Stem cells in bone marrow divide by mitosis to produce blood cells. Every division gives one replacement stem cell and one cell that later differentiates into a blood cell. Fig. 3.1 shows how the DNA mass in a human stem cell from the bone marrow changes across three cell cycles.
(a(i))[2]
Using Fig. 3.1, state what causes the changes in DNA mass per cell at K and at L.
K
L
(a(ii))[1]
the number of blood cells produced from the stem cell in the time shown
(a(iii))[1]
what happens to the number of chromosomes in the stem cell.
(b)[3]
Describe how a red blood cell develops from a stem cell.
(c)[3]
During an immune response, cells divide by mitosis. Describe how mitosis is involved in an immune response.
(d)[3]
Describe the ways T-lymphocytes act during an immune response.
Worked solution & mark scheme
This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: “K indicates DNA replication, also called synthesis” …