Архитектура Аудит Военная наука Иностранные языки Медицина Металлургия Метрология
Образование Политология Производство Психология Стандартизация Технологии
Read the text carefully to fulfil the tasks that follow.
With the availability of the first microscopes, researchers began to observe the microscopic structure of many substances, and in 1665 the Englishman Robert Hooke described having seen what he called cells in a piece of cork. He used this term because the cork appeared to be composed of thousands of tiny chambers that resembled the individual sleeping rooms in monasteries at the time, which were called cells. He was not aware that he was viewing just the cell walls, which were the only structures remaining from what had once been living cells.
Hooke’s initial discovery led to other advances, such as the finding that unlike plant cells, which have thick cell walls, animal cells lack such a wall and instead have only a thinner, generally more flexible plasma membrane.
Cells were then found to exist independently or as one small part of an organism consisting of many cells, a multicellular organism. Hooke was the first to discover that some organisms consist entirely of a single cell. These unicellular organisms, such as thousands of species of bacteria and protozoa, carry out all necessary life-supporting functions within one cell without the help of other cells. In contrast, multicellular organisms have cells with specific functions, and together the aggregate of cells embodies a complex organism.
It took about 150 years after Hooke discovered cells before several important related facts were articulated. Two German scientists, Matthias Schleiden and Theodor Schwann were the first to explain, in 1838 and 1839 respectively, the basic tenets of what we now call cell theory:
1. Cells are the fundamental units of life.
2. Cells are the smallest entities that can be called living.
3. All organisms are made up of one or more cells.
The longest cells are certain nerve cells (neurons), which can reach over a meter in length. While an ostrich egg is 1,500 times the size of a human egg cell – which is 14 times the size of a human red blood cell, itself as much as 35 times the size of many small single-celled microorganisms – most cells do have one thing in common: They tend to be quite small. While the size range reflects considerable diversity, most cells are 0.5 to 40 microns in diameter (1,000 microns equals one millimeter).
Small cell size is thought to be a function of the restriction placed on them by the ratio of surface area to volume. Cells are constantly absorbing molecules from the surrounding medium and releasing molecules into the surrounding medium. These processes are more readily accomplished when a cell is small and the ratio of surface area to volume is quite large. As a cell increases in size, the amount of volume inside the cell increases much more rapidly than the amount of surface surrounding the cell, and in time the cell becomes too large to maintain a stable internal environment.
Many scientists believe that it is more difficult for the nuclear material to maintain control over the entire internal environment when a cell is over a certain size. Therefore, if a small nucleus is most often the rule, then an upper limit is placed on the size of most cells.
1. Discuss in pairs:
a) Robert Hooke’s discovery and cell theory.
b) Cell structure and cell size.
Write an essay about cells, their structure and size.
Ex. 1. Open the brackets putting the verbs in the Past Simple or the Past Continuous tense-forms.
1. It (rain) hard this morning when I (wake up).
2. While I (have) breakfast this morning, my sister (phone) from Mexico.
3. When he (work) in the garden he (hurt) his knee.
4. Linda (wait) for the bus when I (see) her.
5. I (look) out of the window and (see) that it (snow) hard.
6. When the parents (come) from the theatre yesterday evening, the children (sleep).
7. When the guests (arrive) Mrs. Black still (cook) dinner.
8. I (walk) along the road yesterday when I (meet) an old friend of mine. She (go) to the post-office.
9. When I (shave) I (cut) myself.
10. I (go) to Jack's house but (not/find) him in. His mother (say) that she (not/know) what he (do) but (think) he probably (play,) football.
11. "What you (do) between 9.00 and 10.00 yesterday?" (ask) the detective. — "I (clean) my house", said Mrs. Jones. "I always clean my house on Saturday mornings."
12. As Mary (get) out of the boat her foot (slip) and she (fall) into the water.
13. While I (wait) for the bus I (notice) a group of tourists who (listen) intently to a guide.
14. I (try) to explain the situation to my parents, but they just (not/ understand) what I (talk) about.
15. She (injure) her ankle while she (jog) in the park.
16. How often you (visit) your cousins when you (be) in the States last year?
17. John's children (use) to be well-behaved but now they are quite naughty.
18. At school I (dislike) the maths teacher because he always (pick) on me.
19. The plane (crash) into a bridge because it (fly) too low.
20. While I (try) to get my car started, a passing car (stop) and the driver (offer) to help me.
21. Last fall I (drive) along a free way when I (run) out of gas. Luckily a truck (stop) and (give) me a lift.
22. When they (walk) through the countryside one day they (come) across a ruined mansion.
23. While we (clean) the attic, we (come) across our grandmother's old school books.
24. The driver (fall) asleep as he (drive) along.
25. I (not/understand) what (go on). Several people (shout) at me and one (wave) a newspaper in front of my face.
26. At six o'clock this morning I (have) a wonderful dream, but then the alarm (go) off.
27. Laura (not/wear) her glasses at that time, so she (not/notice) what kind of car the man (drive).
28. While I (have) a shower someone (knock) at the door.
29. The only thing I disliked about him when we (study) at college was that he always (borrow) my things without asking.
30. While the boys (skate) they (slip) on the thin ice and (fall) into the water.
31. The sun (shine) so brightly that Maria (have) to put on her sunglasses.
Ex. 2. Put all kinds of questions to the following sentences and make them negative.
