B8 - photosynthesis

• The process of photosynthesis, carried out by plants and algae Is at the foot of every food chain. It captures light energy from the sun and redistributes it to chemical potential energy - we can make use of chemical potential energy. Since photosynthesis involves the transfer of light energy to chemical potential energy in cells, its an endothermic reaction:

  
• photosynthesis occurs in the chloroplasts of plant cells. simple molecules like CO2 and water can’t be used as food. however, glucose and other more complex molecules can - so you can think of photosynthesis as a reaction that produces food.
• the glucose produced in photosynthesis can be:

  • used in respiration in the cells of the plant/algae
  • converted into starch for storage. starch is good for storage as its insoluble - doesn’t affect the osmosis occurring in the plant, unlike glucose
  • used to produce fats or oils (lipids) for storage
  • used to produce cellulose - component of the cell wall - strengthens the cell wall
  • used to produce amino acids, which in turn are used to synthesise proteins (in ribosomes). to produce amino acids, plants also require nitrates from the soil
• simple lab tests can be used to identify starch, glucose and protein:

  • starch - turns iodine a blue-black colour
  • glucose - turns Benedict’s solution orange-red when heated with it
  • proteins - turns biruet’s reagent purple
• what is photosynthesis?

  The endothermic reaction that transfers light energy to chemical potential energy. In it, simple molecules (CO2 and water) are converted into more complex molecules (glucose) that can be used for food
• what are nitrates?

  ions containing nitrogen and oxygen - found in the soil (plants need nitrates to produce amino acids)
• Factors affecting the rate of photosynthesis

  • Temperature
  • CO2 concentration
  • Light intensity
  • Amount of chlorophyll
• Temperature

  All chemical reactions speed up as the temperature increases. However, as photosynthesis is controlled by enzymes, too high a temperature prevents photosynthesis
• CO2 concentration

  The higher the concentration in the air, the more is available for photosynthesis - rate of photosynthesis increases
• Light intensity

  Higher the light intensity, higher the rate of photosynthesis
• Amount of chlorophyll

  More chlorophyll means more light absorbed. Some leaves have pale parts due to a lack of chlorophyll. The rate of photosynthesis is much lower in pale parts compared to the deep green parts