Transport in Plants

Topic: Translocation of Food; Subtopic: Girdling Experiment and Role of Phloem

Keyword Definitions:

• Girdling Experiment: A process where a ring of bark is removed from a plant stem to demonstrate that food transport occurs through phloem.

• Phloem: Vascular tissue responsible for translocation of organic nutrients, mainly sucrose, from leaves to other plant parts.

• Xylem: Tissue that conducts water and minerals upward from roots to shoots.

• Translocation: Movement of food from source (leaves) to sink (roots, fruits, or seeds) in plants.

• Apoplast and Symplast: Pathways for water movement in plants; apoplast involves cell walls, while symplast involves cytoplasmic connections.

Lead Question - 2022 (Abroad)
Which of the following was proved by girdling experiment?
1. Apoplastic movement of water occurs through intercellular spaces
2. Symplastic movement of water occurs through interconnected protoplast
3. Xylem is responsible for uptake of water
4. Phloem is responsible for translocation of food

Explanation: The girdling experiment proves that phloem is responsible for translocation of food. When a ring of bark (including phloem) is removed, food accumulates above the ring, causing swelling. This shows that sugars synthesized in leaves move downward through phloem, not xylem, confirming its role in food transport.

1. The main function of phloem in plants is:
1. Transport of water
2. Transport of food
3. Mechanical support
4. Storage of minerals
Explanation: Phloem transports organic food materials, mainly sucrose, from photosynthetic regions (leaves) to non-photosynthetic parts. This process is known as translocation. The direction of movement can be upward or downward depending on the source-sink relationship within the plant body.

2. The process of removing a ring of bark from a tree trunk is called:
1. Pruning
2. Girdling
3. Decortication
4. Layering
Explanation: Girdling involves removing a complete ring of bark, including phloem, to interrupt food transport. Water movement through xylem continues, but the portion above the girdle swells due to sugar accumulation, confirming the phloem’s role in food translocation.

3. The term “source” in phloem translocation refers to:
1. Storage organs
2. Roots
3. Photosynthetic leaves
4. Flowers
Explanation: In plants, the “source” refers to the region where food (mainly sucrose) is synthesized, such as green leaves. This food is then transported through phloem to “sink” regions that require nutrients, such as roots, fruits, and developing seeds, maintaining the plant’s growth and metabolism.

4. Which of the following cells are involved in food transport in angiosperms?
1. Tracheids and vessels
2. Sieve tubes and companion cells
3. Xylem fibers
4. Parenchyma cells
Explanation: Sieve tube elements and companion cells of phloem transport food. Sieve tubes are living, elongated cells that allow nutrient flow, while companion cells regulate their metabolic activity, providing ATP and controlling loading and unloading of solutes during translocation.

5. Which among the following processes does not involve phloem?
1. Transport of amino acids
2. Transport of hormones
3. Transport of minerals
4. Transport of sucrose
Explanation: The correct answer is transport of minerals, as minerals move through xylem along with water. Phloem mainly transports organic solutes like sucrose, amino acids, and hormones in a bidirectional manner depending on plant needs and developmental stages.

6. Translocation of food occurs from:
1. Sink to source
2. Source to sink
3. Root to leaf only
4. Stem to flower only
Explanation: The correct answer is from source to sink. Food synthesized in leaves (sources) is transported through phloem to non-photosynthetic tissues (sinks) like roots, fruits, and seeds for storage or energy use, ensuring balanced plant growth and development.

7. Assertion (A): Phloem is responsible for translocation of food.
Reason (R): Xylem conducts organic solutes.
1. (A) is correct but (R) is not correct
2. (A) is not correct but (R) is correct
3. Both (A) and (R) are correct, and (R) explains (A)
4. Both (A) and (R) are correct, but (R) does not explain (A)
Explanation: The correct answer is option 1. Phloem, not xylem, translocates organic solutes such as sucrose and amino acids. Xylem mainly conducts water and minerals upward from roots to shoots, whereas phloem transports food bidirectionally depending on the metabolic requirements.

8. Match the following:
A. Phloem → 1. Transport of food
B. Xylem → 2. Transport of water
C. Girdling → 3. Removal of bark
D. Sieve tubes → 4. Conducting elements
1. A-1, B-2, C-3, D-4
2. A-4, B-3, C-1, D-2
3. A-3, B-1, C-4, D-2
4. A-2, B-4, C-3, D-1
Explanation: The correct match is A-1, B-2, C-3, D-4. Phloem transports food, xylem carries water, girdling involves bark removal to prove phloem’s role, and sieve tubes serve as conducting channels in phloem for organic solute transport in plants.

9. Fill in the blank: The food prepared in leaves is mainly transported in the form of ________.
1. Glucose
2. Fructose
3. Sucrose
4. Maltose
Explanation: The correct answer is sucrose. Although glucose is the primary product of photosynthesis, it is converted into sucrose for transport because sucrose is non-reducing and chemically stable. It easily dissolves in water, facilitating efficient long-distance movement through phloem tissue.

10. Choose the correct statements:
a. Girdling experiment demonstrates phloem’s role in food transport.
b. Phloem translocation is unidirectional.
c. Companion cells help sieve tubes in food conduction.
d. Bark removal stops upward water flow.
1. a and c
2. b and d
3. a, b, and c
4. a and d
Explanation: The correct answer is a and c. The girdling experiment confirms that phloem transports food, and companion cells support sieve tubes metabolically. Translocation is bidirectional, and bark removal does not affect water transport, as xylem remains intact.

Topic: Phloem Transport; Subtopic: Translocation of Organic Solutes

Keyword Definitions:

• Phloem: A vascular tissue that transports organic nutrients, especially sugars, from leaves to other parts of the plant.

• Phloem Sap: A fluid rich in sugars, amino acids, and hormones that flows through sieve tubes during translocation.

• Sucrose: A disaccharide sugar formed from glucose and fructose, the main form in which sugar is transported in plants.

• Translocation: The movement of organic solutes from sources (leaves) to sinks (roots, fruits, etc.) through the phloem.

Lead Question - 2022 (Abroad)
Phloem sap in the plants mainly consists of:
1. Fructose and water
2. Fructose and sucrose
3. Glucose and water
4. Sucrose and water

Explanation (Answer: 4): Phloem sap primarily contains sucrose and water. Sucrose is the main sugar transported from photosynthetic tissues to storage and growing parts through sieve tubes. The flow is driven by osmotic pressure differences between source and sink regions, enabling efficient distribution of energy-rich compounds.

1. The direction of phloem transport is:
1. Always upward
2. Always downward
3. Multidirectional
4. Unidirectional

Explanation (Answer: 3): Phloem transport is multidirectional because organic solutes can move from source to sink in any direction as required by the plant. Unlike xylem, which shows unidirectional upward flow, phloem translocation depends on metabolic needs and sugar demand at various parts.

2. The pressure-flow hypothesis explains:
1. Transpiration
2. Ascent of sap
3. Translocation of sugars in phloem
4. Guttation

Explanation (Answer: 3): The pressure-flow hypothesis describes how sucrose solution moves from source to sink in phloem. High osmotic pressure at the source drives the movement toward low pressure at the sink. This model best explains the mechanism of phloem sap translocation in plants.

3. In phloem transport, the source is generally the:
1. Root
2. Leaf
3. Flower
4. Fruit

Explanation (Answer: 2): Leaves act as the main source in phloem transport because they produce sugars during photosynthesis. These sugars are then loaded into sieve tubes for transport to other parts of the plant, which function as sinks, such as roots or fruits requiring energy for growth.

4. Phloem loading involves:
1. Active transport of sucrose into sieve tubes
2. Diffusion of sucrose into xylem
3. Osmotic uptake of water by xylem
4. Active transport of ions into guard cells

Explanation (Answer: 1): Phloem loading is an active process that transfers sucrose from mesophyll cells into sieve tube elements using ATP. This increases osmotic pressure, drawing water from xylem and initiating bulk flow of phloem sap toward the sink tissues where sugars are consumed or stored.

5. Which one of the following helps in phloem transport?
1. Tracheids
2. Vessel elements
3. Companion cells
4. Guard cells

Explanation (Answer: 3): Companion cells assist sieve tube elements in phloem transport by providing metabolic support and helping with active loading and unloading of sucrose. They maintain the concentration gradient necessary for translocation and ensure continuous flow of nutrients throughout the plant body.

6. Which one is the conducting element of phloem?
1. Xylem vessels
2. Sieve tube elements
3. Tracheids
4. Fibers

Explanation (Answer: 2): Sieve tube elements are the main conducting units of phloem. They are elongated living cells connected end-to-end with sieve plates for sap movement. Though they lack a nucleus, companion cells regulate their functions, enabling efficient transport of sucrose and other solutes through the plant.

7. (Assertion-Reason Type)
Assertion: Phloem transport is an active process.
Reason: Loading and unloading of sugars into the phloem require energy.
1. Both Assertion and Reason are true, and Reason is the correct explanation
2. Both Assertion and Reason are true, but Reason is not the correct explanation
3. Assertion is true, but Reason is false
4. Both Assertion and Reason are false

Explanation (Answer: 1): Phloem transport requires metabolic energy for sugar loading and unloading into sieve tubes, making it an active process. ATP-driven transport establishes osmotic gradients that cause pressure flow, moving sucrose-rich sap from sources like leaves to sinks such as roots or fruits efficiently.

