Which blood cell are involved in the immune response of vertebrates?

1. Analyze the question The question asks which blood cell is involved in the immune response of vertebrates. "Immune response" refers to the body's specific defence against pathogens, which involves recognising antigens and producing antibodies.

2. Explain the concept Blood contains different cell types:

• Erythrocytes (red blood cells): carry oxygen using haemoglobin. They play no part in immunity.
• Leucocytes (white blood cells): defend the body. They are divided into: • Phagocytes (neutrophils, monocytes/macrophages): engulf germs by phagocytosis. This is the non-specific defence. • Lymphocytes (B-cells and T-cells): produce antibodies (B-cells) and coordinate or destroy infected cells (T-cells). This is the specific immune response, and it also gives immune memory.

3. Work through the options

• A. Phagocytes: they take part in general defence, but this is not the specific immune response. They are also a functional group, not a single blood cell type.
• B. Lymphocytes: they are the main cells of the immune response. B-lymphocytes make antibodies, and T-lymphocytes handle cell-mediated immunity. ✔
• C. Erythrocytes: they transport oxygen, not defence.
• D. Monocytes: they are phagocytic and help by presenting antigens, but they are not the key cells of the specific immune response.

4. Answer The correct option is B. Lymphocytes.

5. Exam tip Link the words: Lymphocytes = Learn and remember (antibodies and immune memory), while Phagocytes = Pac-Man (they eat germs). When a question says "immune response," think lymphocytes. When it says "engulf" or "ingest," think phagocytes.