Question

1. You are an aspiring scientist, and you are wandering through the forest. You see a population of plants that is growing particularly large in a valley relative to the same species grown at the top of the hill. You hypothesize that this is due to either better nutrients that have settled in the valley, or a mutualistic relationship with a fungus called mycorrhizae. Design an experiment that will tell you which of these factors (if either) is responsible for the different growth patterns, and then what you would need to do to determine if correlation is causation.

Answer 1

We have to make some experimentation. The first analysis here to be made is a chemical test of the soil, as the first suspected factor (nutrients in the valley's soil) depends on it. We are going to take soil from both the valley and the hill and check if there are any nutritional differences for plants in them. If we manage to find differences, we are going to add them to some experimentation in the next step, if not, we can discard this as a factor. Another important step is to make sure the plants in the valley have mycorrhizae while the ones on the hill do not, if both have micorrhizae, then we can discard this factor as the reason for this observed phenomenon.

Now, the next step, experimentation, if we didn't discar the factors in the previous step. We will take 30 plant individuals for each treatment, we are going to measure growth through 3 months, each day we will resgister the cm grown for each individuals. One group will be the control, it will not be exposed to neither the valley's soil nor mycorrhizae in their roots. Another treatment will expose the plants to the valley's soil, another one will include mycorrhizae in their roots, and the final treatment will include both soil and mycorrhizae.

After obtaining our data through 3 months we will apply an ANOVA test to probe if there is any statistically significan difference between the treatments over plant growth. If there is no difference between any treatment, then the factor that is causing our observed phenomenon is none of these we selected.