1.6: magnification core practical

Description

Description

Investigate biological specimens using microscopes, including magnification calculations and labelled scientific drawings from observations

Aims and objectives

Be competent in the use of a microscope at high and low power, including the use of a graticule (eyepiece micrometer) to make measurements, know how to record observations using appropriate biological drawings, understand the importance of staining specimens in microscopy

Safety measures

Skin contact with the stain should be avoided as some are harmful, wear gloves and eye protection when handling the stain, care must be taken when looking down the microscope that the illumination is not too bright as eye damage could be caused, care when handling coverslips and microscope slides as broken glass could cut skin.

Procedure

• Rotate the objectives so that the low power objective lens, eg ×10, is in line with the stage.

• Turn the coarse focus to adjust the space between the stage and the objective lens. Place the microscope slide on the stage.

• Line it up so that the specimen is in the centre of the stage, where the light passes through. Focus the slide by turning the coarse focus adjustment.

• Draw a low power image. Rotate the objectives so that the high power objective, eg ×40, is in line with the stage.

• Bring the slide back into focus using the fine focus adjustment. If you do not succeed, go back to low power and re-focus and start again..

Measuring cell size

1. Place a stage micrometer on the stage of the microscope.

2. Line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.

3. Count the number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer.

4. Calculate the distance in micrometres of one division on the eyepiece graticule.

A stage micrometer is a glass slide etched with an accurate scale on it. You will use this to calibrate the eyepiece graticule