Q1. [4]
Not all plants carry out photosynthesis by the same mechanism. In most plants, it depends directly on gaseous carbon dioxide that diffuses into the leaf. However, some plants can store carbon dioxide in the vacuole of the leaf cells as part of a complex carbon compound. This compound is transported to the chloroplast and releases carbon dioxide when required for photosynthesis. This special mechanism is believed to have evolved as an adaptation in such plants which do not open stomata during the daytime to conserve water for survival in dry conditions (desert conditions).
Read the following passage and answer the questions that follow :
- (a) Attempt either (a) or (b) :
(a)
(i) Which process in these plants is minimised to help the plants survive in dry conditions ?
(ii) Which part of the leaf is responsible for exchange of gases during photosynthesis ? [4]
Previously asked in CBSE board exam
2026 31/3/1 Q15
Generated by claude-sonnet-4-6 · 2026-06-11 09:52 · grounding stimulus
Model Answer
(i) In these plants (desert plants), transpiration is minimised to help them survive in dry conditions. They do not open their stomata during the daytime, which reduces water loss through transpiration, enabling survival in desert conditions.
(ii) The stomata (stomatal pores) present on the surface of the leaf are responsible for the exchange of gases during photosynthesis. Carbon dioxide enters and oxygen exits through these tiny pores. In most plants, stomata open during the day, allowing CO₂ to diffuse directly into the leaf for photosynthesis.
Source: Life Processes, Nutrition — Photosynthesis section
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Explanation
- (i): The passage clearly states these plants "do not open stomata during daytime to conserve water." Stomata closing = less transpiration. Examiners expect the word transpiration specifically.
- (ii): This is standard textbook knowledge linked to the passage — stomata are the gas-exchange structures. Even though the passage focuses on the special mechanism, the question asks about gas exchange in general during photosynthesis.
- Always quote or paraphrase the passage directly in source-based questions to show you've read it carefully.
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