Lesson 5

Lesson 5: Anaerobic Respiration

Respiration Without Oxygen — Animals & Yeast

🏃🥵🍺🍞⚗️

Learning Objectives:

Recall (2.37) – Last lesson: the aerobic equation needs oxygen and makes lots of ATP.
2.38 – Know the word equations for anaerobic respiration in animals and in yeast/plants.

🏆 By the end I will be able to…

All: write the anaerobic equation in animals: Glucose → Lactic Acid.

Most: write the anaerobic equation in yeast: Glucose → Ethanol + Carbon Dioxide.

Some: compare aerobic and anaerobic respiration (oxygen, ATP yield, products).

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Teacher Print Tools – Lesson 5

⏱️ Before We Start · 60 sec

Before We Start: What You Already Know (from L4)

Quick recall, not new content. Last lesson you learned aerobic respiration. Today is the same idea with one thing taken away — oxygen. (It's all on Side A of your bridge sheet if you want it on paper.)

With oxygen vs without oxygen

Same fuel (glucose). Take away oxygen → different waste products and far less ATP.

1. Respiration releases energy from glucose to make ATP — inside your cells (it is not breathing).

2. Aerobic = with oxygen → lots of ATP. You met this in L4.

3. Anaerobic = without oxygen → only a little ATP. That is today.

Hook: a sprinter runs so hard they can't get oxygen fast enough. So what happens inside the muscle then? 👀

Whiteboards — 20 seconds: finish this sentence — "Anaerobic respiration is respiration without ____, and it releases ____ ATP than aerobic." Then we go straight in.

⭐ Fab 4

The Fab 4 – Recall to Get You Started

Instructions: Answer in your books from memory. Q1–3 recall previous lessons. Q4 leads into today.

⭐ The Fab 4 — Quick-Fire Recall

Four to warm up the brain — recall from last lesson (Aerobic Equations). Try all 4 before the reveal!

1. Which gas does aerobic respiration need?

Oxygen

2. Name the two products of aerobic respiration.

Carbon dioxide + water

3. Does aerobic make a lot or a little ATP?

A lot

4. What if a cell runs OUT of oxygen?

It must respire anaerobically

1. Reactants (Recall)

Name the two reactants of aerobic respiration.

Glucose and oxygen.

2. Products (Recall)

Name the two products of aerobic respiration.

Carbon dioxide and water.

3. Oxygen (Recall)

Aerobic respiration needs which gas?

Oxygen.

4. Lead-in: No Oxygen

A sprinter's muscles run out of oxygen. They keep going for a few seconds. How might they still get some energy?

By respiring without oxygen (anaerobically).

1. Word Equation (Recall)

Write the word equation for aerobic respiration.

Glucose + Oxygen → Carbon Dioxide + Water

2. ATP Yield (Recall)

Why does aerobic respiration release so much ATP?

Oxygen lets glucose be broken down completely, releasing almost all the energy.

3. Symbol Equation (Recall)

Write the balanced symbol equation for aerobic respiration.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

4. Lead-in: No Oxygen

If there's no oxygen, glucose can't be broken down fully. Predict: will anaerobic respiration release more or less ATP?

Less ATP — the glucose is only partly broken down.

1. Complete Breakdown (Recall)

Explain the link between oxygen and the amount of ATP aerobic respiration releases.

Oxygen allows glucose to be oxidised completely to CO₂ and water, releasing the maximum energy as ATP.

2. Balancing (Recall)

Prove the aerobic symbol equation is balanced (count C, H, O).

Each side: 6 C, 12 H, 18 O. Balanced.

3. Demand (Recall)

During hard exercise, why might muscle cells not get enough oxygen?

Oxygen is used up faster than the blood can deliver it, so supply can't meet demand.

4. Lead-in: Incomplete

If glucose is only partly broken down without oxygen, suggest why a waste product must be left behind.

The carbon and hydrogen from glucose aren't fully oxidised, so they remain in a product (lactic acid, or ethanol + CO₂).

Starter

Starter: No Oxygen — Which Equation is Right?

