Cell Structure

• Organisms are made up of cells.
• Most organisms are multicellular and have cells that are specialised to do a particular job.
• Microscopes are needed to study cells in detail.
• The limits of the light microscope are around 0.05 mm.
• Animal cells are between 0.01 mm – 0.05 mm in size.
• Plant cells are between 0.01 mm – 0.10 mm in size.
• The human eye can see objects as small as around 0.05 mm.
• A microscope is required to see cells in any detail.
• Microscopes magnify the image of a biological specimen close to the level of the unaided eye.
• In microscopy, a whole organism, cells, tissues, a small piece of tissue, or other structures, such as hair, pollen grains, are viewed with a microscope so that they appear larger.
• The type of microscope used in a school laboratory is a compound microscope.
• The compound microscope uses two lenses to magnify the specimen: the eyepiece, which has a longer focal length than the objective lens and magnifies the image produced by the objective, and the objective lens, which is the lens closest to the specimen and has a very short focal length, producing a greatly magnified image of the specimen.
• In a compound microscope, the lens closest to the specimen has a very short focal length and produces a greatly magnified image of the specimen.
• In most microscopes, there is a choice of objective lenses to use.
• Magnification in a microscope is the amount that an image of something is scaled up when viewed through a microscope, which can be varied according to the size of the specimen and the level of detail required.
• The magnification of a lens is shown by a multiplication sign followed by the amount the lens magnifies, for example, ×10.
• Magnification of the microscope is calculated by multiplying the magnification of the eyepiece by the magnification of the objective, for example, if the magnification of an eyepiece is ×10 and the objective is ×4, the magnification of the microscope is: magnification of eyepiece × magnification of objective = 10 × 4 = 40.
• Microscopes use lenses to magnify the image of a biological specimen so that it appears larger.
• The formula to calculate magnification is: magnification = size of image/real size of object.
• A compound microscope uses two lenses, the objective lens and the eyepiece.
• The very short focal length objective lens in a compound microscope produces a greatly-magnified image, then the short focal length eyepiece in the compound microscope magnifies this further.