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PHOTOSYNTHESIS Photosynthetic Organisms


Cyanobacteria Prokaryotic cells
Evolved between 2.3 and 3.5 billion years ago Produced oxygen on large scale: heterotrophic life becomes possible Are thought to be the “ancestors” of chloroplast–endosymbiosis

Eukaryotic Autothrophs
Algae: mostly marine and unicellular Plants: mostly found on land and multicellular Photosynthesis occurs in chloroplasts



Compare structure/function

Photosynthetic pigments
All biological pigments selectively absorb certain wavelengths of light while reflecting others. The light that is absorbed may be used by the plant to power chemical reactions. The reflected wavelengths of light determine the color the pigment will appear to the eye.

You can separate White Light into its component colors by passing the light through a PRISM.
6. The resulting array of colors, ranging from red at one end to violet at the other is called the VISIBLE SPECTRUM. 7. Each Color of Light has different Wavelengths, and a Different Energy.

Chlorophyll The main photosynthetic pigment
Two forms: Chlorophyll a (primary light absorbing pigment) and chlorophyll b Both have Magnesium molecule at core Porphyrin ring: Double bonds in hydrocarbon rings are delocalized and can absorb light energy Phytol tail: Hydrocarbon tail, hydrophobic, can dissolve in thylakoid membrane and anchor the chlorophyll molecule

Chlorophyll a

Accessory pigments Chlorophyll b
Caretenoids: B-carotene (yellow-orange) Xanthophylls : (yellow) Absorb photons that chlorophyll a cannot: increase absorbed energy Combination of Chlorophyll a and accessory pigments increases absorption range to almost all the visible spectrum.

Absoption Spectrum Absorption Spectrum: results from the ability of pigments to absorb electromagnetic radiation. Light absorbed is plotted as a function of the wavelength of the radiation.

Action Spectrum Action Spectrum: the efficiency of photochemical response to incident electromagnetic radiation. Photochemical reaction is plotted as a function of the wavelength of the radiation. The action spectrum of photosynthesis within an organism resembles the absorption spectra of chlorophyll. The difference arises because accessory pigments play a part in photosynthetic efficiency.

3.3 Photosynthesis: the Details

Light Harvesting Occurs in photosystems in the thylakoid membranes.
Photosystems are associated with electron transport chain

What is a ‘photosystem’ and where is it located?
A cluster of photosynthetic pigments and proteins embedded in the thylakoid membranes of chloroplasts absorb light energy.

excitation photoexcitation fluorescence Ground state

Photosystems I and II Both photosystems are in the thylakoid membranes
Photosystem I contains a special chlorophyll a molecule called P700. The 700 number is its absorption maximum in the red part of the visible spectrum (700 nm). The primary donor receives excitation energy either by absorbing a photon of suitable frequency (colour) or by excitation energy transfer from other chlorophylls within photosystem I Photosystem II contains a special chlorophyll a molecule called P680. The 680 number is its absorption maximum in the red part of the visible spectrum (680 nm).

How a Photosystem Harvests Light
Thylakoid membrane

Each photosystem has a ‘reaction center’ within it
Each photosystem has a ‘reaction center’ within it. What makes up a reaction centre? What does it do? A reaction center is a transmembrane protein complex containing chlorophyll a The electrons in chlorophyll a absorb the light energy and become energized enough to be ejected. (Oxidation). The electrons are captured by the primary electron acceptor (Reduction)

Energy transfer through
SERIES OF REDOX REACTIONS Radiant Energy (visible light spectrum) Glucose (and other energy storing molecules) (many small steps) Energy transfer through Photosynthetic pigments Subsequent intermediate molecules

LIGHT REACTIONS (converted in light-absorbing pigments) Radiant Energy
Electron Transport Chain (constantly losing electrons) Transfer energy H2O supplies electrons to pigments to keep reaction going (as pigments constantly lose electrons) ATP and NADPH (energy carriers)

