ACT (Enhanced)ScienceMedium
A student is investigating the effect of different types of soil on the growth of bean plants. They prepare three pots: Pot A with sandy soil, Pot B with clay soil, and Pot C with loam soil. All pots receive the same amount of water, sunlight, and seeds from the same batch. After three weeks, they measure the height of the plants. To improve the reliability of their results, what is the most important modification the student should make to their experimental design?
- AChange the amount of water given to each pot.
- BUse different types of plants in each pot.
- CMeasure the plant height only once at the end of the experiment.
- DIncrease the number of pots for each soil type.
Show answer & explanationAnswer & explanation
Correct answer: D. Increase the number of pots for each soil type.
Increasing the number of replicates (more pots per soil type) reduces the impact of random errors and individual variations among plants, making the average growth measurement for each soil type more reliable and representative.
Why the other options are wrong
- A. Changing water amounts would introduce another variable, confounding the effect of soil type.
- B. Using different plants would introduce another variable, making it impossible to isolate the effect of soil type.
- C. Measuring only once reduces the ability to observe growth over time and potentially misses important data points; it does not improve reliability.
Experimental Reliability
The consistency and reproducibility of experimental results, often improved by increasing sample size and controlling variables.
- High reliability means repeated experiments yield similar results.
- Replication (multiple trials/samples) is key to assessing reliability.
- Reduced by random error and insufficient sample size.
Memory trick: More samples, fewer surprises.