Photosynthesis & Chloroplast Anatomy

Vocabulary flashcards covering core terms related to chloroplast anatomy, light and dark reactions, photophosphorylation mechanisms, and alternative photosynthetic pathways.

Photosynthesis

Process where light energy is converted into chemical energy (glucose) in plants.

Chloroplast

Double-membraned plant organelle where photosynthesis occurs.

Outer Membrane (Chloroplast)

Exterior lipid bilayer of the chloroplast.

Granum

Stack of thylakoids within a chloroplast.

Thylakoid

Flattened membrane sac containing photosynthetic pigments.

Thylakoid Membrane

Site of the electron transport chain and non-cyclic photophosphorylation.

Thylakoid Lumen

Internal thylakoid space where H⁺ accumulates and photolysis occurs.

Stroma Lamellae

Membranous connections between grana; location of cyclic photophosphorylation.

Stroma

Fluid outside thylakoids; site of the Calvin cycle.

Chlorophyll a

Primary light-absorbing pigment with a porphyrin ring and Mg²⁺ center.

Chlorophyll b

Accessory pigment that broadens the absorption spectrum.

Carotenoids

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

Photosystem II (P680)

First photosystem, absorbs light at 680 nm and starts the light reactions.

Photosystem I (P700)

Second photosystem, absorbs light at 700 nm; can run cyclic or non-cyclic pathways.

Electron Transport Chain (ETC)

Series of carriers that transfer electrons and pump H⁺ to build a proton gradient.

Non-Cyclic Photophosphorylation

Light reaction where electrons flow from H₂O → PSII → PSI → NADP⁺, forming ATP & NADPH.

Cyclic Photophosphorylation

Alternate pathway where PSI electrons recycle through the first ETC to make extra ATP only.

Photophosphorylation

ATP synthesis driven by light-induced electron flow.

Photolysis

Splitting of water into 2 H⁺, 2 e⁻, and ½ O₂ at PSII.

Chemiosmosis (in Chloroplasts)

ATP production using the H⁺ gradient across the thylakoid membrane via ATP synthase.

Calvin Cycle

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

RuBisCo

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

Carboxylation (Calvin Step)

6 CO₂ + 6 RuBP → 12 PGA.

Reduction (Calvin Step)

12 ATP + 12 NADPH convert 12 PGA to 12 G3P.

Regeneration (Calvin Step)

6 ATP convert 10 G3P back to 6 RuBP.

G3P (PGAL)

Three-carbon sugar; two molecules form one glucose.

Action Spectrum

Graph showing photosynthetic efficiency versus light wavelength; peaks in red/blue, trough in green.

C4 Photosynthesis

Spatial separation; CO₂ fixed into 4-C compound in mesophyll, moved to bundle-sheath to reduce photorespiration; costs 1 extra ATP.

CAM Photosynthesis

Temporal separation; CO₂ fixed at night, stored as malate, used in daytime to minimize water loss.

Photorespiration

Wasteful process when RuBisCo fixes O₂ instead of CO₂, reduced by C4 and CAM pathways.