Question

Which of the following statements regarding the response of living organisms to external stimuli is correct?
(A) The external environmental stimuli can be physical, chemical or biological.
(B) All organisms from the prokaryotes to the most complex eukaryotes can sense and respond to environmental stimuli.
(C) Consciousness and response to external stimuli is the defining property of living organisms.
(D) All of these.

Answer 1

Hint: The ability of living organisms to respond to external environments and changes taking place in the environment is called stimuli.

Complete answer:
The ability of living organisms ranging from small unicellular prokaryotes to large multicellular eukaryotes to respond to the changes taking place in the environment is called stimuli. This is the sudden response or reaction to environmental change. The external or environmental stimuli can be physical, chemical or biological. The physical stimulus directly one of the five senses. For example: If we touch a hot plate accidentally, we pull our hands suddenly. The chemical stimulus is the response in which there is a secretion of certain chemicals in response to external stimuli. Plants also show stimuli which is known as tropism and the plants show different movements in response to stimuli called trophic movement. Example- Geotropism- The movement towards earth’s gravitational response is called geotropism. The root of plants is positively geotropic because they move in response to earth’s gravity and shoot or stem of plant is negatively geotropic. Some other examples are the movement of sunflowers towards the direction of light in an example of phototropic movement. The trophic movements are directional movements. The consciousness and response to external stimuli is the defining property of living organisms.

Hence, the correct answer is option (B)

Note: The ability of an organism to respond to stimuli is called sensitivity. Response to external factors is a unique feature of living organisms.