Read any respiration equation in three parts: what goes in, what comes out, and what the released energy is used for. Energy is released from glucose, not created.
This lesson follows comparing aerobic and anaerobic respiration in the SPM Biology cellular respiration chapter.
How do you read an equation in three parts?
For glucose + oxygen → carbon dioxide + water + energy, split the reading:
| Part | In the equation | What to say |
|---|---|---|
| In | Glucose and oxygen | The substrate and the gas the cell takes up |
| Out | Carbon dioxide and water | Waste products that leave the cell |
| Energy | Energy | Released from the chemical bonds of glucose |
Keep the three parts separate in your answer.
Worked example: why a germinating seed warms up
A flask of germinating bean seeds feels slightly warm after two days. A student asks why.
- The seeds use stored food, which contains glucose, as the substrate.
- The cells respire aerobically, using oxygen and releasing carbon dioxide and water.
- The energy released is used for growth. Some of it is also given out as heat.
- The heat raises the temperature of the flask, so it feels warm.
The answer names the substrate, says the energy is released, and explains where the warmth comes from.
The mistake that costs marks
The common slip is to say that “respiration produces energy”. Energy cannot be created. The correct wording is “energy is released from glucose”.
| Wrong | Right | |
|---|---|---|
| Energy | Respiration produces energy | Respiration releases energy from glucose |
| Oxygen | Product | Reactant, used up |
| Carbon dioxide | Reactant | Product, leaves the cell |
A second slip is to swap the sides of the equation. Before writing, say aloud: “glucose and oxygen go in”.
What does the energy do in the cell?
The released energy is used for:
- muscle contraction
- active transport across membranes
- building large molecules such as proteins
- growth and repair
Name at least one use when a question asks “why is respiration important?”.
Check yourself
Yeast in a sugar solution respires anaerobically. State the substrate, the products, and why less energy is released than in aerobic respiration.
Answer
The substrate is glucose. The products are ethanol and carbon dioxide.
Less energy is released because the glucose is only partly broken down. Some energy is still stored in the ethanol.
What to study next
Put these ideas to work on real results in interpreting respiration investigation data. The biological data interpretation trainer builds that skill, and the mistake log and paper-error review records slips.
If you would like a teacher to go through your explanations, see online one-to-one Biology tuition.