Stem cells and totipotencyAQA A-Level Biology: Subtopic test

1. 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.

   (a)

   Which term describes cells that can each develop into a complete embryo, including the placenta?

   [1 mark]

   • AUnipotent
   • BTotipotent
   • CMultipotent
   • DPluripotent

   (b)

   Which statement best explains why cells taken from the embryo a week later can form only some tissues?

   [1 mark]

   • AThey have lost some of their genes from their DNA
   • BThey have gained extra chromosomes
   • CThey have stopped dividing by mitosis
   • DOnly part of their DNA is translated

   (c)

   Explain why a totipotent cell can form many different cell types, but a specialised cell in the same embryo cannot.

   [2 marks]

   Total for question 1: 4 marks

2. 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.

   (a)

   What type of stem cell is found in the bone marrow of an adult?

   [1 mark]

   • ATotipotent
   • BPluripotent
   • CMultipotent
   • DUnipotent

   (b)

   Which statement about pluripotent stem cells is correct?

   [1 mark]

   • AThey are found in embryos and can divide in unlimited numbers to form any type of body cell
   • BThey are found only in mature adult tissues
   • CThey can form only one type of cell
   • DThey translate all of their DNA at all times

   (c)

   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]

   Total for question 2: 4 marks

3. 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.

   (a)

   Describe how induced pluripotent stem (iPS) cells can be produced from the patient's cells.

   [3 marks]

   (b)

   Suggest four advantages of using the patient's own iPS cells rather than embryonic stem cells to treat the disorder.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A clinical trial gave retinal cells, grown from embryonic stem cells, to 18 patients with severe sight loss. After 12 months, 11 patients could read at least five more letters on an eye test chart, 6 showed no change and 1 had worse sight. In two patients, some of the transplanted cells grew abnormally. The trial had no control group.

   (a)

   Evaluate the trial as evidence that this treatment is effective and safe.

   [6 marks]

   (b)

   Evaluate the use of stem cells in treating human disorders, comparing embryonic stem cells with iPS cells.

   [6 marks]

   Total for question 4: 12 marks

End of questions