11.2- THE LIGHT-DEPENDENT REACTION Flashcards
What does LDR of photosynthesis involve?
capture of light
What is the light captured from LDR used for? (2)
to add an inorganic phosphate (Pi) molecule to ADP, thereby making ATP
split water into H+ ions (protons) + OH- ions
as splitting caused by light, known as photolysis
What is oxidation?
when substance gains oxygen or loses hydrogen
What is reduction?
when substance loses oxygen or gains hydrogen
In practice, what is oxidation and reduction?
oxidation- lose of electrons
reduction- gains electrons
What is done to energy due to oxidation?
energy given out
What is done to energy due to reduction?
energy taken in
What happens to a pair of electron when a chlorophyll molecule absorbs light energy?
boosts energy of a pair of electrons within chlorophyll molecule, raising them to higher energy level
When a chlorophyll molecule absorbs light energy and it boosts the energy of a pair of electrons within the chlorophyll molecule, what is the electrons said to be in?
said to be in excited state
As the pair of electrons from the chlorophyll molecule become so excited, what happens?
they leave chlorophyll molecule altogether
As the pair of electrons become so excited and leave the chlorophyll molecule altogether, what happens to the chlorophyll molecule?
chlorophyll molecule becomes ionised + so process called photoionisation
What happens to the electrons that leave the chlorophyll molecules?
taken up by molecule called electron carrier
Is the chlorophyll molecule oxidised or reduced as it has lost a pair of electrons?
oxidised
Is the electron carrier oxidised or reduced as it has gained electrons?
reduced
What do the electrons do as they have left the chlorophyll molecule and have been taken up by the electron carrier?
electrons now passed along number of electron carriers in series of oxidation-reduction reactions
What do the electron carriers form and where?
form transfer chain that’s located in membranes of thylakoids
What position is each new electron carrier than the previous one?
at slightly lower energy level than previous one, and so electrons lose energy at each stage
What is some of the lost energy from the electrons as it passes down the electron transfer chain used for?
used to combine inorganic phosphate molecules with ADP molecule to make ATP
By which theory can the precise mechanism by which ATP is produced be explained by?
chemiosmotic theory
What is each thylakoid and what is pumped into it? #1 chemiosmotic theory
each thylakoid is an enclosed chamber into which protons (H+) pumped from stroma using protein carriers in thylakoid membrane called proton pumps
Where does the energy to pump protons from the stroma using protein carriers in the thylakoid membrane called proton pumps come from? #2 chemiosmotic theory
energy to drive process comes from electrons released when water molecules split by light- photolysis of water
What does the photolysis of water also produce, other than electrons #3 chemiosmotic theory
protons which further increase their conc. inside thylakoid space
What does the protons from the photolysis of water increasing their conc. inside the thylakoid space do? #4 chemiosmotic theory
creates + maintains conc. gradient of protons across thylakoid membrane with high conc. inside thylakoid space + low conc. in stroma
Where can the protons cross through? #5 chemiosmotic theory
protons can cross thylakoid membrane through ATP synthase channel proteins- rest of membrane permeable to protons
these channels form small granules on membrane surface so also known as stalked granules
What do the protons do to the ATP synthase as they pass through them? #6 chemiosmotic theory
cause change to structure of enzyme which then catalyses combination of ADP with inorganic phosphate to form ATP
When light strikes the chlorophyll molecule and it loses electrons, what is it short of?
short of electrons
After the chlorophyll molecule has lost electrons has been lost, what must be done for it to continue absorbing light energy?
these electrons must be replaced
How are the replacement electrons for the chlorophyll molecules provided?
from water molecules that are split using light energy
Equation for photolysis of water
2H20 -> 4H+ + 4e- + O2
When the protons from the photolysis of water pass through the ATP synthase channels what happens to them after?
taken up by electron carrier called NADP
What happens when the NADP take up the protons?
become reduced
What is the main product of LDR and what happens to it?
reduced NADP and it enters LIR taking with it the electrons from chlorophyll molecules
Why is the reduced NADP important?
as it’s a further potential source of chemical energy to the plant
What happens to the oxygen by-product from the photolysis of water?
either used in respiration or diiffuses out of leaf as waste product of photosynthesis
Where does LDR happen?
in thylakoids of chloroplasts
What are the thylakoids?
disc-like structures that are stacked together in groups called grana
How are chloroplasts structurally adapted to their function of capturing sunlight + carrying out LDR? (4)
thylakoid membranes provide large SA
network of proteins in grana
granal membranes have ATP synthase channels within them
chloroplasts contain both DNA + ribosomes
How is the thylakoid membranes providing a large SA an adaptation for chloroplasts?
large SA for attachment of chlorophyll, electron carriers and enzymes that carry out LDR
How is a network of proteins in the grana an adaptation for chloroplasts?
network of proteins in grana hold chlorophyll in very precise manner that allows maximum absorption of light
How is the granal membranes having ATP synthase channels within them chloroplasts an adaptation for chloroplasts?
they catalyse production on ATP
also selectively permeable which allows establishment of a proton gradient
How is the chloroplasts containing both DNA + ribosomes an adaptation for chloroplasts?
so they can quickly + easily manufacture some of the proteins involved in the LDR
