placenta
The yolk supplies all the nutrients for the growing embryo.
The yolk of the egg is the "food" for the growing embryo. When the duckling emerges from the egg the yolk has been all used up.
my sweet heart also the embryo of an olive tree, and some food for the embryo to consume when and if it is able to start growing.
It's a sack and not an egg but the primary food source, the only one, is the placenta and the nutrients go via the umbilical cord.
That depends on what animal because baby chickens feed on the yolk inside the egg while a human embryos get food and oxygen from their mother's umbilical cord.
the ---------- contains food for the embryo?
They get their nourishment from the yolk inside the egg. As the embryo develops, it absorbs the yolk until it's ready to hatch.
The yolk inside the egg.
Embryo gets its food via placenta .
The plant embryo can suvive inside the ssed because it derives its food from the endosperm and cotyledon.
See the related Wikipaedia link for detailed information.
the cotyledons