Practical: Microscopy (SQA National 5 Biology): Revision Note

Examining cells using a light microscope

• Many biological structures are too small to be seen by the naked eye

• Light (optical) microscopes are an invaluable tool for scientists as they allow for tissues, cells and organelles to be seen and studied

Apparatus

• The key components of an optical microscope you will need to use are:

  • The eyepiece lens

  • The objective lenses

  • The stage

  • The light source

  • The coarse and fine focus

• Other apparatus used:

  • Forceps

  • Scissors

  • Scalpel

  • Coverslip

  • Slides

  • Pipette

  • Stain e.g. iodine solution or methylene blue

Viewing plant tissue

Method

• An ideal tissue is the onion epidermis (found between the layers of onions) because it forms a layer just one cell thick

  • Being a non-photosynthetic tissue, the onion epidermis is not green as it does not contain any chloroplasts

  • This tissue can be stained with iodine solution

  

Viewing animal tissue

Method

• Human cheek cells are a good choice for examination under the light microscope because they are:

  • plentiful

  • easy to obtain safely

  • can be obtained without an overly intrusive process

  • relatively unspecialised and so will display the main cell structures

• Cheek cells can be stained with methylene blue solution

• Extra safety precautions should be taken when using human tissue to ensure that:

  • the volunteer does not have a cold, cough, or throat infection that could infect someone else

  • all equipment is appropriately sterilised