A cow is given a growth hormone and then compared to another cow that was not given a growth hormone. Both cows were weighed at 2 years. What is the dependent variable in this scenario?

Mosquito repellent is sprayed on one arm and the other arm is not sprayed. The number of mosquito bites is counted after 2 hours. What is the independent variable?

One grape is placed in tap water and another grape is placed in salt water. The change in their mass is measured after a day. What is the dependent variable?

A stapler is used to staple 100 papers, it jams 5 times during the trial. A different brand of stapler performs the same test; it jams 22 times. What things should be kept constant in this experiment? Select all that apply.

For the science fair, 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 microscopes, the earthworm has a heart rate of 50 bpm (beats per minute). In Test 2, she places a few drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 68 bpm. What is the manipulated (independent) variable in this experiment?

For the science fair, 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 microscopes, the earthworm has a heart rate of 50 bpm (beats per minute). In Test 2, she places a few drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 68 bpm. What is the responding (dependent) variable in this experiment?

For the science fair, 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 microscopes, the earthworm has a heart rate of 50 bpm (beats per minute). In Test 2, she places a few drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 68 bpm. In this experiment, what is the "control group"?

For the science fair, 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 microscopes, the earthworm has a heart rate of 50 bpm (beats per minute). In Test 2, she places a few drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 68 bpm. In this experiment, what is the "experimental group"?

For the science fair, 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 microscopes, the earthworm has a heart rate of 50 bpm (beats per minute). In Test 2, she places a few drops of caffeine on the earthworm’s skin and measures the rate again. In this test, the heart rate is 68 bpm. Which of the following statements could have been a hypothesis for this experiment?