Bacteria

NEET UG Biology 2018

Topic: Oxygen Evolution

Subtopic: Oxygenic vs Anoxygenic Photosynthesis

Keyword Definitions:

• Oxygenic photosynthesis: Type of photosynthesis where oxygen is released, as in plants, algae, and cyanobacteria.

• Anoxygenic photosynthesis: Photosynthesis that does not release oxygen, using molecules like H2S instead of water.

• Chara: Freshwater green algae performing oxygenic photosynthesis.

• Green sulphur bacteria: Photosynthetic bacteria that perform anoxygenic photosynthesis, do not produce O2.

• Cycas: Gymnosperm plant performing oxygenic photosynthesis.

• Nostoc: Cyanobacterium performing oxygenic photosynthesis.

Lead Question (2018):

Oxygen is not produced during photosynthesis by:

(A) Chara

(B) Green sulphur bacteria

(D) Nostoc

Explanation:

The correct answer is (B) Green sulphur bacteria. Green sulphur bacteria perform anoxygenic photosynthesis using H2S or other donors, producing no oxygen. Chara, Cycas, and Nostoc are oxygenic photosynthesizers, releasing O2 by splitting water molecules during light-dependent reactions.

1. Which organism releases oxygen during photosynthesis?

(A) Green sulphur bacteria

(B) Chara

(D) Heliobacteria

Explanation:

The correct answer is (B) Chara. Chara is a green alga performing oxygenic photosynthesis, splitting water to release oxygen. Green sulphur bacteria, purple bacteria, and heliobacteria perform anoxygenic photosynthesis, producing no O2. Oxygen evolution is characteristic of plants, algae, and cyanobacteria.

2. In anoxygenic photosynthesis, the electron donor is usually:

(A) Water

(B) Hydrogen sulfide

(D) Oxygen

Explanation:

The correct answer is (B) Hydrogen sulfide. Anoxygenic photosynthetic bacteria like green sulphur bacteria use H2S or other compounds as electron donors instead of water. This process does not release oxygen, unlike oxygenic photosynthesis where water is split.

3. Which plant type is an oxygenic photosynthesizer?

(A) Gymnosperms

(B) Green sulphur bacteria

(D) Heliobacteria

Explanation:

The correct answer is (A) Gymnosperms. Gymnosperms like Cycas perform oxygenic photosynthesis, releasing O2. Photosynthetic bacteria like green sulphur, purple bacteria, and heliobacteria are anoxygenic and do not produce oxygen. Oxygenic photosynthesis involves water splitting in light reactions.

4. Cyanobacteria such as Nostoc contribute to:

(A) Oxygen production

(B) Hydrogen sulfide production

(D) Nitrogen fixation only

Explanation:

The correct answer is (A) Oxygen production. Nostoc, a cyanobacterium, performs oxygenic photosynthesis producing oxygen and can also fix nitrogen. Cyanobacteria were responsible for the initial oxygenation of Earth's atmosphere.

5. Which pigment is present in green sulphur bacteria?

(A) Chlorophyll a

(B) Bacteriochlorophyll

(D) Carotenoids

Explanation:

The correct answer is (B) Bacteriochlorophyll. Green sulphur bacteria contain bacteriochlorophyll which absorbs light for anoxygenic photosynthesis. Chlorophyll a is in oxygenic photosynthesizers like plants and cyanobacteria. Phycobilins are accessory pigments in cyanobacteria.

6. Oxygen evolution occurs in which photosystem?

(A) Photosystem I

(B) Photosystem II

(D) Cytochrome system

Explanation:

The correct answer is (B) Photosystem II. Photosystem II splits water molecules in oxygenic photosynthesis to release oxygen. Anoxygenic bacteria lack PSII, using other electron donors. Photosystem I mainly participates in NADPH formation.

7. Assertion-Reason Question:

Assertion (A): Green sulphur bacteria do not produce oxygen.

Reason (R): They perform anoxygenic photosynthesis using H2S as electron donor.

