5.6 PHOTOSYNTHESIS Flashcards
Structure of the chloroplast
What are thylakoids in the chloroplast?
- Folded membranes which contain photosynthetic pigment (chlorophyll) and photosystems
What is stroma in the chloroplast?
- fluid centre of the chloroplast with RUBISCO enzymes
What is the grana in the chloroplast?
- stacks of thylakoids
What is the outer membrane of a chloroplast?
- Highly permeable membrane that controls the entry/exit in chloroplast
What is a photosystem and where are they located?
- Photosystems are a bunch of photosynthetic pigments found in the thylakoids
What is meant by a photosynthetic pigment?
- Different pigments that absorb specific wavelengths of light
What are *accessory pigments**, where are they based in photosystems and what do they do?
- Chlorophyll B/ Carotenoids
- Light harvesting system
- Light energy absorbed is passed to the reaction centres
Where is the *primary pigment**, where is it based in photosystems and what does it do?
- Chlorophyll A
- Reaction centres
- Where light dependant stage happens
State the Rf value equation
Where does the light-dependant stage occur?
- Thylakoids
What reactions does the light-dependant stage consist of? (4)
1) Non-cyclic photophosphporilation
2) Cyclic photophosphporilation
3) Photolysis
4) Chemiosmosis
What two things are produced by the light-dependant stage?
- ATP
- Reduced NADP/NADPH
Name the two photosystems used in the light-dependant stage.
- PSII (used first) and PSI (used after)
Describe non-cyclic photophosphporilation
- Light energy absorbed by photosynthetic pigments causes electrons in the reaction centre chlorophyll of PSII to become excited & released to electron carriers
- Electron carriers combine with electron (to become reduced to Fe2+ then donates the electron to next electron carrier to become re-oxidised to Fe3+) which moves excited electrons along the electron transport system to PSI
- The movement of electrons through the electron transport chain results in ATP production at the end via chemiosmosis
- Electrons lost from the reaction centre chlorophyll of PSII are replaced by electrons from photolysis and electrons lost from reaction centre chlorophyll of PSI are replaced by electrons from PSII
- At PSI reaction centre the electrons are released and accepted by the coenzyme NADP along with H+ protons from photolysis to produce reduced NAPD (NADPH)
Describe cyclic photophosphporilation
- Some electrons released from the reaction centres of PSI are not picked up by the coenzyme NADP and are instead recyled back into PSI
- The movement of electrons along the electron transport chain still results in ATP production by chemiosmosis
- However reduced NADP (NADPH) is not produced
Describe photolysis
- Light energy absorbed by chlorophyll in PSII is used (along with an enzyme) to split water into oxygen, H+ and e-
- The H+ proton is picked up by NADP to produce reduced NADP (NADPH)
- The electron from this replaces the electrons lost from the reaction centre chlorophyll of PSII
- The oxygen is used for respiration or diffuses out the leaf
Describe chemiosmosis
- When excited electrons move along the electron transport chain through the embedded electron carriers in thylakoid membrane energy is released
- Some of this energy is used to pump H+ protons from photolysis across the thylakoid membrane from the stroma to the thylakoid space
- This creates an electrochemical gradient as many H+ protons are now in the thylakoid space
- As a result, H+ protons diffuse down the electrochemical gradient, back across the thylakoid membrane through the enzyme ATP synthase
- When H+ protons pass through, ATP synthase converts ADP + Pi into ATP
- The H+ protons now combine with the coenzyme NADP to form reduced NAPD (NAPH)
Draw and describe the calvin cycle
The three limiting factors of photosynthesis?
