Cambridge IGCSE Biology 21 Biotechnology and Genetic Modification Exam Questions

About Cambridge IGCSE Biology 21 Biotechnology and Genetic Modification

Biotechnology and genetic modification is the final topic in Cambridge IGCSE Biology and applies ideas from cells, enzymes, respiration and inheritance. Core candidates explain why bacteria are useful in biotechnology, describe the use of yeast to make biofuels and bread, pectinase in fruit juice production and enzymes in biological washing powders, and define genetic modification with examples. Extended candidates add lactase for lactose-free milk, the use of fermenters to produce insulin, penicillin and mycoprotein, the conditions a fermenter controls, the steps in inserting a human gene into bacteria, and the advantages and disadvantages of genetically modifying crops. Step-by-step genetic modification questions are common.

What you need to know

• 21.1 Why bacteria are useful Bacteria reproduce rapidly and can make complex molecules. Few ethical concerns are raised over their manipulation and growth. They share the same genetic code as other organisms and contain plasmids, which makes transferring genes easier.
• 21.2 Yeast Anaerobic respiration of yeast produces ethanol, which can be used as a biofuel. In bread-making, carbon dioxide from yeast respiration makes the dough rise.
• 21.2 Enzymes in industry Pectinase breaks down pectin in cell walls, increasing the volume and clarity of fruit juice. Biological washing powders contain enzymes such as proteases and lipases that digest stains at lower temperatures. Extended: lactase breaks down lactose to produce lactose-free milk.
• 21.2 Fermenters (Extended) Large-scale fermenters are used to produce insulin, penicillin and mycoprotein. Conditions controlled include temperature, pH, oxygen, nutrient supply and removal of waste products, with sterile conditions to prevent contamination.
• 21.3 Genetic modification Genetic modification is changing the genetic material of an organism by removing, changing or inserting individual genes. Examples include inserting human genes into bacteria to produce human proteins, and crops modified for herbicide or insect resistance or improved nutrition.
• 21.3 GM process and crops (Extended) The human insulin gene is isolated using restriction enzymes, forming sticky ends; plasmids are cut with the same restriction enzyme; DNA ligase joins the gene into the plasmid to form recombinant plasmids; these are inserted into bacteria, which replicate and express the gene. GM crops can increase yields and reduce pesticide use, but raise concerns about reduced biodiversity and cost of seeds.

Common mistakes in 21 Biotechnology and Genetic Modification

• Saying bacteria are used because they are easy to kill or are small. Give the syllabus reasons: rapid reproduction, ability to make complex molecules, few ethical concerns, shared genetic code and plasmids.
• Saying yeast makes bread rise by producing alcohol. Carbon dioxide makes the dough rise; the ethanol evaporates during baking.
• Leaving out restriction enzymes or DNA ligase in GM answers. Restriction enzymes cut DNA to form sticky ends; ligase joins the DNA together.
• Saying fermenters are kept at a high temperature to speed up growth. They are kept at the optimum temperature and cooled because respiration releases heat.
• Saying biological washing powders work at any temperature. Their enzymes have an optimum and are denatured at high temperatures.

Try three 21 Biotechnology and Genetic Modification exam-style questions