Question

The ability of an organism to respond to external stimuli is called
A. Sensitivity
B. Homeostasis
C. Metabolism
D. None of these

Answer 1

Life is a unique, complex organization of ions and molecules that perform certain chemical reactions in order to bring about life activities. All living organisms have some common features which are definite shape and size, organization, cellular structure, protoplasm, metabolism, catabolism, homeostasis, growth and development, movements, response and irritability, healing or repair, excretion, adaptations, genetic continuity, reproduction, evolution, and death.

Complete answer: All living things respond and show irritability. The visible change or reaction of an organism produced as a result of an applied stimulus is called the response.
On the other hand, the ability or power of an organism to produce a response to a stimulus is called irritability (or sensitivity)
For example, phototropic curvature (i.e.bending towards or away from light) in plants due to the external stimulus of light, folding of leaves in the sensitive plant ( Mimosa pudica, Vern Lajwantu or Chhui-mui) due to the external stimulus of touch, etc.

Additional Information:
1. Homeostasis: All living organisms keep themselves stable, maintaining their internal conditions within certain boundaries under adverse temperature, moisture level, acidity, and other physiological factors in order to continue their metabolic processes. It is called homeostasis.
2. Metabolism: Within cells, an increase in the number and diversity of molecules provides a greater opportunity for a vast array of biochemical reactions. All these chemical reactions going on in living cells are collectively termed as metabolism. Metabolism may be defined as the exchange of materials and energy within an organism or between an organism and its environment. The metabolism is further classified as anabolism and catabolism.

So, the correct answer is “Option A Sensitivity”.

Note: Both plants and animals respond differently to the stresses. The responses of animals are rapid and can be easily observed because they escape by moving away from the site of stress. The plants, on the other hand, can not move. They face the stresses and adapt themselves by their slow physiological responses.