B2 Photosynthesis

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  • Photosynthesis
    • Carbon dioxide + Water -> Glucose + Oxygen
    • Photosynthesis is the chemical change which happens in the leaves of green plants
    • During photosynthesis:
      • Light energy is absorbed by chlorophyll, a green substance found in some plant cells and algae
        • Light energy is stored in glucose molecules
          • Absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
            • Some glucose is used for respiration
              • Plants respire all the time and the energy produced is used for growth
            • Some glucose is converted into insoluble starch or oils for storage
              • The stored starch can later be turned back into glucose and used in respiration
                • Glucose can't be stored because glucose is soluble
              • Starch molecules are big and, unlike glucose, cannot diffuse out of cells
                • The stored starch can later be turned back into glucose and used in respiration
                  • Glucose can't be stored because glucose is soluble
            • Some glucose is turned into cellulose, which is used to make cell walls
            • Synthesis
              • Some glucose is combined with nitrates to make amino acids, which make proteins, which are used for growth
      • Absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
        • Some glucose is used for respiration
          • Plants respire all the time and the energy produced is used for growth
        • Some glucose is converted into insoluble starch or oils for storage
          • Starch molecules are big and, unlike glucose, cannot diffuse out of cells
          • Some glucose is turned into cellulose, which is used to make cell walls
          • Synthesis
            • Some glucose is combined with nitrates to make amino acids, which make proteins, which are used for growth
        • Oxygen is released as a by-product
      • Factors limiting photosynthesis
        • Light intensity
          • Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.
        • Carbon dioxide concentration
          • Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.
        • Temperature
          • If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.
        • A limiting factor is an environmental variable, such as light intensity, that limits the rate of a process, such as photosynthesis
      • Greenhouses
        • Growing crops in a greenhouse give the grower a lot of control over the conditions in which the plants live
          • A grower could increase the amount of carbon dioxide by burning a fuel such as propane, which releases CO2 when burned, or adding the gas through PVC tubing
            • They would want to increase the amount of CO2 because there is a very low concentration of it in the atmosphere (about 0.04%), and this can limit the rate of photosynthesis when plants are grown closely together
          • A grower can increase the temperature by heating a greenhouse with a boiler and radiators, but the cost of the fuel might outweigh the increase in what they are paid for the crops
          • A grower can increase light intensity by supplementing natural light with artificial light. They would want to increase light intensity in winter because there are very few hours of daylight in winter so the rate of photosynthesis isn't as high as it could be
          • Advantages of growing crops in a controlled environment are that a higher yield is produced and crops can be grown when the weather and land outside are unsuitable
          • Disadvantages of growing crops in a controlled environment are that it's expensive and extra equipment is needed

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    Swallowtail

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    This mind map covers many of the key areas necessary for the understanding of photosynthesis, which is found in most GCSE specifications. It usefully separates the topics by colour and isn't too crowded. Pictures can help you to remember information more effectively than words, so, where a symbol or picture means something to you, you could usefully add it to the printed diagram.

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