Normal leukocytes use several protective mechanisms in combating disease-causing microbes such as bacteria. Which of the following is NOT a method related to substance uptake by a white blood cell?
a. exocytosis
b. phagocytosis
c. pinocytosis
d. receptor-mediated endocytosis

a; exocytosis

Explanation: leukocytes are blood cells which destroy foreign bodies such as bacteria.they have the ability to engulfing invading microorganisms thus they are said to be involved in defense and immunity.

Leukocytes are capable of engulfing foreign bodies through the processes of pinocytosis, phagocytosis and receptor-mediated endocytosis.

In endocytosis,the membrane of the cell transfers the foreign bodies into the cell.it does this by first trapping the foreign body to form a vesicle .the vesicle then pinches off on the other side of the membrane.

Phagocytosis is a type of endocytosis in which the material is engulfed into the cell cytoplasm.

Pinocytosis is a type of endocytosis in which droplets of fluids are engulfed into the cell.

Receptor-mediated endocytosis is when specific materials are engulfed due to the protein receptors on the cell membrane.

Exocytosis is the opposite of endocytosis and in this process , materials are removed from the cell by pinching of the cell membrane.

Since white blood cells need to engulf bacteria, exocytosis is not used.