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Methods Of Studying Cells Flashcards

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1
Q

What type of lens can act as a basic magnifying glass?

A

A simple convex glass lens can act as a magnifying glass.

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2
Q

Why are compound light microscopes better than a single lens?

A

Magnification is improved using compound light microscopes, which consist of two or more lenses.

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3
Q

What do light microscopes use to form an image?

A

Light microscopes use light rays to form an image.

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4
Q

What limits the resolution of a light microscope?

A

The relatively long wavelength of light limits the resolution

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5
Q

What is the resolution limit of a light microscope?

A

A light microscope can only distinguish between two points if they are ≥ 0.2 um apart (200 nm).

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6
Q

What are light microscopes suitable for viewing?

A

Light microscopes are suitable for viewing whole cells, tissues, or large organelles like nuclei and chloroplasts.

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7
Q

What do electron microscopes use instead of light?

A

Electron microscopes use beams of electrons rather than light.

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8
Q

Why do electron microscopes provide a much higher resolution?

A

Electrons have a shorter wavelength, resulting in a much higher resolution.

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9
Q

What is the resolution limit of an electron microscope?

A

An electron microscope can distinguish between two points ≥ 0.1 nm apart.

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10
Q

What can electron microscopes be used to observe?

A

Electron microscopes allow for visualization of smaller organelles such as ribosomes, membranes, and internal structures of organelles.

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11
Q

State the general formula for magnification.

A

Magnification= size of image/ size of real object

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12
Q

Rearrange the magnification formula to calculate the size of a real object.

A

Size of real object= size of image /magnification

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13
Q

What must you ensure when calculating magnification?

A

You must ensure that the units of length are the same for both the object and the image. Convert units before calculating.

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14
Q

Complete the table below with the correct SI prefixes and standard form:

A

kilometre (km) 10^3 m
metre (m) 1m
millimetre (mm) 10^{-3} m
micrometre (µm) 10^{-6} m
nanometre (nm) 10^{-9} m

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15
Q

What determines the resolving power of a microscope?

A

The resolving power depends on the wavelength or form of radiation used.

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16
Q

Explain why increasing magnification does not always increase resolution.

A

Every microscope has a limit of resolution. Beyond this point, increasing magnification only makes the image bigger but more blurred; without revealing more detail.

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17
Q

Why is cell fractionation used in cell biology?

A

To obtain large numbers of isolated organelles in order to study their structure and function.

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18
Q

Describe the properties of the solution in which tissue is placed before fractionation.

A

The solution must be:
• Cold - to reduce enzyme activity,
• Buffered - to maintain pH changes,
• Isotonic (same water potential) - to prevent organelles from bursting or shrinking.

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19
Q

Describe what happens during the homogenisation stage of cell fractionation.

A

During the homogenisation stage the Cells are broken using a homogeniser to release organelles. The resulting fluid, called homogenate, is filtered to remove large debris and whole cells.

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20
Q

What is ultracentrifugation, and why is it used?

A

Ultracentrifugation separates organelles by spinning homogenate at high speeds to create a centrifugal force, sedimenting organelles by mass.

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21
Q

Outline the steps of ultracentrifugation in animal cells.

A
  1. Spin homogenate at low speed to retrieve nuclei sediment.
  2. Remove supernatant, spin faster to retrieve mitochondria sediment.
  3. Remove supernatant Repeat at higher speed to retrieve lysosomes sediment.
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22
Q

At what speeds are nuclei, mitochondria, and lysosomes separated?

A

Nuclei: 1,000 x gravity
• Mitochondria: 3,500 x gravity
• Lysosomes: 16,500 x gravity

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23
Q

What are the two main advantages of electron microscopes over light microscopes?

A

Electron microscopes are better than light microscopes because They use electron beams with very short wavelengths so have high resolution and magnification

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24
Q

Why must a vacuum be used in an electron microscope?

A

A vacuum is required in an electron microscope because electrons can be scattered or absorbed by air molecules. Removing air creates a vacuum that allows the electron beam to travel in a straight line without interference

