Parts of an Experiment

In a study investigating how different amounts of sunlight affect plant growth, researchers expose plants to varying levels of sunlight (no sunlight, low sunlight, medium sunlight, and high sunlight) over a month and measure their growth in height. What is the independent variable in this experiment?

• The amount of sunlight

• The height of the plants

• The types of plants used

• The duration of the study

The scientists want to test the hypothesis that something in the environment in City A is causing the higher rate of asthma in children. They recruit families for a study of asthma in children ages 10-12. The children are divided into three groups. The first group is sent to a summer camp in the country for eight weeks. The second group is sent to a camp in City B for eight weeks. Children in the third group are sent to day camps in their own neighborhoods. A nurse at each camp keeps a record of any reported breathing problems. At the end of the summer, the scientists will compare the rates of asthma symptoms in each group of children.

  What is the control group in the experiment involving children? 

• the group of children without asthma

• 
  the group of children sent to the country

• 
  the group of children sent to city B 

• the group of children who attend day camps in their own neighborhoods

Three biology students wanted to find out if adding fertilizer to some potting soil would affect the germination of radish seeds. Each student added an equal amount of potting soil from the same bag to each of 10 cups. Student A added 1 gram of fertilizer to each cup of soil in group A. Student B added 2 grams of fertilizer to each cup of soil in group B. Student C added 3 grams of fertilizer to each cup of soil in group C. After stirring the mixture to obtain an even distribution of fertilizer, 8 radish seeds were placed in each cup and covered with 0.5 centimeter of soil. Over the next 6 days, all conditions, including the amounts of water and sunlight, were kept the same. The results are recorded in the data table. What is the dependent variable in this experiment?

• The amount of fertilizer

• The type of plant used

• The number of radish seeds that were germinated

• The amount of days after planting.

In another science fair experiment, Tina asks the question “Does caffeine increase the heart rate of an earthworm?” In Test 1, she measures the heart rate by looking at the earthworm under a microscope, the earthworm has a heart rate of 50 bpm (beats per minute). In Test 2, she places 4 drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 68 bpm. In Test 3, she places 8 drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 78 bpm. What is the experimental group(s) in this experiment?

• Test 1

• Test 2 and 3

• Test 1 and 3

• All test groups

After observing a garden where plants with yellow leaves are found to be drooping, a student notes that the soil is dry and infers that lack of water is causing the drooping. Identify which part of this scenario is an observation and which is an inference?

• Observation: The soil is dry; Inference: Lack of water is causing the drooping.

• Observation: The plants have yellow leaves; Inference: The plants have yellow leaves.

• Observation: Lack of water is causing the drooping; Inference: The soil is dry.

• Observation: The plants are drooping; Inference: The plants are healthy.