Uses of glucose from photosynthesis: The glucose produced in photosynthesis may be:

The idea

Photosynthesis in the chloroplasts of plant cells uses light energy to convert carbon dioxide and water into glucose and oxygen. The glucose formed is not simply stored unchanged; it is a versatile starting material that the plant can direct into several metabolic fates. It may be used immediately in respiration to release energy for cellular processes, converted into insoluble starch for storage in leaves, roots, tubers or seeds, combined with nitrate ions absorbed from the soil to make amino acids and then proteins, converted into lipids for storage in seeds, or used to build cellulose for cell walls. Some glucose may also form sucrose for transport in the phloem. The exact fate depends on the plant's needs, its stage of growth and environmental conditions. Understanding these options links photosynthesis to growth, storage and transport in plants.

What earns the marks

• Glucose can be broken down in respiration to release energy for the plant's metabolic processes.
• Glucose can be converted into insoluble starch, which is compact and osmotically inactive, making it suitable for storage in leaves, roots, tubers and seeds.
• Glucose can be combined with nitrate ions from the soil to form amino acids, which are then joined into proteins for growth and repair.
• Glucose can be converted into lipids, which are stored in seeds and used as an energy source during germination.
• Glucose can be used to synthesise cellulose, a structural carbohydrate that strengthens plant cell walls.
• Glucose may be converted into sucrose for transport through the phloem to non-photosynthetic tissues.

Common mistakes and how to put them right

• Thinking glucose is only stored as glucose.

  Put it right: Glucose is soluble and reactive, so plants usually convert it to starch, sucrose, lipids or other products.

• Confusing the gases involved in photosynthesis and respiration.

  Put it right: Photosynthesis uses carbon dioxide and produces oxygen, while aerobic respiration uses oxygen and produces carbon dioxide.

• Believing plants do not respire.

  Put it right: Plants respire continuously, using some of the glucose made in photosynthesis to release energy.

Exam tips

• Link each use of glucose to a clear purpose, such as energy release, storage, growth or structural support.
• Use precise terms such as insoluble starch, nitrate ions, amino acids, lipids and cellulose rather than vague words like 'food' or 'sugar'.
• When a question asks for multiple uses, give distinct fates of glucose rather than repeating the same idea in different words.