photosynthesis continued

• Photosynthesis


  The process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar
• Importance of photosynthesis


  • Maintains the balance of carbon dioxide and oxygen in the atmosphere and water constant
  • Provides food for heterotrophic organisms
  • fats and proteins made from the sugars and starch produced during photosynthesis
  • Traps radiant energy and stores it as chemical energy during photosynthesis so that it can be released and used
• Factors that influence the rate of photosynthesis

  • Light intensity
  • Carbon dioxide level
  • Temperature
• Increase in light intensity

  Increases the rate of photosynthesis, but only to a certain point
• Carbon dioxide concentration becomes low


  Decreases the rate of photosynthesis
• Increase in carbon dioxide concentration

  Increases the rate of photosynthesis
• Temperatures that are too high or too low

  Inhibit the rate of photosynthesis
• At low temperatures


  Enzymes become inactive
• High temperatures


  Enzymes denature
• Greenhouse


  • Structure that has a glass or plastic roof and/or glass or plastic walls
  • Allows for the control of factors that influence the rate of photosynthesis to ensure maximum plant growth under ideal conditions
  • Maximises the yield of plants
• Managing conditions in greenhouses

  1. Controlling temperature

  2. Controlling light intensity

  3. Controlling carbon dioxide concentration

  4. Ensuring optimal water supply
• In an experiment, a plant is given everything that is needed for photosynthesis, including the factor that is going to be investigated
• In the control, the plant is given everything that is needed for photosynthesis, except the factor that is going to be investigated
• Practical investigation to test whether starch is produced during photosynthesis

  1. Place the leaf in boiling water for 10-30 seconds

  2. Place the leaf in ethanol (alcohol)

  3. Let the test tube stand in a beaker of boiling water (water bath) for about 3 hours
• Starch is stored in the light-independent (Calvin) cycle of photosynthesis
• light intensity:

  • increase in light intensity- increase in rate of photosynthesis, but only to a maximum level
  • if Light intensity becomes too high, stomata close and CO2 becomes a limiting factor
• carbon dioxide concentration :

  • decrease in CO2- decrease in rate of photosynthesis
• Temperature:

  • plants photosynthesise optimally at 25 degrees C
  • low temp, enzymes become inactive
  • high temp, enzymes denature
• Managing conditions in greenhouse: Temperature

  • important to regulate temperatures (thermostat used)
  • thermostat controls ventilation and heating
  • incoming light heats up interior of greenhouse
• Managing conditions in greenhouse: Light

  • translucent material gives even spread of light to all plants.
  • walls and roofs allow light intensity to be controlled
  • light meters used to measure light intensity
• Managing conditions in greenhouse: Carbon dioxide concentration

  • CO2 doesnt easily enter
  • during the day CO2 levels decrease due to photosynthesis
  • carbon dioxide levels raised by : adding sodium bicarbonate or organic material to soil and by pumping CO2 gas into the greenhouse from tanks