What is the independent variable?

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 dependent variable?

Scenario: 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 independent variable?

Scenario: Two different cars are traveling at 60 mph.  At a certain point, both cars slam on the brakes.  

What does the dependent variable measure in the car stopping distance scenario?

Scenario: Pillbugs are placed in a container where they have a choice of a wet or a dry environment.  Researchers record how much time was spent on each side.

What is the independent variable?

Scenario: 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 is the dependent variable?

Scenario: Cockroaches are exposed to a pesticide.  After 3 hours, 95% of the insects are dead.  

What is the independent variable?

Scenario: Two plants are grown using the same light and pots.  One plant is given water that has been microwaved and the other plant is given regular tap water.  Their height is measured after 2 weeks.

What is the dependent variable?

Scenario:  The blood pressure of a soldier is measured while he is resting.  The soldier is then exposed to a stressful environment and his blood pressure is measured again.

What is the independent variable?

Scenario:  An apple is cut into slices. Half of the slices are sprayed with lemon juice. All slices are stored in a sealed plastic bag. After 4 days, they are observed to see how brown they turned.  

What is the independent variable?