Photosynthesis In Bad Conditions

Vocabulary flashcards covering the mechanisms of photosynthesis, the Calvin cycle, photorespiration, and C3, C4, and CAM adaptations.

Light-dependent reactions

The first process of photosynthesis occurring at the thylakoid membranes, which captures solar energy to produce $ATP$ and $NADPH$ while releasing oxygen to replace captured electrons.

Stroma

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

Calvin cycle

The light-independent pathway occurring in the stroma that utilizes $ATP$ and $NADPH$ to synthesize glucose from $CO_2$ across three phases: carbon fixation, reduction, and regeneration.

Ribulose bisphosphate (RuBP)

A five-carbon carrier molecule that binds with $CO_2$ in the initial step of the Calvin cycle.

RuBisCO

The primary enzyme responsible for catalyzing the attachment of $CO_2$ to $RuBP$ during carbon fixation, which can also act as an oxygenase under high-oxygen conditions.

Carbon fixation

The first phase of the Calvin cycle in which $RuBisCO$ attaches $CO_2$ to $RuBP$, creating an unstable six-carbon compound that splits into two three-carbon 3-phosphoglycerate molecules.

Reduction phase

The second phase of the Calvin cycle where $ATP$ supplies energy and $NADPH$ provides electrons and hydrogen to convert an intermediate compound into $G3P$.

Glyceraldehyde 3-phosphate (G3P)

The usable three-carbon carbohydrate product of the Calvin cycle, with two molecules required to form one glucose molecule.

Regeneration phase

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

Photorespiration

A wasteful process occurring in hot, dry conditions when stomata close and oxygen accumulates, causing $RuBisCO$ to bind $O_2$ instead of $CO_2$, degrading stored molecules and oxidizing $RuBP$ to $CO_2$ without producing $ATP$.

C3 photosynthesis

The standard pathway utilized by about $85\%$ of plants, where $CO_2$ is taken directly into mesophyll cells and fixed into a three-carbon molecule via the Calvin cycle.

C4 photosynthesis

An adaptation to hot and dry environments that physically separates carbon capture into a four-carbon molecule in mesophyll cells from glucose production in bundle sheath cells, shielding the Calvin cycle from oxygen accumulation.

Bundle sheath cells

Cells surrounding the leaf veins in C4 plants (such as corn) where the Calvin cycle takes place and sugars are manufactured.

CAM photosynthesis

A temporal adaptation in plants such as cacti, orchids, and lilies that open stomata at night to capture and store $CO_2$ as a four-carbon molecule in the cytoplasm, then close stomata during the day to run the Calvin cycle using stored $CO_2$.