Final answer:
The experiment's main error is the unequal exposure to sunlight for the control and test groups, which should have been kept constant alongside other conditions to isolate the variable being tested—the presence of detergent in the soil. The correct option is c) No control group
Step-by-step explanation:
The biggest flaw in the student's plant growth experiment is the fact that the control group and the test group are not treated equally apart from the independent variable, which in this case is the presence of detergent in the soil. Specifically, the error lies in the fact that the seed pots with detergent were placed in the sun while the seed pots with no detergent were placed in the shade. For a proper experiment, all other conditions must be kept constant except for the independent variable. Therefore, both sets of seed pots should have been exposed to the same light conditions to accurately assess the impact of detergent on plant growth.
Gary's experiment likely involves testing a single variable while keeping other factors consistent. For example, pot size, amount of water, and the amount of sunshine could be controlled while varying something such as soil type or adding plant food. Experiments like this help scientists understand particular aspects of plant growth under controlled conditions.
In a correctly set up experiment with a control group, like the one with two rows of corn, one row would receive fertilizer (test group) and the other wouldn't (control group), with both rows getting equal sun and water. The row without fertilizer serves as the control to compare against the effects of fertilizer on growth in the test group. The correct option is c) No control group