"Zygote" is the name of the first cell formed at conception, the earliest developmental stage of the human embryo, followed by the "Morula" and "Blastocyst" stages. Is it human? Is it just a cell or is it an actual organism, a "being? You should raise them, and then provide the answers.
The zygote is composed of human DNA and other human molecules, so its nature is undeniably human and not some other species.
The best you can do is arm yourself with the facts and deliver them in what you hope will be a winning way for your audience -- meaning you will need to make your case, in most instances, not in the language of faith or religion but in the language of the post-modern secularist.
What follows, therefore, are the best arguments from science, the law, and women's rights to advance the pro-life case against abortion.
You will be able to change minds when you inform them that neither of these assumptions is true. Wade did not create a limited right to abortion but a virtually unlimited right to abortion throughout pregnancy.
Here's how: The case involved an 1854 Texas law prohibiting abortion except "for the purpose of saving the life of the mother." The plaintiff, whose real name is Norma Mc Corvey, desired a purely elective abortion and filed suit claiming the Texas law deprived her of constitutional rights. While admitting that abortion is not in the text of the Constitution, they nevertheless ruled that a right to abortion was part of an implied "right to privacy" that the Court had fashioned in previous rulings regarding contraception regulations.
The new human zygote has a genetic composition that is absolutely unique from itself, different from any other human that has ever existed, including that of its mother (thus disproving the claim that what is involved in abortion is merely "a woman and her body"). This DNA includes a complete "design," guiding not only early development but even hereditary attributes that will appear in childhood and adulthood, from hair and eye color to personality traits. It is also quite clear that the earliest human embryo is biologically alive.
It fulfills the four criteria needed to establish biological life: metabolism, growth, reaction to stimuli, and reproduction. Finally, is the human zygote merely a new kind of cell or is it a human organism; that is, a human being?
If the medicine and science don't persuade your audience, consider citing authorities from the "pro-choice" community itself.
Mention "Pro-choice" feminist Naomi Wolf, who in a ground-breaking article in 1996, argued that the abortion-rights community should acknowledge the "fetus, in its full humanity" and that abortion causes "a real death." More recently, Kate Michelman, long-time president of NARAL Pro-Choice America, acknowledged that "technology has clearly helped to define how people think about a fetus as a full, breathing human being." Those who justify abortion by claiming that "no one knows when life begins" are not arguing science but rather their own brand of politics, philosophy, or even religion.