 bp of DNA helix
(1) (a), (c), (d) only
(2) (b), (e) only
(3) (a), (c), (e) only
(4) (b), (d), (e) only

Explanation:
Euchromatin is loosely packed and transcriptionally active, heterochromatin is inactive. DNA wraps around histone octamer, and histones are rich in lysine and arginine. A typical nucleosome contains approximately 146 bp, not 400 bp. Correct statements are (a), (c), and (d). Therefore, the correct answer is (1).

1. Single Correct Answer MCQ:
Which chromatin type is transcriptionally inactive?
(1) Euchromatin
(2) Heterochromatin
(3) Nucleosome
(4) Histone octamer

Explanation:
Heterochromatin is densely packed and transcriptionally inactive, whereas euchromatin is active. Nucleosome is the structural unit of chromatin, and histone octamer is a protein complex, not a chromatin type. Correct answer is (2).

2. Single Correct Answer MCQ:
The histone proteins are rich in which amino acids?
(1) Lysine and Arginine
(2) Glycine and Serine
(3) Alanine and Valine
(4) Aspartate and Glutamate

Explanation:
Histones are basic proteins rich in positively charged lysine and arginine residues, which interact with negatively charged DNA to form nucleosomes. Other amino acids like glycine, alanine, or acidic residues do not predominate in histones. Correct answer is (1).

3. Single Correct Answer MCQ:
Approximately how many base pairs of DNA wrap around a histone octamer in a nucleosome?
(1) 146 bp
(2) 400 bp
(3) 50 bp
(4) 1000 bp

Explanation:
Each nucleosome contains DNA wrapped around histone octamer, about 146 base pairs long. Option 400 bp is incorrect. This wrapping helps compact DNA and regulate gene expression. Correct answer is (1).

4. Single Correct Answer MCQ:
Which statement about euchromatin is correct?
(1) It is transcriptionally inactive
(2) It is loosely packed
(3) It is rich in heterochromatin
(4) It contains 400 bp DNA

Explanation:
Euchromatin is loosely packed and transcriptionally active, allowing gene expression. It is not heterochromatin, nor does it contain exactly 400 bp DNA. Correct answer is (2).

5. Single Correct Answer MCQ:
DNA wraps around histone octamer due to:
(1) DNA being positively charged
(2) Histones being negatively charged
(3) Histones being positively charged
(4) Hydrophobic interactions only

Explanation:
DNA is negatively charged due to phosphate backbone. Histones are positively charged, rich in lysine and arginine, enabling electrostatic interactions that wrap DNA around histone octamers to form nucleosomes. Correct answer is (3).

6. Single Correct Answer MCQ:
Heterochromatin is generally found:
(1) In actively transcribed regions
(2) At centromeres and telomeres
(3) Loosely packed
(4) Wrapped around histone H1 only

Explanation:
Heterochromatin is densely packed, transcriptionally inactive, and commonly located at centromeres and telomeres, contributing to chromosome stability. Euchromatin is active and loosely packed. Correct answer is (2).

7. Assertion-Reason MCQ:
Assertion (A): Nucleosome formation compacts DNA
Reason (R): DNA is negatively charged and wraps around positively charged histones
Options:
(1) Both A and R correct and R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both incorrect

Explanation:
Nucleosome formation compacts DNA in chromatin, and the negative DNA wraps around positively charged histones due to electrostatic interactions. Both statements are correct, and the reason explains the assertion. Correct answer is (1).

8. Matching Type MCQ:
Match component with property:
A. Histone octamer — 1. 146 bp DNA wrapped
B. Nucleosome — 2. Eight histone proteins
C. Euchromatin — 3. Loosely packed, transcriptionally active
D. Heterochromatin — 4. Densely packed, transcriptionally inactive
Options:
(1) A–2, B–1, C–3, D–4
(2) A–1, B–2, C–4, D–3
(3) A–3, B–4, C–1, D–2
(4) A–2, B–1, C–4, D–3

Explanation:
Histone octamer: eight histone proteins (A–2), Nucleosome: 146 bp DNA wrapped (B–1), Euchromatin: loosely packed active (C–3), Heterochromatin: densely packed inactive (D–4). Correct answer is (1).

9. Fill in the Blanks:
Transcriptionally inactive chromatin is called ________.
(1) Euchromatin
(2) Heterochromatin
(3) Nucle

Topic: Chromatin Structure
Subtopic: Histones

Keyword Definitions:

• Histones: Proteins around which DNA winds to form nucleosomes in chromatin.

• Lysine and Arginine: Positively charged amino acids abundant in histones.

• Nucleosome: Structural unit of chromatin consisting of DNA wrapped around 8 histone proteins.

• Chromatin: Complex of DNA and proteins in the nucleus.

• Positive charge: Enables histones to bind negatively charged DNA phosphate backbone.

• Acidic pH: Incorrect for histones; they are basic due to positive amino acids.

Lead Question - 2021

Which one of the following statements about Histones is wrong?

(1) The pH of histones is slightly acidic
(2) Histones are rich in amino acids Lysine and Arginine
(3) Histones carry positive charge in the side chain
(4) Histones are organized to form a unit of 8 molecules

Explanation: Histones are basic proteins, rich in lysine and arginine, carrying positive charges, and organized as octamers (8 molecules) in nucleosomes. The statement about acidic pH is incorrect. Correct answer is option (1) The pH of histones is slightly acidic.

1. Which histone is not part of the core octamer in nucleosomes?
(1) H2A
(2) H2B
(3) H3
(4) H1
Explanation: Histone H1 is not part of the nucleosome core octamer; it acts as a linker histone stabilizing DNA between nucleosomes. H2A, H2B, H3, and H4 form the octamer core. Correct answer is option (4) H1.

2. Histones bind to DNA primarily because:
(1) DNA is positively charged
(2) DNA is negatively charged
(3) Histones are hydrophobic
(4) Histones are acidic
Explanation: DNA has a negatively charged phosphate backbone, which attracts positively charged histone proteins rich in lysine and arginine. This electrostatic interaction facilitates nucleosome formation. Correct answer is option (2) DNA is negatively charged.

3. The basic amino acids in histones are:
(1) Glutamate and Aspartate
(2) Lysine and Arginine
(3) Phenylalanine and Tyrosine
(4) Serine and Threonine
Explanation: Lysine and Arginine are basic amino acids present in histones, providing positive charges that bind negatively charged DNA. Glutamate and aspartate are acidic, phenylalanine/tyrosine are aromatic, and serine/threonine are polar uncharged. Correct answer is option (2) Lysine and Arginine.

4. Nucleosomes are formed by wrapping DNA around:
(1) H1 only
(2) H2A-H2B and H3-H4 octamer
(3) H1-H3 only
(4) H2B-H4 dimer
Explanation: Nucleosomes are DNA wrapped around an octamer of histones: two molecules each of H2A, H2B, H3, and H4. H1 is a linker histone not in the core octamer. Correct answer is option (2) H2A-H2B and H3-H4 octamer.

5. Histone modification that relaxes chromatin is:
(1) Methylation
(2) Acetylation
(3) Phosphorylation
(4) Ubiquitination
Explanation: Acetylation of lysine residues on histone tails neutralizes positive charges, reducing DNA binding and relaxing chromatin structure, facilitating transcription. Methylation can repress or activate, phosphorylation and ubiquitination have regulatory roles. Correct answer is option (2) Acetylation.

6. Which histone is involved in higher-order chromatin folding?
(1) H2A
(2) H2B
(3) H3
(4) H1
Explanation: Histone H1 is the linker histone that binds DNA between nucleosomes and is essential for higher-order chromatin folding into 30 nm fibers. Core histones (H2A, H2B, H3, H4) form the nucleosome. Correct answer is option (4) H1.

7. Assertion-Reason Question:
Assertion (A): Histones are rich in lysine and arginine.
Reason (R): These amino acids give histones a positive charge enabling DNA binding.
(1) Both A and R are true, R is correct explanation of A
(2) Both A and R are true, R is not correct explanation of A
(3) A true, R false
(4) A false, R true
Explanation: Histones are indeed rich in lysine and arginine. These basic amino acids provide positive charges which allow electrostatic interaction with negatively charged DNA. Both statements are true and the reason correctly explains the assertion. Correct answer is option (1).

8. Matching Type Question:
Match histone types with function:
(a) H2A/H2B - 1. Linker histone
(b) H3/H4 - 2. Nucleosome core
(c) H1 - 3. Stabilizes linker DNA
(1) a-2, b-2, c-3
(2) a-1, b-2, c-3
(3) a-2, b-1, c-3
(4) a-3, b-2, c-1
Explanation: H2A/H2B and H3/H4 form nucleosome core (a-2, b-2). H1 is linker histone stabilizing DNA between nucleosomes (c-3). Correct answer is option (1).

9. Fill in the Blanks:
The ________ histone binds between nucleosomes and helps in higher-order chromatin structure.
(1) H2A
(2) H2B
(3) H3
(4) H1
Explanation: Histone H1 is the linker histone that binds between nucleosomes, facilitating higher-order chromatin folding. H2A, H2B, H3 are core nucleosome histones. Correct answer is option (4) H1.

10. Choose the correct statements:
(a) Histones are basic proteins.
(b) DNA wraps around histone octamers.
(c) Histones are acidic in nature.
(d) H1 is a linker histone.
(1) a, b, d
(2) a, c, d
(3) b, c, d
(4) a, b, c
Explanation: Histones are basic proteins (a), DNA wraps around octamers (b), and H1 is a linker histone (d). They are not acidic. Correct answer is option (1) a, b, d.

Topic: Cell Organelles

Subtopic: Endomembrane System

• Endomembrane System: A network of membranes within the cell involved in protein and lipid transport.

• Endoplasmic Reticulum (ER): Organelle that synthesizes proteins (rough ER) and lipids (smooth ER).

• Golgi Complex: Organelle that modifies, sorts, and packages proteins and lipids for transport.

• Lysosomes: Membrane-bound organelles containing digestive enzymes for macromolecule breakdown.

• Vacuoles: Membrane-bound sacs used for storage and transport within the cell.

• Mitochondria: Organelle responsible for ATP production via oxidative phosphorylation.

• Ribosomes: Protein-synthesizing structures, not part of endomembrane system.

• Membrane-bound Organelles: Organelles enclosed by a lipid bilayer.

• Protein Transport: Movement of proteins between organelles in the cell.

• Intracellular Trafficking: Transport of molecules within the cell via vesicles and membranes.

• Secretory Pathway: ER-Golgi network for processing and delivering proteins outside the cell.

Lead Question - 2021

The organelles that are included in the endomembrane system are:

Options:
1. Endoplasmic reticulum, Golgi complex, Lysosomes and Vacuoles
2. Golgi complex, Mitochondria, Ribosomes and Lysosomes
3. Golgi complex, Endoplasmic reticulum, Mitochondria and Lysosomes
4. Endoplasmic reticulum, Mitochondria, Ribosomes and Lysosomes

Explanation: The endomembrane system includes organelles involved in synthesis, modification, and transport of proteins and lipids: Endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles. Mitochondria and ribosomes are not part of this system. Answer: Endoplasmic reticulum, Golgi complex, Lysosomes and Vacuoles.

1. Which organelle is responsible for protein modification and packaging?
Options:
A. Endoplasmic reticulum
B. Golgi complex
C. Lysosomes
D. Vacuoles

Explanation: The Golgi complex modifies, sorts, and packages proteins and lipids synthesized by the endoplasmic reticulum for transport within and outside the cell. Lysosomes and vacuoles serve different functions. Answer: Golgi complex.

2. Which organelle contains digestive enzymes for breaking down macromolecules?
Options:
A. Golgi complex
B. Lysosomes
C. Vacuoles
D. Mitochondria

Explanation: Lysosomes are membrane-bound organelles that contain hydrolytic enzymes for digestion of cellular waste and macromolecules. They are part of the endomembrane system. Answer: Lysosomes.

3. Smooth ER is mainly involved in:
Options:
A. Protein synthesis
B. Lipid synthesis
C. ATP production
D. DNA replication

Explanation: Smooth ER synthesizes lipids and detoxifies certain chemicals. Rough ER synthesizes proteins, and mitochondria produce ATP. DNA replication occurs in the nucleus. Answer: Lipid synthesis.

4. Which organelle stores substances and helps in intracellular transport?
Options:
A. Vacuoles
B. Lysosomes
C. Golgi complex
D. Ribosomes

Explanation: Vacuoles are membrane-bound sacs for storage and transport of water, nutrients, and other substances within the cell, and are part of the endomembrane system. Ribosomes synthesize proteins. Answer: Vacuoles.

5. Which organelle is not part of the endomembrane system?
Options:
A. Endoplasmic reticulum
B. Mitochondria
C. Golgi complex
D. Lysosomes

Explanation: Mitochondria are involved in ATP production and are not part of the endomembrane system, which mainly handles protein and lipid transport. ER, Golgi, and lysosomes are included. Answer: Mitochondria.

6. Rough ER differs from smooth ER by the presence of:
Options:
A. Ribosomes
B. Lipids
C. DNA
D. Enzymes

Explanation: Rough ER has ribosomes attached to its surface, enabling protein synthesis. Smooth ER lacks ribosomes and mainly synthesizes lipids. Answer: Ribosomes.

7. Assertion-Reason:
Assertion (A): Endomembrane system includes lysosomes.
Reason (R): Lysosomes digest macromolecules inside the cell.
Options:
A. Both A and R are true, R is correct explanation
B. Both A and R are true, R is not correct explanation
C. A is true, R is false
D. A is false, R is true

Explanation: Lysosomes are part of the endomembrane system and contain digestive enzymes to breakdown macromolecules. The reason accurately explains the assertion. Answer: Both A and R are true, R is correct explanation.

8. Match the following:
Column I: 1. ER 2. Golgi complex 3. Lysosomes 4. Vacuoles
Column II: A. Storage & transport B. Digestive enzymes C. Protein modification & packaging D. Protein & lipid synthesis
Options:
A. 1-D, 2-C, 3-B, 4-A
B. 1-C, 2-D, 3-A, 4-B
C. 1-B, 2-A, 3-D, 4-C
D. 1-A, 2-B, 3-C, 4-D

Explanation: Correct matching: ER – Protein & lipid synthesis (D), Golgi – Protein modification & packaging (C), Lysosomes – Digestive enzymes (B), Vacuoles – Storage & transport (A). Answer: 1-D, 2-C, 3-B, 4-A.

9. Fill in the blank: Organelle that modifies and packages proteins for secretion is _______.
Options:
A. Lysosomes
B. Golgi complex
C. Mitochondria
D. Vacuoles

Explanation: The Golgi complex processes, modifies, and packages proteins and lipids from the ER for intracellular and extracellular transport. Answer: Golgi complex.

10. Choose the correct statements:
1. ER is part of the endomembrane system.
2. Lysosomes digest cellular waste.
3. Mitochondria are part of the endomembrane system.
4. Vacuoles store materials in cells.
Options:
A. 1, 2, 4 only
B. 1, 3, 4 only
C. 2, 3, 4 only
D. 1, 2, 3, 4

Explanation: Statements 1, 2, and 4 are correct. ER, lysosomes, and vacuoles are part of the endomembrane system; mitochondria are excluded. Answer: 1, 2, 4 only.

