The shape of the lesson
By the end of the lesson, learners can
- Inside a fermenter: Extended.
- Five conditions to control: Extended.
- Products: insulin (GM bacteria), penicillin (Penicillium), mycoprotein (Fusarium).
- Five conditions: temperature, pH, oxygen, nutrient supply, waste products.
- Always link each condition to enzymes, respiration or growth in your answer.
- Sterile conditions stop contamination by other microorganisms.
One picture every idea returns to
Extended. Fermenters are large, sterile vessels used to grow bacteria and fungi on a large scale so they make useful products such as insulin (genetically modified bacteria), penicillin (the fungus Penicillium) and mycoprotein (the fungus Fusarium). The conditions are controlled: temperature, pH, oxygen, nutrient supply and removal of waste products, so the microorganisms grow fast and give a high yield.
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, Growing microbes by the tonne.. A fermenter is a huge sterile steel vessel in which bacteria or fungi grow under carefully controlled conditions. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Inside a fermenter | Extended. Project tab 6 of the lab (An industrial fermenter) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Five conditions to control | Extended. | Corners |
| 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, 20 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 Five conditions to control, 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.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
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 |
|---|---|
| The water jacket cools the fermenter. | The microorganisms release heat by respiration, so without cooling the temperature would rise and denature their enzymes. |
Fermenters: worksheet
6 questions, 20 marks. Written in the style of the papers; no past paper question is reproduced.
Extended. Name the organism used to make each product in a fermenter: (a) insulin, (b) penicillin, (c) mycoprotein.
Extended. Explain why the temperature inside a fermenter must be controlled and how this is done.
Extended. Explain why sterile air is bubbled into a fermenter used to grow Fusarium.
The table shows the mass of microorganisms in two fermenters. In fermenter B the pH was not controlled.
| Time / hours | 0 | 8 | 16 | 24 | 32 |
|---|---|---|---|---|---|
| Fermenter A / g dm−3 | 1 | 5 | 20 | 34 | 36 |
| Fermenter B / g dm−3 | 1 | 4 | 11 | 15 | 16 |
(a) Calculate the difference in mass between A and B at 32 hours. (b) Explain the difference.
Extended. Suggest why growth in a fermenter eventually stops even when temperature and pH are controlled, if no fresh nutrients are added and no waste is removed.
Extended. Describe how fermenters can be used for the large-scale production of a useful product.
Answer key and marking notes
- (a) Bacteria that have been genetically modified with the human insulin gene.
- (b) The fungus Penicillium.
- (c) The fungus Fusarium.
- The microorganisms respire and release heat, so the temperature rises.
- If it rises above the optimum, enzymes are denatured, so growth and product formation fall.
- If it is too low, enzymes work slowly and growth is slow.
- A water jacket around the tank carries cold water that removes heat; a temperature probe monitors it.
- The air supplies oxygen for aerobic respiration.
- Aerobic respiration releases more energy, so the fungus grows faster and gives a higher yield of mycoprotein.
- The air is sterile so that no other microorganisms contaminate the culture or compete with the fungus.
- (a) 36 − 16 = 20 g dm−3.
- (b) In B, waste products (such as carbon dioxide or acids) change the pH away from the optimum.
- The enzymes of the microorganisms work more slowly (or are denatured) away from their optimum pH.
- So respiration and growth are slower and the final mass is lower; in A acid or alkali is added to keep the pH at the optimum.
- The nutrients (such as sugars) are used up, so there is no more substrate for respiration and growth.
- Toxic waste products build up and can kill the microorganisms.
- So the population stops increasing and may decline.
- The fermenter is sterilised and filled with a sterile nutrient solution, then a pure culture of the bacterium or fungus is added.
- Conditions are kept at the optimum: temperature (water jacket), pH (probe, acid or alkali), oxygen (sterile air), nutrients (inlet), and waste gases removed; the contents are stirred.
- After growth, the culture is drained off and the product (for example insulin, penicillin or mycoprotein) is extracted and purified.
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.
Extended: which product is made in fermenters by genetically modified bacteria?
- Ainsulin
- Bpenicillin
- Cmycoprotein
- Dpectinase
Extended: a fermenter has a jacket through which water flows. Which statement explains why this is needed?
