The enzyme tryptophan synthase is composed of two polypeptide subunits each encoded by one gene in neurospora crassa. a mutant produces no tryptophan synthase due to a single point mutation in each of the genes (a and b) encoding the two protein subunits. a researcher is interested in identifying a revertant which produces fully functional tryptophan synthase. if the reversion rate for point mutations in n. crassa is 1 x 10-6 per haploid gamete, how many spores, on average, would the researcher need to screen to identify one revertant with the genotype a+ and b+ (functional alleles) which therefore can synthesize tryptophan synthase? a. 106 b. 2x106 c. 1012 d. 10-6 e.

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.