That’s probably the hardest question anyone’s asked so far!
You might find that a biologist can give you a better answer than an engineer!
A biologist might tell you about MRS GREN (have you learned about that in school?) which is the seven things all living organisms do:
-Sensitivity (seeing, feeling, hearing and so on)
-Reproduction (making babies)
-Excretion (getting rid of waste – in animals that’s pooing and weeing)
But as far as I know, no-one really knows the answer to this. At least not in scientific terms. What makes one bundle of atoms (you or me) alive and able to grow and move and eat and another bundle of atoms (the desk I’m sitting at, or the road outside or whatever) not able to do those things? I don’t know!
There are some things science can’t tell us the answer to and then you have to decide whether you want to believe any of the answers that faith, religion or philosophy give to those questions!
So if you ask a difficult question you get a difficult answer!!