|Chapter 38 Plant reproduction and Development|
Chapter 10 Photosynthesis Lecture Outline
· Life on Earth is solar powered.
· The chloroplasts of plants use a process called photosynthesis to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules.
A. The Process That Feeds the Biosphere
1. Plants and other autotrophs are the producers of the biosphere.
· Photosynthesis nourishes almost all the living world directly or indirectly.
° All organisms use organic compounds for energy and for carbon skeletons.
° Organisms obtain organic compounds by one of two major modes: autotrophic nutrition or heterotrophic nutrition.
· Autotrophs produce their organic molecules from CO2 and other inorganic raw materials obtained from the environment.
° Autotrophs are the ultimate sources of organic compounds for all heterotrophic organisms.
° Autotrophs are the producers of the biosphere.
· Autotrophs can be separated by the source of energy that drives their metabolism.
° Photoautotrophs use light as a source of energy to synthesize organic compounds.
§ Photosynthesis occurs in plants, algae, some other protists, and some prokaryotes.
° Chemoautotrophs harvest energy from oxidizing inorganic substances, such as sulfur and ammonia.
§ Chemoautotrophy is unique to prokaryotes.
· Heterotrophs live on organic compounds produced by other organisms.
° These organisms are the consumers of the biosphere.
° The most obvious type of heterotrophs feeds on other organisms.
§ Animals feed this way.
° Other heterotrophs decompose and feed on dead organisms or on organic litter, like feces and fallen leaves.
§ Most fungi and many prokaryotes get their nourishment this way.
° Almost all heterotrophs are completely dependent on photoautotrophs for food and for oxygen, a by-product of photosynthesis.
2. Photosynthesis converts light energy to the chemical energy of food.
· All green parts of a plant have chloroplasts.
· However, the leaves are the major site of photosynthesis for most plants.
° There are about half a million chloroplasts per square millimeter of leaf surface.
· The color of a leaf comes from chlorophyll, the green pigment in the chloroplasts.
° Chlorophyll plays an important role in the absorption of light energy during photosynthesis.
· Chloroplasts are found mainly in mesophyll cells forming the tissues in the interior of the leaf.
· O2 exits and CO2 enters the leaf through microscopic pores called stomata in the leaf.
· Veins deliver water from the roots and carry off sugar from mesophyll cells to nonphotosynthetic areas of the plant.
· A typical mesophyll cell has 30–40 chloroplasts, each about 2–4 microns by 4–7 microns long.
· Each chloroplast has two membranes around a central aqueous space, the stroma.
· In the stroma is an elaborate system of interconnected membranous sacs, the thylakoids.
° The interior of the thylakoids forms another compartment, the thylakoid space.
° Thylakoids may be stacked into columns called grana.
· Chlorophyll is located in the thylakoids.
° Photosynthetic prokaryotes lack chloroplasts.
° Their photosynthetic membranes arise from infolded regions of the plasma membranes, folded in a manner similar to the thylakoid membranes of chloroplasts.
B. The Pathways of Photosynthesis
1. Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis.
· Powered by light, the green parts of plants produce organic compounds and O2 from CO2 and H2O.
· The equation describing the process of photosynthesis is:
° 6CO2 + 12H2O + light energy à C6H12O6 + 6O2+ 6H2O
° C6H12O6 is glucose.
· Water appears on both sides of the equation because 12 molecules of water are consumed, and 6 molecules are newly formed during photosynthesis.
· We can simplify the equation by showing only the net consumption of water:
° 6CO2 + 6H2O + light energy à C6H12O6 + 6O2
· The overall chemical change during photosynthesis is the reverse of cellular respiration.
· In its simplest possible form: CO2 + H2O + light energy à [CH2O] + O2
° [CH2O] represents the general formula for a sugar.
· One of the first clues to the mechanism of photosynthesis came from the discovery that the O2 given off by plants comes from H2O, not CO2.
° Before the 1930s, the prevailing hypothesis was that photosynthesis split carbon dioxide and then added water to the carbon:
§ Step 1: CO2 à C + O2
§ Step 2: C + H2O à CH2O
° C. B. van Niel challenged this hypothesis.
° In the bacteria that he was studying, hydrogen sulfide (H2S), not water, is used in photosynthesis.
° These bacteria produce yellow globules of sulfur as a waste, rather than oxygen.
° Van Niel proposed this chemical equation for photosynthesis in sulfur bacteria:
§ CO2 + 2H2S à [CH2O] + H2O + 2S
· He generalized this idea and applied it to plants, proposing this reaction for their photosynthesis:
° CO2 + 2H2O à [CH2O] + H2O + O2
· Thus, van Niel hypothesized that plants split water as a source of electrons from hydrogen atoms, releasing oxygen as a byproduct.
