2.81 Phototropism

Describe positive photo tropisms of stems

- Light --------> Growth -------> towards light.

Where the light is coming from the plant will grow towards the light. If the light is coming from the left than the plant will grow to the left.

- The light from one side causes the movement on the opposite side.
- Auxin is a hormone that causes growth.

2.80 Geo tropism

Describe the Geo tropic responses of roots and stems.

- Geo refers to gravity. Tropic is the growth response to gravity.\
- E.g. If you take a seed, the embryonic root grows downwards. This is positive Geo tropism.
- When the root grows upwards it is called negative Geo tropism.

2.79 Plants and stimuli

Understand that plants respond to stimuli.

- Stimuli ------> Receptor --------> Response
- Stimuli is a change in nature. It could be temperature light or gravity etc...
- Receptors detect a stimuli and turn them into a response.
- Responses offten take the firm of growth
- Growth in response to stimulus is called a tropism. Tropisms that involve light are called photo tropisms. Tropisms involving gravity are called geotropisms.

2.54 Transpiration

2.54 recall that respiration is the evaporation of water from the surface of a plant


- Transpiration is the evaporation of water from the surface of a plant
- H20 Liquid Through heat and sunlight turns into Gas
- Evaporation escapes from the Stomatal pores.
- Water delivered to the leaf from the xylem.
- Sunlight heats the leaf up, Liquid turns into gas and diffusion occurs down the diffusion gradient.

How water is absorbed by root hair cells

- Breaching Surface Area / H2O abs.

- Root Hairs - increase the surface area to absorb water.

- Epidermal root.

- Active transport of minerals.

-Osmosis (H2O) - from dilute region to concentrated region.