Why can an enzyme only break down a
particular shape

according to lock and key model active site of enzyme is rigid and a particular enzyme only break the substrate of particular shape but according to induce fit model active site is rigid and enzyme is not restricted to a particular shape.

Explanation:

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.