Example of Phototropism

2.81 Phototropism

Key Points:

1. Phototropism is the growth in response to light
2. Positive phototropism is the growth of the plant towards the light. With uniform light coming from all directions, the stem will grow upwards
3. However, with the same stem, and light coming from a lateral light source, the stem begins to grow towards the light source
4. In the example in which the stem grows towards the lateral light source, that is called positive phototropism
5. The understanding of this is that a compound called Auxin, which is a plant hormone and it causes more growth on one side, causing the bending of the stem and making the entire stem positively phototropic 

2.80 Geotropism

Key Points:

1. Geotropic responses are growth responses to gravity
2. An example is that in a seed, the embryonic roots grow downwards, and this makes it positively geotropic, or makes positive geotropism
3. And in the seed, the embryonic shoot will grow upwards, making negative geotropism
4. If the seed is rotated, the embryonic roots will continue to grow downwards showing positive geotropism, as will the embryonic shoot, which will grow upwards making negative geotropism
5. This shows that no matter which way you turn the seed, it the shoot will always grow upwards, and the roots will always grow downwards, showing the growth responses to gravity from the seed

2.79 Plants and Stimuli

Key Points:

1. Plants have receptors which detect the stimuli and turn it into a response
2. The responses often take the form of growth, and this is called a tropism
3. Tropisms that involve light are called phototropism, and ones that involve the response to gravity and called a geotropism
4. The connection between the receptor and the response takes the form of plant growth regulators, or hormones
5. Stimuli are usually changes in the environment, such as light and temperature

2.54 Transpritation

Key points:

1. Transpiration is the evaporation of water from the surface of a plant
2. Heat is needed to carry out the evaporation, and this heat comes from sunlight which is absorbed through the leaf's structure
3. Light energy (High Frequency, UV) converted into heat energy (Low frequency) from the leaf's structure
4. Evaporation is right above the stomatal pores, water is delivered there from the xylem, moves through the spongy layer. 
5. Liquid to gas. Evaporation happens in the area right above the stomatal pore. Not all the light energy is used for photosynthesis so some of it converts into heat energy and heats up the water, causing the average kinetic energy of the atoms in the water to increase, turning it into a gas.

2.53 Uptake of Water

Summary

1. Roots branch out to collect more water. Increased surface area means increase water intake.
2. At a closer glance, there are hairs on the roots. They are called root hair cells.
3. Root hair structure is for maximum water intake
4. The mechanism involves active transport of minerals, and this causes osmosis in which the water moves from the dilute region to the concentrated region, in this sense, the water moves from the soil into the roots.
5. The root hair cells are epidermal, meaning they are on the outside of the tissue.

2.53 Root water uptake