18. frogs produce a huge number of gametes at one time - why do you think this (hint: finding nemo)?

19. the frogs toungue is anchored in the very front - opposite to the orientation and anchoring of humans. why do you think this is do

18.Because they are too close to the bottom of the food chain, in order for the survival of the species,when they reproduce, they do so in the millions so only a few of the progeny will be bound survive sometimes.Their mode of fertilization is external. They lay eggs in the water and there is a chance of destruction of these gametes by water current if they are in less quantity. So they lay more and more eggs in order to rule out the possibility of destruction of all eggs. Thus at least some eggs are fertilized by sperm and produce zygote. 
19.Frog's tongues are attached to the front of their mouths rather than at the back like humans. When a frog catches an insect it throws its sticky tongue out of it's mouth and wraps it around its prey. The frog's tongue then snaps back and throws the food down its throat.

https://quizlet.com/23871503/vertebrates-flash-cards/

Hydrosphere is the correct answer