Science — AI-generated practice question

Stomata are tiny pores on leaf surfaces surrounded by guard cells. When water flows into the guard cells, they swell, causing the stomatal pore to open. When guard cells lose water and shrink, the pore closes.

A plant closes its stomata when it does not need CO₂ for photosynthesis — for example, at night or when light is unavailable. Since photosynthesis requires CO₂, keeping stomata open when it is not needed would only cause unnecessary water loss. Closing them prevents this loss while photosynthesis is not occurring.

Source: Chapter 5, Section 5.2.1 — Autotrophic Nutrition

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• Examiners expect two clear parts: (1) mechanism (guard cells swell/shrink → pore opens/closes) and (2) reason for closing (no photosynthesis needed + water conservation).
• Use the exact textbook terms: guard cells, swell, shrink, stomatal pore.
• A common mistake is explaining only the mechanism without explaining why the plant closes stomata — both are needed for full marks.
• The passage explicitly says plants close stomata "when it does not need carbon dioxide for photosynthesis" to prevent water loss — quote this idea directly.