11.2 The light dependent reaction Flashcards
This captures light for two purposes:
. Add an inorganic phosphate to ADP to make ATP
. Split water into H+ and OH- ions in photolysis
What is oxidation
What is reduction
Oxidation is losing a hydrogen ion or gaining oxygen.
So when a substance is oxidised it loses electrons
Reduction is gaining hydrogen ion and losing oxygen.
It gains electrons when being reduced
Oxidation gives off energy whilst reduction takes it in
Process of making ATP:
What happens when chlorophyll absorbs light energy
(Photoionisation)
. It boosts the energy of a pair of electrons within this chlorophyll molecule, raising them to a higher energy level
. So electrons are now in an excited state, so they leave the chlorophyll altogether
. This ionises the chlorophyll molecule, so process is called photoionisation
What happens to the electrons that leave the chlorophyll molecule in photoionisation
Where is electron transfer chain located
. These are electrons are taken up by an electron carrier, which forms an electron transport chain
This electron carrier is reduced as it gains electrons.
.The transfer chain is located in membranes of thylakoids
. Each new carrier is at a slightly lower level than the previous so electrons lose energy at each stage
When electrons lose energy going down electron transfer chain, what is this energy used for
This energy is used for combining an inorganic phosphate molecule with ADP to make ATP
What is process of Chemiosmotic theory
. Process where ATP is produced
- Each thylakoid is an enclosed chamber into which H+ ions are pumped from the stroma with protein carriers called proton pumps.
- Energy for this comes from autolysis where electrons are released when water molecules are split by light.
It also makes H+ ions which increase their concentration in thylakoid space - This creates concentration gradient of protons across thylakoid membrane, so when the protons diffuse out they do via ATP synthase channel (because the rest of the membrane is impermeable to them).
. So when passing through ATP synthase channel they change structure of enzyme which will then catalyse combination of ADP with inorganic phosphate
What is the photolysis of water
. Loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons.
These electrons must be replaces for the chlorophyll to keep absorbing light energy
. So these electrons are provided when water molecules are split with light energy.
This photolysis also yields protons
Equation for photolysis of water
2H2O –> 4H+ + O2 + 4e-
How is NADPH made in this process
. These protons from photolysis of water are passed out of thylakoid membrane by ATP synthase.
. They are taken up by electron carrier called NADP, so it is reduced to make NADPH
This is main product of light dependent stage, and it enters the light independent reaction, taking with it the electrons from chlorophyll molecules
Why is NADPH important
What does the O2 produced do
. It is a further potential source of chemical energy to the plant
. The oxygen by product of photolysis is either used in respiration or diffuses out of leaf as a waste product
Where does light dependent reaction occur
Thylakoid membrane
How are chloroplasts adapted for photosynthesis
Surface area
Chlorophyll held in place
ATP synthase channels
DNA
- Thylakoid membranes provide large surface area for attachment of chlorophyll, electron carriers, and enzymes that carry out light dependent reaction
- Network of proteins in grana hold the chlorophyll in a precise manner allowing for maximum absorption of light
- Granal membranes have ATP synthase channels so catalyse production of ATP. They are also selectively permeable so allow a proton gradient to occur
. Chloroplasts contain circular DNA and ribosomes so can quickly manufacture some proteins required for this reaction