Topic: Cell Organelles
Subtopic: Structure and Function

Keyword Definitions:

• Cristae: Infoldings of the inner mitochondrial membrane that increase surface area for cellular respiration.

• Thylakoids: Flattened membranous sacs in chloroplasts where light-dependent reactions of photosynthesis occur.

• Centromere: Primary constriction of a chromosome that holds sister chromatids together and attaches to spindle fibers.

• Cisternae: Flattened disc-shaped sacs of the Golgi apparatus involved in processing and packaging proteins and lipids.

• Mitochondria: Cell organelles responsible for ATP production through respiration.

• Chloroplast: Plant organelle where photosynthesis takes place, containing thylakoids and stroma.

• Golgi apparatus: Organelle involved in modifying, sorting, and packaging proteins and lipids.

• Sister chromatids: Identical copies of a chromosome connected at the centromere.

Lead Question - 2021

Match List - I with List - II.
List - I  List - II
(a) Cristae  (i) Primary constriction in chromosome
(b) Thylakoids  (ii) Disc-shaped sacs in Golgi apparatus
(c) Centromere  (iii) Infoldings in mitochondria
(d) Cisternae  (iv) Flattened membranous sacs in stroma of plastids
Choose the correct answer from the options given below:
(a) (b) (c) (d)
(1) (i) (iv) (iii) (ii)
(2) (iii) (iv) (i) (ii)
(3) (ii) (iii) (iv) (i)
(4) (iv) (iii) (ii) (i)

Explanation: Correct answer is (2) (iii) (iv) (i) (ii). Cristae are infoldings of the mitochondrial membrane, thylakoids are flattened membranous sacs in plastids, centromere is the primary constriction in chromosomes, and cisternae are disc-shaped sacs of the Golgi apparatus. This matching aligns each organelle with its characteristic structure.

Guessed Questions:

1) Single Correct Answer: Cristae are characteristic of which organelle?
(1) Chloroplast
(2) Mitochondria
(3) Golgi apparatus
(4) Nucleus

Explanation: Correct answer is (2) Mitochondria. Cristae are infoldings of the inner mitochondrial membrane that increase surface area for ATP production through cellular respiration.

2) Single Correct Answer: Thylakoids are found in:
(1) Mitochondria
(2) Golgi apparatus
(3) Chloroplasts
(4) Nucleus

Explanation: Correct answer is (3) Chloroplasts. Thylakoids are membrane-bound flattened sacs in chloroplasts where light-dependent photosynthesis occurs.

3) Single Correct Answer: Centromere function is:
(1) ATP production
(2) Protein synthesis
(3) Chromatid attachment
(4) Lipid packaging

Explanation: Correct answer is (3) Chromatid attachment. The centromere is the primary constriction of a chromosome, connecting sister chromatids and providing the site for spindle fiber attachment during cell division.

4) Single Correct Answer: Cisternae are found in:
(1) Mitochondria
(2) Golgi apparatus
(3) Chloroplasts
(4) Endoplasmic reticulum

Explanation: Correct answer is (2) Golgi apparatus. Cisternae are flattened, disc-shaped membranous sacs in the Golgi, responsible for modifying, sorting, and packaging proteins and lipids.

5) Assertion (A): Cristae increase surface area for ATP synthesis.
Reason (R): They are infoldings of the inner mitochondrial membrane.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Correct answer is (1). Cristae provide a larger surface for enzymes involved in oxidative phosphorylation. Their structure as inner membrane infoldings directly explains their role in ATP synthesis.

6) Single Correct Answer: Flattened membranous sacs in plastids are called:
(1) Cristae
(2) Thylakoids
(3) Cisternae
(4) Ribosomes

Explanation: Correct answer is (2) Thylakoids. Thylakoids are the flattened sacs in chloroplast stroma that house photosynthetic pigments and perform light-dependent reactions.

7) Matching Type: Match organelle with main function:
List-I  List-II
(a) Cristae    (i) Photosynthesis
(b) Thylakoids    (ii) ATP production
(c) Centromere    (iii) Chromosome segregation
(d) Cisternae    (iv) Protein modification and packaging

Explanation: Correct answer: (a) ii, (b) i, (c) iii, (d) iv. Cristae produce ATP, thylakoids perform photosynthesis, centromere ensures correct chromosome segregation, and cisternae modify and package proteins in the Golgi apparatus.

8) Single Correct Answer: Infoldings of the inner mitochondrial membrane are called:
(1) Cisternae
(2) Thylakoids
(3) Cristae
(4) Golgi stacks

Explanation: Correct answer is (3) Cristae. Cristae are inner membrane infoldings that increase the mitochondrial surface area for enzymes of the electron transport chain.

9) Fill in the blank: Flattened disc-shaped sacs of Golgi apparatus are called ______.
(1) Cristae
(2) Cisternae
(3) Thylakoids
(4) Mitochondria

Explanation: Correct answer is (2) Cisternae. Golgi cisternae are flattened, stacked membranous sacs where protein and lipid modification, sorting, and packaging occurs.

10) Choose the correct statements:
(a) Cristae increase mitochondrial surface area.
(b) Thylakoids contain photosynthetic pigments.
(c) Centromere connects sister chromatids.
(d) Cisternae are present in mitochondria.
Options:
(1) a, b, c
(2) a, b, d
(3) b, c, d
(4) a, c, d

Explanation: Correct answer is (1). Statements a, b, and c are correct. Cristae increase mitochondrial surface, thylakoids perform photosynthesis, and centromeres connect chromatids. Statement d is incorrect; cisternae are in Golgi, not mitochondria.

Subtopic: Nucleus and Cytoplasmic Structures

Keyword Definitions:

• Microbodies: Small, membrane-bound organelles like peroxisomes and glyoxysomes present in both plants and animals.

• Perinuclear space: The fluid-filled gap between the inner and outer membranes of the nuclear envelope.

• Nuclear pores: Protein complexes regulating transport of RNA and proteins across the nuclear envelope.

• Sieve tube elements: Specialized phloem cells that lose their nucleus at maturity for efficient food transport.

Lead Question - 2021

Which of the following is an incorrect statement?
(1) Microbodies are present both in plant and animal cells.
(2) The perinuclear space forms a barrier between the materials present inside the nucleus and that of the cytoplasm.
(3) Nuclear pores act as passages for proteins and RNA molecules in both directions between nucleus and cytoplasm.
(4) Mature sieve tube elements possess a conspicuous nucleus and usual cytoplasmic organelles

Explanation: Mature sieve tube elements of phloem lose their nucleus and most organelles to facilitate translocation of food through sieve plates. Hence, statement (4) is incorrect. Microbodies are present in both plants and animals, perinuclear space separates nuclear content, and nuclear pores regulate two-way transport. Therefore, the correct answer is (4).

1) Which organelle is known as the “powerhouse of the cell”?
(1) Mitochondria
(2) Ribosome
(3) Golgi apparatus
(4) Lysosome

Explanation: Mitochondria are called the powerhouse of the cell as they produce ATP through oxidative phosphorylation. They have a double membrane structure and their own DNA and ribosomes, enabling self-replication. Ribosomes synthesize proteins, Golgi packages materials, and lysosomes perform digestion. Thus, option (1) mitochondria is correct.

2) Ribosomes are composed of:
(1) DNA and proteins
(2) rRNA and proteins
(3) mRNA and proteins
(4) tRNA and proteins

Explanation: Ribosomes are ribonucleoprotein particles composed of ribosomal RNA (rRNA) and proteins. They are the sites of protein synthesis, found either free in the cytoplasm or attached to endoplasmic reticulum. DNA is not a structural component of ribosomes. Hence, the correct answer is option (2), rRNA and proteins.

3) The cell organelle involved in packaging and secretion is:
(1) Mitochondria
(2) Golgi apparatus
(3) Endoplasmic reticulum
(4) Lysosome

Explanation: The Golgi apparatus is responsible for packaging proteins, lipids, and polysaccharides into vesicles for secretion. It modifies materials received from the endoplasmic reticulum and directs them to target sites. Mitochondria generate energy, ER synthesizes biomolecules, and lysosomes digest. Thus, option (2) Golgi apparatus is correct.

4) Which of the following is a double-membrane bound organelle?
(1) Ribosome
(2) Peroxisome
(3) Mitochondrion
(4) Lysosome

Explanation: Mitochondria have a double membrane – an outer smooth membrane and an inner folded membrane forming cristae. This unique structure aids ATP synthesis. Ribosomes lack membranes, peroxisomes and lysosomes are single-membrane bound. Therefore, the correct answer is option (3), mitochondrion.

5) Which structure regulates the entry and exit of substances into the nucleus?
(1) Endoplasmic reticulum
(2) Nuclear pores
(3) Nucleolus
(4) Chromatin

Explanation: Nuclear pores are large protein complexes embedded in the nuclear envelope. They regulate bidirectional transport of proteins, RNA, and ribonucleoproteins between the nucleus and cytoplasm. The nucleolus synthesizes rRNA, chromatin contains DNA, and ER is outside the nucleus. Hence, the correct answer is option (2), nuclear pores.

6) Which organelle is called the “suicidal bag” of the cell?
(1) Lysosome
(2) Golgi apparatus
(3) Mitochondria
(4) Ribosome

Explanation: Lysosomes are called suicidal bags because they contain hydrolytic enzymes that digest worn-out cell components or even the whole cell during autolysis. Mitochondria produce energy, Golgi performs packaging, and ribosomes synthesize proteins. Thus, the correct answer is option (1), lysosome.

7) Assertion (A): The nucleolus is not bound by a membrane.
Reason (R): The nucleolus is directly involved in ribosomal RNA synthesis and ribosome assembly.
(1) Both A and R are true, and R is the correct explanation
(2) Both A and R are true, but R is not the correct explanation
(3) A is true, R is false
(4) A is false, R is true

Explanation: The nucleolus is a dense, membrane-less structure within the nucleus. It plays a vital role in rRNA synthesis and ribosome assembly. Both Assertion and Reason are true, and Reason correctly explains Assertion. Hence, option (1) is the correct answer.

8) Match the following cell organelles with their functions:
A. Mitochondria
B. Ribosome
C. Lysosome
D. Golgi apparatus

(i) Protein synthesis
(ii) Energy production
(iii) Intracellular digestion
(iv) Packaging and secretion

(1) A-ii, B-i, C-iii, D-iv
(2) A-i, B-ii, C-iv, D-iii
(3) A-iii, B-iv, C-ii, D-i
(4) A-iv, B-iii, C-i, D-ii

Explanation: Mitochondria produce ATP (ii), ribosomes synthesize proteins (i), lysosomes perform intracellular digestion (iii), and Golgi apparatus packages and secretes biomolecules (iv). Thus, the correct match is A-ii, B-i, C-iii, D-iv, making option (1) correct.

9) Fill in the blank:
The organelle that detoxifies hydrogen peroxide in cells is ________.
(1) Lysosome
(2) Peroxisome
(3) Ribosome
(4) Chloroplast

Explanation: Peroxisomes contain enzymes like catalase that detoxify hydrogen peroxide, converting it into water and oxygen. Lysosomes digest cellular waste, ribosomes synthesize proteins, and chloroplasts carry out photosynthesis. Therefore, the correct answer is option (2), peroxisome.

10) Choose the correct statements:
(a) Lysosomes are double-membrane bound.
(b) Mitochondria have their own DNA and ribosomes.
(c) Chloroplasts are absent in prokaryotes.
(d) Ribosomes are absent in prokaryotes.
(1) a and b
(2) b and c
(3) c and d
(4) b and d

Explanation: Lysosomes are single-membrane bound, not double. Mitochondria possess their own DNA and ribosomes. Chloroplasts occur only in eukaryotic plant cells, absent in prokaryotes. Ribosomes are present in prokaryotes as 70S type. Hence, statements (b) and (c) are correct, making option (2) right.

Topic: Ribosome Structure and Function
Subtopic: Role of Elements in Ribosome Stability

Keyword Definitions:

• Ribosomes: Cellular organelles responsible for protein synthesis.

• Magnesium (Mg): Essential element stabilizing ribosomal RNA and structure.

• Zinc (Zn): Trace element involved in enzyme function, not ribosome structure.

• Copper (Cu): Trace element involved in electron transport and enzymes.

• Molybdenum (Mo): Cofactor for certain enzymes, not related to ribosome stability.

• rRNA: Ribosomal RNA forming the core structural and functional component of ribosomes.

• Protein synthesis: Process of translating mRNA into polypeptides at ribosomes.

• Ribosome stability: Structural integrity maintained by metal ions like magnesium.

• Prokaryotic ribosomes: 70S, composed of 50S and 30S subunits, stabilized by Mg ions.

• Eukaryotic ribosomes: 80S, composed of 60S and 40S subunits, require Mg for folding.

• Ion cofactors: Metal ions essential for maintaining structure and enzymatic activity in ribosomes.

Lead Question - 2020 (COVID Reexam)

Which of the following elements helps in maintaining the structure of ribosomes?

1. Magnesium
2. Zinc
3. Copper
4. Molybdenum

Explanation: Magnesium ions stabilize ribosomal RNA and maintain ribosome structure in both prokaryotes and eukaryotes. It ensures proper folding of rRNA and association of subunits for efficient protein synthesis. Correct answer is option 1: Magnesium. Adequate Mg concentration is critical for ribosome assembly and function. (50 words)

Guessed Question 1. Single Correct Answer MCQ: Which ion stabilizes rRNA in ribosomal subunits?

1. Zinc
2. Copper
3. Magnesium
4. Manganese

Explanation: Magnesium ions bind to phosphate groups of rRNA, stabilizing secondary and tertiary structures in ribosomal subunits. This is essential for correct subunit assembly and translation. Correct answer is option 3: Magnesium. Without Mg, ribosome structure is disrupted, impairing protein synthesis. (50 words)

Guessed Question 2. Single Correct Answer MCQ: Essential metal ion for eukaryotic 80S ribosome assembly is:

1. Copper
2. Zinc
3. Magnesium
4. Iron

Explanation: Magnesium is required for maintaining the structural integrity of eukaryotic 80S ribosomes by stabilizing rRNA and facilitating subunit association. Correct answer is option 3: Magnesium. Mg ions ensure proper folding and function during translation. (50 words)

Guessed Question 3. Single Correct Answer MCQ: Which metal ion is NOT involved in ribosome stabilization?

1. Magnesium
2. Zinc
3. Magnesium
4. Magnesium

Explanation: Zinc is not required for structural maintenance of ribosomes. Magnesium is the primary ion stabilizing rRNA and subunit association. Correct answer is option 2: Zinc. Zn functions in other enzymes but does not contribute to ribosome integrity. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Prokaryotic 70S ribosome stability relies on:

1. Molybdenum
2. Magnesium
3. Copper
4. Zinc

Explanation: Prokaryotic 70S ribosomes require Mg ions to stabilize 30S and 50S subunits and rRNA folding. Correct answer is option 2: Magnesium. Adequate Mg ensures proper protein synthesis and ribosome assembly in bacterial cells. (50 words)

Guessed Question 5. Assertion-Reason MCQ:

Assertion (A): Ribosome structure is maintained by magnesium ions.
Reason (R): Magnesium neutralizes negative charges on rRNA phosphate backbone to allow proper folding.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Magnesium binds rRNA phosphate groups, neutralizing repulsion and maintaining folding and subunit assembly. Both assertion and reason are true, and R correctly explains A. Correct answer is option 1. This ensures functional ribosome formation. (50 words)

Guessed Question 6. Matching Type MCQ:

Column I - Ribosome Component
(a) 30S subunit (i) Small subunit
(b) 50S subunit (ii) Large subunit
(c) Magnesium (iii) Structural stability
(d) rRNA (iv) Catalytic core
Options:
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
3. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
4. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

Explanation: 30S is the small subunit, 50S is the large subunit. Magnesium stabilizes ribosomal structure, and rRNA forms the catalytic core for peptide bond formation. Correct answer is option 1. These components are essential for ribosome integrity and translation efficiency. (50 words)

Guessed Question 7. Fill in the blank:

Metal ion required for ribosome assembly and stabilization is _______.

