Biology Practicals

Question 1

How do you calibrate a microscope?

Answer 1

1. Line up eye piece graticule and stage micrometre, whilst looking through the eyepiece.
2. Count how many divisions in the eyepiece graticule fit into one division on the micrometre scale.
3. Each division on the micrometre is with 10 micrometers, so we use this to calculate how much one division on the eyepiece graticule is worth.
4. Line eyepiece graticule up with specimen to measure how long it is.
   If you change magnification, you need to recalibrate the microscope.

Hence, if two EPG fits into 1 division on stage micrometre, and 1 stage micrometre division is work 10 micrometres, then : 2 EPG = 10 micrometres.
1 EPG = 5 micrometres

Question 2

What is a wet mount used for? How do you do a wet mount?

Answer 2

A wet mount is used for living specimens, like aquatic animals.
1. Use a pipette to put a droplet of water on the slide.
2. Use tweezers to place the specimen on the slide.
3. Use a pipette to add a droplet of appropriate stain on the slide.
4. Place the coverslip on the slide at an angle. Ensure no bubbles are trapped inside.

Question 3

What is a dry mount used for? How to prepare a dry mount?

Answer 3

A dry mount is used for specimens like hair, parts of insects, pollen and parts of flowers.
1. Slice the specimen so its thin enough that light can pass through.
2. Place the specimen on the slide.
3. Place the coverslip on top.