5A Photosynthesis Flashcards
explain relationship between STRUCTURE and FUNCTION of granum in photosynthesis
- thylakoid membrane -> big s.a so absorbs as much light energy as possible
- thylakoid membrane -> contains lots of ATPsynthase = PRODUCES ATP in light DEP. reaction
- thylakoid membrane -> contain photosynthetic pigments
eg. CHLOROPHYLL (attached to proteins) to absorb light
x2 membrane chloroplasts also keeps reactants for p/s close to react
describe how starch is formed FROM PRODUCTS of light indep. stage
- 2 GALP molecules make GLUCOSE
- glucose joined together by GLYCOSIDIC BONDS -> make AMYLOSE and AMYLOPECTIN by CONDENSATION REACTIONS
- amylose + amylopectin = STARCH
where does light DEPENDENT stage take place?
thylakoids of chloroplasts
where does light INDEPENDENT stage take place?
stroma of chloroplasts
how does light DEP. reaction generate ATP?
- light energy excites e- in chlorophyll -> as they leave PS1 they are replaced by e- from PHOTOLYSIS OF H₂O
- e- pass down electron transfer chain of e- carriers
-> lose energy down E.T.C … - … allows chemiosmosis to occur
-
H⁺ ions actively pumped from a low conc. in
stroma-> high conc. in the thylakoid = conc. grad. across thylakoid membrane - ATPsynthase allows H⁺ ions thylakoid->stroma
- movement of H⁺ causes ATPsynthase to generate ATP
in light INDEP. stage
- 3 ADP + Pi made from ATP
- 2 NADP made from NADPH
ADP -> ATP
phosphorylation
ATP -> ADP
hydrolysis
ATP
adenosine triphosphate
phosphorolated nucleotide
metabolism
chemical processes that occur within a living organism in order to maintain life
outline the overall reaction of photosynthesis
IMPORTANT!!!
- in light dependent stage -> light energy breaks strong covalent bonds in H₂O
- O₂ released into atm
- in light indep stage (Calvin cycle) fixation with CO₂ enables H₂ to be stored as glucose a respiratory fuel
describe the light dependent stage of photosynthesis
non-cyclic phosphorylation
- light energy absorbed by PSII and excites e- in chlorophyll
- e- move along E.T.C
-
photolysis of water
H₂O -> 2H⁺ + 2e⁻ + ½ O₂ - e- made replace those lost in PSI
- energy lost by e- down E.T.C used to make ATP
- e- transferred to NADP + H⁺(from stroma) -> ↓ NADP
how do excited e- generate ATP?
- excited e- lose energy down E.T.C
- this energy is used to transport H⁺ into thylakoids
- so thylakoid has higher conc of H⁺ than stroma
- forms H⁺ gradient across membrane
- H⁺ move down conc grad into stroma via ATPsynthase
- (chemiosmosis) - energy from this movement causes
ADP + Pi -> ATP
chemiosmosis
process where movement of H⁺ ions across a membrane generates ATP
how is energy stored in ATP?
stored as chemical energy in the phosphate bond
what enzyme catalyses the phosphorylation of ADP?
ATPsynthase
how does ATP supply energy?
IMPORTANT!!!
- diffuses to part of cell that needs energy …
- … where it is broken down via hydrolysis into ADP and inorganic Pi …
- … causing chemical energy release from Pi bond and used by cell
- ATPase catalyses this reaction
what enzyme catalyses hydrolysis / the breakdown of ATP to ADP?
ATPase
what happens after ATP is broken down into ADP and inorganic phosphate?
they are RECYCLED and process starts again
coenzyme
molecule that aids function of enzyme
how do coenzymes work?
transfer chemical group from one molecule to another
what is the coenzyme used in photosynthesis?
NADP -> tranfers H₂ from one molecule to another
-> so can red. (give H₂) or ox. (take H₂) a molecule
what is the function of the double membrane in chloroplasts?
keeps reactants for p/s close to reaction sites
what are photosynthetic pigments?
coloured substances that absorb light energy needed for photosynthesis
at what wavelength does PSI absorb light best?
700nm
at what wavelength does PSII absorb light best?
680nm
structure and function of stroma
- contains all enzymes, sugars and organic acids
- required for light independent reaction of p/s
- contains oil droplets -> store non-carbohydrate organic material
what happens at the thylakoid membranes in the light dependent reaction of p/s?
