3.8: Photosynthesis

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  1. Define photosynthesis.
    Photosynthesis is the conversion of light energy to chemical energy, e.g. stored in glucose and/or other organic compounds.
  2. Identify the range of colours that make up the visible spectrum and the range of wavelengths in light.
    Visible light extends from wavelengths of 400 nm (violet light) to 700 nm (red light), the range of colours are - red, orange, yellow, green, blue, indigo, violet (GOYGBIV). Some have deleted indigo as one of the colours.
  3. Identify the main photosynthetic pigment.
    Chlorophyll is the main synthetic pigment. It is a green pigment located within chloroplasts of plants. Chlorophyll a is directly involved in the light reaction which converts light energy from the sun to chemical energy.
  4. What is the absorption spectrum?
    The absorption spectrum is the range of wavelengths of light that can be absorbed by a particular pigment.
  5. Identify the three pigments in a chloroplast.
    A chloroplast contains the pigments - chlorophyll a, chlorophyll b and carotenoids.
  6. Outline photolysis.
    Photolysis is the process wehre light splits water in photosynthesis. It is a part of the first stage of photosynthesis. Light energy trapped by chlorophyll is used to split water into hydrogen ions and electrons (to reduce NADP to NADPH) and the by=product - oxygen gas.
  7. Outline carbon fixation.
    Carbon fixation involves hydrogen being added to carbon dioxide to form an organic molecule. The hydrogen ions and ATP needed for the reaction are supplied by the light-dependent stage.
  8. Outline what happens in photosynthesis.
    Light energy is trapped by chlorophyll and with the assistance of enzymes the energy is used to split water into hydrogen and oxygen. The oxygen forms oxygen gas. The hydrogen is added to NADP to form NADPH while energy is absorbed by ADP and P to form ATP. In the last stage the H from NADPH is added to carbon dioxide to form a sugar.
  9. Explain each of the three ways of measuring the rate of photosynthesis.
    • Production of oxygen: Pond weed is placed in a filter funnel in a beaker of water and left in sunlight. Bubbles of oxygen gas are observed rising in the test tube. The amount of oxygen gas produced in the given time shows the rate of photosynthesis.
    • Uptake of Carbon Dioxide: A potted plant is placed in a bell jar and the available carbon dioxde gas is measured before and after thee experiment. The amount of carbon dioxide used in the given time shows the rate of photosynthesis. 
    • Increase in biomass: The rate of photosynthesis cannot be directly measured using biomass. Biomass needs to be measured after dehydrating the plant. An indirect measurement can be inferred by the change in weight of a seedling.
  10. Identify the conditions needed for photosynthesis to occur.
    For photosynthesis to occur, there needs to be a supply of oxygen, water, the presence of chlorophyll and light and a suitable temperature.
  11. Outline how temperature influences photosynthesis.
    Photosynthesis is controlled by enzymes. Each enzyme has an optimal temperature. The rate of reaction will increase with increased temperature until the optimal temperature. Above the optimal temperature enzymes will denature and the reactions will stop.
  12. Outline how light intensity influences photosynthesis.
    Plants need light for photosynthesis. As light intensity increases, the rate of photosynthesis increases until other limiting factors restrict the rate, e.g. number of chloroplasts, amount of carbon dioxide available.
  13. Outline how carbon dioxide concentration influences photosynthesis.
    Plants need carbon dioxide for photosynthesis. As carbon dioxide concentration increases, the rate of photosynthesis increases until other limiting factors restrict the rate, e.g. number of chloroplasts, light intensity.

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3.8: Photosynthesis
2013-12-24 03:29:34

3.8: Photosynthesis
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