Biology: Characteristics of Living Organisms

Study Notes

Growth is a characteristic of living organisms, but it is not exclusive to living organisms, as non-living objects like mountains and boulders can also grow through accumulation of material on the surface.
In living organisms, growth is from inside and is considered as an increase in body mass.
Growth cannot be taken as a defining property of living organisms, as it can be observed in non-living objects as well.

Reproduction is a characteristic of living organisms, but it is not a defining property, as some organisms do not reproduce (e.g. mules, sterile worker bees, infertile human couples).
In multicellular organisms, reproduction refers to the production of progeny possessing features similar to those of parents.
Organisms can reproduce by asexual means, such as fungi producing spores, yeast and hydra reproducing through budding, and Planaria (flat worms) regenerating lost parts of their body.
In unicellular organisms, reproduction is synonymous with growth, i.e., increase in number of cells.

Metabolism is a characteristic of living organisms, where chemicals are constantly being made and changed into other biomolecules through chemical reactions.
Metabolic reactions occur simultaneously inside all living organisms, unicellular or multicellular.
No non-living object exhibits metabolism, but metabolic reactions can be demonstrated outside the body in cell-free systems.

Cellular organisation of the body is a defining feature of life forms.
The ability to sense surroundings or environment and respond to environmental stimuli is a characteristic of living organisms.
Plants respond to external factors like light, water, temperature, other organisms, and pollutants, while animals respond through their sense organs.