Category : 3rd Class
All living things respond to changes in their external environment. Organisms have sense organs like eyes, ear, nose, tongue and skin to detect these changes. Human respond to heat and cold in the surroundings by wearing cotton, light clothes and woolen clothes respectively. There is coordination between the brain and the sense organs to respond to changes in the surrounding. Sense organs receive the changes called the stimulus, which then reaches to brain through nerves. Brain interprets it and sends the message through the nerves to sense organs for respond. Removing hand on touching hot plate is an example of respond to the changes in the environment.
Plants also respond to changes in their surroundings. Sunflower bends towards light. Light is stimulus and bending is response. Movement of root under the ground and stem away from it, Mimosa pudica (touch me not) unfurls its leaves on touching, etc. are the examples of plants reasons to the changes in the surroundings.
Look at the following picture to understand the plants respond to change according to their surroundings:
Insects like ants, cockroaches, and butterflies grasshoppers have a pair of feelers as sense organs. Feelers respond to touch and smell stimulus. Non living things do not respond to any kind of changes in the surrounding.
How do we respond if there is too cold in the surrounding?
(a) By wearing silk clothes
(b) By wearing cotton clothes
(c) By wearing woolen clothes
(d) By wearing rain coat
(e) All of these
Cold is a stimulus and wearing woolen clothes is response. Woolen clothes keep our body warm in cold temperature. Therefore, option (c) is correct and rest of the options is incorrect.
Which one of the following sense organs has largest-surface area?
(e) None of these
The surface area of tongue is largest as compare to above given sense organs. Therefore, option (c) is correct and rest of the options is incorrect.
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