It is false scientist don't need to repeat an experiment
The answer to this question would be: insulin
Insulin is a hormone that produced by the pancreas. Insulin makes sugar go inside cells. Sugar is the food for cells. Without insulin, the sugar can't enter the cell and the cell food is depleted. This will cause the body feel that the sugar is not enough and trying to increase the sugar concentration. This will result in the increases of blood sugar level.
Answer:
That is administered and controlled
Step-by-step explanation:
A variable is the condition or a product that may vary without the influence of any investigator. Such variables can be found abundantly in our daily lives, ranging from air to sunlight. Controlling such variables ensures the limitation of their influence on the outcome of an experiment. In connection to this experiment, the variables that are controlled are the mineral content in the water, the amount of bacteria food, the amount of light and the the constant temperature of 20 degrees C.
If not administered or these variables controlled, the experiment would not clearly explain the impact of caffeine on the heart beat of the water fleas as other variables may have influenced it. Thus variables are controlled to study the singular impact of any agent or effect.