Pearson Edexcel International GCSE Science Single Award 5: Biology: Use of biological resources

Topic 5 examines how growing conditions, microorganisms and genetic engineering can increase biological production. These notes follow only the Science Single Award points in Pearson 4SS0 Issue 4. Fertilisers, pest control, fermenter design and selective breeding belong to broader Pearson routes and are not imported here.

The yeast investigation is named in the theory specification, but the separate practical-skills hub owns detailed planning, measurement and evaluation.

Increasing crop yield under cover

Glasshouses and polythene tunnels create a partly controlled environment around crop plants. They can raise temperature, shelter plants from severe weather, extend the growing season and reduce access by some pests. Growers can also manage irrigation and, in a glasshouse, enrich carbon dioxide or use supplementary lighting.

The mechanism must link to photosynthesis. At low temperature, enzyme-controlled reactions may be slow. Raising temperature toward an optimum can increase photosynthesis and growth. Increasing carbon dioxide can also increase rate while carbon dioxide is limiting. Neither change guarantees an unlimited yield increase. Once another factor such as light, water or mineral availability becomes limiting, further enrichment has little effect. Excessive temperature may reduce photosynthesis by disrupting enzyme function or increasing water loss.

Yield and profit are not identical. Heating, lighting and carbon dioxide enrichment have financial and environmental costs. A sensible grower compares the value of the extra crop with the cost of removing the limiting factor. Controlled conditions can also favour rapid spread of a pest or pathogen if it enters, so monitoring remains necessary.

Yeast in bread production

Yeast is a microorganism that can respire anaerobically. In bread dough it uses sugar and produces carbon dioxide and ethanol:

$$\text{glucose} \rightarrow \text{ethanol} + \text{carbon dioxide}$$