Uses of Glucose in Plants
Master Uses of Glucose in Plants for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Glucose made in photosynthesis is used in respiration or converted into starch, cellulose, proteins and fats or oils.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The glucose made in photosynthesis is used by the plant in five ways, and these are worth learning as a set.
Most is used immediately for respiration, releasing energy. Some is converted into insoluble starch for storage — insoluble because a soluble store would affect osmosis and draw water into the cell.
Glucose is also converted into cellulose to strengthen cell walls, into lipids for storage in seeds, and combined with nitrate ions absorbed from the soil to make amino acids, which are then used for protein synthesis.
Revision notes
Respiration and storage
Most glucose is used straight away in respiration to release energy.
Some is converted to starch for storage. Starch is insoluble, which matters because a soluble store would lower the water potential of the cell and draw water in by osmosis.
Structural and long-term storage uses
Glucose is converted into cellulose, which strengthens plant cell walls.
It is also converted into lipids, which are used as an energy store, particularly in seeds where a compact, energy-dense store is valuable.
Making proteins
Glucose is combined with nitrate ions absorbed from the soil to produce amino acids.
Those amino acids are then used for protein synthesis. This is why a plant short of nitrate shows stunted growth.
Key points
- Most glucose is used for respiration.
- Glucose is converted to insoluble starch for storage.
- Starch is insoluble so it does not affect osmosis.
- Glucose is converted to cellulose for cell walls.
- Glucose is converted to lipids for storage in seeds.
- Glucose plus nitrate ions makes amino acids for proteins.
Worked examples
Example 1
Name three uses of the glucose produced in photosynthesis. [3 marks]
Model answer
Respiration to release energy (1 mark). Conversion to starch for storage (1 mark). Conversion to cellulose to strengthen cell walls (1 mark).
Example 2
Explain why glucose is stored as insoluble starch rather than as soluble glucose. [2 marks]
Model answer
Starch is insoluble so it does not affect the water potential of the cell (1 mark), whereas storing soluble glucose would draw water into the cell by osmosis and could damage it (1 mark).
Example 3
Explain how a plant uses glucose to make proteins. [2 marks]
Model answer
Glucose is combined with nitrate ions absorbed from the soil to produce amino acids (1 mark), and these amino acids are then joined together in protein synthesis (1 mark).
Common mistakes
Saying glucose is stored as glucose.
It is converted to starch, because starch is insoluble.
Forgetting the osmosis reason.
The insolubility of starch is what prevents water being drawn into the cell.
Saying plants make protein directly from glucose.
Nitrate ions are also needed to form amino acids first.
Confusing cellulose with starch.
Cellulose strengthens cell walls; starch is the storage carbohydrate.
Exam tips
- Learn the five uses as a single list.
- Give the osmosis reason when explaining why starch is used for storage.
- Mention nitrate ions whenever protein synthesis is asked about.
- Keep cellulose and starch clearly distinct.
Key terms
- Starch
- The insoluble carbohydrate plants use to store glucose.
- Cellulose
- The carbohydrate that strengthens plant cell walls.
- Amino acid
- The unit from which proteins are built.
- Nitrate ion
- An ion absorbed from soil, needed to make amino acids.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.