About 60% of natural conceptions fail to implant properly. One of the reasons may be the failure of the embryo to generate Trypsin, a chemical which induces a receptive environment in the uterus in order for the fetus to be implanted. The excess or lack of chromosomes of the fertilized egg may also be a factor in implantation failure. A weak immune system of the woman may also be an important factor.
Answer:
they have to be broken down by the body
I’d say the best definition is ‘the process by which the body gets energy from food’.
Hope this helps.