A Levels Biology (9700)•9700/12/M/J/20
Explanation
White blood cells reside beyond circulating blood
Steps:
- White blood cells (leukocytes) originate in bone marrow and circulate in blood.
- They migrate to tissues for immune surveillance and response.
- Storage occurs in lymph nodes and spleen for rapid deployment.
- Thus, they are present in lymph, tissues, and organs like spleen and bone marrow.
Why A is correct:
- White blood cells are found in all three locations (1: lymph system, 2: tissues, 3: bone marrow/spleen) as part of the immune system's distributed network.
Why the others are wrong:
- B excludes 3, but bone marrow produces and stores WBCs.
- C excludes 2, but WBCs infiltrate tissues during infections.
- D excludes 1, but lymph carries WBCs between nodes and blood.
Final answer: A
Topic: The immune system
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