Which of the following is *true* of the placenta? Question 18 options: 1) It fully develops six months after birth. 2) It forms during the seventh month of prenatal development. 3) It is the fluid-filled sac that houses the developing embryo and fetus. 4) It allows the exchange of nutrients between the embryo and the mother, while at the same time filtering out harmful material.

What is the significance of the protein-lined pits? a. protein attracts other proteins needed for atp synthesis within the cell. b. protein-lined pits are able to transport one molecule at a time down the concentration gradient within the cell. c. the polarity of proteins allows other polar molecules to attach and be transported in the cell by transport channels. d. receptors within the pits allow ligands to fuse and be transported into the cell by endocytosis.