Aerobic and Anaerobic Respiration Worksheet GCSE - Free Printable

Here is the complete solution to the “Aerobic and Anaerobic Respiration” worksheet, based on standard GCSE Biology knowledge. I’ll solve each section step-by-step with explanations.

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## ✔ Launch Section

1) Match each chemical substance to its correct formula.

This is a straightforward matching task:

- Glucose → C₆H₁₂O₆
- Oxygen → O₂
- Carbon dioxide → CO₂
- Water → H₂O

✔ *Explanation:* These are the standard chemical formulas for the key molecules involved in respiration.

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2) Complete the equation for aerobic respiration.

#### Word Equation:
> Glucose + Oxygen → Carbon dioxide + Water

✔ *Explanation:* Aerobic respiration uses glucose and oxygen to produce carbon dioxide, water, and energy.

#### Balanced Chemical Equation:
> C₆H₁₂O₂ + 6 O₂ → 6 CO₂ + 6 H₂O

✔ *Explanation:* The balanced equation must have equal numbers of atoms on both sides.
- Left: 6 C, 12 H, 18 O (6 from glucose + 12 from O₂)
- Right: 6 C (from 6 CO₂), 12 H (from 6 H₂O), 18 O (12 from CO₂ + 6 from H₂O)

*(Note: There’s a typo in the worksheet — it says “C₆H₁₂O₂” but should be “C₆H₁₂O₆”. We’ll assume it’s a printing error and use the correct formula.)*

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## ✔ Main Stage Section

1a) Word equation for anaerobic respiration in muscles:

> Glucose → Lactic acid + Energy

✔ *Explanation:* When muscles work hard and oxygen is low, they respire anaerobically to make lactic acid and a small amount of ATP.

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1b) Word equation for anaerobic respiration in yeast:

> Glucose → Ethanol + Carbon dioxide + Energy

✔ *Explanation:* Yeast performs alcoholic fermentation under anaerobic conditions, producing ethanol and CO₂ — this is what makes bread rise and beer/alcohol ferment.

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Choose the correct option to complete the sentences:

✔️ Respiration is an exothermic process.
→ *It releases energy as heat.*

✔️ Respiration/breathing is ventilation.
→ *Actually, this is misleading. Breathing = ventilation (gas exchange). Respiration = cellular process making ATP. But in many curricula, “respiration” is loosely used for breathing. If forced to choose, “breathing” is ventilation. However, the sentence is poorly worded. Best answer: Breathing is ventilation.*

✔️ Aerobic respiration is the oxidation of glucose to produce energy.
→ *Correct — glucose is oxidized (loses electrons/hydrogen) to release energy.*

✔️ Anaerobic respiration in muscles/fungi produces lactic acid.
→ *Partially true — muscles do; fungi (like yeast) produce ethanol, not lactic acid. So this is incorrect if “fungi” is included. Better: “in muscles” only.*

⚠️ *Correction needed:*
The statement should say: “Anaerobic respiration in muscles produces lactic acid.” Fungi/yeast produce ethanol.

✔️ In anaerobic respiration, the glucose is only partially broken down.
→ *True — unlike aerobic respiration, which fully breaks glucose into CO₂ and H₂O, anaerobic stops at lactic acid or ethanol.*

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2) Tick (√) the correct column for each statement:

| Statement | Aerobic Respiration | Anaerobic Respiration |
|--------------------------------------------|---------------------|------------------------|
| Oxygen is needed | ✓ | |
| Small amount of energy released per molecule of glucose | | ✓ |
| Can sometimes produce ethanol | | ✓ (yeast) |
| Occurs in the mitochondria of cells | ✓ | |
| Glucose is completely oxidised | ✓ | |

✔ *Explanations:*
- Oxygen needed? Only aerobic.
- Small energy? Anaerobic yields ~2 ATP vs ~36 ATP in aerobic.
- Ethanol? Only yeast/anaerobic in plants/fungi.
- Mitochondria? Aerobic occurs here; anaerobic starts in cytoplasm.
- Complete oxidation? Only aerobic breaks glucose fully to CO₂ + H₂O.

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3) Henry is baking bread. He forgets to add yeast to the dough. The dough does not rise. Explain fully why yeast is important to make the dough rise.

> Yeast carries out anaerobic respiration (fermentation) in the absence of oxygen. During this process, it breaks down glucose in the dough to produce ethanol and carbon dioxide gas. The carbon dioxide gas gets trapped in the dough, forming bubbles that cause the dough to rise. Without yeast, no CO₂ is produced, so the dough remains flat and dense.

✔ *Bonus:* The ethanol evaporates during baking, leaving behind the light, airy texture of bread.

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## 📝 Final Answer Summary (for easy copying):

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Launch

1) Matching:
- Glucose → C₆H₁₂O₆
- Oxygen → O₂
- Carbon dioxide → CO₂
- Water → H₂O

2) Equations:
- Word: Glucose + Oxygen → Carbon dioxide + Water
- Balanced: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O

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Main Stage

1a) Muscles: Glucose → Lactic acid + Energy
1b) Yeast: Glucose → Ethanol + Carbon dioxide + Energy

Sentences:
- Respiration is an exothermic process.
- Breathing is ventilation.
- Aerobic respiration is the oxidation of glucose...
- Anaerobic respiration in muscles produces lactic acid. *(not fungi)*
- In anaerobic respiration, glucose is only partially broken down.

2) Table:

| Statement | Aerobic | Anaerobic |
|--------------------------------------------|---------|----------|
| Oxygen is needed | ✓ | |
| Small amount of energy... | | ✓ |
| Can sometimes produce ethanol | | ✓ |
| Occurs in mitochondria | ✓ | |
| Glucose is completely oxidised | ✓ | |

3) Explanation:
> Yeast performs anaerobic respiration, producing carbon dioxide gas. This gas gets trapped in the dough, causing it to rise. Without yeast, no gas is produced, so the dough doesn’t rise.

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