The cell. Кулагина Ж.Д. - 29 стр.

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different organs begin to take form. Cells similar in structure and performing the
same function are called tissues, while an organ is a collection of tissues doing a
special work.
     The term tissue is usually used to include not only the living cells but also
structures produced by them and associated with them, such as the cell wall, the
hard material of bone, and the fibers of tendons. Most organs contain a number
of different kinds of tissues. To demonstrate this is easy if we take the heart as
an example. The heart, although a muscular organ and consisting largely of
muscle tissue, contains connective tissue, blood (both in its cavities and in blood
vessels of its muscles) and nerve tissue and is covered and lined with epithelial
tissue.
     It is worth while to pause for a moment and to try to imagine what happens
in any living organism, a man for example, when growth and differentiation of
cells occur. Every organ continues to function and individual cells of the
different tissues continue their vital activities.
     The heart as it growth keeps up its rhythm without missing a single beat.
The lungs continue without intermission to take in air and the oxygen in the air
continues to be absorbed into the blood vessels. The muscles as they grow
continue to respond to stimuli by contraction. The bones while increasing in size
and strength continue their functions of support and protection. Similarly in a
giant tree the stem and roots grow continually in length and thickness. Can you
imagine an automobile or any man-made machine gradually increasing in size
while continuing to operate? Isn’t it a mystery?

       Ex. 10. Answer the following questions. Give extended answers if you
can.

1. In the early stages of an embryo the cells are mach alike, aren’t they? 2. When
does the specialization of cells begin? 3. Do different organs take form at this
stage? 4. What cells form a tissue? 5. What is an organ? 6. Does the term tissue
also mean the structures produced by cells? 7. Do organs consist of only one
kind of tissue? 8. What tissues does the heart consist of? 9. What happens inside
an organism when it grows? Do its organs stop functioning? 10. What can you
say about the reaction of the heart to growth? 11. What happens to muscles and
lungs? 12. And what about the plants? 13. In what way do the roots and stems
grow?

      Ex. 11. Tell your fellow students what tissues the heart consists of and
what is the function of each of them.

       Ex. 12. Let’s do an experiment.
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1. Fill two glasses with water
2. Colour the water in one of the glasses with a food colouring.