Extracellular growth factors are involved in the control of cell cycles in some mammalian cells. One of these growth factors is epidermal growth factor (EGF). Fig. 6.1 shows the events that occur when EGF is present at the surfaces of two cells, A and B. [Figure 6.1]

1. (a)Explain why cell A in Fig. 6.1 responds to EGF, but cell B does not.[2]
2. (b)In the cell cycle, more mRNA is produced in the G₁ phase than during mitosis. Suggest why this is so.[1]
3. (c)DNA is replicated during the S phase of the cell cycle. EGF is one of many factors that stimulate the change from the G₁ phase to the S phase. State the substances used to synthesise DNA during the S phase.[3]
4. (d)(i)Fig. 6.2 is a drawing of chromosome 1 from rice, Oryza sativa, during metaphase of mitosis. State the name and function of the region of the chromosome labelled X. name function[2]
5. (d)(ii)In the outline of the cell below, draw the chromosome from Fig. 6.2 as it would appear in anaphase of mitosis. [Outline of cell][2]

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