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Entitle the text and get ready to answer the questions
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Robert Hooke, an English scientist, who lived at the same time as Leeuwenhoek also made and used microscopes. One day, he cut a very thin slice of cork and put it under his lenses He noticed that it was made of “a great many little boxes” separated by walls. He compared these to the cells of honey comb. All of the cells were filled with air. This explained why cork was light and why it floated so easily. The piece of cork that Hook examined was not alive. At one time, each "cell" had contained living matter, but the living material had died. As scientists continued to examine living things under the microscope, they slowly came to realize, that both plants and animals were made up of cells. One can easily see living plant cells in a very thin strip of onion. These cells fit together much like the bricks in a house. They have a cell wall made of non-living woody matter.
1. Why is cork very light?
2. Why does it float very easy?
4.11 Read the text and fill in the gaps with the words given below:
| a) DNA, b) RNA, c) nucleus, d) divide, e) reproduction, f) nucleoli, g) ability, h) heredity. |
The 1) … is a fairly large, generally spherical body located more or less centrally in the cell. It stains in a distinctive manner and includes one or more dense, heavily staining bodies, the 2) ….
The nucleus is the controlling center of the cell. An enucleated cell, or a cell fragment without a nucleus, can carry on some of its functions for a short period, but its 3) … to grow is limited and 4) … can not occur. On the other hand, fragments containing a nucleus may grow and may eventually 5) …. Correlation of observations on inheritance with details of cell structure shows clearly that, with a few exceptions, the factors that control 6) … are located in the chromosomes, which lie in the nucleus and make up most of its bulk. The chief components of these hereditary factors, the genes, appears to be 7) …. To a great extent DNA controls cell growth and cell function. 8) … performs a function outside the nucleus related to the nuclear activity of the chromosomal DNA.
4.12 Translate the text without a dictionary and guess the meaning of the underlined words:
Date: 2015-04-23; view: 732; Нарушение авторских прав