Instructions: When muscles run out of oxygen, they respire anaerobically. Only ONE equation below is correct for animals. Tick it and be ready to say why. No calling out!

A) Glucose + Oxygen → Lactic Acid

B) Glucose → Lactic Acid

C) Lactic Acid → Glucose

D) Glucose → Carbon Dioxide + Water

🧠 Hint: Anaerobic means no oxygen — so oxygen can't be a reactant. In animals the waste product is lactic acid.

Aspire: For each WRONG equation (A, C, D) — can you say exactly what's wrong with it?

I Do

I Do: Anaerobic Respiration in Animals (Spec 2.38)

Key Idea: When there is no oxygen, animal cells respire anaerobically. Glucose is only partly broken down into lactic acid.

0/2

The Word Equation (Animals)

Glucose → Lactic Acid

No oxygen = no oxygen on the left. No carbon dioxide or water — just lactic acid.

It releases only a little ATP (glucose isn't fully broken down).

⚠️ Oxygen Debt & Cramp

Lactic acid builds up in muscles during hard exercise — this causes fatigue and cramp.

Afterwards you breathe hard to repay the oxygen debt — oxygen breaks the lactic acid down.

Glucose → Lactic Acid

⚠️ Exam Tip: In animals the only product is lactic acid. Don't add carbon dioxide or water — that's aerobic!

Why only a little ATP?

🧠 Memory Trick: "No air → lactic." Animals with no oxygen make lactic acid. Less oxygen used = less energy released.

Aspire: Why do you keep breathing hard after a sprint has finished?

🎬 Watch it flow — animals (no oxygen)

Reactant — IN

🍬 Glucose

→

in the cell · NO O₂

→

Products — OUT

🥵 Lactic acid

🔋 a little ATP

Glucose goes IN → only partly broken down (no oxygen) → lactic acid + a little ATP come OUT.

Don't write: Glucose + Oxygen → Lactic Acid (anaerobic has NO oxygen)

Write: Glucose → Lactic Acid

Anaerobic = without air. Oxygen can't appear on the left of an anaerobic equation.

Talk to your partner: What is the one product of anaerobic respiration in animals, and why does it release less ATP than aerobic? Next we'll build it.

We Do

We Do: Build Both Anaerobic Equations

Instructions: Drag each tile into the right gap to build the anaerobic equation in animals and in yeast/plants. Remember — no oxygen! (Works by touch or mouse.)

Tiles placed: 0/5

Tile bank — drag each into the right place:

Lactic Acid

Glucose

Carbon Dioxide

Glucose

Ethanol

1 · Animals (no oxygen)

Reactant (IN)

fuel
(sugar)

→

Product (OUT)

muscle
waste

2 · Yeast & Plants (no oxygen)

Reactant (IN)

fuel
(sugar)

→

Products (OUT)

alcohol

waste
gas

🧡 Tip: Both start with glucose and have no oxygen. Animals → lactic acid. Yeast → ethanol + carbon dioxide.

Animals: Glucose → Lactic Acid. Yeast/plants: Glucose → Ethanol + Carbon Dioxide. Neither uses oxygen!

I Do

I Do: Anaerobic in Yeast — Fermentation (Spec 2.38)

Key Idea: In yeast and plants, anaerobic respiration is called fermentation. Glucose breaks down into ethanol and carbon dioxide.

0/2

The Word Equation (Yeast)

Glucose → Ethanol + Carbon Dioxide

This is called fermentation. Like animals, it uses no oxygen and releases only a little ATP.

🍺🍞 Why we use it

Brewing: yeast makes the ethanol (alcohol) in beer and wine.

Baking: the carbon dioxide makes bread rise (the bubbles).

Quick recall: vs aerobic (you met aerobic in L4)

	Aerobic	Anaerobic
Oxygen?	✅ Yes	❌ No
ATP	Lots	A little
Animal product	CO₂ + water	Lactic acid
Yeast product	CO₂ + water	Ethanol + CO₂

Aspire: Why does anaerobic respiration release less ATP than aerobic?