Noncyclic electron flow
Stroma Thylakoid lumen Noncyclic electron flow

STEP 1 – Light Energy Forces Electrons to enter a Higher Energy Level in the TWO Chlorophyll a Molecules of Photosystem II. These Energized Electrons are said to be “EXCITED”. STEP 2 – The Excited Electrons have enough Energy to Leave Chlorophyll a Molecules. Because they have lost Electrons, the Chlorophyll a Molecules have undergone an OXIDATION REACTION (lost of Electrons). Each Oxidation Reaction must be accompanied by a REDUCTION REACTION (some substance must Accept the Electrons). The Substance is a Molecule in the Thylakoid Membrane Known as a PRIMARY ELECTRON ACCEPTOR. STEP 3 – The Primary Electron Acceptor then Donates (gives) the Electrons to the First of a Series of Molecules located in the Thylakoid. This Series of Molecules is called an ELECTRON TRANSPORT CHAIN, because it Transfers Electrons from One Molecule to the Next in Series. As the Electrons are pass from molecule to molecule, they LOSE most of the Energy they acquired when they were Excited. The Energy they LOSE is Harnessed to Move Protons into the Thylakoid. STEP 4 – At the same time Light is Absorbed by Photosystem II, Light is also Absorbed by Photosystem I. Electrons move from a Pair of Chlorophyll a Molecules in Photosystem I to another Primary electron Acceptor. The electrons that are LOST by these Chlorophyll a Molecules are REPLACED by the Electrons that have passed through the electron Transport Chain from Photosystem II. STEP 5 – The Primary Electron Acceptor of Photosystem I donates Electrons to different Electron Transport Chain. This Chain brings Electrons to the side of the Thylakoid Membrane that FACES THE STROMA. There Electrons COMBINE with a PROTON and NADP+. NADP+ is an Organic Molecule that ACCEPTS Electrons during REDOX Reactions. This reaction causes NADP+ to be Reduced to NADPH.

Below shows the First Set of Reactions of Photosynthesis, which occurs along the Thylakoid Membrane. These Reactions are called the Light Reactions and occur in the Electron Transport Chain. There are Three Events pictured here: The Electron Transport, The Splitting of Water, and Chemiosmosis- making of ATP.

Below is another view of the Light Reaction – Electron Transport Chain that Occurs along the Thylakoid Membrane within the Chloroplasts.

Non-cyclic photophosphorylation

Ultimately, the light reactions form ATP and NADPH + H+

Photophosphorylation specifically refers to the synthesis of ATP using light

In photosynthesis, the function of water is to supply free electrons When photosynthesis occurs, the oxygen that is released comes from water

Electrons released as a result of photolysis reduce photosystem II chlorophyll molecules



Cyclic Electron Flow Produces ATP, but no NADPH

What is cyclic electron flow?
In cyclic electron flow when photosystem I is struck by a photon with the correct energy, it will release electrons to the same carrier molecules as non-cyclic electron flow. These electrons move through a cytochrome system and cause hydrogen ions to move from the stroma across the thylakoid membrane to the inside of the thylakoid. The higher concentration of hydrogen ions inside the thylakoids can be used to make ATP. The chlorophyll molecule of PS I oxidizes the final electron carrier, gaining electrons to return to its reduced form.

Why is it called ‘cyclic’? The term ‘cyclic’ is used because the chlorophyll of PS I serves as both the electron donor and electron acceptor.

At what times does cyclic electron flow occur?
Cyclic electron flow would appear to occur when reserves of NADP+ are low, which would imply that levels of NADPH are high. This means there will be a shortage of electron acceptors, which results in electrons being accepted by the cytochrome electron carrier system.

