Biogenetics

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  • Created by: lundy334
  • Created on: 13-10-16 18:01

Biogenetics
- Photosynthesis
- Respiration

Photosynthesis
Plants can make their own food by photosynthesis. It takes place in the green parts of the plant (especially the leaves) when it is light.
The process of photosynthesis
The cells in plants leaves have small green parts called chloroplasts, which contain a green substance called chlorophyll.
Photosynthesis is an endothermic reaction. Endothermic reactions need input of energy from the environment.
The equation for photosynthesis is:
Carbon Dioxide + Water  Glucose + Oxygen
6CO2  + 6H20  C6H12O6   + 6O2
Some of the glucose produced is used immediately by the cells of a plant for respiration. A lot of the glucose is converted into insoluble starch and then stored.
Producing oxygen
To show that a plant is photosynthesising by the oxygen gas it gives of as a by-product. In land plants it is difficult to see it being given off the colourless gas (oxygen). However you can see and collect the bubbles of gas being given off in water plants such as Cabomba or Elodea. The gas will relight a glowing splint, if its rich in oxygen.
Plant adaptations
For photosynthesis to be successful, a plant needs carbon dioxide, light and water. The leaves of plants are adapted perfectly for photosynthesis. Some of the adaptations are:
- Most leaves are broad, giving them a big surface for sunlight.
- Most leaves are thin so diffusion for gases takes less time.
- They contain chlorophyll that absorbs the sunlight.
- They have veins, which bring the water in through the xylem (the tube that carries water and minerals) and remove the products of photosynthesis in the phloem.
- They have air spaces that allow carbon dioxide to get to the cells and oxygen to leave by diffusion
- They have guard cells that open and close the stomata to get normal gas exchange.
The adaptations mean that the plant can photosynthesise as much as possible whenever there is light available. 
- Algae are aquatic so they are adapted to photosynthesising in water.
- They have a large surface area and absorb carbon dioxide dissolved in the water around them. The oxygen they produce also dissolve in the water around them as it is released.
Scientists are working hard to make sure crop plants carry out as much photosynthesis as possible. They are trying to increase the amount of chlorophyll in some plants, and make photosynthesis more efficient in others. These changes could help us grow more food. If they also remove more carbon dioxide from the atmosphere it might help reduce global warming.

Plants need light, warmth, and carbon dioxide to photosynthesise and grow fast. Sometimes one or more of these things can be in short supply and limit the amount of photosynthesis a plant can manage. That is why they are known as limiting factors.

Light

Light intensity is one factor affecting the rate of photosynthesis. If there is plenty of light, lots of photosynthesis can take place. Whereas, if there is little or no light, photosynthesis will stop, whatever the other conditions…

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