3.5. Cell Specialisation

• In multicellular organisms, cells are specialised to perform specific functions. Similar cells are then grouped into tissues, tissues into organs and organs into systems for increased efficiency
• All the cells in an organism, such as a human, are produced by mitotic divisions from the fertilised egg. Every cell contains the genes needed for it to develop into any one of the different cells in an organism, but only some of these genes are actually expressed in any one cell
• For example a muscle cell or sperm cells will contain many mitochondria, while a bone cell has very few. White blood cells have many lysosomes while a muscle cell has very few
• The cells of a multicellular organism have evolved
• Epithelial tissues are found in animals and consist of sheets of cells. They line the surfaces of organs and often have a protective or secretory function
• Epithelial tissues have many similar types, including thin, flat cells that lines organs where diffusion takes place. For example, the alveoli of the lungs and ciliated epithelium that lines the trachea.
• The cilia are used to move mucus over the epithelial surface
• Xylem are made of similar cell types, used to transport water and mineral ions and give the plant mechanical support
• An organ is a combination of tissues that are coordinated to perform a variety of functions, although they often have one predominant major function
• The stomach is made up of: muscle to churn and mix contents, epithelium for protection and produce secretions and connective tissue
• A leaf is made up of: Palisade mesophyll made up of leaf palisade cells that carry out photosynthesis, strong mesophyll adapted for gaseous diffusion and phloem to transport organic materials away from the leaf. (And xylem)
• Blood capillaries are not organs but veins and arteries are due to being mde up of multiple tissues and muscle. However all have the role of transporting blood around the body.
• The digestive system digests and processes food. It is made up of organs , including the salivary glands, oesophagus, stomach, duodenum, ileum, pancreas and liver.
• The respiratory system is used for breathing and gas exchange. It is made up of organs that include the trachea, bronchi and lungs
• The circulatory system pumps and circulates blood around the body. It is made up of organs including the heart, arteries and veins.