Question

Johannes wants to know whether soil, water, or both are needed for plant growth. He chooses to conduct experiments on a willow tree for five years to answer his question. How can his experimental methods be changed to improve his experiment?
He needs to ask scientists what they think.
He needs to conduct the experiment for a longer period.
He needs to use a larger sample size.
He needs to test more factors in the environment.

Answer 1

Change the sample size — he needs to use a larger sample size.

Why: one willow tree is only one replicate, so results may be due to chance or that single plant’s health rather than the effect of soil and water. Better replication gives reliable, generalizable results and lets you tell real treatment effects from random variation.

Practical improvements:
- Set up clear treatments (e.g., soil+water, water-only/hydroponic, soil-only/controlled moisture) and have multiple plants per treatment (at least 5–10 replicates if possible).
- Randomly assign plants to treatments and keep other conditions (light, temperature, pot size) the same.
- Measure objective growth metrics regularly (height, leaf number, biomass).
- Run the experiment long enough to see differences (often weeks–months for seedlings rather than five years).
- Optionally consult other scientists for design feedback, but the key change is replication.