Microscopy

Question 1

What is the cell theory?

Answer 1

That plant and animal tissues are made up of cells.
That cells are the basic units of all life.
That new cells are made from existing cells.

Question 2

What is the cell theory a good example of?

Answer 2

Of how scientific theories change overtime as knowledge increases.

Question 3

Name 4 ways of how slides are prepared for light microscopy.

Answer 3

Dry mount
Wet mount
Squash slides
Smear slides

Question 4

Why is staining used to prepare specimen and how is it useful?

Answer 4

To increase the contrast of the cell making structures visible. It is useful because then certain parts of the cell can be identified.

Question 5

What is the Gram stain technique used for?

Answer 5

To separate bacteria into 2 groups. Gram positive and Gram negative bacteria.

Question 6

What is meant by ‘fixing’ a specimen?

Answer 6

Preserving a specimen to near natural state by using chemicals.

Question 7

What is meant by ‘sectioning’ a specimen?

Answer 7

Dehydrating a specimen then making it into a hard block with wax. This can then be sliced thinly.

Question 8

What is meant by ‘mounting’ a specimen?

Answer 8

Securing a specimen to a slide and placing a cover slip on top.

Question 9

What does magnification mean?

Answer 9

How much bigger (whatever your viewing) is than the actual size/original object.

Question 10

What is resolution?

Answer 10

The ability to tell the difference between 2 points.

Question 11

What is resolution limited by?

Answer 11

Resolution is limited by the diffraction of light as it passes through the specimen. Light reflected off structures in a cell can overlap by diffraction.

Question 12

A higher resolving power means more _________ can be seen?

Answer 12

More detail can be seen therefore less diffraction occurs due to shorter wavelengths.

Question 13

Convert these to micrometers.

1) 10 mm
2) 5 m
3) 0.6 nm
4) 200 nm

Answer 13

All in micrometers

1) 10,000
2) 5000,000
3) 0.0006
4) 0.2

Question 14

Give some advantages of light microscopes.

Answer 14

Easily available
Relatively cheap
Able to observe living and dead organisms
Portable, can be used outside and inside.

Question 15

Give some disadvantages of light microscopes.

Answer 15

A low resolving power of 200nm means not much detail can be seen.
A low magnification of x1500

Question 16

Name the 2 types of electron microscopes.

Answer 16

Transmission electron microscope (TEM)

Scanning electron microscope (SEM)

Question 17

Describe how the TEM works.

Answer 17

A beam of electrons is transmitted through the specimen and focuses to produce an image. Black and white images are made.

Question 18

Describe how the SEM works.

Answer 18

A beam of electrons is scanned over the surface of the specimen and the reflected electrons are collected. 3D images of surface of cells are made.

Question 19

Specimen are inside a vacuum in an electron microscope. Why is this?

Answer 19

So that the electrons travel straight and aren’t deflected by air molecules.

Question 20

What is the maximum resolution of a:
transmission electron microscope?
scanning electron microscope?

Answer 20

0.5 nm

3-10 nm

Question 21

Give some disadvantages of electron microscopes.

Answer 21

Expensive.
Can only be used in safe, controlled areas.
Only dead organisms can be viewed.
The preparation of samples is time consuming and labour intensive.

Question 22

Give some advantages of electron microscopes.

Answer 22

Higher resolution means more detail can be seen.

3D images can be made with the SEM.

Question 23

Explain what artefacts are and give an example.

Answer 23

Visible detail in the cell caused by processing the specimen. It is not a feature of the specimen. e.g. Bubbles in the slides of light microscopes.

Question 24

How does a laser scanning microscope work?

Answer 24

LSM use a laser to scan over an object point by point. A computer then makes up the image as slices or as a whole 3D image.

Question 25

What is another name of a laser scanning microscope?

Answer 25

A confocal laser scanning microscope.

Question 26

Give some advantages of LSM.

Answer 26

Non invasive.
High resolution.
Can view the specimen in sections or as a whole.
Can see 3D or 2D images.

Question 26

Give some uses of the LSM.

Answer 26

Used to develop new drugs.

Used to diagnose eye diseases.

Question 27

How does the Atomic Force Microscope work?

Answer 27

The sharp tip of the probe scans the surface and interacts with the surface to cause deflections of the cantilever. The deflections are measured using a laser beam and a detector.

Question 28

Give some advantages of ATM.

Answer 28

3D images of surfaces produced.
Cells do not need preparing so they can be viewed in normal conditions.
High resolution of 0.1 nm.
Saves money and time by identifying new medicines.