IV Read and translate the text about microscope

Microscopy: The Instruments

Light microscopy refers to the use of any kind of microscope that uses visible light to observe specimens. A modern compound light microscope has a series of lenses and uses visible light as its source of illumination. With a compound light microscope, we can examine very small specimens as well as some of their fine detail. This magnification is achieved when light rays from an illuminator, the light source, pass through a condenser, which has lenses that direct the light rays through the specimen. The image of the specimen is magnified again by the ocular lens, or eyepiece. We can calculate the total magnification of a specimen by multiplying the objective lens magnification by the ocular lens.

Most microscopes used in microbiology have several objective lenses, including lOX (low power), 40X (high power), and lOOX (oil immersion, which is described shortly). A general principle of microscopy is that the shorter the wavelength of light used in the instrument, the greater the resolution. The white light used in a compound light microscope has a relatively long wavelength and cannot resolve structures smaller than about 0.2 mm. This fact and other practical considerations limit the magnification achieved by even the best compound light microscopes to about 2000X. By comparison, Van Leeuwenhoek's microscopes had a resolution of 1 mm shows various specimens that can be resolved by the human eye, light microscope, and electron microscope.

To obtain a clear, finely detailed image under a compound light microscope, specimens must be made to contrast sharply with their medium .To attain such contrast, we must change the refractive index of specimens from that of their medium. We change the refractive index of specimens by staining them. As the light rays travel away from the specimen, they spread out and enter the objective lens, and the image is thereby magnified.

To preserve the direction of light rays at the highest magnification, immersion oil is placed between the glass slide and the oil immersion objective lens. The immersion oil has the same refractive index as glass, so the oil becomes part of the optics of the glass of the microscope. The oil has the same effect as increasing the objective lens diameter, therefore, it improves the resolving power of the lenses. If oil is not used with an oil immersion objective lens, the image becomes fuzzy, with poor resolution.

V Remember the following word and word-combinations

Light microscopy, specimens, ocular lens, light rays, fine detail, magnification, image, eyepiece, wavelength, refractive index, immersion oil, objective lenses, coarse focusing knob, fine focusing knob.

VI Find the sentences with the following word-combinations and translate them:

To observe specimens, the total magnification of a specimen, pass through a condenser, series of lenses, the wavelength of light, we can examine, the glass slide and the oil immersion.

VII Insert the missing words

1. The image of the specimen is magnified again by the ocular lens, or …

2. We change the refractive index of … by staining them.

3. If … is not used with an oil immersion objective lens, the image becomes fuzzy, with poor resolution.

VIII Complete the sentences:

1. Light microscopy refers to the use…

2. A modern compound light microscope has a…

3. Most microscopes used in microbiology have…

4. The immersion oil has…

IX Word order

Put the words in the correct order to make questions. Then answer the questions about it.

1. buy/ you/ the/ did/ at/ what/ shops/?

2. is/ who/ teacher/ your/ English/?

3. parents/ moment/ where/ your/ the/ at/ are/?

4. cinema/ you/ go/ last/ when/ did/ the/ to/?

5. learning/ you/ why/ English/ are/?

6. you/ how/ to/ come/ school/ do/?

7. brothers and sisters/ you/ many/ have/ how/ do/?

X Answer the questions:

1. What kind of microscope is used the most common in microbiology?

2. What kind of objective lenses do you know?

3. How is calculated the total magnification of an object?

4. What does light microscope use for to examine specimens?

5. For what is immersion oil used?

11-12 Practical lesson

Rules of reading: Theletter combinations er, ir, yr, ur, or, ar

Word formation: suffix of nouns – ion, -tion

Text:The prokaryotic cell

Assignments to do:

I Remember:

a) Letter combination ar is pronounced as [a:], e.g.: far

Letter combinations er, ir, yr, ur are pronounced as [ә:],e.g.: her, sir

Letter combination or is pronounced as [o:], e.g.: for

a) Suffixes –ic, -al form adjectives from the nouns:

person – personal

history – historical

base – basic

Remember!!!

So is used to express the result of the statement before.

Because expresses the reason or cause of something.

Cause -----------------------------------------------Result

it started to rain, so we stopped playing tennis.

Result------------------------------------------------Cause

We stopped playing tennis because it started to rain.

II Read the words paying attention to the pronunciation:

Large, term, firm, colour, girl, sister, mark, fork, fur, her, similar, their, factor, first, burn, war.

III Read and translate the following words:

Central, experimental, academic, electric, prokaryotic, practical, monumental, historical, bacterial, social.