For two populations of organisms to be considered separate biological species, they must be .a. reproductively isolated from each other;b. unable to produce living offspring;c. physically very different from each other;d. A and C are correct;e. A, B, and C are correct

According to the most accepted scientific hypothesis about the origin of two new species from a single common ancestor, most new species arise when .a. many mutations occur;b. populations of the ancestral species are isolated from one another;c. there is no natural selection;d. a supernatural creator decides that two new species would be preferable to the old one;e. the ancestral species decides to evolve

Which of the following factors would not contribute to allopatric speciation?a. The separated population is small, and genetic drift occurs.b. The isolated population is exposed to different selection pressures than the ancestral population.c. Different mutations begin to distinguish the gene pools of the separated populations.d. Gene flow between the two populations is extensive.

Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species that lived side by side in parts of their ranges. However, recent books show them as eastern and western forms of a single species, the yellow-rumped warbler. Most likely, it has been found that these two kinds of warblersa. live in similar habitats and eat similar foods.b. interbreed often in nature, and the offspring are viable and fertile.c. are almost identical in appearance.d. have many genes in common.

When the ranges of two different species meet, a stable 'hybrid zone' occupied by hybrid individuals may form. How is this possible?a. Two diverged populations are capable of mating and producing viable and fertile offspring.b. Hybrid individuals are always allopolyploid and are thus unable to mate with either of the original species.c. Hybrid individuals may have reduced fitness and thus be strongly selected against.d. One species has a selective advantage, so as hybridization continues, the other species will go extinct.

Which of the following is an example of a postzygotic reproductive barrier?a. One Ceanothus shrub lives on acid soil, another on alkaline soil.b. Mallard and pintail ducks mate at different times of year.c. Two species of leopard frogs have different mating calls.d. Hybrid offspring of two species of jimsonweeds always die before reproducing.

Sexual selection favors individuals with traits that increase their ability to obtain mates, such as mating calls in crickets. Using this example, propose a scenario where sexual selection could contribute to divergence in sympatric speciation.

Explain how molecular chaperones facilitate protein folding in many different polypeptides, each with their own specific shape.

Cells that line your intestines are known to possess a large number of membrane proteins that transport small molecules and ions across the plasma membrane. Which of the following cell structures would you expect to be required for this characteristic of the cells?a. the endoplasmic reticulumb. peroxisomesc. lysosomesd. the cell wall