Question

In an experiment to test the hypothesis that added phosphate will cause marigolds to produce more blooms, the experimenter has two groups of pots planted with marigold seeds. One group gets watered with phosphate added to the water, while the other group gets watered with no phosphate. Both groups get the same amount of water and light. Which is a controlled variable in this experiment?

Answer 1

Phosphate is a controlled variable in this experiment because the experimenter is controlling the amount of phosphate given and which group it is given to. 

Answer 2

Water or light

Step-by-step explanation:

In an experiment there is an experimental variable and all other variables must be kept the same (i.e., the controlled variables) so that any observed change can be attributed to the experimental variable. In this case, the researcher gives one group of marigolds phosphate dissolved in their water while the other group (the control group) only gets water. In the experiment, the variables that are kept the same (i.e., water and light) are the controlled variables. Only phosphate, the experimental variable, is allowed to change.