chapter 8 hw
The Calvin cycle oxidizes the light-reactions product __ to __.
NADPH to NADP+.
Photosynthetic electron transport contributes to the formation of a proton (H+) gradient across the thylakoid membrane in two places.
- In PS II, the oxidation of water releases protons into the thylakoid space. - Electron transport between PS II and the cytochrome complex (through Pq) pumps protons from the stroma into the thylakoid space. The resulting proton gradient is used by the ATP synthase complex to convert ADP to ATP in the stroma.
The Calvin cycle requires a total of 9 ATP and 6 NADPH molecules per G3P output from the cycle (per 3 CO2 fixed).
- In Phase 2, six of the ATP and all of the NADPH are used in Phase 2 to convert 6 molecules of PGA to 6 molecules of G3P. Six phosphate groups are also released in Phase 2 (derived from the 6 ATP used). - In the first part of Phase 3, 5 molecules of G3P (1 phosphate group each) are converted to 3 molecules of R5P (also 1 phosphate group each). Thus there is a net release of 2 Pi. - in the second part of Phase 3, 3 ATP molecules are used to convert the 3 R5P into 3 RuBP. - Note that in the entire cycle, 9 ATP are hydrolyzed to ADP; 8 of the 9 phosphate groups are released as Pi, and the ninth phosphate appears in the G3P output from the cycle.
CARBONS IN calvin cycle
- To produce 1 molecule of G3P (which contains 3 carbons), the Calvin cycle must take up 3 molecules of CO2 (1 carbon atom each). - The 3 CO2 molecules are added to 3 RuBP molecules (which contain 15 total carbon atoms), next producing 6 molecules of 3-PGA (18 total carbon atoms). - In reducing 3-PGA to G3P (Phase 2), there is no addition or removal of carbon atoms. - At the end of Phase 2, 1 of the 6 G3P molecules is output from the cycle, removing 3 of the 18 carbons. - The remaining 5 G3P molecules (15 total carbon atoms) enter Phase 3, where they are converted to 3 molecules of R5P. - Finally, the R5P is converted to RuBP without the addition or loss of carbon atoms.
Phase 1 of the Calvin cycle (carbon fixation) consists of a reaction between a molecule of CO2 and a molecule of RuBP, catalyzed by the enzyme Rubisco. For each molecule of CO2 that enters the Calvin cycle, which equation correctly represents what happens to its carbon (C) as the next intermediate is produced?
1 C + 5 C → 3 C + 3 C In Phase 1 of the Calvin cycle, the enzyme Rubisco catalyzes the addition of CO2 (1 carbon atom) to RuBP (5 carbon atoms). The result is a short-lived 6-carbon compound that immediately breaks down into 2 molecules of 3-phosphoglycerate (PGA), each containing 3 carbon atoms.
RuBP has how many carbons?
5
In the first part of Phase 3, the G3P molecules left over from Phase 2 are converted to R5P with the release of Pi. For the net conversion of 3 molecules of CO2 into 1 molecule of G3P by the Calvin cycle, which of the following equations correctly accounts for the inputs and outputs of phosphate groups in Phase 3?
5 P (in G3P) → 3 P (in R5P) + 2 Pi In the first part of Phase 3, 5 molecules of G3P (a total of 5 phosphate groups) are converted to 3 molecules of R5P (a total of 3 phosphate groups). Thus a net of two inorganic phosphate groups (Pi) are released.
C3 plants
A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.
excited state of the chlorophyll.
A temporarily altered form of chlorophyll after light has been absorbed by the chlorophyll molecule; an electron in the chlorophyll is boosted to a higher energy level.
outputs of calvin cycle
ADP, NADP+, G3P
The electrons derived from this oxidation reaction in the light reactions are used to reduce __ to __
NADP+ to NADPH.
inputs of the light dependent reactions of photosynthesis.
NADP+, ADP, water, light
The electrons derived from this oxidation reaction in the Calvin cycle are used to reduce __ to __.
CO2 to G3P.
inputs of calvin cycle
CO2, ATP, NADPH
How is ATP synthesis in chloroplasts is very similar to that in mitochondria?
Electron transport is coupled to the formation of a proton (H+) gradient across a membrane. The energy in this proton gradient is then used to power ATP synthesis.
In the light reactions, light energy is used to oxidize __ t o __
H2O to O2.
thylakoid space
Inside the thylakoid membranes; where protons accumulate during ATP synthesis in the light reactions
Which of the following statements correctly describes a role of light in the light reactions?
