Differentiation
Multicellular organisms begin life as a single fertilised egg cell called a A fertilised egg cell.. The zygote has a nucleus containing a full set of genes. When the zygote divides by mitosis, the full set of genes are copied and this process continues until a ball of cells called an embryo is formed. At this point cells begin to become adapted to specific functions. This is called When an unspecialised cell becomes a more specialised cell type. and is controlled by genes.
Some specialised cells are shown here.
A nerve cell is long and insulated with a fatty layer to carry electrical impulses around the body.
A sperm cell has a tail so that it can swim to the egg.
A palisade cell is packed with chloroplasts for photosynthesis.
A xylem cell is a long, thin, straw-like waterproof tube which carries water from plant roots to leaves.
Red blood cells are a biconcave shape, have no nucleus, and contain haemoglobin to carry oxygen around the body.
Cells, tissues and organs
Cells with a similar function are grouped together in tissues. A collection of different tissues carrying out a particular function is called an