Soil pH and Growth: The Influence of Environmental Factors

Essential knowledge 4.C.2: Environmental factors influence the expression of the genotype in an organism.

Background: A student wanted to see how pH affects the growth of tomato plants. So, she varied the pHs of the soil the tomatoes were to grow in. She then placed 3 tomato plants in each soil pH type. She let the tomato plants grow for 4 weeks. She recorded their heights at the end of the experiment. The results are listed below:

Plant Group / Soil pH / Plant Height #1 (cm) / Plant Height #2 (cm) / Plant Height #3 (cm)
1 / 4.0 / 15.2 / 15.4 / 15.4
2 / 5.0 / 16.2 / 16.1 / 16.0
3 / 6.0 / 16.4 / 16.3 / 16.4
4 / 7.0 / 18.0 / 18.1 / 18.3
5 / 8.0 / 17.8 / 17.6 / 17.6
6 / 9.0 / 16.6 / 16.6 / 16.5
7 / 10.0 / 15.4 / 15.3 / 15.2

Part One: For each soil pH, calculate the average height of the tomato plants. Then, calculate the standard deviation for each soil pH. Do your work on a separate sheet of paper (do not use a graphing calculator to perform this task). Record your data below.

Plant Group / Soil pH / Average Height / Standard Deviation
1 / 4.0
2 / 5.0
3 / 6.0
4 / 7.0
5 / 8.0
6 / 9.0
7 / 10.0

Part Two: Correlation Analysis: For each soil pH type, plot the heights (not the average) of each tomato plant. Is there a positive or negative correlation with pH and height? Explain.

Part Three: Analysis of Data: Answer the questions below using complete sentences.

1) What soil pH had the lowest average height growth? What soil pH had the highest average height growth?

2) What is pH?

3) Based upon this data, what pH conditions are ideal for tomato plant growth? Justify your answer with data.

4) What could cause the pH of soil to change?

5) Based upon the data above, do you believe that environmental conditions are influencing the genotype amongst the tomato plants in these soil types?

6) Calculate the Hydrogen concentration of a soil sample with a pH of 7. Show your work.