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Science for Class 8



1.01     Introduction


In previous classes you have studied about environment and its components. As you know that every thing surrounding us, is a part of environment. The place where we move, work and live is the environment. The environment also affects our lives. The man and environment have always been interdependent on each other. Now we will study more details about the environment and inter-relationship between living things and their environment with special reference to man.


1.02     Sense organs in man


When there is a loud noise, you close your ears. When you find the room hot, you switch on the fan. When there is a dust storm, you close your eyes. When food tastes good, you feel like eating more. Living organisms can feel the changes which take place in their surroundings — environment. Do you know how organisms detect changes in their environment? They have the ability to sense and respond to these changes. As you have already studied in Class VII this ability of living things is called sensitivity. The information or thing which is sensed and felt by sensory organs and brains about an action is called stimulus. The action of the body which takes place due to the stimulus is called response. In the above situations noise, temperature, dust and taste of good food are stimuli. Closing of ears, switching on the fan, closing of eyes and eating more food are the responses of the body. Try to think of other examples of stimuli and responses by yourself.

Organisms, particularly animals, are sensitive to changes in temperature, light, sound, pressure, taste and smell. Animals have sensory organs. Provided with special cells called receptors which detect these changes. The sensory organs, like skin, have receptors for sound. Eyes have receptors for light. Nose and mouth have receptors for smell and taste.


Do you know how many senses you have? Man has following senses.

1. Sense of Sight

2. Sense of Hearing

3. Sense of Touch

4. Sense of Taste

5. Sense of Smell


Let us study the details of them.