Final answer:
In experimental design, it is critical to distinguish between an experimental group that receives manipulation, a control group that does not, and controlled variables that remain constant. Example: testing the effect of phosphate on algal growth in ponds where the volume of water in each pond is a controlled variable.
Step-by-step explanation:
Understanding Experimental Design Components
In any well-constructed experiment, it is essential to distinguish between different types of variables and controls to ensure valid results. The experimental group is subject to the experimental manipulation, while the control group goes through all experimental phases without exposure to the manipulation, hence serving as a baseline for comparison. Controlled variables are factors that are kept constant across all groups to prevent them from affecting the outcome. An experiment to test if phosphate promotes algal growth in ponds would involve two groups: ponds with phosphate (experimental group) and ponds with an inert substance (control group). The presence or absence of phosphate is the independent variable, and the amount of algal growth is the dependent variable. Maintaining the same volume of water in each pond is an example of a controlled variable. A well-organized experiment must also have adequate statistical tests and sample sizes to discern meaningful differences between groups.
Considering the principles of the scientific method, hypotheses are rejected if they are inconsistent with the experimental data. For instance, if there is no significant difference in algal growth between ponds, the hypothesis that phosphate promotes growth would be rejected.