· Other scientists confirmed van Niel’s hypothesis twenty years later.
° They used 18O, a heavy isotope, as a tracer.
° They could label either C18O2 or H218O.
° They found that the 18O label only appeared in the oxygen produced in photosynthesis when water was the source of the tracer.
· Hydrogen extracted from water is incorporated into sugar, and oxygen is released to the atmosphere (where it can be used in respiration).
· Photosynthesis is a redox reaction.
° It reverses the direction of electron flow in respiration.
· Water is split and electrons transferred with H+ from water to CO2, reducing it to sugar.
° Because the electrons increase in potential energy as they move from water to sugar, the process requires energy.
° The energy boost is provided by light.
2. Here is a preview of the two stages of photosynthesis.
· Photosynthesis is two processes, each with multiple stages.
· The light reactions (photo) convert solar energy to chemical energy.
· The Calvin cycle (synthesis) uses energy from the light reactions to incorporate CO2 from the atmosphere into sugar.
· In the light reactions, light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to NADP+ (nicotinamide adenine dinucleotide phosphate), forming NADPH.
° NADPH, an electron acceptor, provides reducing power via energized electrons to the Calvin cycle.
° Water is split in the process, and O2 is released as a by-product.
· The light reaction also generates ATP using chemiosmosis, in a process called photophosphorylation.
· Thus light energy is initially converted to chemical energy in the form of two compounds: NADPH and ATP.
· The Calvin cycle is named for Melvin Calvin who, with his colleagues, worked out many of its steps in the 1940s.
· The cycle begins with the incorporation of CO2 into organic molecules, a process known as carbon fixation.
· The fixed carbon is reduced with electrons provided by NADPH.
· ATP from the light reactions also powers parts of the Calvin cycle.
· Thus, it is the Calvin cycle that makes sugar, but only with the help of ATP and NADPH from the light reactions.
· The metabolic steps of the Calvin cycle are sometimes referred to as the light-independent reactions, because none of the steps requires light directly.
· Nevertheless, the Calvin cycle in most plants occurs during daylight, because that is when the light reactions can provide the NADPH and ATP the Calvin cycle requires.
· While the light reactions occur at the thylakoids, the Calvin cycle occurs in the stroma.
3. The light reactions convert solar energy to the chemical energy of ATP and NADPH.
· The thylakoids convert light energy into the chemical energy of ATP and NADPH.
· Light is a form of electromagnetic radiation.
· Like other forms of electromagnetic energy, light travels in rhythmic waves.
· The distance between crests of electromagnetic waves is called the wavelength.
° Wavelengths of electromagnetic radiation range from less than a nanometer (gamma rays) to more than a kilometer (radio waves).
· The entire range of electromagnetic radiation is the electromagnetic spectrum.
· The most important segment for life is a narrow band between 380 to 750 nm, the band of visible light.
· While light travels as a wave, many of its properties are those of a discrete particle, the photon.
° Photons are not tangible objects, but they do have fixed quantities of energy.
· The amount of energy packaged in a photon is inversely related to its wavelength.
° Photons with shorter wavelengths pack more energy.
· While the sun radiates a full electromagnetic spectrum, the atmosphere selectively screens out most wavelengths, permitting only visible light to pass in significant quantities.
° Visible light is the radiation that drives photosynthesis.
· When light meets matter, it may be reflected, transmitted, or absorbed.
° Different pigments absorb photons of different wavelengths, and the wavelengths that are absorbed disappear.
° A leaf looks green because chlorophyll, the dominant pigment, absorbs red and blue light, while transmitting and reflecting green light.
· A spectrophotometer measures the ability of a pigment to absorb various wavelengths of light.
° It beams narrow wavelengths of light through a solution containing the pigment and measures the fraction of light transmitted at each wavelength.
° An absorption spectrum plots a pigment’s light absorption versus wavelength.
· The light reaction can perform work with those wavelengths of light that are absorbed.
· There are several pigments in the thylakoid that differ in their absorption spectra.
° Chlorophyll a, the dominant pigment, absorbs best in the red and violet-blue wavelengths and least in the green.
° Other pigments with different structures have different absorption spectra.
· Collectively, these photosynthetic pigments determine an overall action spectrum for photosynthesis.
° An action spectrum measures changes in some measure of photosynthetic activity (for example, O2 release) as the wavelength is varied.
· The action spectrum of photosynthesis was first demonstrated in 1883 in an elegant experiment performed by Thomas Engelmann.
° In this experiment, different segments of a filamentous alga were exposed to different wavelengths of light.
° Areas receiving wavelengths favorable to photosynthesis produced excess O2.
