A NASA scientist receives remotely sensed data indicating that the planet R contains no oxygen gas in its atmosphere. From this she concludes that complex multicellular organisms are unlikely to exist on planet R. What factors lead to this conclusion? A)No other principal electron acceptor is a gas, and so energy-intensive modes of life are unlikely on this planet. B)Oxygen is produced by complex multicellular plants, and so the absence of O₂ suggests that complex multicellularity never evolved on planet R. C)Oxygen is produced by microorganisms in the ocean, and so the absence of atmospheric oxygen suggests that no oceans exist on planet R. D)The scientist is wrong; complex multicellular organisms on planet R could respire using sulfate ions.

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The scientist concludes that complex multicellular organisms are unlikely to exist on planet R because there are no other principal electron acceptors that are gases, therefore, energy-intensive modes of life are unlikely. Complex multicellular organisms require a lot of energy, and one of the most efficient ways to obtain energy is through aerobic respiration, which requires oxygen gas as an electron acceptor. If there is no oxygen gas in the atmosphere, it is unlikely that there are other gases that can serve as an electron acceptor. Therefore, energy-intensive modes of life (such as those found in complex multicellular organisms) are unlikely to exist.

A NASA Scientist Receives Remotely Sensed Data Indicating That the Planet