During photophosphorylation, light causes the splitting of water molecules inside of chloroplasts in order to produce an energized electron and making ATP from ADP and Pi. In cyclic photophosphorylation, the energized electron from photosystem I returns to photosystem I via the cytochrome carrier system. This produces ATP, but not NADPH. In non-cyclic photophosphorylation both photosystems I and II energize an electron to a higher level. And this produces ATP as the electron goes through the cytochrome system and also produces NADPH.

p.145 4. (a) Broad leaves are thin to minimize the distance that gases, such as carbon dioxide, must travel from the stomata to the chloroplasts, thereby maximizing gas diffusion. 5. (a) A: granum B: stroma C: inner envelope membrane D: outer envelope membrane

Why are leaves green and why do these leaves change colour in the fall.
In spring and summer, leaves appear green because of the high concentration of chlorophyll that absorbs at the red and blue ends of the spectrum, leaving green light to be reflected to our eyes. Xanthophyll, carotenoids, and anthocyanins are overshadowed by the green light reflected by chlorophyll. In autumn, plants stop producing chlorophyll, causing the yellow, red, and brown colours of autumn leaves.

What are the products of the light reactions of photosynthesis?
The products of the light reaction of photosynthesis are oxygen, ATP, and NADPH.

b) A photon is a discrete packet of light.
A) Define light. B) What is a photon? C) How are the wavelength and energy of a photon related? D) Which possesses a higher energy value: red light or green light? Explain. a) Light, or electromagnetic radiation, is a form of energy that travels at 3 x 10 8 m/s in the form of photons. b) A photon is a discrete packet of light. c) As wavelength gets longer, the energy in a photon decreases, and as wavelength increases, the energy increases. d) Green light possesses a higher energy value than red light because it has a shorter wavelength.

What pigments are present in green plants?
Explain why yellow-coloured pigments are visible in autumn leaves but not in summer leaves. 8. (a) Green plants contain chlorophyll a, chlorophyll b, B-carotonoids, xanthophylls, and anthocyanins. (b) Yellow-coloured pigments are only visible in autumn leaves, because the chlorophyll pigments mask the yellow-coloured pigments the rest of the year. Plants stop producing chlorophyll in the autumn, so only the yellow, red, and brown colours are visible.

c) What is photosynthetically active radiation (PAR)
c) What is photosynthetically active radiation (PAR)? d) If green plants absorb all the wavelengths in PAR, why do they appear green? (c) Photosynthetically active radiation is the wavelengths of light between 400 nm and 700 nm that supports photosynthesis. (d) Green plants absorb all the wavelengths of photosynthetically active radiation, yet they appear green because the green wavelengths of light are absorbed the least when compared with other photosynthetically active radiation wavelengths.

Outfielders catch balls (pop fly, grounder,etc.) During each play the ball may be passed around the bases, to catcher, or thrown directly back to the pitcher, BUT at the end of each play it ends back at pitcher (REACTION CENTRE) By having 8 players in the field there is a greater chance of catching the ball; likewise by having a group of pigments in a photosystem, there is a greater chance of trapping more light energy and passing that energy to the reaction centre

CO2 (provides basic materials) & ATP + NADPH (supply energy to make molecules) GLUCOSE, ETC. (ENERGY RICH)

The Calvin Cycle is the MOST Common Pathway for Carbon Fixation.
Plant Species that fix Carbon EXCLUSIVELY through the Calvin Cycle are known as C3 PLANTS.

Below Shows the Second Set of Reactions in Photosynthesis, The Calvin Cycle which occurs in the Stroma of the Chloroplasts. In the Calvin Cycle, Carbon Atoms from CO2 are bonded, or “Fixed”, into organic compounds. This incorporation of CO2 into organic compounds is referred to as Carbon Fixation. The Calvin Cycle has Three Major Steps, which occur within the Stroma of the Chloroplasts.

