In plants, the cell wall forms as a young plant cell secretes polysaccharides onto the outer surface of its plasma membrane. being thin and pliable, this primary wall allows the cell to enlarge and change shape. at maturity, cells in some plant tissues deposit material onto the primary wall’s inner surface. why doesn’t this secondary wall form on the outer surface of the primary wall?

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

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