Control and Coordination
Coordination in plants
Explain how plants respond without nerves or muscles.
"Plants have no nerves or muscles. Can they still respond?" Touch a sensitive plant (chhui-mui, touch-me-not) and its leaves fold up at once. The message passes from cell to cell, and cells at the base of the leaves lose water, change shape and droop. No growth is involved. Animals move using muscle proteins; this plant moves using water.
Most plant movements are slow and happen by growth, towards or away from something. This is a tropism:
- Light (phototropism): shoots grow towards it, roots grow away from it.
- Gravity (geotropism): roots grow down, towards it; shoots grow up, away from it.
- Water (hydrotropism): roots grow towards it.
- Chemicals (chemotropism): a pollen tube grows towards the ovule.
A tendril of a pea plant coils round a stick. The side touching the stick grows more slowly than the side away from it, so the tendril curls round the support.
"How does a shoot know to bend towards light?" A plant hormone called auxin is made at the tip of the shoot. When light comes from one side, auxin moves to the shady side. There it makes the cells grow longer. The shady side grows more, so the shoot bends towards the light. (Not the other way round: the side away from the light grows more.)
Other plant hormones:
| Hormone | Job |
|---|---|
| Gibberellins | help stems grow |
| Cytokinins | promote cell division (found where cells divide fast, as in fruits and seeds) |
| Abscisic acid | slows growth; causes leaves to wilt |
Practise this lesson
Questions that get harder as you improve, a Tutor that helps without giving the answer away, and progress you can see. Free for every learner.
No account, no email address. Opens the real product.