Photosynthesis & Chloroplast Anatomy

65 vocabulary flashcards summarizing key terms, structures, and processes involved in photosynthesis and chloroplast anatomy.

Photosynthesis

Process in which light energy is converted to chemical energy to synthesize glucose.

Chlorophyll a

Primary photosynthetic pigment that absorbs red and blue light; contains a porphyrin ring with a central Mg2+ ion.

Chlorophyll b

Accessory green pigment that broadens the spectrum of light usable for photosynthesis.

Carotenoids

Accessory pigments that absorb excess light energy and protect chlorophyll from photo-damage.

Photon

Discrete packet of light energy that excites electrons in photosynthetic pigments.

Porphyrin ring

Ring structure in chlorophyll molecules that binds Mg2+ and captures light energy.

P680

Special pair of chlorophyll a molecules in Photosystem II that absorbs light at 680 nm.

P700

Special pair of chlorophyll a molecules in Photosystem I that absorbs light at 700 nm.

Chloroplast

Double-membraned organelle where photosynthesis occurs in plant cells.

Outer membrane (Chloroplast)

Smooth external membrane that encloses the chloroplast.

Granum

Stack of thylakoids inside a chloroplast.

Thylakoid

Flattened membrane-bound sac that contains the components of the light reactions.

Thylakoid membrane

Site of the photosynthetic electron transport chain and light absorption.

Thylakoid lumen

Internal space of a thylakoid where H+ ions accumulate during light reactions.

Intermembrane space (Chloroplast)

Region between the outer and inner chloroplast membranes.

Inner membrane (Chloroplast)

Membrane that surrounds the stroma and regulates passage of materials.

Stroma lamellae

Membranous connections between grana where cyclic photophosphorylation can occur.

Stroma

Fluid matrix of the chloroplast where the Calvin cycle takes place.

Light reaction

Photo-dependent stage that converts light energy into ATP and NADPH.

Calvin cycle (Dark reaction)

Light-independent stage that fixes CO₂ into glucose using ATP and NADPH.

Photosystem II (PSII)

First protein complex in light reactions that captures photons and initiates electron flow.

Photosystem I (PSI)

Second light-absorbing complex that re-energizes electrons to reduce NADP⁺.

Primary electron acceptor

Molecule that receives energized electrons from a photosystem.

Electron transport chain (ETC)

Series of carriers that transfer electrons and pump protons to create a gradient.

ATP (Adenosine Triphosphate)

Energy currency of the cell produced during photophosphorylation.

NADPH

High-energy electron carrier generated in light reactions and used in the Calvin cycle.

Carbon fixation

Incorporation of inorganic CO₂ into organic molecules during photosynthesis.

RuBisCo

Enzyme that catalyzes the carboxylation of RuBP with CO₂ in the Calvin cycle.

Carboxylation (Stage 1)

Step where 6 CO₂ combine with 6 RuBP to form 12 PGA.

PGA (3-Phosphoglycerate)

First stable 3-carbon product formed in the Calvin cycle.

G3P (Glyceraldehyde-3-Phosphate)

Energy-rich 3-carbon sugar produced during the reduction phase of the Calvin cycle.

PGAL

Alternate name for G3P produced in the Calvin cycle.

Reduction (Stage 2)

Step where 12 ATP and 12 NADPH convert 12 PGA into 12 G3P.

Regeneration (Stage 3)

Phase where 6 ATP convert 10 G3P back into 6 RuBP.

Carbohydrate synthesis (Stage 4)

Two remaining G3P molecules are used to form one glucose molecule.

Cyclic photophosphorylation

Process where PSI electrons cycle back through the first ETC, producing 1 ATP without NADPH.

Non-cyclic photophosphorylation

Linear flow of electrons from H₂O to NADP⁺, yielding ATP, NADPH, and O₂.

Action spectrum

Graph showing the relative effectiveness of different wavelengths for photosynthesis.

Photolysis

Light-driven splitting of water into 2 H⁺, 2 e⁻, and ½ O₂ at PSII.

Chemiosmosis

ATP synthesis driven by a proton gradient across the thylakoid membrane.

ATP synthase

Enzyme that phosphorylates ADP to ATP as protons flow through it.

Proton gradient

Difference in H⁺ concentration and charge across the thylakoid membrane used to drive ATP formation.

C3 photosynthesis

Standard photosynthetic pathway using the Calvin cycle and producing PGA as the first product.

C4 photosynthesis

Adaptation that spatially separates carbon fixation from the Calvin cycle to reduce photorespiration.

Bundle sheath cell

Inner leaf cell where the Calvin cycle occurs in C4 plants.

Photorespiration

Wasteful process where RuBisCo fixes O₂ instead of CO₂, reducing photosynthetic efficiency.

CAM photosynthesis

Adaptation that temporally separates carbon fixation (night) from the Calvin cycle (day) to conserve water.

Water splitting

Alternate term for photolysis producing electrons, protons, and oxygen.

Mg²⁺ ion

Central metal atom in chlorophyll’s porphyrin ring essential for light absorption.

Double membrane (Chloroplast)

Outer and inner lipid bilayers that enclose the chloroplast.

Photophosphorylation

Light-driven phosphorylation of ADP to form ATP.

H⁺ accumulation

Build-up of protons inside the thylakoid lumen creating an electrochemical gradient.

pH gradient

Difference in proton concentration between the thylakoid lumen and stroma.

NADP⁺

Oxidized form of NADPH regenerated after the Calvin cycle.

ADP

Substrate converted to ATP by ATP synthase during photophosphorylation.

Four-carbon compound (C4)

Intermediate (e.g., oxaloacetate/malate) that transports CO₂ to bundle sheath cells.

Spatial separation

Strategy in C4 plants where carbon fixation and the Calvin cycle occur in different cell types.

Temporal separation

Strategy in CAM plants where carbon fixation occurs at night and the Calvin cycle during the day.

Green wavelength reflection

Phenomenon where chloroplasts reflect green light, making it least effective for photosynthesis.

Red light absorption

Chloroplast pigments efficiently absorb red wavelengths to drive photosynthesis.

Blue light absorption

High-energy blue wavelengths strongly absorbed by chlorophyll for maximum photosynthetic activity.

Electron recycling (PSI)

Return of PSI electrons to the first ETC during cyclic photophosphorylation.

Photolysis products

2 H⁺, 2 e⁻, and ½ O₂ generated when water is split in PSII.

Oxygen evolution

Release of molecular O₂ produced as a by-product of water splitting in photosynthesis.

Cytochrome complex

ETC protein group that transfers electrons and pumps protons into the thylakoid lumen.

ATP yield (Non-cyclic)

~1.5 ATP molecules generated as two electrons pass through the first ETC from PSII to PSI.

Intermediary energy molecules

ATP and NADPH produced in light reactions and consumed in the Calvin cycle.