trophoblasts/chorionic villi and the uterus form the placenta
Both
I believe the placenta is directly attached to the uterine wall.
Two or more tissues working together is an organ.
The allantois membrane and the chorion form the placenta in mammals. The chorion is the outermost fetal membrane that encases the embryo and later fuses with the maternal tissue to form the placenta.
trophoblast
placenta
The combining form for placenta is "placent/o." This term is often used in medical terminology to refer to conditions, procedures, or anatomical discussions related to the placenta.
The placenta is composed of tissues from both the mother and the fetus. It is made up of fetal and maternal blood vessels, connective tissue, and other cells that allow for the exchange of nutrients, oxygen, and waste products between the mother and the fetus.
Tissues are formed by cells, tissues form organs and organs form systems.
chorion
placentae or placentas
The placenta is an organ that develops during pregnancy and is responsible for providing nutrients and oxygen to the developing embryo. It also helps in removing waste products from the embryo's bloodstream. The placenta forms from the tissues of both the embryo and the mother's uterus.