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Microscopy and Cell Structure
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Microscopy and Cell Structure
Microscopy and Cell Structure
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1
Question
Why do light microscopes have relatively poor resolution?
1:00
Answer
Resolution is limited by the wavelength of the light used to create the image.
2
Question
Which specimen features can light microscopes preserve in an image?
1:11
Answer
They can image living specimens and produce colour images.
3
Question
How does a transmission electron microscope form an image?
1:23
Answer
Electrons pass through a very thin specimen; differences in electron absorption produce contrast in the image.
4
Question
How does a scanning electron microscope form a three-dimensional image?
12:46
Answer
Electrons interact with the specimen’s surface and scatter or reflect according to its contours, producing a 3D surface image.
5
Question
How does laser scanning confocal microscopy produce depth information?
13:49
Answer
A focused laser scans the specimen point by point, allowing images from different focal planes to be combined into a 3D view.
6
Question
Which microscopy method is suited to imaging internal cell structures in two dimensions?
12:09
Answer
Transmission electron microscopy (TEM), because electrons pass through a very thin specimen.
7
Question
Which microscopy method is suited to viewing three-dimensional specimen surfaces?
12:50
Answer
Scanning electron microscopy (SEM), which images the specimen’s surface contours.
8
Question
How is resolution defined for microscopy?
2:00
Answer
It is the minimum distance between two objects at which they can still be seen as separate.
9
Question
Which wavelength determines resolution in light and electron microscopes?
2:08
Answer
Light microscopes depend on the wavelength of light; electron microscopes depend on the wavelength of electrons.
10
Question
How does magnification relate an image to its actual object?
2:20
Answer
Magnification is how many times larger the image is than the actual object.
11
Question
How does a dry-mount slide prepare a specimen for viewing?
2:37
Answer
A thin slice or whole specimen is placed on a glass slide and covered with a coverslip, without adding water.
12
Question
When is a wet-mount slide useful for observing living specimens?
2:59
Answer
It is used for living aquatic organisms, with the specimen placed in water beneath a coverslip.
13
Question
Why is a mounted needle used when lowering a coverslip onto a wet mount?
3:08
Answer
It helps prevent air bubbles from forming beneath the coverslip.
14
Question
How does a squash slide make cells easier to examine?
3:23
Answer
Pressure on the coverslip spreads the wet specimen into a thin layer so light can pass through it.
15
Question
Which structures can be visualized in an onion or garlic root-tip squash?
3:36
Answer
Chromosomes can be visualized after the thin root-tip sample is stained and squashed.
16
Question
How is a smear slide prepared for examining a blood sample?
3:53
Answer
A drop is placed at one end of a slide, spread across it using the angled edge of another slide, and covered with a coverslip.
17
Question
What does an eyepiece graticule measure during microscopic observation?
4:14
Answer
It provides a scale in the eyepiece for measuring the size of the observed object.
18
Question
Why must an eyepiece graticule be calibrated for each magnification?
4:37
Answer
The value represented by each graticule division changes with microscope magnification.
19
Question
How is a stage micrometer used to calibrate an eyepiece graticule?
5:09
Answer
Align the stage micrometer scale with the graticule, count matching divisions, and use the known stage-micrometer value to calculate the value of one graticule division.
20
Question
If two eyepiece-graticule divisions match one stage-micrometer division worth 10 µm, what is one graticule division worth?
5:51
Answer
5 µm.
21
Question
Which equation calculates microscope magnification?
6:50
Answer
Magnification = image size ÷ actual object size.
22
Question
How should millimetres be converted to micrometres in a magnification calculation?
7:19
Answer
Multiply the millimetre measurement by 1,000 to convert it to micrometres.
23
Question
Why are stains added when some cell structures are difficult to see?
7:35
Answer
Stains increase visual contrast by making structures more distinctly coloured.
24
Question
How does differential staining distinguish different cell components?
7:47
Answer
It uses multiple chemical stains to colour different parts of a cell differently.
25
Question
Why do crystal violet and methylene blue bind to negatively charged cell components?
8:00
Answer
They are positively charged stains and are attracted to negatively charged components.
26
Question
How do nigrosin and Congo red create contrast around cells?
8:17
Answer
These negatively charged stains are repelled from cells, producing a stained background that makes unstained cells stand out.
27
Question
Which features should a scientific biological drawing communicate?
9:47
Answer
It should show the specimen’s size, location, proportion, and structural details.
28
Question
How should lines and shading be handled in a scientific drawing?
9:28
Answer
Use solid, clean lines that touch without overlapping. Do not sketch, colour, or shade.
29
Question
Which information should accompany a scientific drawing of a specimen?
8:54
Answer
A title identifying the specimen and the magnification or scale should be included, with key visible features labelled or annotated.
30
Question
How should label lines be drawn in a scientific diagram?
9:38
Answer
Draw horizontal label lines with a pencil and ruler, without arrowheads.