Important words and concepts from Chapter 10, Campbell et al., 1999 (2/1/2004):
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(1) Chapter title: Photosynthesis
SOME CONCEPTS FROM ECOLOGY
(2) Autotroph (see also autotroph)
(b) Some autotrophs (though not all) obtain their energy from photons (i.e., light)
(d) The most common of the terrestrial autotrophs are the green plants
(e) See Figure: Photoautotrophs
(3) Heterotrophs (see also heterotroph)
(a) See Figure, Focusing in on the location of photosynthesis in a plant
(b) Recall that a chloroplast may be differentiated into the following structures (going from outside to in):
(i) Outer membrane
(ii) Intermembrane space
(iii) Inner membrane
(vi) Thylakoid space (or compartment or lumen)
(c) Recall additionally that the thylakoids are derived from the inner membrane (think of them as sealed off cristae-equivalents)
(a) The overall reaction of photosynthesis may be described in shorthand as:
(b) See Figure, Tracking atoms through photosynthesis (and, no, I don't expect you to know this figure, though do note that the actual reaction is perhaps more complex than expected with water appearing on both sides of the equation)
(c) Note that here energy is "light energy," i.e., photons
(e) In terms of glucose, the above equation may be written as:
(i) 6CO2 + 6H2O + energy --> C6H12O6 + 6O2
(f) Note how this equation is essentially the reverse of the equation for the oxidation of glucose:
(i) C6H12O6 + 6O2 --> 6CO2 + 6H2O + energy
(c) All of the atmospheric molecular oxygen, in fact, came/comes from photosynthesis
(a) Photosynthesis is not a single reaction pathway but two, one dependent on the other
(b) See Figure, An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle
(c) The light reactions represents the "photo" part of photosynthesis
(i) This is where the energy of photons is captured
(ii) The light reaction supplies the energy and reducing electrons to drive forward the Calvin cycle
(d) The Calvin Cycle represents the "synthesis" part of photosynthesis
(e) Both reactions are anabolic, involving the phosphorlyation of ADP (not, in this case, as a product of catabolism), reduction of NADP+ (both products of the light reactions) or carbohydrate formation (the product of the dark reactions)
LIGHT REACTION OF PHOTOSYNTHESIS
(a) The light reactions of photosynthesis involve the following
(vi) Oxidation of water
(vii) Cyclic electron flow
(a) In photosynthesis, reducing electrons are carried by a phosphorylated derivative of NAD+ called NADP+
(b) Analogous to the reduction of NAD+, the reduction of NADP+ occurs thusly:
(i) NADP+ + 2e- + 2H+ --> NADPH + H+
(c) NAD+ and NADP+ otherwise act equivalently, the former in cellular respiration, the latter in photosynthesis (as well as anabolic reactions in general)
(a) The wavelength of light is, among other things, a measure of the energy associated with a photon
(b) Wavelength is also equivalent to the perceived color of a photon
(c) See Figure, The electromagnetic spectrum
(e) See Figure, Why leaves are green; interactions of light with matter in a chloroplast
(11) Chlorophyll (see also chlorophyll)
(a) The molecule that does the actual absorption of photons in chloroplasts is chlorophyll
(b) Chlorophyll is a complex, non-protein, organic-molecule that is embedded, more or less, in the thylakoid membrane
(c) See Figure, Location and structure of chlorophyll molecules in plants
(e) Chlorophylls are arrayed into photosystems
(a) Photosystems are two-dimensional arrays of chlorophyll molecules
(c) These arrays serve as photon-gathering antennae
(e) See Figure, How a photosystem harvests light
(13) Reaction center (see also reaction center)
(b) See Figure, How a photosystem harvests light
(14) Primary electron acceptor (see also primary electron acceptor)
(b) To proceed with another round of photon absorption, the reaction center chlorophyll must obtain a replacement electron
(i) Chlorophyll2+ + H2O --> chlorophyll0 + 2H+ + ˝O2
(e) The H+ are generated in the thylakoid space, thus contributing to a chemiosmotic proton gradient
CHEMIOSMOTIC GENERATION OF ATP
(a) See Figure, How noncyclic flow during the light reactions generates ATP and NADPH
(c) Note that the production of both of these molecules is driven by light energy that has been converted to chemical energy rather than derived from the catabolism of food molecules (such as glucose)
