24. How do scientists calibrate a molecular clock for a group of organisms with known nucleotide sequences?
(A) They use radioactive isotopes to measure the age of DNA material directly.
(B) They graph the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record.
(C) They analyze fossilized DNA of known age and compare its nucleotide sequences to modern DNA sequences.

20. A beetle that feeds exclusively on dead wood is an example of a(n) _______and is part of the________ trophic level. (A) herbivore； first (B) herbivore； second (C) ominvore； second (D) detritivore； first (E) detritivore； second

21. Which feature is typical of an ATP-driven active transport mechanism? (A) The transport protein must cross to the correct side of the membrane before the solute can bind to it. (B) The transport protein is irreversibly phosphorylated as transport takes place. (C) The transport protein catalyzes the conversion of ADP to ATP. (D) The solute moves against the concentration gradient. 

22. The alleles of a gene are found at______ chromosomes.(A) the same locus on nonhomologous (B) different loci on homologous (C) different loci on nonhomologous (D) the same locus on homologous

23. Which statement about evolutionary adaptation is TRUE? (A) An individual who has learned how to survive cold winters has become adapted to the cold. (B) A population that has an increase in frequency of alleles for thicker fur has become adapted to the cold. (C) Adaptation results when cold temperatures cause mutations for longer fur. (D) Adaptation is possible when all the alleles in a gene pool are the same. 

25. Which phylum is most closely related to echinoderms? (A) Annelida (B) Mollusca (C) Arthropoda (D) Chordata

26. Some crocodiles and turtles have an exceptional ability to divert blood flow through the heart when they are diving and no longer breathing and exchanging gases. What most likely occurs when these animals dive? (A)Instead of flowing to the lungs, blood travels to the rest of the body to support bodi (B) Instead of flowing to the body, blood travels to the lungs to exchange gases. (C)Instead of flowing to the capillaries, blood travels to alveoli to exchar (D) Blood flow ceases altogether since gases cannot be exchanged while diving.

27. The hormone prolactin, found in distantly related vertebrates, exerts different effect es. From an evolutionary standpoint, this is an indication that p (A) can only have functions related to childbirth. (B) is an ancient hormone whose function diversified through evolution. (C) was a recent evolutionary adaptation. (D) was not required in fish and amphibians.

28. What form of nitrogen can most plants absorb and use directly? (A) nitrite and nitrate (B) nitrate only (C) ammonium and nitrogen gas (D) nitrate and ammonium

29. Where does the majority of the net primary production go? (A) Being stored in plants after being photosynthesized (B) Being grazed by herbivores (C) Being processed by decomposers and detritivores (D) Being stored in the soil

30. If a turtle and a night heron both eat the same species of fish, what is the relationship between a turtle and a night heron? (A) predation (B) mutualism (C)parasitism (D) competition