2.81 Phototropism

+ Phototropism = light à growth à towards light

+ Tip of stem with light, it will grown upwards

+ stem with lateral light source, the plant bends in growth (example of positive phototropism)

+ Light on one side causes movement on the opposite side.

+ Has a compound called Auxin (hormone) causes more growth on opposite side: bending

2.80 Geotropism

+ Geotropic the word split up means:  Geo =Gravity Tropic = Growth Response
+ Positive Geotropism = Embryotic root growing towards the stimuli (source)
+ Negative Geotropism = Embryotic root growing away from the stimuli (source)

+ When rotated it will cange direction, growing either upwards or downwards

2.79 Plants and Stimuli

+ Stimuli are changed in the environment by for example: Gravity, Light Chances or Temperature
+The plant has Receptors which can detect the stimuli
+ This is then turned it into a Response,
+ Which is taken the form of Growth (Tropism)
+Tropism (light) called Phototropism.
+Tropism (gravity) is called Geotropism
+ Tropisms might include mitosis and cell elongation.

2.54 Transpiration

+ Evaporation of water (liquid -> gas) needs heat. This heat is produced by sunlight as absorbed by leaf structure through the stomatle pores.
+ water goes up the the roots, up the plant structure to the leaf, this is where eveaporation happens.
+ Looking at a cross section of the leaf: not all light is absorbed by the chloroplasts some generates heat.
+ Just above the stomatle pores, phase change occurs (liquid -> gas) = evaporation
+ water vapor gas diffuses down through pore, which has a steep diffusion gradient.

A potometer is used to measure the rate of water uptake up a leafy shoot.

Potometer

Picture of some Roots:

2.53 Root Structure

+ Root Structure has a branching pattern, this increases SURFACE AREA and the ABSORBTION OF WATER.
+ the Root has ROOT HAIR, contains of epidermal cells (surface)
+ the ROOT HAIR activly concentrates minerals, inside the root. This encourages the take of water by OSMOSIS.
+ OSMOSIS = dilute region -> concentrated region
+ water then travels from the ROOT to the XYLEM also using OSMOSIS.