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

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

(D) A false, R true

Explanation:

Correct answer is (A). Green sulphur bacteria are anoxygenic; they use H2S instead of water as electron donor, producing no oxygen. The reason correctly explains the assertion, distinguishing oxygenic and anoxygenic photosynthetic organisms.

8. Matching Type Question:

Match organisms with type of photosynthesis:

(i) Chara – (a) Oxygenic

(ii) Cycas – (b) Oxygenic

(iii) Nostoc – (c) Oxygenic

(iv) Green sulphur bacteria – (d) Anoxygenic

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

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

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

Explanation:

Correct answer is (A). Chara, Cycas, and Nostoc perform oxygenic photosynthesis, producing O2. Green sulphur bacteria are anoxygenic, using H2S and producing no oxygen. Matching reinforces oxygen evolution understanding in various organisms.

9. Fill in the Blanks:

______ performs anoxygenic photosynthesis and does not release ______.

(A) Chara, oxygen

(B) Green sulphur bacteria, oxygen

(D) Nostoc, water

Explanation:

Correct answer is (B) Green sulphur bacteria, oxygen. Green sulphur bacteria use H2S as electron donor and perform anoxygenic photosynthesis, producing no oxygen. Chara, Cycas, and Nostoc are oxygenic and release O2.

10. Choose the correct statements:

(A) Chara produces oxygen

(B) Green sulphur bacteria do not produce oxygen

(D) Nostoc produces oxygen

Options:

(1) A, B, C

(2) A, B, D

(3) B, C, D

(4) A, B, C, D

Explanation:

Correct answer is (4) A, B, C, D. Chara, Cycas, and Nostoc are oxygenic and release oxygen. Green sulphur bacteria are anoxygenic and do not release oxygen. Recognizing oxygenic versus anoxygenic photosynthesis is essential for NEET UG questions on photosynthesis.

NEET UG Biology 2017

Topic: Bacteria and Related Microorganisms

Subtopic: Mycoplasma and Pathogenic Bacteria

Keyword Definitions:

• Mycoplasma – Smallest free-living cells lacking a cell wall, can be pathogenic.

• Cell wall – Rigid layer providing shape and protection to most bacteria.

• Nostoc – Filamentous cyanobacterium, photosynthetic, with a cell wall.

• Bacillus – Rod-shaped, spore-forming bacterium with a cell wall.

• Pseudomonas – Gram-negative bacterium with cell wall, aerobic.

• Obligate aerobe – Organism requiring oxygen for survival.

• Facultative anaerobe – Organism that can survive with or without oxygen.

• Pathogenic – Ability to cause disease in plants or animals.

• Prokaryote – Single-celled organism without a nucleus.

• Smallest cell – Cell with minimal size and genome capable of independent life.

Lead Question – 2017:

Which among the following are the smallest living cells known without a definite cell wall, pathogenic to plants as well as animals and can survive without oxygen:

(A) Nostoc

(B) Bacillus

(D) Mycoplasma

Explanation:

The smallest living cells without a cell wall, capable of causing disease in plants and animals, and able to survive without oxygen are Mycoplasma. Other options have cell walls and different metabolic requirements, making Mycoplasma unique among prokaryotes. (Answer: D)

1) Single Correct Answer MCQ:

Which characteristic distinguishes Mycoplasma from Bacillus and Pseudomonas?

(A) Presence of cell wall

(B) Ability to form spores

(D) Photosynthetic ability

Explanation:

Mycoplasma are unique because they lack a cell wall, unlike Bacillus and Pseudomonas, which have rigid cell walls, allowing them flexibility in shape and resistance to antibiotics targeting cell walls. (Answer: C)

2) Single Correct Answer MCQ:

Which of the following can survive without oxygen?

