Photosynthesis Flashcards
What’s the relationship between photosynthesis & respiration
Products of one = raw materials of the other
Photosynthesis = (exothermic / endothermic) vs respiration = (endothermic / exothermic)
Photosynthesis = endo
Respiration = exo
What’s a ‘compensation point’
Where no net fain / loss of CO2 etc
Rate of photosynthesis = rate of respiration
Chloroplast structure
What’s special about the outer membrane of the chloroplast
Highly permeable to ions / small molecules
What does the inner membrane of chloroplast have (what type of proteins)
Transport, which control flow of molecules between the stroma and the cytosol
What is the stroma, what happens in it, what does it contain
The fluid filled matrix of the chloroplast
- when the light independent sgage occurs
Has:
- enzymes required for light independent stage
- starch grains
- small ribosomes
How is the stroma adapted for its function?
Surround the granum & thylakoid membrane so products of the LDS can be easily & rapidly passed to stroma for the LIS
- it also contains enzymes required for the LIS
What are thylakoids, what occurs in them, & what do they contain
They’re flattened, membrane bound, fluid-filled sacs (folded from thylakoid membranes)
- they contain photosynthetic pigments in photosystems
- where the light dependent state occurs
Where they occur: LDS vs LIS
LDS - thylakoid membranes of the thylakoid in granum
LIS - stroma
What are the granum & how are they adapted
A stack of thylakoids
- these stacks create a large SA to ensure maximum light absorption
Connected together by lamellae
Photosystems are in the thylakoid: what are these & whats their significance
Funnel shaped structures
Antenna complex of photosynthetic pigments
Surrounding chlorophyll A reaction centre
Held in place by proteins embedded in the grana
-> they absorb light energy in a wide range of wavelengths + their arrangement allows for maximum absorption of it, so they can excite the electrons
Photosynthetic pigments examples
Carotenoid
Chlorophyll a & b
Xanthophyll
Absorption peak of PS1 vs PS2
PS1 = 700 nm (but comes after)
PS2 = 680nm (but comes first)
Stages of the light dependent stage in the thylakoid membrane
- Light harvested in photosystems
- Photolysis of water
- Photophosphorylation
- Reduction of NAD
Stage 2 LDS: photolysis of water: what occurs
The splitting apart of water in the presence of light & an enzyme to form:
2H2O -> 4H+ + 4e- + O2
What is photophosphorylation in the lds
The production of ATP from ADP + an inorganic phosphate group
In the presence of light
How are electrons passed along the ETC using iron ions
- captured by electron carrier
- iron ion in the e- carriers accept the e- to be reduced to Fe2+
- Fe2+ then donates the e- to the next electron carrier in chain & is deoxidised to Fe3+
What is an electron carrier
- proteins embedded in the thylakoid membrane
- contain an iron ion which is constantly reduced & oxidised to pass an e- along the ETC
LDS diagram simple
Light dependent stage diagram. Plz familiarise
Light dependent extra notes: what happens before the 1st ETC
- Light energy absorbed by PSII
-> PSII gives off electrons
Electrons from it, enter the first ETC
e- lost in PSII are replaced by e- formed from the photolysis of H2O
Light dependent extra notes: what happens during the 1st ETC
- Electrons from PS2 passed along 1st ETC, releasing energy
- Energy transferred to proteins
- Proteins use energy to pump H+ ions from stroma into the thylakoid space by active transport
- Photolysis of water occurs in thylakoid space
- H+ ions are released into the space
- So a lower pH & higher H+ conc there, so a conc gradient is created
- Chemiosmosis occurs- H+ ions pass through ATP synthase, down the conc gradient, across partially permeable thylakoid membrane by facilitated diffuse
- H+ ions provide energy for ATP synthase to produce ATP from ADP phosphorylation
- Electrons leave the ETC
What happens after the electrons leave etc 1
Non cyclic or cyclic photophosphorylation
Cyclic vs non cyclic photophosphorylation
Cyclic don’t product NADPH
Cyclic = only PS1 involved
What happens in non cyclic photophosphorylation
Electrons enter PS1
light energy is absorbed by PS1
PS1 gives off e-
E- enters 2nd ETC
E- reduce NADP from stroma to NADPH via NADP reducers
Products = oxygen, ATP & NADPH
Products of non-cyclic photophosphorylation
Oxygen
ATP
NADPH
What happens in cyclic photophosphorylation after PS1 gives off e-, and that e- enters the 1st ETC
E- release energy to transport proteins as repassed along ETC 1
Then re-enter PS1
Proteins actively pump H+ ions into the thylakoid space (active transport)
Chemiosmosis
H+ enters stroma & give ATP synthase energy
ADP + Pi -> ATP
Cyclic photophosphorylation occurs in times of […] light intensity
High
Why does cyclic photophosphorylation only use ETC 1
Can’t accept an more e- after as all the ETC proteins have been reduced
Calvin cycle (LIS) reactants
ATP
NADPH
CO2
Calvin cycle products
Complex organic molecules e.g. starch/sucrose etc
Stages of the Calvin cycle
- Carbon fixation stage
- Reduction stage
- Regenation stage
Explain LIS
3C
3C
5C
LIS MOLECULES
3C - GP
3C - TP
5C - RuBP
The Calvin cycle is light independent but only runs in the daylight… why? What does it need
- a continuous supply of ATP & NADPH
# conc of Mg ions increases in daylight - RuBisCo also activated by extra ATP in stroma
When H+ ions are pumped from the stroma -> to thylakoid space, pH raises to around 8, which is optimum pH for RuBisCo
What happens in stage 1 of the Calvin cycle : carbon fixation
CO2 reacts with RuBP (catalysed by RuBisCo)
- RuBP accepts a -COOH groups (becomes carboxylated)
- unstable, 6C intermediate formed
This intermediate immediately splits into 2 GP (3C molecules)
What happens in stage 2 (the reduction stage) of the Calvin cycle (what happens to the 2 GP molecules)
- GP reduced to TP, by ATP & NADPH
- TP, ADP, & an inorganic phosphate group & NADP are formed
ATP = provides energy
NADPH = reducing agent
What happens in the regeneration stage of the Calvin cycle ( to the 3 TP)
- TP used to regenerate RuBP (using energy from ATP)
- ADP, inorganic phosphate group, and RuP formed
- RuP reacts wiry the phosphate group, using the energy, to form RuBP
Why are Mg ions important in the Calvin chcle
Mg ions act as a cofactor for Rubisco
They attach to its active sites to activate it
Factors affecting photosynthesis
Temperature
CO2 conc
Water stress (stomatal closure)
Light intensity
How does light intensity affect photosynthesis
How does carbon dioxide affect photosynthesis
How does water stress, leading to stomatal closure affect photosynthesis
How can temperatures from 25-30°C affect photosynthesis
How do temperatures above 40°C affect photosynthesis