° Engelmann used the abundance of aerobic bacteria that clustered along the alga at different segments as a measure of O2 production.
· The action spectrum of photosynthesis does not match exactly the absorption spectrum of any one photosynthetic pigment, including chlorophyll a.
· Only chlorophyll a participates directly in the light reaction, but accessory photosynthetic pigments absorb light and transfer energy to chlorophyll a.
° Chlorophyll b, with a slightly different structure than chlorophyll a, has a slightly different absorption spectrum and funnels the energy from these wavelengths to chlorophyll a.
° Carotenoids can funnel the energy from other wavelengths to chlorophyll a and also participate in photoprotection against excessive light.
° These compounds absorb and dissipate excessive light energy that would otherwise damage chlorophyll.
° They also interact with oxygen to form reactive oxidative molecules that could damage the cell.
· When a molecule absorbs a photon, one of that molecule’s electrons is elevated to an orbital with more potential energy.
° The electron moves from its ground state to an excited state.
° The only photons that a molecule can absorb are those whose energy matches exactly the energy difference between the ground state and excited state of this electron.
° Because this energy difference varies among atoms and molecules, a particular compound absorbs only photons corresponding to specific wavelengths.
° Thus, each pigment has a unique absorption spectrum.
· Excited electrons are unstable.
· Generally, they drop to their ground state in a billionth of a second, releasing heat energy.
· Some pigments, including chlorophyll, can also release a photon of light in a process called fluorescence.
° If a solution of chlorophyll isolated from chloroplasts is illuminated, it will fluoresce and give off heat.
· Chlorophyll excited by absorption of light energy produces very different results in an intact chloroplast than it does in isolation.
· In the thylakoid membrane, chlorophyll is organized along with proteins and smaller organic molecules into photosystems.
· A photosystem is composed of a reaction center surrounded by a light-harvesting complex.
· Each light-harvesting complex consists of pigment molecules (which may include chlorophyll a, chlorophyll b, and carotenoid molecules) bound to particular proteins.
· Together, these light-harvesting complexes act like light-gathering “antenna complexes” for the reaction center.
· When any antenna molecule absorbs a photon, it is transmitted from molecule to molecule until it reaches a particular chlorophyll a molecule, the reaction center.
· At the reaction center is a primary electron acceptor, which accepts an excited electron from the reaction center chlorophyll a.
° The solar-powered transfer of an electron from a special chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions.
· Each photosystem—reaction-center chlorophyll and primary electron acceptor surrounded by an antenna complex—functions in the chloroplast as a light-harvesting unit.
· There are two types of photosystems in the thylakoid membrane.
° Photosystem I (PS I) has a reaction center chlorophyll a that has an absorption peak at 700 nm.
° Photosystem II (PS II) has a reaction center chlorophyll a that has an absorption peak at 680 nm.
° The differences between these reaction centers (and their absorption spectra) lie not in the chlorophyll molecules, but in the proteins associated with each reaction center.
° These two photosystems work together to use light energy to generate ATP and NADPH.
· During the light reactions, there are two possible routes for electron flow: cyclic and noncyclic.
· Noncyclic electron flow, the predominant route, produces both ATP and NADPH.
1. Photosystem II absorbs a photon of light. One of the electrons of P680 is excited to a higher energy state.
2. This electron is captured by the primary electron acceptor, leaving the reaction center oxidized.
3. An enzyme extracts electrons from water and supplies them to the oxidized reaction center. This reaction splits water into two hydrogen ions and an oxygen atom that combines with another oxygen atom to form O2.
4. Photoexcited electrons pass along an electron transport chain before ending up at an oxidized photosystem I reaction center.
5. As these electrons “fall” to a lower energy level, their energy is harnessed to produce ATP.
6. Meanwhile, light energy has excited an electron of PS I’s P700 reaction center. The photoexcited electron was captured by PS I’s primary electron acceptor, creating an electron “hole” in P700. This hole is filled by an electron that reaches the bottom of the electron transport chain from PS II.
7. Photoexcited electrons are passed from PS I’s primary electron acceptor down a second electron transport chain through the protein ferredoxin (Fd).
8. The enzyme NADP+ reductase transfers electrons from Fd to NADP+. Two electrons are required for NADP+’s reduction to NADPH. NADPH will carry the reducing power of these high-energy electrons to the Calvin cycle.
· The light reactions use the solar power of photons absorbed by both photosystem I and photosystem II to provide chemical energy in the form of ATP and reducing power in the form of the electrons carried by NADPH.
· Under certain conditions, photoexcited electrons from photosystem I, but not photosystem II, can take an alternative pathway, cyclic electron flow.
° Excited electrons cycle from their reaction center to a primary acceptor, along an electron transport chain, and return to the oxidized P700 chlorophyll.
