Photosynthesis Flashcards
What are the colors of wavelengths moving from left to right (350-750nm)
purple, blue, green, red
When does chlorophyl a peak?
between 350-450 nm
When does chlorophyl b peak?
between 450 and 500 nm
Which chlorophyll absorbs morel lightt between 600 and 700nm(orange/red?
Chorophyll a
Where do both chlorophyll a and b barely absorb?
500-650nm because its green
What is the difference between action and absorption spectrums?
Both have wavelength on the x- axis.
Action spectrum has photosynthetic rate on the y
Absorption spectrum has amount of absorption on the y
What is the first step in photosynthesis?
photoactivation- light dependent reaction
Steps in photosynthesis
photoactivation
photolysis
Election transport chain
chemiosmosis
reduction
Explain photo-activation
When light is absorbed by one of the many pigments in photosystem II
1) energy is passed from pigment to pigment until it reaches the rxn center
2) at the rxn center an electron in the reaction center is (releases electrons) and moves to a higher energy level
3) this high-energized electron is passed to an electron acceptor molecule(part of photosystem II) which passes the e- through the ETC
The “chlorophyll a” molecules(rxn center) lose electrons, are oxidized
The primary electron receptor gains electrons and is “reduced”
Why are electrons excited?
So that they can leave the pigment molecule and move through the ETC
What is a phostosystem?
A large complex of protein and pigments embedded in the thylakoid membrane
What is the reaction center?
A special pair of “chlorophyll a” molecules found at the center of the photosystem.
define photoactivation
light is used to energize electrons and pass them on into the electron transport chain
at what wavelength does photosystem II mainly absorb light?
680nm
at what wavelength does photosystem I mainly absorb light?
700nm
Where do light-dependent reactions take place?
In the thylakoid membrane of the chlorophyll.
What is the second step in photosynthesis?
Photolysis
Why does photolysis happen?
To generate electrons that were lost from the chlorophyll rxn center
To create a proton gradient using the H+
Oxygen is a byproduct of this
Explain the main idea of photolysis
Using the energy of light, water is split into electrons and protons, and oxygen as a byproduct
Explain the steps of photolysis
Splitting water using the energy of light:
H_2O -> 2e- + 2H+ 1/2 O
or
2H_2 O -> 4e- + 4H+ + O
The protons (H+) accumulate in the thylakoid lumen and create a proton gradient used for chemiosmosis.
The e- replaces the lost electrons from the ETC
Explain the electron transport chain
The high energy electron moves between electron transport molecules in the thylakoid membrane. This movement drives the pumping of H+ ions from the stroma across the membrane and into the thylakoid lumen, creating an H+ gradient.
The main idea of the ETC
electrons are passed between electron transport molecules in a series of oxidation-reduction reactions, creating an H+ gradient.
The electrons are oxidized as they release energy for the gradient. The electron transport molecules are reduced.
The etc reached PS I where it makes up for the e- lost.
What happens after the ETC?
Chemiosmosis and ATP synthesis
What allows the “passive” manufacture of ATP?
The photolysis of water(splitting) and the pumping of H+ across the thylakoid membrane during the ETC.
What is chemiosmosis
The facilitated diffusion of protons along their concentration gradient through the protein ATP synthase.
Explain chemiosmosis via ATP synthase.
There is a build-up of H+ ions in the thylakoid lumen. This causes the ions to follow their proton gradient through ATP synthase. As the “wheel” of the protein turns, ADP is passively phosphorylated through earlier derived energy from light.
What is phosphorylation?
The addition of a phosphate into ADP, creating ATP, using energy derived from light.
What is the last step in light-dependent reactions of photosynthesis?
The reduction of NADP+ to form NADPH
NADP+ has low energy and is waiting to be reduced into the high-energy NADPH
What is NADP?
It is an electron-carrier molecule
Explain the reduction of NADP+ to NADPH
The electrons that were excited from the reaction center of photosystem I are passed through a series of electron carriers until it reaches the electron carrier molecule NADP. NADP gains electrons (“ is reduced”) and becomes NADPH. This will be used in light-independent reactions..
