A-LevelBiologyThe mitotic cell cycle9700/22 · Feb/Mar 2022 · Q27 Marks

(a) Fig. 2.1 shows a cell at one of the main stages of mitosis in the mitotic cell cycle. [Figure 2.1] (b) State the role of telomeres during DNA replication. (c) Multiple myeloma is a type of cancer in the bone marrow where some of the stem cells start to produce abnormal blood cells. • One treatment is to collect stem cells from the bone marrow of the person with multiple myeloma. Healthy stem cells are isolated and grown in the laboratory. • Radiation is then used to destroy all stem cells and cancerous cells in the bone marrow. • Finally, large numbers of the healthy stem cells grown in the laboratory are returned to the bone marrow. Suggest the role of stem cells in this treatment of multiple myeloma.

(a)(i)Name the stage of mitosis shown in Fig. 2.1. [Figure 2.1][1]
(a)(ii)Fig. 2.2 shows the cell in Fig. 2.1 at the start of cytokinesis. Complete Fig. 2.2 to show the daughter chromosomes in each nucleus. [Figure 2.2][2]
(b)State the role of telomeres during DNA replication.[1]
(c)Multiple myeloma is a type of cancer in the bone marrow where some of the stem cells start to produce abnormal blood cells. • One treatment is to collect stem cells from the bone marrow of the person with multiple myeloma. Healthy stem cells are isolated and grown in the laboratory. • Radiation is then used to destroy all stem cells and cancerous cells in the bone marrow. • Finally, large numbers of the healthy stem cells grown in the laboratory are returned to the bone marrow. Suggest the role of stem cells in this treatment of multiple myeloma.[3]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2022). The mark or mark type is shown in brackets.

[1] 2(a)(i) metaphase ;
[1] 2(a)(ii) 4 chromosomes within dotted line of both newly forming cells and each chromosome consisting of one chromatid ; ignore shape / shading labels not required centromeres do not need to be shown
[1] 2(a)(ii) two obvious pairs (of chromosomes) shown in each of the two re-forming nuclei ; e.g. two dark and two light two longer and two shorter
[1] 2(b) any one from: prevent the loss of, genes / genetic information ; A prevent loss of coding DNA AVP; e.g. prevents the ends of two chromosome from fusing / joining
[1] 2(c) stem cells (grown in the lab) can undergo mitosis, ; A divide
[1] 2(c) stem cells are, undifferentiated / unspecialised ;
[1] 2(c) (when back in the person being treated) stem cells can, differentiate / specialise, into (all) blood cell types ; A are multipotent
[1] 2(c) to, re-populate / replace / bring back to normal levels, the person's own blood cell supply; A tissue repair

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