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

This study guide teaches Topic 18, Biotechnology and genetic modification, for Cambridge O Level Biology 5090. It is aligned to the Cambridge O Level Biology 5090 syllabus for examination in 2026, 2027 and 2028 (version 4), and covers every learning outcome in sections 18.1 Biotechnology and 18.2 Genetic modification. The 5090 syllabus is not tiered, so every candidate studies all of it.

Use it with the revision notes for this topic and the practice questions. The course hub lists every topic, and the printable checklist lets you tick off each outcome. This topic builds on three others: anaerobic respiration in yeast (see the Respiration study guide), enzyme action (see the Enzymes study guide) and the structure of a bacterial cell (see Cell structure and organisation). To find your weak spots quickly, try one of the free 10-minute diagnostics.

What this topic covers

Syllabus ref	What you must be able to do
18.1.1	Explain the role of yeast in the production of bread and ethanol
18.1.2	Understand that bacteria are useful because they reproduce rapidly and can make complex molecules
18.1.3	Discuss why bacteria are useful: no ethical concerns over their manipulation and growth; presence of plasmids
18.1.4	Describe how fermenters are used for large-scale production by bacteria and fungi, and the conditions controlled: temperature, pH, oxygen, nutrient supply and waste products
18.1.5	Describe the use of enzymes in biological washing powders, pectinase for fruit juice and lactase for lactose-free milk
18.2.1	Describe genetic modification as changing the genetic material of an organism by removing, changing or inserting individual genes
18.2.2	Understand that the human insulin gene has been inserted into bacterial DNA for commercial production of insulin
18.2.3	Outline GM crop plants with genes inserted for herbicide resistance, insect pest resistance and additional vitamins
18.2.4	Discuss potential advantages and risks of genetic modification, limited to crop plants and bacteria

Biotechnology means using living organisms, or their enzymes, to make useful products.

18.1.1 Yeast in bread and ethanol production

Both uses depend on anaerobic respiration in yeast:

glucose → ethanol + carbon dioxide

The useful product differs in each case.

Bread

1. Flour, water, sugar and yeast are mixed into a dough. The sugar is the yeast’s respiratory substrate.
2. The dough is left somewhere warm. Yeast respires and releases carbon dioxide.
3. The gas is trapped as bubbles in the stretchy dough, so the dough rises.
4. In the oven, the heat makes the bubbles expand further, then kills the yeast. Most of the ethanol made evaporates during baking.

So in bread, carbon dioxide is the useful product. The dough is kept warm because yeast enzymes work faster near their optimum temperature.

Ethanol

Yeast is grown in a sugar solution (for example, from fruit or grain) with no oxygen. It respires anaerobically and the ethanol builds up. The carbon dioxide is let out. Ethanol is used in alcoholic drinks and can be used as a fuel. Oxygen is kept out because, with oxygen, yeast respires aerobically and makes carbon dioxide and water instead of ethanol.

Worked example 1: dough data

A ball of dough has a volume of 50 cm³. After 60 minutes at 30 °C its volume is 125 cm³. Calculate the percentage increase in volume and the mean rate of increase. Explain the increase.

• Increase = 125 − 50 = 75 cm³
• Percentage increase = (75 ÷ 50) × 100 = 150%
• Mean rate = 75 ÷ 60 = 1.25 cm³ per minute
• Explanation: yeast respires anaerobically, releasing carbon dioxide. The gas is trapped in the dough as bubbles, so the volume increases.

Always divide the change by the starting value for a percentage increase, not by the final value.

18.1.2 and 18.1.3 Why bacteria are useful

The syllabus gives four reasons. Learn them as a set.

Reason	What it means
Rapid reproduction rate	A population grows very quickly, so a large amount of product can be made in a short time
Ability to make complex molecules	Bacteria can make large molecules such as proteins, including human proteins once the right gene is added
No ethical concerns over manipulation and growth	Changing and growing bacteria does not raise the welfare or moral objections that experiments on animals do
Presence of plasmids	Plasmids are small, separate circles of DNA. A new gene can be inserted into a plasmid, and the plasmid taken up by a bacterium

In a “discuss” question, give the feature and then say why it helps: “bacteria have plasmids, so a gene can be inserted into a plasmid and carried into the bacterium”.

Worked example 2: rapid reproduction

In ideal conditions a bacterium divides into two every 30 minutes. Starting with one cell, how many cells are there after 4 hours?

• 4 hours = 240 minutes
• Number of divisions = 240 ÷ 30 = 8
• Number of cells = 2⁸ = 256

Each division doubles the population, so numbers rise very fast.

18.1.4 Fermenters

A fermenter is a large, closed vessel in which bacteria or fungi are grown in controlled conditions to make a useful product on a large scale. Examples include insulin from genetically modified bacteria and the antibiotic penicillin from the fungus Penicillium.

The syllabus limits the conditions to five. For each one, know how it is controlled and why.

Condition	How it is controlled	Why
Temperature	A water jacket around the vessel; cool water flows through it. A temperature probe monitors it	Respiration of the microorganisms releases heat. Too hot denatures their enzymes; too cold slows growth
pH	A pH probe; acid or alkali is added when needed	Enzymes work best at an optimum pH. Waste products can change the pH
Oxygen	Sterile air is bubbled in through an inlet; paddles stir the mixture	Needed for aerobic respiration, so the microorganisms grow and make product. Stirring spreads oxygen and nutrients evenly
Nutrient supply	Nutrients (for example glucose and a nitrogen source) are added through an inlet	Provide energy for respiration and materials for growth and the product
Waste products	Gases such as carbon dioxide leave through an outlet; the product and waste are drained off	Waste builds up and can slow growth or change the pH

Worked example 3: explaining a fault

The cooling water supply to a fermenter fails. Predict and explain what happens to the yield of product.

