Fig. 2 Diagram of mitosis of a living cell Unit 5. Tissues and organ systems.

WARM-UP: Think of words and word-combination you associated with tissues and organs and complete the following diagrams.

VOCABULARY: Learn the following words and word combinations.

bone fiber tendon cavity blood vessels lungs to respond to stimuli protection stem root tentacles shrub herbs support mammal esophagus stomach intestine trachea carbon dioxide kidney spinal cord

Guess the meaning of the following words.

Coordination, to coordinate, nerves, nervous system, respiration, group, result, thickness, length, to continue, contraction, to differentiate, differentiation, large, collection, epithelial, muscular, organ, muscles, to absorb, to circulate, peripheral nerves, excretory system, skeleton.

Practice the following for pronunciation.

blood – [blʌd]

epithelial – [epi:Өi:ljel]

esophagus – [i:’sofəgəs]

fiber – [‘faibə]

giant – [‘dʒaiənt]

intestine – [in’testiŋ]

kidney – [‘kidni]

peripheral – [pə’rifərəl]

respiratory – [ris’paiərətəri]

rhythm – [‘riðəm]

stomach – [‘stʌmək]

tentacle – [‘tentəkl]

trachea – [trə’ki:ə]

READING: Read the text and do the tasks that follow.

In the early stages of an embryo the cells are usually much alike. But later they start specializing to carry on a particular function. This is the stage when different organs begin to take form. Cells similar in function 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 muscular tissue, contains connective tissue, blood (both in its cavities and blood vessels of its muscles) and nerve tissue and is covered and lined with epithelial tissue.

It is worth while to pass 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 growths keep 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 function 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?

When we call a plant or an animal an organism we imply that it is organized, that it consists of part carrying out functions which are correlated and contribute towards the activities of the whole. Thus the filament of Spirogyra is composed of cells which carry out living processes, and each cell is organized into parts such as the chloroplast which manufactures sugar or the plasma membrane which determines what materials can enter or leave the protoplast. Or, taking Hydra, we find that here the body of the animal can be divided into such parts as tentacles, mouth and body wall, each performing a different function. From the correlated activities of these parts these results an organism.

Higher in the scale of organization are the more familiar trees, shrubs and herbs. Here the plant body may be regarded as composed of various organs performing different functions. Thus, to hold the plant in the ground there is a special organ – the root. It also absorbs water and mineral substances from the soil. As to the stem, it is an organ to which is to support the leaves and conduct materials from one part of the plant to another, while the leaves are organs which are concerned chiefly with the manufacture of sugar.

In an animal such a bird, fish or mammal the scale of organization is yet higher, and organs performing related functions are grouped into system of organs. One of such systems is skeletal system, or skeleton, made up of the various bones which form the frame work. The muscular system with its different muscles is responsible for the movement of the body. The digestive system includes the mouth, esophagus, stomach and intestine. It is the system in which food is to be digested and through the walls of which food substances are to be absorbed. The circulatory system consists of the heart and blood vessels to circulate the blood through the body. The respiratory system includes the lungs and trachea. It is bound to bring oxygen to the blood and take carbon dioxide away from it. As to the excretory system it includes the kidneys which are to eliminate waste products. The nervous system consists of brain, spinal cord and peripheral nerves which serve to control and coordinate the activities of all the other systems and organs.