Light supplies the energy to remove electrons from water and to transport those electrons to NADP+.
outputs of light dependent reactions
O2, NADPH, ATP
A mutually dependent relationship exists between chloroplasts and mitochondria in the plant cell.
Photosynthesis, which occurs in chloroplasts, generates the sugars and oxygen gas that are used in mitochondria for cellular respiration. Cellular respiration generates carbon dioxide, which in turn is used as a carbon source for the synthesis of sugars during photosynthesis. Cellular respiration also generates ATP and water, which are used in various chemical reactions in the plant cell.
photosynthesis
Plants use the sun/light's energy to convert water and carbon dioxide into sugars (and oxygen); powering plant metabolism - CO2 diffuses into leaf through small pores, then enters cell, then diffuses into chloroplasts where photosynthesis takes place - chloroplasts uses energy from light to transform carbon dioxide and water into sugar and oxygen light + 6CO2 + 6H2O ------> C6H12O6 + 6O2
The transport of protons across the thylakoid membrane contributes to the proton gradient that drives ATP synthesis. This proton transport is accomplished by one of the small electron carrier molecules that shuttles electrons between the major electron transport complexes. As the carrier transports protons across the thylakoid membrane, it also shuttles electrons across the membrane. Which component of the light reactions is involved in pumping protons across the thylakoid membrane?
Pq (plastoquinone) as it transfers electrons from PS II to the cytochrome complex Plastoquinone (Pq) is found in the interior of the thylakoid membrane. When it is reduced by PS II, Pq picks up two protons from the stroma. When Pq is oxidized by the cytochrome complex, it releases the two protons in the thylakoid space. The net result is pumping of protons from the stroma to the thylakoid space as electrons flow from PS II to the cytochrome complex.
P680
Reaction center chlorophyll in the photosystem II. In Photosystem II (PS II), the excited state of P680 chlorophyll transfers an electron to the PS II primary electron acceptor. The resulting positively charged P680+ is the strongest known biological oxidant (electron acceptor).
P700
Reaction center cholophyll in the photosystem I. In Photosystem I (PS I), the excited state of P700 chlorophyll transfers an electron to the PS I primary electron acceptor. The resulting reduced primary electron acceptor in PS I is one of the strongest known biological reductants (electron donors).
Only 1 of the G3P molecules produced in Phase 2 of the Calvin cycle is exported from the cycle. The remaining G3P molecules are used in Phase 3. What happens to the remainder of the G3P produced in Phase 2 of the Calvin cycle?
The G3Ps are needed to absorb the CO2 that was taken up in Phase 1. Over the course of 3 turns of the cycle, Phase 3 of the Calvin cycle converts 5 molecules of G3P into 3 molecules of RuBP. These 3 RuBP molecules are needed to replace the 3 molecules of RuBP that were consumed during the carbon fixation reactions of Phase 1, thus enabling the Calvin cycle to continue.
How is the energy of the excited state of P680 chlorophyll used in Photosystem II?
The excited state of P680 donates an electron to the primary electron acceptor. in PS II, the excited state of P680 chlorophyll is a better electron donor than the non-excited (ground) state. The loss of an electron from P680 produces P680+ (the oxidized form of P680).
In Photosystem II (PS II), light energy is used to produce an electron acceptor that is strong enough to oxidize water. How does the oxidation of water contribute to the proton gradient across the thylakoid membrane?
The oxidation of water by PS II releases protons in the thylakoid space. In PS II, the oxidation of water to O2 produces protons as a byproduct. Because this reaction occurs on the thylakoid space side of PS II, these protons are released into the thylakoid space.
Suppose that a particular compound X, when added to a solution of functioning chloroplasts, causes the reduction of NADP+ to NADPH in the dark. However, when X is mixed with NADP+ in the absence of chloroplasts, no reduction of NADP+ to NADPH occurs. In other words, compound X cannot directly reduce NADP+ to NADPH. Which of the following must also occur when compound X is added to chloroplasts in order to account for the observed reduction of NADP+ to NADPH in the dark?
The primary electron acceptor of PS I must be reduced A compound that causes NADP+ to be reduced to NADPH in the dark, but cannot donate its electrons directly to NADP+, must reduce some other component of photosynthetic electron transport that can pass its electrons on to NADP+. Of all the electron carriers in photosynthetic electron transport, the only components that can reduce NADP+ without light are those between the primary electron acceptor of PS I and NADP+.
An action spectrum plots the rate of photosynthesis at various wavelengths of visible light, and it shows that blue light with a wavelength of about 490 nm is effective in driving photosynthesis. Based on this information and the absorption spectra shown at left, what role may chlorophyll b and carotenoids play in photosynthesis?
These pigments are able to absorb more wavelengths of light (and thus more energy) than chlorophyll a alone can absorb. As part of light-harvesting complexes in photosystems, they broaden the range of light that can be used in the light reactions.
You obtain the pigments called carotenoids in your diet when you eat carrots. Why do carotenoids appear yellow and orange?
They absorb blue/green light and reflect yellow and red wavelengths of light.
The rate of O2 production by the light reactions varies with the intensity of light because light is required as the energy source for O2 formation. Thus, lower light levels generally mean
___ a lower rate of O2 production. In addition, lower light levels also affect the rate of CO2 uptake by the Calvin cycle. This is because the Calvin cycle needs the ATP and NADPH produced by the light reactions. In this way, the Calvin cycle depends on the light reactions.
Chlorophylls play two roles in the light reactions:
absorption of light and reduction of a primary electron acceptor
cellular respiration produces
carbon dioxide and water and ATP CO2 provides carbon for photosynthesis
In each of the three key phases of the Calvin cycle (carbon fixation, reduction, and regeneration),
carbon skeletons are modified in reactions that lead to the final products.
photosynthesis occurs in
chloroplasts which contain the pigment chlorophyll
What connects the two photosystems in the light reactions?
electron transport chain
where is the high hydrogen ion concentration in light dependent reactions?
inside the thylakoid space
light reactions of photosynthesis
energy in sunlight is converted into chemical and redox energy in the form of ATP and NADPH. This task is accomplished by two photosystems that power linear electron flow from water to NADP+, while generating a proton gradient that is used to make ATP. in thylakoid membranes of chloroplast; light energy is converted into chemical energy; first phase of photosynthesis - small mobile electron carriers that shuttle electrons from one large complex to another 1) photosystem 2 (on left); absorbs light energy, excites electrons that enter the ETC, electrons are replaced with electrons stripped from water, creating oxygen as byproduct 2) energized electrons flow down ETC, releasing energy used to pump Hydrogen ions into thylakoid 3) photosystem 1 (on right); light energy excites electrons, and eelctrons are captured by NADPH(electron carrier molecule) 4) high concentration of hydrogen ions inside thylakoid powers ATP synthase, producing ATPs produced ATP and NADPH, which will power the production of sugar in the calvin cycle
photosynthesis produces
glucose (sugar) and oxygen which are inputs for cellular respiration
The reactions of Phase 2 of the Calvin cycle are identical to several of the reactions in ___
glycolysis (the first stage of cellular respiration), except that the reactions occur in the reverse direction. In glycolysis, for each molecule of G3P that is converted to PGA, 1 Pi is taken up, 1 NAD+ is converted to NADH, and 1 ADP is converted to ATP.
Although many other processes in the chloroplast require ATP and/or NADPH from the light reactions, the vast majority of the ATP and NADPH produced by the light reactions is used ___
in the Calvin cycle for CO2 fixation.
cellular respiration occurs in
mitochondria
What is the role of P680+ in the light reactions?
oxidation of water to O2 In the overall scheme of photosynthetic electron transport, water is oxidized and its electrons are passed eventually to NADP+. Water does not give up its electrons easily (it is difficult to oxidize). Thus a very strong oxidant is required to take electrons from water: This oxidant is the P680+ produced in Photosystem II.
What steps of the photosynthetic electron flow from water to NADP+ (the ETC in the thylakoid membrane of chloroplast) require an input of energy?
p680->pq (plastoquinone) p700->Fd (ferredoxin) In both PS II and PS I, light energy is used to drive a redox reaction that would not otherwise occur. In each photosystem, this redox reaction moves an electron from the special chlorophyll pair (P680 in PS II and P700 in PS I) to that photosystem's primary electron acceptor.
