Process of Photosynthesis (HL) Flashcards
(21 cards)
What are the 2 main stages of photosynthesis?
Light dependent reaction, which relies on light directly
The light-independent reaction, which does not use light directly
Describe the structure of thylakoids and the thylakoid membrane
They are disc like structures that stack up to 100 to form grana, they also contain chlorophyll.
Where do light dependent reactions take place?
Where do light independent reactions take place?
Light dependent: In thylakoid intermembrane space across thylakoid membranes
Light independent: In the stroma of chloroplasts
What is an electron carrier used in photosynthesis? What is its regular and reduced form
NADP+
When NADP+ accepts protons it becomes reduced into NADPH
Describe the process of light dependent reactions in detail
Light dependent reactions convert light energy into chemical energy in the form of ATP and reduced NADP
ATP and NADP are produced from the photolysis of water
When water undergoes photolysis, it is split into oxygen, electrons and protons
Protons are picked up by NADP, which reduces it to NADPH
ATP is formed from the phosphorylation of ADP
The useful products from the light dependent reactions are transferred to light independent reactions
Oxygen is given as a waste product
What are photosystems and what do they contain?
Photosystems are structures where many photosynthetic pigments such as chloroplasts are grouped together.
They contain these pigments and a reaction center
What are the types of photosystems and how do they differ?
Photosystem I and Photosystem II
Photosystem I contains the reaction center P700, which is activited by light of wavelength 700
Photosystem II contains the reaction center P680, which is activated by light of wavelength 680
Describe what happens in Photosystem II in detail
Chlorophyll absorbs light energy in the form of photons and pass it to the reaction center P680
The chlorophylls in the reaction center are then said to be photoactivated
Electrons in the reaction center become “excited” to a higher energy level because of the photons of light
The excited electrons are now capable of being donated to an electron acceptor called plastoquinone in a reduction reaction
Plastoquinone accepts 2 electrons from Photosysetm II and is reduced, it then moves to another position in the thylakoid membrane
The process repeats with another plastoquinone molecule, and in total 2 plastoquinone molecules are reduced and 4 electrons are lost
What is plastoquinone?
An electron acceptor in the light dependent reaction
When does photolysis occur in light dependent reactions and what happens in it?
It occurs following the reduction of plastoquinone in Photosystem II
It produces oxygen protons and electrons:
The oxygen diffuses out of the leaf through stomata
The electrons are passed into the electron transport chain
The protons are picked up by the carrier molecules NADP forming reduced NADP
Photolysis is needed to replace electrons lost in photosystem II
What is Photophosphorylation?
It is the overall term for the process of using light energy and the electron transport chain to generate ATP from ADP4
Where does the electron transport chain occur in plants?
Thylakoid membranes
Describe the electron transport chain in photosynthesis in detail?
Reduced Plastoquinone is carrying 2 excited electrons from the end of photosystem II
Plastoquinone carries the electrons to the start of a chain of electron carriers
The electron carries undergo constant redox reactions as they lose and gain electrons
As this happens the excited electrons gradually lose their energy which generates a proton gradient, their excitation falls until the electrons are picked up by the reaction center of photosystem I
NADP is then reduced by these electrons and passed to light independent reactions
The pathway of electrons is linear, photophosphorylation is referred to as non-cyclic photophosphorylation
ATP and reduced NADP are the main products of photophosphorylation and are passed to light independent reactions
How is the proton gradient formed?
Electrons are passed from carrier to carrier, releasing energy gradually in the process, this energy powers the pumping of protons and forms a proton gradient because of protons accumulating in the intermembrane space
Outline Chemiosmosis in photosynthesis
Protons travel down their concentration gradient through the membrane protien ATP synthase
ATP synthase synthesizes the phosphorylation of ADP to ATP
Outline briefly the reduction of NADP
Excited photoactivated electrons are passed to a protein on the outside of the thylakoid membrane called ferredoxin and reduce it
The ferredoxin and protons from ATP synthase in chemiosmosis are used to reduce NADP
NADP+ + 2H+ + 2e- —> NADPH
Reduced NADP npw moves to light independent reactions
What are the 3 main steps of light independent reactions in detail?
- Carbon fixation:
The enzyme rubisco catalyzes the fixation of carbon dioxide by combining it with a molecule of ribulose biphosphate (RuBP), a 5C compound.
This forms an unstable 6C compound that splits to two glycerate-3-phosphate (GP) molecules, a 3C molecule.
2.Reduction:
GP is reduced to triose phosphate (TP) in a reaction involving reduced NADP and ATP
- Regeneration:
RuBP is regenerated from TP in reactions that use ATP
During the cycle endergonic reactions take place that involve the hydrolysis of ATP and oxidation of reduced NADP
The light dependent reactions are sometimes referred to as the Calvin cycle
What exactly is carbon fixation?
Carbon fixation involves carbon dioxide (1C) being removed from the external environment and becoming part of the plant, and is then said to be “fixed”
Elaborate on the role of reduced NADP and ATP in light independent reactions
Energy from ATP and hydrogen from reduced NADP are used to reduce GP into a TP
What is triose phosphate used for?
Why isn’t all of it used to make useful alternative compounds for the plant?
After reduction one sixth of the triose phosphate is converted into usable products for the plant such as:
1.Hexose phosphates that are used to produce carbs
2.glycerol and fatty acids
3.Production of amino acids for protein synthesis
*The other five sixths of triose phosphate are used in the regeneration of RuBP
What is the size of a chloroplast?
2-10 micro meters
