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Plant Physiology - Exam 2
Respiration, Photosynthesis, Adaptive Forms
Terms in this set (96)
Respiration is the process by which plant cells oxidize (remove electrons from) carbohydrates and eventually capture a portion of the released energy in the form of ATP.
It can also be described as the complete oxidation of glucose to CO2 and H2O.
List the inputs and products of respiration.
Inputs: Glucose, O2
Outputs: CO2, H2O, ATP
Summarize the importance of of respiration in plant growth and development.
Plants must carry out energetically expensive processes for their everyday functioning. They get their energy from ATP. Respiration produces this ATP.
What are the three steps of respiration?
Glycolysis, citric acid cycle, oxidative phosphorylation
Compare and contrast the structures and plant functions of glucose and sucrose. For structures, you should know the carbohydrate type (i.e., monosaccharide, disaccharide, polysaccharide. If disaccharide or polysaccharide, know the base units).
Glucose is a monosaccharide (a carbon with a water added). It is a hexose (6-carbon) sugar. It exists in both ring and chain form. It is the input for respiration. Two different ring structures exist: Alpha and beta.
Sucrose is a disaccharide, consisting of two sugar subunits covalently linked. It consists of glucose and fructose linked together. It is the form in which sugar is transported through plants. Synthesis requires consumption of energy and removal of H2O.
Describe the structural similarities and differences between starch and cellulose. For structures, you should know the identity of the monosaccharide building block, as well as the ring form (alpha or beta) of the monosaccharide building block.
Both starch and cellulose are polysaccharides, linked at the 1 and 4 carbons. However, starch consists of alpha glucose (rings), while cellulose consists on beta glucose (also a ring).
Describe the functional differences between starch & cellulose.
Starch is primarily used for energy storage - both short term (as in a leaf, ,or long term (as in potato).
Cellulose is primarily used for structural support (as in the case of cellulose microfibrils).
Summarize the roles of NADH and FADH2 in cellular respiration.
Both donate electrons. They do this by providing a hydrogen molecule to the oxygen molecule in the electron transport chain. The hydrogen molecule is later used to produce ATP.
Indicate where (which of the three respiration processes) and how O2 is used in respiration.
Glycolysis takes place in the cytosol (cytoplasm).
The citric acid cycle takes place in the matrix of the mitochondrion.
Oxidative phosphorylation also takes place in the inner matrix of the mitochondrion.
The role of oxygen: Electrons go through the electron transport chain and end up on oxygen, which creates water.
Glycolysis is the process in which:
One glucose molecule is converted to two, 3-carbon molecules. (This uses 2 ATP, and produces 4 ATP and 2 NADH.)
After glycolysis (but before the citric acid cycle), each 3-carbon molecule is converted to Acetyl CoA. (This produces 2 CO2 and 2 NADH.) This takes place in the matrix of the mitochondria.
The citric acid cycle takes place in the matrix of the mitochondria. Electrons from Acetyl CoA are put onto NADH and FADH2. Each Acetyl CoA yields 1 ATP, 3 NADH, 1 FADH2, and 2CO2. Because there are two Acetyl CoA's, that means that 2 ATP, 6 NADH, 2 FADH2, and 4 CO2 are produced in this part of the process.
Oxidative phosphorylation relies on the electron transport chain, which is located in the inner matrix of the mitochondrion. In oxidative phosphorylation, NADH and FADH2 deliver electrons to the electron transport chain.
Electrons flow along the electron transport chain.
Electrons ultimately end on oxygen to produce water.
The passing of electrons between carriers creates energy (through redox reactions).
Energy from the passing of electrons is used to pump H+ gradients against the concentration gradient (electrochemical gradient).
There are more H+ in the intermembrane space (above the membrane) than in the matrix.
H+ are pumped from the matrix (low H+) to the intermembrane space (high H+). This pumping against the electrochemical gradient requires energy.
From the intermembrane space, protons are passed back into the matrix via a channel called ATP synthase. This passing back of the electrons produces energy, which is used to produce ATP.
Indicate the specific sub-cellular location of the mitochondrial electron transfer chain.
The mitochondrial electron transport chain is located on the inner matrix of the mitochondrion.
Describe how the mitochondrial electron transfer chain utilizes the energy released by the flow of electrons.
The flow of electrons between electron carriers creates redox reactions, which produce energy. This energy is used to pump H+ protons AGAINST the concentration gradient (from the inner matrix to the intermembrane space). From here, ATP synthase can perform chemiosmosis to pump the electrons back into the inner matrix, and produce ATP along the way.
