56. The role of a metabolite that controls a repressible operon is to
(A) increase the production of inactive repressor proteins.
(B) bind to the repressor protein and activate it.
(C) bind to the repressor protein and inactivate it.
(D) bind to the operator region and block the attachment of RNA polymerase to the promoter.
(E) bind to the promoter region and decrease the affinity of RNA polymerase for the promoter.

52. Mouse mutations can affect an animal's appetite and eating habits. The ob gene produces a satiety factor (the hormone leptin). The db gene product is required to respond to the satiety factor (the leptin receptor). Most obese humans produce normal or increased levels of leptin without satiety. Which might provide an answer to at least some human obesity if a means to do so is found? (A) overexpression of the leptin receptor gene (B) activation of receptors for leptin (C) supplementary leptin (D) inactivation of leptin (E) mutation of the leptin receptor gene

53. The "immunotolerance" of a pregnant woman toward her unborn child is the result of (A) the complete physical separation from her cells and those of the unborn child. (B) the tenacity with which the unborn child's immune system counteracts the woman's immune system. (C) the unborn child having enough of the woman's identity so as to escape detection as foreign. (D) modern medical intervention during every pregnancy. (E) the relative quiescence of a pregnant woman's immune system compared to when she was not pregnant.

54. A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in (A) complete inhibition of transcription of the structural gene controlled by that regulator. (B) continuous transcription of the structural gene controlled by that regulator. (C) irreversible binding of the repressor to the operator. (D) inactivation of RNA polymerase by alteration of its active site. (E) continuous translation of the mRNA because of alteration of its structure.

55. The alternative pathways of photosynthesis using the C4 or CAM systems are said to be compromises. What is the reason? (A) CAM plants allow more water loss, while C4 plants allow less CO2 into the plant. (B) C4 plants allow less water loss but CAM plants allow more water loss. (C) C4 and CAM plants both minimize photorespiration and optimizes the Calvin cycle. (D) C4 and CAM plants minimize both water loss and rate of photosynthesis. (E) C4 plants compromises on water loss and CAM compromises on photorespiration.

57In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. What is the order of these genes on a chromosome map? (A) cn-rb-b-vg (B) b-rb-cn-vg (C) rb-cn-vg-b (D) vg-b-rb-cn (E) vg-cn-b-rb

58. The steps below refer to various stages in transmission at a chemical synapse: 1. The synaptic vesicles release neurotransmitter into the synaptic cleft. 2. The ligand-gated ion channels open. 3. An action potential depolarizes the membrane of the axon terminal. 4. Calcium ions rush into neuron's cytoplasm. 5. Neurotransmitter binds with receptors associated with the postsynaptic membrane. Which sequence of events is CORRECT? (A) 1 → 2 → 3 → 4 → 5 (B) 3 → 4 → 1 → 5 → 2 (C) 3 → 1 → 5 → 4 → 2 (D) 4 → 3 → 1 → 2 → 5 (E) 5 → 1 → 2 → 4 → 3

59. Eukaryotic telomeres replicate differently than the rest of the chromosome. Which of the following is the cause? (A) DNA polymerase that cannot replicate the leading strand template to its 5' end. (B) The evolution of telomerase enzyme. (C) Gaps left at the 3' end of the lagging strand because of the need for a 5' onto which nucleotides can attach. (D) Gaps left at the 3' end of the lagging strand because of the need for a primer. (E) Gaps left at the 5' end of the lagging strand because of the need for a 3' onto which nucleotides can attach. 

60. The same gene that causes various coat patterns in wild and domesticated cats also causes the cross-eyed condition in these cats, the cross-eyed condition being slightly maladaptive. In a hypothetical environment, the coat pattern that is associated with crossed eyes is highly adaptive, with the result that both the coat pattern and the cross-eyed condition increase in a feline population over time. Which statement is supported by these observations? (A) Natural selection reduces the frequency of maladaptive genes in populations over the course of time. (B) Polygenic inheritance is generally maladaptive, and should become less common in future generations. (C) Phenotype is often the result of compromise. (D) In all environments, coat pattern is a more important survival factor than is eye-muscle tone. (E) Evolution is progressive and tends toward a more perfect population.

61. What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth? 1. origin of mitochondria. 2. origin of chloroplasts. 3. origin of multicellular eukaryotes. 4. origin of cyanobacteria. 5. origin of fungal-plant symbioses. (A) 4, 3, 2, 1, 5 (B) 4, 2, 1, 3, 5 (C) 4, 2, 3, 1, 5 (D) 4, 1, 2, 3, 5 (E) 4, 1, 3, 2, 5

62. Fossil evidence indicates that several kinds of flightless dinosaurs possessed feathers. If some of these feather-bearing dinosaurs incubated clutches of eggs in carefully constructed nests, this might be evidence supporting the claim that (A) the earliest reptiles could fly, and the feathers of flightless dinosaurs were vestigial flight surfaces. (B) all fossils with feathers are actually some kind of bird. (C) the feathers were plucked from the bodies of other adults to provide nest-building materials. (D) their feathers originally served as insulation, and only later became flight surfaces. (E) dinosaurs were as fully endothermal (warm-blooded) as modern birds and mammals.