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.
• Light microscope


  Cells range in size: animal cells are between 0.01 mm – 0.05 mm, plant cells are between 0.01 mm – 0.10 mm
• The human eye can see objects as small as around 0.05 mm. A microscope is required to see cells in any detail.
• Microscope


  Magnifies the image of a biological specimen so that it appears larger
• Compound microscope


  Uses two lenses, the objective lens and the eyepiece, to magnify the specimen
• Calculating the magnification of the microscope

  Magnification of the microscope = magnification of eyepiece × magnification of objective
• Cell


  The basic unit of life, which makes up all organisms
• Cells


  • Most organisms are multicellular and have cells that are specialised to do a particular job
  • Microscopes are needed to study cells in detail
• Micrometre (μm)


  The best unit to measure most cells
• Nanometre (nm)


  A smaller unit used to measure sub-cellular structures and organisms like viruses
• 1 metre can be broken down into the following measurements: millimetre (mm), micrometre (μm), nanometre (nm)
• Standard form


  A system in which numbers are written as a number greater than 1 and less than 10 multiplied by a power of 10 which may be positive or negative
• Standard form numbers are written as: A × 10^n, where A is a number greater than one but less than 10, and n is the index or power, always in powers of 10
• Using standard form for large numbers

  • A population of 120,000,000 microorganisms could be written as 1.2 × 10^8
• Using standard form for small numbers

  • A red blood cell's diameter of 7 μm or 0.000007 m could be written as 7 × 10^-6 m
• Calculating the magnification of a cell


  1. Magnification = Measurement of cell in image / Actual size of cell

  2. Example: Magnification = 100 mm / 0.05 mm = 2000
• Sizes of most cells are given in micrometres (μm)
• 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
• Preparing biological samples for examination

  1. Place a small square or circle of thin glass called a coverslip over the specimen

  2. Use a mounted needle to hold the specimen in place as the coverslip is lowered

  3. Ensure no air bubbles are trapped underneath
• Most cells are colourless
• Stains


  Used to add contrast and stain specific cell structures or cell products
• Care must be taken when looking down the microscope if the illumination is too bright
• Care must be taken when using microscope stains
• Care must be taken when handling coverslips, microscope slides and mounted needles
• 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.
• Investigating cells with a light microscope

  1. Rotate the objective lenses so that the low power, eg x10, is in line with the stage

  2. Turn the coarse focus so that the stage is as close to the objective lens as possible

  3. Place the microscope slide on the stage and line it up so that the specimen is in the centre

  4. Focus the slide towards you by turning the coarse focus adjustment

  5. Draw a low power image or record a digital image

  6. Rotate the objectives so that the high power objective, eg x40, is in line with the stage

  7. Bring the slide back into focus using the fine focus adjustment
• Care must be taken when looking down the microscope if the illumination is too bright.
• Care must be taken when using microscope stains.
• Care must be taken when handling coverslips and microscope slides.
• Low power diagram


  Used as a plan to show the arrangement of any distinct regions of the tissue, or to show the outline of individual cells that make up the uniform tissue
• High power diagram


  A detailed image of a part of the slide, usually drawn to show a single cell
• Microscope drawings must be fully labelled.
• 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
• Compound microscope


  • Uses two lenses, the objective lens and the eyepiece
  • The very short focal length objective lens produces a greatly-magnified image, then the short focal length eyepiece magnifies this further