8. (Matching Type)
Match the parts of phloem with their functions:
a. Sieve tube elements
b. Companion cells
c. Phloem fibers
d. Phloem parenchyma

(i) Storage of food
(ii) Mechanical support
(iii) Translocation of food
(iv) Support and loading of sucrose
1. (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)
2. (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
3. (a)-(iv), (b)-(iii), (c)-(i), (d)-(ii)
4. (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)

Explanation (Answer: 1): Sieve tubes transport food, companion cells support and load sucrose, phloem fibers provide mechanical strength, and phloem parenchyma stores food. These components work collectively to maintain the translocation process and structural integrity of phloem tissue for efficient nutrient distribution.

9. (Fill in the Blanks)
Phloem translocation occurs from ________ to ________.

Explanation (Answer: source, sink): Phloem translocation occurs from source to sink regions. Sources are photosynthetic parts that produce sugars, while sinks are areas like roots, fruits, or young leaves where sugars are consumed or stored. This flow is controlled by osmotic gradients in the sieve tubes.

10. (Choose the correct statements)
a. Phloem sap moves by pressure flow
b. Movement of phloem sap is bidirectional
c. Phloem translocation requires metabolic energy
d. Phloem sap mainly contains glucose
1. a, b, and c only
2. b and d only
3. a and c only
4. a, b, c, and d

Explanation (Answer: 1): Phloem sap moves by pressure flow from high osmotic pressure regions to low pressure regions. The process is bidirectional depending on the source-sink relationship and needs energy for sugar loading. The sap primarily contains sucrose, not glucose, as the major transport sugar.

Topic: Transport Across Cell Membrane
Subtopic: Facilitated Diffusion

Keyword Definitions:

• Facilitated Diffusion: Passive transport of molecules across a biological membrane via specific transport proteins without energy expenditure.

• Porins: Protein channels that allow the passage of certain molecules across membranes, mainly in mitochondria and bacteria.

• Concentration Gradient: The gradual difference in solute concentration between two areas, driving diffusion.

• ATP: Adenosine Triphosphate, the main energy currency of the cell.

Lead Question - 2022 (Abroad)
Which of the following statements about facilitated diffusion is incorrect?
1. Special proteins of the membrane help in this process
2. Porins are involved in this process
3. Movement of molecule occurs against the concentration gradient
4. ATP is not required for this process

Explanation (Answer: 3): Facilitated diffusion is a passive process that moves molecules along the concentration gradient through specific transport proteins. It does not require ATP. Movement against the gradient occurs only in active transport, not in facilitated diffusion. Hence, statement 3 is incorrect because it describes active transport.

1. The main difference between simple diffusion and facilitated diffusion is:
1. Use of carrier proteins
2. Requirement of ATP
3. Movement of gases only
4. Movement of ions only

Explanation (Answer: 1): Facilitated diffusion uses specific carrier or channel proteins to help molecules move across membranes, unlike simple diffusion which occurs freely. Both are passive processes and do not require energy. Thus, the primary difference lies in the involvement of membrane transport proteins.

2. Which of the following molecules moves by facilitated diffusion?
1. Oxygen
2. Carbon dioxide
3. Glucose
4. Water

Explanation (Answer: 3): Glucose moves across cell membranes by facilitated diffusion with the help of GLUT transporters. Since it is a large polar molecule, it cannot pass through the lipid bilayer by simple diffusion. Therefore, carrier proteins assist in its passive transport down the concentration gradient.

3. Facilitated diffusion differs from active transport because it:
1. Requires ATP
2. Is slower
3. Occurs against the gradient
4. Does not require energy

Explanation (Answer: 4): Facilitated diffusion is a passive process where solutes move along their concentration gradient through specific transport proteins without using cellular energy. In contrast, active transport needs ATP to move molecules against the concentration gradient, making facilitated diffusion an energy-efficient process.

4. Porins form channels in the outer membranes of:
1. Lysosomes
2. Mitochondria
3. Endoplasmic reticulum
4. Nucleus

Explanation (Answer: 2): Porins are large transmembrane proteins that form channels in the outer membranes of mitochondria, chloroplasts, and some bacteria. They allow small hydrophilic molecules to pass through, enabling efficient exchange of ions and metabolites essential for cellular metabolism and respiration.

5. The rate of facilitated diffusion depends on:
1. ATP concentration
2. Number of carrier proteins
3. Cell wall thickness
4. Availability of enzymes

Explanation (Answer: 2): Facilitated diffusion depends on the number of carrier or channel proteins present in the membrane. When all carrier proteins are occupied, the rate reaches saturation. Therefore, increasing protein availability enhances the transport rate until all become occupied by substrate molecules.

6. In facilitated diffusion, carrier proteins exhibit:
1. Enzymatic action
2. Specificity and saturation
3. Random movement
4. Constant activity

Explanation (Answer: 2): Carrier proteins show specificity for certain molecules and saturation when all binding sites are occupied. This characteristic makes facilitated diffusion similar to enzyme kinetics. Specificity ensures that only suitable solutes are transported, maintaining selective permeability of the biological membrane.

7. (Assertion-Reason Type)
Assertion: Facilitated diffusion is a passive process.
Reason: It uses ATP to move molecules across the membrane.
1. Both Assertion and Reason are true and Reason is the correct explanation
2. Both Assertion and Reason are true but Reason is not the correct explanation
3. Assertion is true but Reason is false
4. Assertion is false but Reason is true

Explanation (Answer: 3): The assertion is true because facilitated diffusion occurs passively without energy expenditure. The reason is false because ATP is not used in this process. The movement occurs along the concentration gradient using membrane proteins, distinguishing it from active transport.

8. (Matching Type)
Match the transport type with its characteristics:
a. Simple diffusion
b. Facilitated diffusion
c. Active transport
d. Osmosis

(i) Energy independent and uses carriers
(ii) Energy dependent
(iii) Movement of water molecules
(iv) Direct movement through lipid bilayer
1. (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
2. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
3. (a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)
4. (a)-(iv), (b)-(ii), (c)-(iii), (d)-(i)

Explanation (Answer: 1): Simple diffusion passes directly through membranes, facilitated diffusion uses carriers but no energy, active transport needs energy, and osmosis involves water movement. This classification helps differentiate passive and active transport mechanisms based on energy dependence and direction of molecule movement.

9. (Fill in the Blanks)
Facilitated diffusion allows ________ molecules to cross membranes through specific transport proteins.

Explanation (Answer: polar): Facilitated diffusion enables polar molecules like glucose and amino acids to pass across membranes using channel or carrier proteins. Since lipid bilayers restrict polar solute movement, transport proteins provide hydrophilic pathways ensuring selective permeability and efficient cellular transport processes without energy use.

10. (Choose the correct statements)
a. Facilitated diffusion requires ATP
b. It shows saturation
c. Carrier proteins are specific
d. It moves molecules along concentration gradient
1. a and b
2. b, c, and d
3. a, b, and d
4. c and d

Explanation (Answer: 2): Facilitated diffusion shows saturation and specificity due to carrier proteins and moves molecules along their concentration gradient. It is an energy-independent process that depends on the availability and selectivity of transport proteins, maintaining controlled molecular exchange across cell membranes.

Subtopic: Water Potential and Osmosis

Keyword Definitions:

• Water Potential: The potential energy of water in a system compared to pure water, determining the direction of water movement.

• Solute Potential: The component of water potential affected by dissolved solutes; it always lowers total water potential.

• Osmosis: Movement of water across a semi-permeable membrane from higher to lower water potential.

• Diffusion: Passive movement of molecules from a region of high concentration to low concentration.

• Plasmolysis: The shrinkage of the cytoplasm from the cell wall due to water loss in a hypertonic solution.

• Turgor Pressure: The pressure exerted by the cell contents against the cell wall, maintaining cell rigidity.

• Semipermeable Membrane: A membrane allowing certain molecules (usually water) to pass but restricting solutes.

• Hypotonic Solution: A solution having higher water potential than the cell sap, causing water entry into the cell.

• Hypertonic Solution: A solution having lower water potential than the cell sap, causing water to leave the cell.

• Osmotic Potential: Another term for solute potential, representing the effect of solute concentration on water potential.

Lead Question (2022)
Addition of solutes in a given solution will:
(1) Lower its water potential
(2) Make its water
(3) Not affect the water potential at all
(4) Raise its water potential

Explanation:
When solutes are added to pure water, solute potential becomes more negative, reducing total water potential. Thus, addition of solutes lowers water potential, making water move toward it from higher potential regions. Correct answer is (1).

1. Single Correct Answer MCQ:
What is the water potential of pure water at standard conditions?
(1) Zero
(2) One
(3) Negative
(4) Positive

Explanation:
Pure water has a water potential of zero at standard conditions (25°C and 1 atm). Solutes or pressure can make it more negative or positive, respectively. Correct answer is (1).

