Back to cells … IB topics

Relative sizes Some organelles can be seen with the light microscope, others cannot  We need an electron microscope Although even the largest cell is too small to see with the unaided eye, it is important to have an understanding of the relative sizes of cells and organelles.  Why?

Relative Sizes Eukaryotic Cell μmμm = m Prokaryotic Cell1-5 μm Nucleus10-20 μm Bacteria1-4 μm Cell Membrane7.5 nm thick Large Virus (HIV)100 nmnm = m DNA Double Helix2 nm diam. Mitochondrion0.5 – 5 μm

Remember the metric system? μm = m  Micrometer; one millionth of a meter nm = m  Nanometer; one thousand millionth of a meter The largest known bacterium was found in fish in tropical waters surrounding Lizard Island, Australia (over 1 mm in length) Some eukaryotic cells are larger than indicated in the table  The yolk of an egg is one cell  Each sap vesicle of an orange is one cell

Metric System Practice 3 m = _____ mm 30 mm = ____ μm 30 μm = _____ nm

Linear Magnification Diagrams and photographs can be shown larger or smaller than reality To indicate the real size, the magnification can be indicated next to the diagram  Scale bar

Calculating Linear Magnification See hand out; we’ll finish with this.

Surface Area : Volume The size of a cell is limited by its needs to exchange materials with its environment If a cell becomes too large, its diffusion distance becomes too great  Why is this a problem? Volume increases more quickly than surface area  This is a problem  So what do cells do?