Cambridge O Level Biology 5090: Biotechnology and genetic modification (5090) – Revision Notes

These revision notes condense Topic 18, Biotechnology and genetic modification, of the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4). They cover every learning outcome in sections 18.1 Biotechnology and 18.2 Genetic modification. The syllabus is not tiered, so all of it applies to every candidate. For full explanations and worked examples, read the study guide first.

When you are ready, try the practice questions. The course hub lists every topic, the printable checklist lets you tick off outcomes, and the free 10-minute diagnostics show where to focus. Two earlier topics feed into this one: the Respiration revision notes (anaerobic respiration in yeast) and the Enzymes revision notes (optimum temperature and denaturing).

Key definitions

Term	Definition
Biotechnology	Using living organisms, or their enzymes, to make useful products
Genetic modification	Changing the genetic material of an organism by removing, changing or inserting individual genes
Plasmid	A small, separate circle of DNA in a bacterial cell
Fermenter	A large, closed vessel in which microorganisms are grown in controlled conditions to make a product on a large scale
Lactose	The sugar in milk
Pectin	A substance in plant cell walls that helps hold cells together

18.1.1 Yeast: bread and ethanol

Equation to know: glucose → ethanol + carbon dioxide (anaerobic respiration in yeast)

	Bread	Ethanol
Useful product	Carbon dioxide	Ethanol
What it does	Bubbles trapped in the dough make it rise	Collected for drinks or fuel
What happens to the other product	Most of the ethanol evaporates during baking	Carbon dioxide is let out
Key condition	Warm, so yeast enzymes work fast	No oxygen, so respiration is anaerobic

Method in steps: explaining why dough rises (or does not)

1. Yeast respires anaerobically, using sugar in the dough.
2. Carbon dioxide is released.
3. The gas is trapped as bubbles, so the dough rises.
4. If the dough rises slowly, check the temperature: too cold and the yeast enzymes work slowly; too hot and they are denatured, so little or no carbon dioxide is made.

18.1.2 and 18.1.3 Why bacteria are used

Four syllabus reasons. Give the feature and the benefit.

1. Rapid reproduction rate → large population, lots of product, quickly.
2. Make complex molecules → can produce proteins such as human insulin.
3. No ethical concerns over their manipulation and growth → no animal-welfare objections.
4. Plasmids → a gene can be inserted into a plasmid and taken into the bacterium.

Method in steps: counting bacteria after repeated division

1. Convert the total time to minutes.
2. Divide by the time for one division to get the number of divisions, n.
3. Number of cells = starting number × 2ⁿ.

Reminder: a cell that divides every 25 minutes gives 100 ÷ 25 = 4 divisions in 100 minutes, so 1 cell becomes 2⁴ = 16 cells.

18.1.4 Fermenter conditions

The syllabus limits you to five. Learn the control and the reason as a pair.

Condition	Controlled by	Reason
Temperature	Water jacket (cooling) + temperature probe	Respiration releases heat; too hot denatures enzymes
pH	pH probe; acid or alkali added	Keeps enzymes at their optimum pH
Oxygen	Sterile air bubbled in; stirring paddles	Aerobic respiration for growth; stirring mixes oxygen and nutrients
Nutrient supply	Added through an inlet	Energy source and raw materials for growth and product
Waste products	Gas outlet; drained off	Build-up slows growth and alters pH

Method in steps: explaining a change in fermenter conditions

1. Name the condition that has changed and which way it moved (for example, pH has fallen).
2. Give the cause (waste products such as acids are building up, or the control has failed).
3. Link it to enzymes: away from the optimum, enzymes in the microorganisms work more slowly; too hot and they are denatured.
4. State the effect on growth and on the yield of product.

Reminder: if the oxygen supply fails, the microorganisms cannot respire aerobically, so growth slows and less product is made.

Examples of fermenter products: insulin (from GM bacteria) and penicillin (from the fungus Penicillium).

18.1.5 Enzymes in industry

Use	Enzyme(s)	What it does	Benefit
Biological washing powder	Proteases, lipases (amylase may be added)	Digest protein and fat stains into small soluble molecules	Stains wash out at lower temperatures, saving energy
Fruit juice	Pectinase	Breaks down pectin in plant cell walls	More juice from the same fruit; clearer juice
Lactose-free milk	Lactase	lactose → glucose + galactose	People who are lactose intolerant can drink the milk

Method in steps: reading washing powder data

1. Compare biological and non-biological powder at the same temperature.
2. Find the temperature where the biological powder works best (its enzymes’ optimum).
3. Above that temperature, explain the fall: the enzymes are denatured.
4. Quote values from the table or graph, with units.

