QUESTION 11 (2 marks)
Adult skeletal stem cells differentiate into intermediate cells and later into specialised bone tissue types.
The table shows how three transcription factors (A, B and C) affect bone tissue formation.
Transcription factor role | Intermediate cell | Cartilage | Compact bone |
Activators | A | B, A | B |
Repressors | — | C | A |
Explain the effect of transcription factors on gene expression and tissue formation. Use an example from the table to support your answer.
QCAA guide · typeset solution
QCAA sample response and mark allocation
11 | Transcription factors either increase (activator) or decrease (repressor) the rate of transcription of a particular gene. For example, transcription factor A increases transcription for the intermediate cells to form, whereas it reduces the rate of or prevents compact bone formation. | • states that transcription factors can both increase and decrease transcription rates [1 mark] • provides a suitable example from the table [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
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