NEET Biology: Plant Physiology questions with solutions

Q1. I. Increase in mass II. Differentiation III. Increase in number of individuals. IV. Response to stimuli Which two points are known as the twin characteristics of growth?

1. I and II
2. II and IV
3. II and III
4. I and III

Answer: I and II

Growth is typically defined by an increase in mass and by differentiation during development. Increase in number of individuals is reproduction, and response to stimuli is a general life characteristic, not a twin characteristic of growth.

Q2. Who proposed the cycle of events leading to the fixation of \( C O_{2} \) in mesophyll and its reduction in bundle sheath?

1. Emerson
2. Melvin Calvin
3. Hatch and Slack
4. Hill and Bendall

Answer: Hatch and Slack

Hatch and Slack proposed the C4 pathway, where CO2 is first fixed in mesophyll cells and then reduced in bundle sheath cells. This is the cycle of events described in the question.

Q3. Which of the following may show photosynthesis in moonlight

1. some thermal algae
2. some marine algae
3. some fresh water algae
4. None of the above

Answer: some marine algae

Some marine algae live in environments where light is scarce and can still carry out photosynthesis under very low illumination. Moonlight is too weak for most plants and algae, but certain marine algae are adapted to use it.

Q4. Root pressure is a

1. Pulling force
2. Pushing force
3. Both A and B
4. None of these

Answer: Pushing force

Root pressure is a positive hydrostatic pressure developed in the roots when ions accumulate and water enters osmotically. This pressure pushes water upward through the xylem, so it is a pushing force.

Q5. Compensation point is the value of the factor where there is

1. Neither photosynthesis nor respiration
2. Little photosynthesis
3. Photosynthesis is equal to the rate of respiration
4. Beginning of photosynthesis

Answer: Photosynthesis is equal to the rate of respiration

The compensation point is when the rate of photosynthesis matches the rate of respiration, so there is no net gain or loss of organic matter. This balance is why the plant is neither accumulating nor losing carbon overall.

Q6. Water transport from roots to leaves is explained by

1. The pressure flow theory
2. Differences in source and sink solute concentrations
3. The pumping force of xylem vessels
4. The cohesion-tension theory

Answer: The cohesion-tension theory

Water transport from roots to leaves is best explained by the cohesion-tension theory. Transpiration from leaves creates negative pressure that pulls a continuous column of water upward, and cohesion keeps the column intact.

Q7. Absorption of mineral elements from the soil occurs through

1. Diffusion
2. Active transportt
3. osmosis
4. All of the above

Answer: All of the above

Mineral elements can enter plants by more than one mechanism: some move by diffusion, water movement is linked with osmosis, and many ions are absorbed by active transport against a concentration gradient. Since all listed processes can contribute, the best choice is the combined option.

Q8. Mimosa pudica displays movement.

1. Phototropic
2. Photonastic
3. Thigmonastic
4. Thermonastic

Answer: Thigmonastic

Mimosa pudica folds its leaves in response to mechanical stimulation such as touch or shaking. That makes it a thigmonastic movement, since thigmo- refers to touch.

Q9. Which of the following statements is a correct distinction between autotrophs and heterotrophs?

1. Only heterotrophs need to acquire chemical compounds from the environment
2. Cellular respiration is unique to heterotrophs
3. Only heterotrophs have mitochondria
4. Autotrophs, but not heterotrophs, can nourish themselves beginning with nutrients that are entirely inorganic

Answer: Autotrophs, but not heterotrophs, can nourish themselves beginning with nutrients that are entirely inorganic

Autotrophs can synthesize their own organic molecules from inorganic inputs such as carbon dioxide, water, and minerals. Heterotrophs cannot do this and must obtain organic compounds from other organisms or their remains.

Q10. Stomata on the surface of the leaf open by

1. Decreasing the solute concentration in the guard cells.
2. Increasing the solute concentration in the guard cells.
3. Increasing the water potential in the guard cells.
4. Both B and C.

Answer: Increasing the solute concentration in the guard cells.

Stomata open when guard cells become turgid. This occurs after solute concentration in the guard cells increases, which lowers their water potential so water enters by osmosis. The resulting turgor pressure bends the guard cells apart and opens the pore.

Q11. Assertion: Dark periods play a more important part in flowering than light period. Reason: Flowering occurs in short-day plant if the dark period is interrupted by light break.

1. If both the assertion and reason are true and the reason is a correct explanation of the assertion
2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
3. If the assertion is true but the reaon is false
4. If both the assertion and reason are false E. If the assertion is false but reason is true

Answer: If both the assertion and reason are true but the reason is not a correct explanation of the assertion

Both statements are true: in many plants, especially short-day plants, the uninterrupted dark period is crucial, and a light break can induce flowering. However, the reason only gives an example of dark-period sensitivity; it does not fully explain why dark periods are generally more important than light periods.

Q12. Photorespiratory reactions are operated in the

1. Chloroplasts, ribosomes and peroxisomes.
2. Chloroplasts, mitochondria and peroxisomes.
3. Mitochondria, preoxisomes and lysosomes.
4. Mitochondria, chloroplasts and ribosomes.

Answer: Chloroplasts, mitochondria and peroxisomes.

Photorespiration is a multi-organelle process because the products of Rubisco oxygenation are processed in chloroplasts, peroxisomes, and mitochondria. These three compartments cooperate to recycle carbon and complete the pathway.

Q13. Passive absorption of mineral salts is not dependent on

1. Diffusion
2. Osmosis
3. Donnan equilibrium
4. Ionic exchange

Answer: Donnan equilibrium

Passive absorption of mineral salts occurs by diffusion, osmosis-related water movement, and ionic exchange across membranes. Donnan equilibrium is a distribution phenomenon, not a direct mechanism on which passive mineral salt absorption depends.

Q14. If there is increase in temperature of about more than \( 35^{0} \mathrm{C} \)

1. Rate of decline of respiration will be earlier than decline of photosynthesis
2. Rate of decline of photosynthesis will be earlier than decline of respiration.
3. Both decline together
4. Both show no fixed variations.

Answer: Rate of decline of photosynthesis will be earlier than decline of respiration.

Photosynthesis is generally more sensitive to temperatures above about 35°C because its enzyme systems and membrane processes are disrupted sooner. Respiration can continue at higher temperatures for longer, so its decline happens later than photosynthesis.