Photosynthesis Flashcards
What are adaptations of thylakoids that help speed up photosynthesis?
- Folded membrane
- Embedded chlorophyll and electron carrier proteins used for LDR
- So if we have more folding = more proteins = speed up rate of LDR
What are adaptations of stroma that help speed up photosynthesis?
It is filled with all the enzymes that are part of the Calvin cycle in the LIR
Describe chlorophyll and its role
- It is a group of 5 pigments
- Each pigment absorbs a different wavelength of light
- the light energy absorbed by chlorophyll is used for photoionization
What are the 5 pigments in chlorophyll?
1) Chlorophyll a: blue green
2) Chlorophyll b: yellow green
3) Carotene: orange
4) Xanthophyll: yellow
5) Phaeophytin: grey
What is a chlorophyll absorbance spectrum?
It is a graph that shows the % of light absorbed at different wavelengths to highlight that different pigments absorb/reflect differing wavelengths
Why is there no absorption at 500-550nm?
- This is the green area on the visible spectrum
- This is not well absorbed by the pigments and the wavelength is reflected
- Therefore most leaves seem green to us
Why is it advantageous to have multiple pigments?
- Causes a wider range of wavelengths for light to be absorbed at = % absorbance is higher
- More light energy for the LDR
What are the steps of photosynthesis?
1) Light dependant reaction
2) Light independent reaction
Where in the plant cell do the photosynthetic reactions take place?
They both take place in the chloroplasts
LDR: Thylakoids
LIR: Stroma
What are the 4 stages of LDR?
1) Photoionization
2) Photolysis
3) Chemiosmosis
4) Production of ATP + NADPH
What are the products of LDR and what are they used for?
- Protons/H+ : Pumped through ATP synthase to provide energy + reduced NADP to NADPH
- Electrons : Go down electron transport chain releasing energy + replace e- in chlorophyll
- Oxygen : Used in respiration + released as waste
- NADPH : Used in LIR
- ATP : Used in LIR
Describe photolysis
- Light energy is absorbed by chlorophyll
- This splits H2O = Oxygen & H+ & e-
- H2O —> 1/2 O2 + 2e- + 2H+
- The products are released into the inter membrane space and used in further photosynthetic processes
Describe photoionization
- Light energy is absorbed by the chlorophyll in PS2
- This excites the e- and causes it to raise energy levels= leaves the chlorophyll
- Chlorophyll has been ionized
- This electron will now go through chemiosmosis
Describe chemiosmosis
- The e- that leave the chlorophyll are picked up by proteins that are embedded in the thylakoid membrane
- It is carried along an electron transfer chain
- Every time the e- moves from protein-protein this releases energy = energy used to activity transport/pump H+ from stroma to IMS
- The pumped H+ and H+ from photolysis both create high concentration of H+ on IMS
- This creates electrochemical gradient = facilitated diffusion through ATP synthase
- Diffusion causes change in shape = provides energy for catalysing ADP + Pi—> ATP
- NADP in the stroma picks up the diffused H+ and an e- from end of ETC to make NADPH
Describe the Calvin cycle
- CO2 from the atmosphere reacts with RuBP catalyzed by Rubisco into 2 GP (3cs)
- GP is reduced into 2 TP by using the energy provided by ATP and an H+ from NADPH
- Carbon leaves TP every cycle to convert into useful organic substances
- After 6 cycles a hexose sugar can be produced
- The rest of the carbon is regenerated into RuBP using energy from ATP
