photosynthesis Flashcards
light dependent reaction
chlorophyll (ps2) absorbs light energy
excites electron - released from ps2 - photoionisation
water split using light energy - photolysis
electrons from water replace electron
high energy electron travels down electron carriers - loses energy for H+ pump - stroma to thylakoid lumen
electrons ps2 replace electrons used by ps 1
electrons ps1 reduce NADP
H+ diffuse into stroma via ATP synthase - photophosphorylation (due to the energy for phosphorylating ATP coming from the sunlight)
oxygen diffuses from chloroplast
light independent reaction
stroma of chloroplast
ribulose bi-phosphate combines with co2 = 2x glycerate phosphate catalysed by rubisco
glycerate phosphate reduced to triose phosphate using electron from NADPH
ATP hydrolysis - energy
1/6 trios phosphate - leaves cycle to form glucose
5/6 form ribulose phosphate
ribulose phosphate phosphorylated to ribulose biphosphate using ATP
where does the light dependent reaction occur and why
occurs on the thylakoid membrane
because contains proteins for photosynthesis:
There are four different types of proteins on the thylakoid membrane:
Photosystems I and II: contain chlorophyll and other photosynthetic pigments, which absorb light energy.
Electron carriers: accept and donate high energy electrons / transfer electrons down the chain.
Proton (H+) pumps: pump H+ against the concentration gradient from stroma to thylakoid lumen.
ATP Synthase: has a channel for H+ to diffuse and active sites for ADP and Pi to bind.
what are the products of the light dependent reaction that are used in the light independent reaction
The products of the LDR that used in the LIR are: NADPH and ATP.
Oxygen leaves the chloroplast by diffusion, leaves the leaf by diffusion through the stomata.
experiments to study photosynthesis
Experiment 1: Chromatography of leaf pigments = RP7.
Experiment 2: Studying electron transfer = RP8.
Experiment 3: Lollipop experiment
photosynthetic pigments
Plants have many different pigments, eg. chlorophyll a, chlorophyll b, xanthophyll, carotene….
The advantage of having multiple pigments is that a wider range of wavelengths can be absorbed.
Advantage of having many photosynthetic pigments:
• A wider range of wavelengths can be absorbed in the LDR.
• More LDR: therefore, more NADPH and ATP made.
• Therefore, more LIR, more glucose.
allows for more GPP, more biomass and more yield
where do the LDR and the LIR reactions occur in plants
light-dependent: in the thylakoids of chloroplasts
light-independent: stroma of chloroplasts
what happens in the electron transfer chain
electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions, which releases energy
how is a proton concentration gradient established during chemiosmosis
some energy released from the ETC is couple to the active transport of protons from the stroma into the thylakoid lumen
How does chemiosmosis produce ATP in the light-dependent stage
protons move down their concentration gradient from the thylakoid lumen into the stroma via the channel protein ATP synthase
ATP synthase catalysis ADP + Pi -> ATP
What happens to the products of the photolysis of water
H+ ions - move out of thylakoid space via ATP synthase and are used to reduce the cofactor NADP
e- - replace electrons lost from chlorophyll
O2 - used for respiration or diffusions out of leaf as waste gas
How and where is reduced NADP produced in the light-dependent reaction
NADP + 2H+ + 2e- -> reduced NADP
- catalysed by dehydrogenase enzymes
- stroma of chloroplasts
name the 3 main stages in the calvin cycle
carbon fixation
reduction
regeneration
what happens during carbon fixing
reaction between CO2 and ribulose biphosphate catalysed by rubisco
forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)
what happens during reduction
2 x glycerate 3-phosphate are reduced into 2 triose phosphate
this required 2 NADPH and 2 ATP
forms 2 NADP and 2 ADP
how does the light-independent reaction result in the production of useful organic substances
1C leaves the cycle
(ie some of the triose phosphate is converted into useful organic molecules)
what happens during regeneration
after 1C leaves the cycle, the 5C compound ribulose phosphate forms
Ribulose biphosphate is regenerated from ribulose phosphate using 1 ATP - forming ADP
state the roles of ATP and NADPH in the light-independent reaction
ATP - reduction of glycerate 3-phosphate to triose phosphate and provides phosphate group to covert ribulose phosphate into ribulose biphosphate
NADPH - coenzyme transport electrons needed for reduction of glycerate 3-phosphate to triose phosphate
describe the structure of a chloroplast
- disc-shaped
- double membrane (envelope)
- thylakoids - flattened discs stack to form grana
- intergranal lamellae - tubular extensions attach thylakoid in adjacent grana
- stroma - fluid-filled matrix
how does the structure of the chloroplast maximise the rate of the light-dependent reaction
ATP synthase channels within the granal membrane
large surface area of thylakoid membrane for ETC
photosystems position chlorophyll to enable maximum absorption of light
how does the structure of the chloroplast maximise the rate of the light-INdependent reaction
own DNA and ribosomes for synthesis of enzymes eg rubisco
concentration of enzymes and substrate in stroma is high
define limiting factor
factor that determines maximum rate of reaction, even if other factors change to become more favourable
name 4 environmental factors that can limit the rate of photosynthesis
light intensity (LDR)
CO2 LIR)
Temp (enzyme-controlled steps)
Mineral / magnesium levels (maintain normal functioning of chloroplasts)
outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis
artificial light and heating
addition of CO2 to greenhouse atmosphere