What do light-dependent reactions produce?
NADPH, ATP and oxygen.
What is the reaction for photosynthesis?
6CO_2 + 12H_2O -> light and chlorophyll -> C6H12O6 + ATP
What is the first step in light-independent reactions( the calvin cycle)?
Carbon fixation
What is the “equation” for carbon fixation?
5C + 1C -> 6C -> 2x3C
What is carbon fixation?
Adding the carbon from an inorganic molecule(CO2) to an organic compound
Why does carbon fixation occur?
To form carbohydrates, which fuel the entire food chain.
Where do all light-independent reactions occur?
In the stroma of chloroplasts.
Explain carbon fixation.
CO2 diffuses into the plant via stomata into the stroma.
CO2 is added to the 5C molecule RuBP (RuBP is carboxylated). It is now a 6C molecule and was FIXATED to the 5C via the enzyme Rubisco(catalyses attachment of CO2 to RuBP(5C)). This 6C immediately splits into two 3C’s called 3-PGA because the 6C is unstable. This requires ATP from the light-dependent reaction, so ATP undergoes hydrolysis and loses phosphate.
What is the addition of a CO2 called?
Carboxylation
What is cyclic photophosphorylation?
It only uses PS I electrons, ETC, and then gradient to produce ATP.
What is non-cyclic photophosphorylation?
It uses both photosystems and involves the reduction of NADP to NADPH. Does not need photolysis as lost electrons from PSI are replaced by those from the ETC from PS II
What replaces electrons lost from Photosystem II?
Photolysis
What are the 3C molecules called which form after carbon fixation?
3- PGA
Why do two PGAs form after the carboxylation of RuBP?
Because the 6C is unstable.
What is a carboxylase enzyme?
Ann enzyme that adds CO2 to another molecule.
What is another word for light independent reactions?
The Calvin cycle.
What is the recond step in the calvin cycle?
Reduction
What is a reduction in simple words?
The reduction of PGA to triosphosphate G3P using ATP and NADH as energy sources.
Explain reduction more thouroughly.
The two 3C molecules “PGA” are reduced (given electrons) by NADPH, now NADP because it was oxidized. PGA’s are converted to the 3C molecules G3P. We now have two of them, one of them is taken to contribute to the build of sugar, the other is recycled to regenerate RuBP.
What 3C molecule is PGA turned into in reduction?
G3P
Explain regeneration in the Calvin cycle.
G3P molecules either build sugars or stay in the cycle to regenerate RuBP. Once 6 G3Ps build up in the cycle, 1 RuBP molecule created and can be reused in carbon fixation. The one 3C molecule can build 1/2 of a sugar molecule.
Give me 3 examples of oxidation.
Oxygen is added
Electrons are lost
Hydrogens are lost
Give me 3 examples of reduction.
Electrons are added
Hydrogens are added
Oxygen is removed
Why is adding oxygen oxidation?
Because oxygen has a negative charge and makes the energy of the particle less.
What is the overall reduction in Photosynthesis?
CO2 is reduced to sugar
What is the overall oxidation in photosynthesis?
Water is oxidized to molecular oxygen
Who discovered light-independent reactions?
Calvin
What was the experiment called where Calvin discovered light-independent reactions?
Lollipop experiment
What did Calvins flask contain?
The single-celled green protocist “Chlorella”
What did Calvin and his co-workers want to find out?
How carbon was fixated into organic substances by plants.
What type of radioactive carbon was used in Calvins experiment?
C14
Explain the lollipop experiment.
The single celled protocist “Chlorella” was put into a lollipop-shaped flask. The flask was lighted on eaach side. After enteriing the Chlorella solution, Calvin took the radioactive carbon and inserted it as well. After 2 seconds he took is first sample and put in into hot methanol, after that in a few more short samples. The samples were seperated using two-way chromatography paper which was then covered using photgraphy film. This was left in the dark for a few days. The radioactive carbon left spots on the paper which allowed calvin to see where it was. Each chromatography paper was cut out and analyzed to see which substance made each spot.
