Photosynthesis Lesson Plan PDF

Photosynthesis-creating sugar using light General Equation: 6 CO2 + 6 H2O +light energy  C6H12O6 + 6 O2 An Overview  Main Similarities Use cytochrome complexes to generate a proton gradient in a double membraned organelle Use ATP synthase Us...

Photosynthesis-creating sugar using light General Equation: 6 CO2 + 6 H2O +light energy  C6H12O6 + 6 O2 An Overview  Main Similarities Use cytochrome complexes to generate a proton gradient in a double membraned organelle Use ATP synthase Use similar energy carriers eg. NADH vs NADPH Photosynthesis Photosynthesis takes place in all green plants, specifically in the organelle called the chloroplasts. During photosynthesis, the chloroplast traps light energy and converts the light energy into chemical energy (glucose). Carbon dioxide and water are necessary for photosynthesis to take place. The products of photosynthesis include carbohydrates specifically glucose and oxygen. Photosynthesis The Leaf The leaf is the photosynthetic organ of green plants. mesophyll cells The cells that perform photosynthesis They contain the largest number of http://web.as.uky.edu/biology/faculty/ palmer/BIO103/Lecture/ch4/04_A02.ht chloroplasts ml  Structures of Photosynthesis The process occurs in organelles called chloroplasts The fluid filled space in the chloroplast is called the stroma Each chloroplast contains an internal membrane system of connected disc-shaped structures called thylakoids Thylakoids stack up to form grana (singular granum) The region in between the thylakoids membranes is the thylakoid space. Inside each thylakoid membrane are many pigment molecules The major pigment is called chlorophyll a The unique molecular structure of chlorophyll a, as well as all the other kinds of pigments, makes it effective to capture energy from the visible light and use this energy to fix CO2 and H20 into glucose. The Chloroplast Outer membrane Inner membrane Stroma Thylakoid Granum Stroma Lamella (connects grana) Thylakoid (contains chlorophyll) Thylakoid Space (Lumen)  Mesophyll Chloroplast 5 µm Outer membrane Thylakoid Intermembrane Thylakoid Stroma Granum Space (thylakoid lumen) space Inner membrane 1 µm  Stomata (pores in leaves) Three functions: H2O out Allow CO2 in Allow O2 out O2 out When water goes H2O in out, the leaves are cooled so they do not overheat (called CO2 in evaporative cooling) Stomata (pores in leaves) Plants regulate size of stomata opening in response to environmental conditions in order to: Maximize CO2 uptake Minimize water loss In general, stomata reduce in size: Sunny, warm, dry and windy  Guard cells The guard cells control the stomata by opening and closing. This is controlled by osmosis: When water is scarce, the guard cells lose H2O and deflate, closing the stomata. When water is abundant, the guard cells swell, opening the stomata. Photosynthesis: Why are Plants Green? Visible light is electromagnetic radiation with wavelengths between 400 and 700 nm Why are Plants Green? Green wavelengths of light are reflected and other wavelengths are absorbed.  Pigments Light Pigments Reflected Light Are substances Chloroplast that absorb visible light The reflected light and transmitted include the colors we see Absorbed Absorbed light light Granum is important in driving Transmitted photosynthesis light  Pigments CH2 CH3 CHO in chlorophyll a in chlorophyll b Chlorophyll a H3 C C CH C C H C C CH3 C C CH2 CH3 Porphyrin ring: Light-absorbing Is the main C N N C H C Mg C H “head” of molecule note magnesium H3 C C N N C atom at center photosynthetic C C C C CH3 H C C C CH2 H H C C pigment CH2 O O C O O O CH3 Chlorophyll b CH2 Is an accessory Hydrocarbon tail: interacts with hydrophobic pigment regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Absorption Spectra Provide clues to the relative effectiveness of different wavelengths for driving photosynthesis  They both have a double peak: in the red/orange and in the blue/violet areas. Between the two they absorb much of the V, B, O and R spectrums, leaving green and yellow (typical leaf colours).  