The second set of Reactions in Photosynthesis involves a Biochemical Pathway known as the Calvin Cycle. This pathway produces Organic Compounds, using the energy stored in ATP and NADPH during the Light Reactions. In the Calvin cycle, Carbon Atoms from CO2 are bonded or “Fixed” into Organic Compounds. This incorporation of CO2 into Organic Compounds is referred to as CARBON FIXATION. The Calvin cycle has THREE Major Steps, which occur within the STROMA of the Chloroplast. STEP 1 – CO2 diffuses into the Stroma from surrounding Cytosol. An Enzyme combines a CO2 molecule with a Five-Carbon Carbohydrate called RuBP. The product is a Six-Carbon molecule that splits immediately into a pair of Three-Carbon molecules known as PGA. STEP 2 – PGA is converted into another Three-Carbon molecule, PGAL, in a two-part process. (1) Each PGA molecule receives a Phosphate Group from a molecule of ATP. (2) The resulting compound then receives a Proton from NADPH and releases a phosphate group producing PGAL, these reactions produce ADP and NADP+, and phosphate. These three products can be used again in the Light Reactions. STEP 3 – Most PGAL is converted back to RuBP – this is necessary to keep the Calvin cycle going. Some PGAL leave the Calvin Cycle and can be used by the Plant Cell to make other organic Compounds, including Amino Acids, Lipids, and Carbohydrates. Among the Carbohydrates are the Monosaccharides Glucose and Fructose, the Disaccharide Sucrose, and the Polysaccharides Glycogen, Starch, and Cellulose.

For a plant to produce a sugar, such as sucrose, that contains 12 carbon atoms the Calvin cycle… Assume noncyclic electron flow only 12 molecules CO2 36 ATP used 24 NADPH used 36 photons absorbed

ribulose bisphosphate carbon dioxide ATP NADH + H+ NADPH + H+ oxygen
Light-Dependent Light-Independent Reactants NADP ADP Pi Water Electron (from water) ribulose bisphosphate carbon dioxide ATP NADH + H+ Products NADPH + H+ oxygen glyceraldehyde-3-phosphate (eventually glucose) Source of energy Light

Define the following terms: ground state, excitation, and fluorescence.
Ground state: the state of a chlorophyll molecule when all the electrons are in their lowest energy levels. Excitation: the process whereby a molecule absorbs a photon of light energy and one electron moves to a higher, less stable energy level. Fluorescence: the emission of electromagnetic radiation, always with a longer wavelength than the excitation light energy, from an excited molecule as an electron returns to its ground state.

What is the primary function of photosynthesis?
Where in the chloroplast do the light reactions occur? What are the products of the light reactions, if you assume they involve noncyclic electron flow? In what phase of photosynthesis are the products of the light reactions used? (a) The primary function of photosynthesis is to capture electromagnetic radiation and convert it to chemical potential energy. (b) The light reactions occur on the thylakoid membranes of chloroplasts. (c) The products of noncyclic electron flow light reactions are ATP and NADPH (d) The products of the light reactions are used during the Calvin-cycle.

Name the gas released as a byproduct of the light reactions of photosynthesis.
Name the molecule that is the source of this gas. 3. (a) The gas released as a byproduct of the light reactions of photosynthesis is oxygen O2(g). (b) The two water molecules are split to produce one molecule of oxygen gas.

a) How many electrons must be removed from photosystem 2 to reduce one molecule of NADP+? B) Name the series of electron carriers that transport electrons from photosystem 2 to photosystem 1. C) What happens to the free energy that the electrons lose in this process? (a) Two electrons must be removed from photosystem II to reduce one molecule of NADP+ to NADPH. (b) Q, b6-f complex, and plastocyanin act as electron carriers between PS II and PS I. (c) The free-energy that the electrons lose in this process is lost as heat.

a) The herbicide 3-(3,4-dichlorophenyl)-1,1,-dimethylurea (DCMU) blocks the transport of electrons from photosystem 2 to the cytochrome b6-f complex. b) Why is DCMU an effective herbicide? (a) The herbicide 3-(3,4-dichlorophenyl)-1, 1, -dimethylurea (DCMU) will not affect ATP initially, because of cyclic electron flow; however, NADPH cannot be produced because electrons are not released. After a short time, depending on light intensity, ATP synthesis will stop because of the absence of reactants ADP and Pi. (b) DCMU is an effective herbicide because it prevents the Calvin cycle from functioning and no glucose or sucrose is created. The plant starves to death..