💡 Real-World Link: The same yeast reaction that puts bubbles in bread also makes the alcohol in beer. The carbon dioxide escapes as bubbles; the ethanol stays behind (and bakes off in the oven).

🎬 Watch it flow — yeast (fermentation, no oxygen)

Reactant — IN

🍬 Glucose

→

yeast · NO O₂

→

Products — OUT

🍺 Ethanol

💨 Carbon dioxide

🔋 a little ATP

Glucose goes IN → yeast ferments it (no oxygen) → ethanol + carbon dioxide + a little ATP come OUT.

#1 exam error: mixing up the products. Animals → lactic acid. Yeast/plants → ethanol + carbon dioxide.

Neither uses oxygen, and both release far less ATP than aerobic respiration.

Talk to your partner: Give one way aerobic and anaerobic respiration are the same, and two ways they are different. Next we'll sort statements into aerobic vs anaerobic.

📺 Observe

Observe: See Anaerobic Respiration Happen

Watch & check: You've met both anaerobic equations — now see them. Use the toggle to switch demos, spot the key thing, then finish the sentences. This is exactly what you'll do on your own next.

sugar + yeast
+ warm water

Yeast ferments the sugar with no oxygen → carbon dioxide gas inflates the balloon. (Same gas that rises bread.)

🏃‍♂️💨

Lactic acid building…

Sprinting hard = not enough oxygen → muscles make lactic acid → burn & fatigue. After, you pant to repay the oxygen debt.

Both demos are real classroom/sport phenomena — switch between them with the toggle. Bench animations replay with Run demo.

🍺 Yeast clip ↗ 🥵 Muscle clip ↗

Listen carefully: a clip may just say "energy" — in your exam, write ATP. And remember: no oxygen on the left of either equation.

✍️ Now finish these — say it out loud first, then jot it down:

In yeast: glucose → ____________ + ____________.
The gas that inflates the balloon is ____________.

In animals: glucose → ____________.
It builds up during a sprint and causes ____________.

Yeast: ethanol + carbon dioxide; the gas is carbon dioxide. Animals: lactic acid; it causes cramp/fatigue (and an oxygen debt).

Ready check: Cover the screen — can you say both anaerobic word equations out loud? If yes, you're ready for the sort and your own work.

We Do

We Do: Aerobic or Anaerobic?

Instructions: Drag each statement into the right bin. Does it describe respiration with oxygen (aerobic) or without oxygen (anaerobic)? (Works by touch or mouse.)

Sorted: 0/6

🫁 Needs oxygen

🥵 Animals make lactic acid

🔋 Releases lots of ATP

🍺 Yeast makes ethanol + CO₂

💨 Products: CO₂ + water

🪫 Releases only a little ATP

✅ Aerobic

WITH oxygen

❌ Anaerobic

WITHOUT oxygen

Ask: "does it use oxygen?" If yes → aerobic (lots of ATP, CO₂ + water). If no → anaerobic (little ATP, lactic acid OR ethanol + CO₂).

Independent Work

Independent Work – Anaerobic Respiration

Instructions: Complete your printed worksheet at your level. You may use the equations from the starter and the knowledge organiser.

Independent Work Timer

08:00

Foundation (Grades U–1)

MCQ + complete the anaerobic equations using a word bank.

Middle (Grades 2–3)

Write both anaerobic equations from memory, plus a 4-mark comparison question.

Higher (Grades 3–5)

Explain oxygen debt and a 5-mark aerobic-vs-anaerobic question.

📋 Scaffolding

Your pack includes both anaerobic equations, the aerobic-vs-anaerobic comparison table, and a key-word glossary (lactic acid, ethanol, fermentation, oxygen debt).

🏆 Success Criteria

Foundation (U–1): I can write the animal equation (Glucose → Lactic Acid) and say anaerobic means without oxygen.

Middle (2–3): I can write both anaerobic equations and say which products belong to animals and which to yeast.

