Photosynthesis and Rates

  • Created by: India.02
  • Created on: 01-05-19 18:35
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  • Photo-synthesis
    • Uses of Glucose
      • Respiration - transfers energy from glucose, which enables the plants to convert the rest of the glucose into other useful substances
      • Making cellulose - glucose converted into cellulose for making strong plant cell walls
      • Making amino acids - glucose combined with nitrate ions to make amino acids - then made into proteins
      • Stored as oils/fats - glucose turned into lipids for strong in seeds
      • Stored as starch - glucose turned into starch and stored in roots, stems and leaves, ready for use when photo-synthesis isn't happening
        • Starch is insoluble - better for storing than glucose - a cell with lots of glucose would take in lots of water and swell
    • Ideal Conditions
      • Greenhouses trap the sun's heat and makes sure that temperature isn't limiting - in winter a heater may be used to do this - in summer it may be too hot so shades and ventilators are used
      • Commercial farmers supply artificial light after the sun goes down to give the plants more quality photo-synthesis time
      • A way to increase carbon dioxide is by using a paraffin heater - as the paraffin burns it makes carbon dioxide as a by-product
      • Enclosure in a greenhouse keeps pests and diseases away from plants - fertilisers can be added to the soil as well for minerals
      • This costs money - if the crops are grown in the right conditions and they are healthy with a large yield, they can be sold
        • A farmer must supply the right amounts because providing too much leads to an unhealthy crop - this wastes money
    • Limiting Factors
      • Depends on time of time (light intensity) - season (temperature) - if it warm and bright enough, carbon dioxide is usually the limiting factor
      • Chlorophyll - amount can be affected by disease or environmental stress (lack of nutrients)
        • chloroplasts become damaged or don't make enough chlorophyll - rate of photo-synthesis is reduced because they can't absorb as much light
      • Light Intensity - as light intensity increases, the rate of photo-synthesis increases steadily - but only to a certain point
        • As it increase, the rate will no longer increase because either the temperature or the carbon dioxide level become a limiting factor
      • Carbon Dioxide - it is the same as light intensity but once the rate no longer increases, the limiting factors are temperature and light
        • As long as light and carbon dioxide are in plentiful supply, temperature will be the limiting factor
      • Temperature - if plant gets too hot, the enzymes needed for photo-synthesis will be damaged -  happens at 45 degrees
    • Graphs
      • If a graph shows two lines that level off at different points, you must see which factor was the limiting one
        • Lower carbon dioxide percentages usually level off first
        • Lower temperatures usually level off first
  • Photos-synthesis uses energy to change carbon dioxide and water into glucose and oxygen
    • Takes place in chloroplasts - green plant cells - contain pigments that absorb light
      • Energy transferred to the chloroplasts from the environment by light
    • An endothermic reaction - energy transferred to surroundings


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