1. scientists believe that ancient ancestors of all animals were (1 point) a) single-celled prokaryotes that reproduced asexually. b) single-celled eukaryotes that sometimes grew in colonies. c) multicellular organisms that were probably autotrophic. d) multicellular organisms with an alternation of generations lifecycle. 2. the cambrian explosion resulted in the evolution of the first (1 point) a) dinosaurs and mammals. b) representatives of most animal phyla. c) bacteria. d) land animals.

Juan and carol were studying invertebrates in biology. they knew that segmented or earth worms preferred a dark, moist habitat. during this lab, they would be investigating the responses of organisms called planaria or dugesia tigrina. these were simple flatworms that still had a one-way digestive system and a very simple nervous system. juan and carol placed the planaria in a petri dish containing cool, distilled water that was partially covered with black paper. they shined a light on the dish. next, they removed the paper and placed a small amount of chicken liver at one end of the dish. they added a few large salt crystals to the water. finally, they added drops of hot water to the cool water in the petri dish. their results can be seen in the data table. according to their experiment, all but one conclusion is valid.