Two Types of Reactions in Photosynthesis Photosynthesis involves 2 main processes: 1. Energy-fixing light reactions Light Dependent Rxns (Light Reactions) require light, which includes exciting electrons and splitting H2O. 2. Carbon fixing dark reactions -Light Independent Rxns (Dark Reactions) do not directly require sunlight, includes Carbon fixation, the Calvin Cycle. http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=sw f::535::535::/sites/dl/free/0072437316/120072/bio13.swf:: Photosynthetic%20Electron%20Transport%20and%20ATP%20S  Light Reactions Occur in the H 2O CO2 granum Light NADP Split water,  ADP + P LIGHT CALVIN release oxygen, REACTIONS CYCLE ATP produce ATP, NADPH starch and form NADPH Chloroplast Sucros O2 e NADH NADPH  Dark Reactions The Calvin cycle – Occurs in the H 2O CO2 stroma Light Forms sugar NADP –  ADP from carbon LIGHT REACTIONS + P CALVIN CYCLE dioxide, using ATP starch ATP for energy NADPH and NADPH for Chloroplast reducing power Sucros O2 e  Stages of Photosynthesis There are two main stages of photosynthesis: Light Reactions Dark Reactions makes some makes NADPH ATP glucose PHOTOSYNTHESIS Homework. Read Ch 3.1 Do p145 #4, 5, 6 and 7. Photosynthesis The Light Reactions Chapter 3.3 Photosynthesis: Two Major Processes 1. The Light Harvests light energy to split water, creating Reactions O2 ATP and NADPH Process of producing 2. Calvin cycle C6H12O6, using ATP for energy and producing NADP+ Photosynthesis: Two Major Processes  The Light Reactions 1. Photoexcitation Absorption of light photons 2. Electron transport Similar to ETC in mitochondria 3. Photophosphorylation ATP synthesis due (chemiosmosis) to electrochemical gradient  Photoexcitation e- gain energy when atoms absorb energy. e- fall back to lowest energy level (ground state) if it isn’t transferred to another molecule Isolated Chlorphyll If an isolated solution of chlorophyll is illuminated It will fluoresce, giving off heat and light Photosystems Made up of a variety of proteins – reaction center surrounded by a number of light- harvesting complexes Contain chlorophyll and other light absorbing pigments Located in the thylakoid membrane  Reaction Centre Contains a primary electron acceptor contains chlorophyll a molecule which the light energy is focused in a photosystem  Two Types of Photosystems Photosystem I (PS Phosystem II (PS I) II) Has P700 Has P680 chlorophyll a within chlorophyll a reaction centre within reaction Best at absorbing centre 700 nm Best at absorbing wavelength 680 nm wavelength  Purposes of Photosystems Two purposes: 1. To collect as much light energy as possible 2. Excite chlorophyll a and transfer its electrons to an electron acceptor and through a series of proteins (electron transport) Electron Transport Electron transport occurs in the thylakoid membrane. Two mechanisms of electron transport: 1. Non-cyclic electron flow (the primary pathway) 2. Cyclic electron flow Non-Cyclic Electron Flow: An Overview H2O CO2 LIGHT NADP+ ADP CALVIN LIGHT CYCLE REACTOR ATP NADPH STROMA O2 [CH2O] (sugar) (Low H+ concentration) Cytochrome Photosystem II complex Photosystem I Light NADP+ reductase 2 H+ 3 Fd NADP+ + 2H+ NADPH + H+ Pq Pc 2 H2O 1 ⁄2 O 2 THYLAKOID SPACE 1 2 H+ +2 H+ (High H+ concentration) To Calvin cycle ATP Thylakoid synthase STROMA membrane ADP (Low H+ concentration) ATP P H + Light Reactions (Light Dependent Reactions) The light reactions begin when light energy is trapped by the chloroplasts. The light energy is absorbed by a complex cluster of chlorophyll molecules called a photosystem located on the thylakoid membrane. The first photosystem involved in the light reactions is photosystem II (discovered second!!)or P680. Photosystem with a Cluster of Chlorophyll molecules Photosynthesis: When photosystem II absorbed solar energy, it becomes excited and loses electrons. The electrons lost by photosystem II are absorbed by a protein which acts as an electron acceptor. The lost electron is passed from one electron acceptor to another, until it reaches photosystem I (discovered first!!)or P700. The electron loses energy as it is passed down the chain of electron acceptors. Both the photosystems I and II and electron acceptors are located on the thylakoid membrane. Photosystem II The ETC between PSII and PSI is made up of: Pq (plastiquinone) - mobile Cytochrome Complex Pc (Plastocyanin) - mobile Pq, CC, Pc: The Details STROMA (Low H+ Concentration)  As Plastoquinone (Pq) transfers electrons to the Cytochrome Complex, protons are pumped across the membrane into the thylakoid space (lumen)  This exergonic “fall” of electrons to a lower energy level provides THYLAKOID MEMBRANE energy for the active transport of H+ ions against its concentration gradient. THYLAKOID SPACE (LUMEN) (High H+ Concentration)  Electrons are then transferred to Plastocyanin (Pc). Photosynthesis: Path of Electron Flow 2 Steps occur at the same time: First Step: The energy lost by the electron as it passes down the chain of electron acceptors is used to pump H+ ions from the stroma into the thylakoid space. When the concentration of H+ ions is large enough in the thylakoid space, they will leak back across the thylakoid membrane into the stroma. They do this through a special protein called ATP synthetase. As this happens ADP, is phosphorylated to form ATP. The creation of ATP in this way is called chemiosmosis- Which is the formation of ATP powered by the diffusion of H+ ions. Non-Cyclic Electron Flow H2O CO2 LIGHT NADP+ ADP CALVIN LIGHT CYCLE REACTOR ATP NADPH STROMA O2 [CH2O] (sugar) (Low H+ concentration) Cytochrome Photosystem II complex Photosystem I Light NADP+ reductase 2 H+ 3 Fd NADP+ + 2H+ NADPH + H+ Pq Pc 2 H2O 1 ⁄2 O 2 THYLAKOID SPACE 1 2 H+ +2 H+ (High H+ concentration) To Calvin cycle ATP Thylakoid synthase STROMA membrane ADP (Low H+ concentration) ATP P H + ATP Synthase  protons pumped into the lumen pass through ATP synthase by facilitated diffusion  ATP produced in stroma  photophosphorylation – light-dependent formation of ATP by chemiosmosis 2nd Step: The electrons lost from photosystem II eventually reach photosystem I. Photosystem I absorbs light energy and becomes excited. When this happens, photosystem I loses electrons to an electron acceptor called ferredoxin. The electron acceptor ferredoxin then transfers the electron to a molecule of NADP, which also accepts a H+ ion, to become NADPH. This molecule of NADPH is used in the dark reactions.  Fd and NADP+ Electrons are transferred to ferrodoxin (Fd) – moveable component on thylakoid surface in stroma Electrons are transferred to NADP+ Final electron acceptor is NADP+ that is reduced to NADPH 2nd Part continued: In order to replace the lost electron in the original P680 molecule, a water molecule breaks down, forming H+ ions and oxygen, and donating an electron to P680. The oxygen is released into the atmosphere. The NADPH and ATP are used in the dark reactions. Non-Cyclic Electron Flow H2O CO2 LIGHT NADP+ ADP CALVIN LIGHT CYCLE REACTOR ATP NADPH STROMA O2 [CH2O] (sugar) (Low H+ concentration) Cytochrome Photosystem II complex Photosystem I Light NADP+ reductase 2 H+ 3 Fd NADP+ + 2H+ NADPH + H+ Pq Pc 2 H2O 1 ⁄2 O 2 THYLAKOID SPACE 1 2 H+ +2 H+ (High H+ concentration) To Calvin cycle ATP Thylakoid synthase STROMA membrane ADP (Low H+ concentration) ATP P H +  Non-Cyclic Electron Flow Summary 1. H2O is split to produce O2 (released from cell) and H+ ions (released into lumen) 2. enzyme complexes pump protons from stroma to lumen 3. NADP+ is final electron acceptor and produces NADPH 4. chemiosmosis to synthesize ATP Light Reaction Animation http://www.youtube.com/ watch?v=hj_WKgnL6MI Cyclic Electron Flow Non-cyclic electron flow produces roughly equal H 2O CO2 amounts of ATP and Light NADPH NAD However, Calvin Cycle P ADP uses more ATP than LIGHT + P CALVIN REACTIO NADPH NS CYCLE ATP – Cyclic electron flow NADPH makes up the [CH difference in ATP Chloroplast 2O] (without producing O2 (su gar more NADPH). )  Cyclic Electron Flow Primary Primary acceptor Fd acceptor Fd Pq NADP+ NADP + reductase Cytochrome NADPH complex Pc ATP Photosystem I Photosystem II  Cyclic Electron Flow Summary 1. only involves photosystem I (P700) 2. ferrodoxin returns electrons back to cytochrome complex 3. Only ATP produced, no NADPH To Do: Section 3.2 Questions (pg. 154- 155) # 1-3, 11 Section 3.3 Questions (pg. 166- 167) #1-4, 6, 8a(i-iii), 8b  The Calvin Cycle The Dark Side (i.e. reactions) of Photosynthesis Calvin Cycle Calvin Cycle Overview Calvin cycle is a cyclical process which: 1. Fixes carbon (make C-C bonds) 2. Utilizes energy molecules 3. Regenerates molecules for another cycle  Calvin Cycle occurs in the stroma of chloroplast reactions are not as linear as Krebs Dark Reactions The dark reactions can occur in the presence or absence of light (light is not required) During the dark reactions, CO2 is used to eventually form glucose. The ATP and NADPH created in the light reactions are needed for this to occur. The dark reactions is also called the Calvin Cycle and they occur in the stroma.  