Describe how the process of oxidative phosphorylation utilizes the proton gradient that is established during electron transfer.
During oxidative phosphorylation, ATP synthase performs chemiosmosis to return the protons to the inner matrix of the mitochondrion. ATP produces ATP during this step.
Describe the role of ATP Synthase in oxidative phosphorylation.
ATP synthase is a channel through which protons can flow back into the matrix of the mitochondrion, with the electrochemical gradient. This movement of protons down the concentration gradient produces energy. This energy is used to produce ATP.
What is chemiosmotic coupling?
Chemiosmotic coupling is the process by which a chemical process is combined with a transport process across a selectively permeable membrane. In the case of ATP synthase, this occurs because the proton gradient across the inner matrix of the mitochondrion has potential energy.
Which process produces the most ATP in respiration?
Oxidative phosphorylation (32 ATP?)
The energy released by the flow of electrons along the mitochondrial electron transport chain is directly used to:
Pump protons against the concentration gradient.
Most of the electron carriers in the mitochondrial electron transport chain are located in:
The inner matrix of the mitochondrion. (OR MEMBRANE??)
How do NADH and FADH2 contribute to the production of ATP in respiration?
They donate electrons to the electron transport chain
Respiration is the process by which plants generate energy by oxidizing _____. In addition to ATP and water, respiration produces ___.
ATP synthase utilizes a gradient of _____ to produce ATP.
What is the role of O2 in respiration?
Oxygen is the ultimate electron acceptor, which produces water.
What molecular feature do the structural and energy-storage polysaccharides have in common? How are structural and energy-storage polysaccharides different at the molecular scale?
Both the energy-storing polysaccharides (starch) and the structural polysaccharides (cellulose) both are polymers of glucose linked at the 1 and 4 carbons. However, cellulose consists of beta glucose, while starch consists of alpha glucose.
What is sucrose hydrolysis?
When sucrose is split into two units (hydrolysis), energy is released.
What are the types of monosaccharide sugar?
Glucose and fructose.
What are the types of disaccharide sugar?
Galactose, sucrose, lactose, and maltose.
What is electronegativity? How does it apply to redox reactions?
Electronegativity is the tendency of an atom to attract an electron towards itself. An atom with a high electronegativity will take an electron from an atom with low electronegativity.
An agent that LOSES an electron. (Agent which complements the oxidation reaction.)
An agent that GAINS an electron. (Agent which complements the reduction reaction.)
Chemical species that GAINED an electron.
Chemical species that LOST an electron.
Electrons are GAINED.
Electrons are LOST.
What is the electronegativity trend in the periodic table?
As you move left to right, electronegativity increases. So, species on the right side of the table will have a higher tendency to take electrons from species on the left side of the table.
What is the relationship between proton concentration and pH?
Proton concentration is inversely related to pH. So, a high concentration of protons correlates to a low pH, and a low concentration of protons correlates to a high pH.
What are the five structures of chloroplasts?
Lumen, stroma, thylakoid, outer envelope, inner envelope
What is the initial reductant in photosynthesis?
A reductant is a species that loses electrons. In the light-dependent reactions of photosynthesis, water is the first species to lose (or donate) an electron.
What is the source of energy needed for the oxidation of water in the light-dependent reactions of photosynthesis?
The oxidation of water first requires energy, because water has a high electronegativity and does not give up electrons easily. The source of energy needed to remove electrons from water comes from light.
Indicate where and how oxygen is produced in the light-dependent reactions of photosynthesis.
When light hits PS II, electrons are excited to a higher energy state. This energy is used to remove electrons from water. This yields oxygen. (This takes place in the lumen of the chloroplast.)
Indicate where and how NADPH is produced in the light-dependent reactions of photosynthesis.
NADPH is produced when electrons are excited to a higher state in PSI. When these electrons are excited to a higher state, it provides the energy required for the subsequent redox reaction in which Ferredoxin (Fd) receives these electrons and yields NADPH. It is produced in the STROMA of the chloroplast.
Describe how the energy produced from redox reactions is used light-dependent reactions of photosynthesis.
First, water (the reductant) loses electrons. Light hits these electrons and excites them to higher energy states. From here, these electrons are passed between carriers, creating redox reactions. These redox reactions produce energy (ATP) which is used to pump protons against the concentration gradient: The redox reactions pump protons from the STROMA (low proton concentration) to the LUMEN (high proton concentration). (REMEMBER, DURING THE DAY, THE pH OF THE STROMA IS HIGHER THAN THE pH OF THE LUMEN.) From here, ATP synthase performs chemiosmosis to move protons back into the stroma, producing more ATP along the way.
