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.
Practise AQA A Level Psychology Research methods with exam-style questions for A Level Psychology. 100 questions covering Experimental method, Observational techniques, Self-report techniques, Correlations, Content analysis (A-level only), Case studies (A-level only), Scientific processes, Data handling and analysis, and Inferential testing (A-level only), matched to the AQA A Level Psychology (7182) specification and written in Paper 1, Paper 2 and Paper 3 style. Every question includes a full worked solution and mark scheme, so you can see where marks are awarded rather than just whether you got the answer right.