Photosynthesis

Green plants absorb light energy using chlorophyll in their leaves.They use it to react carbon dioxide with water to make a sugar called glucose.The glucose is used in respiration, or converted into starch and stored.Oxygen is produced as a by-product.This process is called photosynthesis.Temperature, carbon dioxide concentration and light intensity are factors that can limit the rate of photosynthesis.

Photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.

During photosynthesis: Light energy is absorbed by chlorophyll, a green substance found inchloroplasts in some plant cells and algae Absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose Oxygen is released as a by-product

This equation summarises what happens in photosynthesis:

Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration.

Factors limiting photosynthesis Three factors can limit the speed of photosynthesis: light intensity, carbon dioxide concentration and temperature.

Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.If you plot the rate of photosynthesis against the levels of these three limiting factors, you get graphs like the ones above.In practice, any one of these factors could limit the rate of photosynthesis.

Economics of greenhouses Farmers can use their knowledge of factors limiting the rate of photosynthesis to increase crop yields.This is particularly true in greenhouses, where the conditions are more easily controlled than in the open air outside: The use of artificial light allows photosynthesis to continue beyond daylight hours. Bright lights also provide a higher-than-normal light intensity. The use of artificial heating allows photosynthesis to continue at an increased rate. The use of additional carbon dioxide released into the atmosphere inside the greenhouse also allows photosynthesis to continue at an increased rate.

However, the additional cost of providing extra lighting, heat and carbon dioxide has to be weighed against the increased crop yield and the extra income it will provide. The cost of should not exceed the additional income it generates for the farmer.In practice, the farmer will need to find the optimum growing conditions for the crop, given the costs of providing extra lighting, heat and carbon dioxide.Paraffin lamps have traditionally been used in greenhouses. Their use increases the rate of photosynthesis because as well as the light generated from the lamps, the burning paraffin produces heat and carbon dioxide too.

Storage and use of glucose The glucose produced in photosynthesis may be used in various ways by plants and algae. Storage Glucose is needed by cells for respiration. However, it is not produced at night when it is too dark for photosynthesis to happen. Plants and algae store glucose as insoluble products. These include: Starch Fats and oils

Use Some glucose is used for respiration to release energy. Some is used to produce: Cellulose - which strengthens the cell wall Proteins - such as enzymes and chlorophyll Plants also need nitrates to make proteins. These are absorbed from the soil as nitrate ions.

Photosynthesis

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Economics of greenhouses

Storage and use of Glucose