Photosynthesis (11) Flashcards
Where does the light-independent reaction occur?
stroma
Where does the light-dependent reaction occur?
thylakoids
What is the role of light in photoionisation?
- Chlorophyll molecules absorb energy from photons of light
- 2 electrons are ‘excited’ (raised to a higher energy level) causing them to be lost from the chlorophyll
What are the 7 stages of the light-dependent reaction?
1) Chlorophyll molecules absorb energy from photons of light
2) 2 electrons are ‘excited’ (raised to a higher energy level) causing them to be lost from the chlorophyll
3) electrons released from chlorophyll move down series of carrier proteins embedded in thylakoid membrane
4) undergo series of redox reactions which releases energy at decreasing energy levels
5) energy used to join ADP and Pi to form ATP
6) photolysis of water produces oxygen, electrons and protons
7) NADP reduced by electrons and hydrogen
How is a proton concentration gradient established during chemiosmosis?
some energy released from ETC is coupled to the active transport of hydrogen ions from stroma to thylakoid space
How does chemiosmosis produce ATP during the LDR?
hydrogen ions move down concentration gradient from thylakoid space to stroma via the channel protein ATP synthase
What are the 3 main stages of the calvin cycle?
1) carbon fixation
2) reduction
3) regeneration
What is the role of ATP synthase?
catalyses reaction between ADP + Pi to form ATP
What is the role of chlorophyll in photolysis?
- absorbs light energy
- loses electrons
- accepts electrons from water
What is the role of light in photolysis?
light energy splits water molecules
What is the equation for photolysis of water?
2 H2O — 4H+ + 4e- + O2
What happens to the 4 hydrogen ions from photolysis of water?
- move out of thylakoid space via ATP synthase
- used to reduce NADP
What happens to the 4 electrons from photolysis of water?
replace electrons lost from chlorophyll
What happens to the oxygen from photolysis of water?
used for respiration or diffuses out of leaf as waste gas
What is the equation for reducing NADP?
NADP + 2H+ + 2e- > NADPH
Where is NADP reduced?
stroma
What catalyses the reaction for reducing NADP?
dehydrogenase enzymes
What do dehydrogenase enzymes do?
catalyses reaction to reduce NADP
Where are the 2 hydrogen ions from for reducing NADP?
from photolysis of water
What do the 2 electrons in reducing NADP do?
act as final electron acceptor in ETC
What are the 6 steps of the light-independent reaction?
1) CO2 enters leaf through stomata + combines with RuBP, catalysed by rubisco
2) forms unstable 6C compound that breaks down into 2 GP (3C compound)
3) 2 GP is reduced to 2 triose phosphate using 2 NADPH and energy from 2 ATP
4) forms 2 NADP and 2 ADP
5) 5/6 carbons from triose phosphate forms compound RuP
6) RuBP is regenerated from RuP using energy from 1 ATP
What happens to 1carbon from TP?
leaves cycle and is converted into useful organic molecules e.g. glucose
What is the role of ATP in the LIR?
reduction of GP to triose phosphate
provides phosphate group to convert RuP to RuBP
What is the role of NADPH in LIR?
this coenzyme transports electrons needed for reduction of GP to triose phosphate
What is the structure of chloroplasts?
- usually disc-shaped
- double membrane
- thylakoids stack to form grana
- intergranal lamellae attach thylakoids in adjacent grana
- stroma
What are thylakoids?
flattened discs
What are intergranal lamallae?
tubular extensions
What is the stroma?
fluid-filled matrix
How does the structure of a chloroplast help maximise the rate of the LDR?
- ATP synthase channels within granal membrane
- large SA of thylakoid membrane for ETC
- photosystems position chlorophyll to enable max absorption of light
How does the structure of a chloroplast help maximise the rate of the LIR?
- own DNA + ribosomes for synthesis of enzymes e.g. rubisco
- concentration of enzymes + substrates in stroma is high
What are 4 environmental factors that can limit the rate of photosynthesis?
1) light intensity for LDR
2) CO2 levels for LIR
3) temperature for enzyme-controlled steps
4) mineral + magnesium levels to maintain normal functioning of chlorophyll
What is a limiting factor?
factor that determines the max rate of a reaction, even if other factors change to become more favourable
What is the equation to calculate the Rf value?
distance between origin and centre of pigment spot
_______________
distance between origin and solvent front
What are 3 agricultural practises used to overcome limiting factors?
1) artificial light, especially at night
2) artificial heating
3) addition of CO2 to greenhouse atmosphere
Why do farmers use these agricultural practices?
to increase yield, but additional cost must be balanced with yield to ensure max profit
How do you investigate the effect of a named variable on the rate of photosynthesis?
(3 points)
1) use a potometer (DV = rate of O2 production/CO2 consumption)
2) place balls of calcium alginate containing green algae in hydrogencarbonate indicator
3) colour changes from orange to magenta as CO2 is consumed and pH increases
What is chromatography?
when molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (chromatography paper)
How do you extract photosynthetic pigments?
use a pestle and mortar to grind a leaf with an extraction solvent e.g. propanone
What is the Rf value?
ratio that allows comparison of how far molecules have moved in chromatography
How can chromatography paper be used to separate photosynthetic pigments?
(4 points)
1) use capillary tube to spot pigment extract onto pencil origin (1cm above bottom of paper)
2) place chromatography paper in solvent (origin should be above solvent level)
3) allow solvent to run until almost touching other end of paper
4) pigments will move different distances
