Uses of glucose

Used for energy Energy may be released from glucose in the leaf. All cells need energy, which they obtain by the process of respiration. Some of the glucose which a leaf makes will be broken down by respiration, to release energy.

Stored as starch Glucose may be turned into starch and stored in the leaf. Glucose is a simple sugar. It is soluble in water, and quite a reactive substance. It is not, therefore, a very good storage molecule. Firstly, being reactive, it might get involved in chemical reactions where it is not wanted. Secondly, it would dissolve in the water in and around the plant cells, and might be lost from the cell. Thirdly, when dissolved, it would increase the concentration of the solution in the cell, which could cause damage.

The glucose is therefore converted into starch to be stored. Starch is a polysaccharide, made of many glucose molecules joined together. Being such a large molecule, it is not very reactive, and not very soluble. It can be made into granules which can be easily stored inside the chloroplasts.

Used to make proteins and other organic substances Glucose may be used to make other organic substances. The plantcan use glucose as a starting point for making all the other organic substances it needs. These include the carbohydrates sucrose and cellulose. Plants also make fats and oils.

Plants can also use the sugars they have made in the photosynthesis to make proteins. To do this, they need nitrogen. Unfortunately, even though the air around is 78% nitrogen, this is completely useless to plants because it is very unreactive. Plants have to be supplied with nitrogen in a more reactive form, usually as nitrate ions. They absorb nitrate ions from the soil, through their root hairs, by diffusion and active transport. The nitrate ions combine with glucose to make amino acids. The amino acids are then strung together to form protein molecules.

Another substance that plants make is chlorophyll. Once again, they need nitrogen to do this, and also another element - magnesium. The magnesium, like the nitrate ion, is obtained from the soil.

Changed to sucrose for transport A molecule has to be small and soluble to be transported easily. Glucose has both of these properties, but it is also rather reactive. It is therefore converted to the complex sugar sucrose to be transported to other parts of the plant. Sucrose molecules are also quite small and soluble, but less reactive than glucose. They dissolve in the sap in the phloem tubes, and can be distributed to whichever parts of the plant need them.

The sucrose may later be turned back into glucose again, to be broken down to release energy, or turned into starch and stored, or used to make other substances which are needed for growth.

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Uses of glucose.