- ARespiration releases heat, which must be removed to stop enzymes being denatured
- BThe microorganisms need warm water pumped in to start respiring
- CThe water supplies oxygen to the microorganisms through the wall
- DThe water removes carbon dioxide made by the microorganisms
Extended: why is a fermenter sterilised with steam before a new batch is started?
- ATo kill any microorganisms that would compete with the culture or contaminate the product
- BTo warm the tank to the optimum temperature for the microorganisms
- CTo add water vapour as a nutrient for the microorganisms
- DTo denature the enzymes in the product before it is collected
Extended: the fungus Fusarium is grown to make mycoprotein. Which nutrient must be supplied for the fungus to make protein?
- AA source of nitrogen, such as ammonium salts or amino acids
- BExtra oxygen only, with no other nutrients
- CPure glucose with no other substances added
- DCarbon dioxide gas bubbled through the liquid
Extended: a pH probe shows that the pH in a fermenter is falling below the optimum. What should be done?
- AAdd a small amount of alkali
- BAdd more acid
- CSwitch off the stirrer
- DTurn off the air supply
Extended: the graph shows the mass of fungus in a fermenter where no fresh nutrients were added. Between which times was the rate of growth greatest?
- A16 to 24 hours
- B0 to 8 hours
- C32 to 40 hours
- D48 to 56 hours
Extended: using the graph, calculate the mean rate of growth between 8 and 32 hours.
- A1.7 g per dm3 per hour
- B40 g per dm3 per hour
- C1.4 g per dm3 per hour
- D5.0 g per dm3 per hour
Extended: the mass of fungus on the graph falls after 40 hours. Which is the best explanation?
- ANutrients have been used up and toxic waste products have built up
- BThe fungus has stopped respiring because it has too much oxygen
- CThe temperature control has made the fermenter too cold
- DThe fungus has turned into penicillin, which leaves the tank
Quiz key
Insulin is a human protein made by bacteria that carry the human insulin gene. Penicillin is made by the fungus Penicillium and mycoprotein by the fungus Fusarium, neither of which needs to be genetically modified. Pectinase is an enzyme used in juice production, not a product the syllabus links to GM bacteria in fermenters.
Millions of respiring microorganisms release heat, so cold water in the jacket carries heat away and keeps the temperature at the optimum. The main problem is overheating, not starting the culture. Oxygen is supplied as sterile air bubbled into the liquid. Carbon dioxide leaves through the waste gas outlet, not through the jacket.
Steam kills unwanted microorganisms that would compete for nutrients, lower the yield or contaminate the product. Steam is far hotter than the optimum, so the tank cools before the culture is added. Water is not supplied this way as a nutrient. Denaturing the product would ruin it, and sterilising happens before growth, not at collection.
Proteins contain nitrogen, so the fungus needs a nitrogen source as well as sugar to build them. Oxygen is needed for aerobic respiration but supplies no nitrogen. Glucose provides energy and carbon but no nitrogen. Carbon dioxide is a waste product of the fungus, which does not photosynthesise.
Waste products such as carbon dioxide make the culture more acidic, so alkali is added to bring the pH back to the optimum. Adding acid would lower the pH even further. Switching off the stirrer would leave nutrients, oxygen and heat unevenly spread and would not correct the pH. Turning off the air would stop aerobic respiration.
Between 16 and 24 hours the mass rises from 14 to 34 g per dm3, an increase of 20, the largest in any 8-hour interval. From 0 to 8 hours it rises by only 2 because the population is still small. From 32 to 40 hours it rises by just 1 as growth levels off. From 48 to 56 hours the mass falls.
The mass rises from 4 to 44 g per dm3, a change of 40, over 24 hours: 40 ÷ 24 = 1.7 g per dm3 per hour. 40 is the change in mass with no division by time. 1.4 divides the final mass by the end time (44 ÷ 32). 5.0 divides by 8 hours instead of the 24-hour interval.
With no fresh nutrients the food supply runs out, and waste products build up and become toxic, so more cells die than are produced. Oxygen does not stop respiration. A working temperature control keeps the culture at the optimum rather than too cold. Fusarium makes mycoprotein; penicillin is made by a different fungus, and cells do not turn into a product.
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.