Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

2.1.1 Cell Structure > Microscopes > Flashcards

Microscopes Flashcards

1
Q

What is a microscope?

A

An instrument employing lenses to produce a magnified image and fine detail of objects too small to see with the naked eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is magnification?

A

How many times the size of an image is larger than the object itself (it is indicated by a number)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is resolution?

A

The degree to which it is possible to distinguish between two separate objects which are close to each other (it is indicated by a length)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the two categories of microscopes?

A

Optical and electron microscopes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the key points about the resolution of a optical microscope?

A
  • Resolution of an object/feature in a microscope is limited to half the wavelength of the wave employed
  • Optical microscopes can resolve objects up to 200nm or 0.2µm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the range of wavelengths used by optical microscopes?

A

450-600nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the limit of magnification of an optical microscope?

A

x1500-2000

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does an optical microscope work?

A
  • Objective lens produces a magnified image which is magnified again by the eyepiece lens => object is magnified twice
  • Light is shon through the specimen/object to be viewed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does an electron microscope work?

A
  • A beam of electrons with a wavelength of less than 1nm is used to illuminate the specimen/object
  • The lenses are magnets
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do electrons in electron microscopes produce an image?

A

Electrons produce an image when focused on a fluorescent screen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the limit of magnification and resolution in an electron microscope?

A
  • The limit of magnification is x500,000
  • The limit of resolution is 0.2nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are the two types of electron microscopes?

A
  • Transmission electron microscopes (TEM)
  • Scanning electron microscopes (SEM)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How does a TEM work?

A
  • Tissue/cell is inflitrated with plastic resin (=> very hard) and is cut into very thin slices using a diamon knife
  • A beam of electrons is passed through exceedingly thin slices of the specimen/material and produces an image on a flourescent screen or photographic film
  • This allows for the interior of the cells to be seen
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does a SEM work?

A
  • The specimen is shadowed with a layer of heavy metal and covered with carbon
  • It is scanned by a fine electron beam which is scattered from the surface of a specimen and the transmitted to a detector
  • This allows the surface of specimens to be seen
  • Except when freeze-fracture (the cell is frozen in liquid nitrogen at -70 degrees celcius) is being used where the inside of the cell is exposed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the range of magnification and resolution of a TEM?

A

Magnification: x500,000 - 2,000,000
Resolution: 0.2 - 0.5nm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the range of magnification and resolution of a SEM?

A

Magnification: x100,000 - 500,000
Resolution: 3 - 10nm

17
Q

What is the difference between a TEM and SEM?

A

TEM:
- Higher resolution than SEM
- Higher magnifcation than SEM
- Colour of image is black and white
- Can view interior of cells
- 2D image formed

SEM:
- Lower resolution than TEM
- Lower magnifcation than TEM
- Colour of image is black and white
- Can view exterior of cells (=> can only view interior through freeze fracturing)
- 3D image formed

18
Q

What are the advantages of a light microscope?

A
  • Small and portable
  • Natural colour of the material can be observed
  • Cheap to purchase
  • Material rarely disorted by preparation
  • Living material may be viewed
  • Preparation of material is relatively quick and simple, requires only a little expertise
  • Unaffected by magnetic fields
  • Doesn’t require a vacuum
  • Cheap to operate
19
Q

What are the disadvantages of a light microscope?

A
  • The depth of field is restricted
  • Magnifies objects up to 1500x
  • Can resolve objects 0.2µm apart
20
Q

What are the advantages of the electron microscope?

A
  • Possible to see a greater depth of field (SEM 3D image)
  • Magnifies objects up to 500,000x
  • Can resolve objects up to 0.001µm apart
21
Q

What are the disadvantages of the electron microscope?

A
  • Very large and must be operated in special rooms
  • All images in black and white
  • Expensive to purchase
  • Preparation of material may distort it
  • A high vacuum is required
  • Living material can’t be viewed
  • Preparation of material is length, requires a considerable expertise ad complex equipment
  • Affected by magnetic fields
  • Expensive to operate: requires up to 100,000V to produce an electron beam
  • Can produce artifacts
22
Q

What are the different ways that samples and specimens can be prepared?

A
  • Dry mount
  • Wet mount
  • Squash slides
  • Smear slides
23
Q

How is a dry mount prepared?

A
  • Solid specimens are viewed whole or cut into very thin slices with a sharp blade, this is called sectioning
  • The specimen is placed on the centre of the slide and a cover slip is placed over the sample
  • A cover slip is needed to keep the specimen flat and to maintain the same focal length throughout
24
Q

How is a wet mount prepared?

A
  • Specimen is placed on the slide
  • Drops of a stain/water is put on specimen
  • A cover slip is lowered at an angle using a mounted needle to minimise trapping air bubbles
25
Q

How is a smear slide prepared?

A
  • A spreader slide is pulled backwards across another slide and used to smear the sample
  • The spreader slide is pushed forwards in one smooth motion with constant downward pressure
  • This creates a thin, even coating on the slide
  • A cover slip is placed over the sample
26
Q

How is a squash slide prepared?

A
  • A wet mount is first prepared, then a lens tissue is used to gently press down the cover slip
  • Depending on the material, potential damage to a cover slip can be avoided by squashing the sample between two microscope slides
27
Q

What are the stages of preparing a permanent slide?

A

Fixing: chemicals like formaldehyde are used to preserve specimens in as near-natural a state as possible with minimum distortion

Dehydration: specimens are dehydrated (water I removed) with alcohols (to kill bacteria and prevent any from growing)

Clearing: removing the dehydration alcohol to leave specimen transparent

Embedding: placing it in a mould with wax or resin to form a hard block

Sectioning: using a microtome to produce thin slices to form a block

Staining: treating the thin slices with chemical agents (stain) to “dye” different structures different colours

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

28
Q

What are the advantages of staining?

A
  • Provides contrast between components of cells e.g. organelles
  • Provides contrast between a structure (e.g. cell) and its background
  • Allows different components (e.g. organelles) of cells to be identified
29
Q

Why does a stain give a different colour with different cellular structures?

A

Cellular structures are composed of different molecules which interact differently with the specific stain molecules e.g. a positively charged stain will interact with a negatively charged molecule such as DNA

30
Q

What is differential staining?

A
  • This is staining that uses more than one chemical stain
  • This makes differences between cells or between different structures within cells more visible
31
Q

What is the gram stain technique used for?

A

It is used to separate bacteria into two groups, Gram-positive bacteria and Gram-negative bacteria

32
Q

What are the steps of the Gram stain technique?

A
  • Crystal violet is first applied to a bacterial specimen on a slide
  • Iodine is added to fix the dye
  • The slide is then washed with alcohol
  • Gram-positive bacteria retains the crystal violet stain and will appear blue or purple under a microscope
  • Gram-negative bacteria have a thinner cell wall and so therefore lose the stain
  • Gram-negative bacteria is then stained with Safranin dye which is called a counter stain
  • These bacteria will appear red
33
Q

What is an artificat?

A

A visible structural detail that is due to the processing of the specimen and not a natural feature of the specimen

2.1.1 Cell Structure (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions