24 Questions
True or false: The human eye can resolve objects of the order of 0.2 μm (200 nm).
False
True or false: The transmission electron microscope can resolve objects on the order of 1nm.
True
True or false: A compound microscope has low resolution.
True
True or false: A dissecting microscope is used for dissection to get a better look at the larger specimen.
True
True or false: A scanning electron microscope (SEM) uses electron illumination.
True
True or false: A scanning electron microscope (SEM) has low resolution.
False
True or false: A scanning electron microscope (SEM) can resolve objects on the order of 1nm.
False
True or false: A compound microscope can view individual cells, even living ones.
True
True or false: A dissecting microscope can see individual cells.
False
True or false: A dissecting microscope is also called a stereo microscope.
True
True or false: A virus has a typical linear dimension of 10–100 μm.
False
True or false: A bacterium has a typical linear dimension of 0.5–5 μm.
True
Electron Microscope gives a 3-D view of the specimen.
False
Compound Microscope uses only one set of lenses for magnification.
False
The measure of how greatly a substance slows the velocity of light is called the refractive index.
True
The point at which light rays converge in a convex lens is called the focal point.
True
The distance between the center of the lens and the focal point is called the focal length.
True
A lens with a short focal length has a greater capacity for magnification than a lens with a longer focal length.
True
Bright-field Microscope forms a bright image against a dark background.
False
Total magnification in a compound microscope is calculated by adding the objective and eyepiece magnification together.
False
The resolution of a microscope is increased by using immersion oil to reduce the refraction of light rays.
True
Decreasing the wavelength of light used to illuminate the specimen increases the contrast in a microscope.
False
To increase the contrast in a microscope, direct staining of the microorganisms is not necessary.
False
It is acceptable to touch the lenses with your fingers when cleaning the microscope.
False
Study Notes
- Microscope: a device used to examine organisms that are too small to be seen with the naked eye
- Human eye can resolve objects up to 0.1 mm, while light microscope can resolve objects as small as 0.2 µm (200 nm), and transmission electron microscope can resolve objects as small as 0.1 nm
- Common sizes of objects: Animal cell (20-30 µm), red blood cell (7.6 µm), mitochondrion (2-5 µm), nucleus (10 µm), microvilli (1 µm), cell membrane (10 nm), microfilament (8-10 nm), bacterium (0.5-5 µm), and virus (10-100 nm)
Types of Microscopes:
- Compound Microscope:
- Light-illuminated
- Two-dimensional image
- High magnification
- Low resolution
- Components: lamp, body tube, condenser, stage, diaphragm, objective lenses, and ocular lens
- Principle: light rays are bent at the interface between media, converging at the focal point
- Dissecting Microscope:
- Light-illuminated
- Three-dimensional image
- Low magnification
- Used for dissecting larger specimens
- Scanning Electron Microscope (SEM):
- Electron-illuminated
- Three-dimensional image
- High magnification and resolution
- Specimen coated in gold
- Transmission Electron Microscope (TEM):
- Electron-illuminated
- Two-dimensional image
- Thin specimen slices
- High magnification and resolution
Microscope Functioning:
- Principle: lenses bend and focus light to form images
- Refraction: light rays are bent when passing from one medium to another
- Magnification: compound microscope uses two sets of lenses, with differing focal lengths, to achieve magnification
- Resolution: ability to observe two nearby objects as distinct
- Bright-field Microscope: forms a dark image against a brighter background, three factors determining quality: magnification, resolution, and contrast
- Contrast: ability to detect different regions based on intensity or color
- Microbes: composed of water, nucleic acids, proteins, and lipids, appear colorless, increase contrast through direct or indirect staining
- Microscope Care: handle with care, avoid touching lenses with fingers, use lens paper for cleaning, rotate nosepiece to low power objective, and roll stage down to lowest level.
By Ahmed Safaa Telegram channel : https://t.me/mcqb2
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