Stem cellsIB MYP Biology: Revision notes
Section 1
Differentiation and specialised cells
Most cells in your body are specialised: their shape and contents are suited to one job. A red blood cell carries oxygen, a nerve cell carries impulses and a muscle cell contracts.
Cells become specialised by differentiation. An unspecialised cell changes, because only some of its genes are switched on, and it develops the structures it needs for its job. Once a cell has differentiated, it usually cannot turn into a different type of cell.
Section 2
What is a stem cell?
A stem cell is an unspecialised cell that can divide by mitosis to make more cells and can differentiate into specialised cells.
Stem cells make growth, repair and replacement of cells possible. Different types of stem cell can become different numbers of cell types.
Section 3
Three types of stem cell
- Embryonic stem cells come from very early embryos. They can differentiate into any type of cell in the body.
- Adult stem cells are found in tissues such as bone marrow. They can only become a limited range of cell types, for example bone marrow stem cells make only blood cells.
- Plant meristem cells are found in the tips of roots and shoots. They can differentiate into any type of plant cell and stay active throughout the life of the plant.
Remember the difference: embryonic stem cells can become any cell type, but adult stem cells have a limited range.
Section 4
Uses in medicine and agriculture
- Bone marrow transplants give a patient adult stem cells that make new, healthy blood cells, for example to treat leukaemia.
- Stem cells can be grown in the laboratory and used to repair damaged tissue, such as the cornea of the eye or burned skin.
- Scientists hope that embryonic stem cells could be used to replace cells in conditions such as paralysis caused by spinal injury, or diabetes.
- Plant meristem cells can be grown on nutrient jelly to make many identical plants (clones), including rare plants and disease-free crops.
Section 5
Benefits and risks
Benefits: stem cells can replace damaged or diseased cells and could treat conditions that are currently hard to cure. Cells taken from the patient's own body are not rejected by the immune system.
Risks:
- Stem cells may divide out of control and form tumours.
- Donor cells could carry a virus that infects the patient.
- Donated cells may be rejected by the patient's immune system.
Ethical issues: obtaining embryonic stem cells destroys an embryo, which some people believe is wrong for religious or cultural reasons. Treatments can also be expensive.
Do not say embryonic stem cells are always better. They carry ethical objections and a tumour risk.
Must Know
- Differentiation: an unspecialised cell becomes specialised
- Stem cells divide and can differentiate
- Embryonic cells become any cell type; adult cells only a limited range
- Plant meristems are at root and shoot tips
- Medical uses: bone marrow transplants, tissue repair
- Risks: tumours, viruses, rejection, ethical objections
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Stem cells
- A developmental biologist in Kyoto is watching a fertilised human egg divide by mitosis. In the first few days the cells in the ball of cells look identical and can still become any type of cell. Later, cells in the same embryo become nerve cells, muscle cells and skin cells, each with a different structure.Outline what is meant by differentiation, using one named example.2 marks
- A horticulturist in Nairobi grows roses to export. To produce thousands of identical, disease-free plants, she cuts tiny pieces of tissue from the tips of growing shoots and roots, places them on nutrient jelly and waits for new plants to grow.Explain why the horticulturist takes tissue from the shoot tips rather than from a mature leaf.2 marks
- A nine-year-old boy in Dubai has leukaemia, a cancer of the white blood cells. Doctors destroy his diseased bone marrow with chemotherapy and then give him a transplant of bone marrow from his healthy sister. Her bone marrow contains adult stem cells.Explain how the transplanted bone marrow helps the boy to recover.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).