The shape of the lesson
By the end of the lesson, learners can
- What the energy is for: In the Respiration tab a glucose molecule enters the cell and is broken down; the yellow sparks show the energy released.
- Yeast, sugar and temperature: Yeast is a single-celled fungus.
- Seeds and small animals respire too: The same idea works with germinating seeds or small invertebrates such as maggots or woodlice in a sealed tube.
- Respiration happens in all living cells; breathing is only the movement of air.
- Seven uses: muscle contraction, protein synthesis, cell division, active transport, growth, nerve impulses, constant body temperature.
- Yeast and temperature: rate rises to an optimum (about 35 to 40 °C), then falls as enzymes denature.
- Fair test: same yeast mass, sugar volume and concentration, time; equilibrate in the bath first.
One picture every idea returns to
Respiration is the chemical reactions in cells that break down nutrient molecules to release energy. Organisms use that energy for muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses and the maintenance of a constant body temperature. Respiration is controlled by enzymes, so in yeast its rate rises with temperature up to an optimum and then falls as the enzymes are denatured.
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, Every cell, every second, releasing energy.. Respiration is not breathing. 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: What the energy is for | In the Respiration tab a glucose molecule enters the cell and is broken down; the yellow sparks show the energy released. Project tab 6 of the lab (Respiration in a cell and the uses of energy) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Yeast, sugar and temperature | Yeast is a single-celled fungus. Project tab 7 of the lab (Yeast respiring at different temperatures) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: Seeds and small animals respire too | The same idea works with germinating seeds or small invertebrates such as maggots or woodlice in a sealed tube. | Frayer Model |
| 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, 19 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 Seeds and small animals respire too, 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.
Frayer Model
Pairs fill a four-box grid for the key term: definition, characteristics, examples and non-examples. The non-examples box is where the misconceptions surface, so give it the most time.
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 |
|---|---|
| Respiration releases energy that is already stored in glucose. | Never write that respiration "makes" or "produces" energy, and do not confuse respiration (a chemical process in cells) with breathing (ventilation, moving air in and out of the lungs). |
| The temperature axis is the independent variable and the carbon dioxide volume is the dependent variable. | Do not say the yeast "dies at the optimum": the optimum is where respiration is fastest; it is above the optimum that the enzymes denature. |
Respiration in cells: worksheet
6 questions, 19 marks. Written in the style of the papers; no past paper question is reproduced.
State four uses of the energy released by respiration in the human body.
A student writes: "Respiration is breathing in oxygen and breathing out carbon dioxide." Explain why this is wrong.
Flasks of yeast in sugar solution were kept in water baths for 10 minutes and the carbon dioxide released was collected.
| Temperature / °C | 10 | 20 | 30 | 40 | 50 | 60 |
|---|---|---|---|---|---|---|
| CO2 / cm3 | 20 | 40 | 80 | 123 | 18 | 1 |
(a) Describe the results. (b) Explain the results above 40 °C.
Plan an investigation to find the effect of temperature on the rate of respiration of yeast.
Germinating peas were placed in vacuum flask A and boiled peas, rinsed in disinfectant, in vacuum flask B. After three days flask A was 6 °C warmer than flask B. Explain these results and the reason for each step of the method.
Suggest why the cells of a root hair and the cells of a growing shoot tip both need a lot of energy from respiration.
Answer key and marking notes
Any four of: muscle contraction; protein synthesis; cell division; active transport; growth; the passage of nerve impulses; maintaining a constant body temperature.
- Respiration is the chemical reactions inside cells that break down nutrient molecules (such as glucose) to release energy.
- Breathing (ventilation) is only the movement of air into and out of the lungs; it supplies oxygen for, and removes carbon dioxide from, respiration.
- (a) The volume of carbon dioxide increases from 20 cm3 at 10 °C to a maximum of 123 cm3 at 40 °C (it doubles for each 10 °C rise from 10 to 30 °C).
- Above 40 °C it falls sharply, to 1 cm3 at 60 °C.
- (b) Respiration is controlled by enzymes; at high temperature the enzymes are denatured (their shape changes) so they no longer work.
- So the rate of respiration falls and the yeast cells are killed, releasing little or no carbon dioxide.
- Put the same mass of yeast and the same volume and concentration of sugar solution into flasks; leave each in a water bath at a different temperature (for example 20, 30, 40, 50 °C) until it reaches that temperature.
- Collect the gas in a gas syringe or upturned measuring cylinder (or count bubbles) over a fixed time, such as 10 minutes.
- Calculate the rate as volume of carbon dioxide per minute.
- Control the type of sugar, time and yeast; repeat each temperature and calculate a mean.
- The germinating peas respire, and some of the energy released is lost as heat, so flask A warms up.
- The boiled peas are dead and do not respire; flask B is the control.
- Disinfectant kills microorganisms on the boiled peas so that their respiration does not warm flask B; the vacuum flask reduces heat loss.
- Root hair cells take up mineral ions by active transport, which needs energy.
