Cell differentiation
Animals and plants produced by sexual reproduction begin life as a single cell, a fertilised egg or zygoteA fertilised egg cell.. These cells must divide by mitosisA type of cell division which produces daughter cells identical to the parent. to produce a multicellularHaving more than one cell. organism.
Mitosis happens throughout the bodies of animals but only occurs in specific regions of plants. These are called meristemA region in plant shoots and roots in which cells are dividing, and so are undergoing mitosis. and are found in the tips of roots and shoots. Here new cells are formed.
Plant cells are also able to become longer as they grow. This process is called cell elongation and occurs throughout the plant, not just in the meristems. Cell elongation does not occur in animals.
The cells of multicellular animals and plants must also differentiationWhen an unspecialised cell becomes a more specialised cell type., so that its cells develop features that enable them to fulfil specific roles. Cells that have differentiated have become specialised. Without this specialisation, complex multicellular animals and plants would not exist.
Examples in animals include:
| 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 | To bring about movement. Support and protect internal structures. Produce blood cells. Store and release calcium. |
| Cells of the: | Circulatory system |
|---|---|
| Specialised to: | Transport substances. Defend the body. Regulate temperature. |
| Cells of the: | Excretory system |
|---|---|
| Specialised to: | Remove waste products and unwanted substances. Regulate the water content of the body. |
| Cells of the: | Muscular system |
|---|---|
| Specialised to: | Bring about movement. |
| Cells of the: | Nervous system |
|---|---|
| Specialised to: | Respond to internal and external stimuli and conditions. Carry messages for the body to work as a coordinated whole. |
| Cells of the: | Respiratory system |
|---|---|
| Specialised to: | Deliver oxygen for respiration and remove waste. |
| Cells of the: | Reproductive system |
|---|---|
| Specialised to: | Bring about fertilisation to produce new offspring. |
| Cells of the: | Skeletal system |
|---|---|
| Specialised to: | To bring about movement. Support and protect internal structures. Produce blood cells. Store and release calcium. |
Some specialised cells of plants:
| 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 photosynthesis. | |
| Guard cells | Open and close to control the exchange of gases 鈥 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. |
| Cells of the: | Leaf |
|---|---|
| Palisade mesophyll | |
| Specialised to: | Carry out photosynthesis. |
| Cells of the: | |
|---|---|
| Spongy mesophyll | |
| Specialised to: | Allow gases to circulate for the exchange of gases between the leaf and the environment. Carry out photosynthesis. |
| Cells of the: | |
|---|---|
| Guard cells | |
| Specialised to: | Open and close to control the exchange of gases 鈥 carbon dioxide, water vapour and oxygen. |
| Cells of the: | Phloem |
|---|---|
| Sieve tubes | |
| Specialised to: | Transport products of photosynthesis, including sugars and amino acids, from the leaf to where they are needed. |
| Cells of the: | |
|---|---|
| Companion cells | |
| Specialised to: | Provide the energy required for transporting substances in sieve tubes. |
| Cells of the: | Xylem |
|---|---|
| Xylem vessels | |
| Specialised to: | Transport water and dissolved minerals from the roots, up the plant. |
| Cells of the: | Growing points |
|---|---|
| Meristem | |
| Specialised to: | Produce new cells as they divide. |