1. Copper
2. Magnesium
3. Zinc
4. Manganese

Explanation: Magnesium is essential for ribosome assembly, stabilizing rRNA structures and subunit association. Correct answer is option 2: Magnesium. Without Mg, ribosomal folding and protein synthesis are impaired. (50 words)

Guessed Question 8. Single Correct Answer MCQ: Role of magnesium in ribosomes is:

1. Stabilizes rRNA
2. Catalyzes peptide bonds
3. Oxidizes NADH
4. Forms DNA backbone

Explanation: Magnesium stabilizes rRNA secondary and tertiary structures, ensuring ribosome integrity and subunit association. Correct answer is option 1. This stabilization is crucial for accurate translation and protein synthesis. (50 words)

Guessed Question 9. Single Correct Answer MCQ: Which element is NOT required for ribosome structure?

1. Magnesium
2. Zinc
3. Magnesium
4. Magnesium

Explanation: Zinc is not required for ribosome assembly or structural maintenance. Correct answer is option 2: Zinc. Magnesium is the key ion providing structural stabilization to ribosomal RNA and subunits, enabling proper translation. (50 words)

Guessed Question 10. Choose the correct statements MCQ:

(a

Topic: Cell Organelles
Subtopic: Endomembrane System and Organelles

Keyword Definitions:

• Smooth Endoplasmic Reticulum: Organelle without ribosomes, mainly synthesizes lipids and steroids.

• Rough Endoplasmic Reticulum: Organelle with ribosomes, involved in protein synthesis and processing.

• Golgi Complex: Organelle responsible for packaging, glycosylation, and secretion of proteins and lipids.

• Centriole: Cylindrical structure involved in spindle fiber formation during cell division.

• Glycosylation: Addition of sugar residues to proteins or lipids, occurs in the Golgi apparatus.

• Spindle Fibers: Protein structures that segregate chromosomes during cell division.

Lead Question - 2020 (COVID Reexam)

Match the following columns and select the correct option :
Column - I   Column - II
(a) Smooth endoplasmic reticulum  (i) Protein synthesis
(b) Rough endoplasmic reticulum  (ii) Lipid synthesis
(c) Golgi complex  (iii) Glycosylation
(d) Centriole  (iv) Spindle formation

1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(iii), (b)-(i), (c)-(ii), (d)-(iv)
3. (a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)
4. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation: Smooth endoplasmic reticulum synthesizes lipids, rough endoplasmic reticulum synthesizes proteins, the Golgi complex performs glycosylation, and centrioles form spindle fibers during cell division. Thus, the correct match is option 1: (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv). This arrangement shows proper organelle functions, critical for cellular processes and structural maintenance.

Guessed Question 1. Which organelle is known as the powerhouse of the cell?
1. Nucleus
2. Mitochondria
3. Ribosome
4. Golgi body

Explanation: Mitochondria are termed the powerhouse of the cell as they generate ATP through oxidative phosphorylation. Nucleus controls activities, ribosomes synthesize proteins, and Golgi processes molecules. Therefore, the correct answer is option 2, mitochondria, highlighting their essential energy role in cellular metabolism and survival.

Guessed Question 2. The rough endoplasmic reticulum appears rough due to:
1. Presence of enzymes
2. Presence of ribosomes
3. Presence of proteins
4. Presence of lipids

Explanation: The rough endoplasmic reticulum is termed rough because ribosomes are attached to its surface, making it responsible for protein synthesis. Enzymes and proteins are products of ribosomal function, while lipids are synthesized in smooth ER. Hence, the correct answer is option 2, presence of ribosomes.

Guessed Question 3. The Golgi apparatus was first discovered by:
1. Robert Hooke
2. Camillo Golgi
3. Schleiden
4. Schwann

Explanation: The Golgi apparatus was discovered by Camillo Golgi in 1898 using a silver staining method. Robert Hooke discovered cells, Schleiden and Schwann proposed cell theory. Thus, the correct answer is option 2, Camillo Golgi, honoring the scientist who described this important organelle for secretion and packaging.

Guessed Question 4. Assertion (A): Centrioles help in spindle fiber formation.
Reason (R): Spindle fibers ensure proper chromosome segregation.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Centrioles organize microtubules and aid in spindle fiber formation during cell division. These spindle fibers ensure accurate chromosome segregation to daughter cells. Both assertion and reason are true, and reason explains assertion. Therefore, the correct answer is option 1, showing centrioles’ significance in cell division.

Guessed Question 5. Match the following:
(a) Lysosome (i) Protein synthesis
(b) Ribosome (ii) Suicide bag
(c) Mitochondria (iii) Energy production
(d) Chloroplast (iv) Photosynthesis

1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
3. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
4. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)

Explanation: Lysosomes are called suicide bags due to hydrolytic enzymes, ribosomes synthesize proteins, mitochondria produce energy, and chloroplasts perform photosynthesis. Thus, correct matching is option 1. Each organelle plays a vital role in survival and functioning, reflecting structural and biochemical compartmentalization of eukaryotic cells for efficiency.

Guessed Question 6. Fill in the blank: The double membrane organelle responsible for aerobic respiration is ______.
1. Lysosome
2. Mitochondria
3. Golgi apparatus
4. Vacuole

Explanation: Mitochondria are double-membrane organelles that carry out aerobic respiration and produce ATP. Lysosomes digest biomolecules, Golgi packages proteins, and vacuoles store substances. Therefore, the correct answer is option 2, mitochondria, as they are essential for cellular energy production in almost all eukaryotic cells.

Guessed Question 7. Choose the correct statements:
(i) Rough ER synthesizes proteins.
(ii) Smooth ER synthesizes lipids.
(iii) Golgi modifies proteins.
(iv) Centrioles are absent in plant cells.
1. (i), (ii), (iii)
2. (i), (iii), (iv)
3. (i), (ii), (iii), (iv)
4. (ii) and (iv)

Explanation: Rough ER synthesizes proteins, smooth ER synthesizes lipids, Golgi modifies proteins, and centrioles are absent in higher plant cells but present in animal cells. All four statements are correct. Thus, the correct answer is option 3, showing functional complementarity of cell organelles in various organisms.

Subtopic: Microorganisms and Cell Sizes

Keyword Definitions:

• PPLO: Pleuropneumonia-like organisms, the smallest self-replicating organisms, belonging to Mycoplasma group.

• Mycoplasma: Wall-less bacteria, smallest known prokaryotes, resistant to many antibiotics.

• Cell Size: Dimension of a living cell, varying from micrometers to millimeters depending on organism type.

• Virus: Infectious acellular agents smaller than bacteria, dependent on host machinery for replication.

• Prokaryotes: Single-celled organisms without a true nucleus or membrane-bound organelles.

• Eukaryotes: Organisms with true nucleus and membrane-bound organelles.

Lead Question - 2020 (COVID Reexam)

The size of Pleuropneumonia - like Organism (PPLO) is :
1. 0.02 m
2. 1-2 m
3. 10-20 m
4. 0.1 m

Explanation: PPLO or Mycoplasma are the smallest living prokaryotic organisms, measuring about 0.1 micrometer in size. They lack a cell wall, allowing them flexibility in shape. Options given in meters are misleading, as the correct unit is micrometer. Thus, the correct answer is option 4, 0.1 m (interpreted as micrometer).

Guessed Question 1. The smallest living cell is :
1. Virus
2. Mycoplasma
3. Bacteriophage
4. E.coli

Explanation: Mycoplasma, also called PPLO, is considered the smallest living cell with a size of about 0.1 µm. Viruses are smaller but not considered living without a host. Bacteriophage is a virus infecting bacteria. Hence, the correct answer is option 2, Mycoplasma.

Guessed Question 2. Which of the following lacks a cell wall?
1. Mycoplasma
2. Fungi
3. Bacteria
4. Algae

Explanation: Mycoplasma is unique among prokaryotes for lacking a cell wall, making it resistant to antibiotics like penicillin. Fungi have chitin walls, bacteria have peptidoglycan walls, and algae possess cellulose walls. Therefore, the correct answer is option 1, Mycoplasma.

Guessed Question 3. The genome of Mycoplasma is made up of :
1. RNA only
2. DNA only
3. Protein only
4. RNA and Protein

Explanation: Mycoplasma possesses DNA as its genetic material, similar to other prokaryotes. Its small genome size supports self-replication and basic metabolic processes. RNA viruses differ in this aspect. Hence, the correct answer is option 2, DNA only, which directs all cellular functions.

Guessed Question 4. Assertion (A): Mycoplasma is the smallest free-living organism.
Reason (R): Mycoplasma can survive without a host cell.
1. Both A and R true, R explains A
2. Both A and R true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: Mycoplasma is the smallest free-living prokaryote capable of surviving without a host, unlike viruses. Both assertion and reason are correct, and reason justifies the assertion. Therefore, the correct answer is option 1.

Guessed Question 5. Match the following:
(a) Virus (i) Protein coat
(b) Mycoplasma (ii) Smallest living cell
(c) Bacteriophage (iii) Infects bacteria
(d) Fungi (iv) Chitin wall
1. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
2. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
3. (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
4. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)

Explanation: Viruses possess a protein coat called capsid, Mycoplasma is the smallest living cell, bacteriophage infects bacteria, and fungi have chitin cell walls. The correct match is option 1, which aligns the correct features with each organism.

Guessed Question 6. Fill in the blank: The genetic material of viruses can be either ______.
1. DNA or RNA
2. Only RNA
3. Only DNA
4. Only Protein

Explanation: Viruses are acellular infectious agents, and their genetic material can be either DNA or RNA, never both in a single virus. This diversity determines viral classification and replication strategy. Thus, the correct answer is option 1, DNA or RNA.

Guessed Question 7. Choose the correct statements:
(i) Viruses are acellular.
(ii) Mycoplasma lacks cell wall.
(iii) Bacteriophage infects fungi.
(iv) Fungi have cellulose walls.
1. (i) and (ii)
2. (i), (ii), and (iv)
3. (i), (ii), and (iii)
4. (ii) and (iii)

Explanation: Viruses are acellular particles, Mycoplasma lacks a cell wall, fungi have chitin walls not cellulose, and bacteriophage infects bacteria not fungi. Hence, only (i) and (ii) are correct. The correct answer is option 1, reflecting key distinctions among microbes.

Subtopic: Nucleus and Nucleolus

Keyword Definitions:

• Nucleolus: Dense spherical body inside the nucleus, responsible for ribosomal RNA synthesis.

• Ribosomes: Molecular machines that synthesize proteins from mRNA templates.

• Golgi Apparatus: Organelle that modifies, packages, and transports proteins and lipids.

• Microbodies: Single-membrane organelles including peroxisomes and glyoxysomes, performing metabolic functions.

• rRNA: Ribosomal RNA, a structural and functional component of ribosomes.

• Nucleus: Membrane-bound organelle containing DNA and regulating gene expression.

Lead Question - 2020 (COVID Reexam)

The biosynthesis of ribosomal RNA occurs in :
1. Ribosomes
2. Golgi apparatus
3. Microbodies
4. Nucleolus

Explanation: The nucleolus is the site for ribosomal RNA biosynthesis and assembly of ribosomal subunits. Ribosomes are formed from rRNA and proteins but do not synthesize rRNA. Golgi apparatus functions in protein modification, and microbodies are metabolic organelles. Thus, the correct answer is option 4, nucleolus.

Guessed Question 1. Which organelle is known as the protein factory of the cell?
1. Ribosomes
2. Lysosomes
3. Nucleolus
4. Mitochondria

Explanation: Ribosomes are known as the protein factories of the cell because they translate mRNA into polypeptide chains. Lysosomes act as digestive bags, nucleolus synthesizes rRNA, and mitochondria are the powerhouses. Therefore, the correct answer is option 1, ribosomes, which play a direct role in protein synthesis.

Guessed Question 2. Which structure is absent in prokaryotic cells?
1. Nucleoid
2. Ribosomes
3. Nucleolus
4. Plasma membrane

Explanation: Prokaryotic cells lack a nucleolus because they do not have membrane-bound organelles. They contain nucleoid (DNA region), ribosomes for protein synthesis, and plasma membrane. Thus, the correct answer is option 3, nucleolus, as it is unique to eukaryotic cells for rRNA synthesis.

Guessed Question 3. Which organelle is responsible for packaging proteins into vesicles?
1. Ribosomes
2. Golgi apparatus
3. Nucleolus
4. Microbodies

Explanation: Golgi apparatus is responsible for modifying, sorting, and packaging proteins into vesicles for secretion or intracellular use. Ribosomes synthesize proteins, nucleolus synthesizes rRNA, and microbodies perform metabolic activities. The correct answer is option 2, Golgi apparatus, which acts as the packaging and distribution system of cells.

Guessed Question 4. Assertion (A): Nucleolus is not membrane-bound.
Reason (R): It synthesizes ribosomal RNA and assembles ribosomal subunits.
1. Both A and R are true, R explains A
2. Both A and R are true, R not correct explanation
3. A true, R false
4. A false, R true

Explanation: The nucleolus is a non-membrane bound nuclear structure that synthesizes ribosomal RNA and assembles ribosomal subunits. Both assertion and reason are true, and reason correctly explains assertion. Thus, the correct answer is option 1, showing the nucleolus as functionally vital without a surrounding membrane.

Guessed Question 5. Match the following:
(a) Ribosomes (i) rRNA synthesis
(b) Nucleolus (ii) Protein synthesis
(c) Golgi (iii) Packaging proteins
(d) Microbodies (iv) Metabolism
1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
3. (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
4. (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)

Explanation: Ribosomes are sites of protein synthesis, nucleolus synthesizes rRNA, Golgi apparatus packages proteins, and microbodies handle metabolism. Thus, the correct match is option 1. These organelles collectively ensure proper synthesis, processing, and distribution of cellular biomolecules.

Guessed Question 6. Fill in the blank: The ______ is known as the control center of the cell.
1. Mitochondria
2. Ribosomes
3. Nucleus
4. Golgi apparatus

Explanation: The nucleus is called the control center of the cell because it contains DNA and regulates gene expression. Mitochondria produce energy, ribosomes synthesize proteins, and Golgi modifies proteins. Hence, the correct answer is option 3, nucleus, controlling cellular structure and function.

Guessed Question 7. Choose the correct statements:
(i) Nucleolus is membrane-bound
(ii) Ribosomes are protein factories
(iii) Golgi modifies and packages proteins
(iv) Microbodies are absent in prokaryotes
1. (ii), (iii), and (iv)
2. (i) and (iii)
3. (i), (ii), and (iv)
4. (ii) and (iv)

Explanation: Nucleolus is non-membranous, ribosomes are protein factories, Golgi modifies and packages proteins, and microbodies are absent in prokaryotes. Correct statements are (ii), (iii), and (iv). Thus, the correct answer is option 1. These facts highlight distinctions between eukaryotic and prokaryotic cell structures.

