Something that is constant and does not change.

Controlled variable, if you're talking about scientific variables in experiments. (if not, you can just ignore this.)

Explanation:

Main types of variables are: Independent, Dependent, and controlled.

Independent variable is what is being changed in each experiment by the scientist.

Dependent variable is the change in result of the independent variable.

Controlled variable is other factors that have to remain constant in order for the experiment to remain valid.

For example:

Joshua wants to know how the location of a plant affects it's growth rate. He sets up 3 same plants in different locations in his classroom, and records how much they grow by after a month.

Plant A: On a desk in the middle of the room

Plant B: on a windowsill

Plant C: in a closet

The results are as follows:

Plant A grew by 1.3 inches

Plant B grew by 2 inches

Plant C grew by .5 inches

The independent variable in this experiment is the location in the room. The dependent variable is the growth rate.

The controlled variable is everything else: the type of plant, the type of soil, etc.

hope this helped!

vascular tissue transports materials from the environment into the plant.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme