Week 7 Application Questions Flashcards
1) Some plants have purple leaves rather than green leaves, especially in areas near the equator.
a) Why do purple plants look purple?
• Contain more anthocyanin pigment (absorbs green light) than chlorophyll (reflects green light)
• Still use chlorophyll for photosynthesis, but not all blue/red light is absorbed
1) Some plants have purple leaves rather than green leaves, especially in areas near the equator.
b) What chemical bonding arrangement would anthocyanin and chlorophyll have in common?
Conjugated double bonds
– Able to absorb visible light
– Absorbed light excites electrons
1) Some plants have purple leaves rather than green leaves, especially in areas near the equator.
c) Do you think anthocyanin pigments would interfere with the function of chlorophyll in these plants?
No
• Chlorophyll can still absorb red and blue light to provide energy for photosynthesis
• Anthocyanins absorb green light, which is not used in photosynthesis
– A small amount of this energy is transferred to chlorophyll in the photosystems, but most is lost
1) Some plants have purple leaves rather than green leaves, especially in areas near the equator.
d) Why are purple plants commonly found in equatorial regions?
• Anthocyanin thought to be “plant sunscreen”
– Absorbs excess light energy
– Too much light can damage the photosystems and reduce the efficiency of photosynthesis
• Purple plants are more common in areas that get a lot of sunlight
2) Atrazine is one of the most commonly used herbicides in the United States. It is used to kill weeds in corn and sugarcane crops, as well as in residential lawns and golf course turf. Its mechanism of action is that it blocks the transfer of electrons from Photosystem II to plastoquinone during the light reactions.
a) Would a plant cell exposed to Atrazine be able to produce NADPH using excited electrons from Photosystem I?
No.
• Although NADPH is produced using the light energy absorbed by PSI, the electron starts its journey in PSII. If PSII can’t transfer electrons to the ETC,
no electrons will be available to fill the electron hole in PSI.
2) Atrazine is one of the most commonly used herbicides in the United States. It is used to kill weeds in corn and sugarcane crops, as well as in residential lawns and golf course turf. Its mechanism of action is that it blocks the transfer of electrons from Photosystem II to plastoquinone during the light reactions.
b) Explain why a susceptible plant would die following exposure to Atrazine.
• Immediate direct consequences: no H+ being pumped into lumen,no e- transport is disrupted
• Can’t make ATP or NADPH in light reactions
• More indirect consequences: Can’t fix carbon into sugar in the Calvin Cycle, because there is no energy source
• No fixed carbon or energy available for the plant to make cell structures and carry out cell functions
2) Atrazine is one of the most commonly used herbicides in the United States. It is used to kill weeds in corn and sugarcane crops, as well as in residential lawns and golf course turf. Its mechanism of action is that it blocks the transfer of electrons from Photosystem II to plastoquinone during the light reactions.
c) Would a plant cell exposed to Atrazine be able to carry out cyclic electron flow to produce ATP?
Yes.
• Electrons not passed from PhotosystemII to plastoquinonein cyclic flow (electrons come from ferredoxin)
• Electronmovementwill allow proton gradient to be formed, and ATP to be made
3) Imagine you are a plant geneticist studying lettuce plants, in the hopes of creating a more productive strain of lettuce. You find a mutant version of your lettuce, in which a mutation in the chloroplast DNA has caused the thylakoid membranes to become more permeable to charged ions (i.e. ions can diffuse freely across the thylakoid membrane).
a) How would this mutation affect ATP production in the thylakoids?
It would decrease.
• If protons diffuse across membrane without going through ATP synthase, their energy can’t be used to make ATP.
3) Imagine you are a plant geneticist studying lettuce plants, in the hopes of creating a more productive strain of lettuce. You find a mutant version of your lettuce, in which a mutation in the chloroplast DNA has caused the thylakoid membranes to become more permeable to charged ions (i.e. ions can diffuse freely across the thylakoid membrane).
b) Describe how this mutation would affect the productivity of the Calvin Cycle in this lettuce plant.