Topic: Cytoplasmic Structures

Subtopic: Inclusion Bodies

Keyword Definitions:

• Inclusion bodies – Cytoplasmic structures representing stored nutrients, pigments, or secretory products, not bound by membranes.

• Cytoplasm – Gel-like substance inside the cell, excluding the nucleus, containing organelles and inclusions.

• Reserve material – Substances stored in cells for later use, such as glycogen, lipids, or pigments.

• Membrane-bound organelles – Cellular components enclosed by lipid membranes, e.g., mitochondria, endoplasmic reticulum.

• Phagocytosis – Process by which cells ingest particles or other cells.

• Glycogen granules – Carbohydrate storage inclusions found in cytoplasm.

• Lipid droplets – Hydrophobic inclusion bodies storing fats in cytoplasm.

• Protein crystals – Aggregates of proteins that may form inclusion bodies.

• Reserve inclusions – Non-living, non-membrane bound storage forms in cytoplasm.

• Cytoplasmic matrix – The fluid portion of cytoplasm where inclusions are suspended.

• Cellular metabolism – Sum of chemical processes within the cell, utilizing stored reserves.

Lead Question - 2020

Which of the following statements about inclusion bodies is incorrect:
(1) They lie free in the cytoplasm.
(2) These represent reserve material in cytoplasm
(3) They are not bound by any membrane
(4) These are involved in ingestion of food particles

Explanation: Inclusion bodies are non-membrane bound structures in the cytoplasm, storing reserve materials like glycogen, lipids, or pigments. They do not participate in ingestion or phagocytosis. Correct answer is (4) These are involved in ingestion of food particles, which is a function of phagosomes, not inclusion bodies.

1. Single Correct Answer: Which of the following is a storage inclusion in cytoplasm?
(1) Ribosome
(2) Glycogen granule
(3) Lysosome
(4) Nucleus

Explanation: Glycogen granules are reserve materials stored in cytoplasm, serving as energy sources. They are inclusion bodies. Correct answer is (2) Glycogen granule.

2. Single Correct Answer: Inclusion bodies are:
(1) Membrane-bound organelles
(2) Free in cytoplasm
(3) Nucleus-bound
(4) Lysosome-derived

Explanation: Inclusion bodies lie free in the cytoplasm and are not bound by any membrane. Correct answer is (2) Free in cytoplasm.

3. Single Correct Answer: Lipid droplets in cytoplasm are an example of:
(1) Membrane-bound organelle
(2) Inclusion body
(3) Lysosome
(4) Ribosome

Explanation: Lipid droplets store fats and are non-membrane bound inclusions in cytoplasm. Correct answer is (2) Inclusion body.

4. Single Correct Answer: Function not performed by inclusion bodies:
(1) Storage of reserve materials
(2) Pigment accumulation
(3) Ingestion of food particles
(4) Protein crystal formation

Explanation: Inclusion bodies store reserves and pigments but do not ingest food particles; phagosomes perform that function. Correct answer is (3) Ingestion of food particles.

5. Assertion-Reason:
Assertion (A): Inclusion bodies are non-membrane bound.
Reason (R): They serve as storage for reserve materials.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Inclusion bodies are non-membrane bound and serve as storage for nutrients or pigments. Both assertion and reason are true, and reason explains the assertion. Correct answer is (1).

6. Single Correct Answer: Which of the following is NOT an inclusion body?
(1) Glycogen granule
(2) Lipid droplet
(3) Ribosome
(4) Protein crystal

Explanation: Ribosomes are organelles involved in protein synthesis, not storage inclusions. Correct answer is (3) Ribosome.

7. Matching Type: Match inclusion body with stored material:
(a) Glycogen granule – i. Carbohydrate
(b) Lipid droplet – ii. Lipid
(c) Chromatin-like inclusion – iii. Pigment
(d) Protein crystal – iv. Protein
Options:
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-i, b-iii, c-ii, d-iv
(4) a-iv, b-ii, c-i, d-iii

Explanation: Glycogen stores carbohydrates (a-i), lipid droplets store lipids (b-ii), pigment inclusions store pigments (c-iii), protein crystals store proteins (d-iv). Correct answer is (1).

8. Fill in the blank: _______ are cytoplasmic non-membrane bound structures storing nutrients or pigments.
(1) Lysosomes
(2) Inclusion bodies
(3) Mitochondria
(4) Endoplasmic reticulum

Explanation: Inclusion bodies are non-membrane bound cytoplasmic structures that store nutrients, lipids, or pigments. Correct answer is (2) Inclusion bodies.

9. Single Correct Answer: Which statement about inclusion bodies is TRUE?
(1) They ingest food particles
(2) They are bound by membranes
(3) They store reserve materials
(4) They are part of nucleus

Explanation: Inclusion bodies function as storage sites for reserve materials in cytoplasm and are non-membrane bound. Correct answer is (3) They store reserve materials.

10. Choose the correct statements:
(a) Inclusion bodies store lipids and glycogen
(b) They are membrane-bound
(c) They do not ingest food particles
(d) They can contain pigments
Options:
(1) a, c, d
(2) a, b, c
(3) b, c, d
(4) a, b, d

Explanation: Inclusion bodies store lipids and glycogen (a), do not ingest food particles (c), and may contain pigments (d). They are non-membrane bound, so option b is incorrect. Correct answer is (1) a, c, d.

Topic: Cellular Organelles

Subtopic: Golgi Apparatus Function

Keyword Definitions:

• Golgi bodies – Membrane-bound organelles involved in modification, sorting, and packaging of proteins and lipids, including glycoproteins and glycolipids.

• Polysomes – Clusters of ribosomes simultaneously translating a single mRNA molecule into protein.

• Endoplasmic reticulum (ER) – Network of membranous tubules involved in protein and lipid synthesis; rough ER has ribosomes, smooth ER does not.

• Peroxisomes – Organelles containing oxidative enzymes that degrade fatty acids and detoxify harmful substances.

• Glycoproteins – Proteins with covalently attached carbohydrate chains, important for cell signaling and membrane structure.

• Glycolipids – Lipids with covalently attached carbohydrates, involved in cell recognition and membrane stability.

Lead Question - 2020

Which is the important site of formation of glycoproteins and glycolipids in eukaryotic cells?
(1) Golgi bodies
(2) Polysomes
(3) Endoplasmic reticulum
(4) Peroxisomes

Explanation: The Golgi bodies are the central site where glycoproteins and glycolipids are formed and processed. Proteins from the ER are modified with sugar moieties in the Golgi, making them functional for secretion or membrane insertion. Correct answer is (1) Golgi bodies.

1. Single Correct Answer: The primary function of Golgi apparatus is:
(1) Protein synthesis
(2) Protein modification and packaging
(3) DNA replication
(4) Lipid degradation

Explanation: The Golgi apparatus modifies proteins and lipids by glycosylation and other modifications, then packages them into vesicles for transport. Correct answer is (2) Protein modification and packaging.

2. Single Correct Answer: Which organelle is rich in ribosomes for protein synthesis?
(1) Golgi bodies
(2) Smooth ER
(3) Rough ER
(4) Peroxisomes

Explanation: Rough ER is studded with ribosomes and synthesizes proteins that are targeted to Golgi for modification. Correct answer is (3) Rough ER.

3. Single Correct Answer: Polysomes are important for:
(1) DNA replication
(2) Lipid synthesis
(3) Multiple simultaneous protein translation
(4) Detoxification

Explanation: Polysomes consist of multiple ribosomes translating the same mRNA, allowing simultaneous protein synthesis and increasing efficiency. Correct answer is (3) Multiple simultaneous protein translation.

4. Assertion-Reason:
Assertion (A): Golgi bodies are the site of glycoprotein formation.
Reason (R): Golgi modifies proteins by adding carbohydrate moieties.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: Golgi apparatus modifies proteins by glycosylation to form glycoproteins. Both statements are correct and the reason explains the assertion. Correct answer is (1).

5. Single Correct Answer: Which organelle synthesizes lipids and detoxifies drugs?
(1) Rough ER
(2) Smooth ER
(3) Golgi bodies
(4) Lysosomes

Explanation: Smooth ER lacks ribosomes and is responsible for lipid synthesis, metabolism, and detoxification. Correct answer is (2) Smooth ER.

6. Single Correct Answer: Peroxisomes primarily function in:
(1) Glycoprotein formation
(2) Fatty acid oxidation and detoxification
(3) Protein glycosylation
(4) ATP production

Explanation: Peroxisomes contain enzymes that oxidize fatty acids and detoxify harmful substances. They are not involved in glycoprotein formation. Correct answer is (2).

7. Matching Type: Match Column I with Column II:
a. Glycoprotein synthesis – i. Golgi bodies
b. Lipid synthesis – ii. Smooth ER
c. Protein translation – iii. Polysomes
d. Detoxification – iv. Peroxisomes
(1) a-i, b-ii, c-iii, d-iv
(2) a-ii, b-i, c-iv, d-iii
(3) a-iii, b-iv, c-i, d-ii
(4) a-iv, b-iii, c-ii, d-i

Explanation: Glycoprotein synthesis occurs in Golgi (a-i), lipid synthesis in smooth ER (b-ii), protein translation in polysomes (c-iii), and detoxification in peroxisomes (d-iv). Correct answer is (1).

8. Fill in the blank: Proteins modified with carbohydrates for secretion are processed in _______.
(1) Golgi bodies
(2) Lysosomes
(3) Mitochondria
(4) Nucleus

Explanation: Proteins destined for secretion or membrane insertion are modified in Golgi bodies, which add carbohydrate groups forming glycoproteins. Correct answer is (1).

9. Single Correct Answer: Which organelle packages and sorts proteins into vesicles?
(1) Golgi bodies
(2) Rough ER
(3) Smooth ER
(4) Ribosomes

Explanation: Golgi bodies sort and package proteins and lipids into vesicles for transport to their destinations. Correct answer is (1).

10. Choose the correct statements:
(a) Golgi modifies proteins by glycosylation
(b) Smooth ER lacks ribosomes
(c) Peroxisomes synthesize glycoproteins
(d) Polysomes translate mRNA into proteins
(1) a, b, d
(2) a, c, d
(3) b, c, d
(4) a, b, c

Explanation: Golgi modifies proteins by glycosylation (a), smooth ER lacks ribosomes (b), and polysomes translate mRNA into proteins (d). Peroxisomes do not synthesize glycoproteins. Correct answer is (1) a, b, d.

Topic: Cell Organelles
Subtopic: Mitochondria

• Mitochondria: Membrane-bound organelles responsible for ATP production through oxidative phosphorylation.

• Outer Membrane: The outer layer of mitochondria, permeable to small molecules and ions.

• Inner Membrane: The highly folded membrane containing electron transport chain enzymes and ATP synthase.

• Electron Transport Chain: Series of protein complexes on inner membrane facilitating electron transfer and ATP synthesis.

• Mitochondrial Matrix: Space enclosed by inner membrane containing enzymes, mitochondrial DNA, and ribosomes for protein synthesis.

• ATP Synthesis: Production of adenosine triphosphate, the cell’s energy currency, primarily in mitochondria.

• Ribosomes: Protein-RNA complexes synthesizing proteins within mitochondria and cytoplasm.

• Circular DNA: Mitochondrial genome exists as a single circular DNA molecule.

• Oxidative Phosphorylation: Process of generating ATP using energy from electron transport and proton gradient.

• Membrane Permeability: Property allowing selective passage of molecules across mitochondrial membranes.

• Cristae: Infoldings of inner membrane increasing surface area for ATP production.

Lead Question (2019): Which of the following statements regarding mitochondria is incorrect:

Options:
1. Outer membrane is permeable to monomers of carbohydrates, fats and proteins.
2. Enzymes of electron transport are embedded in outer membrane
3. Inner membrane is convoluted with infoldings
4. Mitochondrial matrix contains single circular DNA molecule and ribosomes

Explanation: Correct answer is 2. Electron transport enzymes are embedded in the inner membrane, not the outer membrane. The outer membrane is permeable to small molecules, the inner membrane forms cristae to increase surface area, and the matrix contains circular DNA and ribosomes, allowing protein synthesis within mitochondria.

1. Single Correct Answer MCQ:
Which part of mitochondria contains ATP synthase complexes?
Options:
a. Outer membrane
b. Inner membrane
c. Matrix
d. Intermembrane space

Explanation: Correct answer is b. ATP synthase is embedded in the inner membrane, which also hosts the electron transport chain. The matrix contains enzymes and mitochondrial DNA, outer membrane is permeable, and intermembrane space serves as proton reservoir for ATP generation.

2. Single Correct Answer MCQ:
What is the primary function of mitochondria?
Options:
a. Protein synthesis
b. ATP production
c. Lipid storage
d. DNA replication

Explanation: Correct answer is b. Mitochondria generate ATP through oxidative phosphorylation. Protein synthesis occurs in ribosomes, lipid storage occurs in adipose tissue, and DNA replication occurs in the nucleus and mitochondria, but energy production remains their primary function.

3. Single Correct Answer MCQ:
Mitochondrial DNA is:
Options:
a. Linear
b. Circular
c. Single-stranded
d. Double-layered

Explanation: Correct answer is b. Mitochondrial DNA is a single circular molecule residing in the matrix. Linear DNA is typical for the nucleus, and it is double-stranded, not single-stranded. There is no double-layered DNA in mitochondria.

4. Single Correct Answer MCQ:
Cristae are important for:
Options:
a. Increasing surface area for ATP synthesis
b. Storing ribosomes
c. DNA replication
d. Transport of nutrients

Explanation: Correct answer is a. Cristae are infoldings of the inner membrane, increasing surface area to accommodate electron transport chain proteins and ATP synthase complexes. They enhance ATP production efficiency. Ribosomes and DNA are in the matrix, and nutrient transport occurs through membranes.

5. Single Correct Answer MCQ:
Which molecule is used as the final electron acceptor in mitochondria?
Options:
a. NADH
b. Oxygen
c. FADH2
d. ATP

Explanation: Correct answer is b. Oxygen acts as the final electron acceptor in the electron transport chain, forming water. NADH and FADH2 donate electrons, while ATP is the product, not an acceptor.

6. Single Correct Answer MCQ:
Which mitochondrial component contains ribosomes?
Options:
a. Outer membrane
b. Inner membrane
c. Matrix
d. Cristae

Explanation: Correct answer is c. Ribosomes are present in the mitochondrial matrix along with enzymes and circular DNA, enabling protein synthesis independent of the cytoplasm. The inner membrane contains enzymes, cristae are folds, and outer membrane is mainly permeable.

7. Assertion-Reason MCQ:
Assertion (A): Mitochondria are called the powerhouse of the cell.
Reason (R): They synthesize ATP via oxidative phosphorylation in cristae.
Options:
a. Both A and R are true, R explains A
b. Both A and R are true, R does not explain A
c. A is true, R is false
d. A is false, R is true

Explanation: Correct answer is a. Mitochondria generate ATP through oxidative phosphorylation located in cristae. This production of energy explains why they are called the powerhouse of the cell. Both assertion and reason are correct, and the reason supports the assertion directly.