1. I finished school in 2014.
2. I studied English at school.
3. They got up at 7 o’clock yesterday.
4. She went to university by tram.
5. He worked at a big plant last year.
6. Pete made a report on Sunday.
7. I saw him in the library.
8. The students wrote a test last week.
9. Our classes began at 10 o’clock yesterday.
10. She worked in the library yesterday.
11. Last night we watched a football match on TV.
12. He translated this text without a dictionary.
13. They saw this film a week ago.
14. Yesterday we got home by bus.
15. He made three mistakes in his last dictation.
16. It rained hard yesterday.
17. I listened to the latest news over the radio.
18. He spent his childhood in the country.
19. My brother left for Moscow two days ago.
20. We came home late yesterday.
Ex. 3. Choose the correct form of the verbs.
ADAM: Hello, Mike. What are you doing / do you do in this part of London?
MIKE: Well, actually, I'm looking / I look at flats round here.
ADAM: Flats? Are you wanting / Do you want to move?
MIKE: Yes, in fact, believe it or not, Mandy and I are getting / get married.
ADAM: That's great! Congratulations. When were you deciding / did you decide?
MIKE: Only last week. It was while we were staying / stayed with her family in Scotland. Now we try / we're trying to find a suitable flat.
ADAM: It'll be great to have you as neighbours. I hope you manage to buy one soon.
MIKE: Oh we aren't looking / don't look for one to buy. We aren't having / don't have enough money yet. We're wanting / We want to find somewhere to rent.
ADAM: Yes, of course. That's what we did / were doing at first. Actually, in the end, my brother was lending / lent us some money. That's how we were managing /managed to buy ours.
MIKE: Really? Perhaps I'll talk to my family before we choose / we're choosing a flat.
ADAM: That's not a bad idea. My family gave / were giving us quite a lot of helpful advice. Now, what about a coffee? There's a good place just round the corner.
MIKE: Oh, yes, I looked / was looking for somewhere to sit down when I bumped into you. Let's go.
Ex. 4. Complete each sentence with a suitable form of the verb given. Use the present simple or continuous, or the past simple or continuous.
1. I remember the day you got engaged. We … tea in the garden when you came out of the house and told us. (have)
2. I tried to explain the situation to my parents, but they just … what I was talking about. (not / understand)
3. What have you put in this sauce? It ... absolutely disgusting. (taste)
4. Peter always claimed that he was innocent, but for many years no one ... him. (believe)
5. It's a lovely shawl, I know, but unfortunately it ... to me. I'm just borrowing it for the party this evening. (not / belong)
6. Why ... that thin dress? You'll freeze to death in this cold wind! (you / wear)
7. Molly's fed up because she injured her ankle when she ... this morning, so she can't dance, (jog)
8. While I was admiring the view, someone stole the bag which ... all my traveller's cheques. (contain)
9. Look! ... that man standing beside the cash desk? I'm sure he's planning to steal something, (you / see)
10. Tea or coffee? I'm making both, so just say which you ... . (prefer)
11. The boys didn't want to come shopping with us because they ... the football on television, (watch)
Ex. 5. Most of these sentences contain one mistake. Correct mistakes.
1. The coffee is smelling wonderful.
2. Last year we visited the States.
3. The ship sank because the engineer wasn't calling for help until it was already sinking.
4. The reason I get fat is that I'm always tasting things while I'm cooking.
5. How is Jennifer? Does her health improve?
6. You're quite right, I'm completely agreeing with you.
7. What did you after you left school?
8. Now I understand what you're trying to say!
9. I can't imagine why you were believing all those rumours.
10. Martin looked forward to a peaceful weekend, when his brother arrived with all his friends from the football club.
11. Philippa heard the result of the election as she was driving to work, so she phoned me when she got there.
12. Oh, I'm so sorry, I've spilt some tea. Where are you keeping the paper towels?
GRAMMAR: PRESENT PERFECT.
TEXTS: HOW THE BODY WORKS. THE SKIN. SEEING. TASTE AND SMELL. HEARING.
Последнее изменение этой страницы: 2016-03-16; Просмотров: 48; Нарушение авторского права страницы