5.7 Photosynthesis Flashcards
Where does the light dependent reaction occur
In the thylakoids of chloroplasts
Where does the light-independent reaction occur
Stroma of chloroplasts
What is the role of the thylakoid membranes in the light dependant stage of photosynthesis?
They have a large surface area with lots of ATP present to produce ATP for the light dependent reaction
What is a photosystem
Clusters of pigments
Each photosystem consists of a specialised chlorophyll molecule called the reaction centre
What happens when a photon of light hits a chlorophyll molecule?
The energy is transferred to the electrons of the molecule
The electrons are excited, and when it is at a sufficiently high energy level it will leave the chlorophyll molecule completely
The excited electron can then be picked up by an electron acceptor then enter either cyclic or non-cyclic phosphorylation
Which photosystem is involved in cyclic phosphorylation?
Photosystem I
What happens during cyclic phosphorylation?
Electron acceptor takes up excited electron and passes it directly along an ETC to produce ATP
The electron is returned to PSI
What happens during non-cyclic phosphorylation?
When a photon hits chlorophyll in PSII electrons are taken up by electron acceptor, passed along ETC chain to PSI chlorophyll
Energy released + ATP synthesised
Photon hits chlorophyll in PSI triggers photolysis
Water dissociates into H and hydroxide ions replacing lost electrons in PSII
Electrons are excited, taken up by acceptor, passed along ETC to NADP
NADP takes up an H+ ion from water and forms reduced NADP
Hydroxide ions react together to form water and oxygen
What do both types of phosphorylation prodce?
Reduced NADP
ATP
Oxygen
What is the role of the stroma in the light-independent reaction
Carbon dioxide enters through the stomata of the leaf and diffuses into the stroma
Outline the process of carbon fixation to form GP in the Calvin cycle
- Carbon is fixed when it combines with 5C ribulose biphosphate (RuBP)
- Catalysed by RUBISCO - This compound is unstable and breaks down into 2 molecules of glycerate 2-phosphate (GP)
How are reduced NADP and ATP used to synthesis GALP
ATP and NADP from the light dependent stage are used to reduce GP to form glyceraldehyde phosphate (GALP)
What is the purpose of GALP
Can be converted into many useful compounds
How is RuBP regenerated
5/6 molecules of triose phosphate produced in the cycle are used to regenerate RuBP
Converted to phosphorylation using ATP
How does light limit rate of photosynthesis?
The amount of light affects the amount of chlorophyll which is excited and therefore the amount of reduced NADP and ATP produced in the light-dependent stage of the process
