Which of the following is true of leukocytes? A. They are very similar in appearance and function as red blood cells. B. Leukocytes are smaller than and more numerous than red blood cells. C. Like red blood cells, mature leukocytes also lack a nucleus and other intracellular organelles. D. Leukocytes always remain in circulation throughout the body. E. The leukocyte is a major component of the body’s defenses against disease.

the correct option is E. (The leukocyte is a major component of the body’s defenses against disease)

Explanation: the leukocyte also called the white blood cells is one of the major types of the hematocytes. There are different types of white blood cells which are classified based on their functions and appearance, they include:

- neutrophils,

- eosinophils,

- basophils,

-lymphocytes, and

- monocytes.

The major function of the white blood cells is to protect the body against disease by phagocytosis of invading microorganisms capable of causing infections.

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