Unit 5-Photosynthesis Flashcards
Equation for photosynthesis?
Carbon dioxide + water —> glucose + oxygen
What happens in the light dependent reaction?
Light energy is used to split water
Making ATP, oxygen and energetic hydrogen atoms
Where does the light dependent stage happen?
Thylakoid membrane
What happens in the light independent stage?
The hydrogen atoms from LDR are fixed with Carbon dioxide using ATP to make glucose
Why can the light independent reaction not happen without the light?
Needs products from LDR (hydrogen atoms)
Where does the light independent reaction occur?
Stroma
Structure of chloroplasts:
Double membrane (envelope)
Disc shaped vesicles called thylakoid
Stacks of thylakoid called grana
Bridges between granum containing ATP synthase called lamellae
DNA,tRNA and ribosomes packed in a large vesicles called the starch grain
What are the 2 main types of photosynthetic pigments?
Chlorophyll (green)
Carotenoids (red/orange)
What does the absorption spectra show?
The specific wavelengths that are absorbed by these different pigments
What is the action spectrum?
A measure of The rate of photosynthesis against different wavelengths
What are photosystems?
A complex structure of many chlorophyll and other pigments held together by proteins and lipids on the thylakoid membrane
Why are photosystems found on the thylakoid membrane?
This is the best location to maximise absorption of photons
What happens in photosystem ii?
Chlorophyll in the huge complex on the thylakoid membrane absorb photons
This excited electrons causing a build up of charge (charge separation)
The charge difference drives the photolysis (splitting) of water into oxygen, protons and electrons
What happens to the oxygen produced in the photolysis of water? And where does this occur?
Occurs in photosystem 2
Oxygen diffuses out of chloroplast into the air
What happens after photosystem 2 up to photosystem 1?
Electrons pass along the chain of proteins in the thylakoid membrane pumping H+ ions into the thylakoid vesicle (lumen)
What happens at photosystem 1?
More photons are absorbed, and the energy excites electrons pumping more H+ ions into the thylakoid lumen from the stroma creating a proton gradient
What terminates the electron chain in photosynthesis?
A final protein complex in the thylakoid membrane combines the electron with a H+ to form hydrogen which then reduces coenzyme NADP into NADPH
How is ATP generated from photosynthesis?
The proton gradient across the thylakoid membrane is used, as H+ ions diffuse through ATP synthase back into the stroma generating an ATP
What is the production of ATP in the light dependent reaction called?
Photophosphorylation (using light energy to phosphorylate ADP)
What part of photosynthesis is the Calvin cycle found?
Light independent
What is the problem with rubisco enzyme?
It is super slow and inefficient, so large amounts of it are needed
Summary of the Calvin cycle
CO2 binds with RuBP —> 2GP (3C), which are reduced by NADPH and activated by ATP (products of LDR) —> GALP, this either binds with another GALP to form glucose (opposite to respiration) or regenerates RuBP
What 2 products of LDR are needed for LIR? And why?
ATP, to activate GP
NADPH, to reduce GP
Where does the Calvin cycle branch off or repeat?
Once GALP is formed, either 2 GALP combine to make glucose or are regenerated into RuBP
What is rubisco?
The enzyme that binds CO2 with RuBP to form 2 molecules of GP
How does temperature effect the rate of photosynthesis?
Temp effects the rate of enzyme reactions, eg rubisco
What factors affect the rate of photosynthesis?
Temp
CO2 concentration
Light intensity
How does CO2 conc effect rate of photosynthesis?
CO2 is needed for Calvin cycle, so the higher the conc the faster the rate of the Calvin cycle
When does cyclic photophosphorylation occur?
When there is no available NADP to get reduced from excited electrons
What occurs in cyclic photophosphorylation?
Photons in photosystem 1 excite an electron, which passes to the next electron carrier
The energy from the excited electron pumps protons into the thylakoid lumen
The electron returns to PS1
The proton gradient is used to make ATP via ATP synthase
What is the purpose of cyclic photophosphorylation?
Non cyclic makes equal quantities of NADP and ATP
Plants need more ATP than NADP
Cyclic only makes ATP
Summary of photophosphorylation?
1) light is absorbed by chlorophyll in PS11 to photolysis water
2) high energy electrons are passed along chain of proteins in thylakoid membrane, the energy pumps H+ across membrane
3) electron is finally taken up by NADP to make NADPH
4) H+ gradient is used to make ATP in the ATP synthase enzyme
What factors may affect/limit rate of photosynthesis?
CO2 levels
Light intensity
Temperature
In tropical climates the rate of O2 production is very high, how may this cause problems?
Oxygen is an inhibitor of carbon fixation as it competes for the active site on rubisco
In a hypothetical experiment how could we tell that temperature was not the limiting factor, looking at just yield
And increase in temperature would have no effect on yield as it is not the limiting factor