• Not enough ATP would be produced
• Calvin Cycle needs ATP to provide energy during the reduction and regeneration steps of the Calvin Cycle
• ATP will run out,and no more G3P will be produced
3) Imagine you are a plant geneticist studying lettuce plants, in the hopes of creating a more productive strain of lettuce. You find a mutant version of your lettuce, in which a mutation in the chloroplast DNA has caused the thylakoid membranes to become more permeable to charged ions (i.e. ions can diffuse freely across the thylakoid membrane).
c) Would cyclic electron flow be able to help these lettuce chloroplasts compensate for this mutation?
No.
• Proton gradient is used to produce ATP during both linear and cyclic flow
• No proton gradient= ATP synthase can’t make ATP
3) Imagine you are a plant geneticist studying lettuce plants, in the hopes of creating a more productive strain of lettuce. You find a mutant version of your lettuce, in which a mutation in the chloroplast DNA has caused the thylakoid membranes to become more permeable to charged ions (i.e. ions can diffuse freely across the thylakoid membrane).
d) You examine the cell walls in this mutant lettuce plant, and observe that the cell walls are thin and weak.
Explain why this mutation may have led to this problem with the cell walls.
• Calvin Cycle makes G3P
• G3P is used to make glucose
• Cellulose is a glucose polymer
• Cellulose microfibrils provide strength to the plant cell wall
4) Hydrogen gas is called the fuel of the future, because its oxidation releases energy that can be used to generate electricity or power vehicles while producing water. Canada and Alberta have developed strategies to become part of the “hydrogen economy” of the future. The goal is to produce at first “blue hydrogen” (producing hydrogen gas using natural gas as an energy source) and then switch to “green hydrogen” (hydrogen gas made using non-fossil resources).
In photosynthesis plants use light to split water and oxidize water into 2H+, 2e- and O2 using the oxygen evolving complex (OEC) associated with the PSII. The structure of this complex has been analyzed using x- and laser-ray crystallography but its mechanism is not well understood.
a) If you were to build an ‘artificial leaf’ to mimick plants’ splitting of water using sunlight and produce H2, which components (complexes that were introduced in the lecture videos) would you need to include?
What is the technological challenge?
- Plastoquinone
- Cytochrome C complex
- PSI
- Oxygen evolving complex
(with PSII) - NADP+reductase
• Needs an agent strong enough to pull e- from H2O, only the OEC or PSII( P680) closely associated can do that in cells, replacing the OEC with other catalysts (been done by U of Waterloo).
— This is the ‘photo-’ part of photosynthesis.
Technological challenge-
• keeping the gases separated, storage of potential energy
4) Hydrogen gas is called the fuel of the future, because its oxidation releases energy that can be used to generate electricity or power vehicles while producing water. Canada and Alberta have developed strategies to become part of the “hydrogen economy” of the future. The goal is to produce at first “blue hydrogen” (producing hydrogen gas using natural gas as an energy source) and then switch to “green hydrogen” (hydrogen gas made using non-fossil resources).
In photosynthesis plants use light to split water and oxidize water into 2H+, 2e- and O2 using the oxygen evolving complex (OEC) associated with the PSII. The structure of this complex has been analyzed using x- and laser-ray crystallography but its mechanism is not well understood.
b) If you were to build an ‘artificial leaf’ to produce a substitute carbon-based fuel (e.g. methanol, CH3OH), which components (complexes that were introduced in the lecture videos) would you need to include?
What is the technological challenge?
• Needs splitting of water (the split water stores the energy that can be used for anabolic processes): OEC or P680 (‘photo-’) plus fixing of the CO2 to build carbon based fuel = RUBISCO (-’synthesis’ part)
Technological challenge-
• Fixing CO2 (or making RUBISCO more efficient) or energy needed to remodel CO2, currently working on hydrogen oxidizing bacteria