Higher (3–5): I can compare aerobic and anaerobic respiration (oxygen, ATP, products) and explain oxygen debt.

Exit Ticket

Exit Ticket – Anaerobic Respiration

Knowledge check: Tap your answer to each question — you'll get instant feedback and a score at the end. Books closed, no notes!

Score: 0/6

🖨️ Print written exit ticket:

Name: ________________________ Class: __________ Date: ____________

🎯 Learning Objective: Understand anaerobic respiration — the same idea as aerobic, with oxygen taken away — and write its equations in animals and in yeast.

🏆 Success Criteria — tick at the END of the lesson:

☐ All: I can write the anaerobic equation in animals: Glucose → Lactic Acid.

☐ Most: I can write the anaerobic equation in yeast: Glucose → Ethanol + Carbon Dioxide.

☐ Some: I can compare aerobic and anaerobic respiration (oxygen, ATP yield, products).

Knowledge Organiser (L5): Anaerobic Respiration

Item	Details
Anaerobic	Respiration without oxygen. Releases only a little ATP.
Animals (equation)	Glucose → Lactic Acid
Yeast/plants (equation)	Glucose → Ethanol + Carbon Dioxide
Fermentation	The name for anaerobic respiration in yeast/plants.
Oxygen debt	Extra oxygen needed after exercise to break down the lactic acid that built up.
Cramp/fatigue	Caused by lactic acid building up in muscles.
Uses of fermentation	Brewing (ethanol in beer/wine), baking (CO₂ makes bread rise).
Aerobic vs anaerobic	Aerobic: needs O₂, lots of ATP, makes CO₂ + water. Anaerobic: no O₂, little ATP, makes lactic acid OR ethanol + CO₂.

Key distinctions: aerobic needs oxygen and releases lots of ATP; anaerobic has no oxygen and releases only a little ATP. Animals make lactic acid; yeast/plants make ethanol + carbon dioxide.

🎵 Memory hook: “Animals = lactic Acid · Yeast = ethanol”. No oxygen → only a little ATP.

⚠️ Common mistakes: saying anaerobic makes no ATP (it makes a little) · swapping the animal and yeast products · forgetting the CO₂ in the yeast equation · writing oxygen as a reactant.

🧠 Self-quiz routine: COVER both equations → WRITE them from memory → CHECK → fix any gaps. Do it twice — the second go is where it sticks.

The Fab 4 – Recall Starter (from Aerobic Equations)

Foundation

1) Name the two reactants of aerobic respiration.

2) Name the two products of aerobic respiration.

3) Which gas does aerobic respiration need?

4) What happens if a cell runs out of oxygen?

Middle

1) Write the word equation for aerobic respiration.

2) Why does aerobic respiration release so much ATP?

3) Write the balanced symbol equation for aerobic respiration.

4) Predict: will anaerobic release more or less ATP than aerobic?

Higher

1) Explain the link between oxygen and the amount of ATP released.

2) Prove the aerobic symbol equation is balanced (count C, H, O).

3) During hard exercise, why might muscles not get enough oxygen?

4) If glucose is only partly broken down, why is a waste product left?

Lesson 5 Starter: No Oxygen — Which Equation is Right?

When muscles run out of oxygen they respire anaerobically. Only ONE equation is correct for animals. Tick it, then explain why.

Tick	Equation
	A) Glucose + Oxygen → Lactic Acid
	B) Glucose → Lactic Acid
	C) Lactic Acid → Glucose
	D) Glucose → Carbon Dioxide + Water

My choice: ________ Why?

Extension – what's wrong with the other three?

A is wrong because:

C is wrong because:

D is wrong because:

Scaffolding Sheet – Foundation (Grades U–1)

Both Anaerobic Equations

Animals: Glucose → Lactic Acid

Yeast/plants: Glucose → Ethanol + Carbon Dioxide

Sentence Starters

Anaerobic respiration happens when there is no ________.

In animals, glucose turns into ________.

In yeast, glucose turns into ________ and ________.