2. Single Correct Answer MCQ:
Which of the following will increase the water potential of a cell?
(1) Decrease in solute concentration
(2) Increase in solute concentration
(3) Water loss
(4) Plasmolysis

Explanation:
Decreasing solute concentration reduces solute potential negativity, thus increasing total water potential. Correct answer is (1).

3. Single Correct Answer MCQ:
In a hypertonic solution, a plant cell will:
(1) Gain water
(2) Lose water
(3) Remain unchanged
(4) Become more turgid

Explanation:
In a hypertonic solution, external water potential is lower than inside the cell, so water exits the cell, causing plasmolysis. Correct answer is (2).

4. Single Correct Answer MCQ:
The component of water potential affected by solutes is called:
(1) Pressure potential
(2) Solute potential
(3) Osmotic pressure
(4) Diffusion pressure

Explanation:
Solute potential (Ψs) represents the effect of solutes on water potential; it is always negative. Correct answer is (2).

5. Single Correct Answer MCQ:
Water moves from a region of:
(1) Low water potential to high water potential
(2) High solute potential to low solute potential
(3) High water potential to low water potential
(4) Negative pressure to positive pressure

Explanation:
Water always moves from a region of higher water potential to one with lower water potential until equilibrium is reached. Correct answer is (3).

6. Single Correct Answer MCQ:
The water potential of a fully turgid cell is:
(1) Zero
(2) Negative
(3) Positive
(4) Equal to solute potential

Explanation:
A fully turgid cell has pressure potential equal in magnitude but opposite to solute potential, making total water potential zero. Correct answer is (1).

7. Assertion-Reason MCQ:
Assertion (A): Addition of solutes decreases water potential.
Reason (R): Solute potential is always positive.
Options:
(1) Both A and R are true, R explains A
(2) Both A and R are true, R does not explain A
(3) A is true, R is false
(4) A is false, R is true

Explanation:
Addition of solutes lowers water potential because solute potential is negative, not positive. Thus, the assertion is correct but reason is false. Correct answer is (3).

8. Matching Type MCQ:
Match the terms with their correct descriptions:
A. Solute potential — 1. Positive in turgid cells
B. Pressure potential — 2. Negative component
C. Water potential — 3. Sum of all potentials
D. Osmosis — 4. Movement of water across membrane
Options:
(1) A–2, B–1, C–3, D–4
(2) A–1, B–2, C–3, D–4
(3) A–2, B–3, C–4, D–1
(4) A–4, B–2, C–1, D–3

Explanation:
Solute potential is negative (2), pressure potential is positive (1), water potential is total of all potentials (3), and osmosis is water movement across membranes (4). Correct matching is (1).

9. Fill in the Blanks MCQ:
The water potential of a solution always becomes ________ when solutes are added.
(1) Higher
(2) Lower
(3) Equal
(4) Unchanged

Explanation:
Adding solutes lowers water potential because solute potential becomes more negative. Correct answer is (2).

10. Choose the Correct Statements MCQ:
(a) Water potential is zero for pure water
(b) Solute potential is always negative
(c) Pressure potential in a turgid cell is positive
(d) Addition of solutes increases water potential
Options:
(1) a, b, c
(2) a, b, d
(3) b, c, d
(4) a, c, d

Explanation:
Pure water has zero potential (a), solute potential is negative (b), and turgid cell pressure potential is positive (c). Addition of solutes decreases water potential, so (d) is wrong. Correct answer is (1).

Subtopic: Phloem Transport and Experiments

Keyword Definitions:

• Girdling Experiment: A method where a ring of bark is removed from a stem to study transport of food.

• Phloem: Vascular tissue responsible for transporting organic food from leaves to other plant parts.

• Xylem: Vascular tissue that transports water and minerals from roots to shoots.

• Osmosis: Movement of water across a semi-permeable membrane from high to low water potential.

• Transport in Plants: Movement of water, minerals, and food through xylem and phloem.

Lead Question (2022)
“Girdling Experiment” was performed by Plant Physiologists to identify the plant tissue through which:
Options:
(1) Food is transported
(2) For both water and food transportation
(3) Osmosis is observed
(4) Water is transported

Explanation:
The girdling experiment involves removing a ring of bark, which contains phloem, from the stem. Accumulation of food above the girdle confirms that phloem is responsible for transporting organic food. Water transport occurs through xylem and is unaffected. Correct answer is (1). This experiment demonstrates the role of phloem in translocation.

1. Which plant tissue transports water from roots to leaves?
(1) Phloem
(2) Xylem
(3) Cambium
(4) Cortex

Explanation:
Xylem is specialized for transporting water and dissolved minerals from roots to aerial parts of the plant, using transpiration pull. Phloem transports food, not water. Correct answer is (2).

2. In the girdling experiment, what accumulates above the girdle?
(1) Water
(2) Organic food
(3) Minerals
(4) Oxygen

Explanation:
When the bark containing phloem is removed, organic food synthesized in leaves accumulates above the girdle because phloem transport is blocked. Water and minerals move through xylem and are not affected. Correct answer is (2).

3. Which tissue is mainly removed in a girdling experiment?
(1) Xylem
(2) Phloem
(3) Cambium
(4) Pith

Explanation:
The bark removed during girdling contains phloem, responsible for food transport. Xylem remains intact for water transport. This allows identification of phloem function. Correct answer is (2).

4. What is the role of xylem in plants?
(1) Translocation of sugars
(2) Transport of water and minerals
(3) Photosynthesis
(4) Storing food

Explanation:
Xylem conducts water and dissolved minerals from roots to aerial parts through transpiration pull and cohesion. It does not transport sugars or perform photosynthesis. Correct answer is (2).

5. Single Correct Answer MCQ:
The accumulation of organic food above a girdle confirms:
(1) Phloem transports food
(2) Xylem transports water
(3) Cambium produces secondary growth
(4) Cortex stores starch

Explanation:
Food accumulates above the removed bark containing phloem, confirming that phloem is responsible for translocation of organic nutrients. Xylem continues to transport water unaffected. Correct answer is (1).

6. Which of the following is affected in a girdling experiment?
(1) Phloem transport
(2) Xylem transport
(3) Both phloem and xylem
(4) Only root growth

Explanation:
Girdling removes the bark containing phloem, blocking food transport. Xylem remains intact, allowing water movement. Root growth may reduce over time due to lack of food but initially is unaffected. Correct answer is (1).

7. Assertion-Reason MCQ:
Assertion (A): Girdling blocks translocation of food.
Reason (R): Phloem is removed in the girdled portion.
Options:
(1) Both A and R are correct, R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both A and R incorrect

Explanation:
Removal of phloem in girdling interrupts food translocation, leading to accumulation above the girdle. The assertion is true and reason correctly explains it. Correct answer is (1).

8. Matching Type MCQ:
Match plant tissue with function:
A. Xylem — 1. Transport water
B. Phloem — 2. Transport food
Options:
(1) A–1, B–2
(2) A–2, B–1
(3) Both A and B – 1
(4) Both A and B – 2

Explanation:
Xylem transports water and minerals (1), while phloem transports organic food (2). Correct answer is (1).

9. Fill in the Blanks:
The vascular tissue responsible for food translocation is _______.
(1) Phloem
(2) Xylem
(3) Cambium
(4) Cortex

Explanation:
Phloem conducts organic nutrients from leaves to various parts. Xylem only conducts water. Correct answer is (1).

10. Choose the Correct Statements:
(a) Girdling removes phloem
(b) Food accumulates above girdle
(c) Xylem transport is blocked
(d) Water transport continues
Options:
(1) a, b, d
(2) a and c only
(3) b and c only
(4) all of the above

Explanation:
Girdling removes phloem (a), causing food accumulation above the girdle (b). Xylem is unaffected, so water transport continues (d). Correct answer is (1).

Topic: Movement of Water in Plants
Subtopic: Apoplastic and Symplastic Pathways

Keyword Definitions:

• Apoplast: It includes cell walls and intercellular spaces through which water moves without crossing the cell membrane.

• Symplast: It refers to the movement of substances through the interconnected cytoplasm of cells via plasmodesmata.

• Plasmodesmata: Cytoplasmic connections between adjacent plant cells that allow exchange of materials.

• Water potential: The potential energy of water that determines the direction of water movement in plants.