Describe how chemiosmosis applies to the light-dependent reactions of photosynthesis.
The redox reactions pump protons from the STROMA (low proton concentration) to the LUMEN (high proton concentration). From here, ATP synthase performs chemiosmosis to move protons back into the stroma, producing more ATP along the way.
What will be the diurnal changes in lumen and stroma pH in the light-dependent reactions?
During the day:
-The lumen has a high concentration of protons, which means it has a lower pH than the stroma.
-The stroma has a low concentration of protons, which means it has a higher pH than the lumen.
-The lumen has a decreased concentration of protons, which means it has a higher pH than the daytime.
-The stroma has an increased concentration of protons, which means it has a lower pH than the daytime.
Justify diurnal changes in stroma and lumen pH by describing the underlying causes.
During the day, the light-induced redox reactions remove more protons from the stroma than are returned via ATP synthase.
During the night, the light-induced redox reactions are discontinued. ATP synthase continues to move protons back to the stroma until equilibrium is reached.
Use relationships among wavelength, frequency and radiant energy to predict relative differences in quantum for light of different wavelengths
Quantum energy is proportionally related to frequency, and inversely related to wavelength. The smaller the wavelength, the larger the quantum energy. The higher the frequency, the lower the quantum energy.
(Wavelength is the distance between successive wave crests. Frequency is the number of waves passing a point in a given amount of time.)
Where are the light-harvesting complexes located?
Inside photosystems II and 1 (PSII and PSI).
What is the general structure of a light-harvesting complex?
Hundreds of antenna pigments surrounding a reaction center.
What are the differences and similarities between antenna pigments and reaction centers?
Similarity: Both of them are located inside of a light-harvesting complex.
Differences: There are hundreds of antenna pigments for any one reaction center.
Antenna pigments are any color compound. The reaction center is a specialized pigment that converts light energy into chemical energy.
Describe the functions for each of the following three pigments: chlorophyll a, chlorophyll b and carotenoids.
Cl a and b: primary energy-harvesting pigments in the light dependent reactions. Their primary function is to collect light energy and pass energy to the reaction center.
Carotenoids (car): absorb some energy and pass some energy to the reaction center, but their primary function is to protect against an overabundance of light energy.
What is photoinhibition?
Photoinhibition is the inhibition of photosythesis due to presence of excess light. This can happen when: 1) The reaction centers can't accept any more energy, 2) carotenoids can't accept any more energy, or 3) reactive oxygen species (ROS) form and damage chloroplast membranes.
Which gas variables can be monitored to measure photoinhibition? Can these gases also be used to measure photosynthesis?
Photoinhibition can be measured by an excess of CO2 around the plant and a lack of O2 output. Yes, these can be used to measure photosynthesis as well.
USE REDOX TERMINOLOGY TO DESCRIBE THE LIGHT-DEPENDENT REACTIONS OF PHOTOSYNTHESIS.
I DON'T KNOW HOW TO DO THIS.
What process supplies the energy needed for carbon fixation?
The light-dependent reactions of photosynthesis.
What is the primary function of carotenoids?
Prevent oxidative damages to chlorophyll and chloroplasts
What is the very next event that happens when a chlorophyll molecule absorbs light?
An electron is boosted to a higher energy state.
In the light-dependent reactions of photosynthesis, where are most of the carriers of the electron transport chain?
In the thylakoid of the chloroplast.
What is the initial reductant in the mitochondrial electron transport chain?
Where are most of the carriers of the electron transport chain in the light-dependent reactions of photosynthesis located?
In the thylakoid of the chloroplast
How is water used in photosynthesis?
It is the initial electron donor as well as the initial reductant.
Where is O2 produced in the light-dependent reactions?
The redox reactions between PSII and Plastoquinone produces energy. In this redox reaction, which chemical species is more electronegative? PSII or Plastoquinone?
Plastoquinone is more electronegative because it receives the electron from PSII.
Is cytochrome b6f reduced or oxidized by Plastoquinone?
Redox reactions in the light-dependent reactions release energy. How is the energy released from redox reactions DIRECTLY used in the light-dependent reactions?
To eastblish a proton gradient needed for ATP formation
Where does the Calvin cycle take place?
Inside the stroma of the chloroplast.
What are the three phases of the Calvin cycle? In which phase in NADPH used?
The three phases of the Calvin cycle are:
NADPH is used in the reduction portion of the cycle.
What is Rubisco's role in carbon fixation?
RUBISCO is an enzyme and it catalyzes the first reaction in C3 plants. It binds with a carbon. This is very unstable, so very quickly, this compound breaks down into two molecules of 3-phosphoglycerate.
