31. Biofuels are mainly produced by:
(A) plants that convert hemicellulose into gasoline.
(B) the breakdown of cell wall biopolymers into sugars that can be fermented.
(C) the genetic engineering of ethanol generating genes into plants.
(D) plants that are easy to grow in arid environments.

27. Which of the following is a correct statement about nitrogen fixation in root nodules? (A) The plant contributes the nitrogenase enzyme. (B) The process is relatively inexpensive in terms of ATP costs. (C) Leghemoglobin helps maintain a low O2 concentration within the nodule. (D) The bacteria of the nodule are autotrophic.

28. In animals, embryonic stem cells differ from adult stem cells in that (A) embryonic stem cells are pluripotent, and adult stem cells are totipotent. (B) embryonic stem cells are totipotent, and adult stem cells are pluripotent. (C) embryonic stem cells have more genes than adult stem cells. (D) embryonic stem cells have fewer genes than adult stem cells. 

29. Which of the following best describes siRNA? (A) a short double-stranded RNA, one of whose strands can complement and inactivate a sequence of mRNA (B) a single-stranded RNA that can, where it has internal complementary base pairs, fold into cloverleaf patterns (C) a double-stranded RNA that is formed by cleavage of hairpin loops in a larger precursor (D) a molecule, known as Dicer, that can degrade other mRNA sequences

30. Which of the following series best reflects what we know about how the flu virus moves between species? (A) An avian flu virus undergoes several mutations and rearrangements such that it is able to be transmitted to other birds and then to humans. (B) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected. (C) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans. (D) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted to humans.

32. A plant will recognize a pathogenic invader (A) if it has many specific plant disease resistance (R) genes. (B) when the pathogen has an R gene complementary to the plant's antivirulence (Avr) gene. (C) when the pathogen secretes Avr protein. (D) if it has the specific R gene that corresponds to the pathogen molecule encoded by an Avr gene.

33. All of the following are responses of plants to cold stress except: (A) the production of a specific solute "plant antifreeze" that reduces water loss. (B) excluding ice crystals from the interior walls. (C) conversion of the fluid mosaic cell membrane to a solid mosaic one. (D) an alteration of membrane lipids so that the membranes remain flexible.

34. Processing of filtrate in the proximal and distal tubules accomplishes what important function? (A) sorting plasma proteins according to size (B) converting toxic ammonia to less toxic urea (C) maintaining a constant pH in body fluids (D) regulating the speed of blood flow through the nephron

35. Your bone cells, muscle cells and skin cells look different because (A) they contain different numbers of genes. (B) different genes are active in different kinds of cells. (C) they are present in different organs. (D) each cell contains different kinds of genes.  

36. In vertebrate animals, spermatogenesis and oogenesis differ, in that (A) oogenesis begins at the onset of sexual maturity, whereas spermatogenesis happens in embryonic development. (B) oogenesis produces four haploid cells, whereas spermatogenesis produces only one functional spermatozoon. (C) cytokinesis is unequal in oogenesis, whereas it is equal in spermatogenesis. (D) spermatogenesis is not completed until after fertilization occurs, but oogenesis is completed by the time a girl is born.

37. Biologists have discovered how to put together a bacteriophage with the protein coat of phage T2 and the DNA of phage lambda. If this composite phage was allowed to infect a bacterium, the phages produced in the host cell would have (A) a mixture of the DNA and proteins of both phages. (B) the protein and DNA of phage lambda. (C) the protein of phage T2 and the DNA of phage lambda. (D) the protein of phage lambda and the DNA of phage T2.