Question

what causes oxidation in living systems?is oxidation good or bad for the living organisms?

Answer 1

oxidation is done due to different reasons like diffusion, osmosis, heat, light and many other

and 

oxidation is good for living organisms because without it respiration couldn't take place

Answer 2

Cause of oxidation in living systems:

Oxidation in living beings happens in light of the fact that we live in an oxygen-rich condition and oxygen is a brilliant electron acceptor. The things that we eat are made out of proteins, starches, and fats.

Our bodies are adjusted to living in an oxygen-rich condition, and the oxidation of these supplements is the thing that gives us the vitality that our cells need to live (there are anaerobic living beings [largely bacteria] that don't have this prerequisite). In this sense, oxidation isn't simply great, it is important for human life.  

Oxidation-Good or bad:

Then again, our cells are made out of proteins, sugars, and fats. Accordingly, oxidation is harming to our cells and we have formulated instruments to help moderate the harm. Thus, in this sense oxidation is harmful for living creatures.