Photosynthesis Comprehensive Notes Flashcards

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Chloroplast

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The organelle where photosynthesis occurs. It contains pigments and the photosynthetic machinery, including the thylakoid membranes for the light-dependent reactions and the stroma for the Calvin cycle.

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Thylakoid

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Flattened membrane-bound sacs inside chloroplasts where the light-dependent reactions take place. They are stacked into granal structures that increase surface area for light harvesting.

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Stroma

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The fluid-filled interior of the chloroplast surrounding the thylakoids. The Calvin cycle operates in the stroma to fix CO2 into sugars.

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Light reactions

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The phase of photosynthesis driven by light that produces ATP and NADPH. Water is split to release O2 in this stage.

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Calvin cycle

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Also called the light-independent reactions; fixes CO2 into sugars using ATP and NADPH. Occurs in the stroma of chloroplasts.

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Photosystems I and II

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Two protein complexes in the thylakoid membranes that harvest light energy. PSII begins the light reactions by energizing electrons from water, while PSI facilitates NADP+ reduction.

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RuBisCO

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The enzyme that fixes CO2 into ribulose-1,5-bisphosphate (RuBP) during the Calvin cycle. It is central to carbon fixation in C3 photosynthesis.

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NADP+

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An electron carrier that accepts electrons during the light reactions to become NADPH, which then powers the Calvin cycle.

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ATP synthase

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An enzyme that uses the proton gradient across the thylakoid membrane to synthesize ATP from ADP and inorganic phosphate.

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CO2

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Carbon dioxide gas taken up from the atmosphere and fixed into organic molecules during the Calvin cycle.

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H2O

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Water is split in the light reactions to provide electrons and protons, releasing O2 as a byproduct.

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G3P

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Glyceraldehyde-3-phosphate; a 3-carbon sugar produced in the Calvin cycle that serves as a precursor for glucose and other carbohydrates.

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ATP

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A nucleotide energy carrier produced during the light reactions and used to power the Calvin cycle.

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NADPH

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A reduced form of NADP+ that carries electrons and provides reducing power for carbon fixation in the Calvin cycle.

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C6H12O6

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Glucose; the primary carbohydrate product that can be synthesized from fixed carbon in photosynthesis.

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Proton gradient

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Difference in proton concentration across the thylakoid membrane that drives ATP synthesis via ATP synthase.

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Photorespiration

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A process that can occur when CO2 is scarce and O2 is abundant, reducing photosynthetic efficiency by consuming energy without producing sugars.

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Grana

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Stacks of thylakoids within the chloroplast that optimize light capture for photosynthesis.

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Carotenoids

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Accessory pigments that broaden the spectrum of light absorbed and help protect the photosynthetic apparatus from damage caused by excess light.

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Stomata

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Pores on the leaf surface that regulate gas exchange, allowing CO2 in and O2 and water vapor out; their opening is linked to photosynthetic demand and water status.