Phototropism

- Photo tropism refers to growth responses as a result of light.

- When uniformed light coming from all directions hits the plant, it causes the stem to grow upwards.

- Positive photo tropism however is when light comes from the side of the stem (a lateral light source), which causes the plant to have a bend in the growth, and tilt towards the direction of the light. The reason why this happens is because of a plant hormone called Auxin.

- Auxin is a plant hormone which is produced in the plant tip. As a plant grows, it needs more water and minerals. Because of this Auxin will build up in the cells on the shady side of the plant. The Auxin will loosen up the cell walls which will allow the cell to elongate. This causes the shady side to grow more than the sunny side so the plant bends towards the light.

- Geo tropic refers to growth responses as a result of gravity.

- An example of this is when in a seed the root grows downwards, this is positive geotropism. Whereas if it grows upwards towards the surface it is negative geotropism.

- If the seed turns for example 90 degrees, the roots will adjust the direction of growth again either towards the surface (negative geotropism) or downwards (positive geotropism).

- Stimuli are changes in the environment. These could be temperature changes or light changes.

- Plants have receptors which can detect stimuli. The receptors then connect with the response section using plant hormones such as Auxin.

- The responses are often in the form of growth. This type of response is called a 'tropism.' If the stimuli is changes in light the response is known as 'phototropism.' The other type of tropism is a response to gravity, known as 'geotropism.'

- Transporation is the evaporation of water from the surface of the plant.

- Water evaporates to a gas because of the heat provided by the sunlight which is absorbed by the structure of the leaf

- Evaporation occurs through the stomatal pores

- Water delivered to the leaf from the xylem.

- In the spongy layer, there is a phase change

- The water vapor diffuses down the diffusion gradient and then through the stomatal pore

Uptake of Water 2.53

- Branching root pattern increases surface area, which speeds up the rate of absorption.

- Cell wall extends, which creates a greater surface area for more intake of water.

- Epidermal also specialised to maximise surface area, again for absorption of Water.

- Active Transport of minerals at the bottom of the root hair to the xylem.

- Osmosis - from dilute region (outside) to a concentrated region (inside where the cells are full of minerals)