Photosynthesis Flashcards
(17 cards)
Where does LDR take place?
Thylakoid membranes of the chloroplast
What are the main types of pigments?
Chlorophyll a - main pigment that absorbs red and blue light and reflects green
Chlorophyll b - accessory pigment found in light harvesting complexes
carotenoids - absorbs different wavelengths to chlorophyll
What are photosystems?
A cluster of pigments in the thylakoid membrane
Each photosystem has:
A light harvesting system
A reaction center - 2 chlorophyll a pigments
What is LDR and LIR?
LDR is the first stage of photosynthesis and requires light to start
LIR is the second stage and doesn’t require light but needs the products produced in LDR - occurs in stroma
How do electrons move from PSII to PSI?
Light energy absorbed by pigments in PSII
Electrons are excited and are passed onto electron carrier
Electrons are passed along ETC to the PSI
Electrons are lost and energy is lost along the ETC
How are lost electrons replaced?
in the LDR
Electrons lost from PSII need to be replaced
Done through photolysis of water
light energy causes water molecule to split and release hydrogen ions, electrons and oxygen
electrons from water replace the electrons lost from PSII
How is a proton gradient formed?
Electrons move along the transport chain form an area of high to low energy
Energy lost by electrons is used to pump hydrogen ions from stroma into the thylakoids
Proton gradient generated across thylakoid memebrane
What happens during chemiosmosis in non-cyclic photophosphorylation?
Protons diffuse down the proton gradient through ATP synthase into the stroma
This catalyzes ADP + Pi -> ATP
NADP takes up proton and electron in the stroma to become NADPH
Describe cyclic photophosphorylation
Light energy is absorbed by pigments and excites electrons in PSI only
Electrons are lost
Electrons are transferred onto electron carrier and it travels down ETC, releasing energy
Energy actively transports protons into thylakoid space
proton gradient forms and protons flow through ATP synthase to produce ATP
Electrons return to PSI and no NADPH is produced
What is the Calvin cycle?
Takes place in stroma and uses products of LDR
Reactions can be divided into carbon fixation, reduction and regeneration
What is carbon fixation?
Carbon dioxide reacts with RuBP to form unstable 6C compound
6C compound splits into 2 GP molecules
Catalysed by Rubisco
What is reduction?
GP is reduced into TP
This uses energy from the hydrolysis of ATP.
Requires H+ and electrons from NADPH
The NADP that is re-formed returns to the light-dependent reaction to be reduced again.
What is regeneration?
Most TP is converted back into RuBP using ATP
Remaining TP used to form organic molecules
The cycle is completed and carbon fixation can happen again
What are the uses of TP?
TP can be used to make:
Sucrose
Large carbs
Amino acids
Lipids
Nucleotides
How does temperature affect the rate of photosynthesis
At low temperatures:
Less energy so slower enzyme reactions so rate of photosynthesis is low
At intermediate temperatures:
Molecules have more kinetic energy so reactions are faster so rate of photosynthesis is higher
At high temperatures:
Enzymes denature so rate of photosynthesis drops
How does light affect rate of photosynthesis?
Low LE:
Limits LDR so less ATP + NADHP is produced. This slows LIR so rate of photosynthesis is low
Med LE:
More ATP and NADPH produced in LDR, more RuBP produced so more GP to TP so rate increases
High LE:
More light than needed so other factor becomes limiting
How does carbon dioxide affect rate of photosynthesis?
Low CO2:
Limits LIR as less CO2 is fixed so less GP and TP produced so rate is lower
Med CO2:
Faster production of GP and TP so rate increases
High CO2:
Other factor becomes limiting
