Presentation on theme: "Lecture 4: PHOTOSYNTHESIS Life’s grand device"— Presentation transcript:
1 Lecture 4: PHOTOSYNTHESIS Life’s grand device ByEdgar Moctezuma
2 TODAY… Photosynthesis Respiration Intro Properties of light and pigmentsChloroplast structure and functionLight reactions“Dark” or Carbon reactionsSummary and conclusionsRespirationEnergy and food chainsCarbon Cycle
3 I. Introduction to photosynthesis From the GreekPHOTO = produced by lightSYNTHESIS = a whole made of parts put together.Definition: PHOTOSYNTHESIS is the process whereby plants, algae, some bacteria, use the energy of the sun to synthesize organic compounds (sugars) from inorganic compounds (CO2 and water).
4 WHY IS PHOTOSYNTHESIS SO IMPORTANT? PHOTOSYNTHESIS is one of the most important biological process on earth!Provides the oxygen we breatheConsumes much of the CO2FoodEnergyFibers and materials
5 GENERAL FORMULA FOR PHOTOSYNTHESIS light6 CO H2O > C6H12O6 + 6 O2 + 6 H2Opigments, enzymes**Oxygen on earth allowed for the evolution of aerobic respiration and higher life-forms.Respiration: extracting energy from compounds (sugars)C6H12O6 + O2 6 CO2 + ATP
6 PROPERTIES OF LIGHT Virtually all life depends on it! Light moves in waves, in energy units called PHOTONSEnergy of a PHOTON inversely proportionalto its wavelengthVisible light (between UV and IR) occurs ina spectrum of colors
7 Visible light contains just the right amount of energy for biological reactions
8 Light is absorbed by pigments The primary pigment for photosynthesis is chlorophyll aIt absorbs blue and red light, not green (green light is reflected back!)Absorption spectrumof chlorophyll a
9 Absorption spectrum of chlorophyll a: BLUE & RED Action spectrum of photosynthesis closely matches absorption spectrum ofchlorophyll a, but not perfectly (due to accessory pigments)
10 Accessory pigments like chlorophyll b and carotenoids (beta-carotene, lycopene): absorb light at different wavelengths, (extending the absorption range)help transfer some energy to chlorophyll aprotect cell from harmful byproducts
11 Chlorophyll a is the primary photosynthetic pigment that drives photosynthesis. Accessory pigments absorb atdifferent wavelengths,extending the range of lightuseful for photosynthesis.
14 III. Chloroplast structure and function: solar chemical factory
15 Chloroplast structure Football shapedDouble membraneStromaThylakoid membraneGrana (stacks)Lumen (inside thylakoid)stromaGranalumenthylakoids
16 Inside a ChloroplastRemember: Structure correlates to function!
17 Overview of photosynthesis: Note: The Light and “Dark”or Carbon reactions happen at different sites in the chloroplastH2OCO2ATPNADPH(ENERGY)LIGHT REACTIONS(Thylakoids)“DARK” or CARBONREACTIONS(Stroma)lightC6H12O6(GLUCOSE)O2(OXYGEN GAS)
18 IV. The Light Reactions 1. Light dependent 2. Occur in the thylakoid membrane of chloroplast3. Water is split into oxygen gas (O2) and H+4. Use light energy (photons) to generate two chemical energy compounds: ATP & NADPH
19 Chemical energy compounds made in the light reactions ADP Pi + Energy ATPadenosine inorganic adenosinediphosphate phosphate triphosphateNADP+ + 2e- + H+ NADPHNicotinamide adenin dinucleotide phosphate
20 Sequence of events in the Light Reactions STROMANADP+ + H+NADPHADP + PiATPATPSPS IIPS Ie-H+2 H2OO H+(gas) (protons)LUMEN (inside thylakoid)
21 Summary of the Light reactions 2 H2O NADP ADP PiO NADPH ATP e H+(gas)Light reactions: Chemical energy compoundsare made from light energy, water is split intoO2 and protons
22 V. The“Dark” or Carbon Reactions 1. Light independent (can occur in light or dark; some enzymes require activation by light)2. Occur in the stroma of chloroplasts3. Use the chemical energy produced in Light Reactions (ATP; NADPH) to reduce CO2 to carbohydrate (sugar).CO2 is converted to sugar by entering theCalvin Cycle
23 The Calvin Cycle RuBP CO2 ADP rubisco ATP carboxylation regeneration Named for M. CalvinRuBPRibulose bisphosphateCO23 phases, 13 stepsADPCO2 goes 6 cyclesto produce 1 glucoserubiscoATPcarboxylationregeneration3-PGA3-phosphoglyceratereductionATPADPGAPGlyceraldehyde 3-phos.NADPHsugarsNADP+Pi
24 The Calvin Cycle CO2 enters the Calvin Cycle First product is a 3-carbon molecule: 3-PGA (phosphoglyceric acid). That’s why it’s also called C-3 cycle.Enzyme RUBISCO (ribulose bisphosphate carboxylase/oxygenase) is the main enzyme that catalyzes the first reactions of the Calvin Cycle.RUBISCO: Is the most abundant protein on earth!
