Which amongst the following are defining features of any living organism?
(a) Growth
(b) Reproduction
(c) Consciousness
(d) Self-consciousness

Growth is shown both by living organisms as well as non-living things. Hence it is not a defining feature of living organisms. Some living organisms do not reproduce and hence it is not a defining feature. Consciousness is the most obvious and technically complicated feature of all living organisms. It is this ability to sense their surroundings or environment and respond to these environmental stimuli which could be physical, chemical or biological. Consciousness, therefore, becomes the defining property of living organisms. Self-consciousness is seen only in humans and hence it is not a defining feature of living organisms.