BRAINCAKEPlant Responses
Plant responses can be grouped into tropisms and nastic responses.
A tropism is a growth response of part of a plant to a directional stimulus. The direction of growth depends on the direction of the stimulus. Growth towards the stimulus is a positive tropism; growth away from it is a negative tropism.
- Phototropism (light): shoots are positively phototropic, so leaves are held in the light; roots are usually negatively phototropic.
- Geotropism, or gravitropism (gravity): roots are positively geotropic and grow down into the soil; shoots are negatively geotropic and grow upwards.
- Hydrotropism (water): roots are positively hydrotropic.
- Thigmotropism (touch): the tendrils of climbing plants such as peas coil around supports.
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Key terms in this lesson
- turgor
- The pressure of the cell contents pushing outwards against the cell wall.
More in Chemical Control
- Hormone Release System
- Pituitary Gland
- Second Messenger System
- Plant Stimuli
- Plant Growth
- Auxins
- How Auxins Work
- Gibberellins
All 30 lessons in Chemical Control · All Edexcel A-level Biology topics