Nerves are cells that can detect any type of pressure, movement, or anything of that nature. If we didn't have nerves, we couldn't feel pain. If the nerves in a foot are damaged, you wouldn't feel the pain of it being burned.
a chemical element or substance required in trace amounts for the normal growth and development of living organisms.
The variables are defined as the factors in an experiment, which are liable to change. The variable can be dependent or independent. The Independent variable is a variable, which is unaffected by the changes in the other variables.
In this case, the brand of the food Shara feeds to the rats is independent factor, but it is changes in the system, so, it is an independent variable.
The effect on the weight of the rat is dependent on the brand of food they are consuming. So, the weight of rats is dependent variable.