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Arctic foxes typically have a white coat in the winter. In summer, when there is...

Nov 11, 2023

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.

Key Concept

Seasonal gene expression changes

Explanation

The change in daylight during the seasons can trigger hormonal changes that lead to alterations in gene expression. This can result in physiological changes such as the seasonal coat color change in arctic foxes, with a white coat in winter for camouflage in the snow and a darker coat in summer to blend in with the snow-free landscape.

The most probable cause for the difference in mean stem length between plants in dish A and plants in dish B is which of the following? (A) Shortening of cells in the stem in response to the lack of light (B) Elongation of seedlings in response to the lack of light (C) Enhancement of stem elongation by light (D) Genetic differences between the seeds

Key Concept

Phototropism and etiolation in plants

Explanation

In the absence of light, plants exhibit a growth response called etiolation, characterized by the elongation of stems. This is a strategy to reach light for photosynthesis. The difference in mean stem length between plants in dish A and dish B is most likely due to the elongation of seedlings in response to the lack of light, rather than shortening of cells, enhancement by light, or genetic differences.

Which of the following best supports the hypothesis that the difference in leaf color is genetically controlled? (A) The number of yellow-leaved seedlings in dish A on day 7 (B) The number of germinated seeds in dish A on days 7 and 14 (C) The death of all the yellow-leaved seedlings (D) The existence of yellow-leaved seedlings as well as green-leaved ones on day 14 in dish B

Key Concept

Genetic Variation

Explanation

The existence of yellow-leaved seedlings as well as green-leaved ones on day 14 in dish B suggests that there is genetic variation in the population, which is a key indicator of genetic control over a trait like leaf color. Environmental factors alone would not likely result in two distinct leaf colors persisting in the same conditions.