📝 Word Bank (Foundation)

Use these words: oxygen · glucose · lactic acid · ethanol · carbon dioxide · fermentation · ATP · energy

⭐ Exam frame

(a) Anaerobic respiration happens when there is no ________.

(b) In animals: Glucose → ________.

Scaffolding Sheet – Middle (Grades 2–3)

Equations

Animals: Glucose → Lactic Acid

Yeast/plants: Glucose → Ethanol + Carbon Dioxide

Key Words

Anaerobic	Without oxygen.
Lactic acid	Animal anaerobic product (causes cramp).
Ethanol	Yeast anaerobic product (alcohol).
Fermentation	Anaerobic respiration in yeast/plants.

Scaffolding Sheet – Higher (Grades 3–5)

Aerobic vs Anaerobic

	Aerobic	Anaerobic
Oxygen	Yes	No
ATP	Lots	A little
Animal product	CO₂ + water	Lactic acid
Yeast product	CO₂ + water	Ethanol + CO₂

Key Terms

Anaerobic, fermentation, lactic acid, ethanol, oxygen debt, incomplete breakdown, fatigue

Independent Work – Foundation (Grades U–1)

Part A: Multiple Choice (circle the correct answer)

1) "Anaerobic" means respiration: A) With oxygen B) Without oxygen C) In the lungs D) With water

2) In animals, anaerobic respiration makes: A) Lactic acid B) Ethanol C) Oxygen D) Water

3) In yeast, anaerobic respiration makes: A) Lactic acid B) Ethanol + carbon dioxide C) Glucose D) Oxygen

4) Anaerobic respiration releases: A) Lots of ATP B) A little ATP C) No energy D) Only heat

Part B: Short Answer (word bank: Glucose · Lactic Acid · Ethanol · Carbon Dioxide)

5) Complete (animals): __________ → __________

6) Complete (yeast): Glucose → __________ + __________

7) Anaerobic respiration happens when there is no __________.

Part C: Long Answer

8) Write the anaerobic equation for animals and the one for yeast. Say which product belongs to which.

Part D: Exam Question [3 marks]

9) Write the word equation for anaerobic respiration in animals and say what causes muscle cramp. [3]

Independent Work – Middle (Grades 2–3)

Part A: Multiple Choice

1) The anaerobic equation in animals is: A) Glucose + Oxygen → Lactic Acid B) Glucose → Lactic Acid C) Lactic Acid → Glucose D) Glucose → Ethanol + CO₂

2) Fermentation is anaerobic respiration in: A) Animals B) Yeast and plants C) The lungs D) Bacteria only

3) Anaerobic respiration releases less ATP because: A) It is slow B) Glucose is only partly broken down C) It happens in the lungs D) It uses too much oxygen

Part B: Short Answer

4) Write the anaerobic equation in animals from memory.

5) Write the anaerobic equation in yeast/plants from memory.

6) Give one use of fermentation in everyday life.

Part C: Long Answer

7) Explain what "oxygen debt" is and why you breathe hard after a sprint.

Part D: Exam Question [4 marks]

8) Compare anaerobic respiration in animals with anaerobic respiration in yeast. Give the equation for each and one similarity. [4]

Independent Work – Higher (Grades 3–5)

Part A: Multiple Choice

1) Anaerobic respiration releases less ATP than aerobic because: A) It is faster B) Glucose is not fully broken down C) It uses more oxygen D) It makes water

2) Lactic acid building up in muscles causes: A) Cramp and fatigue B) More oxygen C) Faster ATP D) Cooling

Part B: Short Answer

3) Explain why anaerobic respiration releases less energy than aerobic respiration.

4) Explain what oxygen debt is and how the body repays it.

Part C: Long Answer

5) Yeast is used in both brewing and baking. Explain how the same anaerobic reaction is useful in each case.

Part D: Exam Question [5 marks]

6) Compare aerobic and anaerobic respiration. In your answer refer to oxygen, the amount of ATP released, and the products in animals and in yeast. [5]

Exit Ticket – Anaerobic Respiration (Foundation U–1)

Name: ______________________ Class: __________ Date: __________

Answer from memory — no notes.

