Biology AQA B2 (2nd section)

this is the 2nd section of my revision cards

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  • Created by: alex
  • Created on: 20-12-09 00:01


carbon dioxide + water --------> glucose + oxygen

  • Photosynthesis produces GLUCOSE using sunlight
  • Photosynthesis happens inside the chloroplasts
  • Four things are needed for photosynthesis to occur:
    • Light - usually from the sun
    • Carbon Dioxide - enters the leaf from the air around it
    • Chlorophyll - the green substance found in chloroplasts
    • Water - comes from the soil, up the roots and stem and into the leaf
  • Leaves are also perfectly adapted because:
    • they have a big surface area for light to be collected on
    • they contain chlorophyll to absorb the light energy
    • they have air spaces which allow carbon dioxide to get to the cells, and oxygen to leave them
    • they have veins, which brings plenty of water to the cells
  • Oxygen is a by-product
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Limiting factors of photosynthesis

Not Enough light :

  • As the light level is raised, the rate of photosynethesis increases steadily
  • But at a certain point it wont make any difference because it would be depending on the other limiting factors
  • So not enough light means the rate of photosynthesis slows down

Too little carbon :

  • Slows down the rate of photosynthesis

Too much temperature:

  • Enzymes need temperature for photosynthesis to work
  • But when it gets to hot the enuzmes will become denatured (about 45 degrees)
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How plants use the Glucose

  • Respiration - the plants make glucose in their leaves
  • Making fruits - it is turned into sucrose for storing in fruits
  • Stored in Starch - it is stored in roots, stems and leaves ready for the winter. Starch is insoluble so it doesnt use osmosis like glucose would
  • Stored in seeds - It is turned into lipids
  • Making Proteins - glucose is combined with nitrates to make amino acids, which are then made into proteins
  • Making cell walls - it is converted into cellulose for making cell walls, especially in rapidly growing plants.
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Why they need the minerals

For Nitrates:

  • It is needed to make amino acids which are then made into protein
  • BUT a lack of nitrates means that the plant will have stunted growth

For Magnesium:

  • It is needed to make chlorophyll which is needed for photosynthesis
  • BUT a lack of magnesium means the leaves will turn yellow

Other problems can be caused by monoculture:

  • Monoculture is when a farmer just grows one type of crop for years, so the minerals are used up in the soil because the crops all need the same minerals
  • This may reduce yields and cause poor growth, so fertiliser is needed
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can you do the rest of B2... ive got retake on friday and only just started to revise!!!!

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