Large, multicellular organisms like humans are made from many different cell types. There are over 200 specialised cells in our bodies. So, stem cells must differentiate so that they develop the features that enable them to fulfil their specific roles. Once they have specialised, they are unable to change into other cell types.
|Cells of the…||Specialised to…|
|Circulatory system||Transport substances, defend the body, regulate temperature|
|Excretory system||Remove waste products and unwanted substances, regulate the water content of the body|
|Muscular system||Bring about movement|
|Nervous system||Respond to internal and external stimuli and conditions, carry messages for the body to work as a coordinated whole|
|Respiratory system||Deliver oxygen for respiration and remove waste|
|Reproductive system||Bring about fertilisation to produce new offspring|
|Skeletal system||Bring about movement, support and protect internal structures, produce blood cells, store and release calcium|
|Cells of the...||Specialised to...|
|Leaf||Palisade mesophyll||Carry out photosynthesis|
|Spongy mesophyll||Allow gases to circulate for the exchange of gases between the leaf and the environment, carry out some photosynthesis|
|Guard cells||Open and close to control the exchange of gases – carbon dioxide, water vapour and oxygen|
|Phloem||Sieve tubes||Transport products of photosynthesis, including sugars and amino acids, from the leaf to where they are needed|
|Companion cells||Provide the energy required for transporting substances in sieve tubes|
|Xylem||Xylem vessels||Transport water and dissolved minerals from the roots, up the plant|
|Growing points||Meristem||Produce new cells as they divide|
Stem cells are cells that have not undergone differentiation. An embryo develops from a fertilised egg. Cells at early stages in the development of the embryo are stem cells.
If cells are removed from the embryo – called embryonic stem cells – they will differentiate into any cell type.
Some stem cells remain in the bodies of adults – adult stem cells.
Adult stem cells are found in limited numbers at certain locations in the body, including the:
Cell division in plants occurs in regions called meristems.
Cells of the meristem can differentiate to produce all types of plant cells at any time during the life of the plant.
The main meristems are close to the tip of the shoot, and the tip of the root.
In a growing shoot, new cells are being produced continuously near the tip. As the cells become older, further away from the tip, they become differentiated – they enlarge and develop vacuoles.