(d) Note in the figure (more or less in order):
(i) Photon capture by photosystem II
(ii) Oxidation of photosystem II
(iv) Oxidation of water
(v) Electron transport
(vii) Reduction of photosystem I
(viii) Photon capture by photosystem I
(ix) Oxidation of photosystem I
(xi) NADP+ reduction
(e) Note that photosystem I and photosystem II absorb photons of light at slightly different wavelengths (700 nm and 680 nm, respectively)
(f) See Figure, A mechanical analogy for the light reactions
(17) Cyclic electron flow (see also cyclic electron flow)
(a) See Figure, How noncyclic flow during the light reactions generates ATP and NADPH
(b) Cyclic electron flow is the same as non-cyclic flow except:
(i) Involves only photosystem I
(iv) Electron reduces photosystem I
(c) See Figure, Cyclic electron flow
(d) The idea is that, because the photosystem I electron serves as the source of electrons for photosystem I, the system is considered cyclic
(e) Note that cyclic electron flow generates ATP, but no NADPH + H+
(f) This essentially gives a plant an opportunity to produce more ATP than NADPH when it is to the plants advantage to do so (particularly, the Calvin cycle requires more ATP than NADPH)
(18) Photophosphorylation (see also photophosphorylation)
(a) See Figure, Comparison of chemiosmosis in mitochondria and chloroplasts
(b) Photophosphorylation is equivalent to oxidative phosphorylation except that:
(i) It is the energy of photons that generates the proton-motive force rather than the high energy electrons found in chemical bonds (though in both cases it is electron transfer that is used to pump hydrogen ions)
(ii) The high proton concentration is generated in the thylakoid space rather than in the intermembrane space
(c) Note that since the are generated from the inner membrane of the chloroplast, the thylakoid space of chloroplasts and intermembrane space of mitochondria are equivalent (though, of course, not identical; think pinching inward of the inner membrane to generate the thylakoids)
(d) Various other reactions contribute to the proton motive force that is found across the thylakoid membrane including:
(i) The oxidation of water generates protons in the thylakoid space
(ii) The reduction of NADP+ sequesters protons otherwise found in the stroma (i.e., outside of the thylakoid space)
(e) See Figure, The light reactions and chemiosmosis: the organization of the thylakoid membrane
(f) FAQ: Photophosphorylation, explain please. Photophosphorylation is similar to oxidative phosphorylation in that both involve a chemiosmotic mechanism of ADP phosphorylation. The difference is that while hydrogen ion pumping is driven in oxidative phosphorylation by electrons donated by NADH or FADH2, in photophosphorylation the electrons that drive pumping are donated by chlorophyl. Similarly, the energy of oxidative phosphorylation is ultimately derived from chemical bonds while the energy of photophosphorylation is ultimately derived from photons. Alternatively, you might consider photophosphoryaltion as the chemiosmotic phosphorylation that makes ATP during photosynthesis. See in particular Figure of your text, page 195 [NOTE, PAGE NUMBER/FIGURE NUMBER MAY BE INCORRECT].
DARK REACTION OF PHOTOSYNTHESIS
(b) The "job" of the Calvin cycle is to convert atmospheric CO2 into carbohydrates
(c) The Calvin cycle technically doesn't require light to progress (and hence is also know as the "dark reaction" of photosynthesis), though, of course, the Calvin cycle does require the products (ATP and NADPH) of the light reaction (that is, these have to come from somewhere and in a functioning plant these substrates of the Calvin cycle come from the light reactions of photosynthesis)
(d) See Figure, The light reactions and chemiosmosis: the organization of the thylakoid membrane
(e) Note that the ATP and NADPH are generated in the stroma
(f) Note that the Calvin cycle takes place in the stroma
(g) See Figure, The Calvin cycle
(h) Don't worry about knowing Figure
(20) Mitochondria (see also mitochondria)
(b) Calvin cycle
(d) Carbon fixing
(l) NADP+ reduction
(s) Reaction center
(22) Practice questions [index]
(a) What is the reducing agent employed during the Calvin cycle?
