Chapter 7 hotosynthesis: Using to Make Food Biology and Society: Biofuels Wood has historically been the main fuel used to produce heat and light. oweroint Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with hysiology, Fourth Edition Eric J. Simon, Jean L. Dickey, and Jane B. Reece Lectures by Edward J. Zalisko Figure 7.0 3 Biology and Society: Biofuels 4 Industrialized societies replaced wood with fossil fuels including coal, gas, and oil. To limit the damaging effects of fossil fuels, researchers are investigating the use of biomass (living material) as efficient and renewable energy sources.
Biology and Society: Biofuels 5 THE BASICS OF HOTOSYNTHESIS 7 There are several types of biofuels. hotosynthesis Bioethanol is a type of alcohol produced by the fermentation of glucose made from starches in crops such as grains, sugar beets, and sugar cane. Bioethanol may be used directly as a fuel source in specially designed vehicles or is used by plants, algae (protists), and some bacteria, transforms light energy into chemical energy, and uses carbon dioxide and water as starting materials. as a gasoline additive. THE BASICS OF HOTOSYNTHESIS 8 Figure 7. 9 The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules. lants (mostly on land) HOTOSYNTHETIC AUTOTROHS hotosynthetic rotists (aquatic) hotosynthetic Bacteria (aquatic) Organisms that use photosynthesis are photosynthetic autotrophs and the producers for most ecosystems. LM Forest plants Kelp, a large, multicellular alga Micrograph of cyanobacteria
Chloroplasts: Sites of hotosynthesis 0 Chloroplasts: Sites of hotosynthesis Chloroplasts are the site of photosynthesis and found mostly in the interior cells of leaves. Inside chloroplasts are interconnected, membranous sacs called thylakoids, which are suspended in a thick fluid called stroma. Thylakoids are concentrated in stacks called grana. The green color of chloroplasts is from chlorophyll, a lightabsorbing pigment that plays a central role in converting solar energy to chemical energy. The green light we see is the light that is not absorbed by these pigments Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits. Stoma is the singular form. Do not confuse with Stroma!!! Stoma is the greek root for mouth. Stomach has the same root. Figure 7.- Figure 7.- 3 hotosynthetic cells Vein hotosynthetic cells Vein Chloroplast C Stomata C Stomata Leaf cross section Leaf cross section Interior cell LM
Figure 7.-3 4 The Simplified Equation for hotosynthesis 5 hotosynthetic cells Vein Chloroplast Inner and outer membranes In the overall equation for photosynthesis, notice that the reactants of photosynthesis are the waste products of cellular respiration. Stroma Thylakoid space Granum C Stomata Leaf cross section Interior cell LM Colorized TEM The Simplified Equation for hotosynthesis 6 The Simplified Equation for Cellular Respiration 7 energy C 6 H O 6 6 6 C 6 H O AT 6 C 6 H O C 6 H O 6 hotosynthesis Carbon dioxide Water Glucose 6 Oxygen gas Glucose Oxygen Carbon dioxide Water Energy
Figure 6. Sunlight energy enters ecosystem 8 The Simplified Equation for hotosynthesis 9 In photosynthesis, hotosynthesis sunlight provides the energy, C 6 H O 6 C H O electrons are boosted uphill and added to carbon dioxide, and sugar is produced. Cellular respiration AT drives cellular work Heat energy exits ecosystem The Simplified Equation for hotosynthesis 0 A hotosynthesis Road Map During photosynthesis, water is split into hotosynthesis occurs in two multistep stages: hydrogen and oxygen. Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar. Oxygen escapes through stomata into the atmosphere.. the light reactions convert solar energy to chemical energy and This occurs in the thylakoid membrane. the uses the products of the light reactions to make sugar from carbon dioxide. This occurs in the stroma
A hotosynthesis Road Map 3 The initial incorporation of carbon from the atmosphere into organic compounds is called carbon fixation. This lowers the amount of carbon in the air. Deforestation reduces the ability of the biosphere to absorb carbon by reducing the amount of photosynthetic plant life. BioFlix Animation: hotosynthesis Figure 7.3- H O Chloroplast 4 Figure 7.3- H O Chloroplast C 5 NAD + reactions reactions AD + AT AT NADH NADH Sugar
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Chloroplasts 6 Figure 7-UN0 H O C 7 are chemical factories powered by the sun and convert sunlight into chemical energy. reactions NAD + AD + AT NADH Sugar The Nature of Sunlight 8 Figure 7.4 Increasing wavelength 9 Sunlight is a type of energy called radiation, or electromagnetic energy. 0 5 nm 0 3 nm nm 0 3 nm 0 6 nm m 0 3 m Gamma rays X-rays UV Infrared Microwaves Radio waves The distance between the crests of two adjacent waves is called a wavelength. Visible light The full range of radiation is called the electromagnetic spectrum. 380 400 500 600 700 750 Wavelength (nm) Wavelength = 580 nm
Figure 7.5 30 Figure 7.5a 3 Chloroplast Reflected light Chloroplast Reflected light Absorbed light Transmitted light (detected by your eye) Absorbed light Transmitted light (detected by your eye) Figure 7.5b 3 The rocess of Science: What Colors of Drive hotosynthesis? 33 Observation: In 883, German biologist Theodor Engelmann saw that certain bacteria tend to cluster in areas with higher oxygen concentrations. Question: Could this information determine which wavelengths of light work best for photosynthesis? Hypothesis: Oxygen-seeking bacteria will congregate near regions of algae performing the most photosynthesis.
