Based on radiometric dating and the rock and fossil record, scientists have concluded that life has been present on earth a. for about 1 billion years. b. for about 50,000 years. c. for no more than 10 million years. d. for at least 3.5 billion years.

Agene pool: a) is the collection of all the alleles found in a single species b) is the collection of all the alleles found in a single population c) is the collection of all the chromosomes found in a single population d) is the collection of genes in a species that allow the individuals to swim

Which worm has eyespots that are used to detect light? a fluke b marine worm c planarian d tapeworm

Ivan is looking at a cross section of a stem taken from a vascular plant. he sees two different types of vascular tissue: the xylem, which is closer to the center of the stem, and the phloem, located around the xylem, closer to the outside of the stem. how do these two structures work together in a living plant?