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Chapter 2 2.3 – The Need for Cell Division The Need for Cell Division • All large plants and animals are composed of many small cells rather than one large cell • This is because there is a limit to how large cells can grow Is Smaller Better? • Cells communicate using chemical messages • Before a nucleus can tell the organelles in the cytoplasm what to do, it must receive messages from the cell’s surroundings Is Smaller Better? • The bigger the cell is, the longer messages take to reach the nucleus, and for the rest of the cell to receive instructions • Cells must be small to receive these messages quickly so they can react to changes in the environment Is Smaller Better? • For example: • Exposure to sunlight triggers a chemical message to skin cells • The message travels to the nucleus of the skin cell • The nucleus sends a message to the ribosomes, telling them to make melanin • The melanin blocks sunlight, preventing sunlight from damaging cells below Is Smaller Better? • Cells also need a constant supply of nutrients and waste must be removed • Molecules enter into and out of cells through the cell membrane • The more cell membrane there is compared with the volume of a cell, the more efficiently the cell can take in nutrients and eliminate waste Some Large, Some Small • Some cells in your body are larger than others • For example fat cells are larger than muscle cells • If you compare the sizes of cells and their functions you will find that cells that do a lot of work are usually smaller than cells that are not as active Some Large, Some Small • The more active a cell is, the more nutrients it needs and the more waste it produces • Many small cells are more efficient at exchanging nutrients and waste than one large cell