5.7 photosynthesis Flashcards
how many stages does photosynthesis have?
two
what are the names of the two stages?
- light dependant reaction
- light independant reaction
where does the light dependant stage take place?
the thylakoid membrane of a chloroplast
what is the process of non-cyclic photophosphorylation?
1- a photon of light hits a chlorophyll molecule in PSII
2- it exites an electron to a higher energy level
3- the electron moves down the electron transport chain pulling H+ ions across the membrane into the lumen
4- in Photosystem I another photon of light re-exites the electron
5-the electron is combined with NADP to form reduced NADP
6- in order to replace the initial electron in PSII water is split (photolysis) by light
7- this releases oxygen as a waste gas and more hydrogen ions into the lumen
8- these H+ ions can then move down an electrochemical gradient via ATPsynthase which form ATP from ADP and Pi
–> this ATP, reduced NADP and oxygen are the products of this reaction
what is the process of cyclic photophosphorylation?
1- a photon of light hits a chlorophyll molecule in PSI and exites an electron to a higher energy level
2- electron is taken up by an elecrton acceptor
3- electrons move down the ETC and pulls across H+ ions
4- H+ ions create ATP through ATP synthase
5- electron returns to PSI and the cycle continues
how is cyclic photophosphorylation different to non-cyclic?
- this only happens at the end of the day when plants run out of NADP
- it involves only PSI and produces only ATP
where does the light independant stage take place?
the stroma of the chloroplast
what does this stage require?
- the products of the light dependant stage (reduced NADP and ATP)
- CO2
what are the steps of the Calvin cycle?
1- CO2 from the air combines with a 5 carbon compound called ribulose bisphosphate (RuBP) by an enzyme caled RUBISCO
2- this makes a 6 carbon molecule that splits immediatly to form two molecules of glycerate 3-phosphate (GP)
3- this is then reduced by the addition of hydrogen from reduced NADP and the energy for this is provided from ATP which are both from the light dependant stage
4- this makes two molecules of glyceraldehyde 3-phosphate (GALP)
5- most of the GALP molecules pass through a series of steps to replace the RuBP however, some is synthesised into the 6 carbon sugar glucose (USING ATP)
what is the main end product of photosynthesis?
GALP
what is GALP used for?
- used in glycolysis
- used to create glucose to be converted into disaccharides like sucrose for transport in plants or polysaccharides like starch for energy storage or cellulose for structural support
what are 3 limiting factors to photosynthesis?
- carbon dioxide
- light intensity
- temperature
how does light act as a limiting factor in photosynthesis?
if there is low light, insufficient NADPH and ATP will be produced in the light dependant reaction to allow the light independant reaction to progress at their maximum rate
how does carbon dioxide act as a limiting factor in photosynthesis?
if there is not enough carbon dioxide available for fixing in the Calvin cycle, the reactions cannot proceed at the maximum rate
how does temperature act as a limiting factor in photosynthesis?
all of the Calvin cycle reactions and many of the light-dependant reactions in photosynthesis are controlled by enzymes and so are sensitive to temperature