° As electrons flow along the electron transport chain, they generate ATP by cyclic photophosphorylation.
° There is no production of NADPH and no release of oxygen.
· What is the function of cyclic electron flow?
· Noncyclic electron flow produces ATP and NADPH in roughly equal quantities.
· However, the Calvin cycle consumes more ATP than NADPH.
· Cyclic electron flow allows the chloroplast to generate enough surplus ATP to satisfy the higher demand for ATP in the Calvin cycle.
· Chloroplasts and mitochondria generate ATP by the same mechanism: chemiosmosis.
° In both organelles, an electron transport chain pumps protons across a membrane as electrons are passed along a series of increasingly electronegative carriers.
° This transforms redox energy to a proton-motive force in the form of an H+ gradient across the membrane.
° ATP synthase molecules harness the proton-motive force to generate ATP as H+ diffuses back across the membrane.
· Some of the electron carriers, including the cytochromes, are very similar in chloroplasts and mitochondria.
· The ATP synthase complexes of the two organelles are also very similar.
· There are differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts.
· Mitochondria transfer chemical energy from food molecules to ATP; chloroplasts transform light energy into the chemical energy of ATP.
· The spatial organization of chemiosmosis also differs in the two organelles.
· The inner membrane of the mitochondrion pumps protons from the mitochondrial matrix out to the intermembrane space. The thylakoid membrane of the chloroplast pumps protons from the stroma into the thylakoid space inside the thylakoid.
· The thylakoid membrane makes ATP as the hydrogen ions diffuse down their concentration gradient from the thylakoid space back to the stroma through ATP synthase complexes, whose catalytic knobs are on the stroma side of the membrane.
· The proton gradient, or pH gradient, across the thylakoid membrane is substantial.
° When chloroplasts are illuminated, the pH in the thylakoid space drops to about 5 and the pH in the stroma increases to about 8, a thousandfold different in H+ concentration.
· The light-reaction “machinery” produces ATP and NADPH on the stroma side of the thylakoid.
· Noncyclic electron flow pushes electrons from water, where they have low potential energy, to NADPH, where they have high potential energy.
° This process also produces ATP and oxygen as a by-product.
4. The Calvin cycle uses ATP and NADPH to convert CO2 to sugar.
· The Calvin cycle regenerates its starting material after molecules enter and leave the cycle.
· The Calvin cycle is anabolic, using energy to build sugar from smaller molecules.
· Carbon enters the cycle as CO2 and leaves as sugar.
· The cycle spends the energy of ATP and the reducing power of electrons carried by NADPH to make sugar.
· The actual sugar product of the Calvin cycle is not glucose, but a three-carbon sugar, glyceraldehyde-3-phosphate (G3P).
· Each turn of the Calvin cycle fixes one carbon.
· For the net synthesis of one G3P molecule, the cycle must take place three times, fixing three molecules of CO2.
· To make one glucose molecule requires six cycles and the fixation of six CO2 molecules.
· The Calvin cycle has three phases.
Phase 1: Carbon fixation
· In the carbon fixation phase, each CO2 molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP).
° This is catalyzed by RuBP carboxylase or rubisco.
° Rubisco is the most abundant protein in chloroplasts and probably the most abundant protein on Earth.
° The six-carbon intermediate is unstable and splits in half to form two molecules of 3-phosphoglycerate for each CO2.
Phase 2: Reduction
· During reduction, each 3-phosphoglycerate receives another phosphate group from ATP to form 1,3-bisphosphoglycerate.
· A pair of electrons from NADPH reduces each 1,3-bisphosphoglycerate to G3P.
° The electrons reduce a carboxyl group to the aldehyde group of G3P, which stores more potential energy.
· If our goal was the net production of one G3P, we would start with 3CO2 (3C) and three RuBP (15C).
· After fixation and reduction, we would have six molecules of G3P (18C).
° One of these six G3P (3C) is a net gain of carbohydrate.
§ This molecule can exit the cycle and be used by the plant cell.
Phase 3: Regeneration
· The other five G3P (15C) remain in the cycle to regenerate three RuBP. In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle to regenerate three molecules of RuBP.
· For the net synthesis of one G3P molecule, the Calvin cycle consumes nine ATP and six NADPH.
· The light reactions regenerate ATP and NADPH.
· The G3P from the Calvin cycle is the starting material for metabolic pathways that synthesize other organic compounds, including glucose and other carbohydrates.
5. Alternative mechanisms of carbon fixation have evolved in hot, arid climates.
· One of the major problems facing terrestrial plants is dehydration.
· At times, solutions to this problem require tradeoffs with other metabolic processes, especially photosynthesis.
