2.80 Geotropism

- Geo = gravity, tropic = growth response
- An example: seed:
- the embryonic roots grow downwards, this is described as positive geotropism
- the embryonic shoot will grow upwards, this is negative geotropism

- Further experiment: take the same germinating seed and rotating it anti-clockwise to face upwards.
- The shoot grow upwards showing negative geotropism
- The roots will grow downwards showing positive geotropism

2.79 Plants and Stimuli

- Stimuli are changes in the environment (e.g. temperature, light)
- Plants have receptors which detect stimuli and turns into a response
- Responses take the form of growth - this type of response (growth in response to stimulus) is called a Tropism
- Tropisms involving light = Phototropism
- Tropism involving response to gravity = Geotropism
- Connection between receptor and response takes form of plant hormones called Plant Growth Regulators (e.g. Auxin)