A desert plant can adopt three possible adaptations to reduce water loss:

- Adaptation A: a thick cuticle that reduces water loss by 40 % and adds a 5 % increase in energy cost.
- Adaptation B: CAM photosynthesis that reduces water loss by 30 % but adds a 10 % increase in energy cost and reduces photosynthetic efficiency by 15 %.
- Adaptation C: a deep taproot that reduces water loss by 25 % and adds a 12 % increase in energy cost.

The plant must keep its total water loss at or below 50 % of the baseline (baseline water loss = 100 units) and its total energy cost must not exceed 15 % of the baseline. Assuming the effects of adaptations on water loss combine multiplicatively (overall reduction = 1‑(1‑a)(1‑b)…), which single adaptation(s) satisfy both constraints, and which combination of two adaptations also satisfies them?

Question

A desert plant can adopt three possible adaptations to reduce water loss:

- Adaptation A: a thick cuticle that reduces water loss by 40 % and adds a 5 % increase in energy cost.
- Adaptation B: CAM photosynthesis that reduces water loss by 30 % but adds a 10 % increase in energy cost and reduces photosynthetic efficiency by 15 %.
- Adaptation C: a deep taproot that reduces water loss by 25 % and adds a 12 % increase in energy cost.

The plant must keep its total water loss at or below 50 % of the baseline (baseline water loss = 100 units) and its total energy cost must not exceed 15 % of the baseline. Assuming the effects of adaptations on water loss combine multiplicatively (overall reduction = 1‑(1‑a)(1‑b)…), which single adaptation(s) satisfy both constraints, and which combination of two adaptations also satisfies them?

Accepted Answer

Adaptation A alone does not meet the water‑loss limit. The only combination that satisfies both the water‑loss (≤50 units) and energy‑cost (≤15 %) constraints is Adaptation A + Adaptation B.

Gce Model Questions Vol1 2025 Biology Question 21

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