AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Metabolism includes: • conversion of glucose to starch, glycogen and…
Full specification wording
Metabolism: Metabolism includes: • conversion of glucose to starch, glycogen and cellulose • the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids • the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins • respiration • breakdown of excess proteins to form urea for excretion.
Metabolism is the sum of all chemical reactions in a cell or organism.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 4 of 4
Study notes
From the checked teaching notes for this specification point.
The idea
Metabolism is the sum of all chemical reactions in a cell or organism. It includes building large molecules from smaller ones and breaking large molecules down. Glucose can be converted into starch for storage in plants, glycogen for storage in animals and fungi, or cellulose for plant cell walls. Lipids are formed when one glycerol molecule joins with three fatty acid molecules. Amino acids are made from glucose and nitrate ions in plants; amino acids then join to synthesise proteins. Respiration releases energy from glucose and is also part of metabolism. If an animal has excess protein, the amino group is removed and converted to urea in the liver, then excreted by the kidneys.
What earns the marks
- Define metabolism as the sum of all chemical reactions in a cell or organism, including both synthesis and breakdown reactions.
- State that glucose is converted to starch in plants, glycogen in animals and fungi, and cellulose in plant cell walls.
- Describe lipid formation as one glycerol molecule combining with three fatty acid molecules.
- Explain that plants use glucose and nitrate ions to form amino acids, which are then joined to synthesise proteins.
- Recognise respiration as a metabolic process that releases energy from glucose.
- Describe the breakdown of excess proteins to form urea, which is excreted, and identify the liver as the organ where urea is formed.
Common mistakes and how to put them right
Thinking metabolism only means breaking down molecules.
Put it right: It also includes synthesis reactions such as building starch, glycogen, cellulose, lipids and proteins.
Confusing glycogen and starch.
Put it right: Glycogen is the storage carbohydrate in animals and fungi, while starch is the storage carbohydrate in plants.
Stating that lipids are made from glycerol and fatty acids in a one-to-one ratio.
Put it right: One glycerol molecule combines with three fatty acid molecules.
Exam tips
- Use the phrase 'sum of all chemical reactions' when defining metabolism to show the full meaning.
- When asked about protein breakdown, name both the product urea and the organ where it is formed, the liver.
- Link each metabolic reaction to its location or organism, for example cellulose in plant cell walls and glycogen in animal cells.
Try the lesson
The start of the Metabolism: Metabolism includes: • conversion of glucose to starch, glycogen and cellulose • the formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids • the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins • respiration • breakdown of excess proteins to form urea for excretion. lesson, made from checked teaching notes for this specification point.
Have a go first
Which polysaccharide is formed from glucose for storage in plant cells?
Listen
Metabolism is the sum of all chemical reactions in a cell or organism. It includes building large molecules from smaller ones and breaking large molecules down. Glucose can be converted into starch for storage in plants, glycogen for storage in animals and fungi, or cellulose for plant cell walls. Lipids are formed when one glycerol molecule joins with three fatty acid molecules. Amino acids are made from glucose and nitrate ions in plants; amino acids then join to synthesise proteins. Respiration releases energy from glucose and is also part of metabolism. If an animal has excess protein, the amino group is removed and converted to urea in the liver, then excreted by the kidneys. A strong answer earns marks for these points. Define metabolism as the sum of all chemical reactions in a cell or organism, including both synthesis and breakdown reactions. State that glucose is converted to starch in plants, glycogen in animals and fungi, and cellulose in plant cell walls. Describe lipid formation as one glycerol molecule combining with three fatty acid molecules. Explain that plants use glucose and nitrate ions to form amino acids, which are then joined to synthesise proteins. Exam tip: Use the phrase 'sum of all chemical reactions' when defining metabolism to show the full meaning.
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