Calvin Cycle: Carbon Fixation 1. Three CO2 (1 carbon) are attached to three 1,5-ribulose bisphosphate (5 carbon) rxn type: synthesis & cleavage 2. Three 6-carbon molecule are split into six 3-carbon molecules Calvin Cycle: Energy Utilization ATP phosphorylates each 3-carbon molecule rxn type: phosphorylation energy: absorbed Calvin Cycle: Energy Utilization NADPH used to synthesize G3P rxn type: redox  Calvin Cycle: Regenerate Molecules 1. 5 G3P and ATP to resynthesize 1,5- ribulose bisphosphate 2. 1 G3P used in another pathway rxn type: synthesis phosphorylation 1 of the 6 molecules of G3P (3-C) goes through a series of complex reactions to form glucose. Glucose is a 6C molecule, therefore the entire Calvin Cycle must happen 2X to get enough C’s to make 1 glucose molecule at this step. Calvin Cycle Review 1. How many CO2 molecules are needed to form a single glucose molecule? 6 CO2 molecules are fixed to form a single glucose molecule the cycle must go around twice to form two G3P molecules, which will then be used to create glucose 1. How many ATP and NADPH molecules are used to form a single glucose molecule? 18 ATP & 12 NADPH molecules used Step by Step Summary of Calvin Cycle Overview Factors Affecting Photosynthesis Factors Overview 1. light intensity, [CO2] and temperature 2. C3 plant limitations 3. C4 plants 4. CAM plants Effect of [CO2] 1. increased [CO2] = increased photosynthesis - up to a certain point until enzyme active sites are filled (photosynthetic rate will plateau) - due to increase in # of reactant molecules in Calvin Cycle  Effect of Temperature 2. increased temperature = increased photosynthesis - up to a certain point until enzymes start to denature causing the photosynthetic rate to decrease - due to movement of reactant molecules within the Calvin Cycle  Effect of Light Intensity 3. increased light intensity = increased photosynthesis only to a certain plateau after which an increase in light intensity results in no increase in the rate of photosynthesis This is because the Calvin cycle cannot keep up with the light reactions  C3 Plant Limitations C3 plants undergo photosynthesis as described stomata are open during the day / closed at night What happens to stomata in hot, arid conditions? C3 Plant Limitations In hot, arid conditions, plants close the stomata to prevent water loss increasing [O2] within the cells At high [O2], rubisco binds to O2 rather than CO2 in the process of photorespiration causes the plant to skip the Calvin cycle. Glucose is not produced. C4 Plant Adaptation adaptation to hot, arid environments e.g. corn, sugarcane, grasses  C4 Plant Adaptation C4 plants have a special mesophyll cell & bundle- sheath cell structure. 1. Mesophyll cells create 4-carbon molecules using PEP carboxylase and release CO2 into the bundle- sheath cells. 2. Bundle-sheath cells only perform the Calvin cycle. In hot, arid conditions, C4 cells provide enough CO 2 to ensure rubisco does not bind to O 2 molecules. CAM Plant Adaptation adaptation to hot, arid environments e.g. cactus, pineapples (water storing plants) Stomata are closed in the day and open at night.  C4 Plant CAM Plant Sugarcane Pineapple C4 CAM CO2 CO2 Mesophyll Cell Night Organic acid 1 CO2 incorporated Organic acid Bundle- into four-carbon sheath organic acids (carbon fixation) Day cell (a) Spatial separation (b) Temporal of steps. In C4 separation of steps. plants, carbon CALVIN 2 Organic acids CALVIN CYCLE In CAM plants, carbon release CO2 to CYCLE fixation and the fixation and the Calvin Calvin cycle occur in Calvin cycle cycle occur in the different Sugar Sugar same cells 10.20 types of cells. at different times.  CAM Plant Adaptation 1. NIGHT: CO2 collected & incorporated into organic molecules 2. DAY: CO2 released from the organic molecules where ATP & NADPH is produced to allow the Calvin cycle to proceed http://www.youtube.com/watch?v=Dq38MpYOb8w