• The temperature inside rises, because respiration of the microorganisms releases heat and it is no longer removed.
• Above the optimum, enzymes in the microorganisms are denatured.
• Growth and product formation slow down or stop, so the yield falls.

18.1.5 Enzymes in industry

(a) Biological washing powders

Biological washing powders contain enzymes:

• proteases digest protein stains (such as blood or egg) into amino acids
• lipases digest fat and oil stains into fatty acids and glycerol
• amylase may also be added to digest starch stains

The products are small and soluble, so they wash out of the fabric. Because the enzymes work at moderate temperatures, clothes can be washed at a lower temperature, which saves energy and protects delicate fabrics. Too hot a wash denatures the enzymes.

(b) Pectinase in fruit juice production

Pectin helps to hold plant cells together and is part of plant cell walls. Pectinase breaks down pectin. Adding it to crushed fruit:

• breaks down the cell walls, so more juice is released from the same mass of fruit
• makes the juice clearer, because the pectin that makes juice cloudy is broken down

Worked example 4: pectinase data

100 g of apple pulp gives 18 cm³ of juice in 10 minutes without pectinase, and 27 cm³ with pectinase. Calculate the percentage increase.

• Increase = 27 − 18 = 9 cm³
• Percentage increase = (9 ÷ 18) × 100 = 50%

In a fair test the mass of pulp, temperature and time stay the same, and the control has boiled (denatured) pectinase added instead.

(c) Lactase for lactose-free milk

Lactose is the sugar in milk. Some people cannot digest it well (they are lactose intolerant). Lactase breaks lactose down:

lactose → glucose + galactose

Milk is treated with lactase so that the lactose is already broken down. People who are lactose intolerant can then drink it.

18.2.1 What genetic modification means

Genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes. A gene from one organism can be put into a different species, which then makes the protein that gene codes for.

18.2.2 Human insulin from bacteria

People with Type 1 diabetes need insulin (see Coordination and control). The gene that controls the production of human insulin has been inserted into bacterial DNA. In outline:

1. The human insulin gene is cut from human DNA.
2. It is inserted into a plasmid.
3. The plasmid is taken up by a bacterium.
4. The bacteria reproduce rapidly in a fermenter, and every new cell carries the gene.
5. The bacteria make human insulin, which is extracted and purified.

This links straight back to 18.1.3: plasmids carry the gene in, rapid reproduction gives a large population, and bacteria can make a complex molecule (a protein).

18.2.3 GM crop plants

The syllabus names three reasons for inserting genes into crop plants.

Gene inserted to	How it helps	Example
(a) Confer resistance to herbicides	The crop survives when the field is sprayed with herbicide, but weeds die. Less competition from weeds means a higher yield	Herbicide-resistant soya or maize
(b) Confer resistance to insect pests	The plant makes a protein that is toxic to certain insect larvae that eat it. Less damage; less insecticide needed	Crops with a gene from the bacterium Bacillus thuringiensis (Bt), such as Bt cotton
(c) Provide additional vitamins	The edible part contains a vitamin, or a substance the body turns into one	Golden Rice, which makes beta-carotene; the body converts this to vitamin A

18.2.4 Advantages and risks of GM

The syllabus limits this to crop plants and bacteria.

Potential advantages

• Higher crop yields, because weeds and insect pests do less damage.
• Less insecticide sprayed, so fewer harmful effects on other insects.
• More nutritious food, for example rice that helps reduce vitamin A deficiency.
• Large amounts of human insulin made cheaply and reliably by GM bacteria, identical to the human hormone.

Potential risks

• Inserted genes could spread to wild relatives by pollination, for example producing herbicide-resistant weeds.
• Insect pests could become resistant to the toxin over time.
• Insects that are not pests could be harmed by the toxin.
• Possible effects on human health (for example allergies) are a concern for some people.
• Farmers may have to buy new seed each year, which can be expensive.

Worked example 5: a “discuss” answer

Discuss whether a farmer should grow a variety of maize that is resistant to insect pests. [4 marks]

• For: less of the crop is eaten, so the yield is higher. [1]
• For: less insecticide is sprayed, saving money and harming fewer other insects. [1]
• Against: the pests may become resistant to the toxin, so the advantage is lost. [1]
• Against: the seed may cost more, and non-pest insects feeding on the crop could be harmed. [1]

A “discuss” answer needs points on both sides.

Common errors

• Saying yeast makes bread rise by making oxygen or alcohol. It is carbon dioxide.
• Forgetting that most of the ethanol in bread evaporates during baking.
• Saying plasmids are in the nucleus. Bacteria have no nucleus.
• Saying fermenters are heated. They usually need cooling, because respiration releases heat.
• Writing that enzymes are “killed” at high temperature. Enzymes are denatured; they are not alive.
• Saying pectinase digests cellulose. It breaks down pectin.
• Writing that lactase turns lactose into “glucose” only. The products are glucose and galactose.
• Describing herbicide resistance as protecting the crop from insects. Herbicides kill weeds.

Next steps

Test yourself with the revision notes, then try the practice questions.

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.