Phototropism Example (in the classroom)

Photo: http://charlottebiology.blogspot.com/

Phototropism example: The stem of the plant detects the sun light which then bends in the direction of the source.

- Phototropism = light  growth  towards light
- If the light hits the tip of the stem it grows upwards
- If the light is coming from the side (lateral light source) then the plant will bend as it grows
- Light on only one side will cause the other side to bend
- If one side contains the compound Auxin (hormone) then it will bend. This is because it is caused by growth on one side but not on the other.

Geotropic: Geo – Gravity, Tropic – Growth Response
Embryotic root growing towards the Stimuli (source) = Positive Geotropism
Embryotic root growing Away from the Stimuli (source) = Negative Geotropism
If rotated it will change direction to grown to either upwards or downwards

- Stimuli are changed in the environment (i.e. Temperature, Gravity or light chances)
- The plant has Receptors which can detect the stimuli
- Turn it into a Response, which take the form of Growth (Tropism)
- Tropism that involves light is called Phototropism.
- Tropism that involved Gravity is called Geotropism
- Tropism's might include Mitosis and cell elongation

- Evaporation of H20 (liquid to gas) involved heat. The heat is provided by Sunlight as it’s absorbed by the leaf structure through the stomatal pores
- Water travels up the plant to the leaf, where sunlight heats up the leaf, providing the heat needed.
- Cross Section: Not all light will be absorbed by the chloroplast; some absorbed by other cell structures and will generate heat.
- Water enters through Xylem, and moves through the spongy mesophyll. Just above the stomatal pore the change occurs from liquid to gas.
- Diffuses through pore at a steep diffusion gradient

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

- 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.