The alien lookalike above is actually a picture of an embryo at around six weeks old! A zygote is formed when an egg is fertilised by a sperm. After fertilisation, the zygote starts to divide, it's now called an embryo. When the embryo reaches the eight-cell stage all the cells are identical to each other and have the ability to become any type of cell. They're embryonic stem cells. These can stay as stem cells or become differentiated (specialised) to become another type of cell such as a muscle cell, red blood cell or a nerve cell. Sometimes you will find adult stem cells among the differentiated cells-these can become differentiated later on.
Function of stem cells
Our chromosomes have thousands of genes that can code for many proteins. We don’t need all of these genetic codes to be active all of the time in our body cells so they're switched off. This way the cell only produces the proteins it needs to function.
Specialised cells produce specific proteins because the genes coding for these proteins are activated or switched on. Embryonic stem cells are able to differentiate into any cell type. This is because any of the genes in their chromosomes are able to be switched on.
Stem cells are important for many reasons. In the embryo, stem cells will develop into the whole body of the organism, including all of the organs such as the heart, lung, skin and other tissues and cells. In some adult tissues, such as bone marrow, adult stem cells are used to replace cells that are lost through normal wear and tear, injury or disease.
Uses of stem cells
The fact that stem cells can undergo cell division and become differentiated to any cell type makes stem cells really interesting to Scientists. Potential new treatments to replace cells lost to injury and disease and research may help develop alternatives to organ transplantation and the effects of new drugs.
Embryonic stem cells can be used in research to help scientists develop new cells to replace damaged or diseased cells. The stem cells could be injected into damaged organs to rebuild the tissues. This would reduce the need for organ transplants. The stem cells would need to have the same genes as the patient, otherwise, they would be rejected by the patient’s immune system. They would need to be clones. The DNA of an embryo cell can be replaced with the DNA from a patient’s cell. The embryo produces stem cells containing the patient’s genes. The cells will not be rejected, so immune-suppressing drugs are not needed. This process is called therapeutic cloning.
There are some risks involved in stem cell treatment:
- there's a risk of infections from the operations involved or from infected stem cells.
- Due to uncontrolled cell division tumours may form.
- Damage to organs- stem cells implanted into damaged tissue may move to healthy areas and cause damage to those areas.
- Immune rejection- when the persons own immune system rejects the stem cells from another person and white blood cells destroy them.
There are different types of issues depending on the type of cells involved. Often with embryonic stem cells and therapeutically-cloned stem cells, the issue of using embryo's can be a sensitive topic. Some peoples religion or personal beliefs view the embryo as representing life and should only be used to create a baby. In science obtaining a balanced view is important and often there is no one correct answer.
Stem cells are not only found in animals, but plants too. Let's find out more below.
In plant cells, cell division only happens in certain areas called meristems. Meristems are found at the tips of roots and shoots and in between the xylem and the phloem tissues. The cells in the meristem can divide over and over again to produce non-specialised cells. Some of these cells continue to divide, allowing the plant to grow taller and wider throughout its life.
Other non-specialised cells that are produced at the meristem can develop into any type of specialised plant cell and go on to form phloem, xylem, leaves and flowers. This activity contributes to plant growth and development.
Like with human stem cells, plant meristem cells have many uses too. For example, they can be used to produce clones of plants very quickly and economically. Also, plants that have special features such as being disease resistant or frost resistant can be cloned to produce lots of crops for example for farmers. Another use is to protect rare plant species from extinction by cloning them.
In the following activity, you will consider the functions and uses of stem cells.