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121 MHC plays an important role in all except –

A: Tissue transplantation

B: Blood transfusion

C: Antigen presentation

D: T-cell response

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122 B-cell recognizes –

A: Internal epitopes

B: Surface epitopes

C: Hydrophobic epitopes

D: Agretopes

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123 Adjuvant increase all of the following except —

A: Number of antigen molecules

B: Time of exposure

C: Processing of antigen

D: Inflammatory response

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124 Plasma cell formation is initiated in –

A: Primary follicle

B: Secondary follicle

C: Germinal centre

D: Marginal zone

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125 Arctic foxes typically have a white coat in the winter. In summer, when there is no snow on the ground, the foxes typically have a darker coat. Which of the following is most likely responsible for the seasonal change in coat color?

A: The decrease in the amount of daylight in winter causes a change in gene expression, which results in the foxes growing a lighter-appearing coat.

B: The diet of the foxes in summer lacks a particular nutrient, which causes the foxes to lose their white coat and grow a darker colored coat.

C: Competition for mates in the spring causes each fox to increase its camouflage with the environment by producing a darker-appearing coat.

D: The lower temperatures in winter denature the pigment molecules in the arctic fox coat, causing the coat to become lighter in color.

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126 Which of the following statements most directly supports the claim that different species of organisms use different metabolic strategies to meet their energy requirements for growth, reproduction, and homeostasis?

A: During cold periods pond-dwelling animals can increase the number of unsaturated fatty acids in their cell membranes while some plants make antifreeze proteins to prevent ice crystal formation in tissues

B: Bacteria lack introns while many eukaryotic genes contain many of these intervening sequences.

C: Carnivores have more teeth that are specialized for ripping food while herbivores have more teeth that are specialized for grinding food.

D: Plants generally use starch molecules for storage while animals use glycogen and fats for storage.

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127 In most freshwater fish, nitrogenous waste is primarily excreted as ammonia, which is highly soluble in water and is toxic at low concentrations. In terrestrial mammals, ammonia is converted to urea before it is excreted. Urea is also highly soluble in water but is less toxic than ammonia at low concentrations. Which of the following best explains why freshwater fish do not convert ammonia to urea for excretion?

A: The metabolic pathways of fish do not normally involve nitrogen consumption.

B: The dilution of ammonia by direct excretion into freshwater conserves energy.

C: Ammonia is concentrated in tissues, where it is stored prior to excretion.

D: The nitrogen in ammonia is recycled for use in protein and nucleotide synthesis.

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128 The diagram above shows the progression of ecological events after a fire in a particular ecosystem. Based on the diagram, which of the following best explains why the oak trees are later replaced by other trees?

A: Eventually the other trees grow taller than the oak trees and form a dense canopy that shades the understory.

B: Oak trees alter the pH of the soil, making the forest better suited for shrubs and other trees.

C: Roots of shrubs proliferate in the soil of the forest and prevent the oak trees from obtaining water.

D: Oak trees succumb to environmental pollutants more readily than do either the shrubs or the other trees.

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129 The area covered by tropical rain forest is reduced by millions of hectares per year due to agriculture and logging. Which of the following best describes a likely result of tropical rain forest deforestation?

A: Populations of plants and animals will decrease as more rain forest disappears, leading to a decrease in biodiversity.

B: An increase of soil moisture will lead to a rapid increase in new vegetation coverage.

C: An increase in atmospheric carbon dioxide will lead to higher levels of ultraviolet radiation reaching the surface of Earth.

D: More oxygen will be available to other organisms as plant numbers decrease.

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130 Which of the following includes the most likely change in the coloration of the beetle population after pollution and a correct rationale for the change?

A: The coloration range shifted toward more light-colored beetles, as in diagram I. The pollution helped the predators find the darkened tree trunks.

B: The coloration in the population split into two extremes, as in diagram II. Both the lighter-colored and the darker-colored beetles were able to hide on the darker tree trunks.

C: The coloration range became narrower, as in diagram III. The predators selected beetles at the color extremes.

D: The coloration in the population shifted toward more darker-colored beetles, as in diagram IV. The lighter-colored beetles were found more easily by the predators than were the darker-colored beetles.

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