Step-by-step explanation:
(i)A response is a change in the organism A response is a change in the organism resulting
from the detection of a stimulus.
(ii)Stimulus: any change in an organism's environment that causes the organism to react. It is a fancy way of saying “cause”.
(iii)A receptor is a protein which binds to a specific molecule. The molecule it binds is known as the ligand. A ligand may be any molecule, from inorganic minerals to organism-created proteins, hormones, and neurotransmitters. This change is shape slightly alters the protein's function.