Phototropism, gravitropism and auxinSpec 14.5.1, 14.5.2, 14.5.4, 14.5.5
In short
Phototropism is a response in which parts of a plant grow towards or away from the direction of the light source, and gravitropism is the same response to gravity. Shoots grow towards light and away from gravity. Auxin, made in the shoot tip, is unequally distributed and stimulates cell elongation, so the side with more auxin grows more.
Gravitropism is a response in which parts of a plant grow towards or away from gravity.
Phototropism is a response in which parts of a plant grow towards or away from the direction of the light source.
- Gravitropism
- A response in which parts of a plant grow towards or away from gravity.
- Phototropism
- A response in which parts of a plant grow towards or away from the direction of the light source.
| Plant part | Response to light | Response to gravity |
|---|---|---|
| Shoot | Grows towards light | Grows away from gravity (upwards) |
| Root | Grows away from light | Grows towards gravity (downwards) |
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanChemical control of plant growth
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanPhototropism and gravitropism of a shoot are examples of the chemical control of plant growth. The chemical is a plant hormone called auxin.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean- Auxin is made in the shoot tip.
- Auxin diffuses through the plant from the shoot tip.
- Auxin is unequally distributed in response to light and gravity.
- Auxin stimulates cell elongation.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanPhototropism of a shoot: when light shines from one side, auxin builds up on the shaded side. Cells on the shaded side elongate more than cells on the lit side, so the shoot bends towards the light.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanGravitropism of a shoot: when a shoot is on its side, auxin builds up on the lower side. Cells on the lower side elongate more, so the shoot bends upwards, away from gravity.
Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels mean
(opens full size in a new tab)Supplement (what this means)
Supplement: only for the Extended papers (2 and 4). Core students can skip it. What the labels meanAlways say auxin is unequally distributed, and that it makes cells elongate. Do not say auxin makes cells ‘divide’ or that the shoot ‘grows towards’ without saying which side has more auxin.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026