LGS A-Level OCR Biology - Unit 5 - Photosynthesis Part 3

Only happens during the day as it needs continuous supply of products from LDR (ATP/ NAPDH)

CO2 from respiration and other organisms (people) enter leaf through stomata

Diffuses to palisade layer then into cells then into stroma

Carbon fixation

Reduction

Regeneration

CO2 combines w/ a CO2 acceptor (RuBP)

Reaction is ctalysed by RuBisCO

By accepting carboxylate group RuBP forms an unstable intermediate 6C compounds that immediately breaks down into GP compounds

CO2 is now fixed

ATP reacts w/ GP to form 1,3 biphosphate which is reduced using H from NADPH into TP

10/12 TP molecules are rearranged into 6 RuBP using phosphate groups from ATP.

Remaining 2 TP are products and can be used to synthesise organic compounds

2 TP can be used to synthesise glucose

Glucose can then be converted into sucrose, starch and cellulose (or used immediately in respiration)

Synthesis of fatty acids, glycerol and amino acids

Regeneration of RuBP

Light Intensity

CO2 conc.

Temp

Water stress

Provides power to produce ATP and NADPH

Light allows stomata to open, enabling gas exchange

Transpiration occurs, allowing water from the roots

RuBP - high

TP - high

GP - low

RuBP - low

TP - low so RuBP cannot be regenerated

GP - high as cannot be reduced to TP

CO2 levels in the atm. and aquatic habitats usually high enough to not become a limiting factor

TP - High

RuBP - low

GP - high

RuBP - High as nothing for to acccept so it accumulates

GP - low as cannot be made

TP - low; cannot be made

25 - 30 degrees: rate increase
30 - 45 degrees: O2 more successfully competes w/ CO2 for active site of RuBisCO

45 degrees: Enzymes denature

CO2 not accepted by RuBP (denaturing/ O2 filling binding sites)

Less GP therefore less TP

RuBP initially accumulates but doesn't regenerate due to lack of RuBP

Light is absorbed by PS2, e- in primary pigment raised to a higher energy level until it leaves PS

Travels down etc releasing energy to pump H+ into thylakoid space

Photolysis of H2O replaces e- lost from reaction centre in PS2

Light absorbed by PS1, excites e-, accepted by NADP and combines w/ excess H+ from ATP synthase

Protons accumulate in thylakoid space, membrane impermeable to H+ so diffuse down channels associated w/ ATP synthase

Use a photosynthometer, measures volume of O2 produced

Use NaHCO3 as source of extra carbon

Change temp, CO2 conc. (by adding NaHCO3 to aerated water), LI (moving lamp)

Allow apparatus to equilibrate for 5 mins

Uses an electrochemical gradient

| Moving down a conc.gradient using a proton motive force

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