Noncyclic electron flow
8. Distinguish between cyclic and noncyclic electron flow. Item Noncyclic electron flow Cyclic electron flow (i) evolution of O2 Yes No (ii) production of NADPH (iii) production of ATP (iv) enabling of the Calvin cycle to fix CO2(g) Yes, however no NADPH prevents Calvin cycle from continuing

(c) The product of the rubisco enzyme is 3-phosphoglycerate.
What is the name of the enzyme that catalyzes the carbon fixation reaction of the Calvin cycle? What are the two substrates of this enzyme when it acts as a carboxylase? What is the name of the product of the first reaction of the Calvin cycle? Where in the chloroplast does this reaction occur? (a) The enzyme that catalyzes the carbon fixation reaction of the Calvin cycle is ribulose bisphosphate caboxylase / oxygenase (rubisco). (b) The two substrates of rubisco are ribulose bisphosphate and carbon dioxide. (c) The product of the rubisco enzyme is 3-phosphoglycerate. (d) The reaction involving rubisco occurs in the stroma of the chloroplast.

A) Why does a suspension of isolated chloroplasts not synthesize G3P in the dark, given carbon dioxide and water? B) What would have to be added to the test tube for photosynthesis to occur? 10. (a) A suspension of isolated chloroplasts will not produce G3P in the dark when given CO2 and H2O, because there is no ATP and NADPH present from the light reactions of photosynthesis. (b) Light energy would have to be added to the test tube to produce G3P.

What is the name of the three-carbon carbohydrate that is a final product of the Calvin cycle? What are the possible fates of this compound? The final product of the Calvin cycle is glyceraldehyde 3-phosphate (G3P). G3P can be used in the chloroplast to produce glucose, which can be stored as starch, or exported to the cytoplasm to be used directly or indirectly as sucrose in cellular respiration, or transported to other parts of the plant as sucrose by translocation.

How many molecules of carbon dioxide must enter the Calvin cycle for a plant to ultimately produce a sugar, such as sucrose, that contains 12 carbon atoms? How many ATP molecules will be used? How many NADPH molecules will be used? How many photons must be absorbed (assume noncyclic electron flow only)? 12. Twelve carbon dioxide molecules must enter the Calvin cycle to produce one molecule of sucrose, which requires 36 ATP, 24 NADPH, and 36 photons.

Which contains more free energy: three molecules of carbon dioxide or one molecule of phosphoglyceraldehyde? Explain. 13. One molecule of phosphoglyceraldehyde has more energy than three carbon dioxide molecules, because phosphoglyceraldehyde contains some of the light energy that was absorbed in the light reactions of photosynthesis.

Which one of the following is not a characteristic of the light reactions?
a.electrons are displaced b.carbon fixation happens c.reduction happens is converted from a physical to a chemical form e.they take place in the thylakoids of chloroplasts b.carbon fixation happens

Which of the following statements concerning the Calvin cycle is true?
I. ATP molecules are needed to keep the reactions going II. the process makes NADPH + H+ III. reduction occurs IV. oxygen is a product V. photophosphorylation occurs VI. carbon fixation occurs VII. takes place in the thylakoids of chloroplasts I, III, VI

Alternate Mechanisms of Carbon Fixation
Is there any energy cost associated with carbon dioxide fixation in the C3 path? NO

When the oxygen levels are higher, photosynthesis decreases. Why?
This is due to PHOTORESPIRATION! (the competition between oxygen and carbon dioxide on the Rubisco enzyme in the Calvin cycle!)

