Revision cards for B2.2 Plants (AQA)

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Carbon dioxide + water -------> glucose + oxygen

Chlorophil absorbs energy from light - can absorb most colours except green so plant can photosyntheise in most daylight conditions

Sunlight is absorbed chlorophil - this provides energy which is used for respiration, growth and reproduction

Experiments to prove chlorophil is needed for phtosynthesis:

Take a variagated leaf, and test with iodine - starch is only found where the plant is green - starch is found where photosynthesis takes place - therfore shows that photosynthesis only takes place where chlorophil is found

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Leaf adaptations

Leaves are adapted in many ways:

  • Large surface area: bugger surface to absorb light
  • Green: contains chlorophyll needed for photosynthesis
  • Thin: gasses diffuse across the leaf faster
  • Pores: for gas exchange
  • Air spaces: lets the gasses through
  • Veins: carry water needed for photosynthesis

The part of the leaf are also adapted:

  • Waxy cuticle: waterproof to stop water loss
  • Palisade cells: close to the light and are tightly packed, all full of chloroplasts
  • Spongy layer: cells not tightly packed so there are air spaces to allow gasses in and out
  • Guard cells: open and close to control gas exchange
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Diagram of leaf structure

the cell includes: a waxt outer cuticle, the upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, stoma, and guard cells with chloroplasts  (

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Transport within a plant

Substances within the plant need to be transported around the plant

There are two separate transport systems:


  • Thin walls of living tissues
  • Transports sugar made in photosynthesis around the plant to growing or storage reasons


  • Thick, strong non-living cells
  • Transports water and minerals
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Limiting factors - temperature

Photosynthesis is effected by many factors, and if any one of these are in short supply, they become a limiting factor

Temperature: as photosynthesis involves enzymes, plants cannot photosynthesise at very low or very high temperatures

rate of photosynthesis plotted against temperature. the rate begins to slow as the temperature continues to increase (

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Limiting factors - light intensity and carbon diox

Light intensity: increasing the light intensity will increase the rate of photosynthesis, up to a point

Carbon dioxide: Even if there is sufficient light, the CO2 concentration need to be high in order for the plants to photosynthesise

 rate of photosynthesis plotted against light intensity. the rate begins to slow as the light intensity continues to increase ( of photosynthesis plotted against carbon dioxide concentration. the rate begins to slow as the carbon dioxide concentration continues to increase (

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The glucose made in photosynthesis is used in:

Respiration: Used immediately for respiration to provide energy to convert the rest of the glucose

Starch: stored in the insoluble form of starch (no osmotic effect unlike glucose), ready for when photosynthesis is not happening

Cellulose: to make plant walls, especially in fast growing plants

Nitrates: Combined with nitrates from the soil to make amino acids which then made proteins needed for growth

Lipids: for storage in seeds

DNA: used when the plant reproduces or repairs

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Plants get the minerals they need to grow from the soil:

  • Nitrates: make proteins for growth, deficiency = stunded growth
  • Magnesium: make chlorophil for photosynthesis, deficency= yellow leaves

Artifical minerals come from fertilisers and are used to replace the minerals the plants take away from the soil

  • Organic: help the soil structure, releases mineralls slowly (eg - manure)
  • Chemical: correct balance of minerals but can harm wildlife when they wash off the soil (eg - amonia nitrates)

Hydropinics: plants are grown without soil, in water with aditional minerals. This increases the growth rate and is helpful in places with bad soil

Crop rotation: different  crops are planted each year so onle minerals won't be compleatly depleated

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