(A) Bacillus

(B) Pseudomonas

(D) Nostoc

Explanation:

Mycoplasma

can survive without oxygen (facultative anaerobic), while Bacillus and Pseudomonas are obligate or facultative aerobes, and Nostoc is photosynthetic, requiring light and oxygen for energy production. (Answer: C)

3) Single Correct Answer MCQ:

Which bacteria are pathogenic to both plants and animals?

(A) Nostoc

(B) Mycoplasma

(D) Bacillus

Explanation:

Mycoplasma can infect multiple hosts, including plants and animals. Nostoc is non-pathogenic, Pseudomonas and Bacillus have limited host specificity. Pathogenicity and lack of cell wall distinguish Mycoplasma. (Answer: B)

4) Single Correct Answer MCQ:

Which is the smallest self-replicating cell known?

(A) Nostoc

(B) Bacillus

(D) Mycoplasma

Explanation:

Mycoplasma are the smallest self-replicating cells capable of independent life. Their minimal genome allows basic metabolic functions without a cell wall. (Answer: D)

5) Single Correct Answer MCQ:

Which cell lacks peptidoglycan in its cell wall?

(A) Bacillus

(B) Mycoplasma

(D) Nostoc

Explanation:

Mycoplasma entirely lack a peptidoglycan cell wall, making them resistant to antibiotics targeting cell wall synthesis, unlike Bacillus, Pseudomonas, and Nostoc, which have cell walls containing peptidoglycan. (Answer: B)

6) Single Correct Answer MCQ:

Which of the following is pleomorphic?

(A) Mycoplasma

(B) Bacillus

(D) Nostoc

Explanation:

Mycoplasma are pleomorphic because of the absence of a rigid cell wall, allowing variable shapes. Other bacteria have rigid walls, maintaining a fixed shape. (Answer: A)

7) Assertion-Reason MCQ:

Assertion (A): Mycoplasma can survive without oxygen.

Reason (R): They have flexible membranes and minimal metabolic requirements.

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

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

(D) A false, R true

Explanation:

Both assertion and reason are true. Mycoplasma have flexible membranes and minimal metabolic needs, allowing survival in anaerobic conditions. (Answer: A)

8) Matching Type MCQ:

Match the organism with its feature:

1. Mycoplasma – (i) Photosynthetic

2. Nostoc – (ii) Lacks cell wall

3. Bacillus – (iii) Spore-forming

4. Pseudomonas – (iv) Gram-negative aerobic

Options:

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

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

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

Explanation:

Correct matching: Mycoplasma – lacks cell wall, Nostoc – photosynthetic, Bacillus – spore-forming, Pseudomonas – Gram-negative aerobic. (Answer: A)

9) Fill in the Blanks MCQ:

Mycoplasma are the smallest living cells without _________ and can survive without oxygen.

(A) Nucleus

(B) Cell wall

(D) DNA

Explanation:

Mycoplasma lack a cell wall, have minimal size, and can survive anaerobically, making them distinct among bacteria. (Answer: B)

10) Choose the correct statements MCQ:

1. Mycoplasma lack cell wall.

2. Bacillus is spore-forming.

3. Nostoc is photosynthetic.

4. Pseudomonas is obligate anaerobe.

Options:

(A) 1, 2, 3

(B) 2, 3, 4

(D) 1, 2, 4

Explanation:

Statements 1, 2, 3 are correct. Pseudomonas is an obligate aerobe, not anaerobe. Mycoplasma is unique for lacking cell wall, Bacillus forms spores, Nostoc performs photosynthesis. (Answer: A)

Chapter: Microbiology

Topic: Extremophiles and Bacterial Diversity

Subtopic: Archaebacteria and Environmental Adaptations

Keyword Definitions:

• Extremophiles – Organisms thriving in extreme environmental conditions like high salinity, temperature, or pH.

• Archaebacteria – Prokaryotic microorganisms often found in extreme environments, distinct from eubacteria.

• Halophiles – Organisms adapted to high-salt environments.

• Mycobacteria – Actinobacteria, some pathogenic, typically not halophilic.

• Cyanobacteria – Photosynthetic bacteria, mostly freshwater or marine.

