Which of the following features can be said to be a true defining feature of living beings without any exception?
(1) They can digest their food
(2) All of them can reproduce
(3) They can regenerate
(4) They can respond to external stimuli
(4) The most obvious and technically complicated feature of all living organisms is their ability to sense their surroundings or environment and respond to these environmental stimuli which could be physical, chemical or biological. All organisms, from the prokaryotes to the most complex eukaryotes can sense and respond to environmental cues eg. Photoperiod affects reproduction in seasonal breeders, both plants and animals. Consciousness therefore, becomes the defining property of living organisms. There are many organisms which do not reproduce e.g. mule. Thus, reproduction cannot be an all-inclusive defining characteristic of living organisms. However no non-living object is capable of reproducing or replicating by itself.