5.1 Photosynthesis Flashcards
Where do the light-dependent & light-independent reactions occur in plants?
light-dependent - thylakoids of chloroplasts
light-independent - stroma of chloroplasts
Explain the role of light in photoionization
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
- Chemiosmosis
What happens in the electron transfer chain (ETC)?
Electrons released from the chlorophyll move down a series of carrier proteins embedded in the thylakoid membranes & undergo a series of redox reactions, which releases energy.
How is a proton concentration gradient established during chemiosmosis?
thylakoidhas a higher concentration of protons than the stroma which froms a proton concentration gradient.
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
2H20 –> 4H+ + 4E- +O2
What happens to the products of the photolysis of water?
. H+ ions: move out of the thylakoid space via ATP synthase & are used to reduce the coenzyme NADP
. e-: reduce electrons lost from the chlorophyll
. 02: 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
. 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 of the Calvin cycle
- Carbon Fixation
- Reduction
- Regeneration
What happens during carbon fixation?
. Reaction between CO2 & ribulose biphosphate (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)?
. 2x GP are reduced to 2x triose phosphate (TP)
. Requires 2x reduced NADP & 2x ATP
. Forms 2x NADP & 2X ATP
How does the light independent reaction result in the production of useful organic substances?
1C leaves the cycle (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 role of ATP & (reduced) NADP in the light-independent reaction
. ATP: reduction of GP to TP & provides phosphate group to convert RuP into RuBP
. (reduced) NADP : 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 (envelope)
. Thylakoids: flattened disc 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
. 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?
. Owns DNA & ribosomes for synthase 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 the other factors change to become more favourable
Name 4 environmental factors that can limit the rate of photosynthesis
. light intensity
. co2 levels
. temperature
. magnesium levels
Outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis
. Artificial light, especially at night
. 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