(b) True or False, chlorophyll molecules consist of green chloroplast proteins.
(c) Follow photosystem II from photon capture through the regenerative reduction of the reaction center. Be as thorough and as detailed as you can. However, note that this question is not asking for a complete description of all of photosynthesis, nor even all of the steps of the light reaction. Relative points will be gained for any relevant detail. Relative points will be lost for incorrect information, so don't BS! Use (properly labeled) figures and diagrams if you like (though these are by no means required). Do try to write both neatly and well.
(d) What specific reaction pathway takes place predominantly within the thylakoid membranes?
(e) Distinguish autotroph from heterotroph. Don't simply define these terms. Make sure you explicitly tell me how they differ!
(f) What specific aspect of the anatomy of a chloroplast are chlorophyll molecules associated with? Remember, "specific" means down to the level of detail at which you should know the answer to this question.
(g) Describe cyclic photophosphorylation including as many relevant details as you can recall. That is, be as thorough and as detailed as you can. However, note that this question is not asking for a complete description of all of photosynthesis, nor even all of the steps of the light reaction. Relative points will be gained for any relevant detail. Relative points will be lost for incorrect information, so don't BS! (All points are lost if you don't at least plausibly describe cyclic photophosphorylation.) Use (properly labeled) figures and diagrams if you like (though these are by no means required). Do try to write both neatly and articulately.
(h) What organelle is employed by plants to utilize most of the energy stored in the carbohydrates produced by the Calvin cycle?
(i) What simple but highly biologically relevant chemical reaction is directly associated with photosystem II's reaction center chlorophyll?
(j) From what do most common autotrophs obtain their carbon and energy (note that this is asking two questions and requires two answers)?
(k) In the following equation, CO2 + H2O + energy --> CH2O + O2, what typically serves in biological systems as the source of energy? (note, though technically perhaps correct, neither ATP nor a reduced electron carrier is the answer to this question that I am looking for)
(l) Write the portion (chemical reaction) of photosynthesis' light reaction--occurring at the end of the non-cyclic pathway--that involves in particular the addition of reduced electrons to the electron carrier that ultimately is employed during the Calvin cycle.
(m) Upon adsorption of a photo of light by a chlorophyll molecule, what immediately occurs, particularly before that chlorophyll molecule interacts with any other molecules?
(n) Where, specifically (structurally), in chloroplasts are the photosynthesis photosystems found? I want you to zoom in as far as you can, i.e., be as specific as you can.
(o) What specific, non-electron-transport chain, multi-molecular complex is involved in both cyclic and non-cycle photophorylation?
(p) What specific molecule oxidizes water in photosynthesis? Note, I that I really want you to be specific here since it is only a specific molecule in a specific place that does the actual oxidizing.
(q) What does CH2O represent?
(r) The most common terrestrial autotrophs are __________.
(s) True or False, the reduction of the reaction center chlorophyll of photosystem II is directly facilitated by electrons energized by the absorption of photons.
(t) The anabolic reactions of photosynthesis in green plants together ultimately result in the formation of what compound?
(u) Write the balanced chemical equation describing the reduction of NADP+.
(v) What is the name of the light-absorbing molecule embedded in the thylakoid membrane of chloroplasts?
(w) The specific name for the two-dimensional arrays of photon absorbing molecules involved in cyclic photophophorylation is __________.
(x) Label the chloroplast regions, membranes, gradients, and photosynthetic products that would be present were ATP synthase is absent.
(y) A general overview of the Calvin Cycle's reactions and products (photosynthesis' dark reaction; not balanced) is __________ + __________ + ATP + __________ -> carbohydrate. Fill in the blanks.
(z) What organelle do plants employ to perform cellular respiration?
(aa) Name three substrates (or coenzymes) that are employed by the Calvin cycle.