Reminder: percentage increase = (change ÷ starting value) × 100. If juice volume rises from 40 cm³ to 50 cm³ with pectinase, the increase is (10 ÷ 40) × 100 = 25%.

18.2 Genetic modification

Insulin (18.2.2): the gene that controls the production of human insulin has been inserted into bacterial DNA. The bacteria multiply in fermenters and make human insulin, which is extracted for people with diabetes.

GM crops (18.2.3):

Gene inserted to	Effect
(a) Resist herbicides	Field sprayed with herbicide kills weeds but not the crop → less competition → higher yield
(b) Resist insect pests	Plant makes a toxin (Bt gene from a bacterium) that kills certain insect larvae → less damage, less insecticide
(c) Provide additional vitamins	e.g. Golden Rice makes beta-carotene, converted to vitamin A in the body

Advantages and risks (18.2.4), crops and bacteria only:

Advantages	Risks
Higher yields	Genes spread to wild relatives by pollen (e.g. herbicide-resistant weeds)
Less insecticide used	Pests become resistant to the toxin
More nutritious crops	Non-pest insects harmed
Plentiful, cheaper human insulin	Possible health effects such as allergies; seed costs for farmers

Method in steps: a “discuss” question on GM

1. Name the GM organism and the inserted gene’s effect.
2. Give at least two advantages, each with its reason.
3. Give at least two risks, each with its reason.
4. Keep every point to crop plants or bacteria, the only examples the syllabus asks for.

Must-know distinctions

• Bread vs ethanol: both use anaerobic respiration in yeast; bread needs the carbon dioxide, ethanol production needs the ethanol.
• Herbicide vs insecticide: herbicides kill weeds (plants); insecticides kill insects. Herbicide resistance protects the crop from the spray, not from insects.
• Pectin vs cellulose: pectinase breaks down pectin, not cellulose.
• Lactose vs lactase: lactose is the sugar; lactase is the enzyme (enzyme names end in -ase).
• Denatured vs killed: enzymes are denatured; microorganisms are killed.
• Plasmid vs chromosome: bacteria have a large circular DNA loop plus small plasmids; there is no nucleus.

Quick self-test

1. State the useful product of yeast in bread making.
2. What happens to most of the ethanol made in dough?
3. Apart from plasmids and ethics, give two reasons why bacteria are useful in biotechnology.
4. A bacterium divides every 20 minutes. How many cells come from one cell in 80 minutes?
5. Why does a fermenter need a water jacket?
6. Name two conditions in a fermenter that are monitored by a probe.
7. Name the two groups of enzymes in biological washing powders that digest protein and fat stains.
8. State the two benefits of adding pectinase to crushed fruit.
9. State the products when lactase acts on lactose.
10. Define genetic modification.
11. Name the three reasons the syllabus gives for inserting genes into crop plants.
12. Juice volume rises from 15 cm³ to 24 cm³ with pectinase. Calculate the percentage increase.

Answers

1. Carbon dioxide (bubbles make the dough rise).
2. It evaporates during baking.
3. Rapid reproduction rate; ability to make complex molecules.
4. 80 ÷ 20 = 4 divisions; 2⁴ = 16 cells.
5. Respiration of the microorganisms releases heat; cooling water stops the temperature rising above the optimum and denaturing enzymes.
6. Temperature and pH.
7. Proteases and lipases.
8. More juice is released; the juice is clearer.
9. Glucose and galactose.
10. Changing the genetic material of an organism by removing, changing or inserting individual genes.
11. Resistance to herbicides; resistance to insect pests; additional vitamins.
12. Change = 9 cm³; (9 ÷ 15) × 100 = 60%.

Where marks are usually lost

• Writing “yeast produces oxygen” or “alcohol makes bread rise”.
• Giving “bacteria are small” or “bacteria are cheap” instead of the syllabus reasons.
• Stating a feature of bacteria without the benefit, for example “they have plasmids” with no mention of inserting a gene.
• Saying a fermenter is heated, rather than cooled.
• Listing fermenter conditions outside the five in the syllabus, and missing one of the five.
• Writing that high temperature “kills” enzymes.
• Saying lactase makes “glucose” only.
• Confusing herbicide resistance with insect resistance.
• Giving only advantages in a “discuss” question about GM.
• Dividing by the final value when calculating a percentage increase.

Official syllabus

Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4), Topic 18: Biotechnology and genetic modification, published by Cambridge Assessment International Education.