In Biology we consider that an organism has the functions of life, if it has these properties

Metabolism - it takes in things, it breaks things down, makes energy, etc. this is a hugely complex web of enzyme driven reactions in the cell. e.g. cellular respiration (biochemical reaction which is the conversion of food into energy that can be used by the cell)

Response - living things can respond to stimuli in their environment - like a sunflower bending towards the sunlight

Growth - living things grow and change shape, even at maturity, they continue to grow, in humans think about weight gain.

Reproduction - all living things have the potential to have offspring - at least the species as a whole should or it would die out. In individuals, (even if past reproductive age, or in the case of a sterile individual), we have cells that are reproducing all the time - your skin cells are constantly being reproduced by mitosis for example.

Excretion - living things excrete the waste processes they do not need, humans expel CO2 gas from their lungs when they exhale - this waste gas is a byproduct of cellular respiration

Nutrition - living things need food - they can eat organic matter like plants or animals that eat plants, or non-organic matter like archae feroplasma acidarmanus, which can live on iron

I would like to mention separately ( though related) Biologists also are proponents of the cell theory..

The Cell Theory

All living things are made of cells

Cells are the smallest unit of life

All cells come from pre-existing cells