1) "Anaerobic" means respiration ______________ oxygen.

2) Complete (animals): Glucose → __________

3) Complete (yeast): Glucose → __________ + __________

4) Does anaerobic respiration release a lot or a little ATP? Circle: A LOT / A LITTLE

5) What waste product builds up in muscles and causes cramp?

6) Name one food or drink made using fermentation.

Exit Ticket – Anaerobic Respiration (Middle 2–3)

Name: ______________________ Class: __________ Date: __________

Answer from memory — no notes.

1) Write the anaerobic equation in animals.

2) Write the anaerobic equation in yeast/plants.

3) What is fermentation?

4) Why does anaerobic respiration release less ATP than aerobic?

5) Give one similarity between anaerobic respiration in animals and in yeast.

6) What is "oxygen debt"?

Exit Ticket – Anaerobic Respiration (Higher 3–5)

Name: ______________________ Class: __________ Date: __________

Answer from memory — no notes.

1) Write both anaerobic equations (animals and yeast).

2) Explain why anaerobic respiration releases far less ATP than aerobic.

3) Explain oxygen debt and how it is repaid.

4) Give two differences between aerobic and anaerobic respiration.

5) A student writes: "Anaerobic respiration in animals makes ethanol." Correct this.

6) Explain why the carbon dioxide from yeast is useful in baking.

Lesson 5: Anaerobic Respiration

🏆 By the end I will be able to…

Teacher Print Tools – Lesson 5

Before We Start: What You Already Know (from L4)

With oxygen vs without oxygen

The Fab 4 – Recall to Get You Started

⭐ The Fab 4 — Quick-Fire Recall

1. Reactants (Recall)

2. Products (Recall)

3. Oxygen (Recall)

4. Lead-in: No Oxygen

1. Word Equation (Recall)

2. ATP Yield (Recall)

3. Symbol Equation (Recall)

4. Lead-in: No Oxygen

1. Complete Breakdown (Recall)

2. Balancing (Recall)

3. Demand (Recall)

4. Lead-in: Incomplete

Starter: No Oxygen — Which Equation is Right?

I Do: Anaerobic Respiration in Animals (Spec 2.38)

The Word Equation (Animals)

⚠️ Oxygen Debt & Cramp

Glucose → Lactic Acid

Why only a little ATP?

We Do: Build Both Anaerobic Equations

I Do: Anaerobic in Yeast — Fermentation (Spec 2.38)

The Word Equation (Yeast)

🍺🍞 Why we use it

Quick recall: vs aerobic (you met aerobic in L4)

Observe: See Anaerobic Respiration Happen

We Do: Aerobic or Anaerobic?

✅ Aerobic

❌ Anaerobic

Independent Work – Anaerobic Respiration

Foundation (Grades U–1)

Middle (Grades 2–3)

Higher (Grades 3–5)

📋 Scaffolding

🏆 Success Criteria

Exit Ticket – Anaerobic Respiration

Knowledge Organiser (L5): Anaerobic Respiration

The Fab 4 – Recall Starter (from Aerobic Equations)

Foundation

Middle

Higher

Lesson 5 Starter: No Oxygen — Which Equation is Right?

Scaffolding Sheet – Foundation (Grades U–1)

Both Anaerobic Equations

Sentence Starters

Scaffolding Sheet – Middle (Grades 2–3)

Equations

Key Words

Scaffolding Sheet – Higher (Grades 3–5)

Aerobic vs Anaerobic

Key Terms

Independent Work – Foundation (Grades U–1)

Independent Work – Middle (Grades 2–3)

Independent Work – Higher (Grades 3–5)

Exit Ticket – Anaerobic Respiration (Foundation U–1)

Exit Ticket – Anaerobic Respiration (Middle 2–3)

Exit Ticket – Anaerobic Respiration (Higher 3–5)

🎓 TA Focus

🎯 Cold Call

📺 Anaerobic Respiration

🏆 Class Progress Board

🎉 Lesson Complete!