• Glucose and starch etc
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  • Created on: 14-06-11 13:20
Preview of Photosynthesis

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B7.2 Photosynthesis
Photosynthesis takes part in the chloroplasts which contains a green pigment called
chlorophyll. The chlorophyll absorbs light and uses the energy to start photosynthesis.
The Light energy splits the water molecules into hydrogen and oxygen atoms. The
hydrogen is combined with the Carbon Dioxide in the air to produce glucose. (The
oxygen is a waste product)
The Glucose can be used for a range of different things...
1) To make other chemicals needed for growth
such as cellulose and starch which are both long chains of glucose. They are
polymers of Glucose.
2) To store energy in starch molecules
Extra glucose is converted into starch. When there isn't enough glucose in the
plant, the starch can be converted back.
3) To release energy in Respiration to release energy.
Why is it stored as starch?
Glucose is soluble, so if it was stored as glucose, the concentration could become too
high and it could upset the osmotic balance.
Starch is insoluble, therefore can be stored without affecting the cells. The starch is
stored in the leaf as it has a small membrane.
Photosynthesis is taking the carbon dioxide out of the air, so the carbon dioxide must
be replaced. This is by respiration.
However, plants can only carry out photosynthesis when they are in light, but they respire
24 hours a day. This could cause some problems, so they have to be balanced.
When photosynthesis and respiration are taking place at the same rate, it is the plants
compensation point.
(This can be shown on a graph when the two lines (one for respiration and the other for
photosynthesis meet.)

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