To explore the relationship between the two variables, it is useful to graph the data in a scatter plot and then draw a regression line. (a) First, place the labels for the dependent and independent variables on the appropriate axes. Explain your choices. (b) Now plot the data points for corn and velvet left using a different symbol for each set of data, and add a key for the two symbols. (For additional information about graphs, see the Scientific Skills Review in Appendix F.)

Carbon dioxide is necessary for photosynthesis. The photosynthesis process increases the growth of the plants. It, in turn, increases the productivity of crops.

The carbon dioxide concentration determines the productivity of the crops, so it is an independent variable. The average dry mass is the productivity that is gained out of the carbon dioxide level.

The labeling is plotted on the x-axis, and the y-axis is made as a concentration of carbon dioxide and average dry mass, respectively. The average dry group is the dependent variable, and the carbon dioxide concentration is an independent variable.

The scattered plot with the given variable is plotted as follows. The velvet plant is represented with the circle. The square symbol represents the average dry mass of the corn plant with three different values.