3.5.1 Photosynthesis Flashcards
Of PS1 and PS2, which is at a higher energy level?
PS1
Which photo system undergoes cyclic photo-phosphorylation?
Photo system 1
What is the process of the electron transport chain in cyclic photo-phosphorylation?
Light enters PS1
Some electrons are excited
These are elevated to a higher energy level
This is oxidation as electrons are lost from the chlorophyll
Electronic carrier gains electrons (reduction)
Electrons move from one carrier at a higher level to one at a lower one
This releases energy
Electron moves back into PS1
How is ATP formed during cyclic photo-phosphorylation?
Energy is created by electrons in redox reactions
The energy released is used to phosphorylate ADP to form ATP
What is the product of cyclic photo-phosphorylation?
ATP
What is the process of non-cyclic photo-phosphorylation?
Occurs at the same time as cyclic Occurs in PS2 PS1 is oxidised Electrons pass down the electron transport chain The energy is used to make ADP Final acceptor is NADP Produces reduced NADP
Why is the process in PS2 non-cyclic?
The chlorophyll did not replace the electrons as it is non-cyclic
Where does PS2 recieve it’s electrons from?
From water
Light can split water in a process called photolysis
Forms oxygen and two hydrogen ions
Hydrogen ions lose electrons which then move into the chlorophyll
What are the products of non-cyclic photo-phosphorylation?
ATP and NADP
Where is the light absorbed in the leaf?
Most is absorbed by the palisade layer
Some is absorbed by the spongy mesophyll
Some moves all the way through
The waxy cuticle and upper epidermis reflects green light
What is photosynthesis?
A process used to convert light energy into chemical energy that can be used to fuel the organism’s activities
What is chlorophyll?
A group of 5 pigments
Why do plants appear green?
The chlorophyll pigments absorb very little green light
Where does photosynthesis occur?
In the photosystem of the thylakoid membrane
Where does light need to reach for photosynthesis?
The reaction centre of the photosystem
What light does each photosystem absorb?
PS1: 700nm
PS2: 680nm
What is a stroma lamellae?
A bridge between two thylakoids on adjacent grana
Where are chlorophyll pigments contained?
In the grana
What is the thylakoid space?
The fluid within the thylakoid membrane
What is a thylakoid?
A flat disc containing of a thylakoid membrane and thylakoid space
What does the double chloroplast membrane consist of?
An outer and inner membrane seperated by an intermembrane space
What is the labelled structure of the reaction centre in chloroplasts?
See card
What are the three main stages of photosynthesis?
Capturing light energy
The light dependent reaction: photolysis, produces NADP + ATP + oxygen, cyclic and non-cyclic
Light independent reaction: protons are used to produce sugars
What is the purpose of the light dependent reaction?
To add Pi to ADP to form ATP
To split water into H+ ions and OH- ions, known as photolysis
What is it called when a substance gains electrons?
Reduction
What is it called when a substance loses electrons?
Oxidation
What is the process involving PS1?
Light enters PS1
Some electrons are excited
These are elevated to a higher energy level
The chlorophyll is oxidised as the electrons are lost
The electrons are taken up by an electron carrier
The electrons move along the electron transfer chain in a series of oxidation reduction reactions from high level electron carriers to increasingly lower ones
This releases energy
After many jumps, the electrons move back into PS1
Where is the electron transfer chain found?
In the thylakoid membrane
Why is PS1 cyclic?
Because the electrons move into PS1 via the electron transport chain
PS2 is non-cyclic as the electrons are not returned
How is the light-independent and light-dependent reaction linked?
NADP and ATP from the light-dependent reaction are used to fuel the light-independent reaction
What happens to reduced NADP in the calvin cycle?
It is oxidised by GP
It is then reformed and sent back to the light dependent reaction to be reduced again
What is the reaction for the hydrolysis of ATP?
ATP = ADP + Pi ( + energy )
What is the full name of GP?
Glycerate 3-phosphate (3C)
How is RuBp converted into GP?
Carbon dioxide is added
CO2 + RuBp = GP
Catalysed by the enzyme rubisco
What is the full name of RuBp?
Ribulose biphosphate (5C)
Where is CO2 obtained from the calvin cycle?
It comes from the air which diffuses into the leaf then into the stroma of the chloroplast
What are the stages of the calvin cycle?
RuBp
\+ CO2
GP x2
ATP = ADP + Pi
RedNADP = NADP
TP x2
Either: organic substances
Or: ATP = ADP + Pi
RuBpWhich photo system is at a higher energy level?
PS1
What is the term for when the chlorophyll loses electrons?
It becomes photoionised
What is the splitting of water called?
Photolysis
What causes photolysis?
Light energy absorbed by the chlorophyll
How does photolysis fuel photosynthesis?
2H2O = 4H+ + 4e- + O2
H+: reduces NADP which then goes into the calvin cycle or moves through ATP synthase channels to produce ATP
e-: goes into PS2 to fuel the electron transport chain
O2: released into the air
What is the process of PS2?
Electrons from the photolysis of water move into PS2
Light enters PS2
These electrons are excited
There are elevated to a higher energy level
The chlorophyll is oxidised as the electrons are lost
The electrons are taken up by an electron carrier
The electrons move along the electron transfer chain in a series of oxidation reduction reactions from high level electron carriers to increasingly lower ones
This releases energy
What is the full name of TP?
Triose phosphate (3C)
What happens to the energy created by the electron transport chain in PS2?
The energy fuels a proton pump which actively transports protons across the thylakoid membrane using energy from the electron transfer chain
The photolysis of water also increases the concentration of H+ ions in the thylakoid membrane
These ions diffuse down the concentration gradient out of the thylakoid membrane through ATP synthase channels
They are forced through these channels as the rest of the membrane is impermeable
As they move through, the channel changes structure which catalyses the combination of ADP and Pi to form ATP
After going through the channel, the ions reduce NADP which moves into the light independent reaction
What are the processes including NADP?
Reduced by electrons from the PS2 electron transport chain
Reduced by hydrogen from the photolysis of water
Is oxidised by the formation of TP from GP
How is RuBp formed from TP?
ATP is hydrolysed
Most of TP is used to reform RuBp
Where does the proton pump operate between?
It is located across the thylakoid membrane
It pumps protons from the stroma to the thylakoid space
How is TP formed from GP?
GP is reduced by ATP and RedNADP
ATP is hydrolysed
RedNADP is oxidised
How is GP formed from RuBp?
CO2 reacts with RuBp
Catalysed by the enzyme rubisco