Describe the RUBISCO carboxylase reaction by listing the names and quantities of the reaction's inputs and outputs.
3 molecules of ribulose bisphosphate
3 molecules of RUBISCO
3 molecules of CO2
6 molecules of 3-phosphoglycerate
Describe the RUBISCO carboxylase reaction by listing the number of carbon atoms for the reaction's inputs and outputs.
3 molecules of ribulose bisphosphate (5 * 3 = 15)
3 molecules of RUBISCO (none: It is an enzyme)
3 molecules of CO2 (1 * 3 = 3)
18 carbons total for input
6 molecules of 3-phosphoglycerate (6* 3 = 18)
18 carbons for output
Predict when (day or night) the Calvin Cycle takes place based on the relationship between pH and RUBISCO activity. Justify your prediction by describing 1) the diurnal changes in stroma pH, and 2) the effects of pH change on RUBISCO.
During the day, the pH of the stroma is relatively HIGH. This pH environment ACTIVATES Rubisco, which allows the Calvin Cycle to take place.
During the night, the pH of the stroma is relatively LOW. This low pH environment DEACTIVATES Rubisco, which does not allow the Calvin cycle to take place.
Describe the output from the Calvin Cycle. To correctly describe the output, you should indicate the molecule's name (glyceraldehyde-3-phosphate) and the number of carbons it has.
The output from one turn of the Calvin Cycle is six molecules of glyceraldehyde 3-phosphate.
glyceraldehyde 3-phosphate has 3 carbons in each molecule, so there are 18 carbons in total.
Predict how many Calvin Cycles are needed to produce a hexose sugar. Justify your prediction using knowledge on the structure of the carbon output from the Calvin Cycle.
Two molecules of glyceraldehyde-3-phosphate are needed to make one hexose sugar. This is because a hexose sugar has six carbons, while one molecule of glyceraldehyde-3-phosphate only has 3 carbons.
Summarize why the titles "Light-independent reactions" or "Dark reactions" are not appropriate for the Carbon Fixation Reactions.
The Calvin cycle does not take place at night. Light indirectly activates RUBISCO.
Indicate how many ATP and NADPH are needed by the Calvin Cycle to produce a hexose sugar.
18 ATP and 12 NADPH (9 ATP and 6 NADHP per one turn, but the cycle turns twice).
Indicate the physiological process that supplies the Calvin Cycle with the ATP and NADPH needed for carbon fixation.
The physiological process that supplies the Calvin Cycle with the ATP and NADPH needed for carbon fixation comes from the light-dependent reactions of photosynthesis.
List the inputs and outputs (products and substrates) of the oxygenation reaction of Rubisco (ribulose bisphosphate carboxylase-oxygenase).
The oxygenation reaction of Rubisco (ribulose bisphosphate carboxylase-oxygenase) requires:
1 molecule of O2
1 molecule of RUBISCO
1 molecule of Ribulose bisphosphate
1 molecule of 3-phosphoglycerate
1 molecule of phosphoglycolate
Describe how Rubisco's oxygenation reaction negatively affects carbon fixation reactions.
Oxygen and CO2 compete for the same binding site on Rubisco.
Oxygen inhibits CO2 binding to Rubisco (O2 inhibits the carboxylase reaction, which is the one we want).
The oxygenation reaction decreases CO2 fixation by reducing the amount of ribulose bisphosphate available for CO2 fixation.
O2 binding to Rubisco yields phosphoglycolate, which cannot be used in the Calvin cycle.
Photorespiration consumes energy (2 ATP) that would not be consumed if the RUBISCO carboxylase reaction took place.
Photorespiration will eventually yield 3-phosphoglycerate, which CAN be used in the Calvin cycle; it just takes more time and energy (2 extra ATP).
Compare and contrast photorespiration and respiration.
Both produce CO2.
Summarize the evolutionary hypothesis predicting why plants perform photorespiration.
Rubisco originated from a time with lower O2 concentrations in the atmosphere. Under lower O2 atmospheres, oxygenation reaction penalties are not as severe.
Describe the two fundamental photosynthetic shortcomings that can limit plant growth.
Photorespiration: The oxygenation reaction of RUBISCO reduces the efficiency of the photosynthetic process.
As CO2 enters the plant, H2O exits the plant. (Plant loses water!)
Predict plant environments that induce high rates of photorespiration. Justify your prediction.
The efficiency of the Calvin Cycle depends on the ratio of CO2 to O2.
