Biology AQA B2 (2nd section)

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

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)

• 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.

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