Stem cellsEdexcel A-Level Biology B: Mind map

Exam questions on Stem cells

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.
   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
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.
   Explain how the introduced genes cause the fibroblasts to become stem cells.2 marks
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.
   Explain why using iPS cells may be less problematic than using cells from embryos.3 marks