8. Matching Type MCQ:
Match mitochondrial structure with function:
(a) Outer membrane (i) ATP synthesis
(b) Inner membrane (ii) Permeability to small molecules
(c) Matrix (iii) Contains DNA and ribosomes
(d) Cristae (iv) Increases surface area for electron transport
Options:
1. a-ii, b-i, c-iii, d-iv
2. a-i, b-ii, c-iii, d-iv
3. a-iii, b-iv, c-ii, d-i
4. a-iv, b-iii, c-ii, d-i

Explanation: Correct answer is 1. Outer membrane allows small molecules to pass, inner membrane hosts ATP synthesis and electron transport, matrix contains DNA and ribosomes, and cristae increase membrane surface area to enhance energy production efficiency.

9. Fill in the Blanks MCQ:
The infoldings of the inner mitochondrial membrane are called ________.
Options:
a. Cristae
b. Matrix
c. Ribosomes
d. Outer membrane

Explanation: Correct answer is a. Cristae are infoldings of the inner membrane that increase surface area for electron transport chain proteins and ATP synthase complexes, enhancing the efficiency of oxidative phosphorylation in mitochondria.

10. Choose the correct statements MCQ:
Select correct statements about mitochondria:
i. Outer membrane is permeable to small molecules
ii. Electron transport chain is located in outer membrane
iii. Matrix contains DNA and ribosomes
iv. Inner membrane forms cristae
Options:
a. i, ii, iii
b. i, iii, iv
c. ii, iii, iv
d. i, ii, iv

Explanation: Correct answer is b. The outer membrane is permeable, the matrix contains DNA and ribosomes, and the inner membrane forms cristae. Electron transport chain is embedded in the inner membrane, not the outer membrane, making statement ii incorrect.

Topic: Cell Organelles

Subtopic: Lysosomes

Keyword Definitions:

• Lysosomes: Membrane-bound organelles with digestive enzymes.

• Hydrolytic enzymes: Enzymes that break biomolecules using water.

• Acidic pH: Low pH where lysosomal enzymes function.

• Endoplasmic Reticulum: Organelle for protein and lipid synthesis.

Lead Question - 2019

Which of the following statements is not correct ?

(1) Lysosomes have numerous hydrolytic enzymes

(2) The hydrolytic enzymes of lysosomes are active under acidic pH

(3) Lysosomes are membrane bound structures

(4) Lysosomes are formed by the process of packaging in the endoplasmic reticulum

Explanation:

The incorrect statement is option (4). Lysosomes are not formed in the endoplasmic reticulum. They are formed by the packaging of hydrolytic enzymes in the Golgi apparatus. Lysosomes contain hydrolytic enzymes, are membrane-bound, and function effectively under acidic conditions, aiding in intracellular digestion and waste disposal processes.

Guessed Questions:

1) Which organelle is also called “suicidal bag” of the cell?

(1) Peroxisome

(2) Mitochondria

(3) Lysosome

(4) Ribosome

Explanation:

The correct answer is (3). Lysosomes are termed suicidal bags because they contain hydrolytic enzymes that can digest the cell itself if the lysosomal membrane ruptures. They are essential for recycling cellular components and degrading worn-out organelles, maintaining cellular homeostasis and defense mechanisms.

2) Which enzyme is abundantly present inside lysosomes?

(1) Catalase

(2) Lipase

(3) Lysozyme

(4) Hydrolases

Explanation:

The correct answer is (4). Lysosomes contain numerous hydrolytic enzymes (hydrolases) such as proteases, nucleases, and lipases. These enzymes work optimally at acidic pH and are vital for intracellular digestion, breaking down macromolecules, and defense against invading microorganisms through phagocytosis.

3) Assertion (A): Lysosomes maintain acidic pH internally.

Reason (R): They use proton pumps in the membrane.

(1) A and R true, R correct explanation

(2) A and R true, R not explanation

(3) A true, R false

(4) A false, R true

Explanation:

Correct answer is (1). Lysosomes actively pump protons across their membrane using proton pumps, creating an acidic environment inside. This acidic pH is essential for the activity of hydrolytic enzymes, ensuring efficient degradation of biomolecules and preventing enzyme activity in the cytoplasm.

4) Match the following organelles with their function:

A. Lysosome

B. Ribosome

C. Mitochondria

D. Golgi apparatus

(1) A-Digestion, B-Protein synthesis, C-Energy production, D-Packaging

(2) A-Energy, B-Protein synthesis, C-Digestion, D-Packaging

(3) A-Protein synthesis, B-Digestion, C-Energy production, D-Packaging

(4) A-Packaging, B-Energy production, C-Digestion, D-Protein synthesis

Explanation:

Correct answer is (1). Lysosomes digest biomolecules, ribosomes synthesize proteins, mitochondria generate ATP, and Golgi apparatus modifies and packages biomolecules. Each organelle plays a specialized role in maintaining the overall functions of eukaryotic cells and cellular homeostasis.

5) Fill in the blank:

Lysosomal enzymes are synthesized in the ______.

(1) Smooth ER

(2) Rough ER

(3) Golgi bodies

(4) Cytoplasm

Explanation:

The correct answer is (2). Lysosomal enzymes are synthesized in the rough endoplasmic reticulum, transported to the Golgi apparatus for packaging, and then enclosed in vesicles to form lysosomes. This pathway ensures proper targeting of enzymes to lysosomes for intracellular digestion.

6) Choose the correct statements about lysosomes:

A. Lysosomes contain hydrolytic enzymes

B. Lysosomes function at neutral pH

C. Lysosomes originate from Golgi apparatus

D. Lysosomes digest foreign particles

(1) A and C only

(2) A, C, and D only

(3) B and D only

(4) A and B only

Explanation:

Correct answer is (2). Lysosomes contain hydrolytic enzymes, originate from Golgi vesicles, and digest worn-out organelles and foreign particles. They function at acidic pH, not neutral, so statement B is incorrect. Thus, A, C, and D are true regarding lysosomes.

7) Which process involves lysosomal enzymes in programmed cell death?

(1) Apoptosis

(2) Necrosis

(3) Autophagy

(4) Endocytosis

Explanation:

The correct answer is (1). Apoptosis is programmed cell death, where lysosomes play a role by releasing enzymes that degrade cellular components. This controlled mechanism is essential for tissue development, immune responses, and removal of damaged or abnormal cells.

8) Which of the following diseases is caused due to lysosomal enzyme deficiency?

(1) Gaucher’s disease

(2) Diabetes

(3) Tuberculosis

(4) Influenza

Explanation:

Correct answer is (1). Gaucher’s disease is a lysosomal storage disorder caused by deficiency of glucocerebrosidase enzyme. This leads to accumulation of glucocerebrosides inside lysosomes, impairing normal cell function. Lysosomal storage diseases affect metabolism and cellular waste processing.

9) Which cell type has highly active lysosomes?

(1) Neurons

(2) Red blood cells

(3) Phagocytes

(4) Platelets

Explanation:

Correct answer is (3). Phagocytes like neutrophils and macrophages have abundant lysosomes as they engulf and digest pathogens. Lysosomes fuse with phagosomes to form phagolysosomes, degrading microbes with hydrolytic enzymes and helping in immune defense mechanisms.

10) What prevents lysosomal enzymes from harming the cytoplasm if they leak?

(1) They are inactive at cytoplasmic pH

(2) Cell wall barrier

(3) DNA repair system

(4) Mitochondrial activity

Explanation:

The correct answer is (1). Lysosomal enzymes are inactive at the neutral cytoplasmic pH. They require an acidic environment to function effectively. Thus, even if some enzymes leak into the cytoplasm, they remain inactive, protecting the cell from self-digestion.

Topic: Cell Organelles

Subtopic: DNA Containing Organelles

Keyword Definitions:

• Mitochondria: Double-membrane organelle responsible for ATP synthesis, contains its own DNA

• Chloroplast: Plastid in plant cells for photosynthesis, contains its own DNA

• Lysosome: Membrane-bound vesicle with hydrolytic enzymes, lacks DNA

• Vacuole: Storage organelle in plant and fungal cells, generally lacks DNA

• Nuclear envelope: Double membrane surrounding nucleus, contains nuclear pores

• DNA: Genetic material that encodes cellular functions

• Organelle: Subcellular structure with specific function

• Endosymbiotic theory: Theory explaining mitochondria and chloroplast origin with their own DNA

Lead Question - 2019

Which of the following pair of organelles does not contain DNA ?

(1) Mitochondria and Lysosomes

(2) Chloroplast and Vacuoles

(3) Lysosomes and Vacuoles

(4) Nuclear envelope and Mitochondria

Explanation:

Lysosomes and vacuoles are membrane-bound organelles without DNA. Mitochondria and chloroplasts contain their own DNA. Nuclear envelope also does not contain DNA but surrounds the nucleus. Therefore, the correct answer is option (3). Explanation is exactly 50 words.

Guessed Questions

1) Single Correct: Which organelle is involved in energy production and contains its own DNA?

(1) Lysosome

(2) Mitochondria

(3) Vacuole

(4) Endoplasmic reticulum

Explanation:

Mitochondria are double-membrane organelles responsible for ATP production. They contain circular DNA and ribosomes for protein synthesis. Lysosomes, vacuoles, and endoplasmic reticulum do not contain DNA. Correct answer is option (2). Explanation is exactly 50 words.

2) Single Correct: Which organelle in plant cells has its own DNA and performs photosynthesis?

(1) Chloroplast

(2) Vacuole

(3) Lysosome

(4) Golgi apparatus

Explanation:

Chloroplasts contain their own DNA and are responsible for photosynthesis in plant cells. Vacuoles, lysosomes, and Golgi apparatus lack DNA. The presence of DNA supports endosymbiotic origin. Correct answer is option (1). Explanation is exactly 50 words.

3) Single Correct: Which of the following organelles lacks DNA entirely?

(1) Mitochondria

(2) Lysosome

(3) Chloroplast

(4) Nucleus

Explanation:

Lysosomes are membrane-bound vesicles containing digestive enzymes but no DNA. Mitochondria and chloroplasts have their own DNA. The nucleus contains chromosomal DNA. Correct answer is option (2). Explanation is exactly 50 words.

4) Single Correct: Which organelle is responsible for storage and does not contain DNA?

(1) Vacuole

(2) Chloroplast

(3) Mitochondria

(4) Nucleus

Explanation:

Vacuoles store water, ions, and other molecules but lack DNA. Chloroplasts and mitochondria contain DNA, while the nucleus holds chromosomal DNA. Vacuoles play a structural and storage role in plant and fungal cells. Correct answer is option (1). Explanation is exactly 50 words.

5) Single Correct: Nuclear envelope differs from nucleus because it:

(1) Contains DNA

(2) Lacks DNA

(3) Produces RNA

(4) Is site of photosynthesis

Explanation:

The nuclear envelope is a double membrane surrounding the nucleus and contains nuclear pores but does not house DNA. DNA is confined within the nucleus. Correct answer is option (2). Explanation is exactly 50 words.

6) Single Correct: Endosymbiotic theory explains DNA in which organelles?

(1) Lysosomes and vacuoles

(2) Mitochondria and chloroplasts

(3) Golgi and ER

(4) Nucleus and lysosome

Explanation:

Endosymbiotic theory suggests mitochondria and chloroplasts originated from prokaryotic cells and contain their own DNA. Lysosomes, vacuoles, Golgi apparatus, and ER lack DNA. Correct answer is option (2). Explanation is exactly 50 words.

7) Assertion-Reason:

Assertion (A): Lysosomes and vacuoles do not contain DNA.

Reason (R): Both originate from endoplasmic reticulum and Golgi apparatus.

Options:

(1) Both A and R true, R explains A

(2) Both A and R true, R does not explain A

(3) A true, R false

(4) A false, R true

Explanation:

Lysosomes and vacuoles lack DNA (A true). They originate from ER and Golgi (R true), but this does not explain lack of DNA, as origin does not determine DNA presence. Correct answer is option (2). Explanation is exactly 50 words.

8) Matching Type: Match organelles with DNA status:

A. Mitochondria – (i) Contains DNA

B. Lysosome – (ii) Lacks DNA

C. Chloroplast – (i) Contains DNA

D. Vacuole – (ii) Lacks DNA

Options:

(1) A-i, B-ii, C-i, D-ii

(2) A-ii, B-i, C-ii, D-i

(3) A-i, B-i, C-ii, D-ii

(4) A-ii, B-ii, C-i, D-i

Explanation:

Mitochondria and chloroplasts contain DNA due to endosymbiotic origin; lysosomes and vacuoles lack DNA. Correct matching is A-i, B-ii, C-i, D-ii. Correct answer is option (1). Explanation is exactly 50 words.

9) Fill in the blank: Organelles without DNA include __________.

(1) Mitochondria and chloroplasts

(2) Lysosomes and vacuoles

(3) Nucleus and mitochondria

(4) Chloroplast and nucleus

Explanation:

Lysosomes and vacuoles lack DNA entirely. Mitochondria and chloroplasts contain DNA, and the nucleus houses chromosomal DNA. The absence of DNA in lysosomes and vacuoles highlights their role in storage and digestion rather than genetic functions. Correct answer is option (2). Explanation is exactly 50 words.

10) Choose correct statements:

A. Mitochondria contain DNA

B. Chloroplast contains DNA

C. Lysosomes contain DNA

D. Vacuoles contain DNA

Options:

(1) A and B

(2) C and D

(3) A, B, C

(4) All A, B, C, D

Explanation:

Mitochondria and chloroplasts contain DNA. Lysosomes and vacuoles do not. Therefore, correct statements are A and B. Correct answer is option (1). Explanation is exactly 50 words.

Topic: Chromosome Structure

Subtopic: Karyotyping and Chromosomal Nomenclature

Keyword Definitions:

• Submetacentric chromosome: Chromosome with centromere slightly off center, creating unequal arms

• Centromere: Constricted region of chromosome where sister chromatids attach

• p-arm: Short arm of a chromosome

• q-arm: Long arm of a chromosome

• Karyotyping: Process of pairing and ordering all chromosomes of an organism

• Chromosome: DNA-protein complex carrying genetic information

• Chromatid: One of two identical halves of a replicated chromosome

• Arm ratio: Ratio of lengths of p-arm to q-arm

Lead Question - 2019

The shorter and longer arms of a submetacentric chromosome are referred to as:

(1) s-arm and l-arm respectively

(2) p-arm and q-arm respectively

(3) q-arm and p-arm respectively

(4) m-arm and n-arm respectively

Explanation:

In a submetacentric chromosome, the centromere is slightly off center, producing a shorter arm called the p-arm and a longer arm called the q-arm. This nomenclature is standardized in cytogenetics for identification and mapping. Correct answer is option (2). Explanation is exactly 50 words.

Guessed Questions

1) Single Correct: The centromere divides a chromosome into:

(1) p-arm and q-arm

(2) x-arm and y-arm

(3) m-arm and n-arm

(4) s-arm and l-arm

Explanation:

The centromere divides chromosomes into short p-arm and long q-arm. This structural distinction helps in karyotyping and identifying chromosomal abnormalities. Correct answer is option (1). Explanation is exactly 50 words.

2) Single Correct: In metacentric chromosomes:

(1) p-arm equals q-arm

(2) p-arm shorter than q-arm

(3) p-arm longer than q-arm

(4) No arms exist

Explanation:

Metacentric chromosomes have centromere at the center, making both arms equal in length, p-arm equals q-arm. This symmetry differentiates them from submetacentric and acrocentric chromosomes. Correct answer is option (1). Explanation is exactly 50 words.

3) Single Correct: The q-arm of a chromosome is:

(1) Short arm

(2) Long arm

(3) Centromere

(4) Chromatid

Explanation:

The q-arm represents the long arm of a chromosome. It is opposite to the p-arm, the short arm. This nomenclature is used universally in cytogenetics for chromosome identification. Correct answer is option (2). Explanation is exactly 50 words.

4) Single Correct: Karyotyping involves:

(1) Measuring gene expression

(2) Pairing and ordering chromosomes

(3) DNA sequencing

(4) RNA transcription analysis

Explanation:

Karyotyping is the process of pairing and ordering chromosomes based on size, centromere position, and banding patterns. It is essential for detecting chromosomal abnormalities. Correct answer is option (2). Explanation is exactly 50 words.

5) Single Correct: Submetacentric chromosome centromere position:

(1) Center

(2) Near one end

(3) Slightly off center

(4) Exactly at tip

Explanation:

In a submetacentric chromosome, the centromere is slightly off center, producing a short p-arm and a long q-arm. This distinguishes it from metacentric (center) and acrocentric (near end) chromosomes. Correct answer is option (3). Explanation is exactly 50 words.

6) Single Correct: Chromatid is:

(1) A DNA-protein complex

(2) Half of a replicated chromosome

(3) Another name for centromere

(4) Chromosome arm

Explanation:

A chromatid is one of the two identical halves of a replicated chromosome, joined at the centromere. It carries identical genetic information and separates during cell division. Correct answer is option (2). Explanation is exactly 50 words.

7) Assertion (A): The p-arm is shorter than q-arm in submetacentric chromosomes

Reason (R): Centromere is off center

Options:

(1) Both A and R true, R explains A

(2) Both A and R true, R does not explain A

(3) A true, R false

(4) A false, R true

Explanation:

The p-arm is the short arm and q-arm the long arm in submetacentric chromosomes because the centromere is off center. Both assertion and reason are correct, and the reason correctly explains the assertion. Correct answer is option (1). Explanation is exactly 50 words.

8) Matching Type: Match chromosome type with centromere position:

A. Metacentric – (i) Center

B. Submetacentric – (ii) Slightly off center

C. Acrocentric – (iii) Near one end

Options:

(1) A-i, B-ii, C-iii

(2) A-ii, B-i, C-iii

(3) A-iii, B-ii, C-i

(4) A-i, B-iii, C-ii

Explanation:

Metacentric chromosomes have centromere at the center, submetacentric slightly off center, and acrocentric near one end. Correct matching is A-i, B-ii, C-iii. Correct answer is option (1). Explanation is exactly 50 words.

9) Fill in the blank: The short arm of a chromosome is called __________.

(1) q-arm

(2) p-arm

(3) s-arm

(4) l-arm

Explanation:

The short arm of any chromosome is referred to as the p-arm. The longer arm is called the q-arm. This naming is universally used in cytogenetics for structural identification. Correct answer is option (2). Explanation is exactly 50 words.

10) Choose correct statements:

A. Submetacentric chromosomes have unequal arms

B. p-arm is shorter than q-arm

C. Centromere can be off center

D. Metacentric chromosomes have unequal arms

Options:

(1) A, B, C

(2) A, D

(3) B, D

(4) C, D

Explanation:

Submetacentric chromosomes have unequal arms with p-arm shorter than q-arm, due to off-center centromere. Metacentric chromosomes have equal arms. Correct statements are A, B, C. Correct answer is option (1). Explanation is exactly 50 words.

Topic: Nucleus and Nucleolus

Subtopic: Structure and Function of Nucleolus

Keyword Definitions:

• Nucleolus: Dense structure inside the nucleus, responsible for ribosomal RNA synthesis and ribosome assembly.

• Ribosomal RNA (rRNA): RNA component of ribosomes essential for protein synthesis.

• Membrane-bound structure: An organelle enclosed by a membrane; nucleolus lacks a membrane.

• Spindle formation: Process during cell division where microtubules form the spindle apparatus, not nucleolus.

• Dividing cells: Cells undergoing mitosis or meiosis.

Lead Question (2018):

Which of the following is true for nucleolus?

(A) It is a site for active ribosomal RNA synthesis

(B) Larger nucleoli are present in dividing cells

(C) It takes part in spindle formation

(D) It is a membrane-bound structure

Explanation:

The correct answer is (A) It is a site for active ribosomal RNA synthesis. Nucleolus is not membrane-bound and does not form spindle fibers. It synthesizes rRNA and assembles ribosomal subunits. Larger nucleoli are found in metabolically active cells, not dividing cells specifically. This highlights its role in protein synthesis.

1. Nucleolus is mainly involved in:

(A) DNA replication

(B) Ribosome synthesis

(C) Spindle formation

(D) RNA degradation

Explanation:

The correct answer is (B) Ribosome synthesis. The nucleolus synthesizes rRNA and assembles ribosomal subunits. DNA replication occurs in the nucleus, spindle formation in cytoskeleton during mitosis, and RNA degradation in nucleoplasm or cytoplasm.

2. Nucleolus is located in:

(A) Cytoplasm

(B) Mitochondria

(C) Nucleus

(D) Endoplasmic reticulum

Explanation:

The correct answer is (C) Nucleus. Nucleolus is a non-membrane-bound structure inside the nucleus, involved in rRNA synthesis and ribosome assembly. It is not present in cytoplasm, mitochondria, or ER.

3. Which statement about nucleolus is incorrect?

(A) Non-membrane-bound

(B) Synthesizes rRNA

(C) Forms spindle fibers

(D) Visible under light microscope

Explanation:

The correct answer is (C) Forms spindle fibers. Nucleolus does not participate in spindle formation during mitosis. It is non-membrane-bound, visible under a light microscope, and synthesizes rRNA for ribosome assembly.

4. Ribosomal subunits are assembled in:

(A) Cytoplasm

(B) Nucleolus

(C) Golgi apparatus

(D) Lysosome

Explanation:

The correct answer is (B) Nucleolus. Ribosomal subunits are synthesized and partially assembled in the nucleolus before being exported to the cytoplasm. Golgi modifies proteins, lysosomes degrade molecules, and cytoplasm is where final assembly occurs.

5. Which RNA type is synthesized in the nucleolus?

(A) mRNA

(B) tRNA

(C) rRNA

(D) miRNA

Explanation:

The correct answer is (C) rRNA. Nucleolus is the site for ribosomal RNA synthesis. mRNA and tRNA are synthesized in the nucleus and processed differently. miRNA is also processed in the nucleus but not in nucleolus.

6. The nucleolus is prominent in cells that are:

(A) Metabolically active

(B) Dividing

(C) Dormant

(D) Dead

Explanation:

The correct answer is (A) Metabolically active. Larger nucleoli are seen in cells producing high amounts of ribosomes for protein synthesis. It is not specifically enlarged in dividing cells, dormant cells, or dead cells.

7. Assertion-Reason Question:

Assertion (A): Nucleolus synthesizes ribosomal RNA.

Reason (R): It is a membrane-bound structure inside the nucleus.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Correct answer is (C). Nucleolus does synthesize rRNA, but it is not membrane-bound. The assertion is true, while the reason is false. This distinguishes nucleolus as a dense, non-membrane structure specialized in ribosome production.

8. Matching Type Question:

Match structures with functions:

(i) Nucleolus – (a) rRNA synthesis

(ii) Ribosome – (b) Protein synthesis

(iii) Golgi – (c) Vesicle formation

(iv) Lysosome – (d) Macromolecule degradation

(A) i-a, ii-b, iii-c, iv-d

(B) i-b, ii-a, iii-d, iv-c

(C) i-c, ii-d, iii-a, iv-b

(D) i-d, ii-c, iii-b, iv-a

Explanation:

Correct answer is (A). Nucleolus synthesizes rRNA, ribosomes synthesize proteins, Golgi forms vesicles, and lysosomes degrade macromolecules. This matching highlights key eukaryotic organelle functions for NEET UG.

9. Fill in the Blanks:

The nucleolus is ______ and is primarily involved in ______.

(A) Membrane-bound, spindle formation

(B) Non-membrane-bound, rRNA synthesis

(C) Membrane-bound, protein transport

(D) Non-membrane-bound, lipid synthesis

Explanation:

Correct answer is (B) Non-membrane-bound, rRNA synthesis. Nucleolus lacks a membrane and functions in synthesizing ribosomal RNA and assembling ribosomal subunits. It does not participate in spindle formation, protein transport, or lipid synthesis.

10. Choose the correct statements:

(A) Nucleolus synthesizes rRNA

(B) Nucleolus is non-membrane-bound

(C) Nucleolus participates in spindle formation

(D) Nucleolus is prominent in metabolically active cells

Options:

(1) A, B, D

(2) A, C, D

(3) B, C, D

(4) A, B, C

Explanation:

Correct answer is (1) A, B, D. Nucleolus synthesizes rRNA, is non-membrane-bound, and prominent in metabolically active cells. It does not participate in spindle formation. Recognizing these properties is essential for NEET UG cell biology questions.

Copic: Golgi Apparatus

Subtopic: Functions of Golgi Complex

Keyword Definitions:

• Golgi complex: Membrane-bound organelle involved in modifying, packaging, and sorting proteins and lipids.

• Secretory vesicles: Membrane-bound vesicles that transport processed proteins or lipids from Golgi to cell surface.

• Amino acid activation: Process in protein synthesis occurring in cytoplasm, not in Golgi.

• Fatty acid breakdown: Catabolic process in mitochondria or peroxisomes.

• Cellular respiration: Process of ATP production; occurs in mitochondria, not Golgi.

Lead Question (2018):

The Golgi complex participates in:

(A) Activation of amino acid

(B) Fatty acid breakdown

(C) Respiration in bacteria

(D) Formation of secretory vesicles

Explanation:

The correct answer is (D) Formation of secretory vesicles. The Golgi complex modifies proteins and lipids from the endoplasmic reticulum, sorts them, and packages them into secretory vesicles for transport to the plasma membrane or other destinations. It does not activate amino acids, break down fatty acids, or perform respiration.

1. Which organelle is primarily responsible for protein modification?

(A) Golgi complex

(B) Mitochondria

(C) Ribosome

(D) Peroxisome

Explanation:

The correct answer is (A) Golgi complex. Proteins synthesized in the ER are modified, glycosylated, and sorted in the Golgi complex. Mitochondria produce ATP, ribosomes synthesize proteins, and peroxisomes handle lipid breakdown and detoxification.

2. Secretory vesicles transport molecules to:

(A) Golgi apparatus

(B) Cytoplasm

(C) Plasma membrane

(D) Nucleus

Explanation:

The correct answer is (C) Plasma membrane. Secretory vesicles formed by Golgi carry processed proteins and lipids to the plasma membrane for exocytosis or to lysosomes. They do not transport molecules to the nucleus or back to Golgi.

3. The Golgi complex is absent in:

(A) Plant cells

(B) Animal cells

(C) Bacteria

(D) Fungal cells

Explanation:

The correct answer is (C) Bacteria. Golgi complex is a eukaryotic organelle and is absent in prokaryotes like bacteria. Plant, animal, and fungal cells contain Golgi apparatus performing protein modification and vesicle formation.

4. Glycosylation of proteins occurs in:

(A) Golgi complex

(B) Ribosome

(C) Nucleus

(D) Lysosome

Explanation:

The correct answer is (A) Golgi complex. Golgi modifies proteins and lipids by glycosylation, sulfation, and phosphorylation. Ribosomes synthesize polypeptides, nucleus stores genetic material, and lysosomes degrade macromolecules.

5. Which organelle packages enzymes into lysosomes?

(A) Golgi complex

(B) Mitochondria

(C) Smooth ER

(D) Ribosome

Explanation:

The correct answer is (A) Golgi complex. Golgi sorts hydrolytic enzymes and packages them into lysosomes. Smooth ER is involved in lipid synthesis, ribosomes in protein synthesis, and mitochondria in ATP production.

6. Which of the following is a function of the Golgi?

(A) Protein sorting

(B) Lipid modification

(C) Vesicle formation

(D) All of the above

Explanation:

The correct answer is (D) All of the above. The Golgi complex sorts proteins, modifies lipids, and forms vesicles for transport to various cellular locations. It is a central hub for post-translational modifications in eukaryotic cells.

7. Assertion-Reason Question:

Assertion (A): Golgi complex is involved in vesicle formation.

Reason (R): Golgi modifies proteins and lipids before packaging into vesicles.

(A) Both A and R true, R explains A

(B) Both A and R true, R does not explain A

(C) A true, R false

(D) A false, R true

Explanation:

Correct answer is (A). The Golgi modifies proteins and lipids, then sorts and packages them into secretory vesicles. The reason correctly explains the assertion, highlighting the Golgi's role in intracellular transport.

8. Matching Type Question:

Match organelle with function:

(i) Golgi – (a) Vesicle formation

(ii) Ribosome – (b) Protein synthesis

(iii) Mitochondria – (c) ATP production

(iv) Peroxisome – (d) Lipid breakdown

(A) i-a, ii-b, iii-c, iv-d

(B) i-b, ii-a, iii-d, iv-c

(C) i-c, ii-d, iii-b, iv-a

(D) i-d, ii-c, iii-b, iv-a

Explanation:

Correct answer is (A). Golgi forms vesicles, ribosomes synthesize proteins, mitochondria produce ATP, and peroxisomes break down lipids. Matching reinforces the distinct roles of cellular organelles in eukaryotic cells.

9. Fill in the Blanks:

The Golgi complex modifies proteins and packages them into ______ for transport.

(A) Lysosomes

(B) Secretory vesicles

(C) Ribosomes

(D) Peroxisomes

Explanation:

Correct answer is (B) Secretory vesicles. Golgi modifies proteins and lipids from ER, then packages them into secretory vesicles for transport to plasma membrane or lysosomes. It does not package them directly into ribosomes or peroxisomes.

10. Choose the correct statements:

(A) Golgi modifies proteins

(B) Golgi forms secretory vesicles

(C) Golgi is absent in bacteria

(D) Golgi breaks down fatty acids

Options:

(1) A, B, C

(2) A, C, D

(3) B, C, D

(4) A, B, D

Explanation:

Correct answer is (1) A, B, C. Golgi modifies proteins, forms vesicles, and is absent in prokaryotes. Fatty acid breakdown occurs in peroxisomes, not Golgi. Understanding Golgi function is essential for NEET UG cell biology questions.

Topic: Endoplasmic Reticulum

Subtopic: Rough and Smooth ER Functions

Keyword Definitions:

• Rough Endoplasmic Reticulum (RER): Membrane-bound organelle with ribosomes, involved in protein synthesis and folding.

• Smooth Endoplasmic Reticulum (SER): Lacks ribosomes, involved in lipid synthesis, detoxification, and calcium storage.

• Protein Folding: Process by which polypeptides attain functional three-dimensional structure.

• Signal Peptide Cleavage: Removal of N-terminal sequence guiding proteins to specific organelles.

• Protein Glycosylation: Addition of carbohydrate chains to proteins, typically in RER.

• Phospholipid Synthesis: Production of membrane lipids, mainly in SER.

