Final answer:
In a bean plant experiment, 'd' typically represents an independent variable manipulated by the experimenter, such as the amount of fertilizer, to observe its effect on plant growth.
Step-by-step explanation:
The variable 'd' in the context of the bean plant experiment would typically represent an experimental factor that is being changed or manipulated to observe an effect on plant growth. Generally, this could refer to variables such as the amount of fertilizer or water given to each group of bean plants, or conditions such as the amount of sunlight they receive. In a controlled experiment, if 'd' refers specifically to the amount of fertilizer given, it would be the independent variable. The dependent variable, which is the outcome observed, might be the growth rate or final height of the bean plants. Remember, all other conditions such as water amount, pot size, and sunlight should be kept constant (controlled) to ensure the results can be attributed to the changes in the independent variable.