2.1- 2.3 Microscopy

Question 1

What is a microscope?

Answer 1

an instrument which enabes you to magnify an object hundreds, thousands and even hundreds of thousands of times

Question 2

The first type of microscopes to be developed were?

Answer 2

light microscopes

Question 3

When was light microscopes developed?

Answer 3

16th to 17th century

Question 4

What does cell theory state?

Answer 4

1) both plant and animal tissue is composed of cells
2) cells are the basic unit of all life
3) cells only develop from existing cells

Question 5

Advantages of light microscopes?

Answer 5

• easily available, relatively cheap
• used out in the field
• observe living organisms as well as dead, prepared speciments

Question 6

a compound light microscope has two lenses. What are they

Answer 6

objective lens, placed near to specimen and eyepiece lens, through which the specimen is viewed

Question 7

what do the objective and eyepiece lens do?

Answer 7

objective lens- produces a magnified image

eyepiece lens- magnifies it again by eyepiece lens

Question 8

what does this objective/ eyepiece lens configuration allow?

Answer 8

allows for much higher magnification and reduced chromatic aberration than that in a simple light microscope

Question 9

Illumination is provided where?

Answer 9

light underneath the sample

Question 10

How may opaque specimens be illuminated

Answer 10

can be illuminated from above with some microscopes

Question 11

What is the dry mount method of sample preparation

Answer 11

• sectioning (solid specimens are viewed whole/ cut into very think slices with a sharp blade)
• speciment placed on the centre of the slide and a cover slip is placed over sample
  e. g. hair, polen and insect parts. Muscle tissue or plants can be sectioned and viewed in this way.

Question 12

what is the squash slides method of sample preparation

Answer 12

-good technique for soft samples
-wet mount first prepared
-lens tissue is used to gently press down cover slip
-depends on material, potential damage to a cover strip can be avoided by squashing the sample between two microscope slides
-

Question 13

what is the smear slides method of sample preparation

Answer 13

-edge of a slide is used to smear the sample, creating a thin, even coating on another slide.

Question 14

what is the wet mount sample preparation

Answer 14

• specimens suspended in a liquid such as water or an immersion oil
• cover slip placed on from an angle

Question 15

what needs to be cared for in squash slides

Answer 15

cover slip is not broken when being pressed

Question 16

what is an example of a smear slide?

Answer 16

sample of blood, good way to view the cells in the blood

Question 17

wet mount method can be used for what method?

Answer 17

aquatic samples and other living organisms

Question 18

what is necessary in scientific drawings

Answer 18

• a title
• magnification
• sharp pencil for drawings and labels
• white unlined paper
• use as much of paper as possible
• smooth continuous lines
• do not shade
• draw clearly defined structures
• ensure proportions are correct
• label lines should not cross and no arrow heads
• label lines should be parallel to the top of page and drawn with a ruler

Question 19

What can differential staining do?

Answer 19

• distinguish between two types of organisms that would otherwise be hard to identify
• can also differentiate between different organelles of a single organism with a tissue sample

Question 20

What is the Gram stain technique used for?

Answer 20

To separate bacteria into two groups, Gram-positive bacteria and Gram-negative bacteria

Question 21

How is the gram stain method carried out?

Answer 21

Crystal violet is first applied to a bacterial specimen on a slide, then iodine, which fixes the dye. Slide is washed with alcohol

Question 22

How do we tell which one in gram-negative bacteria and one is gram-positive bacteria?

Answer 22

Gram Stain technique- Gram positive bacteria retain the CRYSTAL VIOLET STAIN and will appear blue or purple under a microscope
Gram negative bacteria- thinner walls, and therefore LOSE THE STAIN

Question 23

What happes after the gram-negative bacteria is identified by the gram stain technique?

Answer 23

They are then stained with safranin dye, which is called a counterstain. Bacteria will appear red

Question 24

Gram-positive bacteria are susceptible to what?

Answer 24

antibiotic penicillion, which inhibits the formation of cell walls

Question 25

Why is gram-negative bacteria have not susceptible to penicillin?

Answer 25

• has much thinner cell walls

- penicillin inhibits the formation of cell walls

Question 26

What is the acid-fast technique used for?

Answer 26

to differenciate species of Mycobacterium from other bacteria

Question 27

How is the acid fast technique carried out?

Answer 27

a lipid solvent is used to carry carbolfuchsin dye into the cells being studied
-cells are then washed with a dilute acid- alcohol solution

Question 28

How can we tell which one is a mycrobacterium or other bacteria

Answer 28

mycrobacterium- not affected by the acid-alcohol and retain the carbolfuchsin, which is bright red
other bacteria- lose the stain, and are exposed to a methylene blue stain, which is blue

Question 29

What do stains do?

Answer 29

Increase contrast as different components within a cell take upp stains to different degrees

Question 30

The increase in contrast allows?

Answer 30

components to become visible so they can be identified

Question 31

How do we prepare a sample for staining?

Answer 31

it is first placed on a slide and allowed to air dry

• then heat-fixed by passing through a flame
• specimen will adhere to the microscope side and will then take up stains

Question 32

Images of light microscope tends to have low contrast why?

Answer 32

-most cells do not absorb a lot of light -resolution is limited by the wavelength of light and diffraction of light as it passes through the sample

Question 33

The cytosol (aqueous interior) of cells and other cell structures are often transparent

Answer 33

Stains increase contrast

Question 34

What are the stages involved in the production of tgese slides that have been pre-prepared

Answer 34

1. Fixing
2. Sectioning
3. Staining
4. Mounting

Question 35

Describe the FIXING in the production of these slides

Answer 35

chemicals like formaldehyde are used to PRESERVE SPECIMENS in as near -natural a state as possible

Question 36

Describe the SECTIONING in the production of these slides

Answer 36

specimens are dehydrated with alcohols and then placed in mould with wax or resin to form a hard block
-this can then be sliced thinly with a knife called a microtome

Question 37

Describe the STAINING in the production of these slides

Answer 37

specimens are often treated with multiple stains to show different structures

Question 38

Describe the MOUNTING in the production of these slides

Answer 38

specimens are then secured to a microscope slide and a cover slip placed on top

Question 39

Many of the stains used in the preparation of slides are toxic or irritants, then what must be carried out?

Answer 39

a risk assesment before any practical, identifies any procedures involved that may result in harm

Question 40

What does CLEAPSS do?

Answer 40

provide student safety sheets that identify specific risks, advice on the measures to be taken to reduce these risks and the action to be taken in emergency

Question 41

in schools, many of the microscopy slides that are used are bought in ready prepared and pre-stained. Why?

Answer 41

Not only because of the harmful nature of the stains but also because of the long complex process needed to produce high quality sections