For the following examples explain whether the experiment de

For the following examples, explain whether the experiment described is well-controlled or not (or if you have insufficient information to make a decision) and give reasons for your answer.

Please give detailed, full explanations to the answers. Thank you! This is for an ecology class, so please have the answers relate back to ecology.

a) An ecologist wants to determine how well the seedlings of various trees survive in different amounts of light. He or she measures the average amount of light occurring on the ground under a variety of adult trees in the same area, records how long newly sprouted seedlings live near the parent tree, and then compares the relationship between light intensity and survival.
b) The same scientist does a similar experiment indoors in a greenhouse. He or she plants various seeds individually in large pots and then builds canopies using shade cloth of varying darkness over different pots. (Shade cloth is made with a variety of hole sizes in the mesh to limit the amount of light which passes through. It can be made to allow 95% light transmission, 90%, 85%, etc.)
c) The scientist repeats the experiment described in part b, but this time one of the greenhouse maintenance staff accidentally sprays some of the plants with a small amount of herbicide halfway through the experiment

Solution

a) This is not a well controlled set up.This is because when the plants are grown under trees,amount of light that occurs in the ground will be used by both the plants and the seedlings and there can be an unequal access to the intensity of light by the seedlings.We cannot say exactly how the light intensity affects the growth of seedlings.

b)This is a well controlled set up.From this experimental set up , we can actually infer how the amount of light affects the survival of the plants since the canopies build on the pots with plants allow different intensities of light to pass through.

c) This is not a well controlled set up.This is because herbicides are mainly used to retard the plant growth and this will interfere with the purpose of our experiment.Since we want to study the effect of light on plant growth, spraying of herbicide halfway will alter the actual results as and we would not be able to infer if it is the light intensity or the herbicide that affects the survival of the plants.