EXAM 3 Chapter 10 Spring 2018 PDF

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Review chapter 10...

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BSC 2010 Review Sheet – Chapter 10 Photosynthesis

Answer the following questions as completely as possible, referring to your class notes and textbook. They are designed to help you process and review course material. Questions on quizzes and exams will also deal with these topics, but will be specific and in a M/C and T/F format. Quiz and exam questions may not be limited to the topics covered here.

1. Define the terms autotroph and heterotroph. Identify to which group each of the following organisms (from the lab course) belong: onion, Elodea, potatoes, yeast, cyanobacteria, lactobacillus, Paramecia, Amoebae, Euglena, rotifers, and humans. • Autotroph: Self-feeders; they sustain themselves without eating anything derived from other living beings • Heterotroph: get energy from compounds produced by other organisms

2. Write the summary equation for the process of photosynthesis. Indicate which reactant becomes oxidized and which reactant becomes reduced. Explain how each reactant is imported into a leaf, and how each product is exported from the leaf. • Photosynthesis: 6CO2 + 6H2O + energy --> C6H12O6 + 6O2

3. Name the three membranes and the three aqueous compartments found in a chloroplast. In which membrane are the enzymes of the light reactions embedded? In which compartment are the enzymes of the Calvin Cycle found? Indicate where in photosynthesis—the light reactions or the Calvin Cycle—each reactant is consumed and each product is produced. • Chloroplasts are found in the cells of mesophyll, the interior tissue of the cell. The chlorophyll is in the membranes of thylakoids (connected sacs in the chloroplast). Thylakoids may be stacked in columns called grana. Chloroplasts contain stroma, a dense interior fluid. • Light reactions occur in the thylakoids. • Calvin cycle occurs in the stroma. • ATP and NADPH

4. What two products are made by the light reactions for use in the Calvin Cycle? (See Fig. 10.5) • ATP and NADPH 5. What is the original source of electrons for the manufacture of sugar? What byproduct is created when electrons are stripped away? With what energy are the electrons excited? 

Water is split, providing a source of electrons and protons.

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The light reactions generate ATP and increase the potential energy of electrons by moving them from water to NADPH.

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The Calvin cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH.

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The Calvin Cycle forms sugar from CO2. O2 is created when electrons are stripped away.

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Electrons are excited by ATP.

6. Which coenzyme carries electrons in photosynthesis? How is it similar and different from NAD+? Where in photosynthesis—the light reactions or the Calvin Cycle—is the coenzyme reduced? Where is it oxidized? • NADP+ • NADP+ is simply NAD+ with a third phosphate group attached • NADP+ - is reduced to NADPH in the light stage and the NADPH is oxidized to NADP+ in the Calvin Cycle. 7. Why are several different pigments used in photosystems? What is the main pigment used? •Different pigments absorb light better at different wavelengths. the different pigments allow plants to obtain as much energy as possible by using multiple wavelengths of light •Chlorophyll is the main pigment used

8. According to the absorption spectrum of chlorophyll, which wavelengths/colors of visible light does it absorb? Which wavelengths are reflected and transmitted? •Chlorophyll a absorbs light in the blue-violet region, chlorophyll b absorbs red-blue light, and both a and b reflect green light (which is why chlorophyll appears green)

9. What are the three parts of a photosystem, and how do they function together to harvest light? Identify the first redox reaction of photosynthesis.

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i.100s of chlorophylls (antennae complex) ii. oxidizing agent (primary electron acceptor) iii. chlorophylls next to the PEA (reaction center chlorophylls)

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Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light-independent reactions.

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In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll; that energy is converted into stored chemical energy in the form of NADPH (nicotinamide adenine dinucleotide phosphate) and ATP (adenosine triphosphate). Protein complexes and pigment molecules work together to produce both NADPH and ATP

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Photosystem I is referred to by the wavelength at which its reaction center best absorbs light, or P700; photosystem II is also known by this characteristic, or P680

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[H.] ions reduce the carbon in CO2

10.Describe the steps of the light reactions, as presented in lecture. I am not so interested in the step numbers, but that you understand WHAT happens and why. Summarize the path energy takes from entering the light reactions as a photon to moving onward as energized electrons. During the light reactions, there are two possible routes for electron flow: cyclic and linear 1. A photon hits a pigment and its energy is passed among pigment molecules until it excites P680 2. An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+) 3. H2O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680

-P680+ is the strongest known biological oxidizing agent -O2 is released as a by-product of this reaction 4. Each electron "falls" down an electron transport chain from the primary electron acceptor of PS II toPS I 5. Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane -Diffusion of H+ (protons) across the membrane drives ATP synthesis 6. In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron acceptor 7. Each electron "falls"down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd). 8. The electrons then reduce NADP+ to NADPH, which is then available for the Calvin cycle - The energy changes of electrons during linear flow through the light reactions can be shown in a mechanical analogy 11. Explain how ATP is made by photophosphorylation, (FROM what reactants, and WITH what energy source) and where in chloroplasts it occurs. Where is this ATP USED?

12.What are the three phases of the Calvin Cycle, and what does each accomplish? In which decade did Melvin Calvin, Andrew Benson, and colleagues work out the cycle

(a.k.a. the Calvin-Benson Cycle)? When did Calvin receive the Nobel Prize in Chemistry? (He is going to appear on the Forever Stamp!) 

In phase 1 (Carbon Fixation), CO2 is incorporated into a fivecarbon sugar named ribulose bisphosphate (RuBP). The enzyme which catalyzes this first step is RuBP carboxylase or rubisco. It is the most abundant protein in chloroplasts and probably the most abundant protein on Earth. The product of the reaction is a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate.

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In phase 2 ( Reduction), ATP and NADPH2 from the light reactions are used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate, the three-carbon carbohydrate precursor to glucose and other sugars.

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In phase 3 (Regeneration), more ATP is used to convert some of the of the pool of glyceraldehyde 3-phosphate back to RuBP, the acceptor for CO2, thereby completing the cycle.

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Published in 1948

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Nobel Prize in 1961

13.Explain what carbon fixation is. Why is it important for both animal and plant life? 

Carbon fixation is the conversion of carbon dioxide into organic compounds during photosynthesis. It mostly refers to the processes found in autotrophs, usually driven by photosynthesis, whereby carbon dioxide is changed into sugars

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It is part of the process for food conversion

14.How many CO2 molecules are consumed in one cycle of the Calvin Cycle? How many CO2 must enter the cycle to produce one molecule of the sugar product of the cycle? How many cycles would be required for a leaf cell to make one molecule of glucose from this sugar product? Name the sugar product of photosynthesis. 

Each turn of the Calvin Cycle uses 1 CO2.

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3 CO2 (3 cycles) are needed for 1 G3P (glyceraldehyde 3-phosphate)

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G3P is not a glucose, but a three-carbon sugar

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For the net synthesis of one molecule of G3P, the cycle must take place three times, fixing three molecules of CO2

15.Review where electrons come FROM and where they END UP in cellular respiration and in photosynthesis. In which process do electrons LOSE potential energy and in which do they GAIN it?...