(bb) All of the various steps involved with photophosphorylation are associated specifically with what organelle/structure found within chloroplasts?
(cc) What is the primary end product of cyclic electron flow?
(dd) What is the primary waste product (i.e., that is, a chemical not used in any photosynthesis reaction) of non-cyclic electron flow in chloroplasts?
(ee) What is the name of a non-protein organic molecule (other than ADP, ATP, NADP+, or NADPH) that is intimately involved in the photosynthesis light reaction?
(ff) Which is more likely to be found at the base of a food chain, an autotroph or a heterotroph?
(gg) What are the two major products of the photosynthesis light reactions?
(hh) The Calvin cycle:
(i) Involves a proton gradient across the thylakoid membrane
(ii) Makes G3P which is used to make carbohydrate
(iii) Occurs because the dark reactions require more ATP
(iv) Requires darkness
(v) Requires light
(vi) All of the above
(ii) How many NADH are employed by plants in the reactions directly involved in fixing carbon?
(jj) Name one molecule involved in photosynthesis that is found embedded in the thylakoid membrane.
(kk) Which photosystem is involved in both cyclic and non-cyclic electron flow (in photosynthesis)?
(ll) (bonus) In studying photosynthesis we mostly employed the chemical reaction 6CO2 + 6H2O + energy --> C6H12O6 + 6O2 as a shorthand for what is required for the production of one glucose. This equation is a bit of lie, however. What is the true overall equation for the production of glucose, i.e., that takes into account the origin of all of the atoms found on the right-hand side of the equation?
(mm) In photosynthesis the mechanism of ATP generation is equivalent to the oxidative phosphorylation observed with mitochondria. However, rather than "oxidative phosphorylation," the process instead is described as __________ to take into account that the energy ultimately driving the reactions was derived from light.
(nn) Three reactions that take place in the stroma of chloroplasts are the synthesis of ATP, the synthesis of _________, and the Calvin cycle.
(oo) What is this: CO2 + H2O + energy --> CH2O + O2?
(pp) What are the two reactions of photosynthesis? (note that each of these "reactions" is a multistep process)
(qq) Which of the following is least associated with the production of NADPH?
(i) Capture of a photon of light by a chlorophyll photosystem
(ii) Capture of this chemical energy by the reaction center chlorophyll of a photosystem
(iii) Conversion of photon energy to energy stored by electrons (chemical energy)
(iv) Cyclic electron flow
(v) Non-cyclic electron flow
(vi) Oxidation of the reaction center chlorophyll by the primary electron acceptor
(vii) Oxidation of water
(rr) What is a photosystem?
(ss) In photosynthesis, what is a reaction center?
(tt) What is the correct order of the following?
(i) Electron transport
(ii) NADP+ reduction
(iii) Oxidation of photosystem I
(iv) Oxidation of photosystem II
(v) Photon capture by photosystem I
(vi) Photon capture by photosystem II
(uu) Describe the direction of flow of protons in terms of the anatomy of chloroplasts observed over the course of photophosphorylation. Ignore the flow associated with generation of the proton motive force.
(23) Practice question answers [index]
(c) Wavelength 680 nm (1) photons (2) are absorbed by chlorophyll (3) found embedded in the thylakoid membrane (4) of chloroplasts (5). Typically, absorption is done by an antennae chlorophyll (6) of the photosystem II. Energy associated with this absorbed photon is passed from adjacent chlorophyll to chlorophyll molecules (7) until that energy is passed to the reaction center chlorophyll (8). All chlorophyll in the photosystem are identical chemically (9) but differ in that the reaction center chlorophyll is adjacent to a primary electron acceptor (10). The primary electron acceptor accepts the energized electron from the reaction center chlorophyll (11) thus oxidizing the photosystem (12). For subsequent photon absorption followed by electron donation to the primary electron acceptor to occur, the reaction center chlorophyll must be rejuvenated, i.e., reduced (13). Reduction of the oxidized reaction center chlorophyll is accomplished via the oxidation of water (14) thus generating molecular oxygen (15) and protons (16). The protons are generated in the thylakoid space (17) thus contributing to the proton electrochemical gradient (18) employed during photophosphorylation (19).
