Subtopic 1: Defining Living Organisms
The central challenge: finding a property that is present in ALL living organisms and ABSENT in ALL non-living entities.
| Property | Universal to Life? | Why It Fails as Sole Criterion |
|---|---|---|
| Growth | No | Crystals grow by accumulation |
| Reproduction | No | Mules, worker bees, infertile humans are alive but cannot reproduce |
| Response to stimuli | No | Thermostats also respond |
| Metabolism | Yes | No non-living entity shows metabolism — DEFINING feature |
| Consciousness | Proposed | Broad but harder to measure |
Key NEET fact: Metabolism (anabolic + catabolic reactions together) is the only universally accepted defining feature of life.