Space scientists Anna-Lisa Paul, Stephen M. Elardo, and Robert Ferl planted seeds of Arabidopsis thaliana in samples of
lunar regolith—the surface material of the Moon—and, serving as a control group, in terrestrial soil. They found that while all
the seeds germinated, the roots of the regolith-grown plants were stunted compared with those in the control group.
Moreover, unlike the plants in the control group, the regolith-grown plants exhibited red pigmentation, reduced leaf size, and
inhibited growth rates—indicators of stress that were corroborated by postharvest molecular analysis.
It describes an experiment that addressed an unresolved question about the extent to which lunar regolith resembles
terrestrial soils.
It compares two distinct methods of assessing indicators of stress in plants grown in a simulated lunar environment.
It presents evidence in support of the hypothesis that seed germination in lunar habitats is an unattainable goal.
It discusses the ﬁndings of a study that evaluated the effects of exposing a plant species to lunar soil conditions.
Choice D is the best answer. The text describes an experiment wherein space scientists compared plant growth in terrestrial
and lunar soil conditions. It then discusses the ﬁndings of the study, including the fact that all the seeds germinated but that
the plants grown in lunar soil exhibited signs of stress.
Choice A is incorrect. The text doesn’t address this question, and never describes any speciﬁc characteristics of either soil. It
merely describes the outcome of an experiment that exposed a plant species to lunar soil conditions. Choice B is incorrect.
The text never compares methods of assessing indicators of stress—instead, it simply mentions several stress indicators
observed in the study (red pigmentation, reduced leaf size, and inhibited growth rates). Choice C is incorrect. The text doesn’t
present any evidence that we could never achieve seed germination in lunar habitats, and in fact states that the seeds in the
lunar soil did germinate.