During phagocytosis, how does a macrophage consume a bacterium?

• A. It injects cytotoxic granules into the bacterium through a perforin pore to trigger bacterial apoptosis.
• B. It extends pseudopodia to engulf the bacterium into a phagosome, then fuses the phagosome with lysosomes for digestion.
• C. It internalizes the bacterium through receptor-mediated endocytosis into clathrin-coated vesicles that become peroxisomes.
• D. It secretes antibodies that bind the bacterium and directly dissolve the bacterial cell wall outside the cell.

Answer: (B)

Verified step by step guidance

1. Understand that phagocytosis is a process where a cell, such as a macrophage, engulfs and digests foreign particles like bacteria.
2. Recognize that macrophages use extensions of their cell membrane called pseudopodia to surround and engulf the bacterium, forming an internal vesicle known as a phagosome.
3. Know that the phagosome then fuses with lysosomes, which are organelles containing digestive enzymes, creating a phagolysosome where the bacterium is broken down.
4. Note that this process is different from receptor-mediated endocytosis, which involves clathrin-coated vesicles and is typically for smaller molecules, not whole bacteria.
5. Also understand that macrophages do not inject cytotoxic granules through perforin pores (a mechanism used by cytotoxic T cells) nor do they secrete antibodies; antibody secretion is a function of B cells.