Stem cellsEdexcel A-Level Biology B: Subtopic test

1. 1
   Stem cells are found at several stages of human life. Cells of the very early embryo can each form every cell type, including the placenta. Cells of the inner cell mass of the blastocyst can form every cell type of the body but not the placenta. Haematopoietic stem cells in the bone marrow of an adult can form only the different types of blood cell.

   (a)

   Which term describes the haematopoietic stem cells in the bone marrow?

   [1 mark]

   • ATotipotent
   • BMultipotent
   • CPluripotent
   • DFully differentiated

   (b)

   Which term describes the cells of the inner cell mass of the blastocyst?

   [1 mark]

   • ATotipotent
   • BMultipotent
   • CUnipotent
   • DPluripotent

   (c)

   Explain how cells of the early embryo change from being able to form every cell type, including the placenta, to forming every cell type except the placenta.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Researchers take fibroblasts from a patient's skin. Using a modified virus, they introduce four genes, including the genes for the transcription factors Oct4 and Sox2, into the fibroblasts. After several weeks some of the cells divide indefinitely and can be made to form many different cell types.

   (a)

   What type of cell have the reprogrammed fibroblasts become?

   [1 mark]

   • APluripotent stem cells
   • BTotipotent stem cells
   • CMultipotent stem cells
   • DDifferentiated somatic cells

   (b)

   Why are cells made from the patient's own fibroblasts less likely to be rejected when transplanted back into the patient?

   [1 mark]

   • AThey are totipotent
   • BThey have no DNA
   • CThey are genetically identical to the patient and have the same surface antigens
   • DThey can no longer divide

   (c)

   Explain how the introduced genes cause the fibroblasts to become stem cells.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A man has a spinal cord injury. Two research teams each propose transplanting neurones grown from stem cells. Team A would use pluripotent stem cells taken from spare embryos created during IVF treatment and no longer needed. Team B would use fibroblasts from a skin sample taken from the patient and reprogramme them to form induced pluripotent stem (iPS) cells.

   (a)

   Explain why using iPS cells may be less problematic than using cells from embryos.

   [3 marks]

   (b)

   Discuss the ethical considerations of using pluripotent stem cells from embryos to treat the patient.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A research group wants to treat type 1 diabetes, in which the patient's immune system destroys the insulin-secreting beta cells of the pancreas. They plan to produce replacement beta cells from stem cells. The group also studies how a fertilised egg gives rise to all the different cell types of the body.

   (a)

   Explain how a fertilised egg gives rise to differentiated cells, with reference to totipotent, pluripotent and multipotent stem cells and epigenetic modification.

   [6 marks]

   (b)

   Evaluate the use of iPS cells made from the patient's own fibroblasts, rather than embryonic stem cells, as the source of replacement beta cells. Justify your conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions