A student performed an experiment to determine the effect of acid rain on plant growth. The student divided 80 seeds of a fast-growing plant species into four groups of 20 seeds each. The four groups of seeds were then planted in soil. After all of the seeds germinated in the same growing conditions, they were watered once a day with simulated rainwater that had different levels of acidity. The acidity of the four different watering solutions was as follows: neutral water, 0.1%, 1.0%, and 10%. The average height of the plants in each group was measured over a two-week period.

Complete the following items using the information above

a. Identify the independent variable in the experiment.
b. Describe the control in the experiment.
c. Based on the described experiment, state a valid hypothesis for the experiment.
d. The experiment was repeated and each soil had the addition of crushed limestone. Describe how the modification of the study would affect the results.

a) The independent variable is the variable which is being taken as the source of an observation. It is the variable which is unaffected (changed) by other factors in the experiment

Here the independent variable is the acidity (concentrations) of the watering solutions

b, The control in the experiment is the plant group which are not administered the treatment of the experiment, such that they are kept the same through out to aid in validation of the correlation between the dependent and the independent variables

The control in the experiment are the group of 20 plants that received neutral water

c. A valid hypothesis is that there is no difference in the level of growth of a plant grown in acid rain and one grown with natural water

d. Limestone is composed of calcium carbonate, which is an alkaline that dissolves in water to form a basic solution that neutralizes the effect of the added acid such that it will invalidate the correlation of the level of plant growth with exposure to acid rain

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