Final answer:
Among the provided factors, genetic modification is not an environmental factor that has been observed to affect cannabinoid content in hemp plants. It involves altering the plant's DNA, unlike light, temperature, and soil pH.
Correct answer is option d
Step-by-step explanation:
The cannabinoid content in hemp plants can be influenced by various environmental factors such as soil pH, light exposure, and temperature fluctuations. These variables can affect the growth and development of hemp plants, which in turn can influence their chemical composition, including cannabinoids like CBD or THC. Among the options provided, genetic modification is an intrinsic factor - it involves altering the plant's DNA to achieve desired traits. While genetic modification can potentially influence cannabinoid content, it is not considered an 'environmental' factor like the others listed.
When designing an experimental setup like the one Gary is conducting, it's crucial to control variables to ensure that any observed differences are due to the experimental treatment. Factors such as individual plant variation, differences in soil temperature due to container color, water loss due to evaporation, and the effect of insects could introduce uncontrolled variability into Gary's experiment, potentially confounding the results.