Light depdent reaction Flashcards
What does a light-dependent reaction involve?
Capture of light whose energy is used for two purposes
What are the two purposes of the light-dependent reaction?
(purpose of capturing the light energy)
- To add inorganic phosphate (Pi) molecule to ADP, thereby making ATP
- Spilt water into H + ions (protons) and OH- ions. As the spiltting is caused by light it is known as photolysis
What is oxidation?
- Loss of electrons
- Loss of hydrogen
- Or gain of oxygen
What is the reduction?
- Gain of electrons
- Gain of hydrogen
- Or loss of oxygen
What does oxidiation result in terms of energy?
Energy being given out
What does reduction result in terms of energy?
Results in energy being taken in
What is the first step of light-dependent reaction?
The chlorophyll molecule is absorbing light energy, and it boosts the energy of a pair of electrons within this chlorophyll molecule, raising them to a higher energy level. They are in an excited state
What happens to electrons in that excited state?
The electrons become so energetic (kinetic enerygy)
What is the second stage of light-dependent reaction?
Electrons are so energetic that they leave the chlorophyll molecule all together
As a result the chlorophyl molecule becomes ionised - the process is called photoionisation
What is the third stage of the light-dependent reaction?
The electrons that leave the chlorophyll are taken up by a molecule called an electron carrier
What is the fourth step of light-dependent reaction?
Having lost a pair of electrons, the chlorophyll molecule has been oxidised
The electron carriers which has gained electrons has been reduced
What is the fifth step of the light-dependent reaction?
The electrons are now passing along a number of electrons in a series of oxidation-reduction reaction
Electrons are carried from a transfer chain that is located in the membranes of thylakoids
Each carrier is at a slightly lower level than the previous one in the chain so electrons lose energy at each stage
Some of this energy is used to combine inorganic phosphate molecules with ADP molecules in order to make ATP
What is the sixth stage of light-dependent reaction?
The precise mechanisms by which ATP is produced explained by chemiosmotic theory
What is the first step of chemiosmotic theory?
Each thylakoid is an enclosed chamber into which protons (H+) are pumped from the stroma using protein carriers in the thylakoid membrane called proton pumps
What is the second step of chemiosmotic theory?
- The energy to drive this process from electrons released from water molecules are spilt by light - photolysis of water
What is the third step of chemiosmotic theory?
The photolysis of water also produces protons which further increases their concentration inside the thylakoid space
What is the fourth step of chemiosmotic theory?
Overall this creates and maintains a concentration gradient of protons across the thylakoid membrane with a high concentration inside the thylakoid space with a low concentration in the stroma
What is the fifth step of chemiosmotic theory?
Protons can only cross the thylakoid membrane through ATP synthase channel proteins - the rest of the membrane is impermeable to protons
These channels form small granules on the membrane surface and so are known as stalked granules
What is the sixth step of chemiosmotic theory?
As protons pass through these ATP synthase channels they cause changes to the structure of the enzyme which then catalyses the combination of ADP with inorganic phosphate to form ATP
What are the seventh steps of the light-dependent reaction?
Photolysis of water
water molecules are spilt using light energy
What are the eighth steps of light-dependent reaction?
protons pass out of the thylakoid space through the ATP synthase channels and are taken up by an electron carrier called NADP- makes protons reduced
oxygen by-product from the photolysis of water is either used in respiration or diffuses out of leaf as a waste product of photosynthesis
Why is photolysis used?
loss of electrons when light strikes a chlorophyll molecule leaves it short of electrons
if chlorophyll molecule is to continue absorbing light energy, these electrons must be replaced
Photolysis gives these replacement electrons and yields protons
Equation of photolysis of water - chemical
2H2O -> 4H+ 4e - + O2
Equation of photolysis of water - word
water -> protons + electrons + oxygen
Why is reducing NADP used for?
it is the main product of the light-dependent reaction and enters into the light-independent reaction taking with it the electrons from chlorophyll molecules
Why was reduced NADP important?
It is a further potential source of chemical energy to the plant
What is grana?
Thylakoids are disc-like structures that are stacked up together in groups
How are chlorplasts structurally adapted for?
Their function of capturing sunlight and carrying out light-dependent reaction of photosynthesis in following ways
How are thylakoid membranes adapted for the light-dependent reaction?
Provide a large surface area for the attachment of chlorophyll, electron carries and enzymes that carry out this reaction
How are network of proteins in grana adapted for the light-dependent reaction?
They hold the chlorophyll in a very precise manner that allows maxiumum absorbption of light
How are chloroplasts adapted having DNA and ribosomes for the light-dependent reaction?
They can easily manufacture some of the proteins involved in this reaction
What is oxygen used up as (by-product of photolysis of water)
Either used in respiration
or
diffuses out a leaf as a waste product
What is photosystems?
Made up of pigments (e.g chlorophyll) plus protein
Function - absorb light
What is electron carriers?
Proteins that transfer electrons
What is a co-enzyme?
Proteins that transfer chemical groups
What is photo-phosphorylation?
Using light energy to add a phosphate
What is an electron transport chain?
When an electron flows through proteins/electron carriers
What is photolysis?
Using light energy to spilt a molecule
(Hydrogen uses energy from water to spilt a molecule)
H20 -> light 2H+ + 2e - +0.5 O2 (unbalanced)
What type of reaction is photosynthesis?
Endothermic (requires/trap energy)
What are the two types of photosynthesis? LDP
Non-cyclic phosphorylation
Cyclic phosphorylation
What happens in both cases of cyclic and non=cyclic
- Photosystems absorb light energy
- Electrons in chlorophyll become excited
- A phosphate group is added to ADP to re-synthesise ATP
What happens to electrons at each level?
Release some energy
Used to transport H+
H+ + e- -> NADPH
Diagram of cyclic and non-cylcic
