Photosynthesis: Light Reactions and Calvin Cycle

Vocabulary flashcards reviewing key concepts, steps, stoichiometry, and test traps of photosynthesis (Light Reactions and the Calvin Cycle).

Light reactions

Reactions taking place in the thylakoid membrane that use light and water to generate $O_2$, ATP, and NADPH.

Calvin cycle

The carbon-building cycle occurring in the stroma that uses $CO_2$, ATP, and NADPH to synthesize G3P and sugars.

Water splitting

The reaction during the light reactions that supplies replacement electrons and releases $O_2$.

Photosystem II (PSII)

The photosystem that functions first in non-cyclic electron transport, preceding the electron transport chain and PSI.

Proton ($H^+$) gradient

The concentration gradient built inside the thylakoid lumen by electron transport; $H^+$ flows through ATP synthase into the stroma to produce ATP.

Cyclic flow

An alternate electron pathway utilizing PSI only that produces extra ATP without generating NADPH or $O_2$.

Fixation (Calvin cycle Step 1)

The initial phase of the Calvin cycle where the enzyme Rubisco attaches $CO_2$ to RuBP, producing 3-PGA.

Reduction (Calvin cycle Step 2)

The phase of the Calvin cycle where ATP and NADPH convert 3-PGA into G3P.

Recycle / Regeneration (Calvin cycle Step 3)

The phase of the Calvin cycle where ATP is consumed to regenerate RuBP.

Calvin cycle stoichiometry ($3\text{--}9\text{--}6 \rightarrow 1$)

The chemical balance where $3\text{ }CO_2 + 9\text{ }ATP + 6\text{ }NADPH \rightarrow 1\text{ net }G3P$.

G3P to glucose requirement

Two G3P molecules supply sufficient carbon to produce one glucose molecule.

Origin of released $O_2$ vs. sugar's carbon

Released oxygen is derived from water, whereas the carbon in sugars is derived from $CO_2$.

Photorespiration

A process occurring when Rubisco binds $O_2$ instead of $CO_2$, leading to wasted energy and the loss of fixed carbon.

$C_4$ pathway

An photosynthetic adaptation that separates carbon fixation and the Calvin cycle by place to conserve water and reduce photorespiration.

CAM pathway

An photosynthetic adaptation that separates carbon fixation and the Calvin cycle by time to conserve water and reduce photorespiration.

Chlorophyll light absorption

The optical characteristic of chlorophyll by which it absorbs red and blue wavelengths and reflects green light.