The shape of the lesson
By the end of the lesson, learners can
- One cell becomes millions: Press Start dividing.
- Few ethical worries, and plasmids: Extended.
- Core reasons: rapid reproduction rate; ability to make complex molecules (e.g. proteins).
- Extended reasons: few ethical concerns over their manipulation and growth; they contain plasmids.
- Doubling: number = 2n, where n = time ÷ time for one division.
- Plasmid: small circular DNA, separate from the chromosome, copied every time the cell divides.
One picture every idea returns to
Bacteria are useful in biotechnology and genetic modification because of their rapid reproduction rate and their ability to make complex molecules, such as proteins. Extended: there are few ethical concerns over their manipulation and growth, and they contain plasmids, small circular pieces of DNA that can be cut open and used to carry new genes into them.
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, Small, fast and easy to change.. Biotechnology uses living organisms to make products people need, and bacteria are the workhorses. 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: One cell becomes millions | Press Start dividing. Project tab 1 of the lab (Bacteria dividing every 20 minutes) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Few ethical worries, and plasmids | Extended. | Mix-Pair-Share |
| 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 Few ethical worries, and plasmids, 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.
Mix-Pair-Share
Students mix around the room until you call pair; they pair with the nearest classmate, discuss the prompt, then mix again. Three prompts of rising difficulty, three different partners.
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 |
|---|---|
| Doubling is not adding. | After 1 hour there are 8 bacteria, not 3 or 4: each 20 minutes the number is multiplied by 2 (1, 2, 4, 8,...). |
| A plasmid is not the bacterial chromosome and it is not a nucleus. | Bacteria have no nucleus: the chromosome lies free in the cytoplasm, and plasmids are extra small rings of DNA. |
Why bacteria are used: worksheet
6 questions, 18 marks. Written in the style of the papers; no past paper question is reproduced.
State two reasons why bacteria are useful in biotechnology.
A bacterium divides once every 20 minutes. Starting with a single bacterium, calculate the number of bacteria present after 4 hours. Show your working.
The table shows the number of bacteria in a culture.
| Time / min | 0 | 25 | 50 | 75 | 100 |
|---|---|---|---|---|---|
| Number of bacteria | 100 | 200 | 400 | 800 | 1600 |
(a) State the time taken for the population to double. (b) Predict the number of bacteria at 150 minutes.
Extended. Discuss why bacteria, rather than animals, are usually used when an organism is genetically modified to make a human protein.
Extended. Describe what a plasmid is and state where it is found.
A company can make an enzyme either by extracting it from the pancreas of cattle or by growing bacteria that make it. Suggest three advantages of using bacteria.
Answer key and marking notes
- They have a rapid reproduction rate, so large populations are grown quickly.
- They can make complex molecules, such as proteins (for example enzymes or insulin).
- 4 hours = 240 minutes; 240 ÷ 20 = 12 divisions.
- Number = 212.
- = 4096 bacteria.
- (a) 25 minutes (the number doubles every 25 minutes).
- (b) 150 minutes is two more doubling times after 100 minutes.
- 1600 × 2 × 2 = 6400 bacteria.
- Bacteria reproduce very rapidly, so a large population making the protein is produced quickly.
- They can make complex molecules such as proteins using the instructions in a gene.
- There are few ethical concerns over the manipulation and growth of bacteria, because they are single-celled with no nervous system; modifying animals raises more objections.
- Bacteria contain plasmids, which can be used to carry the human gene into the cell and are copied every time the cell divides.
- A small, circular piece of DNA.
- Found in the cytoplasm of bacteria (prokaryotic cells).
- Separate from the main circular chromosome; it carries a few genes and is copied when the cell divides.
- Bacteria reproduce rapidly, so large quantities can be made quickly, all year round.
- No animals need to be killed, so there are fewer ethical concerns.
- The supply does not depend on the number of cattle slaughtered; the product is consistent and there is less risk of passing on animal diseases.
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 pair of features makes bacteria useful in biotechnology and genetic modification?
- AThey reproduce rapidly and can make complex molecules
- BThey are large cells and can carry out photosynthesis
- CThey have a nucleus and reproduce only sexually
- DThey grow slowly and make only simple molecules
The table shows the growth of a bacterial culture. What is the time taken for the population to double?
