GCSE AQA Biology 2 Plants & Photosynthesis

Plant tissues & organs
1. Organs in a plant...
  1. Stem
  2. Roots
  3. Leaves
2. Tissues in a leaf...
  1. Mesophyll - where most of photosynthesis happens
  2. Xylem & phloem - transport water, mineral ions & sucrose
  3. Epidermal - covers the plant
Photosynthesis equation
How photosynthesis works
1. Photosynthesis produces 'food' - glucose
2. Happens inside chloroplasts
  1. Chloroplasts contain chlorophyll which absorbs sunlight & uses its energy to...
    1. Convert carbon dioxide and water into glucose, oxygen is produced as by-product
3. Happens in the leaves of all green plants
The rate of photosynthesis
1. Affected by 3 factors...
  1. Light
    Anmerkungen:
    - Provides energy needed for photosynthesis
    1. Too little slows down rate
    2. As light level increased, rate increases steadily up to certain point
      1. Past that point, increasing light levels further won't make any difference
        Anmerkungen:
        Carbon dioxide or temperature has become a limiting factor
  2. Carbon dioxide
    Anmerkungen:
    - One of the raw materials needed for photosynthesis
    1. Too little slows down rate
    2. Increasing levels will only increase rate up to certain point
      1. After that, carbon dioxide is no longer limiting factor
  3. Temperature
    Anmerkungen:
    - Has to be right
    1. If temp. is limiting - usually because too low
      1. Enzymes needed work more slowly at lower temp.
    2. If plant is too hot - enzymes denatured
      Anmerkungen:
      - Happens at about 45 degrees C
Creating the ideal conditions for growing crops in a greenhouse
1. Heat
  1. Greenhouses trap Sun's heat - temp. isn't limiting
  2. In winter, farmers might use heaters
  3. In summer, farmers might use shades and ventilation
2. Light
  1. Supply artificial light at night
3. Carbon dioxide
  1. Use paraffin heaters to heat greenhouse - makes carbon dioxide as by-product
4. Pests & diseases
  1. Keeping plants enclosed makes it easier to keep them free from pests & diseases
  2. Can add fertilisers to soil to provide minerals
How plants use glucose
1. For respiration
  1. Releases energy enabling plant to convert rest of glucose into other useful substances
    1. Need minerals from soil as well
2. Making cell walls
  1. Glucose converted into cellulose for making strong cell walls
    1. Especially in rapidly growing plant
3. Making proteins
  1. Glucose combined with nitrate ions (from soil) to make amino acids which are made into proteins
4. Storing in seeds
  1. Glucose turned into lipids for storing in seeds
5. Storing as starch
  1. Glucose turned into starch & stored in roots, stems & leaves for when photosynthesis isn't happening
    1. Starch is insoluble - better for storing than glucose

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GCSE AQA Biology 2 Plants & Photosynthesis

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