13. Photosynthesis Flashcards
Define photosynthesis
PHOTOSYNTHESIS: process by which cells synthesise organic compounds from inorganic molecules in the presence of sunlight and chlorophyll
Equation:
Photosynthesis - respiration relationship
Photosynthesis (anabolism) - respiration (catabolism) reverse reactions
Explain what is cholorphyll and why needed
Chlorophyll - green pigment responsible for light absorption - when absorbs releases e - used to synthesise ATP
Different chlorophylls but mostly absorb blue and red light, reflects green
Distinguish absorption spectrum and action spectrum
Absorption spectrum - which wavelengths chlorophyll absorbs
Action spectrum - which wavelengths needed for overall photosynthesis (all of pigments)
Main steps of photosynthesis
- Light dependent reactions: light absorbed by chlorophyll - ATP production - light absorbed by water -> photolysis of water -> O2 and H2 = in intermembrane space of thylakoids
- Light independent reactions: ATP and H2 (carrried by NADPH) transferred to light indep site - H2 combined with CO2 - organic compounds - ATP provides E for these anabolic reactions (fixing C molecules) = in stroma
What is chromatography used for?
Chromatography is used to separate componenst of a mixture
Procedure of pigment chromatography
- A mixture containing the pigment is dissolved - mobile phase
- Mobile phase is passed through a static material (stationary phase)
- Different pigments travel at different speed due to differences in mass - separated
- Retardation factor (Rf) calculated to compare components:
Rf = distance component travels/distance solvent travels
Conditions which influence photosynthesis
- Temperature
- Light intensity
- CO2 conc
Effect of temperature fluctuation on rate of photosynthesis
- As temp increased - rate increases (more Ek) to a certain point - enzymes denature - rate falls
- Photosynthesis controlled by temp sensitive enzymes
How does light intensity influence the arte of photosynthesis
- The higher light intensity - the higher rate (more photoactivated chlorophyll) to a certain point - raise light but no change - no more chlorophyll
- Different wavelengths of light - different rate
How does CO2 conc influence photosynthesis rate?
- The higher CO2 conc - the higher rate until certain point - plateau - enzymes for carbon fixation are saturated
What are the experiments to measure rate of photosynthesis in plants?
- CO2 uptake: changes water pH (alkaline)
- O2 release: attaching a sealed container to gas syringe
- Increase in biomass: weighted (dehydration must be done) / change in amount of starch - measured with calorimeter
Explain oxygenation of the Earth
- Earth was anoxic, non-aerobic organisms thrived, iron dominated rocks, oceans
- Rising O2 levels nurtured aerobic life instead of anaerobic - evolution of respiring organisms - rise in atmosphere oxygen to 20%
List light dependent reactions
In light dependent reactions pigments convert light E into chemical E
- Excitation of photosystems
- Production of ATP in ETC
- Reduction of NADP+ and phtolysis
Explain the first step of light dependent reactions
Excitation of photosystems
- Photosystems - groups of photosynthetic pigments embedded in thylakoid membrane
- Two types of photosystmes; PSI and PSII - according to max absorption wavelength
- When PS absrob light - delocalised e become excited
- Excited e are transferred to carrier molecules in thylakoid membrane
Explain the second step of light dependent reactions
Production of ATP via ETC
- Excited e from PSII transported to ETC in thylakoid membrane
- As e pass through ETC - lose E - used to translocate H+ into thylakoids - electrochemical gradinet - proton motive force
- H+ return to stroma due to gradinet through ATP synthase (chemiososmosis) - ATP produced - photophosphorylation
- De-energised e are taken up by PSI - re-energised by light
Third step of light dependent reactions
Reduction of NADP+ and photolysis
- Excited e from PSI might be trasnferred to NADP+ to reduce it into NADPH - needed for light indep reactions
- Lost e from PSII are replaced by e from photolysis - water split by light E into H+, e and O2
Overview of light dependent reactions
Steps of light independent reactions
Light independent reactions use chemical E from light dependent to synthesise organic molecules
- Carbon fixation
- Reducation of glycerate-3-phosphate
- Regeneration of RuBP
First step of light independent reactions (Calvin cycle)
Carbon fixation
- Calcin cycle begins with 5C (rubisco biphosphate - RuBP) - RuBP carboxylase (Rubisco) catalyses CO2 attachment to RuBP - 6C
- 6C unstable - breaks down into two 3C (glycerate-3-phospahte - GP)
- One Calvin cycle involves 3 RuBP combining with 3 CO2 => 6 GP
Second step of light independent reactions (Calvin cycle)
Reduction of glycerate-3-phosphate (GP)
- GP converted into triose phosphate (TP) using oxidation of NADPH and ATP - binds H and ATP supplies E for that
Third step of light dependent reactions (Calvin cycle)
Regeneration of RuBP
- In one cycle 6 TP produced - one may be used for half sugar molecule - two cycles for single glucose
- Other 5TP - combined to regenerate stocks of RuBP (5 x 3C into 3 x 5C) - uses ATP
Lollipop experiment
Determines order of compounds (RuBP, GP, TP) in Calvin cycle - how C fixed in sugars
- Radioactive C-14 injected into lollipop container containing green algae (Chlorella)
- Light shone to induce phtotsynthesis - C-14 taken from solution
- Some algae taken - killed by hot alcohol
- Samples analysed in 2D chromatography - separates compounds - any radioactive compounds identified with x-ray film
- Comapring samples from different periods of light exposure - order of compounds identified by mass difference => Calvin cycle determined by this experiment
Calvin cycle (light independent reactions) compounds
