Light microscopy: observing and identifying microorganisms | Biology

Starter quiz

What do we call a series of questions used to help identify organisms?

puzzle

key ✓

quiz

riddle

choice
Which part of the microscope is labelled E?

the objective lens

the stage ✓

the light source

the course focus wheel
True or false? Bacteria are multicellular prokaryotes.

True

False ✓
Which type of drug is a doctor likely to prescribe to a patient with a bacterial infection?

'Antibiotics' ✓
Which part of the microscope would you use to bring your specimen into focus?

A

B

C

D ✓
Put these steps in order to explain how to make a temporary mount of onion tissue.

1

⇔

Cut a thin slice of onion.

2

⇔

Place the slice of onion on the glass slide.

3

⇔

Add a drop of iodine stain.

4

⇔

Place a cover slip over the onion.

Exit quiz

Match the part of the microscope to its description.

a

⇔

Eyepiece lens: viewing lens with ×10 magnification. ✓

b

⇔

Objective lenses: three lenses with different magnifications. ✓

c

⇔

Stage: specimen or slide is placed here. ✓

d

⇔

Light source: illuminates the specimen so that it can be observed. ✓

e

⇔

Coarse focus wheel: for adjusting the focus in larger increments. ✓

f

⇔

Fine focus wheel: for adjusting the focus in smaller increments. ✓
Put these steps in order to explain how a light microscope is set up.

1

⇔

Turn the objective lenses (b) to the lens with the lowest magnification.

2

⇔

Place the slide on the stage (c) under the clips.

3

⇔

Turn on the light source (d).

4

⇔

Looking from the side, turn the coarse focus wheel (e) to move the stage up.

5

⇔

Turn the coarse focus wheel (e) to move the stage away from the lens and focus.

6

⇔

Turn the fine focus wheel (f) to make the image as sharp and clear as possible.
How can you increase the magnification of a light microscope?

increase the power of the objective lens ✓

decrease the power of the objective lens

increase the power of the light source

move the stage closer to the lens
What can we use to make living material easier to see under a microscope?

'stains' ✓
We can use a ______ to identify types of bacteria.

'key' ✓
The image below shows bacteria growing on an agar plate containing penicillin. Penicillin works best on gram-positive bacteria. What can we conclude about the bacteria growing on the plate?

They are killed by penicillin.

They are not killed by penicillin. ✓

They are most likely gram-positive bacteria.

They are most likely gram-negative bacteria. ✓

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Lesson Details

Key learning points

A light microscope can be used to observe microorganisms.
Observations from a light microscope can be used to identify microorganisms, including pathogens causing a disease.
The observed shape of a microorganism can help to identify it.
Use of a key and stains can help to identify a microorganism.
Growing microorganisms in specific conditions can also help to identify them.

Common misconception

Students often use the term "zoom in" instead of focus.

You must correct the term "zoom in" to focus. You are not making the image larger, you are focussing to make the image clearer.

Keywords

Microorganism - A living thing that is too small to see with the unaided eye.
Light microscope - A type of microscope that uses visible light and a system of lenses to generate magnified images of small objects.
Pathogen - A microorganism that causes disease.
Key - A series of questions about the features of an organism that help us to identify it.
Stain - A coloured liquid put onto a specimen so that the cells and their structures can be more easily seen with a light microscope.