- A30 minutes
- B60 minutes
- C15 minutes
- D120 minutes
Using the same culture in the table, how many bacteria would be present at 180 minutes if growth continued at the same rate?
- A32 000
- B12 000
- C16 000
- D64 000
A company wants to make a large amount of an enzyme as quickly as possible. Why is it better to use bacteria than to extract the enzyme from a crop plant?
- AThe bacteria can produce a huge population making the enzyme in hours
- BThe bacteria contain larger amounts of DNA than plant cells
- CThe bacteria do not need any nutrients or suitable conditions
- DThe bacteria can make enzymes without using any of their genes
Which of these is a complex molecule that bacteria are used to make?
- AHuman insulin, a protein
- BWater, a product of respiration
- COxygen, a waste gas
- DSodium chloride, a salt
Which description of a plasmid is correct?
- AA small circular piece of DNA found in the cytoplasm of a bacterium
- BThe large circular chromosome that carries most of a bacterium's genes
- CA protein in the cell membrane that carries DNA into a cell
- DThe membrane around the nucleus of a bacterial cell
Why are plasmids especially useful when bacteria are genetically modified to make a human protein?
- AA gene inserted into a plasmid is copied every time the bacterium divides
- BPlasmids cut DNA at specific base sequences to remove a gene
- CPlasmids join two pieces of DNA together permanently
- DPlasmids stop the bacteria from reproducing so they make more protein
A student says: 'Bacteria are chosen for genetic modification mainly because they are dangerous, so changing them makes them safe.' Which reply best corrects the student?
- ABacteria are chosen because there are few ethical concerns over their manipulation and growth
- BBacteria are chosen because every species of bacterium causes disease in humans
- CBacteria are chosen because changing their genes always kills them
- DBacteria are chosen because they have no DNA that could be changed
Quiz key
The syllabus reasons are a rapid reproduction rate and the ability to make complex molecules such as proteins. Bacteria are very small cells and most do not photosynthesise. They have no nucleus and reproduce asexually by dividing in two. Slow growth and simple products would make them useless for large-scale production.
The number goes 500, 1000, 2000, 4000, 8000: it doubles every 30 minutes. In 60 minutes it multiplies by 4, not 2. 15 minutes is half the real doubling time. 120 minutes is the whole time shown, in which the population increases sixteen times.
From 120 to 180 minutes is 60 minutes, which is two doubling times of 30 minutes, so 8000 × 2 × 2 = 32 000. 12 000 comes from adding 2000 each half hour instead of doubling. 16 000 is only one doubling. 64 000 is three doublings, which would take 90 minutes.
Bacteria can divide every 20 to 30 minutes, so a large population, and therefore a large amount of product, can be grown in hours rather than the months a crop needs. Bacterial cells contain less DNA than plant cells, not more. Bacteria still need nutrients, a suitable temperature and pH. Every enzyme is a protein made using the instructions in a gene.
Insulin is a protein, a large complex molecule built from amino acids using a gene, and genetically modified bacteria make it. Water and oxygen are small simple molecules, and bacteria do not release oxygen as a waste product of respiration. Sodium chloride is a simple inorganic salt, not something cells need to build.
Plasmids are small rings of DNA in the bacterial cytoplasm, separate from the chromosome. The large circular chromosome is a different structure that carries most of the genes. Plasmids are DNA, not proteins. Bacteria have no nucleus, so they have no nuclear membrane.
A plasmid carrying the human gene is copied each time the cell divides, so every bacterium in the growing population inherits the gene and makes the protein. Cutting DNA is done by restriction enzymes and joining by DNA ligase, which are enzymes rather than plasmids. GM bacteria are wanted to reproduce rapidly, not to stop.
Few ethical concerns arise because bacteria are single-celled with no nervous system, so growing, changing and killing them in huge numbers raises few objections. Most bacteria do not cause disease, and harmless strains are used. GM bacteria must survive and reproduce to be useful. Bacteria have DNA in their chromosome and plasmids, which is what is modified.
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.