What is Metabolism? Revision Notes | GCSE AQA Higher Biology

1. What Happens Inside Every Living Cell?

Right now, inside every cell in your body, thousands of chemical reactions are happening every second. Your cells are building proteins, breaking down food, making DNA, and powering muscle contractions. This non-stop chemical activity has a name: metabolism.

Think of your body like a busy factory that never shuts down. Raw materials come in, products get made, waste gets removed, and energy powers the whole operation. That's metabolism in action.

Trap: Many students think metabolism only means 'how fast you burn calories'. Actually, metabolism includes ALL chemical reactions - building molecules, breaking them down, and everything in between.

2. The Two Sides of Metabolism

Metabolism includes reactions that build larger molecules and reactions that break larger molecules down.

Here's the clever bit: the energy released by catabolic reactions powers the anabolic reactions. It's like using the heat from burning old wood to forge new metal tools.

3. Where Does the Energy Come From?

All these metabolic reactions need energy to happen. But where does this energy come from? The answer is respiration - the process that releases energy from glucose in every living cell.

Think of respiration as the power station of the cell. Glucose is the fuel, oxygen helps burn it efficiently, and the energy released powers all the metabolic 'machinery' in the cell.

The energy from respiration doesn't just disappear after one reaction. It gets transferred from reaction to reaction, powering the continuous enzyme-controlled processes that keep you alive.

4. Examples of Metabolic Processes

Let's see metabolism in action with some real examples you can relate to. These processes are happening in your body right now:

Anabolic examples: Building muscle proteins after exercise, making new DNA when cells divide, synthesising hormones like insulin, creating fat stores from excess glucose.

Catabolic examples: Digesting food into smaller molecules, breaking down glucose in respiration, recycling old cell components, converting fat back to glucose when you're hungry.

Notice how these processes are perfectly balanced. When you eat, anabolic reactions store energy. When you need energy, catabolic reactions release it. This balance keeps your metabolism running smoothly.

5. Why Enzymes Are Essential

Every single metabolic reaction is controlled by enzymes. Without enzymes, these reactions would be too slow to sustain life. Enzymes act like molecular machines, speeding up reactions by millions of times.

This is why body temperature matters so much. Enzymes work best at around 37°C. Too cold and metabolism slows down dangerously. Too hot and enzymes denature, stopping metabolism completely.

Each enzyme is highly specific - it only catalyses one particular reaction. Your body makes thousands of different enzymes to control all the different metabolic pathways.

6. Exam Technique - Getting Full Marks on Metabolism

Metabolism questions often appear in 6-mark extended response questions. Here's how to structure your answer for maximum marks:

Worked example: Worked Example: Applying What is Metabolism?

Use this method to answer an exam-style question about what happens inside every living cell?.

1. Underline the key term in the question and write a one-line definition linked to what is metabolism?. — This prevents vague answers and anchors the response in required terminology.
2. Describe the process in logical order using scientific vocabulary and direction words (increase/decrease, faster/slower). — Examiners award marks for clear causal chains, not isolated facts.
3. If data is provided, show each step of working and include units. — Method marks depend on visible working, even if the final answer is not fully correct.
4. Finish with a sentence explaining what the result shows about what is metabolism?. — Interpretation secures higher-band marks.

Answer: A complete response links mechanism, evidence, and conclusion for what is metabolism?.

Exam depth extension: In what is metabolism?, connect what happens inside every living cell? to the two sides of metabolism using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.

Common mistakes to avoid: Don't confuse metabolism with just 'burning calories'. Don't forget to mention enzymes. Don't say respiration 'is' metabolism - respiration provides energy FOR metabolism.