2.9 photosynthesis

photosynthesis chemical equation

6 CO2 + 6 H2O → (light en, chlorophyll) → C6H12O6 + 6 O2

chloroplast structure

double membrane (inner & outer)

thylakoids - thylakoid space (fluid filled, membranous sac, thylakoid membrane)

stacks = granum

intergranal lamellae

starch grain

lipid droplet

stroma

photosynthetic pigments

chlorophylls (light absorbing)

• chlorophyll a: absorbs blue, red, purple. reflects green. *most abundant

• chlorophyll b: absorbs blue. reflects yellow.

carotenoids (accessory)

• fucoxanthin: reflects brown

• carotene: absorbs blue, green, purple. reflects red, yellow, orange wavelengths

absorption spectrum & wavelengths

shorter wavelength → longer

high → low en

violet → green → red

violet/blue/purple: about 400-480nm

green: middle — v low absorption spectrum

red: about 700nm

action spectrum: largely similar to absorption spectrum (2 peaks), but less defined.

factors: light intensity

light: not usually LF

low to med LI (increasing): as LI increases, rate of PS increases → LI = LF

• directly impacts light dependent rxns & calvin cycle indirectly (they need ATP & NADPH from light dep rxns)

high LI (plateau): LI no longer LF → other LFs

factors: CO2 conc

major LF

low conc: as CO2 conc increases, rate of PS increases

high conc: even if CO2 increases, rate of PS doesnt increase.

in general, opt co2 conc is higher than the natural atmosphere → so Co2 is generally the LF in nature.

CO2 is req in calvin cycle, used to synthesise glucose → limits rate of PS

factors: temp

enzs are used to catalyse rxns in both light dep & indep rxns

if temp increases beyond opt temp, enz denatures → drastic drop in rate of PS.

investigating PS

by measuring:

amt of O2 prod: count no of bubbles or use gas syringe

amt of CO2 used: use pH indicator or pH meter. CO2 is weakly acidic when dissolved → as CO2 conc decreases (when absorbed by plant), pH decreases.