In optimizing foraging, birds often stop feeding in an area and move on, even though there are still some seeds left. What is the best explanation for this observation?
A. Other areas may have food at a lower density.
B. They will leave some seeds to create the next generation of plants.
C. The density of the food becomes low, so it will take too much energy to find.
D. They are more likely to find a mate if they move around.
E. They are safer from predators when moving.
C. The density of the food becomes low, so it will take too much energy to find.
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In a classic experiment, Otto Loewi stimulated the vagus nerve of a frog heart electrically. He let the fluid bathing the heart he was stimulating flow to and thus contact a second, nonstimulated heart. Both the first and second hearts slowed down with this stimulation. Based on this response, you can assume the nerve he stimulated was part of the
A. parasympathetic system. B. sympathetic system. C. somatic system. D. atrioventricular system. E. central nervous system.
After a decline to an historic low about 300 million years ago, carbon dioxide levels in the Earth's atmosphere rose again for a while. Hypothesize a reason why this occurred.
A. All the vegetation that had been produced prior to the historic low decayed, releasing carbon dioxide. B. Higher oxygen levels resulted in the proliferation of aerobic bacteria; their respiration released large amounts of carbon dioxide. C. Higher temperatures caused an increase in plant growth, resulting in an increase in the amount of carbon dioxide synthesized. D. Lower temperatures resulted in reduced plant growth; with less vegetation to absorb carbon dioxide, the carbon dioxide levels rose. E. Higher oxygen levels promoted large-scale fires across the landscape; the breakdown of organic molecules in these fires released carbon dioxide.
____ stimulates rapid elongation of a floral stalk in many plant species
a. Abscisic acid b. Gibberellin c. Cytokinin d. Ethylene e. Auxin
RNA is believed to have preceded DNA because _____.
A. DNA contains thymine and RNA does not. B. DNA is double stranded and requires more components. C. DNA can store more protein-building instructions in less space. D. RNA can also function as an enzyme. E. RNA cannot replicate itself.