In one region, the rainfall decreased and a new insect pest arrived in the same year. The yield of wheat in the region fell by 40%. A student concludes that the pest caused the fall in yield. Why is this conclusion not valid?
Two factors changed, so the effect of each one cannot be separated.
Insect pests only affect crops that are grown by using hydroponics.
Lower rainfall would increase the yield of wheat, not decrease it.
A fall of 40%40\%40% is too small to show that the pest had any effect.
127 exam-style questions on OCR GCSE Biology 6.2 Feeding the human race, covering 6.2.1 Biological factors affecting food security, 6.2.2 Agricultural solutions to growing demand, 6.2.3 Selective breeding, 6.2.4 Genetic engineering, 6.2.5 Steps in genetic engineering, 6.2.6 Benefits and risks of gene technology in agriculture, and 6.2.7 Biotechnological solutions to growing demand. Each one has a worked solution and a mark scheme showing where the marks go.