Stem cells and totipotencyAQA A-Level Biology: Mind map

Exam questions on Stem cells and totipotency

1. A fertilised mammalian egg divides several times to form a ball of cells. If the cells are separated at the 4-cell stage, each one can develop into a complete embryo, including the placenta. If cells are taken from the same embryo a week later, they can form only some of the tissues of the body.
   Explain why a totipotent cell can form many different cell types, but a specialised cell in the same embryo cannot.2 marks
2. Bone marrow in an adult contains stem cells that divide to produce red blood cells, several types of white blood cell and platelets. These cells never produce nerve cells or muscle cells. Bone marrow transplants are used to treat patients with leukaemia, whose own blood-forming cells have been destroyed by treatment.
   Explain why a transplant of bone marrow stem cells can replace the blood cells of a leukaemia patient but could not be used to replace damaged nerve cells.2 marks
3. A patient has a heart muscle disorder. Researchers took skin cells from the patient, treated them with a set of protein transcription factors and obtained cells that behave like embryonic stem cells. They then induced these cells to form cardiomyocytes (heart muscle cells) to test drugs and possibly to transplant into the patient's heart.
   Describe how induced pluripotent stem (iPS) cells can be produced from the patient's cells.3 marks