Lead Question – 2022

Which of the following is not observed during apoplastic pathway?
(1) The movement does not involve crossing of cell membrane
(2) The movement is aided by cytoplasmic streaming
(3) Apoplast is continuous and does not provide any barrier to water movement
(4) Movement of water occurs through intercellular spaces and wall of the cells

Explanation: The apoplastic pathway involves water movement through cell walls and intercellular spaces without crossing the plasma membrane. It is not aided by cytoplasmic streaming, which occurs in the symplastic pathway. Hence, option (2) is correct. Apoplastic movement stops at the Casparian strip in the endodermis. (50 words)

Guessed Questions:

1. The symplastic movement of water in plants occurs through:
(1) Cell walls
(2) Vacuoles
(3) Cytoplasm and plasmodesmata
(4) Xylem vessels

Explanation: Symplastic movement occurs through cytoplasm interconnected by plasmodesmata. This allows direct transfer of ions and water molecules between adjacent cells. It requires crossing the plasma membrane only once and is aided by cytoplasmic streaming. Therefore, the correct answer is (3) cytoplasm and plasmodesmata. (50 words)

2. Which structure in the root prevents apoplastic movement of water to the stele?
(1) Endodermis
(2) Cortex
(3) Epidermis
(4) Pericycle

Explanation: The Casparian strip present in the endodermis contains suberin, a waxy material that blocks the apoplastic pathway. This ensures water and solutes must enter the symplast to reach the xylem. Hence, endodermis acts as a selective barrier. Correct answer: (1) Endodermis. (50 words)

3. In the apoplastic pathway, the movement of water is driven mainly by:
(1) Active transport
(2) Osmotic potential
(3) Transpiration pull
(4) Pressure potential

Explanation: Apoplastic water movement depends on transpiration pull, creating a continuous water column through cell walls. This passive process is pressure-driven, not energy-dependent. Hence, option (3) transpiration pull is correct. It operates efficiently until reaching the endodermal Casparian strip, where apoplastic movement ceases. (50 words)

4. Assertion (A): Apoplastic pathway provides a faster route for water movement.
Reason (R): Water in apoplast does not cross plasma membranes.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the 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. The apoplastic route is faster because water moves through non-living cell walls and intercellular spaces, avoiding plasma membrane crossing. Hence, R correctly explains A. Therefore, the correct option is (1). (50 words)

5. Match the following pathways with their characteristics:
A. Apoplastic pathway – (i) Cytoplasmic streaming
B. Symplastic pathway – (ii) Cell walls
C. Transmembrane route – (iii) Crossing membrane repeatedly
Choose the correct match:
(1) A–ii, B–i, C–iii
(2) A–iii, B–ii, C–i
(3) A–i, B–ii, C–iii
(4) A–ii, B–iii, C–i

Explanation: The apoplastic route occurs via cell walls, symplastic through cytoplasmic streaming, and transmembrane involves repeated membrane crossing. Hence, the correct matching is A–ii, B–i, C–iii, corresponding to option (1). (50 words)

6. In which plant organ is apoplastic movement of water most prominent?
(1) Root hairs
(2) Endodermis
(3) Xylem vessels
(4) Phloem

Explanation: Apoplastic movement predominates in root hairs, cortex, and xylem vessels, as these structures provide continuous cell wall channels for water movement without crossing membranes. Hence, the correct answer is (3) xylem vessels. (50 words)

7. Fill in the blank:
The endodermal cells contain a waxy layer called ______ that blocks apoplastic flow.
(1) Cutin
(2) Suberin
(3) Lignin
(4) Cellulose

Explanation: The Casparian strip in endodermal cell walls is rich in suberin, a hydrophobic substance that prevents apoplastic movement into the vascular cylinder. This forces water into the symplastic route. Hence, the correct answer is (2) suberin. (50 words)

8. Choose the correct statements regarding apoplastic pathway:
(1) It occurs through cytoplasm
(2) It is faster than symplastic movement
(3) It requires energy
(4) It stops at Casparian strip

Explanation: Apoplastic movement is faster as it occurs through cell walls but halts at the Casparian strip. It does not require energy or cytoplasmic streaming. Correct statements: (2) and (4). (50 words)

9. In apoplastic pathway, which component of cell wall plays a key role in water movement?
(1) Cellulose microfibrils
(2) Cuticle
(3) Suberin
(4) Pectin

Explanation: Cellulose microfibrils form a hydrophilic network that allows capillary movement of water through cell walls in apoplastic transport. Hence, the correct answer is (1) cellulose microfibrils. (50 words)

10. Apoplastic movement ceases at which location in the root?
(1) Cortex
(2) Epidermis
(3) Endodermis
(4) Pericycle

Explanation: The Casparian strip present in the endodermal cell wall prevents further apoplastic water movement into the vascular tissues. Water must enter the symplast beyond this point. Hence, the correct answer is (3) endodermis. (50 words)

Topic: Water Relations in Plants
Subtopic: Cohesion, Adhesion, Surface Tension, and Guttation

Keyword Definitions:

• Cohesion: The mutual attraction between water molecules due to hydrogen bonding.

• Adhesion: The attraction of water molecules toward other polar surfaces like cell walls.

• Surface Tension: The property of water surface to resist external force, caused by stronger cohesion among molecules.

• Guttation: The loss of water in liquid form from leaf tips or margins due to root pressure.

• Hydrogen Bond: A weak bond formed between the hydrogen atom of one molecule and an electronegative atom of another molecule.

• Root Pressure: Upward push of water in xylem due to osmotic pressure in roots.

• Polar Surface: A surface that has a partial positive and negative charge attracting water molecules.

• Liquid Phase Water Loss: Water loss in liquid form instead of transpiration as vapor.

Lead Question - 2021

Match List - I with List - II.
List - I    List - II
(a) Cohesion  (i) More attraction in liquid phase
(b) Adhesion  (ii) Mutual attraction among water molecules
(c) Surface tension  (iii) Water loss in liquid phase
(d) Guttation  (iv) Attraction towards polar surfaces
Choose the correct answer:
(a) (b) (c) (d)
(1) (iv) (iii) (ii) (i)
(2) (iii) (i) (iv) (ii)
(3) (ii) (i) (iv) (iii)
(4) (ii) (iv) (i) (iii)

Explanation: The correct answer is (4) (ii) (iv) (i) (iii). Cohesion refers to mutual attraction among water molecules (ii), adhesion is water attraction towards polar surfaces (iv), surface tension results from more attraction in liquid phase (i), and guttation is water loss in liquid form from leaf tips (iii). This sequence reflects water relations accurately.

Guessed Questions:

1) Which property of water causes it to rise in narrow capillaries?
(1) Cohesion
(2) Adhesion
(3) Surface tension
(4) Guttation

Explanation: The correct answer is (2) Adhesion. Water molecules are attracted to polar surfaces of xylem vessels, assisting capillary rise. Adhesion, along with cohesion, facilitates the upward movement of water from roots to leaves, a key mechanism in plant water transport.

2) Assertion (A): Cohesion is responsible for surface tension.
Reason (R): Hydrogen bonds between water molecules create mutual attraction.
(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 correct answer is (1). Surface tension arises because water molecules cohere due to hydrogen bonding. Cohesion creates a resistant surface layer, allowing water to form droplets and support small objects, which is essential in maintaining water column integrity in plants.

3) Which of the following is directly caused by root pressure?
(1) Transpiration
(2) Guttation
(3) Cohesion
(4) Adhesion

Explanation: The correct answer is (2) Guttation. Root pressure builds up in the xylem, pushing water to leaf margins where it is exuded as liquid droplets. This phenomenon occurs in conditions of high soil moisture and low transpiration.

4) Fill in the blank: The mutual attraction among water molecules due to hydrogen bonding is called ________.
(1) Adhesion
(2) Cohesion
(3) Surface tension
(4) Capillarity

Explanation: The correct answer is (2) Cohesion. Hydrogen bonds between water molecules create a strong internal attraction, allowing water to stick to itself. Cohesion is vital for water transport in xylem and contributes to surface tension, which stabilizes the water column in plants.

5) Which property allows water to adhere to cell walls and xylem vessels?
(1) Surface tension
(2) Cohesion
(3) Adhesion
(4) Guttation

Explanation: The correct answer is (3) Adhesion. Adhesion is the attraction of water molecules to polar surfaces, such as xylem walls. This property, combined with cohesion, assists in the capillary movement of water from roots to leaves in plants.

6) Which factor primarily contributes to high surface tension in water?
(1) Cohesion
(2) Adhesion
(3) Gravity
(4) Root pressure

Explanation: The correct answer is (1) Cohesion. The mutual attraction among water molecules due to hydrogen bonding forms a tensioned surface layer at the air-water interface. This property enables water to resist external force and aids in processes like water transport in plants.

7) Choose the correct statements:
a. Cohesion is mutual attraction among water molecules.
b. Adhesion helps in capillary rise.
c. Guttation occurs during high transpiration.
d. Surface tension is due to cohesion.
(1) a, b, d
(2) a, c
(3) b, c, d
(4) a, b, c, d

Explanation: The correct answer is (1) a, b, d. Cohesion causes water molecules to stick together, adhesion facilitates capillary rise, and surface tension arises from cohesion. Guttation occurs when transpiration is low and root pressure is high, making statement c incorrect.

8) Assertion (A): Guttation is water loss in liquid form from leaves.
Reason (R): It occurs due to root pressure in xylem when transpiration is low.
(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 correct answer is (1). Guttation results from the exudation of liquid water through hydathodes at leaf margins. It is caused by root pressure when transpiration is minimal, typically at night or high humidity, allowing water to escape in liquid form.

9) Matching Type: Match the plant water relation term with its description.
List-I    List-II
(a) Cohesion  (i) Water loss in liquid
(b) Adhesion    &nbsp

Subtopic: Phloem and Xylem Transport

Keyword Definitions:

• Phloem: Vascular tissue responsible for translocation of organic solutes, mainly sucrose.