- light energy absorbed by photosynthetic pigments (eg. chlorophyll) in photosystems …
- … and converted to chemical energy
what does NADPH transfer to light independent reaction?
H₂
what happens to H₂O in light dependent reaction?
ox. to O₂
what does the calvin cycle rely on?
products of light dependent reaction
what is ATP and NADPH from the light dependent reaction used for in the Calvin cycle?
3ATP used supply energy to catalyse GP->GALP and GALP->RuBP (regeneration of RuBP)
2NADPH used to catalyse GP->GP
cyclic phosphorylation
understand this
- only uses PSI
- e- from chlorophyll are NOT passed onto NADP -> are passed back to PSI via e- carriers
- e- are recycled and repeatedly flow through PSI
- only produces small amount of ATP
what is stage 1 of the Calvin cycle called?
carbon fixation
describe the process of carbon fixation in the Calvin cycle
- CO₂ enters leaf through stomata and diffuses into stroma of chloroplast
- here it is combined with RuBP , catalysed by RUBISCO
- this gives an unstable 6C compound which immediately splits into 2 3C compunds called GP
what is stage 2 of the Calvin cycle called?
reduction of GP
describe the process of reduction of GP in the Calvin cycle
- hydrolysis of ATP from light dep. reaction provides energy to turn GP -> GALP (3C)
- this reaction requires H⁺ (come from NADPH from light dep.)
NADPH is recycled to NADP - 1/6 GALP is converted into useful organic compounds
rest continues in Calvin cycle to regenerate RuBP
check if its 1/6
what is stage 3 of the Calvin cycle called?
regeneration of RuBP
describe the process of regeneration of RuBP in the Calvin cycle
- 2 GALP molecules used to make hexose sugar BUT 5/6 GALP used to regenerate RuBP
- regenerating RuBP uses rest of ATP from light dep. reaction
what organic substances can be made from products of the Calvin cycle?
products being GP and GALP
- CARBS -> simple sugars eg. glucose
-> polysaccharides eg. starch and cellulose (join hexose sugars) - LIPIDS made using …
-> glycerol made from GALP
-> fatty acids made from GP - A.A -> some made from GP
- NUCLEIC ACIDS -> sugar in RNA (ribose) made using GALP
go into more detail for how lipids and nucleic acids made in diff flashcards -> for 3 marks
why is the production of simple sugars eg. glucose from products of the Calvin cycle essential for an organism?
- glucose is used in respiration …
- … which provides energy needed for biological processes
what is the role of e- in PS1?
- generate ATP in chemiosmosis
-> movement of H⁺ down conc grad via ATPsynthase - reduce NADP in photophosphorylation
- produce O₂ in photolysis of H₂O
design an experiment to investigate photosynthesis using isolated chloroplasts
(Hill reaction)
- using pestle + mortar, grind 5g chopped spinach leaves with 10cm³ cold (0.5M) sucrose sol
- strain this liquid (funnel + muslin cloth) into cool centrifuge tube + centrifuge for 10 mins high speed
- pipette liquid from top of centrifuge and discard -> now have pellet
- add 2cm³ cold sucrose sol + 20cm³ cold pH 7 phosphate buffer sol + mix
- add 5cm³ chloroplast / buffer sol to 2 test tubes (A + B)
- add 10cm³ DCPIP each -> leave A under bench lamp (well lit) -> wrap B in tin foil (no light)
- observe A until DCPIP decolourises -> pop A + B sols in cuvettes + use colorimeter to compare % absorbance
NOTE: control = test tube only containing DCPIP + cilled isolation sol (NO CHLOROPLASTS) -> proves DCPIP colour doesn’t just deteriorate over time!!!
explain how DCPIP can be used to investigate p/s
hill reaction depends on e- released in light-dep stage being picked up by DCPIP (e- acceptor)
- so DCPIP takes the place of NADP so allows photolysis to continue even when all NADP used up
- DCPIP decolourises when it has accepted e- (been reduced) -> so can see that light-dep stage happened!!!
suggest why sucrose sol is used in hill reaction
to prevent H₂O being drawn from chloroplasts by osmosis
describe how triglycerides are made using products of the Calvin cycle
(3 marks)
- GALP used to produce glycerol…
- which is used for building lipid molecules eg. phospholipids, triglycerides
- GP used to produce fatty acids
-> triglyceride = 1 glycerol + 3 fatty acids joined by condensation reactions
