[Notwithstanding]

Personhood is not a biological phenomenon.

It is a metaphysical phenonmena that the law also recognizes.

The embryo if fully human and fully alive at conception (when egg unites with sperm). But that is biology.

Now, I advocate that such a human life should be protected by law from the moment of conception in the mother. That is because the moment of personhood is not certain but we presume it is very early.

We don’t know for certain that the human being in the petri dish is a person and the Church certainly teaches that we should NOT implant such embryos hoping to give them a chance to develop (into what we would eventually be certain are persons).

Does that help?

[paladinan]

We don’t know for certain that the human being in the petri dish is a person[...]

Er... I'm afraid I need to offer a correction, there: we most certainly DO know that the human being (i.e. living human zygote) in the Petri dish is a person; the Catholic Church, at least (which you referenced in subsequent comments) teaches that human life and personhood both begin at conception. Among other things, it's a corollary of the doctrine of the Immaculate Conception; since only human persons can have souls to which sin can be charged [whether Original or actual sin], and since it's infallible dogma that the Blessed Virgin Mary was free from Original Sin from the moment of her conception, it follows that the immortal human soul--the sine qua non of human personhood--was present from the moment of her conception. Since Mary is as human as we are, it also follows that our own souls--and the souls of all human beings--were created at the moment(s) of our own conception(s).