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CELLS PRINCIPLES OF THE CELL THEORY The mid 1660s saw the advent of the microscope. In 1665, Robert Hooke (an Englishman) saw a thin slice of cork (a plant material) with the use of a compound microscope. The cork was made up of thousands of tiny chambers which Hooke called cells. • The Discovery of the Cell – The mid 1660s saw the advent of the microscope. – In 1665, Robert Hooke (an Englishman) saw a thin slice of cork (a plant material) with the use of a compound microscope. • The cork was made up of thousands of tiny chambers which Hooke called cells. – Anton van Leeuwenhoek (a Dutchman) around the same time looked at pond water with a single lens microscope and found tiny organisms. LIFE IS CELLULAR – The Cell Theory • Some after the previous discoveries, scientists were sure that the cell was the basic unit of life. • New discoveries: including all plants were made of cells, all animals were made of cells, and new cells were produced by the division of existing cells. • The cell theory states: – All living things are composed of cells. – Cells are the basic unit of structure and function in living things. – New cells are produced from existing cells. THE COMPOUND MICROSCOPE • Microscopes produce magnified images of structures that are too small to see with the unaided eye. • Light microscopes produce magnified images by focusing visible light rays. Electron microscopes produce magnified images by focusing beams of electrons. • Two problems exist – How large can an object become – How sharp can the image be THE COMPOUND MICROSCOPE • Light Microscopes – These can produce clear images at magnifications of 1000 times. – Compound light microscopes allow light to pass through the specimen and use two lenses to form an image. – Chemical stains , or dyes, can show specific structures in the cells. THE COMPOUND MICROSCOPE • Electron Microscopes – These can study objects smaller than 0.2 micrometers which light microscopes cannot. – They use beams of electrons, rather than light, to produce images. – These images are 1000 times more detailed than light microscopes. • Two types: – Transmission electron – Scanning electron • Scanning Probe Microscopes Trace surfaces of samples with a fine probe LIGHT MICROSCOPE ELECTRON MICROSCOPE THE COMPOUND MICROSCOPE • Contains a combination of lenses • The eyepiece lens has a magnification of 10X. • Objective lenses are at the bottom of the body tube. • These can be rotated at the nosepiece. – Have a 10X – Have 40X or 43X THE COMPOUND MICROSCOPE • Carry with two hands, one beneath the base and the other on the arm. • Place gently on the table with the arm facing you. • Raise body tube by turning the coarse adjustment knob. • Rotate the nosepiece so that the 10X is in line with the body THE COMPOUND MICROSCOPE • Look through the eyepiece and switch on the lamp or adjust the mirror to see a circle of light or field of view. • Place the prepared slide on the stage so that the specimen is over the center of the opening. • Look at the microscope from the side and use the coarse adjustment knob so that the lowerpower objective almost touches the slide. THE COMPOUND MICROSCOPE • Look through the eyepiece and observe the specimen. • Do not lower the body tube when looking through the eyepiece. • Adjust the diaphragm to allow the correct amount of light to enter. • Rotate the nosepiece to change the magnification. THE COMPOUND MICROSCOPE • Use the fine adjustment to bring the specimen into focus. • After use, remove the slide, put the low power objective in place, clean everything with lens paper. PREPARING A WET MOUNT SLIDE • Obtain a clean microscope slide and coverslip. • Place the specimen in the middle of the slide and add a drop of water with a pipette. • Carefully lower the coverslip over the specimen. • Remove excess water with a paper towel from the edge of the coverslip. STAINING TECHNIQUES • Obtain clean slide and coverslip. • Place specimen in middle of slide. • Place drop of water with pipette on specimen and add coverslip. • At the edge of the coverslip, add the stain . • Using forceps, touch a small piece of lens paper to the opposite edge of the coverslip drawing the stain under the coverslip.