Which experimental procedure would provide the best evidence for the effect of light on plant growth?

Question

Plant seeds in different soils and expose them to different amounts of light, then measure plant growth.
Plant seeds in different soils and expose them to different amounts of light, then measure plant growth.

Measure plants receiving different amounts of light in their natural environments.
Measure plants receiving different amounts of light in their natural environments.

Plant seeds of the same variety in the same conditions and vary only the amount of light, then measure plant growth.
Plant seeds of the same variety in the same conditions and vary only the amount of light, then measure plant growth.

Measure plants of the same variety grown in environments that receive different amounts of light.

Answer 1

The best experimental procedure for providing evidence of the effect of light on plant growth is:

Plant seeds of the same variety in the same conditions and vary only the amount of light, then measure plant growth.

This approach ensures that you are controlling for other variables (such as soil type, water, temperature, and nutrients) and isolating the amount of light as the primary factor affecting plant growth. By using the same variety of seeds, you also minimize genetic variation, allowing you to attribute differences in growth more directly to changes in light exposure. This method follows the principles of a controlled experiment, making it more reliable for determining causal relationships.