Light Microscopes & Cells
- Many biological structures are too small to be seen with the naked eye
- Light microscopes allow tissues, cells, and sub-cellular structures to be seen and studied
Light microscope diagram
Light microscopes, also known as optical microscopes, can be used to study cells
Preparing & viewing microscope slides
- Specimens often observed in a school laboratory are cheek cells and onion cells
- Biological stains are used to highlight structures within cells and allow more detail to be seen, e.g.
- Methylene blue is used to stain cheek cells
- Iodine can be used to stain onion cells
- Specimens must be prepared on a microscope slide for observation under a light microscope, e.g. to prepare a slide for viewing onion cells the following procedure might be used:
- Remove a thin layer of onion cells from an onion; tweezers can be used for this process
- Place the layer of cells onto a glass slide and add a drop of water
- Add a drop of iodine stain and gently lower a coverslip over the specimen
- The prepared slide can then be placed onto the microscope stage for viewing
Using a light microscope diagram
A light microscope can be used to view cells in a school laboratory
Calculating total magnification
- The magnification at which a light microscope is viewing a specimen can be calculated by multiplying the power of the eyepiece lens by the power of the objective lens:
Total magnification = power of eyepiece lens x power of objective lens
Worked example
A light microscope has an eyepiece lens with 10X magnification and the objective lens is set to a power of 40X.
Calculate the total magnification of the light microscope.
Step 1: Recall the equation
Total magnification = power of eyepiece lens x power of objective lens
Step 2: substitute figures into the equation
Total magnification = 10 x 40
Total magnification = 400X
Limitations of light microscopes
- Light microscopes are limited to a maximum magnification of around 1500X, meaning that they can only be used to view whole cells and the largest cellular structures
- The magnification of light microscopes is limited by their relatively low resolution
- Light microscopes are generally only useful for viewing 2D structures
Comparing light & electron microscopes
- For detailed examination of cells and cellular structures an electron microscope must be used
- Electron microscopes are capable of much higher magnification than light microscopes
Comparison of electron and light microscopes table
Electron microscope | Light microscope |
Very large so can only be used in the science lab in which they are installed | Small and easy to carry |
Vacuum needed (so specimens must be dead) | No vacuum needed (so specimens can be living) |
Complicated sample preparation | Easy sample preparation |
Over 500 000X magnification | Up to 2000X magnification |