Required Practical 1 - Use of a light microscope

Question 1

METHOD: Preparing a slide (5)

Answer 1

• Add a drop of water in the middle of a slide.
(acts as an adhesive for the specimen)

• Cut up an onion and separate it into layers. Use tweezers to peel off epidermal tissue from one of the layers.
• Place the epidermal tissue into the water on the slide using tweezers.

• Add a drop of iodine solution to the onion layer.
(stains the specimen with colour so it is visible under the lens)

• Place a cover slip on top. Do this by first placing the edge of the cover slip down and lowering it to cover the specimen.
(placing edge-first helps prevent air bubbles, which obstruct view)

Question 2

Parts of a light microscope (6)

Answer 2

Eyepiece - where you look through

Coarse adjustment knob

Fine adjustment knob

Objective lens - changes magnification

Stage - raise and lower position of the slide

Light - under slide, lights it up so slide is visible

Question 3

METHOD: Using a light microscope (6)

Answer 3

• Clip the slide onto the stage.
• Select the lowest-powered objective lens (lowest magnification)
• Use the coarse adjustment knob to move the stage up to just below the objective lens
• Look down the eyepiece. Use the coarse adjustment knob to move the stage down until the image is roughly in focus.
• Adjust the focus with the fine adjustment knob until the stage is focused clearly.
• If the slide needs greater magnification, swap the objective lens and refocus.

Question 4

METHOD: Drawing observations (5)

Answer 4

• Draw your observation with a sharp pencil.
• Make sure the drawing is large and is drawn with clear, unbroken lines.
• Drawing should not include colouring or shading.
• All structures should be drawn in proportion.
• Title your observation and write down its magnification.
• Label the important features using straight, uncrossed lines.

Question 5

Things to do when drawing an observation

Answer 5

• Use unbroken, clear lines for the drawing
• Use straight, uncrossed lines for labels
• Title your observation
• Write down its magnification
• Draw everything in proportion
• Draw with a sharp pencil

Question 6

Things not to do when drawing an observation

Answer 6

• Sketch
• Shade
• Add colour
• Draw crossed lines for labels