2.1, 2.2, 2.3 Sample Preparation, Key Terms

Question 1

What term should you use instead of “clarity” when discussing microscopy?

Answer 1

“Distinction” and “resolution”

Question 2

What is a dry mount?

Answer 2

-Specimens are viewed whole or cut into thin slices with a sharp blade (sectioning).
-Specimen is placed on the slide and a cover slip is placed over the sample.

Question 3

Give examples of things that can be observed using a dry mount.

Answer 3

Hair, pollen, insect parts, muscle tissue, plants.

Question 4

What is the name of the mount/slide whereby solid specimens are viewed whole or cut into thin slices?

Answer 4

Dry mount.

Question 5

What is a wet mount?

Answer 5

-Specimens are suspended in a liquid such as water or an immersion oil.
-Cover slip is placed on at an angle

Question 6

In a wet mount, why is the cover slip placed on at an angle?

Answer 6

To reduce air bubbles and artefacts.

Question 7

What is the name of the slide/mount whereby specimens are suspended in a liquid?

Answer 7

Wet mount.

Question 8

Give examples of specimens that can be viewed using a wet mount.

Answer 8

Aquatic samples, living organisms

Question 9

What is a squash slide?

Answer 9

A wet mount is first prepared, then cover slip is applied and pressed down gently

Question 10

What can squash slides be used for?

Answer 10

Soft samples, for example root tips can be squashed to look at cell division.

Question 11

What is a smear slide?

Answer 11

-The edge of a slide is used to smear the sample to create a thin even coating on another slide
-A cover slip is then placed over the sample

Question 12

What can smear slides be used for?

Answer 12

Samples of blood, to see all the cells.

Question 13

What are the benefits of wet mounts?

Answer 13

• Can allow you to observe behaviour and natural colour of animals
• Greater resolution and magnification

Question 14

What are the problems with wet mounts?

Answer 14

-Greater chance of artefacts being produced (eg air bubbles)
-Slides tend to dry out under the light of the microscope.

Question 15

What are the benefits of dry mounts?

Answer 15

It is easy to prepare slides

Question 16

What are the problems with dry mounts?

Answer 16

-Mounts are temporary unless you seal them
-It is harder to see more intricate structures.

Question 17

Why do specimens need to be thin for sample preparation?

Answer 17

So that light can pass through it and form an image

Question 18

What is an artefact?

Answer 18

Something observed in a scientific investigation that is not naturally present but occurs as a result of the investigative procedure.

Question 19

Why do we stain samples in microscopy?

Answer 19

-Stains increase the contrast of specimens because the different components in the cells absorb the stains to different degrees.
-The increase in contrast allows components to become visible so they can be identified.

Question 20

Why is it difficult to see specimens under a microscope without staining them first?

Answer 20

-Because cells do not absorb much light
-The cytosol (aqueous interior) of cells, and other cell structures, are often transparent.

Question 21

What is differential staining?

Answer 21

Using specific stains to distinguish different types of cell

Question 22

Describe the process of FIXING in microscopy.

Answer 22

Formaldehyde is used to preserve the specimen

Question 23

Describe the process of SECTIONING in microscopy.

Answer 23

Specimens are dehydrated and placed in a wax mould, then thinly sliced with a microtome.

Question 24

Describe the process of STAINING in microscopy.

Answer 24

Specimens are often treated with multiple stains to show different structures

Question 25

Describe the process of MOUNTING in microscopy.

Answer 25

The specimens are secured to a microscopy slide and a cover slip is placed on top.

Question 26

Explain the process of the NEGATIVE STAIN TECHNIQUE.

Answer 26

Negatively charged dyes are repelled by the negatively charged cytosol so they stay outside of the cell, making the unstained cells stand out against the stained background.

Question 27

Explain the process of the POSITIVE STAIN TECHNIQUE.

Answer 27

Positively charged dyes are attracted to the negatively charged materials in the cytoplasm (eg cytosol), which leads to the staining of the cell components.

Question 28

What is Gram stain technique?

Answer 28

Used to separate bacteria into Gram-positive and Gram-negative categories.

Question 29

Describe the process of the Gram stain technique

Answer 29

-Crystal violet dye is first applied to a bacteria specimen on a slide, then iodine (which fixes the dye), -The slide is then washed with alcohol -If the bacteria retain the stan and appear blue or purple, they are Gram-positive -If not, they are then stained with safranin, making them appear red.

Question 30

What do we use to stain starch?

Answer 30

Iodine.

Question 31

Define "Magnification"

Answer 31

The number of times larger an image is compared to the real size of an object

Question 32

Define "Resolution"

Answer 32

The minimum distance between 2 objects where they can still be seen as 2 separate objects

Question 33

Define "Empty Magnification"

Answer 33

When you magnify an image to make it larger, but it does not appear more defined