B4 - Photosynthesis

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  • Created by: Naomi
  • Created on: 20-01-13 13:57
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  • Photosynthesis
    • Carbon Dioxide + Water ---> Glucose + Oxygen
      • Glucose can be:
        • Converted into cellulose (for cell walls)
        • Used in respiration (to get energy)
        • Converted into proteins (for growth and repair)
        • Converted into starch, fats and oils (for storage)
          • Starch is not used for storage because it is insoluable and does not move from storage areas.
            • Unlike glucose it does not affect the water concentration of cells and cause osmosis
    • Historical understanding of Photosynthesis
      • Greek scientists believed that plants took minerals out of the soil to grow and gain mass
        • Van Helmot concluded from his experiment on a willow tree that plant growth must depend on something else as well as minerals
      • Priestley's experiment showed that plants produce oxygen
    • Photosynthesis is a 2 STAGE PROCESS
      • Water is split up by light energy, releasing oxygen and hydrogen ions
        • Carbon dioxide combines with hydrogen ions producing glucose
      • Carbon Dioxide + Water ---> Glucose + Oxygen
        • Glucose can be:
          • Converted into cellulose (for cell walls)
          • Used in respiration (to get energy)
          • Converted into proteins (for growth and repair)
          • Converted into starch, fats and oils (for storage)
            • Starch is not used for storage because it is insoluable and does not move from storage areas.
              • Unlike glucose it does not affect the water concentration of cells and cause osmosis
    • The rate of photosynthesis can be increased by the plant having:
      • More light
      • More Carbon Dioxide
      • Higher temperature, which increases enzyme action
      • Since photosynthesis depends on light, temperature and carbon dioxide a lack of one of these factors will limit the rate of photosynthesis
        • Called limiting factors
    • Leaves are adapted for efficient photosynthesis
      • The upper epidermis is transparent, so does not block out any light
      • The upper palisade layer contains lots of chloroplasts as they will receive most of the light
      • The spongy mesophyll cells are loosly spaced so diffusion of gases between the cells and outside atmosphere can take place
        • The arrangement of mesophyll cells creates a large survace area:volume ratio so that large amounts of gases can enter and exit the cells
      • Leaves are broad so that they have a large surface area
      • Leaves are thin so gases can diffuse through easily and light can get to all cells
      • They contain many pigments (chlorophyll a and b, carotene and xanthophylls) so the plant cells can maximise the use of the suns energy as they all absorb light of different wavelengths
      • Have a network of vascular bundles (veins) for support and transport of chemicals such as water and glucose
      • Have specialised guard cells which control the opening and closing of stomata, regulating the flow of carbon dioxide and oxygen as well as water loss

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