The shape of the lesson
By the end of the lesson, learners can
- Yeast: bread and biofuel: Choose bread-making or biofuel (ethanol), set the temperature slider (5 to 60 °C) and press Start.
- Pectinase: more, clearer juice: Two funnels hold apple pulp.
- Biological washing powders: The cloth carries three stains: egg (protein), butter (fat) and gravy (starch).
- Lactase and lactose-free milk: Extended.
- Yeast: glucose → ethanol + carbon dioxide; bread uses the CO2, biofuel uses the ethanol.
- Pectinase: breaks down pectin in cell walls: more juice, clearer juice.
- Washing powders: protease, lipase, amylase digest stains to small soluble molecules; work at low temperatures.
- Lactase (Extended): lactose → glucose + galactose; lactose-free milk for lactose-intolerant people.
One picture every idea returns to
Yeast respires anaerobically: glucose → ethanol + carbon dioxide. In biofuel production the ethanol is the useful product; in bread-making the carbon dioxide makes the dough rise. Pectinase breaks down pectin in fruit cell walls, so more juice is released and it is clearer. Biological washing powders contain enzymes that digest stains into small soluble molecules at low temperatures. Extended: lactase breaks lactose into glucose and galactose to make lactose-free milk.
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, Living factories, in the kitchen and the plant.. People have used yeast for thousands of years to make bread, and now use it to make fuel. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 11 min | Teach and check: Yeast: bread and biofuel | Choose bread-making or biofuel (ethanol), set the temperature slider (5 to 60 °C) and press Start. Project tab 2 of the lab (Yeast in bread-making and biofuel production) and let a student drive it while the class predicts. | Whole class, then pairs |
| 11 to 17 min | Teach and check: Pectinase: more, clearer juice | Two funnels hold apple pulp. Project tab 3 of the lab (Pectinase and fruit juice production) and let a student drive it while the class predicts. | Pairs |
| 17 to 23 min | Teach and check: Biological washing powders | The cloth carries three stains: egg (protein), butter (fat) and gravy (starch). Project tab 4 of the lab (Biological and non-biological washing powders) and let a student drive it while the class predicts. | Pairs |
| 23 to 30 min | Teach and check: Lactase and lactose-free milk | Extended. Project tab 5 of the lab (Making lactose-free milk with lactase) and let a student drive it while the class predicts. | Jigsaw |
| 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, 22 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 Lactase and lactose-free milk, 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.
Jigsaw
Split the content into expert pieces. Expert groups master one piece each, then regroup so every home team has one expert per piece, and each expert teaches their piece to the team.
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 |
|---|---|
| In bread-making the dough rises because of carbon dioxide, not ethanol and not oxygen. | For biofuel, the useful product is ethanol. |
| Very hot water does not help a biological powder: above about 60 °C its enzymes are denatured, so it cleans no better than a non-biological powder. | Return to Biological washing powders: ask a pair to state the correct version and show it on the lab before moving on. |
| Lactase does not remove the sugar from milk. | It breaks lactose into two smaller sugars, glucose and galactose, which the body can absorb. |
Yeast and enzymes in industry: worksheet
6 questions, 22 marks. Written in the style of the papers; no past paper question is reproduced.
Describe the role of anaerobic respiration in yeast during bread-making.
Describe how yeast is used to produce ethanol for biofuel.
Apple pulp was treated with pectinase or with water and filtered for 20 minutes.
| Treatment | Volume of juice / cm3 | Appearance |
|---|---|---|
| pectinase at 45 °C | 38 | clear |
| water at 45 °C | 15 | cloudy |
| boiled pectinase at 45 °C | 16 | cloudy |
(a) Calculate the percentage increase in juice volume caused by pectinase compared with water. (b) Explain the results.
Plan an investigation to compare how well a biological and a non-biological washing powder remove egg stains at 40 °C.
Explain why biological washing powders can be used at lower temperatures than non-biological powders and why this is an advantage.
Extended. Explain how lactase is used to produce lactose-free milk and why this milk is useful.
Answer key and marking notes
- Yeast is mixed with flour, water and sugar to make dough, which is left in a warm place.
- The yeast respires anaerobically, breaking down sugar into ethanol and carbon dioxide.
- Bubbles of carbon dioxide are trapped in the dough, making it rise.
- During baking the ethanol evaporates and the heat kills the yeast.
- Sugars are obtained from crops such as sugar cane or maize.
- Yeast respires the sugar anaerobically, producing ethanol and carbon dioxide.
- The ethanol is separated from the mixture (by distillation) and used as a fuel, for example mixed with petrol.
- (a) (38 − 15) ÷ 15 × 100 = 153% (accept 150%).
- (b) Pectinase breaks down pectin in the fruit cell walls, so more juice is released.
- Breaking down pectin also makes the juice clearer.
- Boiling denatures the pectinase, so the boiled enzyme gives about the same result as water (it acts as a control).
- Stain identical squares of the same cloth with the same volume of egg and let them dry.
