Cellular Organisation

Cellular Organisation

Cells are specialised to perform specific functions. Similar cells are then grouped together into tissues, tissues into organs and organs into organ systems for increased efficiency.

Cell Differentiation

• Single-celled organisms perform all essential life functions inside the boundaries of a single cell. Although they perform all functions adequately, they cannot be totally efficient at all of them, because each function requires a different type of cellular structure.
• For example, one activity may be best carried out by a long, thin cell, while another might suit a spherically shaped cell.
• No one cell can provide the best conditions for all functions, for this reason the cells of multicellular organisms are adapted in different ways to perform a particular role.
• All cells in an organism are indentical; but as it matures, each cell takes on its own individual characteristics that suit it to the function that it will perform when it is mature - the cell becomes specialised; this is known as cell differentiation.
• All cells in an organism are derived by mitotic divisions of the fertilised eggs and all cells contain exactly the same genes.
• Cells become differentiated because, only a few of the genes that the cell possess are switched on (expressed). 
• Different genes are switch on (expressed) in each type of differentiated cell, the rest of the genes are switched off.
• Both shape and number of organelles within each cell varies from cell to cell, e.g. muscle or sperm cell have many mitochondria, while a bone cell has very few.
• The cells of a multicellular organism have therefore evolved to become more and more suited…