· The stomata are not only the major route for gas exchange (CO2 in and O2 out), but also for the evaporative loss of water.
· On hot, dry days, plants close their stomata to conserve water. This causes problems for photosynthesis.
· In most plants (C3 plants), initial fixation of CO2 occurs via rubisco, forming a three-carbon compound, 3-phosphoglycerate.
° C3 plants include rice, wheat, and soybeans.
· When their stomata partially close on a hot, dry day, CO2 levels drop as CO2 is consumed in the Calvin cycle.
· At the same time, O2 levels rise as the light reaction converts light to chemical energy.
· While rubisco normally accepts CO2, when the O2:CO2 ratio increases (on a hot, dry day with closed stomata), rubisco can add O2 to RuBP.
· When rubisco adds O2 to RuBP, RuBP splits into a three-carbon piece and a two-carbon piece in a process called photorespiration.
° The two-carbon fragment is exported from the chloroplast and degraded to CO2 by mitochondria and peroxisomes.
° Unlike normal respiration, this process produces no ATP.
§ In fact, photorespiration consumes ATP.
° Unlike photosynthesis, photorespiration does not produce organic molecules.
§ In fact, photorespiration decreases photosynthetic output by siphoning organic material from the Calvin cycle.
· A hypothesis for the existence of photorespiration is that it is evolutionary baggage.
· When rubisco first evolved, the atmosphere had far less O2 and more CO2 than it does today.
° The inability of the active site of rubisco to exclude O2 would have made little difference.
· Today it does make a difference.
° Photorespiration can drain away as much as 50% of the carbon fixed by the Calvin cycle on a hot, dry day.
· Certain plant species have evolved alternate modes of carbon fixation to minimize photorespiration.
· C4 plants first fix CO2 in a four-carbon compound.
° Several thousand plants, including sugarcane and corn, use this pathway.
· A unique leaf anatomy is correlated with the mechanism of C4 photosynthesis.
· In C4 plants, there are two distinct types of photosynthetic cells: bundle-sheath cells and mesophyll cells.
° Bundle-sheath cells are arranged into tightly packed sheaths around the veins of the leaf.
° Mesophyll cells are more loosely arranged cells located between the bundle sheath and the leaf surface.
· The Calvin cycle is confined to the chloroplasts of the bundle-sheath cells.
· However, the cycle is preceded by the incorporation of CO2 into organic molecules in the mesophyll.
· The key enzyme, phosphoenolpyruvate carboxylase, adds CO2 to phosphoenolpyruvate (PEP) to form oxaloacetate.
° PEP carboxylase has a very high affinity for CO2 and can fix CO2 efficiently when rubisco cannot (i.e., on hot, dry days when the stomata are closed).
· The mesophyll cells pump these four-carbon compounds into bundle-sheath cells.
° The bundle-sheath cells strip a carbon from the four-carbon compound as CO2, and return the three-carbon remainder to the mesophyll cells.
° The bundle-sheath cells then use rubisco to start the Calvin cycle with an abundant supply of CO2.
· In effect, the mesophyll cells pump CO2 into the bundle-sheath cells, keeping CO2 levels high enough for rubisco to accept CO2 and not O2.
· C4 photosynthesis minimizes photorespiration and enhances sugar production.
· C4 plants thrive in hot regions with intense sunlight.
· A second strategy to minimize photorespiration is found in succulent plants, cacti, pineapples, and several other plant families.
° These plants are known as CAM plants for crassulacean acid metabolism.
° They open their stomata during the night and close them during the day.
§ Temperatures are typically lower at night, and humidity is higher.
° During the night, these plants fix CO2 into a variety of organic acids in mesophyll cells.
° During the day, the light reactions supply ATP and NADPH to the Calvin cycle, and CO2 is released from the organic acids.
· Both C4 and CAM plants add CO2 into organic intermediates before it enters the Calvin cycle.
° In C4 plants, carbon fixation and the Calvin cycle are spatially separated.
° In CAM plants, carbon fixation and the Calvin cycle are temporally separated.
· Both eventually use the Calvin cycle to make sugar from carbon dioxide.
6. Here is a review of the importance of photosynthesis.
· In photosynthesis, the energy that enters the chloroplasts as sunlight becomes stored as chemical energy in organic compounds.
· Sugar made in the chloroplasts supplies the entire plant with chemical energy and carbon skeletons to synthesize all the major organic molecules of cells.
° About 50% of the organic material is consumed as fuel for cellular respiration in plant mitochondria.
° Carbohydrate in the form of the disaccharide sucrose travels via the veins to nonphotosynthetic cells.
§ There, it provides fuel for respiration and the raw materials for anabolic pathways, including synthesis of proteins and lipids and formation of the extracellular polysaccharide cellulose.
