Which of the following is a defining property of living organisms?

To determine the defining property of living organisms, let us analyze the given biological concepts:

1. Cellular organisation of the body: All living organisms are made up of cells, which are the basic structural and functional units of life. Non-living objects do not exhibit cellular structure. Therefore, cellular organization is a defining, universal property of all living organisms without any exception.
2. Consciousness: Consciousness is the ability of an organism to sense its surroundings or environment and respond to these environmental stimuli (physical, chemical, or biological). All living organisms, from simple prokaryotes to complex eukaryotes, show consciousness and respond to external stimuli. Non-living things do not possess consciousness. Hence, consciousness is also a defining property of living organisms.

Since both cellular organization and consciousness are defining properties of living organisms, the correct choice is both a and b.