Cambridge O Level Biology · Syllabus 5090 · Coordination and Response in Plants
Positive Gravitropism
What is Positive Gravitropism?
The growth of a plant organ toward gravity. A root laid horizontally curves downward and grows in the direction in which gravity acts, which carries it into the soil where it anchors the plant and absorbs water and mineral ions.
This definition is part of the Coordination and Response in Plants chapter in Cambridge O Level Biology.
Common mistakes with Positive Gravitropism
- 12. “The root must work the same way as the shoot.” Why it is wrong: applying “more auxin on the lower side, so it elongates more” to a root predicts the root curving upward, which is the opposite of what is observed. SayThe root grows toward gravity — positive gravitropism — which anchors the plant and reaches water and mineral ions. State the observable response and its advantage, and stop there.
Questions students ask about Positive Gravitropism
Can the auxin explanation be used for roots?
Not unless the question supplies the root mechanism. The syllabus states that auxin stimulates cell elongation in shoots. For a root, describe the observable response — it grows toward gravity — classify it as positive gravitropism and give its advantage: anchorage and the uptake of water and mineral ions.
Last reviewed Syllabus 2026-2028