Glossary of Key Photosynthesis Terms

Essential Terms for PP-01

Term	Definition	Related Concept
Photosynthesis	Conversion of light energy to chemical energy (glucose) using $CO_{2}$ and $H_{2}O$	Overall: 6 $CO_{2}$ + 12 $H_{2}O$ → glucose + 6 $H_{2}O$ + $6O_{2}$
Thylakoid	Membrane-bound disc within chloroplast; site of light reactions	Stacked = grana; unstacked = stroma lamellae
Stroma	Fluid matrix of chloroplast; contains Calvin cycle enzymes	Site of dark reactions
Photosystem (PS)	Molecular complex containing reaction centre + antenna pigments	PS I (P700), PS II (P680)
Reaction centre	Chlorophyll a molecule at core of photosystem that drives photochemistry	P680 (PS II), P700 (PS I)
Accessory pigment	Pigment that transfers energy to Chl a but cannot perform photochemistry directly	Chl b, carotenoids, xanthophylls
Z-scheme	Non-cyclic electron transport pathway from $H_{2}O$ to NADPH via two photosystems	Named for zigzag energy diagram
Hill reaction	Photolysis of water at PS II releasing $O_{2}$ , $H^{+}$ , and electrons	2 $H_{2}O$ → 4 $H^{+}$ + 4 $e^{-}$ + $O_{2}$
Chemiosmosis	ATP synthesis driven by proton gradient across thylakoid membrane	Via $CF_{0}$ - $CF_{1}$ ATP synthase
Calvin cycle	Three-stage cycle fixing $CO_{2}$ into glucose in the stroma; CRR stages	18 ATP + 12 NADPH per glucose
RuBisCO	Ribulose bisphosphate Carboxylase/Oxygenase; $CO_{2}$ fixing enzyme in stroma	Most abundant protein on Earth
Carboxylation	First stage of Calvin: $CO_{2}$ + RuBP → 2 × 3-PGA via RuBisCO	C3 pathway
G3P	Glyceraldehyde-3-phosphate; 3C sugar phosphate; primary carbohydrate product	Made in Reduction stage
3-PGA	3-phosphoglyceric acid; first stable $CO_{2}$ fixation product in C3 plants	3-carbon compound
PEP carboxylase	Enzyme fixing $CO_{2}$ to PEP in C4/CAM plants; higher $CO_{2}$ affinity than RuBisCO	No oxygenase activity
OAA	Oxaloacetate (4C); first stable $CO_{2}$ fixation product in C4/CAM plants	Formed by PEP + $CO_{2}$
Kranz anatomy	Structural arrangement in C4 plants: large bundle sheath cells surrounded by mesophyll	Unique to C4 plants
Photorespiration	Wasteful C2 cycle initiated by RuBisCO's oxygenase activity; no ATP produced	Absent in C4 and CAM plants
Blackman's law	Rate of photosynthesis limited by the factor in minimum supply	Light, $CO_{2}$ , temperature
Absorption spectrum	Wavelengths of light absorbed by pigments	Peaks at blue and red for Chl a
Action spectrum	Photosynthesis rate vs. wavelength	Closely matches Chl a absorption