Sunlight provides energy for _________
photosynthesis
CAM plants
plants close their stomata during the day, collect CO2 at night, and store the CO2 in the form of acids until it is needed during the day for photosynthesis
C4 plants
plants that have adapted their photosynthetic process to more efficiently handle hot and dry conditions; prefaces the Calvin cycle with reactions that incorporate CO2 into four-carbon compounds, the end product of which supplies CO2 for the Calvin cycle. ex: corn
Two types of processes that contribute to the formation of the proton gradient are:
processes that release H+ from compounds that contain hydrogen, and processes that transport H+ across the thylakoid membrane.
photosystems
proteins in the thylakoid membrane organize chlorophyll and other pigments into clusters; large complexes of proteins and chlorophyll; capture light energy
What is the role of the reduced PS I primary electron acceptor in the light reactions?
reduction of NADP+ to NADPH In the overall scheme of photosynthetic electron transport, water is oxidized, and its electrons are passed eventually to NADP+. NADP+ does not readily accept electrons (it is difficult to reduce NADP+). Thus a very strong reductant is required to donate electrons to NADP+: This reductant is the reduced PS I primary electron acceptor.
processes that occur in both PS II and PS I
reduction of primary electron acceptor and light absorption the key function of each of the two photosystems is to absorb light and convert the energy of the absorbed light into redox energy, which drives electron transport.
red and violet-blue light were more effective than green light in driving photosynthesis
some wavelengths of light attracted more bacteria, suggesting that these wavelengths drive more photosynthesis than others .most of the bacteria were attracted to the regions of the alga illuminated by red or violet-blue light. This distribution of bacteria shows that red and violet-blue wavelengths are most effective in driving photosynthesis. - The distribution of chloroplasts within each algal cell was approximately the same. - The number of bacteria clustered at each wavelength (color) was approximately proportional to the amount of oxygen being produced by that portion of the alga
site of atp synthesis
stroma
where does the calvin cycle take place?
stroma of the chloroplast
photosystem 2
the first photosystem in the light-dependent reactions; uses electrons from photolysis, and produces ATP and NADPH; P680 is oxidized (which in turn oxidizes water!), and the PS II primary electron acceptor is reduced (which in turn reduces the electron transport chain between the photosystems); reaction Center is P680(red) - oxidation of water - reduction of electron transport chain between the two photosystems
if absorption of a certain light by a certain chloroplast pigment is high (high on graph)...
the pigment does absorb that light; we can predict that the chloroplast pigment would be effective in driving photosynthesis. if it absorbs little light, it would not be effective in driving photosynthesis
Suppose that the concentration of CO2 available for the Calvin cycle decreased by 50% (because the stomata closed to conserve water). Which statement correctly describes how O2 production would be affected? (Assume that the light intensity does not change.)
the rate of O2 production would decrease because the rate of ADP and NADP+ production by the Calvin cycle would decrease if the Calvin cycle slows (because of a decrease in the amount of available CO2), the light reactions will also slow because the supply of NADP+ and ADP from the Calvin cycle would be reduced.
The net production (output) of one molecule of G3P requires __ complete turns of the Calvin cycle
three; The net production (output) of one molecule of G3P requires three complete turns of the Calvin cycle, with one CO2 entering at each turn of the cycle.
Site of H+ release
thylakoid space
Photosystem I
uses the P700 reaction-center chlorophyll; reduction of NADP+oxidation of electron transport chain between the two photosystems; the PS1 primary electron acceptor is reduced (which in turn reduces other compounds that ultimately reduce NADP+ to NADPH), and P700 is oxidized (which in turn oxidizes the electron transport chain between the photosystems). - reduction of NADP+ - oxidation of electron transport chain between the two photosystems
the Calvin/C3 cycle (sometimes called the dark or carbon reactions)
uses the products of the light reactions (ATP and NADPH)to produce sugar takes place outside thylakoids, in stroma (thick fluid of chloroplast) 1) co2 molecules (entered the leaf as a gas) combine with Rubp 2) resulting molecules go through series of reactions powered by ATP and NADPH from light reactions=> G3Ps (simple sugar molecules) are produced most G3Ps are rearranged back into Rubps, that begin calvin cycle again important product of photosynthesis is the remaining G3p sugar! - some g3ps are used to build glucose, which can combine into starch or cellulose - other g3ps form sucrose some sugar is broken down by cellular respiration using oxygen in the plant's mitochondria, generating ATPs that can power other work - excess oxygen diffuses out of the leaf through pores, while more CO2 enters glyceraldehyde-3-phosphate (G3P). The net production (output) of one molecule of G3P requires three complete turns of the Calvin cycle, with one CO2 entering at each turn of the cycle. In each of the three key phases of the Calvin cycle (carbon fixation, reduction, and regeneration), carbon skeletons are modified in reactions that lead to the final products.
