ADDITIONAL TEXT. a) Read the text carefully to fulfil the tasks that follow.

a) Read the text carefully to fulfil the tasks that follow.

CELLS

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 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.

II. POST-READING TASKS.

I. Discuss in pairs:

1. Robert Hooke’s discovery and cell theory.

2. Cell structure and cell size.

II. Write an essay about cells, their structure and size.

UNIT 3

PRE-READING AND READING TASKS.

Study the vocabulary which is intended to aid your comprehension of the text:

contract (v)	[kqn'trxkt]	сжимать, сокращать;
occur (v)	[q'kE:]	случаться, происходить
attachment	[q'txtSmqnt]	прикрепление, рисоединение
bladder	['blxdq]	мочевой пузырь
brain	[breIn]	головной мозг
dioxide	[daI'Pks(a)Id]	двуокись
excess	['ekses]	излишний, избыточный
harm	[hQ:m]	зло, беда, вред; неприятность
intestine	[In'testIn]	кишечник; кишка
joint	[dZOInt]	сустав, сочленение
kidney	['kIdnI]	почка
liver	['lIvq]	печень
lung	[lAN]	лёгкое
muscle	['mAs(q)l]	мышца, мускул
ribcage	[rIb keIdZ]	грудная /рёберная/ клетка
sense	[sens]	чувство
smell	[smel]	обоняние
taste	[teIst]	вкус
touch	[tAtS]	осязание
urine	['jV(q)rIn]	моча
vessel	['ves(q)l]	сосуд
vision	['vIZ(q)n]	зрение
appropriate	q'prqVprIIt]	соответствующий, подходящий
various	['ve(q)rIqs]	различный, разный;

Make sure you can supply an adequate translation for each of the following word combinations:

to get rid of	heart rate
human being	at birth
respond appropriately	spinal cord
the number of times	portal vein

III. Read and translate the text.

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