Question

katherine wants to investigate if the time of day a plant is watered affects the growth of the plant. she waters different plant varieties with the same amount of water at different times in the day. the plants are sitting in the same location and get the same amount of sunlight. which variable is missing from the experiment?
independent variable, plants should be watered at different times of the day
controlled variable, experiment should use the same types of plants
dependent variable, the amount of sunlight should change daily
controlled variable, experiment should use the same amount of water

Explanation:

In an experiment, the independent variable is what is changed (time of watering here). The dependent variable is what is measured (plant growth). Controlled variables are kept the same. Here, the amount of sunlight is a controlled variable (same amount), plant varieties (same type), and amount of water (same amount) are also controlled. But the problem is about identifying the missing variable from the experiment description. Since the experiment is about the effect of watering time (independent variable) on plant growth (dependent variable), and other factors like sunlight, plant type, water amount are controlled. There is no mention of measuring plant growth (the dependent variable which should be observed to see the effect of watering time).

Answer:

Dependent variable, plant growth (or a measure of plant growth like height, number of leaves etc. which would show the effect of watering time) is missing from the experiment description.