A-LevelBiologyThe mitotic cell cycle9700/23 · May/June 2020 · Q510 Marks

Blood cells are formed from tissue stem cells in the bone marrow. These bone marrow stem cells go through a number of mitotic cell cycles to form the fully functioning blood cell. Fig. 5.1 shows the three main stages of the cell cycle. [Figure 5.1]

(a)Explain what is meant by a gene.[2]
(b)Name the main stage of the cell cycle in Fig. 5.1 during which most mRNA and ATP is formed.[1]
(c)(i)Fig. 5.2 is an incomplete diagram of an ATP molecule. [Figure 5.2] On Fig. 5.2: • complete the diagram of the ATP molecule • write the name of the base in the space provided • write the name of the sugar in the space provided.[3]
(c)(ii)The base shown in Fig. 5.2 has a double ring structure. State the term for a base that has a double ring structure.[1]
(d)Suggest and explain the role of mitosis in the formation of blood cells by the bone marrow stem cells.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[2] any two from
sequence of DNA nucleotides ;
forms part of a DNA molecule / length of DNA/AW ;
coding for a polypeptide; A protein
[1] interphase; I phases of interphase
[3] two phosphates added to existing phosphate;
base = adenine ;
sugar = ribose ;
[1] purine ;
[3] any three from
to produce, many / AW, new blood cells ;
idea that large numbers are required to, transport oxygen / maintain immune system ;
produce genetically identical cells ;
loss of genetic material may not allow function / cells maintain function / cells are able to function ;
replacement of, old / damaged / dead, cells ;
AVP; e.g. to maintain healthy numbers of cells
red blood cells have short life

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