Photosynthesis
NADP
"Empty" Electron Carrier
Describe a chlorophyll molecule
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Photosynthesis converts light energy to the chemical energy of food
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The Calvin Cycle uses the chemical energy of ATP and NADPH to reduce CO2 to sugar
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In general, photosynthesis:
1. 200-400 pigment molecules linked together in antenna array 2. 1 pair of chlorophyll a molecules in reaction center which are able to transfer electrons. 3. Resonance energy transfer between array of pigments and reactions center.
What happens to the products of photorespiration?
1. Glycolic acid shipped to peroxisome and metabolized into glycine 2. Glycine is sent to the mitochondria and metabolized into serine 3. Serine is sent back to peroxisome and metabolized into glycerate 4. Glycerate is shipped to chloroplast and enter Calvin Cycle as PGA
What is the cost of photorespiration?
2 NADH and 1 ATP
Photorespiration
A metabolic pathway that consumes oxygen and ATP, releases carbon dioxide, and decreases photosynthetic output. Photorespiration generally occurs on hot, dry, bright days, when stomata close and the O2/CO2 ratio in the leaf increases, favoring the binding of O2 rather than CO2 by rubisco.
Which of the following equations represents photosynthesis? 6CO2 + 6O2 → C6H12O6 + 6H2O 6H2O + 6O2 → C6H12O6 + 6CO2 C6H12O6 + 6O2 → 6CO2 + 6H2O C6H12O6 + 6CO2 → 6O2 + 6H2O 6CO2 + 6H2O → C6H12O6 + 6O2
6CO2 + 6H2O → C6H12O6 + 6O2 Photosynthesis requires carbon dioxide and water for the production of sugar and oxygen.
Reaction-center complex
A complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor. Located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. Excited by light energy, the pair of chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain.
Light harvesting complex
A complex of proteins associated with pigment molecules (including chlorophyll a, chlorophyll b, and carotenoids) that captures light energy and transfers it to reaction-center pigments in a photosystem.
Thylakoids
A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.
Thylakoids
A flattened, membranous sac inside a chloroplast. Thylakoids often exist in stacks called grana that are interconnected; their membranes contain molecular "machinery" used to convert light energy to chemical energy.
Chlorophyll
A green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes. Chlorophyll a participates directly in the light reactions, which convert solar energy to chemical energy.
Photosystem I
A light-capturing unit in a chloroplast's thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P700 chlorophyll a at its reaction center. remaining pigments = antenna pigments
Photosystem
A light-capturing unit located in the thylakoid membrane of the chloroplast or in the membrane of some prokaryotes, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes. There are two types of photosystems, I and II; they absorb light best at different wavelengths.
C4 Plants
A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle.
CAM plants
A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. In this process, carbon dioxide entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.
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.
Glyceraldehyde 3-phosphate (G3P)
A three-carbon carbohydrate that is the direct product of the Calvin cycle; it is also an intermediate in glycolysis.
What two molecules are produced by the light reactions and used to power the Calvin cycle? CO2 and O2 C6H12O6 and O2 C6H12O6 and RuBP ATP and NADPH G3P and H2O
ATP and NADPH ATP and NADPH are both products of the light reactions and are used to power the Calvin cycle.
The light reactions of photosynthesis supply the Calvin cycle with
ATP and NADPH.
What is the advantage of CAM metabolism?
Allows plants to function well under limited water supply as well as high light intensity.
Carotenoids
An accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.
What connects the two photosystems in the light reactions? Chlorophyll A thylakoid An electron transport chain A chain of glucose molecules The Calvin cycle
An electron transport chain
PEP carboxylase
An enzyme that adds CO2 to phosphoenolpyruvate (PEP) to form oxaloacetate in mesophyll cells of C4 plants. It acts prior to photosynthesis.
Heterotrophs
An organism that obtains organic food molecules by eating other organisms or substances derived from them.
CAM Photosynthesis
At night, stomata are open. CO2 combined with PEP to form 4C organic acids, which accumulate at night. During the day when stomates are closed, CO2 is released and enters carbon fixation reactions.
Which of the following statements is a correct distinction between autotrophs and heterotrophs? Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic. Only heterotrophs require oxygen. Cellular respiration is unique to heterotrophs. Only heterotrophs have mitochondria. Only heterotrophs require chemical compounds from the environment.
Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.
C4 pathway: Where is CO2 released from the 4C organic acid?
Bundle sheath cell. This is the site of carbon fixation.
How do CAM and C4 plants differ?
C4: light and dark reactions separated by space CAM: light and dark reactions separated by time
What are the three phases of The Calvin cycle?
Carbon Fixation Reduction; Regeneration of RuBP
What provides the carbon atoms that are incorporated into sugar molecules in the Calvin cycle? Sucrose (C12H22O11) RuBP Carbon dioxide (CO2) Glucose (C6H12O6) G3P (C3H6O3)
Carbon dioxide (CO2) Carbon dioxide provides the carbon atoms that are incorporated into sugars in photosynthesis. Carbon dioxide initially combines with RuBP, and RuBP is regenerated to continue the Calvin cycle.
