The Calvin cycle uses chemical energy captured during the light-dependent reactions to build organic molecules from carbon dioxide. Understanding this cycle explains how inorganic carbon from the air becomes part of carbohydrates and other molecules used by living things.
In plants, carbon dioxide enters a leaf through small openings called stomata. It diffuses through spaces between cells and into mesophyll cells, then reaches the stroma, the fluid-filled region inside chloroplasts where the light-independent reactions occur.
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What is carbon fixation?
The incorporation of inorganic carbon from CO₂ into organic molecules, beginning when RuBisCO joins CO₂ to RuBP.
What does RuBisCO do in the Calvin cycle?
It catalyzes the reaction between CO₂ and RuBP during carbon fixation.
What are the three stages of the Calvin cycle?
Fixation, reduction, and regeneration.
How do ATP and NADPH support the reduction stage?
ATP supplies energy and NADPH supplies reducing power to convert 3-PGA into G3P.
What happens to G3P after three Calvin-cycle turns?
One of six G3P molecules can leave as a net product; the other five help regenerate RuBP using ATP.
Quiz questions
Why is “dark reaction” a potentially misleading name for the Calvin cycle?Answer: The cycle does not require light directly, but it depends on ATP and NADPH supplied by light-dependent reactions.
After three turns of the Calvin cycle, how much ATP and NADPH are used in total?Answer: Nine ATP and six NADPH.
How do some desert plants reduce water loss while acquiring carbon dioxide?Answer: They capture CO₂ at night and use the stored carbon during the day with stomata closed.
How do plants use carbohydrates made through photosynthesis?Answer: They break them down through cellular respiration to release energy for cellular activities.
How does energy behave differently from matter in living systems?Answer: Energy flows through organisms and is eventually dispersed as heat, while matter is recycled.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.