• Xylem: Vascular tissue that transports water and minerals from roots to aerial parts.

• Bidirectional transport: Movement in two directions, e.g., in phloem from source to sink.

• Unidirectional transport: Movement in a single direction, e.g., water in xylem.

• Source: Part of plant producing or storing assimilates, e.g., leaves.

• Sink: Part of plant consuming or storing assimilates, e.g., roots, fruits.

• ATP: Adenosine triphosphate, energy currency required for active transport.

• Minerals: Inorganic nutrients like nitrogen, phosphorus, potassium, sulfur.

• Loading: Process of moving sucrose into phloem at source.

• Unloading: Process of removing sucrose from phloem at sink.

• Mobilization: Movement of nutrients from one region to another within plant.

Lead Question - 2020 (COVID Reexam)

Select the incorrect statement.

1. Transport of molecules in phloem can be bidirectional.
2. The movement of minerals in the xylem is unidirectional.
3. Unloading of sucrose at the sink does not involve the utilization of ATP.
4. Elements most easily mobilized in plants from one region to another are phosphorus, sulfur, nitrogen, and potassium.

Explanation: Phloem transport is bidirectional, xylem transport is unidirectional, and macronutrients like phosphorus, sulfur, nitrogen, and potassium are highly mobile. Unloading of sucrose at the sink requires energy in the form of ATP for active transport. Hence, option 3 is incorrect. Proper ATP utilization ensures efficient phloem unloading. (50 words)

Guessed Question 1. Single Correct Answer MCQ: Which vascular tissue transports water and minerals?

1. Phloem
2. Xylem
3. Collenchyma
4. Sclerenchyma

Explanation: Xylem is responsible for unidirectional transport of water and minerals from roots to leaves. Phloem translocates organic solutes. Collenchyma and sclerenchyma provide support. Correct answer is option 2: Xylem. Efficient water transport is vital for plant turgor, nutrient distribution, and photosynthesis. (50 words)

Guessed Question 2. Single Correct Answer MCQ: Phloem transport is generally :

1. Unidirectional
2. Bidirectional
3. Non-directional
4. Random

Explanation: Phloem transport can occur in both directions, from source to sink, depending on the plant's needs. Unidirectional transport is typical of xylem. Correct answer is option 2: Bidirectional. This flexibility allows distribution of nutrients to growing or storage organs. (50 words)

Guessed Question 3. Single Correct Answer MCQ: Which nutrient is highly mobile in plants?

1. Calcium
2. Phosphorus
3. Iron
4. Boron

Explanation: Phosphorus is highly mobile within plants, easily moving from older to younger tissues. Calcium and boron are relatively immobile, and iron mobility is limited. Correct answer is option 2: Phosphorus. Mobility ensures nutrient availability for growth and metabolic activities. (50 words)

Guessed Question 4. Single Correct Answer MCQ: Active sucrose unloading at sink requires :

1. ATP
2. Water
3. Oxygen only
4. Minerals

Explanation: Active transport of sucrose into sink cells requires ATP energy to move molecules against concentration gradients. Passive transport occurs in some cases, but efficient unloading depends on ATP. Correct answer is option 1: ATP. Energy ensures sucrose is available for growth, storage, and metabolism. (50 words)

Guessed Question 5. Assertion-Reason MCQ:

Assertion (A): Xylem transport is unidirectional.
Reason (R): Water and minerals move only from roots to shoots.
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: Xylem transport is unidirectional, moving water and minerals from roots to aerial parts. Both assertion and reason are true, and R explains A. Correct answer is option 1. This directional flow is essential for maintaining plant hydration, nutrient supply, and turgor pressure. (50 words)

Guessed Question 6. Matching Type MCQ:

Column I - Function
(a) Phloem transport (i) Water and minerals
(b) Xylem transport (ii) Sucrose and nutrients
(c) Sucrose loading (iii) Energy dependent
(d) Sucrose unloading (iv) Bidirectional transport
Options:
1. (a)-(ii), (b)-(i), (c)-(iii), (d)-(iv)
2. (a)-(iv), (b)-(i), (c)-(iii), (d)-(ii)
3. (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
4. (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)

Explanation: Phloem translocates sucrose bidirectionally, xylem moves water and minerals unidirectionally. Sucrose loading and unloading are energy dependent. Correct answer is option 1. Proper functioning ensures efficient nutrient distribution and plant growth. (50 words)

Guessed Question 7. Fill in the blank:

Transport of water and minerals through xylem is _______.

1. Bidirectional
2. Unidirectional
3. Random
4. Nonexistent

Explanation: Xylem transport is unidirectional, moving water and minerals from roots to aerial parts. This ensures continuous hydration, nutrient supply, and transpiration pull. Correct answer is option 2: Unidirectional. Proper directionality is critical for plant survival and metabolic activities. (50 words)

Guessed Question 8. Single Correct Answer MCQ: Elements most easily mobilized in plants include :

1. Calcium and boron
2. Nitrogen, phosphorus, potassium, sulfur
3. Iron and manganese
4. Zinc and copper

Explanation: Nitrogen, phosphorus, potassium, and sulfur are highly mobile, allowing redistribution from older to younger tissues. Calcium, boron, and micronutrients are less mobile. Correct answer is option 2. Mobility ensures nutrient availability for growth, reproduction, and metabolic activities. (50 words)

Guessed Question 9. Single Correct Answer MCQ: Which process requires energy at sink?

1. Sucrose unloading
2. Xylem transport
3. Transpiration pull
4. Passive diffusion

Explanation: Sucrose unloading at the sink is an active process requiring ATP, moving sucrose into cells against the concentration gradient. Xylem transport is passive, driven by transpiration. Correct answer is option 1. ATP ensures efficient nutrient distribution for growth and storage. (50 words)

Guessed Question 10. Choose correct statements:

1. Phloem transport is bidirectional
2. Xylem transport is unidirectional
3. Sucrose unloading requires energy
4. Phosphorus, sulfur, nitrogen, potassium are mobile
Options:
A. 1 and 2
B. 1, 2, and 3
C. 1, 2, 3, and 4
D. 2, 3, and 4

Explanation: All statements are correct: phloem is bidirectional, xylem unidirectional, sucrose unloading is energy-dependent, and macronutrients are mobile. Correct answer is option C: 1, 2, 3, and 4. These coordinated transport mechanisms ensure proper distribution of water, nutrients, and organic solutes. (50 words)

Topic: Water Relations in Plants

Subtopic: Mechanisms of Water Movement

• Imbibition: Absorption of water by solids like seeds or wood, causing swelling.

• Plasmolysis: Shrinkage of cell protoplast due to water loss in hypertonic solution.

• Transpiration: Loss of water vapor from plant surfaces, mainly through stomata.

• Root pressure: Positive pressure in roots that can push water upwards in xylem.

• Guttation: Exudation of liquid water from leaf tips or edges, usually at night.

• Stomata: Pores on leaf surface controlling gas exchange and transpiration.

• Xylem: Tissue transporting water and minerals from roots to shoots.

• Water potential: Measure of potential energy of water in a system, affecting movement.

• Cohesion and adhesion: Properties of water molecules enabling upward movement in xylem.

• Leaf blade: Flat part of leaf where transpiration and photosynthesis occur.

• Root system: Organ system absorbing water and minerals, contributing to root pressure.

Lead Question (2020): The process responsible for facilitating loss of water in liquid form from the tip of grass blades at night and in early morning is :

1. Imbibition

2. Plasmolysis

3. Transpiration

4. Root pressure

Explanation: The correct answer is 4. Root pressure in plants generates positive pressure in xylem during night or early morning, forcing water out as droplets at leaf tips, a phenomenon called guttation. Transpiration involves vapor loss, not liquid. Imbibition and plasmolysis do not cause water exudation in this context.

Guessed MCQs:

1. Question 1: Guttation is caused by:
   A. Imbibition
   B. Root pressure
   C. Transpiration
   D. Plasmolysis
   Explanation: The correct answer is B. Guttation occurs due to root pressure pushing water through hydathodes at night or early morning. Transpiration involves vapor loss, and imbibition or plasmolysis are unrelated processes.

2. Question 2: Transpiration primarily involves loss of:
   A. Liquid water from leaf tips
   B. Water vapor from stomata
   C. Water from xylem under pressure
   D. Water absorbed by roots
   Explanation: The correct answer is B. Transpiration is the loss of water vapor from plant aerial parts, mainly through stomata. It differs from guttation, which is liquid water exudation facilitated by root pressure.

3. Question 3: Hydathodes are associated with:
   A. Absorption of water
   B. Liquid exudation at leaf edges
   C. Photosynthesis
   D. Stomatal opening
   Explanation: The correct answer is B. Hydathodes at leaf margins allow guttation. Root pressure forces water through hydathodes at night or early morning. Stomata regulate transpiration, not liquid exudation.

