Question

Which characteristics are always present in all living organisms

Answer 1

Let's think about this question and ask our selves what is life?
Think about a non-living thing, like a bike. 

Does this bike have kids? Does it need to eat or sleep? What is it made up of? What does it need to survive? Does it need to be able to sense the environment around itself? 

You're probably saying, no the bike doesn't do a lot of these things.

Humans, animals, and pretty much all living things need to perpetuate their genes by means of reproduction, whether it is asexual or sexual. 
We need to animals need to eat and sleep, but you can just categorize this as a metabolic process. Plants need Nitrogen and CO2 and sunlight, to undergo metabolic processes and make glucose (another metabolic process). We also must be able to maintain an equilibrium while conducting metabolism (homeostasis).
We need to be able to sense the environment around ourselves to survive. 
If you look at simple organisms, they are often able to detect different chemicals and know to be attracted or stay away from certain substances. 

All living things are made up of cells.