A study compares replacement tissue made from a patient's own stem cells with tissue made from donor stem cells. The first group is monitored for one month and the second for one year. Fewer tumours are recorded in the first group.
Why does this comparison not establish that the first source has a lower tumour risk?
The longer monitoring period guarantees that donor cells will be rejected.
The shorter monitoring period gives less time for tumours to be detected.
The longer monitoring period makes donor cells become embryonic cells.
The shorter monitoring period proves that the cells divide more slowly.
46 exam-style questions on Edexcel GCSE Biology 2.2 Stem cells, covering 2.2.1 Function of stem cells and meristems and 2.2.2 Benefits and risks of stem cells. Each one has a worked solution and a mark scheme showing where the marks go.