18.1 Biotechnology
Biotechnology is the use of living organisms, or substances from them, to make useful products.
Yeast
Yeast is a single-celled fungus. It respires anaerobically when there is no oxygen (fermentation):
- Bread: yeast ferments the sugar in the dough. The carbon dioxide makes bubbles that make the dough rise. (The ethanol evaporates during baking.)
- Ethanol (alcoholic drinks and biofuel): the ethanol made by yeast is used in alcoholic drinks, and as a fuel.
Bacteria
Further reasons:
- there are no ethical concerns over their manipulation and growth (unlike animals);
- they contain plasmids, which can be used to carry new genes (in genetic modification).
Fermenters
A fermenter is a large container in which bacteria or fungi are grown on a large scale to make a useful product, such as an antibiotic, a hormone or an enzyme.
The conditions that must be controlled to give the best rate of growth and product:
| Condition | Why |
|---|---|
| temperature | enzymes work best at the optimum temperature (a water jacket cools the vessel, since respiration releases heat) |
| pH | enzymes work best at the optimum pH |
| oxygen | needed for aerobic respiration (air is pumped in) |
| nutrient supply | glucose, nitrogen sources and minerals for growth |
| waste products | removed, because they could poison the culture or slow growth |
A stirrer mixes the contents so that the microorganisms get nutrients and oxygen and the temperature is even.
Enzymes in industry
| Enzyme | Use |
|---|---|
| in biological washing powders (proteases, lipases) | digest proteins and fats in stains, so that clothes are cleaned at lower temperatures |
| pectinase | breaks down pectin in fruit cell walls, so more fruit juice is released and it is clearer |
| lactase | breaks down lactose to glucose and galactose, to make lactose-free milk for people who are lactose intolerant |
18.2 Genetic modification
Making human insulin
The gene that controls the production of human insulin is cut from human DNA and inserted into the DNA of bacteria (using a plasmid). The bacteria are grown in fermenters, and they make human insulin, which can be collected and used to treat diabetes. The insulin is cheaper and purer than that taken from animals.
Genetically modified crop plants
Genes can be inserted into crop plants:
- to give resistance to herbicides (so that weeds can be killed without damaging the crop);
- to give resistance to insect pests (so less insecticide is needed);
- to provide additional vitamins (for example "golden rice", which contains extra vitamin A).
Advantages and risks
| Advantages | Risks |
|---|---|
| a higher yield, so more food | the gene may spread to wild plants (for example, herbicide resistance spreading to weeds) |
| less insecticide used | possible harm to other organisms (for example insects that are not pests) |
| food with more nutrients | possible effects on human health (allergies), not fully known |
| crops grow in difficult conditions | cost: the seeds are expensive, and farmers may have to buy them each year |
| bacteria can make useful products such as insulin | loss of biodiversity if only GM crops are grown |
Bacteria reproduce rapidly, can make complex molecules such as proteins, have plasmids that can carry the human gene, and there are no ethical concerns about growing them.
Practise this chapter
Every past-paper question on these topics, with the mark scheme.