As an organism develops cells differentiate to form
different types of specialised cells.
Most types of animal cells differentiate at an early stage of development whereas some plant cells
retain the ability to differentiate throughout life.
As a cell differentiates
it gets different sub-cellular structures that enable it to carry out a particular function.
It has become a specialised cell. Some specialised cells such as egg and sperm cells
work individually. Others are adapted to work as part of a tissue, organ or whole organism
Nerve cells are specialised to carry electrical impulses around the body of an animal. They provide a rapid communication system betweenthe different parts of the body. They have several adaptations including:
Lots of dendrites to make connections to other nerve cells.
• An axon that carries the nerve impulse from one place to another.
• The nerve endings or synapses are adapted to pass the impulses to another cell or between a nerve cell and a muscle in the body using special transmitter chemicals. They contain lots of mitochondria to provide the energy needed to make the transmitter chemicals.
Muscle cells are
specialised cells that can contract and relax. Muscles contract and relax in pairs to move the bones of the skeleton.
Striated (striped) muscle cells work together in tissues called muscles.
Striated muscle cells have three main adaptations:
• They contain special proteins that slide over each other making the fibres contract.
• They contain many mitochondria to transfer the energy needed for the
chemical reactions that take place as the cells contract and relax.
• They can store glycogen, a chemical that can be broken down and used in cellular respiration by the mitochondria to transfer the energy needed for the fibres to contract.
Sperm cells are usually released a long way from the egg they are going to fertilise.
They contain the genetic information from the male parent.
Depending on the type of animal, sperm cells need to move through water or the female reproductive system to reach an egg. Then they have to break into the egg. Sperm cells have several adaptations to make all this possible:
• A long tail whips from side to side to help move the sperm through water or the female reproductive system.
• The middle section is full of mitochondria which transfer energy needed for the tail to work
• The acrosome stores digestive enzymes for breaking down the outer layers of the egg.
• A large nucleus contains the genetic information to be passed on.
