9700 · 15.2
Control and coordination in plants — FAQ
Frequently asked questions for 9700 Control and coordination in plants. Direct answers first, then deeper explanation — then practise with marking.
What are the main plant hormones in A Level Biology 9700?
In Cambridge A Level Biology 9700, the main plant hormones you need to understand are auxins, gibberellins, abscisic acid (ABA), and ethene. Each has specific roles in controlling plant growth, development, and responses to environmental stimuli. For a comprehensive review, check out our free revision course and practice with past papers.
How do auxins control phototropism and gravitropism in plants?
Auxins control phototropism and gravitropism by causing differential growth. In phototropism, auxins move to the shaded side of shoots, promoting faster growth towards light. In gravitropism, auxins accumulate on the lower side of horizontal shoots (promoting growth upwards) and roots (inhibiting growth downwards), leading to directional growth. The key is the differential sensitivity of shoots and roots to auxin concentrations.
Why is it important for roots to be positively gravitropic?
Roots being positively gravitropic (growing downwards with gravity) is crucial for a plant's survival. This ensures roots grow into the soil, anchoring the plant securely and allowing efficient uptake of water and mineral ions. Without this response, roots might grow upwards, exposing them to desiccation and preventing proper nutrient acquisition.