Why can embryonic stem cells be used for more treatments than adult stem cells?

Embryonic stem cells can differentiate into any kind of human cell. Adult stem cells can usually only differentiate into certain types, such as blood cells.

Do all stem cells come from embryos?

No. Adult stem cells are found in places such as bone marrow, and plant stem cells are found in meristems. These sources can also produce certain specialised cells.

Why are embryonic stem cells controversial if they could help patients?

Some people believe embryos should not be used in experiments because each embryo is a human life or could become one. There is also a practical risk that stem cells grown in a lab could be contaminated with a virus and pass it to a patient.

Cell Differentiation and Stem Cells

Cell differentiation produces specialised animal and plant cells adapted to their functions, while stem cells from embryos, adult bone marrow and plant meristems can form cells for repair, medicine, cloning and conservation, with ethical and contamination risks. AQA GCSE Biology Higher, specification references 4.1.1.4, 4.1.2.3 and 1.3.

GCSE
AQA
Biology
Higher
Spec 4.1.1.4 · 4.1.2.3 · 1.3
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Introduction

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Differentiation and specialised cells

Cells do not all look the same. Different cells have different structures because they have different functions, so their shape and their subcellular structures suit the specific job they do.

Differentiation is the process by which a cell changes to become specialised for carrying out its function.

Most differentiation happens as an organism develops. In animals, most cells then lose the ability to differentiate at an early stage, once they have become specialised. Many types of plant cell are different: they keep the ability to differentiate throughout the plant's life.

Learning

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3 cells

Specialised animal cells and their adaptations

Every adaptation in the table below exists for one reason: it makes the cell better at the job it has to do. In an exam answer, always say what the feature is and then what it lets the cell do.

Notice that both sperm cells and muscle cells have lots of mitochondria. That is because both need a lot of energy, one for swimming and one for contracting.

Cell	Function	Adaptations
Sperm cell	To get the male DNA to the female DNA	A long tail and a streamlined head to help it swim to the egg; lots of mitochondria to provide the energy needed; enzymes in the head to digest through the egg cell membrane
Nerve cell	To carry electrical signals from one part of the body to another	Long, so it covers more distance; branched connections at the ends to connect to other nerve cells and form a network throughout the body
Muscle cell	To contract quickly	Long, so there is space to contract; lots of mitochondria to generate the energy needed for contraction

3 cell types

Specialised plant cells

Root hair cell
Absorbs water and mineral ions from the soil. It has a long 'projection' sticking out, which gives the root a big surface area for absorption.
More surface area means more water and mineral ions can be taken in at once.
Phloem cells
Form phloem tubes, which transport substances such as food around the plant. The cells are long and joined end to end, and have very few subcellular structures so that substances can flow through them.
Xylem cells
Form xylem tubes, which transport water around the plant. Like phloem cells they are long and joined end to end, but xylem cells are hollow in the centre so substances can flow through.

1 min read

What stem cells are, and division in mature animals

A stem cell is an undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise by differentiation.

So a stem cell has two options. It can divide to produce lots more undifferentiated cells like itself, or it can differentiate into a particular type of cell, depending on the instructions it is given.

In mature animals, cell division is mainly restricted to repair and replacement, for example making new skin cells or new blood cells. It is not mostly about growing new body parts.

As a cell differentiates it acquires the specific subcellular structures it needs to carry out its job. At that point it has become a specialised cell.

An undifferentiated stem cell with a round nucleus changes, by developing specific subcellular structures, into a specialised white blood cell with a lobed nucleus and granules.

3 sources compared

Stem cells in embryos, adults and plant meristems

Stem cells in early human embryos can turn into any kind of cell; all human cell types come from these few cells. They can be cloned and made to differentiate into most human cell types.

Stem cells from embryos and bone marrow can be grown in a lab to produce clones, genetically identical cells, for medicine or research.

Source	Where found	What it can become
Embryo	Early human embryos	Any kind of cell
Adult animal	Only certain places, e.g. bone marrow	Only certain types, including blood cells
Plant meristem	Parts of the plant where growth occurs	Any type of plant cell, throughout the plant's life

Reference

Using stem cells in medicine

Stem cells can be grown in a lab and made to differentiate into specialised cells, so faulty cells in a sick person could be replaced with working ones. You are not expected to know the specific techniques used, only what stem cells are used for and the issues around them.

Adult stem cells: already in use
Medicine already uses adult stem cells to cure some diseases. Stem cells transferred from the bone marrow of a healthy person can replace faulty blood cells in the patient who receives them.
Embryonic stem cells: possible future uses
Because they can become most types of human cell, they could replace faulty cells in sick people.
Insulin-producing cells for people with diabetes, or nerve cells for people paralysed by spinal injuries.
Therapeutic cloning
An embryo is made with the same genetic information as the patient. The stem cells produced from it share the patient's genes, so they would not be rejected by the patient's body when used to replace faulty cells.

2 min read

Risks, benefits and ethical issues of embryonic stem cells

Embryonic stem cells come from human embryos, so research using them divides opinion.

There is also a practical risk, separate from the ethics: stem cells grown in a lab may become contaminated with a virus, which could then be passed on to the patient they are given to.

Arguments against	Arguments for
Some people feel human embryos should not be used for experiments, because each one is a human life, or has the potential to become one.	Some people think that curing patients who are suffering matters more than the rights of embryos.
Some people feel scientists should concentrate on finding and developing other sources of stem cells, so patients could be helped without using embryos.	The embryos used are usually unwanted ones from fertility clinics, which would probably just be destroyed anyway.

2 key uses

Using stem cells from plant meristems

Stem cells taken from a plant's meristems can be used to produce clones, meaning identical copies, of whole plants. It can be done quickly and cheaply.

One use is conservation. Rare species can be cloned to grow more plants of that species, which helps protect them from extinction.

The other use is farming. Growers can produce large numbers of identical crop plants that all have the features farmers want, such as resistance to disease.

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Describe how a root hair cell is specialised for its function

Describe how a root hair cell is specialised for its function. [2 marks]

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How can stem cells be used to preserve rare plant species?

How can stem cells be used to preserve rare plant species? [2 marks]

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Common questions

Why can embryonic stem cells be used for more treatments than adult stem cells?: Embryonic stem cells can differentiate into any kind of human cell. Adult stem cells can usually only differentiate into certain types, such as blood cells.
Do all stem cells come from embryos?: No. Adult stem cells are found in places such as bone marrow, and plant stem cells are found in meristems. These sources can also produce certain specialised cells.
Why are embryonic stem cells controversial if they could help patients?: Some people believe embryos should not be used in experiments because each embryo is a human life or could become one. There is also a practical risk that stem cells grown in a lab could be contaminated with a virus and pass it to a patient.