§ Cellulose, the main ingredient of cell walls, is the most abundant organic molecule in the plant, and probably on the surface of the planet.
· Plants also store excess sugar by synthesis of starch.
° Starch is stored in chloroplasts and in storage cells in roots, tubers, seeds, and fruits.
· Heterotrophs, including humans, may completely or partially consume plants for fuel and raw materials.
· On a global scale, photosynthesis is the most important process on Earth.
° It is responsible for the presence of oxygen in our atmosphere.
° Each year, photosynthesis synthesizes 160 billion metric tons of carbohydrate.
|Chapter 10 Photosynthesis|
|The Process That Feeds the Biosphere
1. Distinguish between autotrophic and heterotrophic nutrition.
2. Distinguish between photoautotrophs and chemoautotrophs.
3. Describe the structure of a chloroplast, listing all membranes and compartments.
The Pathways of Photosynthesis
4. Write a summary equation for photosynthesis.
5. Explain van Niel’s hypothesis and describe how it contributed to our current understanding of photosynthesis. Explain the evidence that supported his hypothesis.
6. In general terms, explain the role of redox reactions in photosynthesis.
7. Describe the two main stages of photosynthesis in general terms.
8. Describe the relationship between an action spectrum and an absorption spectrum. Explain why the action spectrum for photosynthesis differs from the absorption spectrum for chlorophyll a.
9. Explain how carotenoids protect the cell from damage by light.
10. List the wavelengths of light that are most effective for photosynthesis.
11. Explain what happens when a solution of chlorophyll a absorbs photons. Explain what happens when chlorophyll a in an intact chloroplast absorbs photons.
12. List the components of a photosystem and explain the function of each component.
13. Trace the movement of electrons in noncyclic electron flow. Trace the movement of electrons in cyclic electron flow.
14. Explain the functions of cyclic and noncyclic electron flow.
15. Describe the similarities and differences in chemiosmosis between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts.
16. State the function of each of the three phases of the Calvin cycle.
17. Describe the role of ATP and NADPH in the Calvin cycle.
18. Describe what happens to rubisco when O2 concentration is much higher than CO2 concentration.
19. Describe the major consequences of photorespiration. Explain why it is thought to be an evolutionary relict.
20. Describe two important photosynthetic adaptations that minimize photorespiration.
21. List the possible fates of photosynthetic products.
|Carolina Larkspur (Delphinum carolinium) – 4′ tall.
Blooms May – July. These spurred flowers may be deep blue, reddish – blue, or white. Native perennial. OZ, OU, CP.
|Mexican Hat (Ratibida columnifera) ― 2 – 3′ tall.
Blooms June – October. A widely planted form of a native perennial. Statewide.
|Queen Ann’s Lace (Daucus carota) ― 1 – 4′ tall
Blooms May – frost. This is the ancestor of the cultivated carrot. Introduced biennial. Statewide.
|Black-eyed Susan (Rudbeckia hirta) ― 2 – 3′ tall with one 2″ flower head on each hairy stem.
Blooms May – October. Native Biennial or short-lived perennial. Statewide.
|Showy Evening Primrose (Oenothera speciosa) ― 1 – 2′ tall.
Blooms April – July. White or pink flowers. Native perennial. Statewide.
|Pale Purple Coneflower (Echinacea pallida) – 3′ tall.
Blooms May – July. Native perennial. OZ, OU, CP.
|Lance-leaved Coreopsis (Coreopsis lanceolata) – 3′ tall.
Blooms April – June. Native perennial. Statewide.
|Chicory (Coreopsis intybus) – 4′ tall.
Blooms May – October.
This European native’s roots are sometimes used as a coffee substitute or additive. Perennial. OZ, OU.
|Rough Blazing Star (Liatrus aspera) ― 3 – 4′ tall.
Blooms July – October. The unopened flower buds resemble small cabbages. Native perennial. Statewide.
|Cardinal Flower (Lobelia cardinalis) – 3′ tall.
Blooms August – October. This flower attracts hummingbirds. Native perennial. Statewide.
|Arkansas Beard Tongue (Penstemon arkansanus) – Less than 2′ tall.
Blooms April – June. The 3/4″ whitish flowers have lavender streaking. Native perennial. OZ, OU.
|Purple Coneflower (Echinacea purpurea) – Up to 4′ tall.
Blooms from June – October.
The ray flowers are more purple than those of pale purple coneflower. Native perennial. OZ, OU.
|Downy Phlox (Phlox pilosa) – 2′ tall.
Blooms April – July.
Flowers can be pink, pale pink, or sometimes white with purple centers. Native perennial. OZ, OU, CP.
|Spider Lily (Hymenocallis caroliniana) – 3′ tall.
