5A Photosynthesis Flashcards
Where in the chloroplast does the light dependent reaction occur?
thylakoid membrane
What is the simple description of what happens during the light dependent reaction?
- makes ATP
- photolysis of water
Compare and contrast oxidation and reduction in 3 ways
oxidation
- loses e-
- loses H
- gains O
reduction
- gains e-
- gains H
- loses O
What happens when light is absorbed by psII up until the electron energy is lost?
- psII becomes photoionised, increasing the energy potential of an electron
- electron released and travels along ETC via redox reactions
- electron energy decreases during transport
What happens to the energy lost from the electron that is released by psII?
CHEMIOSMOSIS
- energy is transferred to proton pumps which move H+ ions from the stroma to the thylakoid lumen
- this creates an electrochemical gradient of H+ ions
- H+ ions return to stroma down proton gradient via ATP synthase enzyme
What kind of enzyme is involved in chemiosmosis for transport of H+ ions?
transmembrane ion ATP synthase
What is the movement of H+ ions in chemiosmosis used for?
- used to catalyse ATP synthesis
- this is called photophosphorylation
Where do the electrons from psII that have lost energy go after their transport along ETC?
- the newly de-energised electron is taken up by psI
- excited electron from psI may be transferred to an electron carrier and used to reduce NADP+
- this produces NADPH
What is NADPH needed for?
the light independent reaction
What are the electrons lost from psI replaced by?
de-energised electrons from psII
What are the electrons lost from psII replaced by?
electrons released from water via photolysis
Describe photolysis
- water-splitting
- water is split by light energy into H+ ions, oxygen and electrons
What are the products of photolysis used for in photosynthesis?
- H+ ions = used in chemiosmosis
- oxygen = released as a by product
- electrons = used to reduce NADP+ and synthesise ATP
Describe the simple outcome of the light independent reaction
- uses ATP and NADP to reduce glycerate 3-phosphate
Where does the light independent reaction occur?
the stroma of chloroplasts
Describe the first step of the calvin cycle
- co2 diffuses from the atmosphere into the leaf through the stomata and dissolves in water around the walls of the mesophyll cells
- it then diffuses through the cell surface membrane, cytoplasm and chloroplast membranes into the stroma of the chloroplast
What happens in the calvin cycle when co2 has diffused into the stroma?
- in the stroma the co2 reacts with the 5 carbon compound RIBULOSE BISPHOSPHATE (RuBP)
- this reaction is catalysed by an enzyme called ribulose bisphosphate carboxylase (aka rubisco)
What happens in the calvin cycle when co2 has reacted with RuBP?
- 2 molecules of GP are produced
What is GP?
GP is a 3 carbon compound called glycerate 3-phosphate
What enzyme catalyses the reaction between co2 and RuBP?
rubisco / ribulose bisphosphate carboxylase
What happens in the calvin cycle when 2 molecules of GP are produced?
- reduced NADP from the light dependent reaction is used to reduce GP to TP using energy from ATP
What is TP?
triose phosphate
What happens in the calvin cycle when GP has been reduced to TP?
- the NADP is reformed and goes back to the light dependent reaction to be reduced again
What happens to the TP that is produced in the calvin cycle?
- some TP molecules are converted into organic substances that plants require
- most TP molecules are used to regenerate RuBP using ATP from the light independent reaction
What kinds of substances could TP be converted into that plants require?
organic substances such as starch, cellulose, lipids, glucose, amino acids and nucleotides