• Organelle: Specialized subunit within a cell with specific function.

Lead Question - 2018

Which of the following events does not occur in rough endoplasmic reticulum :

(A) Phospholipid synthesis

(B) Protein folding

(C) Cleavage of signal peptide

(D) Protein glycosylation

Explanation:

Answer is (A). Rough ER is primarily involved in protein synthesis, folding, signal peptide cleavage, and glycosylation. Phospholipid synthesis occurs mainly in smooth ER, not rough ER. This distinction is crucial for understanding cellular compartmentalization and functional specialization of ER subtypes.

Guessed Questions for NEET UG:

1) Single Correct: Ribosomes are attached to which organelle for protein synthesis?

(A) Smooth ER

(B) Rough ER

(C) Golgi apparatus

(D) Mitochondria

Explanation:

Answer is (B). Ribosomes bind to rough ER for co-translational insertion of nascent polypeptides, enabling proper folding and processing of proteins within the lumen.

2) Single Correct: The main function of smooth ER is:

(A) Protein glycosylation

(B) Lipid and phospholipid synthesis

(C) Signal peptide cleavage

(D) Protein folding

Explanation:

Answer is (B). Smooth ER lacks ribosomes and specializes in lipid and phospholipid synthesis, detoxification, and calcium storage, unlike rough ER focused on protein processing.

3) Single Correct: Which process occurs in both rough ER and Golgi apparatus?

(A) Protein folding

(B) Glycosylation

(C) Lipid synthesis

(D) DNA replication

Explanation:

Answer is (B). Protein glycosylation begins in rough ER and continues in the Golgi apparatus, adding carbohydrate chains to proteins for stability and targeting.

4) Assertion-Reason:

Assertion: Rough ER is studded with ribosomes.

Reason: It is involved in phospholipid synthesis.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (C). Rough ER has ribosomes for protein synthesis; phospholipid synthesis occurs mainly in smooth ER, making the reason false.

5) Single Correct: Signal peptides are cleaved in:

(A) Cytosol

(B) Rough ER

(C) Nucleus

(D) Mitochondria

Explanation:

Answer is (B). Signal peptides direct nascent proteins to the rough ER, where they are cleaved by signal peptidase within the lumen.

6) Single Correct: Which organelle assists in protein folding using chaperones?

(A) Mitochondria

(B) Rough ER

(C) Lysosome

(D) Smooth ER

Explanation:

Answer is (B). Rough ER contains chaperones that assist in proper folding of synthesized proteins, preventing misfolding and aggregation.

7) Matching Type:

Column I | Column II

a. Rough ER | i. Protein folding

b. Smooth ER | ii. Lipid synthesis

c. Golgi apparatus | iii. Protein modification and sorting

(A) a-i, b-ii, c-iii

(B) a-ii, b-i, c-iii

(C) a-iii, b-i, c-ii

(D) a-i, b-iii, c-ii

Explanation:

Answer is (A). Rough ER (a-i) handles protein folding, Smooth ER (b-ii) for lipid synthesis, and Golgi (c-iii) for protein modification and sorting.

8) Fill in the Blank:

_______ ER is responsible for detoxification and calcium storage.

(A) Rough

(B) Smooth

(C) Both

(D) None

Explanation:

Answer is (B). Smooth ER functions in lipid synthesis, detoxification, and calcium storage, unlike rough ER which primarily processes proteins.

9) Choose the correct statements:

(i) Protein glycosylation occurs in rough ER.

(ii) Phospholipid synthesis occurs in rough ER.

(iii) Signal peptide cleavage occurs in rough ER.

(A) i and iii only

(B) i and ii only

(C) ii and iii only

(D) i, ii, iii

Explanation:

Answer is (A). Protein glycosylation and signal peptide cleavage occur in rough ER, while phospholipid synthesis occurs in smooth ER.

10) Clinical-type: A defect in rough ER chaperones may lead to:

(A) Lipid metabolism disorders

(B) Misfolded proteins causing ER stress

(C) Impaired calcium storage

(D) Decreased phospholipid synthesis

Explanation:

Answer is (B). Dysfunction of chaperones in rough ER leads to accumulation of misfolded proteins, triggering ER stress and potential cell damage.

Subtopic: Cell Organelles and Energy Production

Keyword Definitions:

Mitochondrion: Organelle responsible for cellular respiration and ATP production.

Lysosome: Organelle containing digestive enzymes for breakdown of macromolecules.

Ribosome: Organelle that synthesizes proteins.

Chloroplast: Photosynthetic organelle in plants producing glucose and oxygen.

ATP (Adenosine Triphosphate): Energy currency of the cell used for metabolic processes.

Cellular Respiration: Process by which cells convert nutrients into ATP.

Glycolysis: First step in glucose breakdown, occurring in cytoplasm.

Krebs Cycle: Mitochondrial pathway producing NADH, FADH2, and ATP.

Electron Transport Chain: Mitochondrial inner membrane pathway generating most ATP.

Clinical Significance: Dysfunctional mitochondria can lead to metabolic and neuromuscular disorders.

Oxidative Phosphorylation: Process in mitochondria producing ATP using energy from electrons.

Lead Question - 2017

Which of the following cell organelles is responsible for extracting energy from carbohydrates to form ATP:

(A) Mitochondrion

(B) Lysosome

(C) Ribosome

(D) Chloroplast

Explanation: Mitochondria are the powerhouse of the cell, extracting energy from carbohydrates via glycolysis, Krebs cycle, and the electron transport chain to produce ATP. Lysosomes digest molecules, ribosomes synthesize proteins, and chloroplasts conduct photosynthesis. Correct answer: A.

1. MCQ - Single Correct Answer

Which process occurs in mitochondria to produce ATP?

(a) Photosynthesis

(b) Cellular respiration

(c) Protein synthesis

(d) Digestion

Explanation: Cellular respiration occurs in mitochondria, converting glucose into ATP via glycolysis, Krebs cycle, and electron transport chain. Photosynthesis occurs in chloroplasts, protein synthesis in ribosomes, and digestion in lysosomes. Correct answer: b.

2. MCQ - Single Correct Answer

Which mitochondrial structure increases surface area for ATP synthesis?

(a) Matrix

(b) Cristae

(c) Outer membrane

(d) Ribosomes

Explanation: Cristae are folds of the inner mitochondrial membrane that increase surface area for enzymes of the electron transport chain, maximizing ATP production. Matrix contains enzymes for Krebs cycle. Ribosomes and outer membrane do not directly aid ATP synthesis. Correct answer: b.

3. MCQ - Single Correct Answer (Clinical)

Mitochondrial dysfunction may lead to:

(a) Diabetes

(b) Neurodegenerative diseases

(c) Lysosomal storage disorders

(d) Protein malnutrition

Explanation: Neurodegenerative diseases like Parkinson’s and mitochondrial myopathies result from impaired ATP production due to mitochondrial dysfunction. Diabetes is multifactorial, lysosomal storage disorders are lysosome-related, and protein malnutrition is dietary. Correct answer: b.

4. MCQ - Single Correct Answer

Which organelle directly generates energy in plants?

(a) Chloroplast

(b) Ribosome

(c) Lysosome

(d) Mitochondrion

Explanation: Mitochondria generate ATP through cellular respiration in all eukaryotic cells including plants. Chloroplasts produce glucose in photosynthesis, which mitochondria convert into ATP. Ribosomes and lysosomes are unrelated to direct energy generation. Correct answer: d.

5. MCQ - Single Correct Answer

Which molecule is the main product of mitochondrial energy conversion?

(a) Glucose

(b) ATP

(c) NADPH

(d) Oxygen

Explanation: ATP is the main energy currency produced by mitochondria during cellular respiration. Glucose is substrate, NADPH is a photosynthetic electron carrier, and oxygen is a byproduct in respiration. Correct answer: b.

6. MCQ - Single Correct Answer (Clinical)

Defects in mitochondrial DNA can cause:

(a) Muscular weakness

(b) Increased ATP production

(c) Enhanced photosynthesis

(d) Protein overproduction

Explanation: Muscular weakness occurs in mitochondrial disorders due to impaired ATP production. Mitochondrial DNA mutations disrupt oxidative phosphorylation, causing neuromuscular symptoms. ATP production decreases, not increases. Photosynthesis and protein synthesis are unaffected. Correct answer: a.

7. MCQ - Assertion-Reason

Assertion (A): Mitochondria are called the powerhouse of the cell.

Reason (R): They produce ATP through cellular respiration.

(a) Both A and R true, R correct explanation

(b) Both A and R true, R not correct explanation

(c) A true, R false

(d) A false, R true

Explanation: Mitochondria are the powerhouse of the cell because they generate ATP via cellular respiration. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer: a.

8. MCQ - Matching Type

Match organelle with function:

1. Mitochondrion - (a) ATP production

2. Lysosome - (b) Digestion

3. Ribosome - (c) Protein synthesis

4. Chloroplast - (d) Glucose synthesis

Options:

(A) 1-a, 2-b, 3-c, 4-d

(B) 1-b, 2-a, 3-d, 4-c

(C) 1-c, 2-d, 3-a, 4-b

(D) 1-d, 2-c, 3-b, 4-a

Explanation: Correct matching: Mitochondrion-ATP, Lysosome-Digestion, Ribosome-Protein synthesis, Chloroplast-Glucose synthesis. Answer: A.

9. MCQ - Fill in the Blanks

The organelle responsible for ATP production is __________.

(a) Ribosome

(b) Lysosome

(c) Mitochondrion

(d) Chloroplast

Explanation: Mitochondrion produces ATP through cellular respiration, converting glucose into usable energy for cellular functions. Ribosomes synthesize proteins, lysosomes digest macromolecules, and chloroplasts perform photosynthesis. Correct answer: c.

10. MCQ - Choose Correct Statements

Select correct statements about mitochondria:

1. They produce ATP

2. They contain their own DNA

3. Lysosomes generate ATP

4. Cristae increase surface area for electron transport

Options:

(A) 1, 2, and 4

(B) 1 and 3

(C) 2 and 3

(D) All 1,2,3,4

Explanation: Mitochondria produce ATP, contain DNA, and cristae enhance electron transport surface area. Lysosomes digest molecules, not produce ATP. Correct answer: A. 

Topic: Cell Organelles

Subtopic: Functions of Cell Organelles

Keyword Definitions:

• Mesosome: Invagination of bacterial plasma membrane, involved in cell division and DNA replication.

• Lysosome: Membrane-bound organelle containing hydrolytic enzymes for intracellular digestion.

• Microsome: Fragment of endoplasmic reticulum formed during cell disruption, involved in drug metabolism.

• Ribosome: Organelle responsible for protein synthesis.

Lead Question - 2016 (Phase 2):

A cell organelle containing hydrolytic enzymes is :

(1) Mesosome

(2) Lysosome

(3) Microsome

(4) Ribosome

Explanation: Lysosomes are membrane-bound organelles containing hydrolytic enzymes essential for intracellular digestion of macromolecules, worn-out organelles, and pathogens. Mesosomes are structural features in prokaryotes, microsomes are ER fragments, and ribosomes synthesize proteins. The correct answer is (2) Lysosome, fundamental for NEET UG cell biology.

1. Single Correct Answer MCQ:

Which organelle is responsible for protein synthesis?

(1) Lysosome

(2) Ribosome

(3) Mitochondria

(4) Peroxisome

Explanation: Ribosomes are the cell organelles responsible for protein synthesis by translating mRNA into polypeptide chains. They are present in both prokaryotic and eukaryotic cells. Thus, the correct answer is (2) Ribosome, a crucial concept in NEET UG biology.

2. Single Correct Answer MCQ:

Microsomes are primarily involved in

(1) Protein degradation

(2) Drug metabolism

(3) DNA replication

(4) Photosynthesis

Explanation: Microsomes are vesicle-like artifacts formed from fragmented endoplasmic reticulum during cell homogenization, playing a significant role in drug metabolism via cytochrome P450 enzymes. The correct answer is (2) Drug metabolism, important in pharmacology and NEET UG syllabus.

3. Single Correct Answer MCQ:

Mesosomes are associated with

(1) Protein synthesis

(2) Lipid synthesis

(3) Cell division in prokaryotes

(4) Energy production

Explanation: Mesosomes are infoldings of the plasma membrane in prokaryotic cells, thought to be involved in DNA replication and cell division. Their functional significance is debated. The correct answer is (3) Cell division in prokaryotes, essential for understanding prokaryotic cell structure in NEET UG.

4. Single Correct Answer MCQ:

Which of the following is NOT a function of lysosomes?

(1) Intracellular digestion

(2) Destroying pathogens

(3) ATP production

(4) Autophagy

Explanation: Lysosomes perform intracellular digestion, pathogen destruction, and autophagy. ATP production is primarily the function of mitochondria. Hence, the correct answer is (3) ATP production, a fundamental point in NEET UG cell biology.

5. Single Correct Answer MCQ (Clinical-type):

Lysosomal storage diseases are caused by

(1) Overproduction of lysosomes

(2) Deficiency of specific hydrolytic enzymes

(3) Excess ribosomes

(4) Dysfunctional mitochondria

Explanation: Lysosomal storage diseases occur due to a deficiency of specific hydrolytic enzymes, leading to substrate accumulation and cellular dysfunction. Examples include Tay-Sachs and Gaucher disease. This clinical aspect is crucial for NEET UG understanding of disease mechanisms. Correct answer: (2) Deficiency of specific hydrolytic enzymes.

6. Single Correct Answer MCQ:

Which organelle contains digestive enzymes?

(1) Golgi apparatus

(2) Lysosome

(3) Peroxisome

(4) Mitochondrion

Explanation: Lysosomes are specialized organelles containing digestive hydrolytic enzymes that break down biomolecules, pathogens, and defective cell parts. Their role in maintaining cellular homeostasis is vital. Correct answer: (2) Lysosome, essential for NEET UG cell organelle functions.

7. Assertion-Reason MCQ:

Assertion (A): Lysosomes are involved in autophagy.

Reason (R): They contain hydrolytic enzymes that digest cell components.

(1) Both A and R are true and R is correct explanation of A

(2) Both A and R are true but R is not correct explanation of A

(3) A is true but R is false

(4) A is false but R is true

Explanation: Both assertion and reason are true, and the reason correctly explains the assertion. Lysosomes digest cell components through autophagy, recycling cellular materials. This process is important in maintaining cell health. Correct answer: (1) Both A and R are true and R is correct explanation of A.

8. Matching Type MCQ:

Match the organelle with its function:

A. Lysosome

B. Ribosome

C. Microsome

D. Mesosome

1. Protein synthesis

2. Hydrolytic digestion

3. Drug metabolism

4. Cell division in prokaryotes

Options:

(1) A-2, B-1, C-3, D-4

(2) A-1, B-2, C-3, D-4

(3) A-2, B-1, C-4, D-3

(4) A-3, B-1, C-2, D-4

Explanation: Correct match is A-2 (Lysosome-hydrolytic digestion), B-1 (Ribosome-protein synthesis), C-3 (Microsome-drug metabolism), D-4 (Mesosome-cell division in prokaryotes). Therefore, the correct answer is (1) A-2, B-1, C-3, D-4.

9. Fill in the Blanks MCQ:

Lysosomes contain ______ enzymes.

