Evidence of Phototropism in the lab

Credits to Charlotte :)

2.81 Phototropism

2.81 describe positive phototropism of stems

Photo; light

Tropism; growth

Growth in response to light

And the positive suggests that it is towards the light

A stem-

Take the tip of stem, where uniform light coming from all directions hits it. This causes it to grow forwards and upwards

If we use the same stem but instead of the light coming from a uniform source, the light comes from a lateral source.

The plant bends in the growth towards the light. This is also another example of phototropism.

The light on the left side is the reason of the movement to the opposite (right) side. This is caused by a compound called auxin (a plant hormone) which causes more growth on both side resulting in the plant bending.

2.80 Geotropism

2.80 describe the geotropic responses of roots and stems

Geotropic

Geo; gravity

Tropic; growth response

Therefore is the growth response to gravity.

For example if we experiment a germinating seed, when observing the growth one finds that the embryonic roots are grown downwards, this is known as positive geotropism.

Whereas the shoot will grow upwards to the soil surface. This is known as negative geotropism.

If we experiment further by taking the same seed however rotating it 90 degrees to the left, we find that the shoot grows upwards (negative geotropism) and the root grows downwards (positive geotropism).

Below is a diagram showing the experiment described above:

2.79 Plants and Stimuli

2.79 Understand the plants respond to stimuli

Stimuli are the changes in the environment for example temperature and light.

The receptor detects stimuli and then turns it into response

Response takes form of growth. There are two types of response to stimuli (tropism).

A tropism involving a response to:

1. Light is known as phototropism

2. Gravity is known as geotropism

The connection between the receptor and the response usually takes the form of plant hormones which also can be identified as plant growth regulators for example auxim.

2.54 Transpiration

2.54 recall that transpiration is the evaporation of water from the surface of a plant

Water goes from a liquid phase to a gas phase, which requires heat, and that heat is provided by sunlight (Light energy to heat energy).

 As the leaf structure absorbs the light, the liquid turns to gas, and the evaporation is seen through the stomatal pores.

Water is taken up by osmosis through the xylem which travels up the stem and out through the petiole (evaporation through the stomatal pores). Above the stomal pore the phase change occurs (liquid to gas- evaporation)

Gas water vapour diffuses through the stomatal pore, down a steep diffusion gradient to the outside atmosphere

1. Sunlight warms leaf to create heat

2. Phase change of water to gas

3. Diffusion of water vapour

Diagram of Uptake of water

2.53 Uptake of Water

2.53- explain how water is absorbed by root hair cells

 Root structure
 Branching pattern occurs, this increases surface area for absorption of water, and also they branch out to find water sources.

The smallest ends of a root are called root hairs (epidermal). The extended (the root hair structure) root hair cell increases absorption of water. When zoomed in the epidermal cells of the roots further illustrate the surface area of the structure concept for the absorption of water.

The plant actively transports the minerals (active transport against the transport movement with the involvement of minerals). This encourages the plant to take up water by the process known as osmosis (water moves from a dilute to a concentrated solution). The dilute solution being the soil water surrounded by root hairs and the concentrated being the minerals in the cell.

It is a two part transportation process. First the active transport of minerals and then the osmosis of water.

Water moves across the cortex of the root to the xylem by osmosis.