Stem cells and differentiation – GCSE Combined Science Biology

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Your body is made of many different kinds of cell. Nerve cells, muscle cells and blood cells all have different jobs. But they all began as cells that had no job yet. Those starting cells are stem cells.

This matters because doctors hope to use stem cells to repair damaged parts of the body. Farmers can use plant stem cells to grow many copies of a plant.

By the end you will be able to explain what a stem cell is and where stem cells come from. You will describe how they are used. You will also discuss the risks and the ethical issues.

What stem cells are

Most cells are specialised. This means they have changed to do one job, like a muscle cell. The change is called differentiation. A stem cell is undifferentiated, so it has not become specialised yet.

A stem cell can divide by mitosis to make more cells. It can also differentiate into specialised cells. Think of a trainee who has not yet picked a job.

Embryonic stem cells come from early human embryos. They can become any type of human cell. Adult stem cells are found in places such as bone marrow. They can only form some types of cell, such as blood cells.

Using stem cells to treat disease

Stem cells could be used to replace damaged or diseased cells. They could make new insulin-producing cells for people with diabetes. They could make new nerve cells for people with paralysis from a spinal injury.

Adult bone marrow stem cells are already used in bone marrow transplants. These treat some blood diseases.

There is a problem. If the new cells have different genes from the patient, the immune system may attack them. In therapeutic cloning, an embryo is made with the same genes as the patient. Its stem cells are not rejected.

Risks of treatment

Stem cell treatments carry risks. Stem cells grown in a laboratory can be contaminated with viruses. These could infect the patient.

Stem cells also divide very fast. If they divide out of control, they can form a tumour. A tumour is a lump of cells growing where it should not.

Scientists are still testing and improving the treatments to make them safer. Doctors must weigh up the possible benefit against the risk for each patient.

Ethical issues

An ethical issue is a question about what is right or wrong. Some people object to using embryonic stem cells, because embryos are destroyed. They believe an embryo has the right to life.

Others disagree. They point out that the cells often come from embryos that would have been thrown away. They argue that the cures could save many lives.

In an exam, give both sides. Say what the benefit is and what the concern is. Use the word because to link each point to a reason.

Plant stem cells

Plants have stem cells in areas called meristems. They are found at the tips of roots and shoots. Meristem cells divide by mitosis, and they can differentiate into any type of plant cell.

Plant stem cells keep working for the whole life of the plant. Adult stem cells in animals can only make some types of cell.

This is why a cutting can grow roots and become a whole new plant. The meristem cells make new xylem, phloem and root hair cells as needed.

Uses of plant stem cells

Meristem cells can be used to make clones of a plant quickly and cheaply. A clone has exactly the same genes as the parent. Think of making photocopies of a good page.

This can save rare plants from extinction. It can also grow large numbers of identical crop plants that resist disease.

There is a catch. Clones have the same genes, so they all have the same weaknesses. If a new disease arrives, they are all equally at risk.

Recap

A stem cell is undifferentiated. It can divide and become specialised.

Embryonic stem cells make any cell type. Adult stem cells make a limited range.

Stem cells can replace damaged cells. The risks are viruses, tumours and ethical objections.

Meristems in plants have stem cells throughout life and can make clones.