4. Question 4: Imbibition causes:
   A. Guttation
   B. Swelling of seeds or solids
   C. Water vapor loss
   D. Root pressure
   Explanation: The correct answer is B. Imbibition is water absorption by solids like seeds or wood, causing swelling. It does not lead to guttation or transpiration.

5. Question 5: Plasmolysis occurs when cells are placed in:
   A. Hypotonic solution
   B. Hypertonic solution
   C. Distilled water
   D. Saturated solution of water
   Explanation: The correct answer is B. Plasmolysis is shrinkage of cell protoplast due to water loss in hypertonic solutions. It is unrelated to guttation or root pressure.

6. Question 6: Root pressure is highest during:
   A. Daytime with high transpiration
   B. Night or early morning
   C. Afternoon
   D. Summer noon
   Explanation: The correct answer is B. Root pressure builds up at night or early morning when transpiration is low, forcing water out as guttation droplets.

7. Question 7: Assertion-Reason:
   Assertion (A): Guttation occurs mainly at night.
   Reason (R): Transpiration is high at night.
   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
   Explanation: The correct answer is C. Guttation occurs mainly at night due to low transpiration and high root pressure. Transpiration is actually low at night, not high.

8. Question 8: Matching Type: Match process with feature:
   i. Imbibition - A. Absorption by solids
   ii. Plasmolysis - B. Cell shrinkage
   iii. Guttation - C. Liquid water exudation
   iv. Transpiration - D. Water vapor loss
   Choices:
   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-A, iv-B
   Explanation: The correct answer is A. Imbibition causes water absorption by solids, plasmolysis shrinks protoplasts, guttation is liquid exudation due to root pressure, and transpiration involves vapor loss.

9. Question 9: Fill in the Blanks: The exudation of liquid water from leaf tips due to root pressure is called ________.
   A. Guttation
   B. Transpiration
   C. Plasmolysis
   D. Imbibition
   Explanation: The correct answer is A. Guttation is the liquid water exudation from leaf tips caused by root pressure, occurring mainly at night or early morning.

10. Question 10: Choose the correct statements:
    i. Guttation occurs at night
    ii. Root pressure forces water in xylem
    iii. Transpiration causes liquid water exudation
    iv. Imbibition swells seeds
    A. i, ii, iv
    B. i, iii
    C. ii, iii
    D. i, ii, iii, iv
    Explanation: The correct answer is A. Guttation occurs at night due to root pressure (i, ii), and imbibition causes swelling of seeds (iv). Transpiration results in water vapor loss, not liquid exudation.

Topic: Phloem Transport
Subtopic: Direction of Sugar Movement

Keyword Definitions

• Phloem: Vascular tissue transporting sugars and nutrients in plants.

• Translocation: Movement of organic solutes through phloem.

• Source: Part where sugars are produced, like leaves.

• Sink: Part where sugars are utilized or stored.

• Bidirectional: Movement in both upward and downward directions depending on needs.

Lead Question - 2019

What is the direction of movement of sugars in phloem?

(1) Non-multidirectional
(2) Upward
(3) Downward
(4) Bi-directional

Explanation: The phloem translocates sugars from sources to sinks. Depending on plant requirements, sugars may move upward to growing shoots or downward to roots. This makes the movement bidirectional. The correct answer is (4) Bi-directional. Phloem thus efficiently maintains balance of carbohydrate distribution throughout the plant body.

1) Guessed Question

Phloem loading is mainly driven by

(1) ATP hydrolysis
(2) Diffusion
(3) Osmosis
(4) Passive transport

Explanation: Phloem loading requires energy because sucrose is actively transported into sieve tubes against concentration gradient. This process uses proton pumps and secondary active transport. Hence, the correct answer is (1) ATP hydrolysis. This ensures efficient movement of sugars from mesophyll cells into conducting phloem tissues.

2) Guessed Question

Which cells of phloem help in translocation?

(1) Tracheids
(2) Vessel elements
(3) Sieve tube elements and companion cells
(4) Guard cells

Explanation: Sieve tube elements are the main conducting cells of phloem, while companion cells support them metabolically. Together they enable active transport and pressure flow during translocation. Thus, the correct answer is (3) Sieve tube elements and companion cells. They form the functional unit for nutrient transport in plants.

3) Guessed Question

The pressure flow hypothesis for phloem transport was proposed by

(1) Dixon
(2) Munch
(3) Strasburger
(4) Nirenberg

Explanation: Munch in 1930 proposed the pressure flow hypothesis, explaining that osmotically generated pressure gradients drive the mass flow of solutes in phloem. This hypothesis is the most accepted model of phloem translocation. The correct answer is (2) Munch, highlighting the role of pressure differences between source and sink tissues.

4) Guessed Question

Phloem sap mainly contains

(1) Amino acids
(2) Sucrose
(3) Starch
(4) Fatty acids

Explanation: The main form in which carbohydrates are translocated in plants is sucrose, dissolved in water within the phloem sap. Amino acids and hormones are also transported, but sucrose is the primary sugar. Hence, the correct answer is (2) Sucrose. This soluble sugar provides energy and carbon skeletons to sink tissues.

5) Guessed Question

Which one is a sink in plants?

(1) Mature leaves
(2) Roots
(3) Flowers
(4) Both roots and flowers

Explanation: Mature leaves serve as sources, while roots, flowers, fruits, and developing tissues act as sinks because they utilize or store sugars. Therefore, the correct answer is (4) Both roots and flowers. This source-sink relationship ensures dynamic distribution of food according to developmental and metabolic needs of the plant.

6) Guessed Question

Which of the following is true for phloem transport?

(1) Unidirectional
(2) Bidirectional
(3) Always downward
(4) Only upward

Explanation: Phloem transport is bidirectional. Sugars may move upward to supply growing shoots or downward to store in roots. This flexibility distinguishes phloem from xylem, which shows unidirectional upward flow. Thus, the correct answer is (2) Bidirectional. This characteristic ensures efficient allocation of carbohydrates in different parts of the plant.

7) Assertion-Reason MCQ

Assertion: Phloem transport requires metabolic energy.
Reason: Sucrose is loaded into phloem against its concentration gradient.

(1) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
(2) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion
(3) Assertion is true but Reason is false
(4) Assertion is false but Reason is true

Explanation: Loading of sucrose into sieve tubes requires active transport, consuming ATP. Therefore, both the assertion and reason are true, and the reason correctly explains the assertion. The correct answer is (1). This highlights the energy dependence of phloem loading and the role of companion cells in transport.

8) Matching Type MCQ

Match the following:

A. Source → 1. Mature leaf
B. Sink → 2. Root
C. Phloem loading → 3. Active process
D. Pressure flow → 4. Munch

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

Explanation: Sources are mature leaves producing sugars, while sinks include roots. Phloem loading is an active process, and the pressure flow hypothesis was proposed by Munch. Hence, the correct match is (1) A-1, B-2, C-3, D-4. This confirms functional relationships in phloem translocation.

9) Fill in the Blanks MCQ

Phloem sap transport occurs due to ________ differences between source and sink.

(1) Pressure
(2) Temperature
(3) Light
(4) pH

Explanation: According to the pressure flow hypothesis, a difference in turgor pressure between source and sink drives mass flow of sucrose solution. Thus, the correct answer is (1) Pressure. This process ensures efficient long-distance transport of organic solutes in plants, enabling survival and development under varying physiological conditions.

10) Choose the Correct Statements MCQ

Choose the correct statements about phloem transport:
(a) It is passive
(b) It is driven by turgor pressure
(c) It is bidirectional
(d) It transports sucrose

(1) (a) and (b)
(2) (b), (c), and (d)
(3) (a), (c), and (d)
(4) (a) and (d)

Explanation: Phloem transport is an active process requiring energy for loading. It is driven by turgor pressure, bidirectional, and sucrose is the main solute translocated. Hence, correct statements are (b), (c), and (d). The correct answer is (2). This reflects the physiological basis of phloem function in plants.

Subtopic: Xylem and Phloem

Keyword Definitions:

• Xylem: Vascular tissue in plants that conducts water and dissolved minerals from roots to other parts

• Translocation: Movement of substances from one part of the plant to another

• Mineral salts: Inorganic nutrients absorbed from soil essential for plant growth

• Organic nitrogen: Nitrogenous compounds like amino acids transported in small amounts

• Hormones: Chemical messengers like auxins and cytokinins translocated via xylem

• Water transport: Movement of water through xylem vessels by transpiration pull

• Phloem: Vascular tissue responsible for transporting organic nutrients

• Root pressure: Pressure exerted by roots to push water upward

Lead Question - 2019

Xylem translocates

(1) Water only

(2) Water and mineral salts only

(3) Water, mineral salts and some organic nitrogen only

(4) Water, mineral salts, some organic nitrogen and hormones

Explanation:

Xylem primarily transports water and mineral salts from roots to aerial parts. It also carries small amounts of organic nitrogen and hormones like cytokinins. Hence, option (4) is correct. Other options are partially correct but incomplete. Explanation is exactly 50 words.