- Wash one square in each powder, using the same mass of powder in the same volume of water at 40 °C (water bath), for the same time, stirred in the same way.
- Measure the stain left (for example compare against a colour chart, or time how long it takes for the stain to disappear).
- Repeat several times for each powder and calculate a mean.
- The enzymes (protease, lipase, amylase) digest stains into small soluble molecules that wash away, even at about 30 to 40 °C.
- Above about 60 °C the enzymes would be denatured, so they are designed for low temperatures.
- Washing at lower temperatures saves energy (and money) and does less damage to delicate fabrics.
- Milk is passed over the enzyme lactase (often immobilised in beads in a column).
- Lactase breaks down lactose into glucose and galactose.
- Some people are lactose intolerant: they do not produce enough lactase, so lactose in milk causes pain, wind and diarrhoea.
- Lactose-free milk lets them drink milk and gain its nutrients without these symptoms.
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 word equation shows the anaerobic respiration of yeast used in bread-making and biofuel production?
- Aglucose → ethanol + carbon dioxide
- Bglucose → lactic acid
- Cglucose + oxygen → carbon dioxide + water
- Dethanol + carbon dioxide → glucose
A baker leaves one batch of dough in a warm room at 30 °C and another in a fridge at 4 °C for one hour. What is the most likely result?
- AThe warm dough rises more because its yeast respires faster
- BThe cold dough rises more because carbon dioxide is more soluble
- CBoth rise equally because the same mass of yeast was used
- DNeither rises because yeast respires only in the oven
How does pectinase increase the volume of juice obtained from fruit?
- AIt breaks down pectin in the cell walls so the cells release more juice
- BIt breaks down starch in the cells into extra sugar solution
- CIt makes the fruit cells absorb water so they swell and burst
- DIt joins small molecules together to make the juice thicker
The table shows the percentage of an egg stain removed by two washing powders. Which conclusion is supported by the data?
- AThe biological powder works best at 40 °C, and its enzymes are denatured above this
- BThe biological powder works better than the non-biological powder at every temperature
- CThe non-biological powder contains enzymes with an optimum of 80 °C
- DBoth powders remove the most stain at the highest temperature tested
Using the table, how many times more egg stain did the biological powder remove than the non-biological powder at 40 °C?
- A3.2 times
- B65 times
- C2.1 times
- D0.32 times
Which enzyme in a biological washing powder is most important for removing a greasy butter stain?
- ALipase
- BProtease
- CAmylase
- DPectinase
Extended: which products are formed when lactase acts on the sugar in milk?
- Aglucose and galactose
- Bglucose and fructose
- Ctwo molecules of glucose
- Damino acids and glucose
Extended: in lactose-free milk production, lactase is often held in beads packed into a column. Why is this useful?
- AThe enzyme stays in the column and can be reused, and the milk is not contaminated
- BThe beads add extra lactose to the milk so it tastes sweeter
- CThe beads denature the lactase so it stops working after one use
- DThe beads absorb the lactose so no sugar at all is left in the milk
Quiz key
Yeast respires glucose without oxygen to give ethanol and carbon dioxide. Lactic acid is the product of anaerobic respiration in human muscle. The equation with oxygen is aerobic respiration. The last equation is written backwards: ethanol and carbon dioxide are products, not reactants.
At 30 °C the yeast enzymes work quickly, so more carbon dioxide is made and the dough rises more. At 4 °C the enzymes work very slowly, so little gas is made. The mass of yeast is the same but its rate of respiration is not. The oven heat actually kills the yeast; the dough rises before baking.
Pectinase breaks down pectin, which helps hold plant cell walls together, so the cells break open and more juice is released; the juice is also clearer. Breaking starch is the job of amylase. Pectinase does not cause osmosis. Enzymes that break down pectin make juice less thick and cloudy, not thicker.
The biological powder removes 95% at 40 °C but less at 60 and 80 °C, the pattern of enzymes being denatured above their optimum. At 60 and 80 °C the non-biological powder removes more, so 'every temperature' is wrong. The non-biological powder has no enzymes; it simply cleans better in hotter water. The biological powder does not remove most at 80 °C.
95 ÷ 30 = 3.17, about 3.2 times. 65 is the difference (95 − 30), not the ratio. 2.1 compares the biological powder at 40 °C with itself at 20 °C (95 ÷ 45). 0.32 is the ratio upside down (30 ÷ 95).
Butter is mainly fat, which lipase digests into fatty acids and glycerol that wash away. Protease digests protein stains such as egg or blood. Amylase digests starch stains such as gravy. Pectinase is used in fruit juice production, not washing powders.
Lactase breaks lactose into glucose and galactose. Glucose and fructose are the products of breaking down sucrose. Two glucose molecules come from maltose. Amino acids are products of protein digestion, not of a sugar.
An immobilised enzyme stays in the column while the milk flows through, so it can be used again and the milk does not contain the enzyme. The beads add no lactose. Denaturing the enzyme would defeat the purpose. The lactose is broken into glucose and galactose, which stay in the milk; it is not absorbed by the beads.
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.