WVGSA Grade 5 Science Practice Questions - West Virginia General Summative Assessment Grade 5 Science Exam

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A sealed mesocosm containing a green plant, soil, and micro-organisms is monitored over 24 hours under a 12-hour light / 12-hour dark cycle: - Light Hours (06:00 to 18:00): $O_2$ rises from 21% to 26%, $CO_2$ drops from 0.08% to 0.02%. - Dark Hours (18:00 to 06:00): $O_2$ drops from 26% to 22%, $CO_2$ rises from 0.02% to 0.06%. Why does carbon dioxide ($CO_2$) increase during dark hours?

Photosynthesis speeds up in darkness. Photosynthesis stops without light, while continuous cellular respiration by the plant and soil decomposers releases carbon dioxide. Soil water evaporates into carbon dioxide gas. Nitrogen gas in air decays into carbon dioxide.

Correct Answer:

Photosynthesis stops without light, while continuous cellular respiration by the plant and soil decomposers releases carbon dioxide.

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