Most animal cells are specialised. They have adaptations that help them perform specific functions. Humans are made up of trillions of cells; however, there are only about 200 different types.
Red blood cells carry oxygen around the body for aerobic respiration. They have no nucleus, so they can contain more oxygen-carrying haemoglobin. As red blood cells have no nucleus, they also have no DNA.
Also, red blood cells are a biconcave disc shape to make them more flexible and allow the cells to move smoothly through the circulatory system. This shape also maximises the absorption of oxygen.
The function of nerve cells is to carry electrical impulses around the body. A nerve cell has a cell body which contains most of the subcellular structures. There are extensions connected to the cell body:
The axon is covered in a fatty myelin sheath, which increases the speed of nerve impulses.
Sperm cells are found in males and their function is to pass on the DNA from the father. A sperm cell joins with an egg cell and this is called fertilisation. During fertilisation, the genetic information of the sperm cell and the egg cell combine.
Sperm cells have many adaptations:
Muscle cells create a pulling force to move parts of the body. They can contract (get shorter) because they contain filaments of protein that slide over each other. Muscle cells have plenty of mitochondria packed into them to provide energy (through respiration) for muscle contraction.
There are three types of muscle in animals:
Egg cells are found in females and their function is to pass on genetic material to the next generation. They have a unique cell membrane which only allows one sperm to penetrate through. After fertilisation, the membrane changes so that no more sperm can enter.
Most of the genetic information is contained within the nucleus of the egg cell. Egg cells are also gametes, so they only contain half the amount of genetic information as a body cell.
Ciliated epithelial cells move particles or fluid over the epithelial surface. They are found in the lungs and fallopian tubes. They have many cilia on the top surface of each cell.