In which of the following organelles does photosynthesis take place? Chloroplast Mitochondrion Ribosome Central vacuole Nucleus
Chloroplast Chloroplasts use energy from light to transform carbon dioxide and water into sugar and oxygen.
What is the role of Rubisco in the presence of O2?
Combines RuBP with O2 and H2O resulting: 1 molecule of PGA (3C) 1 molecule of Glycolic acid (2C)
C4 pathway
Decouples light reactions and carbon fixation reactions. CO2 converted to 4C organic acid in MESOPHYLL cells.
What provides electrons for the light reactions? CO2 The Calvin cycle H2O Light O2
H2O Electrons are stripped from water in the light reactions of photosynthesis. Light provides the energy to excite electrons.
Which of the following sequences correctly represents the flow of electrons during photosynthesis? NADPH → chlorophyll → Calvin cycle H2O → NADPH → Calvin cycle NADPH → O2 → CO2 NADPH → electron transport chain → O2 H2O → photosystem I → photosystem II
H2O → NADPH → Calvin cycle
What is the advantage of photorespiration?
Helps C3 plants survive under hot dry conditions
Bundle-sheath cells
In C4 plants, a type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf.
How is photosynthesis similar in C4 plants and CAM plants?
In both cases, rubisco is not used to fix carbon initially.
Primary electron acceptor
In the thylakoid membrane of a chloroplast or in the membrane of some prokaryotes, a specialized molecule that shares the reaction-center complex with a pair of chlorophyll a molecules and that accepts an electron from them.
What transports electrons from the light reactions to the Calvin cycle? NADH NADPH An electron transport chain FADH2 Chlorophyll
NADPH NADPH is an electron carrier that picks up electrons in the light reactions and releases them in the Calvin cycle. An electron transport chain conveys electrons from one photosystem to the other within the light reactions.
What is photorespiration?
O2 out competes CO2 at active site of Rubisco resulting in 1 PGA and 1 Glycolic Acid
Photo system II
One of two light-capturing units in a chloroplast's thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P680 chlorophyll a at its reaction center. Pheophytin = primary electron acceptor Electrons recovered by splitting H2O Mn complex catalyzes splitting of H2O
C4 pathway: What enzyme is the primary enzyme?
PEP carboxylase adds a CO2 to PEP forming oxaloacetate which can be converted to malate and asparate.
Stroma
The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.
Where does the Calvin Cycle take place?
The Calvin cycle is a complex series of chemical reactions carried out in the stroma.
Photosynthesis
The conversion of light energy to chemical energy that is stored in glucose or other organic compounds; occurs in plants, algae, and certain prokaryotes.
Light Reactions
The first of two major stages in photosynthesis (preceding the Calvin cycle). These reactions, which occur on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes, convert solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process.
Carbon Fixation
The initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote).
Photophosphorylation
The process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton-motive force generated across the thylakoid membrane of the chloroplast or the membrane of certain prokaryotes during the light reactions of photosynthesis.
Calvin cycle
The second of two major stages in photosynthesis (following the light reactions), involving fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrate.
Describe Carbon Fixation in the Calvin Cycle
Three molecules of carbon dioxide are added to three molecules of a five-carbon sugar abbreviated RuBP. These molecules are then rearranged to form six molecules called 3-PGA, which have three carbons each.
Chloroplasts
absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
carotenoids
accessory pigment
chlorophyll b
accessory pigment
Chlorophyll a
all photosynthetic organisms
With regard to the structure of chlorophyll a, what is the significance of the hydrophobic tail?
all these pigments end up embedded in membranes.
What are the two stages of photosynthesis
light dependent and light independent reactions
In mechanism, photophosphorylation is most similar to
oxidative phosphorylation in cellular respiration.
Stomata
pores on the leaf where O2 exits and CO2 enters
Autotrophs
produce their own organic molecules from CO2
Which of the following does not occur during the Calvin cycle? release of oxygen regeneration of the CO2 acceptor oxidation of NADPH consumption of ATP carbon fixation
release of oxygen
Which process is most directly driven by light energy? creation of a pH gradient by pumping protons across the thylakoid membrane removal of electrons from chlorophyll molecules reduction of NADP+ molecules ATP synthesis carbon fixation in the stroma
removal of electrons from chlorophyll molecules
Mesophyll
specialized for photosynthesis. In C3 and CAM plants, mesophyll cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis.
The light reactions take place in the _________ and the Calvin cycle takes place in the _________. stroma; thylakoids thylakoids; stroma inner membrane; outer membrane chloroplasts; mitochondria mitochondria; chloroplasts
thylakoids; stroma Within the chloroplast, the light reactions take place in the flattened sacs called thylakoids and the Calvin cycle takes place in the thick fluid called the stroma.
