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Unit 2: Cells Mr. Nagel Meade High School Research • What did the following scientists contribute to our knowledge about CELLS? – Hooke – von Leeuwenhoek – Schleiden – Schwann – Virchow IB Syllabus Statements • 2.1.1 – Outline the cell theory. • 2.1.2 – Discuss the evidence for the cell theory. • 2.1.3 – State that unicellular organisms carry out all the functions of life. • 2.1.6 – Explain the importance of the surface area to volume ratio as a factor limiting cell size. • http://click4biology.info/c4b/2/cell2.htm Cell Theory Cell Theory • Robert Hooke (1665) – Cork cells (30x) • Anton von Leeuwenhoek (same time) – Unicellular organisms (300x) • Schleiden (plants) and Schwann (animals) (1839) – Animal and plant cells • Rudolph Virchow (1855) – Determines cells only come from other cells • Sum of conclusions lead to Cell Theory Cell Theory • Cell Theory: – Cells are the fundamental unit of life. – All living things are composed of cells. – Cells can only come from pre-existing cells. • Unicellular organisms carry out all life functions. • What is the difference between a Law, Theory, and Fact? • Why is this only a Theory? Cell Structure • Balloons and improvised tape measures: – Surface Area vs. Volume • Measure the circumference of your balloon at three varying sizes. – Calculate: • Volume • Surface Area • SA/V ratio Cell Structure • What do you notice about the SA:V ratio as the balloon (model cell) expands? • Why would it be important for a cell to have a much greater surface area than volume? IB Syllabus Statements • 2.1.6 – Explain the importance of the surface area to volume ratio as a factor limiting cell size. • 2.1.4 – Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit. • 2.1.5 – Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification. • http://click4biology.info/c4b/2/cell2.htm Cell SA:V Ratio Hierarchy of Biology • Organize the following from smallest to greatest: – Tissue, atom, organism, organelle, organ, population, cell, community, ecosystem, organ system, molecule • Provide an example of each! Cell Stats • Biggest Cell – Giraffe nerve (2m) • Smallest Cell – Bacteria (0.2µm) Microscopy Early microscopes were similar to the ones used in today’s classrooms (Light microscopes) -Visible light passes through the specimen and then through the glass lens which magnifies the image. Microscopy • Several things are important in the world of microscopes: – Resolution – ability to clearly see between points • Limits of Resolution: π*r2 (area of light) – Magnification – just how LOW can we go? • Light microscopes are limited to 0.2 µm (2000x) (size of a small bacterium) and are effective at about 1000 times the size of the specimen. Light microscopes can NOT see organelles. Microscopy • Electron microscopes have magnets to focus an electron beam. The wavelength of the electron beam is far shorter than that of light, and the resulting image resolution is far greater (about 0.5 nm). – Scanning electron microscopes (SEM) • Exterior (spray with fine metallic mist) – 50,000x • Electrons project onto photographic plate – Transmissions electron microscopes (TEM) • Interior (thin slices) – 2,000,000x Light Microscopy Electron Microscopy Size and Scale Size and Scale Calculating Magnification • When drawing cells and cell ultrastructures… – Include a scale bar: |---| = 1µm – Include magnification: x250 • To find magnification: – M = Measured size of diagram / Actual Size of object – M = objective lens * eyepiece lens • In the next slide: – Find the magnification. (Hint: Think of map scales) – State the size of one of the beads. Calculating Magnification • 4 cm / 200 µm = 4 x 10-2 m / 200 x 10-6 m – =0.02 x 104 = 200x Homework • Create a “double bubble map” comparing and contrasting Prokaryotic cells with Eukaryotic cells. • Be as thorough as possible… a complete map will be an excellent reference!