Question

Sally wants to test how the type of light affects the height of bean plants. She uses three different types of light bulbs: LED, incandescent, and CFL. She exposes the plants to the lights for the same amount of time and plants the seeds in containers that are the same size, with the same type of soil, and waters them with the same amount of water each day. She measures the height of the plants using a ruler and records the growth each day. Which of the following is/are control(s) in the experiment? (Choose all that apply)

a)The type of light.
b)The height of the plant.
c)The type of plant.
d)The amount of light.

Answer 1

In Sally's experiment, the controls include the container size, soil type, water amount, and type of plant, which are kept constant to ensure that differences in plant height can be attributed solely to the type of light. Gary's experiment suggests additional uncontrolled factors might include individual plant variation, container color affecting soil temperature, water evaporation, and insect attacks. He took measures to prevent container size and water amount from affecting plant growth.

Step-by-step explanation:

In Sally's experiment to test how the type of light affects the height of bean plants, the controls are factors that are kept constant to ensure that the experiment tests only the variable of interest, which in this case is the type of light bulb used (LED, incandescent, CFL). The following are controls in Sally's experiment:

• The size of the containers in which the seeds are planted.
• The type of soil used in the containers.
• The amount of water given to the plants each day.
• The type of plant, as she uses bean plants.

Controls are essential in an experiment because they allow us to compare the results against a standard and conclude that any differences observed are due to the independent variable, which is the type of light in this case.

Gary's hypothetical experiment suggests that other uncontrolled factors could influence the growth of the plants as well, such as:

• Individual plant variation.
• Soil temperature affected by the color of the containers.
• Water loss due to evaporation from the soil.
• The effect of insects, which may attack one set of plants but not another.

Gary also had a good reason to insist on consistent container sizes, soil amount, and watering schedule:

• To ensure the size of the container did not affect differential plant growth.
• To control the amount of water provided to all plants equally.