Plant Sensitivity

The leaves are bending towards the light

Positive Phototropism

Auxin crowds to the side that lacks light and makes the stems bend towards light
Auxin stimulates cell elongation and cell division.
Auxin on the opposite side causes growth where there is less light.

2.81

Describe positive phototropism of stems

Positive Phototropism (growth in response to light, growing towards the light).

When the light source is directly above the plant, the plant grows upwards.

However, if there is a lateral light source (light coming from the side), the plant bends towards the light (like sunflowers!). The light causes the movement of auxin to the darker side. Auxin is a plant hormone that allows more growth to happen on one side of the plant. So the plant bends towards the side with less growth, more light.

2.80

Describe the geotropic responses to roots and stems

Geotropism: Geo – gravity, Tropism – growth response

When the embroic root grows downwards, it is called a positive geotropism.

When the shoot grows upwards through the surface it is called negative geotropism.

If you rotate the seed around instead of continuing to grow on the right and the left, it will either grow upwards or downwards (negative and positive geotropism).

2.79

Understand that plants respond to stimuli

Stimuli à Receptor à Response

Stimuli: changes om the environment, including temperature, light

Response: e.g. Growth

Tropism: Growth in response to stimulus

1.     Phototropism (light)

2.     Geotropism (gravity)

2.54

2.54 NOTES SCAN

2.53

The branching pattern of roots increase surface area to allow more absorption of H₂O to take place. When you zoom in on the roots, they have root hairs.

From a microscopic level you can see the following:

1)     Active transport of minerals against the concentration gradient takes place.

2)     This encourages Osmosis to take place, encouraging the roots to take up water.

3)     The water is transported through the xylem, once again through osmosis.