Photosynthesis is the process which produces "food" in plants. The product is a sugar, known as "glucose" and is used by plants in various ways, such as to produce cell walls and protein. Any glucose that the plant does not use is converted into either lipids or starch, and is stored for later use.


So how does a plant "photosynthesise"? What happens?


You probably already know, or will have heard at some point that plants take carbon dioxide and produce oxygen, a pretty useful thing considering that we have too much of the one and I don't suppose we can ever quite have enough of the other, so the fact that plants are quite willing to do this for us is pretty decent of them :-)



Plants use a substance called chlorophyll, which is green and found in structures in a plant leaf called chloroplasts. There are four raw materials to consider:


  • Chlorophyll
  • Carbon dioxide
  • Water
  • Sunlight


The word equation for photosynthesis makes the process look quite simple, it is in fact quite complicated:


Carbon Dioxide + Water (in the presence of Sunlight and Chlorophyll) -> Glucose + Oxygen


Although I have stated "sunlight" because this is where the plant normally gets its light source from, photosynthesis can occur in the laboratory with artificial light sources such as desk lamps. In fact one of the required practicals in the biology specification is to investigate the effects of various light intensities on the production of oxygen using pondweed, and to perform tests on leaves using iodine to see whether or not they contain starch (which is one of the ways that plants will store glucose for later use).


You will find in many biology books that chlorophyll is not mentioned in the equation as I have shown it above, it is the chlorophyll which absorbs light to enable the process to take place, but of course if there was no chlorophyll there would be no light absorption and therefore photosynthesis would not be able to occur.


Q. Name the structure in which chlorophyll will be found in the leaf of the plant.


A. The structure is known as a chloroplast.



Q. What is the name of the "food" produced in the process of photosynthesis?


A. Glucose


Q. Would you expect to find chloroplasts in the roots of a plant, explain your answer.


A. No - you wouldn't expect to find chloroplasts in the root or root hair cells of a plant because chloroplasts are used to photosynthesise and require light to perform this function. In most plants the roots are underground, and therefore not exposed to light.


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