Metabolism
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of aerobic respiration.
What is the main purpose of aerobic respiration?
To release energy for the cell to use.
Name one process in the body that requires energy.
Muscle contraction / active transport / protein synthesis.
Which organelle carries out aerobic respiration in cells?
The mitochondria.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains metabolism, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
What is Metabolism?
Metabolism is the sum of all the chemical reactions that happen inside a cell or a living organism. These reactions keep the organism alive and functioning.
What is Metabolic Rate?
Metabolic rate is the speed at which these chemical reactions happen in the body. It can be affected by:
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Age (metabolic rate decreases with age).
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Gender (men tend to have a higher metabolic rate than women as they tend to have more muscle compared to fat. They also have higher levels of testosterone).
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Exercise level (regular exercise helps build muscle).
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Genetics (Some people are born with naturally faster or slower metabolisms).
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Proportion of muscle to fat (individuals with more muscle have a higher metabolic rate).
Why Is Energy From Respiration Important?
The energy released by aerobic respiration is used to drive metabolic reactions. This includes:
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Building larger molecules from smaller ones, such as building proteins from amino acids.
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Breaking down molecules to release energy or recycle materials.
Examples of Metabolic Reactions
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Reaction Type |
Example |
|---|---|
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Anabolic (building up) |
Glucose → starch (in plants only) |
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Glucose + nitrates → amino acids → proteins |
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Glycerol + fatty acids → lipids |
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Formation of glycogen from glucose (in animals only) |
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Catabolic (breaking down) |
Breakdown of excess proteins in the liver into urea (in animals only) |
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Breakdown of glucose in respiration |
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Breakdown of lipids for energy |
Key Terms
- Metabolism -The sum of all chemical reactions in a cell or in the body.
- Metabolic rate - The speed at which chemical reactions take place in the body / in a cell.
- Anabolic reaction - Reaction that builds larger molecules from smaller ones.
- Catabolic reaction - Reaction that breaks down larger molecules.
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Exam Tip
Learn some examples of metabolic reactions. Easy ones to remember are- respiration and protein synthesis (occur in all living things), making starch in plants and making glycogen in animals.
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Practice Question
Define metabolism and give two examples of metabolic reactions. (3 marks)
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Metabolism is the sum of all chemical reactions that happen in the body (1)
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An example is the conversion of glucose to glycogen in liver and muscle cells (1)
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Another example is protein synthesis (making proteins from amino acids) (1)
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!