2020-01-14
458
Lecture on Bacteria
Bacteria is the common name for a very large group of one-celled microscopic organisms that may be the smallest, simplest, and perhaps even the very first forms of cellular life that evolved on Earth. Because they are so small, bacteria must be measured in microns, with one micron measuring about 0.00004 inches long. Most bacteria range from about 0.1 micron to about 4 microns wide and about 0.2 microns to almost 50 microns long. We can observe them only under the microscope. Bacteria are very primitive and simple. They are unicellular, which means that they are made up of a single cell. They probably evolved about three and a half billion years ago. Some of the oldest fossils are bacterial organisms. They’ve been found almost everywhere on Earth, including all the continents, seas, and fresh water habitats, and in the tissues of both plants and animals.
They grow in colonies and can reproduce quite rapidly, in fact, by a process called fission. In fission, the cell increases in size and then splits in two parts. Fission is also referred to as asexual budding. There is also a process that is called conjugation, and that’s when two separate bacteria exchange pieces of DNA. So, there are two ways that reproduction can occur, but fission is though to be more common.
Bacteria were virtually unknown until about 1600 when microscopes were introduced, and at that time, bacteria were observed and classified into three main types according to their shapes, and that classification hasn’t changed that much over the years.
The first type is bacilli. The bacilli are a group of bacteria that occur in the soil and air. They’re shaped like rods, and if you were to see them in motion, they’d be rolling or tumbling under the microscope. These bacteria are largely responsible for food spoilage.
The next type of bacteria is referred to as cocci group, and it tends to grow in clusters or chains. This specimen is one of the common streptococci bacteria that cause strep throat.
Spirilla look like little corkscrews, and they are responsible for a number of diseases in humans. But, although it is true that some species of bacteria do cause diseases, for the most part, bacteria are benign.
There’s a lot of bacteria in the air, they live harmless on the skin, in the mouth, and in the intestines. In fact, bacteria are very helpful to researchers because bacteria cells resemble the cells of other life forms in many ways, and may be studies to give us insights. Since bacteria reproduce very rapidly genetic engineers use them to determine how certain characteristics are inherited.
But within these basic groups there are virtually hundreds of variations that make them somewhat more difficult to identify and classify. Sometimes more than one type of bacteria may be found together in a specimen. In addition to identifying bacteria by their shape it’s better to study the biochemistry of genetic structure of the specimen. They have one chromosome of double-stranded DNA in a ring, when can be analyzed fairly easily.
Choose the best answers for the following
1. Bacteria reproduce by
a) fission or budding; b) splitting or budding; c) cloning themselves; d) seeding or fission
2. Cocci bacteria cause
a) typhoid; b) AIDS; c) strep throat; c) fevers
3. Bacilli are responsible for
a) diseases in humans; b) food spoilage; c) strep throat; d) human evolution
4. Spirilla look like
a) rods; b) corkscrews; c) dots; d) sticks
5. Which two characteristics are common in bacteria?
a) they have one cell; b) they are harmful to humans;
c) they reproduce quickly; d) They die when exposed to air
VOCABULARY
Создайте логические пары, выбирая из a, b, c или d:
1. month – year
day - ____a) minute; b) hour; c) season; d) week
2. dark – light
small - ____ a) big; b) bright; c) thin; d) little
3. night – day
evening - ____ a) morning; b) time; c) dark; d) afternoon
4. bring – take
arrive - ____ a) catch; b) carry; c) leave; d) come
5. good – bad
cheap - _____ a) free; b) expensive; c) nice; d) high
6. first – last
best - _____ a) next; b) worst; c) most; d) least
7. office – work
school - _____ a) learn; b) write; c) play; d) test
8. write – letter
tell - _____ a) book; b) report; c) story; d) word
9. book – read
radio - _____ a) sound; b) listen to; c) put out; d) catch
10. bank – money
shop - _____ a) price; b) basket; c) food; d) supermarket
GRAMMAR
I. Заполните пропуски соответствующими формами глагола “to be” и “to have”.
1. Last year their son ____ 26, so he ____ 27 now.
2. Today the weather ____ nice, but yesterday it ____ cold.
3. I ____ cold. Can I have something hot to drink?
4. I ____ hungry last night, so I ____ something to eat.
5. I called you yesterday but you ____ at home. Where ____ you?
6. He ____ a good job in a bank.
7. My sister and her husband ____ three children.
8. “What’s wrong?” – “I ____ something in my eye”.
9. Where... you... in two days?
10. When... you at home yesterday?
II. Выберите правильную форму глагола.
1. All of her belongings (was/were) in a suitcase.
2. Athletics (is/are) very popular nowadays.
3. Aerobics (do/does) people a lot of good.
4. Chocolate (makes/make) you put on weight.
5. Most people (enjoy/enjoys) Easter.
6. The money she makes (is/are) enough for her.
7. The police (is/are) looking for the murderer.
8. His good looks (get/gets) him what he ants.
9. The government (is/are) passing new laws.
10. No news (is/are) good news.
III. Заполните пропуски соответствующими личными местоимениями.
1. She is very handsome. I envy ____.
2. They are not reliable. He doubts ____.
3. We asked for his advice. ____ advised ____ not to come.
4. This book belongs to me. This is ____ book.
5. The man put ____ hand into ____ pocket.
6. They were whispering among ____.
7. His grandmother lives by ____.
8. After ____ they decided not to come.
9. What are you doing ____ summer?
10. Which shoes do you like most? ____ or those?
IV. Вставьте some, any или no, где необходимо.
1. She went to the shop, but she didn’t buy... eggs.
2. He has read... 20 pages.
3. Did they send you... letters from England?
4. Why have... students gone home?
5. Have you found... mushrooms in the wood?
6. Are there... fruit-trees in your garden?
7. Did they ask you... questions? – Yes, they asked.....
8. Does he make... mistakes in his dictations?
9. My friend has bought... new shoes.
10.... people there are very unfriendly.
