5A Photosynthesis Flashcards
Chloroplast structure
flattened organelles surrounded by a double membrane. Thylakoids are stacked up into grana which are linked by lamellae
Where are photosynthetic pigments found
in chloroplasts, in the thylakoid membranes attached to protein
What wavelength does photosystem 2 absorb light at
680nm
Examples of photosynthetic pigments
chlorophyll a, chlorophyll b and carotene
What is a photosystem
the protein and the pigment
What wavelength does photosystem 1 absorb light at
700nm
What is the stroma
a gel like substance containing enzymes, sugars and organic acids
What are starch grains
carbohydrates produced by photosynthesis and not used straight away are stored as starch grains
Describe light dependent reaction
Requires light energy
Takes place in thylakoid membranes
Light energy is absorbed by the chlorophyll
Light energy excites electrons in the chlorophyll
Chlorophyll has been photoionized
Some of the energy from the released electrons is used to add phosphate group to ADP to form ATP and some is used to form reduced NADP. ATP transfers energy and reduced NADP transfers hydrogen to the light independent reaction
During this process H2O is oxidised to O2
Describe non cylic phosphorylation stage 1
Light energy is absorbed by PSII
Light energy excites electrons in chlorophyll
Electrons move to a higher energy level
High energy electrons are released from the chlorophyll and move down the electron transport chain to PSI
Describe non cylic phosphorylation stage 2
As the excited electrons from chlorophyll leave PSII to move down the electron transport chain they need to be replaced
Light energy splits water into protons (H+ ions) electrons and oxygen - photolysis
Describe non cylic phosphorylation stage 3
Excited electrons lose energy as the move down the electron transport chain
The energy is used to transport protons into the thylakoid membrane so that there is a higher concentration of in the thylakoid than the stroma this forms a proton gradient across the thylakoid membrane
Protons move down their concentration gradient into the stroma via the enzyme ATP synthase which is embedded in the thylakoid membrane this movements adds a phosphate to ADP to form ATP
Describe non cylic phosphorylation stage 4
Light energy is absorbed by PSI which excites the electrons to an even higher energy level
Finally the electrons are transferred to NADP along with a proton from the stroma to form reduced NADP
Cyclic phosphorylation only produces ATP because
the electrons from the molecule aren’t passed on to NADP they are passed back to PSI by electron carriers
What is the light independent reaction called
the calvin cycle
Where does the calvin cycle take place
in the stroma
What are the products of the calvin cycle
triose phosphate and ribulose biphosphate
Describe stage 1 of the calvin cycle
CO2 enters the leaf through stomata and diffuses into the stroma
CO2 is combined with ribulose biphosphate the reaction is catalysed by the enzyme rubisco
This gives an unstable 6 carbon compound which breaks down into glycerate 3-phosphate
Describe stage 2 of the calvin cycle
the hydrolysis of ATP provides energy to turn the 3 carbon compound GP into a different a different 3 carbon compound triose phosphate
This reaction requires H+ ions which come from Reduced NADP which is recycled to NADP
some triose phosphate is then converted into useful organic compounds and some continues in the calvin cycle to regenerate RuBP
Describe stage 3 of the calvin cycle
Five out of every six molecules of TP in the cycle are used to regenerate RuBP
This uses the rest of the ATP produced by the light dependent reaction
How many turns of the calvin cycle produces six molecules of triose phosphate
six
How many triose phosphate molecules to make one hexose sugar
2
What does six turns of the cycle need
18 ATP and 12 reduced NADP from the light dependent reaction
