2.81 Phototropism

Phototropism is growth in response to light
                      growth towards the light

Light towards the top - the plant will grow towards the light, in the usual upwards position

Lateral Light - the plant will grow laterally towards the light, causing it to bend

Auxin (a hormone) causes more growth on one side of the stem, causing the bend. The auxin builds up on the shady side.

2.80 Geotropism

Geotropic gravity growth response

Positive Geotropism - the process where the roots of a plant grow downwards towards the earths       gravitational pull

Negative Geotropism - Process where the roots of a plant grown upwards (away from the soil)

The growth towards a stimuli - positive

2.79 Plants response to Stimuli

Stimuli
Changes in the environment (e.g light, temperature)


STIMULI -> RECEPTOR -> RESPONSE


Receptors
Plants have receptors which detect the stimuli.
They respond to it.

The response is often growth.

The receptors and response = plant hormones

2.55 Rate of Transpiration

Transpiration: loss of water from the leaf (diffusion from inside of leaf, to outside atmosphere)

If the Concentration Gradient is    Large Different    (high rate of diffusion)
                                                      Small Difference  (low rate of diffusion)

High Rate/Large Difference in concentration: 
- low humidity
- high wind                                                                          = Fast diffusion/transpiration
- high temp (more evaporation)
- high light intensity (more photosynthesis)        

Low Rate/Large Difference in concentration:
- high humidity
- small wind speed                                                                = Slow diffusion/transpiration
- low tempt (low rate of evaporation)
- low light (low rate of photosynthesis)

2.54 Transpiration

Evaporation
- H2O Liquid -> Gas
- The heat that makes this process possible is provided by the sun, which is absorbed by the leaf structure. The Light energy is changed into heat energy.

- Evaporation occurs through the stomatal pores


Heat and Sunlight
- Not all light that enters the leaf is used for photosynthesis, so is used by others cells to generate heat

- Just above the stomatal pores is where this reaction from liquid to gas takes place

- Heat turns the water, into water vapour, which will diffuse down the pore to the outside atmosphere, through the diffusion gradient. There is full humidity inside the leaf, but a lower concentration below, so the water diffuses out.

2.53 Root Structure

Roots
- The branching patterns of roots, increase the surface area, increasing the rate of H2O absorption

Root Hair (smaller hairs on the root)
- Made up of the root epidermis layer, caused by the cell wall extended outwards
- Increases the surface area, increasing rate of H2O absorption

Process of Absorption
- The active transport of minerals from the root
- Waters moves across cortex through to the xylem

- Active Transport, water moves to the concentrated cytoplasm  of the root hair cell by osmosis