Babies are important because of what they can become, and that their death hurts their parents in many ways.
Humans are important because when they die, you lose a life, years of building knowledge and experience that contributes massively to the lives around them.
Cells in a test tube, even a in-vivo, functional human mind, are not morally relevant. I don't believe in the importance of human life, over other life, innately (without my selfish "I like humans to be taken care of"), and cells in a test tube, or a disembodied brain with no life experience are worthless.