Blooms May – August. These large white flowers have a distinctive spider-like shape. Native perennial. OU, GP, AP.
|Rose Vervain (Glandularia canadensis) – Plants less than 2′ tall.
Blooms March – September. The source of many garden hybrids. Native perennial. OZ, OU, CP, AP.
|Indian Paintbrush (Castilleja coccinea) ― 1 – 2′ tall. The bracts that surround the small flowers displays brilliant colors.
Blooms April – June. Native annual. Found on prairies in the OZ, CP, AP.
|Wild (Monarda fistulosa) ― 2 – 4′ tall.
Blooms June – September. Also called Bee Balm. Flowers pinkish, lavender, or lilac. Statewide.
|Goldenrod (Solidago canadensis) ― 4 – 6′ tall.
Blooms July – September. Native perennial. Statewide.
|Ohio Spiderwort (Tradescantia ohiensis) – Stems 3′ tall.
Blooms May – July.
So named because the internal jellylike substance resembles a spider’s web. Native perennial. OZ, OU, CP.
|Plains Coreopsis (Coreopsis tinctoria) – 3′ tall.
Blooms June – September. Native annual. Statewide.
|Bird’s Foot Violet (Viola pedata) – 6″ tall.
Blooms April – May. This violet occurs in several different colors: light violet, dark violet, or dark violet with 2 dark purple petals. Native perennial. OZ, OU, CP.
|Butterfly Weed (Asclepias tuberosa) ― 1 – 2′ tall.
Blooms May – September. Flower’s nectar attractive to butterflies. Native perennial. Statewide.
|Ox-eyed Daisy (Chrysanthemum leucanthemum) – 2″ flower heads.
Blooms May – July. Introduced perennial. OZ, OU, CP.
|Tickseed (Bidens aristosa) ― 1 – 6′ tall.
Blooms August – November. This late bloomer is often found in large stands. Native perennial. Statewide.
|AP Biology: Chapter 10|
1. What role do autotrophs fill in the biosphere?
2. Indicate the role of each structure within the leaf:
a. stomates _______________________________________________________________
b. mesophyll cells __________________________________________________________
c. thylakoid membranes _____________________________________________________
d. stroma _________________________________________________________________
3. What is the source of oxygen released from photosynthesis?
4. In the overview of photosynthesis, indicate the most significant function of:
a. Light reaction ___________________________________________________________
b. Calvin cycle ____________________________________________________________
5. Light is a form of energy known as _____________________________________________
and visible light has a wavelength range of _______________________________________ .
6. Plant light receptors absorb _________________________________________ wavelengths
of light and reflect ___________________________________________wavelengths of light.
7. The porphyrin ring of chlorophyll contains the element ______________________________
and the role of the ring is to ___________________________________________________
8. What does chlorophyll do when excited by photons? _______________________________
9. Label the diagram and explain the difference between Photosystem I and Photosystem II.
10. With 2 different colored pencils, follow the energy paths of both noncyclic and cyclic electron
flow in the diagram.
11. How does cyclic differ from noncyclic photophosphorylation?
12. To generate ATP, chloroplasts rely on the ETC to _________________________________
and ATP is synthesized when: _________________________________________________
13. Within the thylakoid membrane and stroma, indicate what happens to each of the following:
a. water __________________________________________________________________
b. high energy electrons _____________________________________________________
c. H+ ____________________________________________________________________
d. oxygen ________________________________________________________________
e. NADP+ ________________________________________________________________
f. ADP __________________________________________________________________
14. Where in the chloroplast is the H+ concentration highest? ___________________________
15. What happens during carbon fixation? __________________________________________
16. List the materials the plant uses during the Calvin cycle and the source of the materials.
17. The products of the Calvin cycle are ____________________________________________
18. What environmental and internal challenges have forced both C4 and CAM plants to evolve
alternatives to the photosynthesis system used by other plants?
19. Why do high oxygen levels inhibit photosynthesis? ________________________________
20. What happens during photorespiration and why is it considered bad for plants?
21. What evolutionary adaptations to the Calvin cycle are seen in C4 plants like sugar cane?
22. Draw a diagram to show the anatomical adaptations seen in C4 plants to accommodate their variation on the Calvin cycle.
23. What evolutionary adaptation to the Calvin cycle is seen in CAM plants like cacti?
AP Biology: CHAPTER 29 & 30- PLANT DIVERSITY
1. Chart the four phyla of the plant kingdom. Include common names of each, the approximate
number of extant species, and the major characteristics.
