Question 30 Answer and Explanation _ACT December 2018 Form B05 Science Section

Passage V

Two scientists discussed the evolution of 3 animal groups: crocodiles, nonavian dinosaurs (all dinosaurs except modern birds), and modern birds. The scientists characterized the animals in each group by their resting metabolic rate, RMR (the rate at which an animal uses caloric energy when at rest), and according to whether they were poikilothermic (had body temperatures that varied significantly) or homeothermic (had body temperatures that remained relatively constant).

Scientist 1

Crocodiles and nonavian dinosaurs evolved from a common ancestor that had a low RMR and was poikilothermic. Crocodiles retained these traits. However, nonavian dinosaurs had a high RMR and were homeothermic. Modern birds inherited these traits when the group first evolved from nonavian dinosaurs, and both traits have beenretained by all modern birds.

The bones of nonavian dinosaurs had a porous structure, no growth rings, and extensive vascularization (channels containing blood vessels). Extensive vascularization, which is also seen in modern birds, is evidence of an efficient circulatory system and a high RMR. Efficient circulation distributes heat evenly throughout the body. Thus, nonavian dinosaurs were homeothermic and could have survived in cold climates.

Scientist 2

Crocodiles and nonavian dinosaurs evolved from a common ancestor that had a low RMR and was poikilothermic. Crocodiles retained these traits. Nonavian dinosaurs also had a low RMR and were poikilothermic. In contrast, modern birds have had a high RMR ever since the group first evolved from nonavian dinosaurs. Modern birds only became homeothermic after nonavian dinosaurs went extinct 65 million years ago.

The bones of nonavian dinosaurs were dense and had growth rings. Each of these features indicates a low RMR, and neither is seen in the bones of modern birds. Nonavian dinosaur bones also lacked extensive vascularization, suggesting an inefficient circulatory system that would not have been able to distribute heat evenly throughout the body. Thus, nonavian dinosaurs were poikilothermic and could not have survived in cold climates.

30. Consider a crocodile and a modern bird, each having the same body mass. Based on Scientist 2’s discussion, which animal would more likely produce ${CO}_{2}$ at a faster rate: the crocodile or the modern bird?

F. Crocodile; Scientist 2 argues that modern birds have a high RMR and that crocodiles have a low RMR.

G. Crocodile; Scientist 2 argues that modern birds have a low RMR and that crocodiles have a high RMR.

H. Modern bird; Scientist 2 argues that modern birds have a high RMR and that crocodiles have a low RMR.

J. Modern bird; Scientist 2 argues that modern birds have a low RMR and that crocodiles have a high RMR.

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

General knowledge questions.

Scientist 2 believes that crocodiles are low RMR, which means that the metabolism is relatively slow, so the energy consumption is small, and the CO2 emission is relatively small; while the birds are high RMR, so the energy consumption is large, and the CO2 emission is also more