• Eubacteria – True bacteria, wide range of habitats, not all extremophiles.

• Clinical relevance – Studying extremophiles aids biotechnology, industrial enzymes, and understanding microbial survival.

Lead Question – 2017:

Which of the following are found in extreme saline conditions ?

(A) Mycobacteria

(B) Archaebacteria

(D) Cyanobacteria

Explanation:

Archaebacteria, particularly halophilic archaea, thrive in extreme saline conditions like salt lakes and salt pans. Mycobacteria, eubacteria, and cyanobacteria generally inhabit normal or moderately saline environments. Halophiles possess specialized adaptations for osmotic balance and protein stability, making archaebacteria ideal models for extremophile studies. (Answer: B)

1) Which archaebacteria are halophilic?

(A) Methanogens

(B) Halophiles

(D) Cyanobacteria

Explanation:

Halophiles are archaebacteria adapted to high-salt environments, maintaining osmotic balance using compatible solutes and specialized proteins. Methanogens produce methane, thermoacidophiles tolerate heat and acidity, while cyanobacteria are photosynthetic. Understanding halophiles aids biotechnology, saline agriculture, and enzyme research. (Answer: B)

2) Extremophiles that produce methane belong to:

(A) Halophiles

(B) Methanogens

(D) Mycobacteria

Explanation:

Methanogens are archaebacteria that generate methane in anaerobic environments. They are extremophiles but not halophilic. Halophiles tolerate high salinity. Extremophiles’ study informs renewable energy, waste treatment, and microbial ecology. (Answer: B)

3) Which organism is photosynthetic but rarely halophilic?

(A) Cyanobacteria

(B) Halophiles

(D) Methanogens

Explanation:

Cyanobacteria are photosynthetic bacteria, usually in freshwater or marine habitats. Only few tolerate moderate salinity; extreme halophilic cyanobacteria are rare. Halophilic archaebacteria are specialized for high salt. Cyanobacteria contribute to oxygen production and nitrogen fixation. (Answer: A)

4) Clinical/biotechnological relevance of halophiles:

(A) Enzyme production

(B) Salt-tolerant crops

(D) All of the above

Explanation:

Halophiles produce salt-tolerant enzymes, compatible solutes, and osmoprotectants. They inform biotechnology, industrial processes, and saline agriculture. Their study enhances understanding of microbial adaptation in extreme environments and can lead to novel bioproducts. (Answer: D)

5) Which group can survive in salt-saturated ponds?

(A) Mycobacteria

(B) Halophilic archaebacteria

(D) Cyanobacteria

Explanation:

Halophilic archaebacteria survive in salt-saturated ponds due to osmotic adaptation and stable proteins. Eubacteria, mycobacteria, and cyanobacteria are less tolerant of extreme salinity. Studying halophiles helps understand microbial ecology and extremophile adaptations. (Answer: B)

6) Adaptation mechanism in halophiles:

(A) Osmotic balance using compatible solutes

(B) Thick peptidoglycan

(D) Photosynthesis

Explanation:

Halophiles maintain osmotic balance with compatible solutes like potassium ions and organic molecules. Thick peptidoglycan and spores are structural or survival features in other bacteria. Photosynthesis is not a primary halophilic adaptation. These strategies prevent desiccation and protein denaturation in extreme saline habitats. (Answer: A)

7) Assertion-Reason type:

Assertion (A): Archaebacteria are found in extreme saline conditions.

Reason (R): They have specialized osmotic adaptations and salt-tolerant proteins.

