Question

Photosynthesis ceases when leaves wilt, mainly because

(A) the chlorophyll in wilting leaves is degraded.

(B) accumulation of CO₂ in the leaf inhibits enzymes.

(C) stomata close, preventing CO₂ from entering the leaf.

(D) photolysis, the water-splitting step of photosynthesis, cannot occur when there is a water deficiency.

Short answer

(A) The option “the chlorophyll in wilting leaves is degraded” is false.

(B) The option “accumulation of CO2 in the leaf inhibits enzymes” is false.

(C) The option “stomata close, preventing CO2 from entering the leaf” is true.

(D) The option “photolysis, the water-splitting step of photosynthesis, cannot occur when there is a water deficiency” is false.

Step-by-step solution

Photosynthesis

Photosynthesis is a chemical process through which the green plants use chlorophyll pigments, energy from the sun, water and minerals from the roots, and carbon dioxide from the atmosphere to produce molecules of sugars and oxygen as a byproduct.

The photosynthetic activity in the plants depends on the presence or absence of these pigments.

Explanation of option ‘(A)’

Photosynthesis does not cease in wilting of leaves due to the degradation of chlorophyll. Chlorophyll degradation occurs due to the presence of undesirable chemicals like pheophorbide and pheophytin. Additionally, it also occurs due to the toxic effects of insecticides and industrial effluents.

Thus, photosynthesis does not cease due to the degradation of chlorophyll.

Therefore, the given option is false.

Explanation of option ‘(B)’

When the carbon dioxide levels in the plants increase, this can cause an elevated rate of photosynthesis. Carbon dioxide increases the activity of Rubisco, and hence the photosynthesis occurs efficiently. Additionally, the carbohydrate formation increases; therefore, such plants have higher starch reserves.

Thus, the accumulation of carbon dioxide does not cease photosynthesis.

Therefore, the given option is false.

Explanation of option ‘(C)’

Photosynthesis ceases in plants when leaves wilt because in such leaves, the stomatal apertures close to prevent the entry of carbon dioxide molecules from the atmosphere. When the key element for photosynthesis that is carbon dioxide is absent, photosynthesis cannot occur.

Thus, photosynthesis stops in wilting leaves due to the closure of the stomatal aperture.

Therefore, the given option is true.

Explanation of option ‘(D)’

Photosynthesis in wilting leaves does not occur due to the absence of water during photolysis. Photolysis is a process that occurs under the influence of electrons from the sun, chlorophyll pigment, and oxygen.

Thus, photosynthesis does not stop in wilting leaves due to a deficiency of water to take part in photolysis.

Therefore, the given option is false.