How light intensity affects the rate of photosynthesis.

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HOW LIGHT INTENSITY AFFECTS THE RATE OF PHOTOSYNTHESIS.

Photosynthesis is the process in which plants make their own food using light. To make the food they also require Carbon Dioxide, Chlorophyll and water. This can be shown in an equation:

Carbon  + Water       light                 Glucose + Oxygen.

Dioxide                    Chlorophyll

The balanced word equation for this is:

6CO2   +  6H2O                  C6H12O6   + 6O2

The plant takes in light energy from the sun, using the palisade cells, which are situated in the leaf. The cells contain Chlorophyll, which is the green substance inside the leaf, and also chloroplasts, which trap the sun’s energy. This then reacts with the water. The plant uses light energy to separate 1 hydrogen atom from the water. This gives the OH – ion, which is hydroxyl, and the H+ ion that is hydrogen. These are then unsatisfied bonds so they join together to form 2 water molecules, 1 oxygen and 4 hydrogen molecules. (The hydrogen ions are turned into glucose), this means that the more light there is, the more water is split and hence there is more oxygen. This is all part of the light stage. The light stage involves this splitting of water and also the production of ATP, this is a source of energy which is later used in the dark stage. The light stage traps the sunlight and converts it into chemical energy. Oxygen produced in the light stage is evolved as oxygen gas, and the hydrogen reduces the carbon dioxide to carbohydrate. ATP is formed in the light stage and is used as energy for the dark stage, the reduction of carbon dioxide into carbohydrates takes place in a number of steps, each controlled by an enzyme. Melvin Calvin has proved these steps by illuminating the chlorophyll in the plant in the presence of carbon dioxide and allowing it to photosynthesise for a certain period of time. It is then killed with boiled alcohol (ethanol). This inactivates the enzymes and stops the reactions. This chain of reactions is known as the Calvin cycle. It produces starch and amino acids. For amino acids to be produced nitrates are required. Nitrates are needed to make proteins and if there is a shortage it leads to yellow older leaves and stunted growth. The root hair cells in the roots can absorb this mineral. The amino acids are then converted into ammonium ions.

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Water is needed by the plant to photosynthesise; it diffuses from the soil, into the root hair cells via osmosis. It can then be transported to the growing regions of the plant by the xylem cells.

     Carbon dioxide is another product used in photosynthesis, it diffuses from the atmosphere into the plant by the stomata, which are situated in the plant’s leaves and controlled by the guard cells. They control the size of the stomata, enabling it to open and close, the plant needs to do this because although the stomata needs to open in order to ...

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