Ribulose bisphosphate carboxylase/oxygenase (Rubisco)
the enzyme that catalyzes the carbon fixation to RuBP. the most abundant enzyme on Earth is also the culprit of photorespiration since it cannot distinguish between CO2 and O2 This is the second enzyme to fix carbon dioxide in C4 and CAM plants!

In PHOTORESPIRATION, oxygen replaces carbon dioxide in a non-productive, wasteful reaction!

Glycolate undergoes subsequent metabolism, which releases CO2
Glycolate undergoes subsequent metabolism, which releases CO2. This is a waste, both in terms of the energy required to carry out the process and the CO2 lost.

C4 Photosynthesis: A way to overcome photorespiration! This is SPATIAL SEPARATION!

Which one is a C3 plant, and which is a C4 plant?

C4 PLANTS PEP carboxylase functions in the mesophyll, during the day to fix CO2 into a 4 carbon molecule These 4C molecules are transferred to the bundle sheath, where they are decarboxylated to release CO2, which enters the Calvin cycle – SPATIAL SEPARATION During the Hottest part of the day, C4 plants have their Stomata Partially Closed. Such plants lose only about half as much water as C3 plants when producing the same amount of Carbohydrate. C4 plants include corn, sugar cane and crabgrass.

What is the name of the first enzyme in the C4 pathway?
PEP carboxylase (phosphoenolpyruvate carboxylase) What is the name of the first enzyme in the C3 pathway? rubisco

Malate and pyruvate go through plasmodesmata “cell-cell connection” to move from one cell to another.

The number of carbons in the first product of the calvin cycle.
C4 refers to??? The number of carbons in the first product of the calvin cycle. Is there any energy cost associated with carbon dioxide fixation in the C4 path? YES!

THE CAM PATHWAY Cactus, pineapples have different adaptations to Hot, Dry Climates. Plants that use the CAM Pathway Open their Stomata at NIGHT and Close during the DAY, the opposite of what other plants do. At NIGHT, CAM Plants take in CO2 and fix into Organic Compounds. During the DAY, CO2 is released from these Compounds and enters the Calvin Cycle. TEMPORAL SEPARATION Because CAM Plants have their Stomata open at night, they grow very Slowly, But they lose LESS Water than C3 or C4 Plants.

How will stomata closure affect photosynthesis?

CO2 diffuses into mesophyll cells, through stomata, where it becomes available for photosynthesis.
When the stomata close, CO2 levels drop rapidly within the leaf, inhibiting the light-independent reactions. This then causes photosynthesis to stop.

oxaloacetate Do CAM and C4 plants have a C3 pathway within them? Yes!
What is the product of the first carbon fixation reaction in C4 and CAM paths? oxaloacetate Where is the site of the Calvin cycle for both? Bundle sheath cells

This is TEMPORAL separation!
CAM night vs. day This is TEMPORAL separation!


(b) Oxygen gas competes for the binding site of the enzyme rubisco.
Define photorespiration. What gas can compete with carbon dioxide for the binding site of the enzyme rubisco? Under normal conditions, what proportion of fixed carbon is affected by photorespiration in C3 plants? Compare the end products of photosynthesis and photorespiration. 1. (a) Photorespiration refers to the addition of oxygen to ribulose bisphosphate to produce phosphoglyceraldehyde and glycolate, which subsequently releases carbon dioxide. (b) Oxygen gas competes for the binding site of the enzyme rubisco. (c) Under normal conditions in C3 plants, approximately 20% of the fixed carbon is lost to photosynthesis. (d) Photosynthesis produces glyceraldehydes 3-phosphate (G3P), while photorespiration produces phosphoglyceraldehyde (PGA) and glycolate.

How does temperature affect the relative amounts of photosynthesis and photorespiration that occur in C3 plants? 2. As temperature increases, the amount of photorespiration in C3 plants increases, as does the rate of photosynthesis. However, the optimum temperature for photorespiration is higher than that for photosynthesis, so photorespiration rates may still be increasing even though photosynthsis rates are decreasing.

