6.3 Light-independent reactions and C3/C4/CAM Photosynthesis (Vocabulary Flashcards)

Vocabulary flashcards covering Calvin cycle, photorespiration, and C3/C4/CAM plant photosynthesis concepts from the notes.

Calvin cycle

The light-independent reactions in the chloroplast stroma that fix CO2 into carbohydrates through carbon fixation, reduction, and RuBP regeneration.

Light-independent reactions

Also called the dark reactions; use ATP and NADPH to convert CO2 into sugars.

Stroma

Fluid surrounding the thylakoids in chloroplasts where the Calvin cycle takes place.

RuBP (ribulose-1,5-bisphosphate)

A 5-carbon sugar that accepts CO2 in carbon fixation to form an unstable 6-C intermediate.

Rubisco (RuBP carboxylase/oxygenase)

The enzyme that fixes CO2 (and sometimes O2) to RuBP during carbon fixation.

3-phosphoglycerate (3-PGA)

The 3-carbon product produced after RuBP carboxylation and cleavage.

1,3-bisphosphoglycerate

Phosphorylated intermediate formed from 3-PGA by ATP during the reduction phase.

Glyceraldehyde-3-phosphate (G3P)

A 3-carbon sugar produced in the reduction phase; one molecule can exit the cycle to form sugars.

Regeneration of RuBP

Process by which most G3P is rearranged using ATP to regenerate RuBP for continued CO2 fixation.

ATP

Adenosine triphosphate; energy currency used to phosphorylate Calvin cycle intermediates.

NADPH

Nicotinamide adenine dinucleotide phosphate; provides reducing power to reduce 1,3-bisphosphoglycerate to G3P.

Carbon fixation

Phase where CO2 is fixed into RuBP by Rubisco to form 3-PGA.

Reduction

Phase in which 3-PGA is reduced to G3P using ATP and NADPH.

Regeneration (Calvin cycle phase)

Phase where most G3P is converted back into RuBP, consuming ATP.

G3P leaves cycle

One molecule of G3P exits the cycle per set of CO2 fixed to contribute to sugar synthesis.

Glucose synthesis from G3P

Two G3P molecules can be combined/rearranged to form glucose and other carbs.

Photorespiration

A wasteful process where Rubisco fixes O2 instead of CO2, consuming energy and releasing CO2.

C3 plant

Plants that fix CO2 via the Calvin cycle in mesophyll cells; first product is 3-PGA; Kranz anatomy is absent.

Krantz anatomy

Leaf anatomy with two cell types (mesophyll and bundle sheath) around veins, typical of C4 plants.

C4 plant

Plants that fix CO2 via the Hatch-Slack pathway in mesophyll cells and run the Calvin cycle in bundle sheath cells; Kranz anatomy present.

Hatch-Slack pathway

CO2 fixation pathway in C4 plants where CO2 is fixed by PEP carboxylase to form oxaloacetate in mesophyll cells.

PEP carboxylase

Enzyme that fixes CO2 to phosphoenolpyruvate (PEP) forming oxaloacetate; high CO2 affinity and no O2 affinity, active in mesophyll cells.

Oxaloacetate (OAA)

4-carbon product of PEP carboxylase fixation; quickly reduced to malate.

Malate

4-carbon molecule transported to bundle sheath cells and decarboxylated to release CO2 for the Calvin cycle.

Bundle sheath cell

Chloroplast-containing cell surrounding the leaf veins in C4 plants where the Calvin cycle concentrates CO2.

Mesophyll cell

Photosynthetic cell in leaves where initial CO2 fixation occurs in C3 and C4 plants.

PPDK (pyruvate phosphate dikinase)

Enzyme that regenerates phosphoenolpyruvate (PEP) from pyruvate in the C4 pathway.

CAM (Crassulacean Acid Metabolism)

Adaptation for arid conditions; CO2 is fixed at night by PEPC and stored as malate in vacuoles, then used during the day in the Calvin cycle.