Photosynthesis

• Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light.
• The sugars produced by photosynthesis are used to make all the substances a plant needs, as well as being used in respiration to release energy.
• equation for photosynthesis:

  carbon dioxide + water → glucose + oxygen
• balanced photosynthesis equation:

  6CO2 + 6H20 → C6H12O6 + 6O2
• The leaves of the plant are where most photosynthesis takes place, in specialised mesophyll cells which are packed with chloroplasts containing chlorophyll to absorb as much light energy as possible.
• • Carbon dioxide diffuses into the leaf through the stomata.
• • Water is taken up by the roots and transported through the xylem to the leaves.
• • Glucose is used to make the substances needed by the plant: used in respiration to release energy.
• • Oxygen diffuses out of the leaf through the stomata and is used in respiration.
• In order to photosynthesise a plant needs light, water and carbon dioxide.
• Lower temperatures decrease particle kinetic energy, leading to fewer successful collisions between reactants and enzymes in the plant.
• Higher temperatures boost kinetic energy, increasing the likelihood of collisions between reactants and enzymes, promoting formation of the products.
• At higher temperatures, however, enzymes that control the processes of photosynthesis can be denatured, which reduces the overall rate of photosynthesis.
• Effect of temperature on rate of photosynthesis

  
• The intensity of the light available to the plant will depend on the amount of energy that it has to carry out photosynthesis. The more light a plant receives, the faster the rate of photosynthesis. This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply.
• Carbon dioxide is one of the raw materials required for photosynthesis. This means the more carbon dioxide that is present, the faster the reaction can occur. This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply.
• The number of chloroplasts (as they contain the pigment chlorophyll which absorbs light energy for photosynthesis) will affect the rate of photosynthesis. The more chloroplasts a plant has, the faster the rate of photosynthesis.
• The amount of chlorophyll can be affected by:

  • diseases (such as tobacco mosaic virus)
  • lack of nutrients (such as magnesium)
  • loss of leaves (fewer leaves means fewer chloroplasts)