See diagram on page 172 (a) A: oxaloacetate B: carbon dioxide C: pyruvate D: mesophyll cell E: bundle-sheath cell (b) Malate and pyruvate move through plasmodesmata.

(b) C4 plants: corn and sugar cane
What is the main difference between the ideal environments of C4 plants and CAM plants? Name two C4 plants and two CAM plants. 4. (a) C4 plants grow best in hot, wet environments whereas CAM plants grow best in hot, dry environments. (b) C4 plants: corn and sugar cane CAM plants: pineapple, any succulent including cacti and jade plants

6. (a) The most malate in a CAM plant would be found late at night.
At what time of the day would you expect to find the most malate in CAM plants? When would you find the least amount of malate in CAM plants? Why do plants that use CAM photosynthetic pathways close their stomata during the day? 6. (a) The most malate in a CAM plant would be found late at night. (b) The least malate in a CAM plant would be found at the end of the day. (C) CAM plants close their stomata during the day to prevent water loss, as they live in dry environments.

D) During the cool of evening, CAM plants open their stomata
D) During the cool of evening, CAM plants open their stomata. What gas is preferentially absorbed at this time? E) Explain how this gas is stored for daytime use. (D) The gas that is preferentially absorbed during the cool evening is CO2. (E) During the dark, CAM plants take in CO2 and incorporate it into C4 organic acids using PEP caboxylase. These are stored in vacuoles until morning.

3.5 Photosynthesis and the Environment Read p. 173 – 178 #1, 2
The light compensation point the point on a light-response curve at which the rate of photosynthetic carbon dioxide uptake exactly equals the rate of respiratory carbon dioxide evolution. In other words there is no net uptake or evolution of carbon dioxide at this light intensity even though both photosynthesis and cellular respiration are occurring.

What happens at the light saturation point?
The dark reactions can not handle any more ATP/NADPH produced by the light reactions for carbon fixation!

How do the light response curves of C3 plants and C4 plants differ?
C4 photosynthesis is more efficient. Curve A above shows how the light response curve of an idealized C4 plant compares with that of a C3 plant (curve B).

C4 plants increase the amount of CO2 available to the Calvin cycle.
C4 plants, 1) the light saturation point is higher and 2) the light compensation point is lower than for C3 plants. C4 plants increase the amount of CO2 available to the Calvin cycle.

How would an O2 evolution curve appear if the stomata of a leaf closed during an experiment?
C. The rate of O2 evolution will slow as photosynthesis ceases, due to lack of CO2. When the rate of the light-independent reaction slows due to a lack of CO2, the overall rate of photosynthesis and O2 evolution will begin to slow. D is incorrect because we would not expect the the amount of O2 in the leaf chamber to drop rapidly when photosynthesis stops


Which letter represents a plant with elevated carbon dioxide concentrations?
D is the correct answer because: An increase in the light saturation point, and maximal rate of photosynthesis A is incorrect because: Higher CO2 levels only affect photosynthesis at the highest light levels

How would warming of the leaf affect the O2 evolution curve?
Curve B. As the leaf warms, the Calvin cycle enzymes catalyze reactions more rapidly, and the rate of photosynthesis increases, until enzyme saturation occurs If the temperature becomes too high the enzymes become less efficient.

How does photosynthesis differ between “sun” or “shade” plants?
shade-leaves (curve B) often are more efficient in harvesting sunlight at low light levels sun-leaves (curve A) display a higher light saturation point and maximum rate of photosynthesis

TEXT QUESTIONS ON PAGE 178 What process limits the rate of photosynthesis at low light levels? 1. Irradiance limits the overall rate of photosynthesis under low light conditions. As irradiance increases, photosynthesis begins.

