Core Practicals

eduqas biology core practicals

How to calibrate a microscope

• each large section on an eyepiece graticule is 10 epu so each small line is 1

• each large section on a stage micrometer is 10 smu so each small line is 1. Each smu is 0.1 mm

• Line up the eyepiece graticule with the stage micrometer

• 1epu: smu = number of epu/ number of smu

• x that number by 0.1 and then x again by 1000 to find the image size in micrometers

Describe the core practical for the onion skin

• place two drops of water on a microscope slide

• using forceps peel off some onion membrane from the underside

• lay it flat on the side, making sure there are no fold

• add three drops on iodine 

• place the coverslip on carefully, with one side down first and gently lowering it to make sure there are no air bubbles, and using a papertowel to dry any excess of anything.

• go through the objective lenses, focusing on the cell

• draw at least three

What is the risk assessment for the onion cell practical?

What are the rules for doing a microscope drawing?

• 2-3 of the cells

• two lines for the cell wall (close together) and another for the cell membrane (further away)

• sharp pencil

• labels drawn with straight lines, touching the part of the cell and to the side

• draw everything you can see

• key, title and calculations