Cell differentiation

Animals and plants produced by sexual reproduction begin life as a single cell, a fertilised egg or zygote. These cells must divide by mitosis to produce a multicellular organism.

Mitosis happens throughout the bodies of animals but only occurs in specific regions of plants. These are called meristems 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 differentiate, 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 systemTransport substances. Defend the body. Regulate temperature.
Excretory systemRemove waste products and unwanted substances. Regulate the water content of the body.
Muscular systemBring about movement.
Nervous systemRespond to internal and external stimuli and conditions. Carry messages for the body to work as a coordinated whole.
Respiratory systemDeliver oxygen for respiration and remove waste.
Reproductive systemBring about fertilisation to produce new offspring.
Skeletal systemTo 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:
LeafPalisade mesophyllCarry out photosynthesis.
Spongy mesophyllAllow gases to circulate for the exchange of gases between the leaf and the environment. Carry out photosynthesis.
Guard cellsOpen and close to control the exchange of gases – carbon dioxide, water vapour and oxygen.
PhloemSieve tubesTransport products of photosynthesis, including sugars and amino acids, from the leaf to where they are needed.
Companion cellsProvide the energy required for transporting substances in sieve tubes.
XylemXylem vesselsTransport water and dissolved minerals from the roots, up the plant.
Growing pointsMeristemProduce new cells as they divide.