Why do C4 plants generally exhibit higher photosynthetic rates at higher temperatures than do C3 plants? 2. C4 plants generally exhibit higher rates of photosynthesis when compared with C3 plants because of the fact that although photorespiration rates increase with increasing temperatures in C3 plants, the loss of CO2 by photorespiration in C4 plants is almost nonexistent. C4 plants spatially separate the light reactions and the Calvin cycle. The separation means that the concentration of CO2 fixation does not go down because of increase in photorespiration.

3.6 Comparing Photosynthesis and Cellular Respiration
Read p #1,2,3,5,6 Venn Diagram: Brainstorm similarities and differences that belong to both the mitochondria and chloroplast and list these in the overlapping section of the two circles (C). Brainstorm traits that belong to either concept and list these in the non-overlapping sections of the circles (A & B).

Organic molecules (e.g.; glucose) CO2 + H2O
Table 1: Comparison of the Overall Reactions RESPIRATION PHOTOSYNTHESIS Reactants Products energy Organic molecules (e.g.; glucose) CO2 + H2O CO2 + H2O Organic molecules (e.g.; glucose) released stored

Organic molecules (e.g.; glucose) water
Table 2: Electrons RESPIRATION PHOTOSYNTHESIS Source carriers Organic molecules (e.g.; glucose) water NAD+, FAD NADP+

Electron source Electron sink NADH AND FADH2 WATER products
Table 3: Electron Transport System RESPIRATION PHOTOSYNTHESIS Electron source Electron sink products NADH AND FADH2 WATER OXYGEN NADPH ATP ATP AND NADPH

ATP synthesis by chemiosmosis
Table 4: ATP SYNTHESIS RESPIRATION PHOTOSYNTHESIS H+ ions pumped by ETC ATP synthesis by chemiosmosis Membrane-embedded ATPase complex YES YES YES YES YES YES

Inner membrane functions
Table 5: ORGANELLE STRUCTURE AND FUNCTION Mitochondrion (cristae) Chlorplast (thylakoid) Inner membrane functions Location of H+ reservoir Location of ATP synthesis Contains DNA, ribosomes, etc. for replication Electron transport H+ ion transport ATP synthesis Electron transport H+ ion transport ATP synthesis Intermembrane space Thylakoid lumen matrix stroma yes yes

TEXT QUESTIONS PAGE 182! 1. Are photosynthesis and respiration exact opposites? Explain. Photosynthesis and cellular respiration are exact opposites with respect to reactants and products. The two metabolic processes are different with respect to the series of reactions that take place in each. Also, photosynthesis absorbs light energy and cellular respiration transfers energy from glucose to ATP.

An electron gains energy as a chlorophyll molecule absorbs a photon,
2. Describe the potential energy change in an electron as it is transported from water to NADPH in light reactions. An electron gains energy as a chlorophyll molecule absorbs a photon, loses some free-energy as it is passed from Q to b6-f complex to plastocyanin, gains energy in PS I when a chlorophyll molecule absorbs a second photon, and finally, the electron loses some energy as it passes its energy to the NADPH molecule. The “lost” energy appears as heat.

What would happen to humans and most other living organisms on Earth if photosynthesis stopped?
Why would this happen? 3. (a) If photosynthesis stopped, almost all life on Earth would cease to exist. (b) The base of all food webs would disappear. The only organisms that would survive would be those that relied on alternate forms of energy, such as hydrothermal vents on the ocean floor.

Explain why the energy profile for photosynthesis is a zig-zag line while the line for respiration is straight. The energy profile for photosynthesis is a zigzag because of the absorption of light energy twice during the light reactions of photosynthesis. The energy profile for cellular respiration is straight because the molecules continually lose energy throughout the process, and no additional energy is added.

6. How does a tropical fish aquarium containing fish and plants demonstrate the relationships between photosynthesis and cellular respiration? A tropical fish aquarium illustrates the relationship between photosynthesis and cellular respiration as plants photosynthesize and create carbohydrates that the fish consume and use in cellular respiration. Moreover, plants release oxygen, which is used in cellular respiration, and the fish produce carbon dioxide, which is used by the plants in photosynthesis.

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