The microscope in cell studies
Introduced| English | Meaning |
|---|---|
| microscope/ˈmaɪkrəskəʊp/ | An instrument used to magnify objects too small to see clearly with the unaided eye. |
| light microscope/laɪt ˈmaɪkrəskəʊp/ | An instrument that uses visible light and lenses to produce a magnified image of a specimen. |
| specimen/ˈspesɪmən/ | An individual organism, sample or prepared material selected for observation or study. |
| electron microscope/ɪˈlektrɒn ˈmaɪkrəskəʊp/ | An instrument that forms a highly magnified image using a beam of electrons. |
| magnification/ˌmæɡnɪfɪˈkeɪʃn/ | The ratio of an image's size to the corresponding actual size of the object. |
| resolution/ˌrezəˈluːʃn/ | The ability to distinguish fine detail or closely separated features. |
| stain/steɪn/ | A colouring substance used to increase contrast or identify particular structures in a specimen. |
Seeing the invisible
- Cells are far too small to see with your eyes — you need a microscope 显微镜.
- A light microscope 光学显微镜 shines light through a thin specimen 标本; an electron microscope 电子显微镜 sees far more detail.
- Two ideas you must keep separate: magnification 放大倍数 and resolution 分辨率.
Microscope decision lab
Choose the right microscopy idea from what the student wants to see.
Light and electron microscopes
- A light microscope shines light through a thin specimen on a slide (with a stain 染色剂 to show parts, and a cover slip on top).
- An electron microscope uses beams of electrons, which have a much shorter wavelength — so its resolution is far higher and it shows tiny structures.
- Two kinds: scanning (SEM, 3-D surface) and transmission (TEM, inside detail through a thin slice).
A light microscope shines light up through the stained specimen and lenses magnify the image
Why does an electron microscope have a much higher resolution than a light microscope?
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Shorter wavelength → higher resolution, so finer detail can be seen.
Match each feature to the right microscope.
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Light microscopes are simpler and can view living material; electron microscopes have far higher resolution but the specimen must be dead and in a vacuum.
Magnification and actual size
- The top and bottom must use the same unit. Cells are tiny: $1\ \text{mm} = 1000\ \mu\text{m}$, $1\ \mu\text{m} = 1000\ \text{nm}$.
- Worked: at $\times 5000$, a chloroplast measures $25\ \text{mm}$ → actual size $= 25 \div 5000 = 0.005\ \text{mm} = 5\ \mu\text{m}$.
Calibrating the eyepiece graticule against a stage micrometer
Which equation gives magnification?
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Magnification = size of image ÷ actual size (no units).
How many micrometres (µm) are in 1 mm?
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1 mm = 1000 µm (and 1 µm = 1000 nm).
At magnification ×5000, a structure measures 25 mm in the image. What is its actual size, in µm?
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25 mm ÷ 5000 = 0.005 mm = 5 µm.
Resolution vs magnification
- Magnification = how many times bigger the image is.
- Resolution = the smallest distance between two points that still lets you see them as two separate points.
- Making an image bigger does not always show more detail — past a point you just get a bigger blur. Resolution sets the real limit.
With low resolution two close points blur into one; higher resolution keeps them separate
Resolution is:
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Resolution is the detail limit; magnification alone cannot show detail finer than the resolution.
The smallest distance between two points that can still be seen as two separate points is the ______.
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Resolution is the real detail limit; magnifying beyond it just gives a bigger blur.
Magnifying an image more and more always reveals more and more detail.
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No — beyond the resolution limit you just get a bigger blur. Resolution, not magnification, sets the finest detail you can see.
You've got it
- light microscope (light, lower resolution) vs electron microscope (electrons, much higher resolution)
- $\text{magnification} = \dfrac{\text{image size}}{\text{actual size}}$ — same units top and bottom ($1\ \text{mm}=1000\ \mu\text{m}$)
- resolution = smallest distance to see two points apart — it sets the real detail limit
- magnifying more doesn't add detail beyond the resolution