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25
How does a TEM work?
A beam of electrons is transmitted through a thin specimen. Areas that absorb electrons appear dark; areas that let electrons pass appear light.
26
What is the resolving power of a TEM? Why is it not always achieved?
TEM has a resolution of 0.1 nm, but it may not be reached due to specimen preparation difficulties and possible damage from high-energy electron beams.
27
List four limitations of the TEM.
Requires a vacuum so living specimens cannot be used. Requires complex staining so image is not in colour. Specimen must be very thin. May produce artefacts that aren't part of the natural specimen.
28
Why does the TEM produce 2D images?
TEM produces 2D images because the electron beam passes through thin sections of the specimen.
29
How can a 3D image be formed using TEM?
A 3D image can be achieved using TEM By taking multiple sections of the specimen and building a 3D image from a series of photomicrographs. However this is time-consuming and complex.
30
How does the SEM differ from the TEM in how it works?
SEM directs a beam of electrons across the surface of a specimen from above, rather than through it.
31
How is a 3D image formed using SEM?
Electrons are scattered based on the surface contours and a computer processes the pattern of scattered and secondary electrons to produce a 3D image.
32
What is the resolution of an SEM?
SEM has a resolution of 20 mm-lower than TEM but about 10 times better than a light microscope.
33
What is one key advantage of SEM over TEM?
SEM does not require specimens to be extremely thin.
34
Do TEM and SEM share any limitations?
Yes, both require a vacuum and complex preparation, and they cannot view living specimens.
35
What is an eyepiece graticule?
Eyepiece graticule is A glass disc with a scale placed in the eyepiece of a microscope used to measure cell size.
36
Why must the eyepiece graticule be calibrated for each objective lens?
Because each lens magnifies differently, the scale must be calibrated for accurate measurement.
37
What is a stage micrometer used for?
A stage micrometer is a microscope slide with a known scale, used to calibrate the eyepiece graticule.
38
In a calibration where 10 micrometer units = 40 graticule units, and each micrometer unit = 10 um, what is one graticule unit equal to?
Total length of 10 micrometer 1.units- 10units x 10um = 100um 2. 100um/40=2.5um per graticule unit
39
If an objective lens of ×40 gives a calibration of 25 um/graticule unit, what would be the value under a ×400 lens?
25um= 40 40 x 10 =400 25/10=2.5um You are seeing 1/10 of the specimen because you zoomed in thats why you divide
40
Rearrange the magnification formula to calculate image size.
Image size = magnification x actual size
41
What does increasing magnification do to image detail?
Magnification increases the size of the image, not the level of detail.
42
Define resolution in the context of microscopy.
Resolution is the ability to distinguish between two points that are close together.
43
What does higher resolution mean in a microscope?
A microscope with higher resolution shows more detail.
44
What happens if two points are closer than the resolution limit of a microscope?
If two points are closer than the resolution limit, they will appear as one point.
45
What do optical microscopes use to form an image?
Optical microscopes use light to form an image.
46
Name three organelles that cannot be seen with an optical microscope.
Ribosomes, endoplasmic reticulum, and lysosomes.
47
Name four structures that can be seen with an optical microscope.
Nucleus, cell membrane, cytoplasm, and mitochondria (not in detail).
48
What is the maximum useful magnification of an optical microscope?
Approximately ×1500.
49
What do electron microscopes use to form an image?
Electron microscopes use They use beams of electrons instead of light.
50
How does the resolution of an electron microscope compare to an optical microscope?
The resolution of electron microscope is 1000x better than a optical microscope.
51
How does a TEM form an image?
It uses electromagnets to focus a beam of electrons, which passes through a thin specimen.
52
Why do some areas of a TEM image appear darker?
Denser areas absorb more electrons and appear darker.
53
What kind of image does a TEM produce?
A 2D image
54
What is the main advantage of a TEM?
It has very high resolution, allowing internal structures like chloroplast membranes to be seen in detail.
55
Give three limitations of a TEM.
1. Must be used on very thin specimens. 2. Only works in a vacuum - living specimens can't be viewed. 3. Involves complex preparation, which may produce artefacts.
56
How does an SEM form an image?
It scans a beam of electrons across the surface of the specimen, knocking off electrons that are collected to form an image.
57
What kind of structures does an SEM image show?
The external structure (surface) of the specimen.
58
What kind of image does an SEM produce?
A 3D structure
59
Give two advantages of an SEM.
1. Can be used on thick specimens. 2. Produces detailed surface images.
60
Give two limitations of an SEM.
1.Lower resolution than TEM. 2. Requires a vacuum, so live specimens cannot be viewed.
61
Why should the specimen be thin when preparing a slide?
So that light can pass through it, allowing clearer viewing.
62
Name two stains and what they are used for.
Eosin: stains cytoplasm. lodine in potassium iodide solution: stains starch grains in plant cells.
63
Why should air bubbles be avoided under the cover slip?
Air bubbles must be avoided because it can obscure the view of the specimen.
64
What is the purpose of cell fractionation?
The purpose of cell fractionation is to isolate organelles from cells to study them, for example under an electron microscope.
65
What is the role of a buffer solution in sample preparation?
A buffer solution maintains a constant pH, preventing damage to proteins and enzymes.
66
How are cells broken open in homogenisation, and what does this release?
Cells are broken open by grinding (e.g., using a blender) or vibrating them, which breaks the plasma membrane and releases the organelles into the solution.
67
What is the purpose of filtering the homogenised solution?
Filtration removes large debris, such as connective tissue, while allowing smaller organelles to pass through the gauze.
68
How does ultracentrifugation separate organelles?
Ultracentrifugation separates organelles by spinning the solution at increasing speeds; heavier organelles pellet first, and lighter ones remain in the supernatant.
69
Which organelle forms the pellet at the lowest centrifuge speed?
The nucleus forms the pellet first because it is the heaviest organelle.
70
What is the correct order of organelle separation from heaviest to lightest?
Model Answer: 1. Nuclei 2. Chloroplasts (in plant cells) 3. Mitochondria 4. Lysosomes 5. Endoplasmic Reticulum 6. Ribosomes
71
What is the correct order of steps for preparing a wet mount slide?
1. Pipette a drop of water onto a slide. 2. Use forceps to place a thin specimen. 3. Add a stain (e.g. iodine or eosin). 4. Carefully place a cover slip at an angle to avoid air bubbles.
72
Name and describe one alternative slide preparation method.
A squash slide involves gently pressing the sample to flatten the cells.
73
What are artefacts in microscopy, and what causes them?
Artefacts are objects not part of the sample, like air bubbles or dust, caused by slide preparation or microscope technique.
74
List three requirements for a proper biological drawing.
A biological drawing must have: • Clear, smooth lines • Accurate proportions • Straight label lines with no arrowheads
75
What should be avoided in biological drawings?
Shading, colour, and crossed label lines should be avoided.

Cell (13 decks)

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