I think the most critical consequence of the advancement of the amniotic egg it the tetrapods were no longer attached to the water for reproduction.The amniotic egg permits reptiles, flying creatures, and warm-blooded creatures to lay eggs ashore without drying out. The liquid filled depression containing the incipient organism is isolated from the outer condition by an amniotic sac that is impermeable to water.
I believe the last option is the correct one for the illustration of the single celled organism provides and the environment that it is found living in.
