Stem cells and differentiationEdexcel International A Level Biology: Mind map

Exam questions on Stem cells and differentiation

1. An embryologist at a fertility clinic is observing the early development of a human embryo created by in vitro fertilisation. Three days after fertilisation the embryo is a solid ball of cells. By day five it has developed into a hollow structure with a cluster of cells on one side.
   Explain why a single cell from the morula could develop into a complete organism, whereas a single cell from the inner cell mass of the blastocyst could not.2 marks
2. A pancreatic β cell and a skeletal muscle cell from the same person both contain the gene for insulin and the gene for myosin. The β cell makes large amounts of insulin and no myosin, whereas the muscle cell makes large amounts of myosin and no insulin.
   Explain why the muscle cell does not produce insulin even though its nucleus contains the insulin gene.2 marks
3. A single human gene contains four exons separated by introns. When the gene is transcribed, the primary mRNA transcript is processed before it leaves the nucleus. In different tissues the same gene is used to make different proteins.
   Describe how the primary mRNA transcript is processed to give mature mRNA, and how this can produce different mature mRNAs from the same gene.3 marks