What are stem cells, where are they found, and how might they treat disease?
Stem cells as undifferentiated cells that can divide and differentiate, the sources of stem cells (embryonic, adult and plant meristems), the uses of stem cells in medicine and agriculture, and the ethical issues raised by their use.
A focused answer to the OCR Gateway GCSE Biology A topic B2 on stem cells, covering undifferentiated cells and differentiation, embryonic, adult and plant stem cells, their uses in medicine and agriculture, and the ethical issues.
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What this dot point is asking
OCR wants you to define a stem cell, describe the sources of stem cells (embryonic, adult and plant meristems), explain how stem cells could be used in medicine and agriculture, and discuss the ethical issues their use raises.
What a stem cell is
Most cells in the body are specialised for a particular job and cannot change into other types. Differentiation happens as an organism develops: stem cells switch on different genes to become the specialised cells the body needs.
Sources of stem cells
There are three sources you must know:
- Embryonic stem cells. Found in early embryos, these can differentiate into almost any type of cell in the body, which makes them the most versatile.
- Adult (tissue) stem cells. Found in some adult tissues, for example the bone marrow. These can differentiate into a more limited range of cell types (bone marrow stem cells form blood cells).
- Plant meristems. Found at the growing tips of roots and shoots. The stem cells in meristems can differentiate into any type of plant cell, and plants keep these cells throughout their life, so they can grow and repair continuously.
Uses of stem cells
In medicine, stem cells could replace cells that are damaged or not working:
- Type 1 diabetes could be treated by making stem cells differentiate into insulin-producing cells.
- Paralysis from spinal injury might be treated by replacing damaged nerve cells.
- Other possible uses include treating blindness and replacing damaged organs.
In agriculture, plant meristem stem cells are used to clone plants quickly and cheaply. Growers can produce many identical plants with desirable features (such as disease resistance or high yield), and can save rare species from extinction.
Risks and ethical issues
Stem cell use raises practical and ethical concerns:
- Risks. Transferred stem cells might be rejected by the patient's immune system, or might divide uncontrollably and cause cancer. There is also a small risk of transferring viral infection.
- Ethical issues. Embryonic stem cells are taken from embryos, which are destroyed in the process. Some people believe an embryo is a potential human life and so this is wrong; others argue the embryo cannot consent. People weigh these concerns against the potential to cure serious diseases.
Using a patient's own adult stem cells avoids both rejection and the embryo ethics, but adult stem cells are less versatile.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20184 marksStem cells could be used to treat people with type 1 diabetes. Explain how stem cells might be used to treat this condition, and describe one ethical issue with using embryonic stem cells.Show worked answer →
A B2 application question worth 4 marks.
Treatment (Explain): a stem cell is undifferentiated, so it can divide and differentiate into specialised cells. To treat type 1 diabetes, stem cells could be made to differentiate into insulin-producing cells (the cells in the pancreas that are not working). These could be transferred into the patient so they can make their own insulin again. Reward the link from undifferentiated stem cell to differentiated insulin-producing cell.
Ethical issue (Describe): using embryonic stem cells means destroying an embryo, which some people believe is a potential human life, so they consider it wrong. Other accepted issues: the embryo cannot give consent; views differ on when life begins. Markers reward a clearly stated ethical point, not just "some people disagree".
OCR 20203 marksCompare embryonic stem cells, adult stem cells and the stem cells found in plant meristems, in terms of the cell types they can become.Show worked answer →
A 3-mark Compare question.
Embryonic stem cells can differentiate into almost any type of specialised cell in the body. Adult (tissue) stem cells, such as those in bone marrow, can differentiate into a more limited range of cell types (for example blood cells). Plant meristem stem cells can differentiate into any type of plant cell, and plants keep these throughout their life.
Markers reward the comparison points: embryonic are the most versatile (almost any cell), adult are more limited, and plant meristem cells remain able to form any plant cell throughout the plant's life. A strong answer notes plants can therefore be cloned easily from meristem tissue.
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