GCSE Combined Science revision · Biology: cells, organisation and disease

Mitosis and stem cells

The idea

In the cell cycle the cell grows, copies its DNA and organelles, then divides by mitosis into two genetically identical cells. Mitosis is for growth and repair. Stem cells are undifferentiated cells that can become other cell types: embryonic stem cells can become most types, adult bone marrow stem cells form blood cells, and plant meristems can form any plant cell throughout life.

Describe the stages: growth and DNA copying, mitosis, then division of the cytoplasm.
State that the two cells are identical.
Weigh the benefits and ethical issues of stem cell use.

Watch out Mitosis makes identical body cells; meiosis makes different gametes.

See it worked

Worked example

Give one advantage and one risk of using embryonic stem cells in medicine.

Advantage: they can become many cell types, so could treat conditions such as diabetes or paralysis.
Risk: transferred cells could be infected with a virus, or patients may reject them; some people object on ethical grounds.

Answer They can form many cell types, but there are risks of infection and rejection, and ethical objections

Your turn

Question 1Calculator allowed1 mark

What is produced when a cell divides by mitosis?

Question 2Calculator allowed1 mark

Where are plant stem cells found?

Question 3Calculator allowed3 marks

Explain why therapeutic cloning may reduce rejection.

Write your answer, then see a model answer

Same genes as the patient.
So no immune rejection.

Answer An embryo is made with the same genes as the patient, so stem cells from it are not rejected by the patient's immune system.

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