The transmission electron microscope

The TEM is used to study the details of the internal structure of cells. Extremely thin samples of the specimen are needed. To make these the specimen is supported in a resin block to prevent in collapsing during cutting, and is sliced with a diamond or glass knife. The section is then impregnated with a heavy-metal stain, such as osmium tetroxide.

As the beam passes through the specimen, electrons are absorbed by heavily stained parts but pass readily through the lightly stained parts. Electromagnets bend the electron beam to focus an image onto a fluorescent screen or photographic film. Photograph taken through an electron microscope is called an electron micrograph.

The most modern TEMs distinguish objects as small as 0.2nm. This means that they can produce clear images magnified up to 250 000 times. The magnification is varied by changing the strength of the electromagnets.

The scanning electron microscope

The SEM is used to produce three-dimensional images of the surface of specimens. Electron are reflected from the surface of a specimen stained with a heavy metal. This enables the SEM to produce images of whole specimens: cells, tissues, or even organisms.

Although electron microscopes have revolutionized cell biology, they have not completely replaced light microscopes. Light microscopes are used to examine living and unstained specimens. Preparation of specimens for electron microscopy is complicated and time-consuming. Electron microscopes are very expensive and can be used only to study dead specimens stained with heavy metal, which might well produce artifacts.

■ Glossary of essential terms for you to know.

№	English term	Russian equivalent
	magnified	увеличенный
	specimen	образец, особь
	to explore	исследовать
	toinvent	изобретать
	lens	линза
	to refract	преломлять
	magnification	увеличение
	apparent	видимый
	compound	составной, сложный
	blurred	смазанный
	to distinguish	различать
	resolution	разрешение
	wavelength	длина волны
	clarity	ясность, четкость
	beam	луч, пучок лучей
	ray	луч
	internal	внутренний
	sample	образец
	to impregnate	оплодотворять, пропитывать, насыщать
	stain	пропитка
	readily	легко
	to reflect	отражать
	to enable	позволять
	tissues	ткани
	to replace	заменять

■ Your Essential Assignments

I. Quick check

1. How is the magnification varied in:

a) a light microscope

b) an electron microscope?

2. Why is the resolving power of an electron microscope so much better than of a light microscope?

3. What is the approximate size of the smallest structure that can be observed with a light microscope?

 

II. Fill in the missing words:

Term (verb)	Noun	Adjective
magnify	.......	.......
multiply	.......	.......
reflect	.......	.......
absorb	.......	.......
prevent	.......	.......

III. Use monolingual English dictionary and write down what could the words given below mean:

microscope, to refract, magnification, sample, ray.

 

IV. Match these words with their definitions:

1.	beam	A.	a piece of curved glass which makes things look bigger or smaller
2.	toinvent	B.	the power of a microscope to give a clear picture of things, or a measure of this
3.	eyepiece	C.	to change the position of the lens on a microscope so that you can see something clearly
4.	lens	D.	to make a substance spread completely through something
5.	resolution	E.	a shining line of light from the sun, a lamp
6.	to focus	F.	a picture of a subject in a mirror or in the lens of a camera
7.	specimen	G.	easily noticed
8.	to impregnate	H.	to make, design, or produce something new for the first time
9.	image	I.	made up of two or more parts or substances
10.	apparent	J.	a small amount or piece of something that is taken from a plant or animal, so that can be tested or examined
11.	compound	K.	the glass piece that you look through in a microscope

V. Find English equivalents to the following word combinations:

№	Russian term	English equivalent
1.	научное использование микроскопов
2.	электронный микроскоп
3.	стеклянные линзы
4.	окуляр
5.	видимый размер объекта
6.	зависеть от ч.-л.
7.	длина волны света
8.	без потери четкости
9.	сканирующий электронный микроскоп
10.	внутренняя структура клетки
11.	легко проходить через ч.-л.
12.	трехмерное изображение
13.	поверхность образца

VI. Give Russian equivalents to the following English terms:

№	English term	Russian equivalent
	a magnified image of sth.
	a compound light microscope
	to pass through
	to refract (bend) the light
	structures lying close together
	the resolving power
	to be limited by sth.
	a beam of light
	thetransmission electron microscope
	to focus an image
	to produce clear images
	complicated and time-consuming
	dead specimens
	pass readily through the lightly stained parts
	to be impregnated with sth.

VII. Find synonyms among the pool of words:

Pool of words	Synonyms
1)1. multiply /2. sample /3.increase /4. specimen
2)1. image / 2. visible / 3. apparent / 4. picture
3)1.beam/2.refract/3.examine/4.bend/5.explore/6. ray
4)1.organism/2.compound/3.living thing/4. complex

VIII. Answer the following questions. Use all information given before:

1. What are microscopes used for?

2. What types of microscopes are most commonly used today?

3. What is a compound light microscope?

4. What does the magnificationof an instrument depend on?

5. How do electron microscopes differ from compound light microscopes?

6. What are the main types of electron microscopes?

7. What is the difference between thetransmission electron microscope and the scanning electron microscope?

 

IX. Match the sentence halves. Make complete centences:

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