trophoblasts/chorionic villi and the uterus form the placenta
Trophoblast cells. Form about 2 weeks into the pregnancy
fetus
Both
I believe the placenta is directly attached to the uterine wall.
Two or more tissues working together is an organ.
placenta
trophoblast
Tissues are formed by cells, tissues form organs and organs form systems.
choroin
placentae or placentas
chorion
Cells form tissues, and tissues form organs. And you need them to live.
Cells are structural and functional unit of an organism. Two or more cells combine to form a tissue. Many tissues join to form a organ.