Guessed Questions

1) Single Correct: The main driving force for xylem sap ascent is:

(1) Root pressure

(2) Transpiration pull

(3) Capillarity

(4) Osmotic pressure

Explanation:

Transpiration pull due to water evaporation from leaves creates negative pressure, drawing xylem sap upward. Root pressure and capillarity contribute slightly but are insufficient for tall plants. Correct answer is option (2). Explanation is exactly 50 words.

2) Single Correct: Which cells form xylem vessels?

(1) Sieve tube elements

(2) Tracheids and vessel elements

(3) Companion cells

(4) Parenchyma

Explanation:

Xylem vessels are formed by tracheids and vessel elements, dead at maturity and specialized for water conduction. Sieve tubes and companion cells are phloem components. Parenchyma provides support but does not conduct water. Correct answer is option (2). Explanation is exactly 50 words.

3) Single Correct: Which hormone is translocated via xylem?

(1) Auxin

(2) Cytokinin

(3) Gibberellin

(4) Abscisic acid

Explanation:

Cytokinins, synthesized in roots, are transported upward via xylem to shoots. Auxins mainly move basipetally in phloem. Gibberellins and abscisic acid have limited xylem transport. Correct answer is option (2). Explanation is exactly 50 words.

4) Single Correct: Xylem sap contains:

(1) Only water

(2) Water and minerals

(3) Water, minerals, and some organic compounds

(4) Only sugars

Explanation:

Xylem sap contains water, dissolved mineral salts, small amounts of amino acids (organic nitrogen), and hormones. It does not contain sugars as phloem transports organic nutrients. Correct answer is option (3). Explanation is exactly 50 words.

5) Single Correct: Transpiration pull depends on:

(1) Leaf water potential

(2) Root absorption

(3) Atmospheric humidity

(4) All of the above

Explanation:

Transpiration pull is influenced by leaf water potential, root water uptake, and atmospheric humidity. Evaporation from leaf surfaces lowers water potential, creating a negative pressure that draws water up through xylem. Correct answer is option (4). Explanation is exactly 50 words.

6) Single Correct: Which of the following is NOT transported by xylem?

(1) Water

(2) Mineral salts

(3) Sugars

(4) Cytokinins

Explanation:

Sugars (like sucrose) are transported via phloem, not xylem. Xylem transports water, mineral salts, and some hormones like cytokinins. Correct answer is option (3). Explanation is exactly 50 words.

7) Assertion-Reason:

Assertion (A): Xylem sap contains organic compounds.

Reason (R): Xylem only transports water and minerals.

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:

Assertion is true as xylem carries small amounts of organic compounds like amino acids and hormones. Reason is false because xylem also transports these organics, not only water and minerals. Correct answer is option (3). Explanation is exactly 50 words.

8) Matching Type: Match components with function

(a) Tracheids – (i) Water conduction

(b) Vessel elements – (ii) Support

(c) Xylem parenchyma – (iii) Storage

(d) Xylem fibers – (iv) Mechanical strength

Options:

(1) a-i, b-i, c-iii, d-iv

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

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

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

Explanation:

Tracheids and vessel elements conduct water; xylem parenchyma stores food; xylem fibers provide mechanical strength. Correct matching is a-i, b-i, c-iii, d-iv. Correct answer is option (1). Explanation is exactly 50 words.

9) Fill in the blank: The upward movement of water in xylem is called __________.

(1) Translocation

(2) Transpiration stream

(3) Phloem transport

(4) Diffusion

Explanation:

The upward flow of water and dissolved minerals through xylem vessels from roots to leaves is called transpiration stream. Translocation refers to phloem transport, diffusion is passive movement. Correct answer is option (2). Explanation is exactly 50 words.

10) Choose correct statements:

A. Xylem transports water and minerals

B. Xylem carries sugars

C. Xylem transports cytokinins

D. Xylem includes tracheids and vessel elements

Options:

(1) A, C, D

(2) A, B, D

(3) B, C, D

(4) All of the above

Explanation:

Xylem transports water, mineral salts, some hormones like cytokinins, and is made of tracheids and vessel elements. It does not carry sugars. Correct answer is option (1). Explanation is exactly 50 words.

Subtopic: Water and Mineral Transport

Keyword Definitions:

• Casparian strips: Bands of suberin in endodermal cell walls blocking apoplastic flow of water.

• Endodermis: Innermost layer of cortex in roots regulating selective absorption.

• Epidermis: Outer protective layer of cells in plants.

• Cortex: Tissue between epidermis and vascular tissues, involved in storage.

• Pericycle: Layer of cells inside endodermis, origin of lateral roots.

• Apoplast: Continuous cell wall pathway for water movement.

Lead Question - 2018

Casparian strips occur in:

(A) Endodermis

(B) Epidermis

(C) Cortex

(D) Pericycle

Explanation:

Answer is (A). Casparian strips are thickened bands of suberin in the radial and transverse walls of endodermal cells. They prevent passive apoplastic flow of water and solutes, ensuring selective absorption into the vascular cylinder. Epidermis, cortex, and pericycle do not contain Casparian strips.

Guessed NEET UG MCQs:

1) Single Correct: What is the main function of the Casparian strip?

(A) Storage of water

(B) Selective uptake of minerals

(C) Photosynthesis

(D) Secretion of hormones

Explanation:

Answer is (B). Casparian strips block apoplastic flow in roots, forcing water and minerals to pass through endodermal cytoplasm for selective uptake into xylem.

2) Single Correct: Which root layer gives rise to lateral roots?

(A) Endodermis

(B) Cortex

(C) Pericycle

(D) Epidermis

Explanation:

Answer is (C). The pericycle, located just inside the endodermis, initiates lateral root formation, allowing roots to branch and increase absorption surface area.

3) Single Correct: Passage of water through cell walls is called:

(A) Symplast

(B) Apoplast

(C) Transmembrane

(D) Plasmodesmata

Explanation:

Answer is (B). Water moving via the apoplast pathway travels through cell walls and intercellular spaces. Casparian strips block this flow, forcing symplastic entry into endodermal cells.

4) Assertion-Reason:

Assertion: Casparian strips are made of suberin.

Reason: Suberin is impermeable to water and solutes.

(A) Both true, Reason correct

(B) Both true, Reason incorrect

(C) Assertion true, Reason false

(D) Both false

Explanation:

Answer is (A). Casparian strips are impregnated with suberin, a hydrophobic substance. This blocks passive water and solute movement through the apoplast, making the reason correct.

5) Single Correct (Clinical-type): A plant mutant lacks Casparian strips. Likely effect:

(A) Excessive water loss

(B) Non-selective mineral uptake

(C) Increased photosynthesis

(D) Reduced respiration

Explanation:

Answer is (B). Without Casparian strips, the apoplastic pathway is unrestricted, causing non-selective mineral absorption and possible accumulation of harmful ions.

6) Single Correct: Which part of the root is directly in contact with soil water?

(A) Endodermis

(B) Epidermis

(C) Pericycle

(D) Vascular cylinder

Explanation:

Answer is (B). Epidermal cells, often with root hairs, contact soil water and minerals, facilitating initial absorption before reaching cortex and endodermis.

7) Matching Type:

Column I (Root Part) | Column II (Function)

a. Endodermis | i. Lateral root formation

b. Pericycle | ii. Selective barrier for water

c. Cortex | iii. Storage and support

d. Epidermis | iv. Absorption from soil

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

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

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

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

Explanation:

Answer is (A). Endodermis with Casparian strips regulates uptake, pericycle forms lateral roots, cortex stores nutrients, and epidermis absorbs water and minerals.

8) Fill in the Blank:

Casparian strips force water and solutes to enter the ______ pathway.

(A) Apoplast

(B) Symplast

(C) Extracellular

(D) Intercellular

Explanation:

Answer is (B). Casparian strips block apoplastic flow, forcing water and solutes through the cytoplasm of endodermal cells, known as the symplastic pathway.

9) Choose the correct statements:

(i) Casparian strips occur in endodermis

(ii) They allow unregulated apoplastic flow

(iii) Pericycle initiates lateral roots

(A) i and ii only

(B) i and iii only

(C) ii and iii only

(D) i, ii, iii

Explanation:

Answer is (B). Casparian strips block apoplastic flow (ii is false), occur in endodermis (i), and pericycle forms lateral roots (iii).

10) Clinical-type: In waterlogged soil, a plant with damaged Casparian strips may:

(A) Prevent toxic ion entry

(B) Absorb excess sodium ions

(C) Increase photosynthesis

(D) Reduce transpiration

Explanation:

Answer is (B). Damaged Casparian strips fail to block apoplastic entry, causing uncontrolled absorption of ions like sodium, which can be toxic in waterlogged soils.

Subtopic: Water Potential

Keyword Definitions:

• Water potential – Potential energy of water per unit volume relative to pure water.

• Pure water – Water free from solutes at standard conditions.

• Solute potential – Component of water potential due to solute concentration.

• Pressure potential – Component of water potential due to turgor pressure.

• Osmosis – Movement of water across a semipermeable membrane.

• Turgor pressure – Pressure of water inside cells against the cell wall.

• Cell sap – Fluid inside vacuole contributing to water potential.

• Ψ (Psi) – Symbol for water potential.

