Photsynthetic Pigments/Chloroplast Structure Flashcards
Describe chloroplasts structure
Grana/Granum - Inner parts of chloroplasts made of stacks of thylakoid membranes, where light dependents photosynthesis takes place.
Envelope- it is double membrane bound.
Thylakoids- flattened [discs] membrane-bound sacs in chloroplasts which contains photosynthetic pigments/photosystems. It is the site of light-dependent photosynthesis.
Stroma - fluid-filled space of chloroplasts surrounding the thylakoids. It is the site of light-independent photosynthesis.
70s ribosomes, starch grains and circular DNA.
What are photosynthetic pigments?
Found in the photo system.
They are pigments that absorb specific wavelengths of light that traps the energy associated with the light. Used for photosynthesis.
What are photosystems?
They are funnel shaped structure found thylakoids which contain accessory pigments which trap the light and pass the energy along to the primary pigment reaction centre.
Light-dependent photosynthesis.
What are accessory pigments?
A range of photosynthetic pigments found in the antenna complex of a photosystem, which absorbs different wavelengths of light.
How many chlorophyll types are there?
- [A,B,C,D,E]
What is the primary pigment?
Chlorophyll A
What are the 2 stages of photosynthesis
Light-dependent and independent stages
Why are photosynthetic pigments important in photosynthesis?
Absorb a wide range of wavelengths of light which increases the rate of photosynthesis.
Primary pigment which absorbs mainly red and blue light wavelengths is oxidised using the photons to excite electrons.
Accessory pigments then channel light energy towards primary pigments
This produces ATP and reduced
Explain the mechanism of the light dependent reaction. (Non-cyclic photophosphorylation)
- Photon of light is channeled through photosystem II towards the reaction centre. Photons hit chlorophyll A which excites electrons. Water is split in a process called photolysis by a water splitting enzyme in to H+ and oxygen. Each H atom splits into a photon and an e-.
- Excited electrons are accepted by an electron acceptor protein.
- Electrons lose energy as they move through a chain of e- carrier proteins. This energy is transferred to H+, which pumps them from the stroma, across the thylakoid membrane, into the thylakoid lumen which creates a steep proton gradient.
- H+ flow through the ATP synthase channels down their electrochemical gradient (chemiosmosis). They allowed ADP + Pi to form ATP [photophosphorylation]. e- are accepted by photosystem I =, and e- are excited by another photon to a higher energy level.
- Electrons pass through another chain of e- protein carriers, e- then recombine with H+ to form H atoms, which then are added to NADP to reduce it.
Explain the mechanism of the light-independent reaction [calvin cycle]
It occurs in the stroma and requires the product of the light-dependent reaction which are NADPH and ATP.
RuBP is used in carbon fixation where CO2 is fixated using RUBISCO to form an unstable 6carbon intermediate.
The unstable compound splits into 3 carbon compounds called GP.
ATP is hydrolysed and NADPH is oxidised into ADP + Pi and NADH+.
ADP and NADH+ are ten used to converse GP into TP another 3 carbon compound.
1/6 of TP then leaves the cycle to be converted into things like glucose, starch cellulose etc.
the other 5/6 is regenerated back into RuBP by using ADP. And the Calvin cycle repeats.
What is photolysis?
Splitting of water molecules using light energy. Catalysed by a water splitting enzyme.
Explain the mechanism of cyclic photophosphorylation.
Electrons are excited from photosystem I and are unable to be accepted by NADP.
They return to photosystem I via another chain of e- carrier.
A steep proton gradient is maintained so ATP contains to be made.
This CANNOT make NADPH.
How does light intensity affect photosynthesis?
A= as light intensity increase = photons increase and therefore excitation of electrons increases. This increases the amount of ATP formed and amount of reduced NADP.
B= LI is no longer the limiting factor regardless of it increasing as other factors such as temperature are now the limiting factor. [the graph plateaus]
How does CO2 concentration affect photosynthesis?
A= increase in CO2 = increase in rate of carbon fixation by RUBISCO.
B= other factors become limiting instead e.g. temp and light intensity. [graph plateaus]
How does temperature affect photosynthesis?
A= at low temps enzymes and substrate have limited kinetic energy and therefore are unlikely to form enzyme-substrate complexes. Then as temp increases enzymes and substrate gain kinetic energy and therefore the frequency of successful collisions increases.
B= Above optimum, active site starts to change and tertiary structure changes and therefore denaturing of enzymes and proteins occurs.
