Photosynthesis: Light Reactions and the Calvin Cycle

Vocabulary flashcards covering the components, mechanisms, and stages of the light reactions and the Calvin cycle in plant photosynthesis.

Light reactions

The initial stage of photosynthesis occurring in the thylakoid membrane where chlorophyll absorbs light energy, water is oxidized to release oxygen ($O_2$), and $NADP^+$ is reduced to $NADPH$ along with the production of $ATP$.

Calvin cycle

The light-independent stage of photosynthesis occurring in the stroma where carbon dioxide ($CO_2$) is fixed and reduced into sugar using $NADPH$ and $ATP$ produced by the light reactions.

Stroma

The fluid-filled space surrounding the thylakoid stacks within the chloroplast where the Calvin cycle takes place.

Thylakoid

A disc-shaped membrane structure inside the chloroplast that contains chlorophyll and serves as the site for the light reactions.

Lumen

The interior compartment of a thylakoid disc into which protons ($H^+$) are pumped during electron transport to create a concentration gradient.

Chlorophyll

The primary green pigment embedded in the thylakoid membrane that absorbs light energy to drive the light reactions.

Photosystems

Congregated clusters of pigment molecules, including chlorophyll, embedded in the thylakoid membrane that absorb light.

Electron transport chain

A series of membrane-bound proteins that capture excited electrons from chlorophyll and pass them down a pathway to pump protons into the thylakoid lumen.

Redox reaction

A coupled pair of chemical reactions in which one substance is oxidized (loses electrons) and another substance is simultaneously reduced (gains electrons).

Proton gradient

A high concentration of protons ($H^+$) established inside the thylakoid lumen relative to the stroma, functioning as stored potential energy.

ATP synthase

A membrane-spanning enzyme equipped with a rotating molecular rotor that utilizes the facilitated diffusion of protons from the lumen to phosphorylate $ADP$ into $ATP$.

NADP reductase

The final protein enzyme in the electron transport chain of the light reactions that reduces $NADP^+$ to $NADPH$ by adding electrons.

Transpiration

The process that pulls water upward from the plant roots through the stem and into the leaves.

Stomate

A microscopic pore on the leaf surface that regulates gas exchange by allowing carbon dioxide ($CO_2$) to enter and water vapor and oxygen ($O_2$) to exit.

Guard cells

Paired specialized epidermal cells that flank each stomate, swelling to open the pore when filled with water and shrinking to close it when water is scarce.

Flaccid

A limp or shrunken state of plant cells resulting from water loss, which causes guard cells to collapse and close the stomate.

Organic molecule

A chemical compound containing both carbon and hydrogen atoms, such as glucose and ribulose bisphosphate ($RuBP$).

Inorganic molecule

A chemical compound lacking both carbon and hydrogen atoms together, such as carbon dioxide ($CO_2$) and water ($H_2O$).

Carbon fixation

The first phase of the Calvin cycle in which an inorganic carbon dioxide ($CO_2$) molecule is bonded to an organic molecule ($RuBP$).

Ribulose bisphosphate (RuBP)

A five-carbon organic sugar possessing two negatively charged phosphate groups that binds with carbon dioxide ($CO_2$) during carbon fixation.

Reduction (Calvin cycle)

The second phase of the Calvin cycle where fixed carbon intermediates gain hydrogens from $NADPH$, converting $NADPH$ back to $NADP^+$ while forming three-carbon sugars.

Regeneration (Calvin cycle)

The final phase of the Calvin cycle where remaining three-carbon sugars are rearranged back into five-carbon $RuBP$ molecules using energy supplied by $ATP$.