2.81 Phototropism

Describe positive phototropism of stems.

Phototropism is the growth of a plant in response to light.
Positive phototropism suggests that this growth is towards the light.
The stem of a leaf will grow in the direction where there is the highest concentration of light. if the direction of light changes, the plant will grow to whichever direction has the highest concentration of light. This is called positive phototropism. this occurence is cause by the hormone auxin.

light -> growth -> towards light

2.80 Geotropism

Describe the geotropic responses of roots and stems.

Geotropism is the growth repsonse to gravity. Observing a seed shows that the embryo of the seed grows downwards. this is called positive geotropism. A shoot of the seed grows upwards. this is called negative geotropism. Rotating the leaf produces the same effect because of Geotropism.

2.79 Plants and Stimuli

Understand that plants respond to stimuli.

Stimuli -> Receptor -> Response

Changes in the environment leads to the plant receptors detecting stimuli which is then converted into a response, usually in the form of growth. This is called a tropism. tropism involving light is called phototropism while gravity related tropism is called geotropism. connections between the receptors and the response is the plant hormones such as auxin.

2.54 Transpiration

Recall that transpiration is the evaporation of water from the surface of the plant.
Liquid --heat/sunlight--> Gas
In order for the water in the plant to turn into a gas, it will need heat. Heat is absorbed by the plant through the leaves in the form of sunlight.
excess gas diffuses out of the stomatal pores.
As sunlight enters the leaf for photosynthesis and the water is spread around the spongy mesophyll, the water is heated up by the sunlight, turning it into a gas. this occurs near the stomatal pore to allow it to evaporate out of the leaf.

2.53 Uptake of Water

Explain how water is absorbed by root hair cells.

Roots branch out over a wide surface area to find water source. The epidermis of the root is lined with root hair cells. Root hair cells branch out, also over a wide surface area. Minerals are actively transported into the root hair cell, which then allows osmosis to occur and bring water into the cell. This is because the soil water around the root hair cell is now dilute making the water move into the more concentrated area inside the root hair cell.