How do you unlock survival endless in Plants vs Zombies?

What is a Medusa and which groups have them? Is sheesham hardwood susceptible to termite attack? Do snails eat grasshoppers? Do caterpillar have four eyes? Are insects born live? What do roaches eat? Why are sponges classified as animals rather than plants? Do Praying mantis pinch? Can a common octopus change color? What insect spreads dysentery bacteria? How did mr krabs and plankton go from bff to enemies? What does red spotting purple butterfly eat? Can a wriggler breathe in dissolved oxygen? Why sponge are called hermaphrodite? Are vertebrates or invertebrates more common? How do you get rid of gnats in a mausoleum with lots of flowers? What is an Jack Spider? When did Oslo Mosquito raid happen? Where does quicksand occur? Do water fleas have tracheae?