Photosynthesis and the Calvin Cycle

VOCABULARY flashcards covering the processes, structures, and chemical reactions of C3 photosynthesis and the Calvin Cycle.

Photosynthesis

The process by which organisms such as plants and algae convert sunlight, water, and carbon dioxide ($CO_2$) into usable energy in the form of sugar and other biomolecules.

G3P (Glyceraldehyde 3-phosphate)

An important three-carbon precursor to the carbohydrate glucose ($C_6H_{12}O_6$) and other biomolecules; two molecules of $G3P$ are required to create one molecule of glucose.

Chloroplasts

Specialized organelles located in the cells of green plant tissues where photosynthesis occurs.

Mesophyll

A type of leaf tissue found between layers of epidermis and a waxy cuticle where chloroplasts are abundant.

Stomata

Openings in the leaf epidermis that allow for the diffusion of $CO_2$ and $O_2$ to and from the chloroplasts.

Thylakoids

Membrane-bound sacs inside the chloroplast where light-dependent reactions take place; a stack of these is called a granum (plural: grana).

Stroma

The fluid-filled space surrounding the thylakoids where light-independent reactions (Calvin cycle) take place.

Photosystem II (PS II)

The initial phase of photosynthesis where water molecules are split into hydrogen ions ($H^+$), electrons ($e^-$), and oxygen.

Chemiosmosis

The process where the buildup of $H^+$ in the thylakoid lumen establishes a concentration gradient, allowing $H^+$ to flow through ATP-synthase to create $ATP$.

ATP-synthase

An enzyme that joins $ADP$ with phosphate to form $ATP$ as $H^+$ flow through its internal structure from the lumen back into the stroma.

Photosystem I (PS I)

The second phase of photosynthesis where electrons from PS II are energized by sunlight again before being moved to the enzyme NADP-reductase.

NADP-reductase

The enzyme that attaches energized electrons from Photosystem I and $H^+$ from the stroma to $NADP^+$ to form $NADPH$.

Calvin cycle

The light-independent reactions occurring in the stroma that intake atmospheric $CO_2$ and utilize $ATP$ and $NADPH$ to produce $G3P$.

RuBP

A five-carbon molecule (ribulose bisphosphate) that combines with $CO_2$ at the start of the Calvin cycle to begin carbon fixation.

Carbon Fixation

The first phase of the Calvin cycle where three molecules of $CO_2$ are combined with three molecules of five-carbon $RuBP$ by the enzyme RubisCO.

RubisCO

The enzyme responsible for combining $CO_2$ with $RuBP$ during the carbon fixation phase of the Calvin cycle.

3PG (3-PGA)

A three-carbon molecule formed when the unstable six-carbon intermediate from carbon fixation immediately breaks down.

Reduction (Calvin cycle phase)

The phase where six molecules of $ATP$ and $NADPH$ are used to convert $3PG$ into $BPG$ and then into $G3P$.

Regeneration (Calvin cycle phase)

The final phase of the Calvin cycle where five molecules of $G3P$ are converted back into $RuBP$ using three molecules of $ATP$.