- Shoot tip cells are dividing and growing, and they make proteins (protein synthesis), which needs energy.
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.
Which process in a neurone (nerve cell) depends directly on energy released by respiration?
- AThe passage of nerve impulses along the neurone
- BThe diffusion of oxygen into the neurone
- CThe movement of water into the neurone by osmosis
- DThe absorption of light energy by the neurone
Where does respiration take place in a human?
- AIn every living cell of the body
- BOnly in the cells lining the lungs
- COnly in the cells of working muscles
- DOnly in the red blood cells
A potted plant is kept in complete darkness for 24 hours. Which statement about its leaf cells is correct?
- AThey respire but do not photosynthesise
- BThey photosynthesise but do not respire
- CThey neither respire nor photosynthesise
- DThey respire only when they photosynthesise
Yeast in sugar solution was kept at different temperatures and the bubbles of gas released per minute were counted. Which conclusion is supported by the graph?
- AThe rate rises up to about 40 °C and then falls sharply
- BThe rate keeps rising as the temperature increases to 60 °C
- CThe rate is highest at 30 °C and lowest at 10 °C
- DThe rate falls steadily from 10 °C up to 60 °C
In a yeast investigation a second flask contains boiled yeast in the same sugar solution. What is the purpose of this flask?
- ATo show that the gas is produced by living yeast
- BTo provide extra oxygen for the living yeast
- CTo keep the temperature of the water bath constant
- DTo measure how fast the sugar dissolves in water
Yeast at 25 °C released 18 cm3 of carbon dioxide in 6 minutes. What was the mean rate of carbon dioxide production?
- A3.0 cm3 per minute
- B0.33 cm3 per minute
- C108 cm3 per minute
- D12 cm3 per minute
Before starting the timer, each flask of yeast and sugar solution was left in its water bath for 10 minutes. Why?
- ASo the contents reach the temperature of the water bath
- BSo the yeast can use up all the sugar in the solution
- CSo the yeast cells are killed before the test begins
- DSo the carbon dioxide can escape from the solution
A mouse and a lizard of the same mass are kept at 5 °C. The mouse uses oxygen about ten times faster than the lizard. The best explanation is that the mouse:
- Arespires faster to release energy that keeps its body temperature constant
- Bneeds extra oxygen because it photosynthesises in its fur at low temperature
- Chas a slower rate of respiration, so it needs to breathe in more oxygen
- Duses oxygen to make glucose for growth because it is colder than the lizard
Quiz key
The passage of nerve impulses is one of the uses of energy from respiration listed in the syllabus. Oxygen enters cells by diffusion, which uses the kinetic energy of the molecules, not energy from respiration. Osmosis is also passive. Neurones do not absorb light energy; only chlorophyll in plant cells traps light for photosynthesis.
Respiration is a chemical process that releases energy in all living cells, because every cell needs energy. The lungs are where gas exchange happens; confusing them with respiration mixes up respiration and breathing. Muscles respire faster when working, but other cells respire too. Red blood cells carry oxygen to the respiring cells; they are not the only site of respiration.
Photosynthesis needs light, so it stops in the dark, but respiration continues day and night in every living cell. Saying the cells photosynthesise in darkness ignores the need for light energy. Saying they stop respiring would mean the cells were dead. Respiration does not depend on photosynthesis happening at the same moment; the cells use stored sugars and starch.
The bubble count rises from 4 per minute at 10 °C to a peak of 26 per minute at 40 °C, then drops to 8 at 50 °C and 0 at 60 °C. The rate does not keep rising: above about 40 °C the enzymes are denatured. 30 °C (18 per minute) is not the highest point, and the lowest value is at 60 °C, not 10 °C. The rate does not fall steadily from 10 °C; it first rises.
Boiled yeast is dead, so it acts as a control: if no gas is produced there, the gas in the other flask must come from respiration by the living yeast. The control flask is not joined to the other flask, so it cannot supply oxygen. A water bath, not a second flask, keeps the temperature constant. The investigation measures gas from respiration, not how fast sugar dissolves.
Rate = 18 ÷ 6 = 3.0 cm3 per minute. 0.33 is time divided by volume, which is upside down. 108 comes from multiplying the volume by the time instead of dividing. 12 is the difference between 18 and 6, which has no meaning as a rate.
A flask at room temperature takes time to warm or cool to the bath temperature; waiting means the yeast is really respiring at the stated temperature during the measurement. Using up all the sugar would leave nothing to respire during the test. Killing the yeast would stop respiration and spoil the investigation. Gas escaping before timing is irrelevant; the aim is to measure gas produced during the timed period.
Mammals maintain a constant body temperature; in cold surroundings they respire faster, releasing energy (as heat) to replace the heat lost, and that needs more oxygen. The lizard's body temperature falls with its surroundings, so it respires slowly. Animals do not photosynthesise. A slower rate of respiration would use less oxygen, not more. Oxygen is used to break glucose down in respiration, not to make glucose.
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.