B1.1.3 Light Microscopy

Question 1

Who was the first brudda (scientist) too see cells? When?

Answer 1

Robert Hooke, 350 years ago

Question 2

How does a light microscope work? (3)

Answer 2

The microscope passes light through an object placed on a slide on the stage
Then through two glass lenses - the objective lens and the eyepiece lens.
The lenses magnify the object, so when you view it through the eyepiece, you can see it in more detail.

Question 3

What are the first and second steps to observe cells through a microscope?

Answer 3

Move the stage to its lowest position

Select the objective lens with the lowest magnification.

Question 4

What are the third and fourth steps to observing a cell through a microscope?

Answer 4

Place the slide, which has cells on it, on the stage.
Raise the stage to its highest position, taking care that the slide does not touch the lens.

Question 5

What are the fifth and sixth steps to observing cells through a microscope

Answer 5

Lower the stage slowly using the coarse focus knob until you see your object. (blurred at this point)
Turn the fine focus knob until your object comes into clear focus.

Question 6

What are the last two steps to observing a cell through a microscope? (If you want higher clarity)

Answer 6

Switch to a higher magnification objective lens without moving the stage.
Use the fine focus knob to bring the object into clear focus again.

Question 7

Name the seven parts of a microscope:

Answer 7

Eyepiece lens
Objective lens
Coarse focus known
Fine focus knob
Slide
Stage
Light

Question 8

Why does a light microscope have two focusing knobs?

Answer 8

The coarse focus is to rapidly locate the approximate focus for an object as the fine focus is used to bring the object clearly into focus.

Question 9

Why might a scientist stain a cell?

Answer 9

Many cells are colourless so this could make them easier to observe

Question 10

What are the three common stains?

Answer 10

Methylene blue
Iodine
Crystal violet

Question 11

What is the function of methylene blue?

Answer 11

Makes it easier to see the nucleus of animal cells

Question 12

What is the function of crystal violet?

Answer 12

Stains bacterial cell walls

Question 13

What is the function of iodine?

Answer 13

Makes it easier to see the nuclei of plant cells

Question 14

What are the first and second steps to applying stain?

Answer 14

• Place the cells on a glass slide
• Add one drop of stain

Question 15

What are the last two steps to applying stain?

Answer 15

Place a coverslip on top
Tap the coverslip gently to remove air bubbles

Question 16

State which stain you would apply to cucumber cells before observing them under the microscope? Why?

Answer 16

Iodine as cucumber cells are plant cells and iodine stains plant cell nuclei.

Question 17

State the structures light passes through in a microscope from the object to the eyepiece:

Answer 17

Sample - objective lens - eyepiece lens

Question 18

What does resolution mean?

Answer 18

The ability to distinguish two points on the amount of detail

Question 19

What is magnification?

Answer 19

How many times bigger the image of a specimen observed is in compared to the actual size of the specimen.

Question 20

What are some advantages of using a light microscope instead of TEM?

Answer 20

• cheaper
• portable
• sample can be alive
• sample easy to prepare
• natural colours seen

Question 21

What is the smallest measurement you can see a structure with a light microscope?

Answer 21

0.2 micrometers (2x10^-7m)

Question 22

What do electron microscopes use instead of light?

Answer 22

Electrons

Question 23

What are the two types of electron microscopes?

Answer 23

Transmission electron microscopes
Scanning electron microscopes

Question 24

Compare TEM and SEM microscopes (2)

Answer 24

Advantage: TEM create the most magnified image
Disadvantage: SEM creates a 3D image of the specimen, whereas TEM only magnifies a certain area of the sample

Question 25

What are two advantages of light microscopes over an electron microscope?

Answer 25

• they’re cheaper, electron microscopes are far more expensive
• samples are easier to prepare for a light microscope

Question 26

Why did scientists not know what viruses looked like before the 1930s? (3)

Answer 26

Since they used light microscopes which only have a resolution up to 0.2um, viruses are far smaller than that.
The electron microscope was introduced in 1931, having a resolution of 0.1nm, allowing viruses to be seen

Question 27

Why can’t a light microscope be used to see inside a sub cellular structure?

Answer 27

Because it has too low a resolution

Question 28

How (simply) does a TEM work?

Answer 28

A beam of electrons is sent through a thin sample of the specimen then focused enough til an image is produced