Microscopes

Question 1

Define resolution

Answer 1

The ability of a microscope to distinguish details of a specimen- the minimum distance visible between two points

Question 2

What is the magnification equation?

Answer 2

Image= Actual size x Magnification

Question 3

Describe Cell Theory

Answer 3

1- Cells are the most basic unit of life
2- All living tissue is composed of cells
3- Cells can only come from previously existing cells

Question 4

State the three different microscopes

Answer 4

Scanning electron microscope
Transmission electron microscope
Light microscope

Question 5

How is resolution limited?

Answer 5

Resolution is limited by the diffraction of light as it passes through samples, as structures are very close and light rays can overlap, ao detail is lost.

Question 6

How is this image formed? Cross section, Black and white, resolved at 0.5nm.

Answer 6

Transmission electron microscope

Question 7

How is this image formed? 3D, black and white, resolved at 3-10nm

Answer 7

Scanning electron microscope

Question 8

Which microscope has the best resolution?

Answer 8

Transmission electron microscope

Question 9

To enter an electron microscope, specimens must be… ? Because…. ?

Answer 9

Specimens must be dead because the microscope is a vacuum.

Question 10

What is the fine structure of a cell called?

Answer 10

Ultrastructure

Question 11

Define an artefact in microscopy

Answer 11

An artefact is a visible structural detail caused by the process of preparing the specimen- ie not a viable detail of the specimen. EG- an air bubble in a slide, or mesosomes (folds in prokaryotic cell membranes)

Question 12

How do electron microscopes improve resolution?

Answer 12

By using electron beams which have shorter wavelengths than light.

Question 13

State and describe four different methods of sample preparation.

Answer 13

Dry mount- Solid specimens are cut thinly and placed on a zlide with a cover slip. Wet mount- Specimens are suspended jn a liquid and a cover slip is put down at an angle. Squash slides- a wet mount is prepared and squished together. Smear slides- the edge of a sterile slide smears the sample, creating a thin smear on another slide.

Question 14

What is differential staining used for?

Answer 14

To differentiate between types of organisms that would otherwise be hard to identify.

Question 15

Why is staining used in light microscopy?

Answer 15

To increase contrast between structures and help distinguish detail, as different components take up stain to different degrees.

Question 16

Give two examples of positively charged dyes and how they are used.

Answer 16

Crystal violet and methylene blue- attracted to negative cytosol and stain the cells.

Question 17

Give two examples of negatively charged dyes and how they are used.

Answer 17

Nigrosin and congo red- repelled by negative cytosol and stain the background.

Question 18

Describe the basic steps of the Gram Stain technique.

Answer 18

1- Crystal violet is applied to bacterial specimen. 2- iodine fixes dye. 3- Slide is washed with alchohol. 4- A counter stain (safranin) is applied.

Question 19

Why do Gram negative bacteria stay blue?

Answer 19

Because they have thick cell walls so they can retain the dye.

Question 20

Give two ways scanning electron microscope samples are prepared

Answer 20

1- fracturing
2- coated with heavy metals (eg gold)

Question 21

Name a few ways transmission electron microscope samples are prepared.

Answer 21

1- set in resin and restained.
2- freezing.
3- dehydration.

Question 22

Define magnification.

Answer 22

How many times larger an image size is compared to the actual size.

Question 23

Where is the objective lens of a light microscope?

Answer 23

Next to the specimen.

Question 24

What is the purpose of having two lenses in the light microscope?

Answer 24

Allows for a much higher magnification

Question 25

Define chromatic aberration.

Answer 25

Occurs when a lens cannot bring all wavelengths of light to a single converging point.