2. Why are Charophyceans thought to be ancestors of land plants?
3. List several adaptations of land plants significant for terrestrial survival.
4. Label the generic diagram to explain Alternation of Generations.
5. Describe a few features common to Bryophytes.
6. What is the dominant phase of the moss life cycle?
7. List a couple of adaptations of Pteridophytes (ferns) not seen in Bryophytes.
8. What is the dominant phase of the fern life cycle? _________________________________
9. How is the reduced gametophyte an adaptation for seeded plants?
10. What is the significance of the seed? ___________________________________________
11. What was the advantage of pollen? _____________________________________________
12. List the four phyla of gymnosperms. Which is the most common? _____________________
13. Identify five differences between monocots and dicots.
14. What is the adaptive value of the flower to plants? _________________________________
15. Describe the role of ovaries and ovules in the flowering plants.
16. List several features of angiosperms that aid in seed dispersal.
|Unit 8B – Plants|
|Know the following:
The Floating Leaf Disk Assay for Investigating Photosynthesis
Trying to find a good, quantitative procedure that students can use for exploring photosynthesis is a challenge. The standard procedures such as counting oxygen bubbles generated by an elodea stem tend to not be “student” proof or reliable. This is a particular problem if your laboratory instruction emphasizes student-generated questions. Over the years, I’ve found that the floating leaf disk assay technique to be reliable and understandable to students. Once the students are familiar with the technique they can readily design experiments to answer their own questions about photosynthesis. I plan to add to this page as I have time to elaborate on the technique and provide suggestions for modifications.
|1. Sodium bicarbonate (Baking soda)
2. Liquid Soap
3. Plastic syringe (10 cc or larger)—remove any needle!
4. Leaf material
5. Hole punch
6. Plastic cups
8. Light source
Colored Cellophane or filters
Leaf material of different ages
Variegated leaf material
Clear Nail polish
- Prepare 300 ml of bicarbonate solution for each trial.
- The bicarbonate serves as an alternate dissolved source of carbon dioxide for photosynthesis. Prepare a 0.2% solution. (This is not very much—it’s about 1/8 of a teaspoon of baking soda in 300 ml of water.) Too much bicarbonate will cause small bubbles (CO2)to form on the surface of the leaf which will make it difficult to sink the leaf disk.
- Add 1 drop of dilute liquid soap to this solution. The soap wets the hydrophobic surface of the leaf allowing the solution to be drawn into the leaf. It’s difficult to quantify this since liquid soaps vary in concentration. Avoid suds. If your solution generates suds then dilute it with more bicarbonate solution.
- Cut 10 or more uniform leaf disks for each trial
- Single hole punches work well for this but stout plastic straws will work as well
- Choice of the leaf material is perhaps the most critical aspect of this procedure. The leaf surface should be smooth and not too thick. Avoid plants with hairy leaves. Ivy, fresh spinach, Wisconsin Fast Plant cotyledons—all work well. Ivy seems to provide very consistent results. Any number of plants work. My classes have found that in the spring, Pokeweed may be the best choice.
- Avoid major veins.
- Infiltrate the leaf disks with sodium bicarbonate solution.
- Remove the piston or plunger and place the leaf disks into the syringe barrel. Replace the plunger being careful not to crush the leaf disks. Push on the plunger until only a small volume of air and leaf disk remain in the barrel (< 10%).
- Pull a small volume of sodium bicarbonate solution into the syringe. Tap the syringe to suspend the leaf disks in the solution.
- Holding a finger over the syringe-opening, draw back on the plunger to create a vacuum. Hold this vacuum for about 10 seconds. While holding the vacuum, swirl the leaf disks to suspend them in the solution. Let off the vacuum. The bicarbonate solution will infiltrate the air spaces in the leaf causing the disks to sink. You will probably have to repeat this procedure several times in order to get the disks to sink. You may have difficulty getting the disks to sink even after applying a vacuum three or four times. Generally, this is usually an indication that you need more soap in the bicarbonate solution. Some leaf surfaces are more water repellent than others are. Adding a bit more soap usually solves the problem.
- Pour the disks and solution into a clear plastic cup. Add bicarbonate solution to a depth of about 3 centimeters. Use the same depth for each trial. Shallower depths work just as well.
- This experimental setup includes a control. The leaf disks in the cup on the right were infiltrated with a water solution with a drop of soap—no bicarbonate.
- Place under the light source and start the timer. At the end of each minute, record the number of floating disks. Then swirl the disks to dislodge any that are stuck against the sides of the cups. Continue until all of the disks are floating.
- The control is on the left in each image. In the experimental treatment, on the right, leaf disks are rising and floating on the surface.
- Sample results:
|Time (minutes)||Disk Floating|
- The point at which 50% of the leaf disks are floating is the point of reference for this procedure. By interpolating from the graph, the 50% floating point is about 11.5 minutes. Using the 50% point provides a greater degree of reliability and repeatability for this procedure.