4. what is the function of the iris? a it converts light into electrical signals that are sent to the brain through the optic nerve. b it contracts and expands to control the amount of light that enters the eye. c its curved surface to focus light entering the eye. d it focuses the light onto the light-sensor cells at the back of the eye.

B It contracts and expands to control the amount of light that enters the eye.

Explanation:

The iris is the circular and thin structure of the eye. It is responsible for regulating the size of the pupil. This when expands and contracts controls the amount of light entering the eye's retina.

When the bright light enters the eye the iris closed the pupil so that less light enters the eye. But when the light is low, the iris open the pupil to allow more light to enter the eye and focuses the light rays onto the retina.

chemical energy is stored in the chemical bonds of atoms and molecules. it can only be seen when it is released in a chemical reaction. when chemical energy is released, the substance from which the energy came is often changed into an entirely different substance.

this chemical reaction releases energy in the form of light and heat. chemical energy is the potential energy stored in the arrangement of atoms within molecules. breaking chemical bonds requires energy, while forming new chemical bonds releases energy.

the atp molecule can store energy in the form of a high energy phosphate bond joining the terminal phosphate group to the rest of the molecule. in this form,energy can be stored at one location, then moved from one part of the cell to another, where it can be released to drive other biochemical reactions.

the answer is minerals.