Astudent is conducting their science experiment on the effect of caffeine on dogs. he has 3 groups of test subjects. the 1st group of dogs receives plain water. the 2nd group of dogs receives 10 mg of caffeine each, and the 3rd group receives 50 mg of caffeine each. he will measure their activity levels by recording how long each dog runs without stopping, after giving them the pills. what is the independent variable in this experiment?

The independent variable of an experiment is the one that is intentionally changed or manipulated to see the results of changing said variable.

We are told that in each different group, the amount of caffeine that is given to the dogs changes - in the control group, they get no caffeine, in the 2nd group, they get 10 mg of caffeine each, and in the 3rd group, they get 50 mg of caffeine each.

Therefore, since the amount of caffeine that is given to the dogs is the only variable that is being manipulated, this is the independent variable.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c