As temperature increases, the solubility of CO2 DECREASES DRAMATICALLY.
As temperature increases, the solubility of O2 DECREASES VERY SLIGHTLY.
So as temperature increases, there is a sharp decline in the solubility of CO2, and only a modest decline for the solubility of O2.
Therefore, photorespiration is most likely to occur under warm conditions. The chances for photorespiration increase as the environment becomes hotter.
Compare and contrast RUBISCO and PEPCase in terms of substrates and products.
RUBISCO uses the following substrates:
CO2 (a 1-carbon molecule), and
Ribulose bisphosphate (a 5-carbon molecule).
RUBISCO yields the following products:
2 molecules of 3-phosphoglycerate (a 3-carbon molecule).
PEPCase uses the following substrates:
CO2 (a 1-carbon molecule), and
Phosphoenol-pyruvate (PEP) (a 3-carbon molecule).
PEPCase yields the following products:
Malate (a 4-carbon molecule)
Important to understand: PEPCASE cannot perform an oxygenation reaction.
Important to understand: PEPCase does NOT replace RUBISCO. Plants with PEPCase also have RUBISCO and all other Calvin cycle enzymes.
Describe the fate of malate produced by PEPCase in the C4 photosynthetic pathway.
Malate is decarboxylated near RUBISCO, which means it is able to detach a CO2 molecule from itself, which then binds to RUBISCO, and then the Calvin cycle takes place as per usual.
Indicate which cell type (bundle sheath or mesophyll) has relatively low levels of O2.
Bundle sheath cells
Indicate which cell type (bundle sheath or mesophyll) has relatively high levels of O2.
Indicate which cell type (bundle sheath or mesophyll) contains the enzyme phosphoenol pyruvate carboxylase (PEPCase).
Indicate which cell type (bundle sheath or mesophyll) contains the rubisco.
Indicate which cell type (bundle sheath or mesophyll) is enriched in CO2.
Explain the physiological basis for the advantage of C4 photosynthesis under hot conditions.
Under hot conditions, concentrations of CO2 are going to be decreased compared to O2. For this reason, it is advantageous for plants to have the C4 pathway because the stroma will have high concentrations of both CO2 and O2 (which can lead to photorespiration)! Instead, plants use the C4 pathway so that rather than diffusing CO2 from the atmosphere, it is derived from Malate, so there is no chance for O2 (and therefore photorespiration) to occur.
Explain the physiological basis for the disadvantage of C4 photosynthesis under cool conditions - be sure to consider the cost for recreating phosphoenol-pyruvate.
Under cool conditions, there will be a smaller chance for photorespiration to occur because there will be a higher CO2 to O2 concentration (since CO2 concentration increases in cool temperatures). Therefore, photorespiration is a smaller threat in cool conditions. Also, the C4 pathway uses energy that the C3 pathway does not. The C4 pathway requires ATP in order to regenerate phosphoenol-pyruvate. This is a balanced trade-off is the threat of photorespiration is high, but if it is not, then the plant is just wasting ATP.
Which environments favor plants with CAM carbon fixation?
Dry ecosystems favor CAM plants because the CAM carbon fixation pathway reduces the tradeoff between H2O vapor loss and CO2 uptake.
At what time of day do CAM plants have open versus closed stomata?
CAM plants have open stomata at night, and closed stomata during the day.
When is RUBISCO active in CAM plants?
What is the role of malic acid in CAM carbon fixation?
CO2 diffuses into the plant at night, and is stored as malic acid! Then, during the day, this malic acid is broken down to release CO2 to be used in the Calvin cycle.
How do CAM plants fix carbon with minimal loss of water vapor?
They only open their stomata at night, which decreases loss of water vapor in hot environments.
Explain the photosynthetic factor that severely limits the growth of CAM plants.
The photosynthetic capability for CAM plants is severely limited by the vacuole's ability to store malic acid. Therefore, carbohydrate production is often decreased as a result of diminshed malic acid storage.
Predict leaf pH for CAM and C3 plants at different times of the day (day vs. night). Justify predictions.
C3 plants will have similar leaf pH throughout the day and night. CAM plants will have a higher pH during the day and a lower pH at night. This is because CAM plants have a decreased conentration of malic acid during the day compared to night.
List similarities and differences among CAM, C4, and C3 photosynthetic pathways.
All have light-dependent reactions.
All have daily changes in stroma/lumen pH (in the same way).
All have the Calvin cycle.
Rubisco is activated during the day.
RUBISCO is in the stroma.
CAM plants look like C3 leaves.
Only CAM plants open stomata at night.
CAM plants reduce H2O loss.
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