Question

cientific process often begins with observations. For example, you may observe that plants die during a drought. Based on this observation, you form a hypothesis: If plants do not get enough water, then they will wilt or die. A valid hypothesis is a testable statement, usually based on observations. It is often stated using an “if … then” format. The next step in the scientific process would be to test your hypothesis by performing a scientific experiment.

Scientific experiments have an independent variable, a dependent variable, and a control group. An independent variable is the variable that will be deliberately changed by the experimenter. A dependent variable is the target variable that will be measured during the experiment. The control group are other variables that might change the results of the experiment unless they are kept constant. By controlling as many variables as possible, a relationship between the independent variable and dependent variable can be better established. As an experiment is carried out, scientists collect and record data. They also run multiple trials to increase the validity of the results. Next, they analyze the data to see if their hypothesis is supported or not. Making observations, asking questions, forming hypotheses, designing and performing experiments, analyzing data, and drawing conclusions are all parts of the scientific process.

Review the following scenarios and analyze the hypothesis and all variables. Evaluate the reporting procedures and outcome. Consider how each scenario might be improved.

Scenario 1: Can rose plants grow well in the shade?
A company advertises that it has developed a new variety of rose plant that grows well in the shade. A scientist decides to test this statement to see if evidence supports it. She purchases 40 one-gallon pots of this new variety and splits them into two groups in her greenhouse. The 20 rose plants in Group A are exposed to 12 hours of direct sunlight per day. The 20 rose plants in Group B are exposed to 12 hours of indirect sunlight (shade) per day. All other variables (such as watering, fertilization, and air flow) are kept constant. At the end of a 40-day period, she collects data for each group. The results are shown in the table below.

A 3 column table with 4 rows. Column 1 is unlabeled with entries Average height of plants in meters, Average number of flowers produced per plant, Average number of leaves produced per plant, Other Observations. Column 2 is labeled Group A with entries 1, 52, 157, Leaves were smaller and yellow compared to leaves on plants in Group B. Column 3 is labeled Group B with entries 2, 99, 229, Plants in this group appeared green, healthy, and robust.
Use the rose experiment to answer the question. What are the independent and dependent variables?

Answer 1

Independent variable: Type/amount of light—exposure condition (12 hours direct sunlight for Group A vs 12 hours indirect light/shade for Group B).

Dependent variables: the measured plant outcomes — average plant height (m), average number of flowers per plant, average number of leaves per plant, and the qualitative observations of leaf color/overall plant health.