25 Most plants use the Calvin Cycle to Convert CO2 into sugars.These plants are called C-3 plants
26 Summary of Carbon Reactions 6 CO ATP + 12 NADPH + 12 H2OC6H12O ADP + 18 Pi + 12 NADP++ 6 H2O + 6 O2glucoseCarbon reactions: Use CO2 and chemical energy (ATP &NADPH) to produce sugars by means of the Calvin Cycle
27 Limitations on Photosynthesis Photosynthesis is not perfect in C-3 plants,it is only % efficientLow efficiency due to photorespirationPhotorespiration occurs when internal CO2concentration becomes too low (drought);rubisco begins fixing oxygen.
28 C-4 plants are more efficient C-4 plants first product is a 4-carbon moleculeThe C-4 plants (sugar cane, corn, etc.), are more efficient than C-3 plants – they grow in hotter climates with more light.For example, sugar cane’s photosynthetic efficiency is 7%C-4 plants have a different leaf anatomy
29 C-3 vs. C-4 leaf anatomyNet venation Parallel venation
30 VI. Summary of Photosynthesis: Light energy absorbed by chlorophyll a drives the reactions of photosynthesis.2. Converts light energy into chemical energy to make organic compounds.3. CO2 and H2O used to produce C6H12O6 (glucose) and O2 (gas).
31 4. Light Reactions occur in thylakoids of the chloroplasts; ATP and NADPH are formed; water is split to O2 (gas) and protons.5. Carbon Reactions occur in stroma – Calvin Cycle fixes CO2 to produce C6H12O6 (glucose).6. Low efficiency, about 1- 4% in C-3 plants.7. Nevertheless, PHOTOSYNTHESIS is still the most important biological process on earth!
32 Importance of photosynthesis and the impact that it has in all our lives. Without photosynthesis, virtually all plants and animals would become extinct.
33 Respiration, Energy & Carbon Cycle Virtually all organisms require energy of food for:Making chemicals (proteins, carbs, etc.)MovementCell divisionHeat, electricity and light productionThe way living organisms obtain energy is through Cell respiration
34 RESPIRATION Process of making energy of food available in the cell… Involves breaking downComplicated molecules into simple molecules(C6H12O6, sugars) (CO2, water)
35 RESPIRATIONThe energy held by complicated molecules is held temporarily as ATP (energy currency)C6H12O6 + 6 O2 6CO2 + 6 H2O + 36 ATP(glucose) (energy)Respiration occurs mainly inMitochondria and Cytoplasm
36 Stages of Respiration Cellular Respiration has three main stages: GlycolysisKrebs CycleElectron transport system
37 3 Stages of cellular respiration Glycolysis: Splitting of glucose – 2 net ATP generatedKrebs Cycle: Energy of glucose molecule is harvested as ATP (2) – it occurs in the mitochondria (matrix)Electron Transport System: also happens in the mitochondria, more ATP are generated (32).For each glucose molecule, total ATP = 36Only 39% efficient, rest is lost as heat.
38 Photosynthesis Respiration Chapter 4: Table 4.1, p. 63Photosynthesis RespirationReaction: CO2+H2O+sunC6H12O6+O2+H2O C6H12O6+O2CO2+H2O+36ATPReactants: Carbon dioxide, water, sun Glucose, oxygenProducts: Glucose EnergyBy-products: Oxygen Carbon dioxide, waterCellular location: Chloroplasts Cytoplasm, mitochondriaEnergetics: Requires energy Releases energyChemical paths: Light reactions & Glycolysis, Krebs cycle Calvin cycle & Electron Transport Syst.Summary: Sugar synthesized using Energy released from energy from the sun sugar breakdown
39 Photosynthesis and respiration Photosynthesis and respiration are complimentary reactions…
41 ENERGY: ability to do work Newton’s First Law of Thermodynamics:“Energy cannot be created or destroyed, it can only be transformed from one form to another”Once a cell has used energy to do work, it cannot be used again by any organism.(1701)
42 ENERGY ENERGY FLOW IS LINEAR Energy flows into ecosystem from the sun Sun Earth Producers 1o consumers 2o consumheat resp, heat resp, heat resp, heatEnergy flows into ecosystem from the sunEnergy travels in a straight line by way offood chains.
43 ENERGYHowever, much energy is lost as heat along the way – as a result of respiration.Approximately 90% energy is lost on each step!Newton’s Second Law ofThermodynamics:“In any transfer of energy there is always a loss of useful energy to the system, usually in the form of heat”
44 Food Chains (Not referring to SHOPPERS, SAFEWAY or GIANT !!!) Food chains demonstrate linear nature of energyProducers are the base of the food chain, they include photosynthetic organisms like:PlantsAlgaeCertain bacteria
46 Food chainsDecomposers – obtain energy by breaking down remaining organic material of the other members of the food chain.Fungi and bacteria.
47 Matter All important elements move in cycles; Environment Organisms Cycles called biogeochemical cycles:Water cycleCarbon cycleNitrogen cycle
48 The Carbon CycleCarbon from the atmosphere (CO2) enters the biosphere by way of plants!CO2 used in photosynthesisCarbon moves into food chainCarbon is released to the physical environment by respirationRelease CO2 during respirationAmount CO2 fixed in photosynthesis = the amount released by respiration
49 Carbon CycleCarbon moves from atmosphere to plants to animals and back to atmosphere.
50 “Look deep into nature, and then you will understand everything better “Look deep into nature, and then you will understand everything better.” Albert Einstein