how do tadpole and bird organisms develop without placenta
The tadpoles take their food from the yolk of an egg. The egg yolk is equivalent to the placenta. The placenta attaches itself to the uterus to provide the developing fetus with blood and oxygen.
they are in an egg. the egg yolk provides all the nutrients the organism needs while developing. short answer, the yolk takes the job of the placenta.
hope that helped! ;)