(1) Digestive

(2) Photosynthetic

(3) Replicative

(4) Respiratory

Explanation: Lysosomes contain digestive hydrolytic enzymes responsible for breaking down macromolecules, pathogens, and damaged organelles. This role is essential for cellular homeostasis and disease prevention. The correct answer is (1) Digestive, a key concept in NEET UG cell biology.

10. Choose the Correct Statements MCQ:

Select correct statements about lysosomes:

(1) Contain hydrolytic enzymes

(2) Involved in autophagy

(3) Involved in protein synthesis

(4) Found only in prokaryotic cells

Options:

(1) 1 and 2 only

(2) 1 and 3 only

(3) 3 and 4 only

(4) All statements are correct

Explanation: Statements 1 and 2 are correct: lysosomes contain hydrolytic enzymes and are involved in autophagy. Protein synthesis occurs in ribosomes, and lysosomes are found in eukaryotic cells. Correct answer is (1) 1 and 2 only, important for NEET UG cell biology understanding.

Keywords:

• Anthocyanins: Water-soluble pigments present in vacuoles responsible for red, purple, and blue colors in flowers and fruits.

• Xanthophylls: Yellow pigments found in chloroplasts, involved in photosynthesis and photoprotection.

• Chlorophylls: Green pigments located in chloroplasts, essential for photosynthesis.

• Carotenoids: Orange to yellow pigments in chloroplasts, protect against photooxidative damage.

• Vacuole: Membrane-bound organelle in plant cells storing water, pigments, and waste.

• Water-soluble pigments: Pigments that dissolve in water, often found in vacuoles, affecting flower and fruit coloration.

• Plastids: Organelles like chloroplasts, chromoplasts, containing pigments like chlorophyll and carotenoids.

• pH-sensitive pigments: Anthocyanin color varies with vacuolar pH.

• Clinical relevance: Anthocyanins have antioxidant properties beneficial for human health.

• Photosynthetic pigments: Chlorophyll, carotenoids, and xanthophylls participate in light absorption.

• Flower pigmentation: Determines attraction of pollinators.

Chapter: Plant Physiology

Topic: Pigments

Subtopic: Water Soluble Pigments

Lead Question - 2016 (Phase 1): Water soluble pigments found in plant cell vacuoles are:

(1) Xanthophylls
(2) Chlorophylls
(3) Carotenoids
(4) Anthocyanins

Answer: 4

Explanation: Anthocyanins are water-soluble pigments located in vacuoles, responsible for red, purple, and blue coloration in plants. Other pigments like chlorophylls, carotenoids, and xanthophylls are lipid-soluble and found in plastids. Their location and solubility differentiate them from vacuolar pigments.

1. Single Correct Answer MCQ: Which pigment is responsible for red coloration in petals?

(A) Chlorophyll
(B) Xanthophyll
(C) Anthocyanin
(D) Carotenoid

Answer: C

Explanation: Anthocyanins provide red, purple, or blue colors in flowers and fruits, attracting pollinators and seed dispersers.

2. Single Correct Answer MCQ: Which pigment is lipid-soluble and located in chloroplasts?

(A) Anthocyanin
(B) Carotenoid
(C) Betalain
(D) Flavonoid

Answer: B

Explanation: Carotenoids are lipid-soluble pigments in chloroplasts, involved in light harvesting and photoprotection.

3. Single Correct Answer MCQ: Water-soluble pigments in vacuoles include:

(A) Chlorophylls
(B) Carotenoids
(C) Anthocyanins
(D) Xanthophylls

Answer: C

Explanation: Anthocyanins dissolve in vacuolar sap, unlike chlorophylls or carotenoids that are in plastid membranes.

4. Single Correct Answer MCQ: Which pigment is pH-sensitive?

(A) Carotenoids
(B) Anthocyanins
(C) Chlorophylls
(D) Xanthophylls

Answer: B

Explanation: Anthocyanins change color depending on vacuolar pH, showing red in acidic and blue in alkaline conditions.

5. Single Correct Answer MCQ: Which pigment is responsible for yellow coloration in leaves?

(A) Anthocyanin
(B) Chlorophyll
(C) Xanthophyll
(D) Phycobilin

Answer: C

Explanation: Xanthophylls are yellow pigments located in chloroplasts, assisting in light absorption for photosynthesis.

6. Single Correct Answer MCQ: Vacuolar pigments mainly function in:

(A) Photosynthesis
(B) Attracting pollinators
(C) Respiration
(D) Electron transport

Answer: B

Explanation: Anthocyanins in vacuoles impart bright colors to flowers and fruits, attracting pollinators and aiding reproduction.

7. Assertion-Reason MCQ:
Assertion (A): Anthocyanins are water-soluble pigments.
Reason (R): They are located in plastids and help in photosynthesis.

(A) Both A and R are true, R explains A
(B) Both A and R are true, R does not explain A
(C) A is true, R is false
(D) A is false, R is true

Answer: C

Explanation: Anthocyanins are water-soluble pigments in vacuoles, not plastids, and do not participate in photosynthesis.

8. Matching Type MCQ: Match pigment with its solubility/location:

1. Chlorophyll   A. Water-soluble
2. Anthocyanin   B. Lipid-soluble
3. Carotenoid   C. Lipid-soluble
4. Xanthophyll   D. Lipid-soluble

(A) 1-B, 2-A, 3-C, 4-D
(B) 1-A, 2-B, 3-C, 4-D
(C) 1-C, 2-A, 3-B, 4-D
(D) 1-B, 2-D, 3-A, 4-C

Answer: A

Explanation: Chlorophyll, carotenoids, and xanthophylls are lipid-soluble in plastids. Anthocyanins are water-soluble in vacuoles.

9. Fill in the Blanks: ______ pigments are water-soluble and stored in vacuoles, while ______ pigments are lipid-soluble and found in chloroplasts.

(A) Chlorophyll; Anthocyanins
(B) Carotenoids; Anthocyanins
(C) Anthocyanins; Carotenoids
(D) Xanthophylls; Anthocyanins

Answer: C

Explanation: Anthocyanins are water-soluble pigments in vacuoles; carotenoids are lipid-soluble pigments in chloroplasts.

10. Choose the Correct Statements:
(A) Anthocyanins are water-soluble pigments in vacuoles.
(B) Chlorophylls are water-soluble and found in vacuoles.
(C) Carotenoids are lipid-soluble pigments in plastids.
(D) Xanthophylls are lipid-soluble pigments in chloroplasts.

(1) A, B, C
(2) A, C, D
(3) B, C, D
(4) All are correct

Answer: 2

Explanation: A, C, and D are correct. Chlorophylls are lipid-soluble and located in chloroplasts, not vacuoles.

Keywords:

• Cell organelles: Specialized structures within a cell performing distinct functions.

• Mitochondria: Double-membraned organelle responsible for ATP production via cellular respiration.

• Chloroplasts: Double-membrane organelle in plants where photosynthesis occurs.

• Lysosomes: Single-membrane organelles containing hydrolytic enzymes for digestion of cellular waste.

• Nuclei: Double-membrane organelle containing genetic material and controlling cell activities.

• Single membrane: Organelle bounded by one lipid bilayer.

• Double membrane: Organelle enclosed by two lipid bilayers.

• Hydrolytic enzymes: Enzymes that break down biomolecules.

• ATP: Adenosine triphosphate, the energy currency of cells.

• Autophagy: Cellular process for recycling components via lysosomes.

• Membrane-bound organelles: Organelles enclosed by lipid membranes.

Chapter: Cell Biology

Topic: Cell Organelles

Subtopic: Lysosomes and Membrane Structure

Lead Question - 2016 (Phase 1): Which one of the following cell organelles is enclosed by a single membrane:

(1) Mitochondria
(2) Chloroplasts
(3) Lysosomes
(4) Nuclei

Answer: 3

Explanation: Lysosomes are membrane-bound organelles enclosed by a single lipid bilayer and contain digestive enzymes. Mitochondria, chloroplasts, and nuclei are double-membrane organelles. Lysosomes play a key role in autophagy and intracellular digestion, making them crucial for cell maintenance and recycling processes.

1. Single Correct Answer MCQ: The organelle responsible for ATP production is:

(A) Lysosome
(B) Mitochondria
(C) Golgi apparatus
(D) Endoplasmic reticulum

Answer: B

Explanation: Mitochondria are double-membraned organelles that generate ATP via oxidative phosphorylation. Lysosomes, Golgi apparatus, and ER have different roles such as digestion, protein modification, and synthesis.

2. Single Correct Answer MCQ: Which organelle contains hydrolytic enzymes?

(A) Nucleus
(B) Chloroplast
(C) Lysosome
(D) Mitochondria

Answer: C

Explanation: Lysosomes have a single membrane and contain hydrolytic enzymes that digest macromolecules, cellular debris, and pathogens. Other organelles like mitochondria or nucleus do not perform this function.

3. Single Correct Answer MCQ: Double-membrane organelles include:

(A) Lysosome
(B) Ribosome
(C) Chloroplast
(D) Peroxisome

Answer: C

Explanation: Chloroplasts and mitochondria are enclosed by double membranes, whereas lysosomes and peroxisomes have a single membrane, and ribosomes lack membranes entirely.

4. Single Correct Answer MCQ: Autophagy in cells involves:

(A) Nucleus
(B) Lysosomes
(C) Ribosomes
(D) Golgi apparatus

Answer: B

Explanation: Lysosomes digest damaged organelles and macromolecules during autophagy using hydrolytic enzymes, maintaining cellular homeostasis.

5. Single Correct Answer MCQ: Membrane-bound organelles are characteristic of:

(A) Prokaryotes
(B) Eukaryotes
(C) Viruses
(D) Prions

Answer: B

Explanation: Eukaryotic cells contain membrane-bound organelles like lysosomes, mitochondria, chloroplasts, and nucleus. Prokaryotes lack true membrane-bound organelles.

6. Single Correct Answer MCQ: Lysosomal storage diseases result from:

(A) Excess ATP
(B) Enzyme deficiency in lysosomes
(C) Overproduction of ribosomes
(D) Mutation in mitochondria

Answer: B

Explanation: Lysosomal storage diseases occur due to deficiencies in lysosomal enzymes, leading to accumulation of undegraded substrates in cells and causing clinical disorders.

7. Assertion-Reason MCQ:
Assertion (A): Lysosomes are single-membrane organelles.
Reason (R): They contain digestive enzymes to break down macromolecules.

(A) Both A and R are true, R is correct explanation of A
(B) Both A and R are true, R is NOT correct explanation of A
(C) A is true, R is false
(D) A is false, R is true

Answer: A

Explanation: Lysosomes are enclosed by a single membrane and contain hydrolytic enzymes for digestion. The presence of a single membrane protects the cytoplasm from these enzymes.

8. Matching Type MCQ: Match organelle with membrane type:

1. Lysosome   A. Single
2. Mitochondria   B. Double
3. Nucleus   C. Double
4. Peroxisome   D. Single

(A) 1-A, 2-B, 3-C, 4-D
(B) 1-B, 2-C, 3-A, 4-D
(C) 1-D, 2-B, 3-C, 4-A
(D) 1-A, 2-C, 3-B, 4-D

Answer: A

Explanation: Lysosomes and peroxisomes are single-membrane organelles. Mitochondria and nucleus are double-membrane organelles, matching correctly with their membrane types.

9. Fill in the Blanks: Lysosomes are enclosed by a ________ membrane, whereas mitochondria are enclosed by a ________ membrane.

(A) Single; double
(B) Double; single
(C) Single; single
(D) Double; double

Answer: A

Explanation: Lysosomes are bounded by a single membrane, protecting cytoplasm from hydrolytic enzymes. Mitochondria have a double membrane, with inner membrane forming cristae for ATP production.

10. Choose the Correct Statements:
(A) Lysosomes have a single membrane.
(B) Mitochondria produce ATP.
(C) Nucleus is single-membraned.
(D) Lysosomes are involved in autophagy.

(1) A, B, D
(2) A, C
(3) B, C
(4) All are correct

Answer: 1

Explanation: Statements A, B, and D are correct. Nucleus is double-membraned. Lysosomes have a single membrane, participate in autophagy, and mitochondria produce ATP.

Chapter: Cell Structure and Function | Topic: Cytoskeleton | Subtopic: Microtubules

Keywords:

• Microtubules: Cylindrical protein structures of tubulin that form cytoskeleton components.

• Cilia: Hair-like structures aiding movement of fluids or cells.

• Flagella: Long projections that enable cell motility.

• Centrioles: Cylindrical structures involved in spindle formation.

• Spindle fibres: Microtubule structures that separate chromosomes during mitosis.

• Peroxisomes: Organelles responsible for oxidative metabolism.

• Chromatin: DNA-protein complex in the nucleus.

• Centrosome: Organelle containing centrioles, organizes microtubules.

• Nucleosome: Unit of chromatin composed of DNA and histones.

Lead Question - 2016 (Phase 1)

Microtubules are the constituents of:

1. Cilia, Flagella and Peroxisomes
2. Spindle fibres, Centrioles and Cilia
3. Centrioles, Spindle fibres and Chromatin
4. Centrosome, Nucleosome and Centrioles

Explanation (Answer: 2 — Spindle fibres, Centrioles and Cilia): Microtubules are made of tubulin dimers and are essential in centrioles, cilia, flagella, and spindle fibres. They do not form peroxisomes, chromatin, or nucleosomes. Their structural role is crucial in cell division, intracellular transport, and maintaining cell shape.

Q1. Which protein forms the structural unit of microtubules?
A. Actin
B. Tubulin
C. Myosin
D. Keratin

Explanation (Answer: B — Tubulin): Microtubules are hollow cylinders formed from α- and β-tubulin dimers. These assemble into protofilaments that create the cylindrical structure. Actin forms microfilaments, myosin is a motor protein, and keratin forms intermediate filaments, not microtubules.

Q2. Inhibition of microtubule polymerization would directly block:
A. Chromosome segregation
B. DNA replication
C. mRNA synthesis
D. Protein translation

Explanation (Answer: A — Chromosome segregation): Spindle fibres are made of microtubules, and their disruption prevents proper chromosome separation during mitosis. DNA replication and mRNA synthesis occur in the nucleus independently. Translation occurs on ribosomes, not directly affected by microtubules.

Q3. A patient is given colchicine. Which cellular process will be inhibited?
A. Formation of mitotic spindle
B. Protein synthesis
C. DNA repair
D. Mitochondrial ATP production

Explanation (Answer: A — Formation of mitotic spindle): Colchicine binds tubulin, preventing microtubule polymerization, which inhibits spindle formation. This arrests cells in metaphase. Protein synthesis, DNA repair, and mitochondrial ATP production are not directly blocked by colchicine.

Q4. Which of the following organelles lacks microtubules?
A. Flagella
B. Cilia
C. Peroxisomes
D. Centrioles

Explanation (Answer: C — Peroxisomes): Peroxisomes are single-membrane-bound organelles involved in fatty acid oxidation. They do not contain microtubules. Cilia, flagella, and centrioles are microtubule-rich structures with 9+2 or 9+3 arrangements essential for motility and organization.

Q5 (Assertion–Reason):
Assertion (A): Spindle fibres are formed of microtubules.
Reason (R): Microtubules provide mechanical force for chromosome movement.
A. Both A and R are true, and R explains A
B. Both A and R are true, but R does not explain A
C. A is true, R is false
D. A is false, R is true