Lymph nodes, white blood cells and antibodies
Answers are for parents and teachers.
1
In a sample of 5 000 lymphocytes, 80 % are T cells and 12 % are B cells. How many cells of each kind, and what share is left for natural killer cells?
T cells: 5 000 × 0.80 = 4 000. B cells: 5 000 × 0.12 = 600. Left: 100 − 80 − 12 = 8 %, which is 5 000 × 0.08 = 400 natural killer cells, inside the book’s 5 to 10 %.
2
In a sample of 3 000 lymphocytes, 300 are natural killer cells. What share is that, and is it inside the book’s range?
300 ÷ 3 000 = 0.10, which is 10 %. It is at the top of the book’s range of 5 to 10 %.
3
Explain the difference between interleukins and interferons.
Interleukins carry messages between immune cells, for example from helper T cells to B cells. Interferons are made by virus-infected cells and make neighbouring healthy cells stop the virus copying itself.
4
A sample holds 400 antibody molecules, each with two binding sites. If every site holds one antigen, how many antigens are held?
400 × 2 = 800 antigens.
5
Why do phagocytes finish the job in every way that antibodies work?
Clumped, settled or burst material is easy for phagocytes to swallow.