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

(B) Both A and R are true, but R is not the correct explanation

(D) A is false, R is true

Explanation:

Both assertion and reason are correct; halophilic archaebacteria survive high salinity due to specialized osmotic adaptations and salt-stable proteins. This enables them to thrive in extreme saline habitats like salt lakes and salt pans. (Answer: A)

8) Matching type:

Match bacteria with environment:

(A) Halophiles – (i) Salt lakes

(B) Thermoacidophiles – (ii) Hot acidic springs

(D) Cyanobacteria – (iv) Freshwater/marine

Options:

(A) A-i, B-ii, C-iii, D-iv

(B) A-ii, B-i, C-iv, D-iii

(D) A-iv, B-iii, C-ii, D-i

Explanation:

Correct matches: Halophiles – salt lakes, Thermoacidophiles – hot acidic springs, Methanogens – anaerobic mud, Cyanobacteria – freshwater/marine. These adaptations allow survival in extreme conditions, aiding biotechnological and ecological studies. (Answer: A)

9) Fill in the blanks:

_______ are extremophiles that thrive in high-salt environments.

(A) Halophiles

(B) Methanogens

(D) Eubacteria

Explanation:

Halophiles, mostly archaebacteria, thrive in high-salt environments due to osmotic adaptations and salt-stable proteins. They are models for extremophile research and industrial enzyme applications. Other bacteria may tolerate mild salinity but not extreme levels. (Answer: A)

10) Choose the correct statements:

1. Archaebacteria include halophiles and methanogens.

2. Halophiles survive in extreme saline conditions.

3. Cyanobacteria are mostly freshwater or marine.

4. Mycobacteria are extreme halophiles.

(A) 1, 2, 3 only

(B) 2, 3, 4 only

(D) All are correct

Explanation:

Statements 1, 2, and 3 are correct. Statement 4 is false; Mycobacteria are not extreme halophiles. Recognizing extremophiles and their habitats is essential for microbial ecology, industrial applications, and biotechnological research. (Answer: A)

Chapter: Microbiology

Topic: Bacterial Cell Structure

Subtopic: Glycocalyx and Cell Envelope

Keyword Definitions:

• Glycocalyx – Polysaccharide or glycoprotein layer surrounding some bacterial cells; provides stickiness and protection.

• Cell wall – Rigid structure made of peptidoglycan; maintains shape and prevents osmotic lysis.

• Plasma membrane – Phospholipid bilayer controlling substance entry and exit.

• Nuclear membrane – Membrane surrounding the nucleus; absent in prokaryotes.

• Capsule – Dense glycocalyx layer protecting bacteria from phagocytosis.

• Biofilm – Community of bacteria adhering to surfaces via glycocalyx.

• Clinical relevance – Capsules enhance bacterial virulence and biofilm formation, important in infections like pneumonia and urinary tract infections.

Lead Question – 2017:

Which of the following components provides sticky character to the bacterial cell ?

(A) Glycocalyx

(B) Cell wall

(D) Plasma membrane

Explanation:

The glycocalyx provides stickiness to bacterial cells. Composed of polysaccharides or glycoproteins, it enables adherence to surfaces and host tissues, forming biofilms and capsules. This contributes to bacterial virulence and immune evasion. Cell wall and plasma membrane provide structural integrity, but stickiness is characteristic of glycocalyx. (Answer: A)

1) The bacterial capsule primarily helps in:

(A) Nutrient absorption

(B) Protection from phagocytosis

(D) Ribosome assembly

Explanation:

The bacterial capsule, a dense form of glycocalyx, protects cells from phagocytosis by host immune cells. This increases virulence in pathogens like Streptococcus pneumoniae. Capsules also aid in biofilm formation and environmental resistance. Their presence is clinically significant in infections requiring immune evasion strategies. (Answer: B)

2) Which bacterial structure is absent in prokaryotes?

(A) Plasma membrane

(B) Ribosomes

(D) Cell wall

Explanation:

Prokaryotes lack a nuclear membrane; their genetic material is free in the nucleoid. Ribosomes, plasma membrane, and cell wall are present. This structural simplicity differentiates prokaryotes from eukaryotes and influences antibiotic targeting strategies. (Answer: C)

3) Clinical case: A patient develops urinary tract infection caused by E. coli. Which component contributes most to bacterial adhesion in the urinary tract?

