What are stem cells?
This week we will introduce teaching and learning strategies that help you and your students to make links between the topic of stem cells and other areas of the curriculum. To be clear, we are not talking about the cells in the stem of a plant, we are talking about a type of cell.
We’ll begin with a brief introduction to stem cells.
Unicellular organisms consist of a single cell that carries out all the processes needed to keep that organism alive. Examples include Bacteria, the Amoeba and some algae.
Multicellular organisms are composed of many different types of cells which each have a different job to do. These are called specialised cells. The structure of a specialised cell is adapted to carry out its specific function. Examples include nerve cells (which are very long), muscle cells (which can contract) and root hair cells.
A stem cell is a cell which has the ability to divide and produce different types of specialised cells in an organism. Once a cell has become specialised, we say it has ‘differentiated’. A stem cell is ‘undifferentiated’.
Stem cells can divide to form more identical stem cells, or they can differentiate into specialised cells. The division of a cell to form two genetically identical daughter cells is called ‘mitosis’. The type of specialised cell that a stem cell differentiates into is controlled by the genes that are switched on or switched off inside its nucleus.
The early embryos of animals contain stem cells. These very first stem cells to form in an animal embryo are ‘totipotent’, meaning that they have the potential to differentiate into any of the specialised cells that are found in the body of an adult. In other words, an entire body can be grown from totipotent stem cells.
Stem cells can also be found in certain tissues within the adult’s body, such as the bone marrow. However in animals, these adult stem cells can only differentiate into a few different types of specialised cell, having lost the ability to become any type of cell in the body (they are no longer totipotent and instead they are referred to as multipotent). For example, the stem cells in bone marrow can produce specialised cells in blood and the immune system, but not other cell types.
In plants, stem cells are found in the growing tips of roots and shoots, in specialised structures called meristems. These stem cells can differentiate into any of a plant’s specialised cell types, allowing the plant to form different tissues as it grows.
Unlike animals, many mature plant cells remain totipotent, able to differentiate into any type of cell. This is why a fragment of a mature plant, such as part of a leaf, can be used to regenerate an entire plant, whereas animals cannot regenerate an entire individual from a fragment of an organ.
What prior knowledge will your students need before they begin to learn about stem cells? Add a list below.
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