When a splinter breaks the skin and bacteria get into the wound, certain white blood cells travel to the site and begin engulfing the bacteria one by one. What is this type of white blood cell called, and what is it doing?
- A red blood cell, carrying oxygen to the wound so that the bacteria are starved of the air they need to survive
- A phagocyte, carrying out phagocytosis by surrounding each bacterium with its own cell membrane and digesting it
- A platelet, releasing chemicals that dissolve the bacteria's outer cell wall on contact
- An antibody, physically trapping each bacterium inside a hard protein shell until it can be removed
Why B? And why not the others?
Correct answer: B. A phagocyte, carrying out phagocytosis by surrounding each bacterium with its own cell membrane and digesting it
The white blood cells described are phagocytes, and the process of surrounding and digesting a bacterium using their own cell membrane is called phagocytosis; this is one of the body's first lines of defence against infection at the site of a wound. The option describing red blood cells is wrong because their job is carrying oxygen around the body, not attacking bacteria, and bacteria are not destroyed simply by being deprived of air at a wound site. The option describing platelets is wrong because platelets are involved in clotting blood to seal a wound, not in dissolving the cell walls of invading bacteria. The option describing antibodies is wrong because antibodies are proteins that mark or neutralise pathogens rather than cells that physically trap them inside a shell; that description does not match how either antibodies or phagocytes actually work.
Source: BBC Bitesize GCSE Biology: The immune system