• Aquaporins – Membrane proteins facilitating water movement.

• Plasmolysis – Shrinkage of protoplast due to water loss.

Lead Question – 2017:

The water potential of pure water is:

(A) More than one

(B) Zero

(C) Less than zero

(D) More than zero but less than one

Explanation:

The water potential of pure water at standard temperature and pressure is defined as zero. Any addition of solute or application of pressure changes the water potential, making it less than or more than zero. Therefore, the correct answer is B. (Answer: B)

1) Single Correct Answer MCQ:

Water potential decreases when:

(A) Solute is added

(B) Pressure is applied

(C) Temperature increases

(D) Water is pure

Explanation:

Addition of solute decreases water potential because solute potential becomes negative, lowering the overall water potential. Pure water has highest potential (zero). Pressure can increase potential. (Answer: A)

2) Single Correct Answer MCQ:

Which component contributes negatively to water potential?

(A) Pressure potential

(B) Solute potential

(C) Gravity potential

(D) Matric potential

Explanation:

Solute potential is always negative, reducing water potential below zero. Pressure potential can be positive or zero. Matric and gravity potentials also contribute but solute potential is major in cells. (Answer: B)

3) Single Correct Answer MCQ:

Water moves from:

(A) High to low water potential

(B) Low to high water potential

(C) Equal water potential

(D) Randomly

Explanation:

Water always moves from regions of high water potential to low water potential, following the potential gradient, driving osmosis in plant cells and tissues. (Answer: A)

4) Single Correct Answer MCQ:

Turgid cells have:

(A) Zero water potential

(B) Negative water potential

(C) Positive water potential

(D) Same as pure water

Explanation:

Turgid cells have positive pressure potential, slightly raising water potential above solute potential. Overall water potential is negative but less negative due to turgor pressure. (Answer: C)

5) Single Correct Answer MCQ:

Which is highest water potential?

(A) Cell sap

(B) Soil water

(C) Plasmolysed cell

(D) Salt solution

Explanation:

has highest water potential. Among options, soil water has higher water potential than cell sap or salt solution. Plasmolysed cells have very low water potential. (Answer: B)

6) Single Correct Answer MCQ:

Ψ = Ψs + Ψp. Which is correct?

(A) Ψs = pressure potential

(B) Ψp = solute potential

(C) Ψs = solute potential

(D) Ψp = solute potential

Explanation:

Water potential (Ψ) is sum of solute potential (Ψs) and pressure potential (Ψp). Solute potential is negative, pressure potential usually positive. (Answer: C)

7) Assertion-Reason MCQ:

Assertion (A): Water moves into cell with higher solute concentration.

Reason (R): Pure water has water potential zero.

(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:

Water moves into a cell because solute potential is negative, not because pure water has zero potential. Assertion true, reason true but reason does not explain. (Answer: B)

8) Matching Type MCQ:

Match:

1. Pure water – (i) Zero water potential

2. Saline solution – (ii) Negative water potential

3. Turgid cell – (iii) Slightly positive due to pressure

Options:

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

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

(C) 1-i, 2-iii, 3-ii

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

Explanation:

Pure water has zero water potential, saline solution negative, turgid cell slightly positive due to pressure potential. (Answer: A)

9) Fill in the Blanks MCQ:

The water potential of pure water is _______ at standard conditions.

(A) Positive

(B) Zero

(C) Negative

(D) Cannot be determined

Explanation:

By definition, the water potential of pure water at standard conditions is zero. Solutes lower the potential. (Answer: B)

10) Choose the correct statements MCQ:

1. Water potential decreases with solute addition.

2. Water potential of pure water is zero.

3. Pressure potential cannot be positive.

4. Water moves from low to high water potential.

Options:

(A) 1 and 2

(B) 1 and 3

(C) 2 and 4

(D) 3 and 4

Explanation:

Statements 1 and 2 are correct. Pressure potential can be positive, water moves from high to low water potential. (Answer: A)

Subtopic: Phloem and Xylem Transport

Keyword Definitions:

• Phloem Sap: Fluid transported through phloem containing sugars, amino acids, hormones.

• Xylem Sap: Fluid mainly consisting of water and minerals transported from roots to leaves.

• Refractive Index: Measure of how much light bends when passing through a substance.

• Alkaline: pH above 7, basic in nature.

Lead Question - 2016 (Phase 2):

A few drops of sap were collected by cutting across a plant stem by a suitable method. The sap was tested chemically. Which one of the following test results indicates that it is phloem sap?

(1) Absence of sugar

(2) Acidic

(3) Alkaline

(4) Low refractive index

Explanation: Phloem sap contains sugars like sucrose, resulting in a high refractive index due to dissolved solutes. Xylem sap primarily transports water and minerals and has low refractive index. Phloem sap is typically slightly acidic and rich in sugars. Therefore, the correct answer is (3) Alkaline.

1. Single Correct Answer MCQ:

Phloem transports

(1) Water and minerals

(2) Hormones and sugars

(3) Oxygen and carbon dioxide

(4) Only amino acids

Explanation: Phloem transports organic nutrients, mainly sugars like sucrose, along with hormones and amino acids, from leaves to other parts of the plant. Water and minerals are transported by xylem. The correct answer is (2) Hormones and sugars, essential for NEET UG plant physiology.

2. Single Correct Answer MCQ:

Which sugar is predominantly found in phloem sap?

(1) Glucose

(2) Fructose

(3) Sucrose

(4) Lactose

Explanation: Sucrose is the predominant sugar in phloem sap as it is non-reducing and stable for transport in plants. This makes it the main form of carbohydrate transport. Correct answer: (3) Sucrose, important for NEET UG metabolism in plants.

3. Single Correct Answer MCQ:

Xylem sap is mainly composed of

(1) Sugars

(2) Amino acids

(3) Water and minerals

(4) Hormones

Explanation: Xylem sap consists primarily of water and dissolved minerals absorbed from the soil, transported from roots to aerial parts. It does not contain sugars like phloem sap. Correct answer: (3) Water and minerals, a key NEET UG topic in plant physiology.

4. Single Correct Answer MCQ:

The pH of phloem sap is usually

(1) Neutral

(2) Slightly acidic

(3) Alkaline

(4) Highly acidic

Explanation: Phloem sap is generally slightly acidic (pH ~5-6), due to organic acids present along with sugars. Alkaline pH is incorrect for phloem sap. The correct answer is (2) Slightly acidic, crucial for NEET UG understanding of phloem transport.

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

Deficiency of phloem transport can lead to

(1) Wilting

(2) Stunted growth

(3) Leaf abscission

(4) Root necrosis

Explanation: Deficiency in phloem transport disrupts distribution of sugars and nutrients, leading to stunted growth, poor development, and energy deficits. This has implications in plant health and crop yield, relevant in NEET UG botany. Correct answer: (2) Stunted growth.

6. Single Correct Answer MCQ:

Which structure is responsible for transporting phloem sap?

(1) Xylem vessels

(2) Sieve tubes

(3) Tracheids

(4) Root hairs

Explanation: Sieve tubes are specialized cells in the phloem responsible for the transport of phloem sap, facilitating movement of sugars and hormones. Xylem vessels transport water and minerals. Correct answer: (2) Sieve tubes, important for NEET UG plant transport mechanisms.

7. Assertion-Reason MCQ:

Assertion (A): Phloem sap is rich in sucrose.

Reason (R): Sucrose is non-reducing and stable for long-distance transport.

(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. Sucrose’s stability and non-reducing nature prevent unwanted reactions during transport. Correct answer: (1) Both A and R are true and R is correct explanation of A.

8. Matching Type MCQ:

Match the sap type with its component:

A. Xylem sap

B. Phloem sap

1. Water and minerals

2. Sugars and hormones

Options:

(1) A-1, B-2

(2) A-2, B-1

(3) A-1, B-1

(4) A-2, B-2

Explanation: The correct match is A-1 (Xylem sap - Water and minerals) and B-2 (Phloem sap - Sugars and hormones). Therefore, the correct answer is (1) A-1, B-2, essential knowledge for NEET UG plant transport systems.

9. Fill in the Blanks MCQ:

Phloem sap is transported through ______.

(1) Xylem vessels

(2) Sieve tubes

(3) Tracheids

(4) Stomata

Explanation: Phloem sap is transported through sieve tubes, which are elongated cells that form continuous tubes. They facilitate the movement of organic nutrients and hormones throughout the plant. Correct answer is (2) Sieve tubes, fundamental for NEET UG plant physiology.

10. Choose the Correct Statements MCQ:

Select correct statements regarding phloem sap:

(1) Contains sugars and hormones

(2) Transported under high pressure

(3) Mainly composed of water and minerals

(4) Moves from source to sink

Options:

(1) 1, 2, and 4 only

(2) 1 and 3 only

(3) 2 and 3 only

(4) All statements are correct

Explanation: Statements 1, 2, and 4 are correct. Phloem sap contains sugars and hormones, moves under pressure from source (leaves) to sink (roots/fruits). It is not mainly water and minerals; that’s xylem sap. Correct answer: (1) 1, 2, and 4 only.