Interestingly enough "religious people" do not have a homogenous opinion on everything.
I think that deserves a "No duh?!?" Thank you for stating the obvious

The fact that you feel the need to state that shows your incessant need to say anything.
why is the definition of life variable according to what life form you are looking at?
Define life form. That's a term you used, not me.
The distinction you are trying to draw doesn't make any sense.
Again, "No duh?!?" You are looking at it specifically from a scientific stand point. Which is fine. And is why you are confused. There's a distinct difference between the scientific definition (biological life) and the philosophical definition (human life). Which is what was meant originally.
One cell fertilizing another is life in biological terms (as is on skin cell, or one muscle cell), but isn't yet human life (in the philosophical sense).
Thus, IMO, 'human life' doesn't start at contraception (fertilization or the act of sex).
Now then, you can continue to spout all your "well, according to science it's life" internet research all you want. That's not in dispute to me. But, to me, that's not what the issue is about.
Meaning (so that you are clear) a fertilized cell is no more human life than the hair I just had cut and swept up 35 minutes ago.
why is "consciousness" the definining moment?
Explained above.
A question I don't have an exact answer to. For me, it would be most likely when the organism develops a nervous system, and not before.
Because comatose and persistently vegatative people fail your definition how do you square that?
No they don't.
Now then, if you don't share these ideas/concepts, that's fine. The thread was "does life begin at conception?", not "obtuseobserver says life starts at conception, and it will tell you why it's right and you're wrong if you disagree with it".
Satisfied or not, that's my answer to your questions.