GCSE Biology  - Plants

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  • Chloroplasts absorb light energy used for photosynthesis
  • Plants use the light energy to react carbon dioxide with water to make glucose
  • Glucose is used in respiration or converted to starch and stored
  • Oxygen is a by-product

Photosynthesis - a process where green plants use water and carbon dioxide and sunlight to produce carbohydrates and release oxygen. It is a chemical change which happens in the leaves of green plants.

The conversion of carbon dioxide and water to glucose and oxygen requires energy which is aquired from the sun by the chlorophyll.

carbon dioxide + water (+ light energy) ---> glucose + oxygen

Light energy is in brackets because it is not a substance

Plants absorb water through their roots and carbon dioxide through their leaves

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If some of the glucose is turned into insoluable starch, it can be turned back into glucose later and used in repiration.

Limiting Factors: Light intensity, carbon dioxide, temperature

Light intensity: without light, plants cannot photosynthesise very quickly

Carbon dioxide concentration: a plannt cannot photosynthesise very quickly with an insufficient carbon dioxide concentration

Temperature: The rate of photosynthesis will decrease if it gets too hot or too cold

Farmers use their knowledge of limiting factors to increase crop growth by artificial means

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Nitrates - needed for making amino acids which are needed to make protein.

Defficient in nitrates - it will suffer from stunted growth

Magnesium - for making chlorophyll

Defficient in magnesium - its leaved will turn yellow

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