(d) the light reaction of photosynthesis.
(e) An autotroph can live without eating other organisms whereas a heterotroph cannot
(f) the membranes of the thylakoids
(g) Reception of a photon (1) by photosystem I (2) boosts (3) two chlorophyll molecule (4) electrons (5) to a higher energy state (6). This electron is then passed from chlorophyll to chlorophyll in the photosystem (7) until it is passed to the reaction center chlorophyll (8) so named because of its close proximity (9) to the primary electron acceptor (10). In cyclic photophosphorylation this electron is not then passed down to NADP+ reductase (11) but instead handed off to the electron transport chain coming from photosystem II (12). Passage down this electron transport chain pumps protons (13) into the thylakoid space (14) where they are then employed, via chemiosmosis (15) to phosphorylate ADP (16). The electron, having passed down the electron transport chain is returned to the photosystem I reaction center chlorophyll (17)
(i) H2O --> 2H+ + ˝O2 + 2e- where the electrons are used to reduce photosystem II's reaction center chlorophyll; Don't worry about stoichiometry
(j) Light and CO2
(l) 2e- + 2H+ + NADP+ + energy (supplied by the electrons) --> NADPH + H+
(m) an electron is excited and enters an elevated orbital
(n) The thylakoid membrane
(o) Photosystem I
(p) The reaction-center chlorophyll of photosystem II
(q) CH2O is an individual unit of a carbohydrate
(s) False (it is the oxidation of photosystem II that is facilitated by electrons energized by photons)
(t) Glucose; carbohydrate; G3P
(u) NADP+ + 2e- + 2H+ (or, alternatively, 2Ho) -> NADPH + H+
(w) Photosystem I
(y) CO2 + H2O + NADPH
(aa) ATP, NADPH, CO2, H2O
(ff) An autotrophy
(gg) ATP and NADPH
(hh) (ii) Makes G3P which is used to make carbohydrate
(ii) Zero (it is NADPH that is employed)
(jj) Chlorophyll; also the ATP synthetase, as well as all of the additional light reaction macromolecules
(kk) Photosystem I
(ll) 6CO2 + 12H2O + energy --> C6H12O6 + 6H2O + 6O2 (i.e., where all of the O2 come from H2O)
(oo) This is the net result of photosynthesis
(pp) Light reaction and Calvin cycle (a.k.a., dark reaction)
(qq) (iv) Cyclic electron flow
(rr) A photosysytem is an array of chlorophyll molecules located around a common reaction center
(ss) A reaction center is the chlorophyll that passes the electron to the primary electron acceptor
(tt) (vi) --> (iv) --> (i) --> (v) --> (iii) --> (ii)
(uu) from the lumen of the thylakoids into the stroma
Chapter 10, Bio 113 questions:
(#) In addition to H2O, what are the three substrates required for production of carbohydrate in the Calvin cycle?
A: CO2, NADPH, and ATP
(#) What is generated in the thylakoid space that is one of the things that differentiates photophosphorylation and oxidative phosphoryation?
A: Proton-motive force, i.e,. the high proton concentration occurs by pumping proteins into the thylakoid space.
(#) Which of the following involves photosystem II?
(i) Cyclic electron flow
(ii) Oxidation of NADP+
(iii) Oxidation of water
(iv) Reduction of NADP+
(v) Reduction of water
A: (iii) Oxidation of water
(#) The primary electron acceptor in photosynthesis accepts electrons from what and passes electrons on to what? Please be as specific as you can be.
A: reaction center chlorophyll and electron transport chain
(#) What molecule in chloroplasts captures photons, resulting in a boosting of electrons to a higher energy shell?
(#) Correctly order the following, going from outside to inside:
(i) Inner membrane
(ii) Intermembrane space
(iii) Outer membrane
(vi) Thylakoid space
A: (iii) Outer membrane, (ii) Intermembrane space, (i) Inner membrane, (iv) Stroma, (v) Thylakoid, (vi) Thylakoid space.