The shape of the lesson
By the end of the lesson, learners can
- Glucose plus oxygen: In the Respiration tab choose aerobic.
- Balancing the equation: Extended.
- More work, more respiration: Working muscles respire faster, so they need more oxygen and make more carbon dioxide.
- Definition: chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
- Word equation: glucose + oxygen → carbon dioxide + water.
- Extended: C6H12O6 + 6O2 → 6CO2 + 6H2O; count atoms to check.
- Energy is released, not made, and is not written in the balanced equation.
One picture every idea returns to
Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy. Word equation: glucose + oxygen → carbon dioxide + water. Extended: the balanced chemical equation is C6H12O6 + 6O2 → 6CO2 + 6H2O.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Oxygen in, all the energy out.. When oxygen is available, cells break glucose down completely to carbon dioxide and water. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Glucose plus oxygen | In the Respiration tab choose aerobic. Project tab 6 of the lab (Aerobic respiration in a mitochondrion) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Balancing the equation | Extended. | Pairs |
| 21 to 30 min | Teach and check: More work, more respiration | Working muscles respire faster, so they need more oxygen and make more carbon dioxide. Project tab 5 of the lab (Breathing at rest and during exercise) and let a student drive it while the class predicts. | Connect-Extend-Challenge |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 18 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in More work, more respiration, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Connect-Extend-Challenge
After the new idea, each student writes three lines: how it connects to what they knew, how it extends their thinking, and what still challenges them. Pairs compare, then the challenges become the plenary.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Oxygen is a reactant, not a product, and water is a product. | Students often swap them when writing the word equation in a hurry. Plants respire aerobically all the time too, in light and in darkness. |
| Write the formulae exactly: C 6 H 12 O 6, O 2, CO 2, H 2 O. "6O" or "H 2 O 6 " loses the mark, and energy is not a substance, so it is not written as a product in the balanced equation. | Return to Balancing the equation: ask a pair to state the correct version and show it on the lab before moving on. |
Aerobic respiration: worksheet
6 questions, 18 marks. Written in the style of the papers; no past paper question is reproduced.
Describe what is meant by aerobic respiration and state its word equation.
Extended. Write the balanced chemical equation for aerobic respiration.
Extended. Use the balanced equation to show that the numbers of carbon, hydrogen and oxygen atoms are the same on both sides. Then state how many molecules of carbon dioxide are released when 5 molecules of glucose are respired aerobically.
Sperm cells and muscle cells contain many mitochondria. Explain why.
A student's breathing was measured at rest and during exercise.
| Breaths per minute | Volume per breath / dm3 | |
|---|---|---|
| At rest | 12 | 0.5 |
| Jogging | 28 | 1.8 |
(a) Calculate the volume of air breathed per minute in each case. (b) Explain why the volume increases during exercise.
Compare the word equations for photosynthesis and aerobic respiration. State two similarities and one difference.
Answer key and marking notes
- The chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
- glucose + oxygen →
- carbon dioxide + water
- C6H12O6 + 6O2 → 6CO2 + 6H2O
- One mark for correct formulae, one mark for correct balancing.
- Carbon: 6 on the left, 6 × 1 = 6 on the right. Hydrogen: 12 on the left, 6 × 2 = 12 on the right.
- Oxygen: 6 + (6 × 2) = 18 on the left; (6 × 2) + (6 × 1) = 18 on the right.
- 5 × 6 = 30 molecules of carbon dioxide.
- Mitochondria are where most of the reactions of aerobic respiration take place.
- Aerobic respiration releases a large amount of energy from glucose.
- Muscle cells need the energy for contraction, and sperm cells need it to swim (move the tail); more mitochondria release more energy.
- (a) At rest: 12 × 0.5 = 6.0 dm3 per minute. Jogging: 28 × 1.8 = 50.4 dm3 per minute.
- (b) During exercise the muscles contract more, so they need more energy.
- Their rate of aerobic respiration increases, so they use more oxygen and produce more carbon dioxide.
- Faster, deeper breathing supplies the extra oxygen and removes the extra carbon dioxide.
- Similarity: both involve the same four substances, glucose, oxygen, carbon dioxide and water.
- Similarity: both are chemical reactions controlled by enzymes in cells (both happen in plant cells in the light).
- Difference: respiration uses glucose and oxygen and releases energy; photosynthesis uses carbon dioxide and water and needs light energy absorbed by chlorophyll (the reactants and products are reversed).
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
What are the products of aerobic respiration?
