Rate of photosynthesis

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Manal javed

Aim

For my biology coursework I will be investigating the affect of light intensity on the rate of photosynthesis, at a determined distance. The investigation will be carried out with experiment using scientific techniques. I will then make possible predictions, which I will be, explaining using appropriate scientific knowledge.  

 

Background knowledge

Photosynthesis is light dependant reaction. In photosynthesis water splits to make hydrogen and oxygen. This stage needs light, so is called light reaction. The second stage of photosynthesis is called dark reaction three hydrogen combine with carbon dioxide to make glucose. In this stage enzymes are involved, so by looking at the equation below the factors which affect the rate of photosynthesis can be found which are:

                             (Light)

6CO2 + 6H2O A C6H12O6 + 6O2 (in the presence of chlorophyll)

  • Light intensity
  • Carbon dioxide
  • Temperature

Each of the above factors is dependant on each other, therefore

Four things are needed for photosynthesis to happen.

  • Light form the sun
  • Chlorophyll, the green substance which is found in chloroplasts
  • Carbon dioxide, enters the leaf form the air around
  • Water comes from the soil, up the stem and into the leaf

Photosynthesis takes place in the leaves of all green plants. The leaves are best for photosynthesis, because:

  • Leaves are thin and flat to provide a large surface area to catch lots of sunlight.

  • The palisade cells are near the top of leaf and are packed with chloroplasts.

  • The guard cells control the movement of gases into and out of the leaf.

Light intensity

Temperature, carbon dioxide and light intensity are factor that affect the rate of photosynthesis. At any given time one or other of the three factors will be the limiting factors, which are keeping the photosynthesis down at the rate, it is.  

The chlorophyll uses light energy to perform photosynthesis. It can only do it as fast as the light energy is arriving.

1) As the light level is raised, the rate of photosynthesis increases steadily but only up to a certain level.

2) Beyond that, it won’t make any difference because then it will either be the temperature or the carbon dioxide level, which is the limiting factor.

Ordinary white light (sunlight) is made up of different colour lights of different wavelengths. Chlorophyll absorbs blue and red light, but reflects green light (which is why chlorophyll looks green). When growing plants in artificial light (e.g. indoor), it is important that they get enough blue and red light.  (Special lights.)

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Very bright sunlight can actually damage plants, because of the ultraviolet rays.  

Carbon dioxide  

Carbon dioxide, this is one of the key ingredients for photosynthesis. Carbon dioxide and water are the raw materials. Water is never really in short supply in a plant but only 0.035 of the air around is carbon dioxide so it is scarce to a plant.

1) As with light intensity the amount of carbon dioxide will only increase the rate of photosynthesis up to ...

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