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Cell Division » Stem Cells

What you'll learn this session

Study time: 30 minutes

AQA spec: 4.1.2.3

What a stem cell is and where stem cells are found
How stem cells could be used to treat diseases
The risks of stem cells and why some people object to them
How plant stem cells are used to make clones

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What is a stem cell?

Most cells in your body do one job. A nerve cell carries messages. A red blood cell carries oxygen. Once a cell has become specialised, it usually stays that way.

Stem cells are different. They have not yet become specialised. They can divide to make lots more cells of the same type, and they can also change into other types of cell. Remember from the lesson on specialised cells that this change is called differentiation.

Key terms:

Stem cell: an undifferentiated cell of an organism. It can give rise to many more cells of the same type, and other cells can arise from it by differentiation.
Undifferentiated: not yet changed into a specialised cell.
Meristem: plant tissue made of stem cells, found in the growing tips of roots and shoots.
Therapeutic cloning: making an embryo with the same genes as a patient, so that its stem cells can be used for treatment.

Where are stem cells found?

You need to be able to describe what stem cells do in embryos, in adult animals and in plants.

👶 Embryos

Stem cells from human embryos can be cloned, which means copied to make many identical cells. They can also be made to differentiate into most of the different types of human cell.

🦴 Adult bone marrow

Adults keep stem cells in the bone marrow, the soft tissue inside some bones. These stem cells can form many types of cell, including blood cells.

🌱 Plant meristems

Meristem tissue in plants can differentiate into any type of plant cell. It does this throughout the whole life of the plant.

This is why a plant can keep growing new roots, shoots and leaves throughout its life.

Using stem cells to treat disease

Doctors hope that stem cells could be used to replace cells that are damaged or missing. Treatment with stem cells may be able to help conditions such as:

Diabetes: where the body cannot control the level of glucose in the blood properly. Stem cells could be made to differentiate into healthy cells that do the job.
Paralysis: where nerve cells have been damaged, so messages cannot get through. Stem cells could be made to differentiate into new nerve cells to replace them.

Notice the wording in the spec: stem cells may be able to help. These are possible treatments, not cures that work for everyone today.

Do not need to know

You do not need to know how scientists carry out stem cell techniques in the laboratory. You only need to know what stem cells can do and the arguments for and against using them.

Therapeutic cloning

If a patient is given cells from another person, their immune system may see the new cells as foreign and attack them. This is called rejection.

In therapeutic cloning, an embryo is produced that has the same genes as the patient. Stem cells from this embryo are not rejected by the patient's body, because they are genetically identical to the patient's own cells. This means they may be used for medical treatment.

Worked example

A patient needs new nerve cells. Explain why stem cells from a therapeutic clone are better than stem cells from an unrelated embryo.
The clone has the same genes as the patient. So the patient's body does not see the cells as foreign and does not reject them.

Risks and objections

You may be asked to evaluate the risks and benefits of using stem cells. The benefits are the possible treatments above. The issues on the other side are:

⚠ Risk of viral infection

Stem cells are grown in the laboratory. A virus in the cells could be transferred to the patient, who might then become ill with a viral infection.

⚖ Ethical and religious objections

Some people think it is wrong to use human embryos, because an embryo has the potential to become a person. Some people have religious objections too. Others argue that the benefit to patients is worth it.

A good answer gives both sides. Say what the possible benefit is, then name the risk or objection, then reach a conclusion.

Stem cells in plants: making clones

Stem cells from the meristems of plants can be used to produce clones of plants quickly and economically. Economically means cheaply. A clone is an organism that is genetically identical to its parent.

🌿 Rare species

A rare plant species can be cloned to protect it from extinction.

🌾 Crop plants

A crop plant with a special feature, such as disease resistance, can be cloned. This produces large numbers of identical plants for farmers.

Common mistakes

1. Saying that stem cells are specialised. They are the opposite: they are undifferentiated.
2. Saying that adult stem cells can become any cell. The spec says adult bone marrow stem cells form many types of cell, including blood cells. Plant meristems are the ones that can become any plant cell.
3. Saying that stem cells definitely cure diseases. Treatment may be able to help.
4. Giving only one side when asked to evaluate. Always give a benefit and a risk or objection.

Exam-style question

Stem cells may be used to treat people with paralysis.

(a) What is a stem cell? [2 marks]

(b) Therapeutic cloning could be used to produce stem cells for a patient. Explain why the patient's body would not reject these cells. [2 marks]

(d) Give one reason why some people object to the use of embryos as a source of stem cells. [1 mark]

Model answer

(a) An undifferentiated cell (1) that can divide to make many more cells of the same type, or can differentiate into other types of cell (1).
(b) The embryo has the same genes as the patient (1), so the stem cells are not seen as foreign and are not rejected (1).
(c) A virus could be transferred from the cells to the patient, causing a viral infection (1).
(d) Some people believe an embryo is a potential human life, or they have a religious objection (1).

Exam tip

In (b), the mark is for linking the same genes to no rejection. Do not just say the cells are the patient's own without saying why.

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