Biological Resources

IGCSE Edexcel Biology
5.1–5.16 Crop yields, fermentation, selective breeding, and genetic modification
Key Concepts: Humans manipulate living organisms to produce food and useful products. Techniques include optimising growing conditions, selective breeding, fermentation using microorganisms, and genetic engineering.

Section A — Improving Crop Yields

1. State four ways in which farmers can increase crop yields. [4]
2. Explain how the use of fertilisers increases crop yield. [2]
3. State one advantage and one disadvantage of using pesticides on crops. [2]

Section B — Fermentation

4. Define fermentation in the context of microorganism use. [2]
5. Describe the role of yeast in bread-making and beer/wine production. [4]
6. Describe the role of bacteria in the production of yoghurt. [3]
7. State the conditions needed in an industrial fermenter to maximise production of a useful product. [4]

Section C — Selective Breeding

8. Describe the process of selective breeding. [3]
9. Give two examples of selective breeding in animals and two in plants, stating the desired characteristic in each case. [4]
10. State one disadvantage of selective breeding. [1]

Section D — Genetic Modification

11. Describe the process of genetic engineering to produce human insulin in bacteria. Include all the key steps. [6]
12. State two advantages and two disadvantages of genetically modified (GM) crops. [4]
13. Explain the difference between selective breeding and genetic modification. [2]

Total marks: 41

Mark Scheme

1. Any four: use of fertilisers; pesticides (kill pests/diseases); herbicides (remove weeds); irrigation (ensure adequate water); use of glasshouses; selective breeding for higher-yielding varieties [4]
2. Fertilisers provide mineral ions (e.g. nitrates) [1]; these are needed for plant growth (e.g. to make proteins/chlorophyll), so plants grow faster and produce more [1] [2]
3. Advantage: kills pests that damage crops, increasing yield; Disadvantage: kills other non-target organisms / accumulates in food chains (bioaccumulation) / causes pollution [2]
4. The use of microorganisms (such as bacteria or fungi) to break down organic molecules to produce useful products [2]
5. Bread: yeast anaerobically respires glucose → produces CO₂ → dough rises [2]; ethanol also produced but evaporates during baking; Beer/wine: yeast respires glucose anaerobically → produces ethanol (alcohol) and CO₂ [2] [4]
6. Bacteria (Lactobacillus) are added to warm milk [1]; bacteria ferment lactose (milk sugar) producing lactic acid [1]; lactic acid causes milk proteins to denature/coagulate → milk thickens into yoghurt [1] [3]
7. Any four: controlled temperature (optimum for microorganism growth); pH control; stirring/mixing (ensure even distribution of nutrients); aseptic conditions (prevent contamination); nutrient supply; O₂ supply (for aerobic fermentation) or absence of O₂ (anaerobic) [4]
8. Select individuals with the desired characteristic [1]; breed them together [1]; select offspring with the best expression of the desired characteristic and breed again; repeat over many generations [1] [3]
9. Animals: e.g. cows bred for high milk yield; dogs bred for herding ability/size; pigs bred for lean meat; Plants: e.g. wheat bred for disease resistance; tomatoes bred for high yield; any valid examples [4 — 1 per example with characteristic]
10. Reduces genetic diversity (inbreeding) [1]; makes population vulnerable to new diseases [1]; (accept: can take many generations to achieve desired trait) [1]
11. Human insulin gene is identified and cut from human DNA using restriction enzymes [1]; a bacterial plasmid is cut open with the same restriction enzyme [1]; insulin gene is inserted into the plasmid using ligase enzyme [1]; the recombinant plasmid is inserted into a bacterium [1]; bacteria multiply and produce human insulin [1]; insulin is extracted and purified [1] [6]
12. Advantages (any two): higher crop yields; pest/disease resistance; improved nutritional content; reduced need for pesticides; Disadvantages (any two): possible ecological effects (gene transfer to wild plants); reduced biodiversity; ethical concerns; unknown long-term effects [4 — 1 per point]
13. Selective breeding selects for naturally occurring variation within a species over many generations [1]; genetic modification directly inserts genes from a different species into an organism's DNA [1] [2]