2. Stem Cells & Meristems

What you need to know...
  • Stem cells are the sites of production of specialised cells in animals and have the potential to become different types of cell. 
    • Stem cells are involved in growth and repair
  • Meristems are the sites of production of non-specialised cells in plants and are the only sites for cell division in a plant. 
    • These cells have the potential to become any type of plant cell and they contribute to plant growth.

Source: SQA
Notes

As we discussed in the last topic, one of the key features of multicellular organisms is that they (we!) have specialised cells. However, where do these cells come from? You already know that new cells arise from other cells as a result of cell division from the last unit. In this topic you will learn a little more about the cells which carry this out. 

Stem Cells

Cells which are able to divide to create new cells are described as stem cells in animals. These cells divide by mitosis to create new cells. Some stem cells, such as the cells which are formed immediately after fertilisation can divide to produce cells which can go on to become any form of specialised cell. These stem cells are therefore crucial for growth. However, as the animal develops its stem cells become more restricted. Firstly, stem cells are restricted to producing groups of tissues and can eventually be restricted to only one tissue. 
In a fully grown animal, its stem cells are restricted to producing cells of a particular tissue. For example, the stem cells which divide to replace your blood cells can only divide to become blood cells. These stem cells therefore are crucial for repair

There is currently a lot of interest in the potential for the use stem cells in the treatment of disease. You can find out more about this on this website, and in this video clip.

Meristems

Plants grow by a combination of cell division and cell elongation. Cell division in plants only occurs at meristems. Meristems are found at various points in the plant as shown in the diagram below.
Meristems can be found at the root and shoot tips which allows the stem and root to lengthen. Meristems can also be found in the stem between the phloem cells and the xylem, we'll learn more about these later in this unit. Meristems in the stem allows it to thicken to give the stem support as it grows. Meristems divide to form unspecialised cells which can then become any type of plant cell.

Here's a little video which discusses meristems in a little more detail.