Photosynthesis Flashcards
Where does the light dependent reaction occur?
In the thylakoid membrane of the chloroplasts
Where does the light independent reaction occur?
In the stroma of the chloroplasts
Explain the role of light in photoionisation
Chlorophyll molecules absorb energy from photons of light. This ‘excites’ 2 electrons (raises them to a higher energy level), causing them to
be released from the chlorophyll.
Name the 2 main stages involved in ATP
production in the light-dependent
reaction.
Electron Transfer Chain and Chemiosmosis
What happens in the electron transfer
chain (ETC)?
Electrons released from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane & 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 coupled to the active transport of H+ ions (protons) from the stroma into the thylakoid space.
How does chemiosmosis produce ATP in the light-dependent stage?
H+ ions move down their concentration gradient from the thylakoid space into the stroma via the channel protein ATP synthase. ATP synthase catalyses ADP + Pi → ATP
Explain the role of light in photolysis.
Light energy splits molecules of water
2H2O → 4H+ + 4e-+ O2
What happens to the products of the
photolysis of water?
H+ ions: move out of thylakoid space via ATP synthase & are used to reduce the coenzyme NADP.
e-: replace electrons lost from chlorophyll.
O2: used for respiration or diffuses 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 in the stroma of chloroplasts.
Where do the H+ ions and electrons used to reduce NADP come from?
H+ ions: photolysis of water
Electrons: NADP acts as the final electron acceptor of the electron transfer chain
Name the 3 main stages in the Calvin
cycle.
- Carbon fixation
- Reduction
- Regeneration of RuBP
What happens during carbon fixation?
Reaction between CO2 & ribulose
bisphosphate (RuBP) catalysed by rubisco.
Forms unstable 6C intermediate that
breaks down into 2x glycerate 3-phosphate
(GP)
What happens during reduction (in the
Calvin cycle)?
2 x GP are reduced to 2 x triose phosphate (TP)
Requires 2 x reduced NADP & 2 x ATP
Forms 2 x NADP & 2 x ADP
How does the light-independent reaction
result in the production of useful organic
substances?
1C leaves the cycle (i.e. some of the TP
is converted into useful organic
molecules).
What happens during regeneration (in
the Calvin cycle)?
After 1C leaves the cycle, the 5C compound RuP forms
RuBP is regenerated from RuP using 1x ATP
Forms 1x ADP
State the roles of ATP & NADPH in the light-independent reaction.
ATP: reduction of GP to TP & provides phosphate group to convert RuP into RuBP.
NADPH: coenzyme transports electrons needed for reduction of GP to TP.
State the number of carbon atoms in
RuBP, GP & TP
RuBP: 5
GP: 3
TP: 3
Describe the structure of a chloroplast
Usually disc-shaped.
Double membrane.
Thylakoids: flattened discs stack to form grana.
Intergranal lamellae: tubular extensions attach thylakoids 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 granal membrane =ATP synthesis +proton gradient
-Large surface area of thylakoid membrane for ETC and the attachment of chlorophyll, electrons and enzymes
-photosystems position chlorophyll to enable maximum absorption of light.
-Chloroplasts contain DNA and ribosomes allowing them to synthesise proteins needed in
the LDR
How does the structure of the chloroplast maximise the rate of the light-independent reaction?
Own DNA & ribosomes for synthesis of enzymes e.g. rubisco.
Concentration of enzymes & substrates in stroma is high.
Define ‘limiting factor’.
Factor that determines maximum rate of a 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 levels (LIR). Temperature (enzyme-controlled steps). Mineral/ magnesium levels (maintain normal functioning of chlorophyll).
Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis
Artificial light.
Artificial heating.
Addition of CO2 to greenhouse atmosphere.
Why do farmers try to overcome the effect of limiting factors?
To increase yield.
Additional cost must be balanced with
yield to ensure maximum profit.
Suggest how a student could investigate the effect of a named variable on the rate of photosynthesis.
dependent variable: rate of O2 production/ CO2 consumption
- Use a potometer
- Place balls of calcium alginate containing green algae in hydrogencarbonate indicator (colour change orange → magenta as CO2is consumed & pH
increases) .
State the purpose and principle of paper
chromatography.
Molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (chromatography paper).
Outline a method for extracting photosynthetic pigments.
Use a pestle and mortar to grind a leaf
with an extraction solvent e.g. propanone.
Outline how paper chromatography can
be used to separate photosynthetic
pigments.
- Use a capillary tube to spot pigment extract onto pencil ‘start line’ (origin) 1 cm above bottom of paper.
- Place chromatography paper in solvent (origin should be above solvent level).
- Allow solvent to run until it almost touches the other
end of the paper. Pigments move different distances.
What are Rf values? How can they be
calculated?
Ratios that allow comparison of how far
molecules have moved in chromatograms.
Rf value = distance from origin/ distance between origin and solvent front.