(A) Flagella

(B) Glycocalyx

(D) Ribosome

Explanation:

Glycocalyx enables E. coli to adhere to the urinary epithelium, promoting biofilm formation and persistent infection. This adhesive property complicates treatment. Flagella help motility, not adhesion. Understanding glycocalyx-mediated attachment is important for developing therapeutic interventions in UTIs. (Answer: B)

4) The bacterial cell wall is primarily made of:

(A) Peptidoglycan

(B) Cellulose

(D) Lipopolysaccharide only

Explanation:

Bacterial cell walls are primarily composed of peptidoglycan, a polymer of sugars and amino acids providing rigidity and protection against osmotic pressure. Gram-positive bacteria have thick peptidoglycan layers, while Gram-negative bacteria have thinner layers with an outer membrane. Disruption of cell wall synthesis is a key antibiotic target. (Answer: A)

5) Which structure aids in bacterial movement?

(A) Capsule

(B) Flagella

(D) Glycocalyx

Explanation:

Bacterial flagella provide motility, allowing movement toward nutrients or away from harmful conditions (chemotaxis). Capsules and glycocalyx assist in adhesion, not movement. Understanding flagella function is clinically relevant in pathogenicity and vaccine development. (Answer: B)

6) Lipopolysaccharides are found in:

(A) Gram-positive bacteria

(B) Gram-negative bacteria

(D) Only in archaea

Explanation:

Gram-negative bacteria possess lipopolysaccharides in their outer membrane, contributing to endotoxin activity and immune responses in infections. Gram-positive bacteria lack this component. LPS detection is important in sepsis diagnosis and treatment strategies. (Answer: B)

7) Assertion-Reason type:

Assertion (A): Biofilms increase bacterial resistance to antibiotics.

Reason (R): Glycocalyx in biofilms protects bacteria from drugs and immune cells.

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

(B) Both A and R are true, but R is not the correct explanation

(D) A is false, R is true

Explanation:

Both assertion and reason are true, and R explains A. Biofilms, mediated by glycocalyx, shield bacteria from antibiotics and host defenses. This structural protection makes infections persistent, especially in indwelling devices. Understanding glycocalyx in biofilms aids in clinical infection management. (Answer: A)

8) Matching type:

Match bacterial structures with their functions:

(A) Glycocalyx – (i) Adhesion

(B) Flagella – (ii) Motility

(D) Cell wall – (iv) Structural integrity

Options:

(A) A-i, B-ii, C-iii, D-iv

(B) A-ii, B-i, C-iv, D-iii

(D) A-iv, B-iii, C-i, D-ii

Explanation:

Correct match: Glycocalyx – adhesion, Flagella – motility, Pili – conjugation, Cell wall – structural integrity. These structures are critical for bacterial survival, virulence, and reproduction. Knowledge of these components is essential in microbiology and clinical infection control. (Answer: A)

9) Fill in the blanks:

The dense polysaccharide layer surrounding some bacteria that prevents phagocytosis is called ______.

(A) Flagella

(B) Capsule

(D) Peptidoglycan

Explanation:

The capsule is a dense glycocalyx layer that surrounds certain bacteria, protecting them from phagocytosis and host immune defenses. It also facilitates adhesion and biofilm formation. Capsules are key virulence factors in pathogens like Streptococcus pneumoniae and Haemophilus influenzae. (Answer: B)

10) Choose the correct statements:

1. Glycocalyx provides stickiness and adhesion.

2. Bacterial cell wall maintains shape.

3. Nuclear membrane is present in bacteria.

4. Biofilms are formed by bacterial communities.

(A) 1, 2, 4 only

(B) 2 and 3 only

(D) All are correct

Explanation:

Statements 1, 2, and 4 are correct; statement 3 is wrong because bacteria lack a nuclear membrane. Glycocalyx-mediated adhesion and biofilm formation contribute to virulence, while the cell wall maintains structure. This knowledge is important in clinical microbiology and antibiotic strategies. (Answer: A)

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