2.81 Phototropism

POSITIVE - PHOTO - TROPISM
- photo --> light
- positive photo --> towards light
- tropism --> growth response
- positive phototropism :: growth response towards light
- even if the light is to the side of the plant ( unilateral light source ) the plant will bend over to catch the light
- Auxin is a hormone in the plant where cells divide and elongate.
- When the light hits only one side of the plant the Auxins which are usually evenly spread out in the plant move to the opposite side.
- Because Auxins is where the cells divide, the cells are only dividing on one side of the plant, the plant is only growing from one side.
- This is how it grows towards the sun.

2.80 Geotropism

- GEO--TROPIC
geo --> gravity
tropic --> growth response
GEOTROPIC ---> growth response to gravity
- positive geotropism --> when an embryonic root grows downwards it is described as positive geotropism
- negative geotropism --> when an embryonic shoot grows it grow upwards this is described as negative geotropism
- even if the seed is flipped around the embryonic shoot would still find its way to grow upwards showing negative geotropism and the embryonic root would find its way to grow downwards showing positive geotropism.

2.79 Plants and stimuli

- stimuli is the changes in the environment such as temperature and light.
- plants can detect the changes in the environment through their receptors.
- response to stimuli detected by the receptors often is growth. response in growth is called tropism.
- examples of tropisms include
tropism that involves light :: phototropism
tropism that involves gravity :: geotropism
- connection between the receptor and response usually takes the form of plant hormones which are sometimes called plant growth regulators. (an example: Auxim)

2.54 Transpiration

Heat from sunlight evaporate water from the surface of the plant (changes the liquid into gas) through a process called transpiration.

1. The sunlight warms the leaf.
2. Water travels into the leaf through the xylem.
3. Heat from the sunlight changes the liquid into gas, phase change occurs above the stomatal pores.
4. Evaporation through the stomatal pores down a diffusion gradient.
5. When the vapour leaves the stomatal pores it pulls another vapour particle with it and the pulling chain goes all the way down to the roots, this is how the plant transports the water.

2.53 uptake of water

- Branching pattern of the roots increase surface area for the maximum absorbtion of water.
- There are root hairs are the epidermist of the root cells which increases the surface area further for the absorbtion of water.
- ACTIVE TRANSPORT takes in minerals to the roots against the concentration gradient.
- Through OSMOSIS water is taken into the roots up the concentration gradient. The water from the dilute soil is taken into the root where it is concentrated because of the the minerals that were taken up through active transport.