An environmental scientist is investigating the relationship between the ratio of organic compost to synthetic fertilizer in soil and the total yield of tomato plants (in kg) after a 12-week growing period.
In a controlled greenhouse trial, 11 tomato plants of the same variety (Ailsa Craig) were grown in individual 10-litre pots. The total mass of compost and fertilizer added was kept constant at 500 grams per pot. Each plant (labelled A to K) was allocated a different ratio of compost to synthetic fertilizer, as shown in Table 1.
Table 1: The mass (in grams) of organic compost and synthetic fertilizer added to each pot
| A | B | C | D | E | F | G | H | I | J | K | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Organic Compost (g) | 500 | 450 | 400 | 350 | 300 | 250 | 200 | 150 | 100 | 50 | 0 |
| Synthetic Fertilizer (g) | 0 | 50 | 100 | 150 | 200 | 250 | 300 | 350 | 400 | 450 | 500 |
Suggest one other variable that the scientist should have controlled or kept constant for all the plants. Explain how failing to control this variable might have affected the final tomato yield.
689 exam-style questions on AQA A Level Psychology Scientific processes. Each one has a worked solution and a mark scheme showing where the marks go.