Light microscopy

• How do light microscopes work?


  Optical microscopes use white light to illuminate a specimen.
• Describe the steps involved (1).

  Light passes through a specimen.
• What is step 2?

  Into the magnifying lenses of the microscope.
• What is step 3?

  Into the objective viewing lense.
• What is step 4?


  Into the observer's eye where the brain forms an image. The light can also pass to a camera linked to a computer which can display the image on the screen.
• What are the objective lenses?


  The objective lenses are the optical element found closest to the slide, it gathers the light from the specimen and focuses it to produce the real image.
• What is the eyepiece lens (or ocular lens)


  It is found un the eyepiece, closets to the eye. It is placed near to the focal point of the objective lens and this enables it to magnify the image. Usually has magnifying power of 10x.
• What are the limitation of it?


  Low resolution- optical microscopes use normal white light, the limit of their resolution is 200 nm and has a long wavelength. Low magnification- the maximum mag is x1500.
• Why may different people calculate different mitotic indices?

  Garlic roots are a different age.

  Grown in different conditions e.g. temperature.

  Sample is from a different species/plant.

  Single field of view is not representative of a root tip.

  Roots undergo mitosis at different rates.