- ACarbon dioxide and water
- BGlucose and oxygen
- CLactic acid only
- DAlcohol and carbon dioxide
Which is the best description of aerobic respiration?
- AChemical reactions in cells that use oxygen to break down nutrients and release energy
- BChemical reactions in cells that make energy from oxygen and carbon dioxide
- CThe exchange of oxygen and carbon dioxide across the walls of the alveoli
- DChemical reactions in cells that break down nutrients without using oxygen
Which cell would you expect to contain the largest number of mitochondria?
- AA heart muscle cell
- BA mature red blood cell
- CA fat storage cell
- DA xylem vessel element
Woodlice are kept in a sealed tube above some hydrogencarbonate indicator, in the dark. After an hour the indicator has changed from red to yellow. Why?
- AThe woodlice respire and release carbon dioxide into the tube
- BThe woodlice respire and release oxygen into the tube
- CThe woodlice photosynthesise and take carbon dioxide from the tube
- DThe woodlice take in water vapour, so the air in the tube becomes dry
In this respirometer, soda lime absorbs carbon dioxide. After 20 minutes the coloured liquid has moved towards tube A. What does this show?
- AThe seeds in A take in oxygen, so the volume of gas in A falls
- BThe seeds in A give out carbon dioxide, so the volume of gas in A rises
- CThe glass beads in B respire, so the volume of gas in B rises
- DThe seeds in A give out oxygen, so the volume of gas in A falls
Extended: three molecules of glucose are respired aerobically. How many molecules of water are produced?
- A18
- B6
- C3
- D12
Extended: in the balanced equation for aerobic respiration, how many oxygen atoms are shown on the products side?
- A18
- B12
- C6
- D24
Extended: when a person respires only glucose aerobically, what is the ratio of molecules of carbon dioxide released to molecules of oxygen used?
- A1 : 1
- B6 : 1
- C1 : 6
- D2 : 1
Quiz key
glucose + oxygen → carbon dioxide + water, so carbon dioxide and water are the products. Glucose and oxygen are the reactants (and the products of photosynthesis). Lactic acid is the product of anaerobic respiration in muscles. Alcohol and carbon dioxide are the products of anaerobic respiration in yeast.
Aerobic respiration happens in cells, uses oxygen, breaks down nutrient molecules such as glucose and releases energy. Energy is never "made", and carbon dioxide is a product, not a reactant. Gas exchange in the alveoli is a separate process that supplies the oxygen. Breaking down nutrients without oxygen is anaerobic respiration.
Heart muscle contracts continuously throughout life, so it needs a large, steady supply of energy from aerobic respiration and is packed with mitochondria. Mature red blood cells have no mitochondria (or nucleus), leaving more room for haemoglobin. Fat storage cells are mostly a store of lipid and are not very active. Xylem vessels are dead, hollow tubes with no cytoplasm.
The respiring woodlice give out carbon dioxide, which dissolves in the indicator and makes it more acidic, turning it yellow. Respiration uses oxygen rather than releasing it. Animals do not photosynthesise, and removing carbon dioxide would turn the indicator purple, not yellow. The indicator responds to carbon dioxide, not to humidity.
The germinating seeds respire aerobically and use oxygen. The carbon dioxide they release is absorbed by the soda lime, so the total volume of gas in A falls and the liquid is pulled towards A. If carbon dioxide stayed in the tube, the volume would not fall; but it is absorbed, so it cannot raise the volume. Glass beads are not alive and do not respire; they are the control of the same volume. Respiring seeds use oxygen rather than giving it out.
C6H12O6 + 6O2 → 6CO2 + 6H2O, so each glucose gives 6 water molecules: 3 × 6 = 18. 6 is the number for only one glucose. 3 assumes one water per glucose. 12 would be correct for two glucose molecules, not three.
6CO2 contains 6 × 2 = 12 oxygen atoms and 6H2O contains 6 × 1 = 6, giving 18 in total, the same as the 6 + 12 on the reactants side. 12 counts only the carbon dioxide. 6 counts only the water (or only glucose). 24 counts two oxygen atoms in each water molecule as well.
The balanced equation uses 6O2 and releases 6CO2 per glucose, so the ratio is 6 : 6 = 1 : 1. 6 : 1 and 1 : 6 compare carbon dioxide (or oxygen) with glucose instead of with each other. 2 : 1 comes from the two oxygen atoms in each carbon dioxide molecule, which is about atoms, not molecules.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.