Cell Differentiation and Specialisation

Differentiation is the process by which a cell changes to become specialised for its job. As cells change, they develop different subcellular structures and turn into different types of cells. This allows them to carry out specific functions. Most differentiation occurs as an organism develops. In most animal cells, the ability to differentiate is then lost at an early stage, after they become specialised. However, lots of plant cells don't ever lose this ability. The cells that differentiate in mature animals are mainly used for repairing and replacing cells, such as skin or blood cells. Some cells are undifferentiated cells called stem cells.

Sperm cells are specialised for reproduction. The function of a sperm is to get the male DNA to the female DNA. It has a long tail and a streamlined head to help it swim effeciently to the egg. There are also lots of mitochondria in the cell to provide the energy needed to swim to the egg. It also containes enzymes in its head to digest through the egg cell membrane.

Nerve cells are specialised for rapid signalling. The function of a muscle cell is to carry electrical signals from one part of the body to another. These cells are long (to cover more distance) and have brached connections at their ends to connect to other nerve cells and form a network throughout the body.

Muscle cells are specialised for contraction. The function of a muscle cell is to contract quickly. These cells are long (so they have the space to contract) and contain lots of mitochondria to generate the energy needed for contraction.

Root hair cells are specialised for absorbing water and minerals. Root hair cells are cells on the surface of plant roots, which grow into long hairs that stick out onto the soil. This gives the plant a large surface area for absorbing water and mineral ions from the soil.

Phloem and xylem cells are specialised for transporting substances. Phloem and xylem cells form phloem and xylem tubes, which transport substances such as food and water around plants. To form tubes, the cells are long and joined end to end. Xylem cells are hollow in the center and phloem cells have very few subcellular structures, so substances can flow through them.

The xylem is specialised to transport water up the stem of a plant and into the leaves. Xylem vessels are made up of a series of connected dead xylem cells. The end walls of the dead cells are broken to allow water to move through. A substance called lignin strengthens the cell walls of xylem cells.

The phloem is specialised to transport food products to parts of the plant where they are needed. Phloem vessels are made up of columns of living cells. The end walls of phloem cells contain small holes to allow food products to move up and down the phloem vessels.

Embryonic stem cells can turn into any type of cell. Undifferentiated cells, also know as stem cells, can divide to produce lots more undifferentiated cells. They can differentiate into different types of cells, depending on what instructions they're given. Stem cells are found in early human embryos. They have the potential to turn into any kind of cell. Adults also have stem cells but they're only found in certain places such as the bone marrow. Unlike embryonic stem cells, they can't turn into any type of cell. Stem cells from embyros and bone marrow can be grown in a lab to produces clones (genetically identical cells) and made to differentiate into specialised cells to use in medicine or research.

Medicine already uses adult stem cells to cure diseases. For example, 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 could also be used to replace faulty cells in sick people. In a type of cloning, called therapeutic cloning, an embryo could be made to have the same genetic information as the patient. This means that the stem cells produced from it would also contain the same genes and so it wouldn't be rejected by the patient's body if used to replace faulty cells. However there is risk involved in using stem cells in medicine. For example, stem cells grown in the lab may become contaminated with a virus which could be passed on to the patient and make them sicker.

Some people are against stem cell research because they feel that human embryos shouldn't be used for experiments since each one is potential human life. Others think that curing existing patients who are suffering is more important than the rights of embyros. One fairly convincing argument in favour of this point of view is that the embyros used in research are usually unwanted ones from fertility clinics which would probably be destroyed if not used. These campaigners feel that scientists should concentrate more on finding and developing other sources of stem cells, so people could be helped without having to use embyros. In some countries, stem cell research is banned. It's allowed in the UK as long as it follows strict guidelines.

In plants, stem cells are found in the meristems (parts of the plant where growth occurs). Throughout the plant's entire life, cells in the meristem tissues can differentiate into any type of plant cell. These stem cells can be used to produce clones (identical copies) of whole plants quickly and cheaply. They can be used to grow more plants of rare species (to prevent them being wiped out). Stem cells can also be used to grow crops of identical plants that have desired features for farmers.