Final answer:
The independent variable in a study on the impact of nitrogen on plant growth is the amount of nitrogen because it is what the researcher manipulates. Other variables like soil moisture must remain constant, and a control group, such as a row of corn without fertilizer, is used to compare the effects on plant growth. The correct option is a) the amount of nitrogen
Step-by-step explanation:
In a study focused on the role of nitrogen on plant growth, the independent variable is the amount of nitrogen. This is because the independent variable is what the researcher changes or manipulates in order to observe the effect on the dependent variable, which in this case is plant growth. Therefore, other factors like soil moisture, the control field, and the method of controlling other variables must remain constant to ensure that any changes in plant growth can be attributed to the amount of nitrogen provided.
In any experiment, the control group is used as a baseline to compare the results of the test group(s). For instance, if a scientist plants two rows of corn and only applies fertilizer to one, the row without the fertilizer acts as the control. This allows the scientist to isolate the effects of the fertilizer on corn growth, making it the independent variable while the corn growth itself is the dependent variable. The correct option is a) the amount of nitrogen