Photosynthesis Flashcards
Where does LDR take place?
Thylakoid membranes of the chloroplast
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
How do electrons get to the PSI?
Light is absorbed by PSII
Light excites electrons in PSII and causes them to move to higher energy state
electrons passed onto electron carriers in the transport chain to PSI
How are lost electrons replaced?
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 is chemiosmosis?
protons flow down concentration gradient through ATP synthase
Energy from movement of protons is used for photophosphorylation
ADP -> ATP
What is non-cyclic photophosphorylation?
Light absorbed by PSI causes another electron to become excited and passed along the rest of electron transport chain
electron is passed onto NADP to form reduced NADP
reduced NADP is an electron carrier which transfers electrons between molecules
ATP and reduced NADP move into stroma for next stage of photosynthesis
explain cyclic photophosphorylation
Electrons leave PSI
instead of being accepted by NADP they flow down to first electron acceptor
ATP is produced but no reduced NADP
may happen when reduced NADP is in plentiful supply
more common in plants with high ATP demands
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 is fixed by adding a 5-carbon molecule called ribulose biphosphate (RuBP)
catalysed by Rubisco
The 6C molecule is unstable and breaks down to form two 3C compounds called glycerate-3-phosphate (GP)
What is reduction?
an isomerisation reaction which converts GP into another 3C compound called glyceraldehyde-3-phosphate (GALP)
this reaction requires energy so ATP is hydrolysed into ADP
reaction requires electrons form reduced NADP which transfers electrons to GP to produce GALP
some GALP is converted to organic molecules
some used to regenerat RuBP
for every 6 GALP:
- 5 for RuBP regeneration
- 1 for organic molecules
What is regeneration?
GALP is coverted back into RuBP - requires energy from hydrolyses of ATP
The cycle is completed and carbon fixation can happen again
How does temperature affect the rate of photosynthesis
higher temperatures mean faster rate because enzymes have more kinetic energy so collide more frequently
If temperature is too high then rate decreases as enzymes denature
How does light affect rate of photosynthesis?
higher light intensity means faster rate because light energy is required to produce ATP and NADPH in LDR
Low ATP + NADPH means that less GP and TP is produced in the calvin cycle
How does carbon dioxide affect rate of photosynthesis?
Higher concentration means higher rate because carbon dioxide is a reactant in carbon fixation with RuBP
With less CO2, there is more RuBP so less TP and GP produced