The rocess of Science: What Colors of Drive hotosynthesis? 34 The rocess of Science: What Colors of Drive hotosynthesis? 35 Experiment: Engelmann Results: Bacteria laid a string of freshwater algal cells in a drop of water on a microscope slide, mostly congregated around algae exposed to redorange and blue-violet light and added oxygen-sensitive bacteria to the drop, and rarely moved to areas of green light. used a prism to create a spectrum of light shining on the slide. Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum. 36 Figure 7.6 37 rism Microscope slide Number of bacteria Bacteria Algal cells Bacteria Animation: and igments Right click slide / select lay 400 500 600 700 Wavelength of light (nm)
Chloroplast igments 38 Chloroplast igments 39 Chloroplasts contain several pigments: Carotenoids. Chlorophyll a absorb mainly blue-green light, absorbs mainly blue-violet and red light and participates directly in the light reactions.. Chlorophyll b absorbs mainly blue and orange light and participates indirectly in the light reactions. participate indirectly in the light reactions, and absorb and dissipate excessive light energy that might damage chlorophyll. The spectacular colors of fall foliage are due partly to the yellow-orange light reflected from carotenoids. Figure 7.7 40 How hotosystems Harvest Energy 4 behaves as photons, a fixed quantity of light energy. Chlorophyll molecules absorb photons. Electrons in the pigment gain energy. As the electrons fall back to their ground state, energy is released as heat or light.
Figure 7.8 4 How hotosystems Harvest Energy 43 Absorption of a photon excites an electron. Excited state The electron falls to its ground state. In the thylakoid membrane, chlorophyll molecules are organized with other molecules into photosystems. hoton Chlorophyll molecule Heat (fluorescence) Ground state A photosystem is a cluster of a few hundred pigment molecules that function as a lightgathering antenna. (a) Absorption of a photon (b) Fluorescence of a glow stick How hotosystems Harvest Energy 44 Figure 7.9 45 The reaction center of the photosystem consists of chlorophyll a molecules that sit next to another molecule called a primary electron acceptor, which traps the light-excited electron from chlorophyll a. Chloroplast Cluster of pigment molecules hoton Another team of molecules built into the thylakoid membrane then uses that trapped energy to make AT and NADH. Thylakoid membrane Transfer of energy hotosystem Electron transfer rimary electron acceptor Reactioncenter chlorophyll a igment molecules Reaction center
How the Reactions Generate AT and NADH 46 Figure 7.0-47 Two types of photosystems cooperate in the light reactions:. the water-splitting photosystem and rimary electron acceptor. the NADH-producing photosystem. H O H + + Reactioncenter chlorophyll Water-splitting photosystem Figure 7.0-48 Figure 7.0-3 49 rimary electron acceptor Energy to make AT rimary electron acceptor Energy to make AT rimary electron acceptor 3 NAD + NADH Reactioncenter chlorophyll H O Reactioncenter chlorophyll H O Reactioncenter chlorophyll NADH-producing photosystem H + + Water-splitting photosystem H + + Water-splitting photosystem
How the Reactions Generate AT and NADH 50 Figure 7. 5 The light reactions are located in the thylakoid membrane. An electron transport chain H + NADH NAD + AD + H + To AT connects the two photosystems and releases energy that the chloroplast uses to make AT. Stroma Thylakoid membrane Inside thylakoid H O hotosystem Electron transport chain H + hotosystem H + H + H + AT synthase Electron flow H + Thylakoid membrane Figure 7. AT 5 THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE The 53 NADH functions like a sugar factory within a chloroplast and regenerates the starting material with each turn. Water-splitting photosystem NADH-producing photosystem
54 Figure 7-UN03 55 H O C reactions NAD + AD + AT NADH Blast Animation: hotosynthesis: -Independent Reactions Select lay Sugar Figure 7.3- C (from air) 56 Figure 7.3- C (from air) 57 RuB sugar Three-carbon molecule RuB sugar Three-carbon molecule AT AD + NADH NAD + G3 sugar
Figure 7.3-3 C (from air) 58 Figure 7.3-4 C (from air) 59 RuB sugar Three-carbon molecule AT AD + NADH RuB sugar 4 AD + AT Three-carbon molecule AT AD + NADH G3 sugar 3 NAD + G3 sugar G3 sugar 3 NAD + G3 sugar G3 sugar Glucose (and other organic compounds) G3 sugar Glucose (and other organic compounds) Evolution Connection: Solar-Driven Evolution 60 Evolution Connection: Solar-Driven Evolution 6 C 3 plants C 4 plants use C directly from the air and are very common and widely distributed. close their stomata to save water during hot and dry weather and can still carry out photosynthesis. CAM plants are adapted to very dry climates and open their stomata only at night to conserve water.
Figure 7.4 ALTERNATIVE HOTOSYNTHETIC ATHWAYS C4 athway (example: sugarcane) CAM athway (example: pineapple) 6 Figure 7.4a C 4 athway (example: sugarcane) CAM athway (example: pineapple) 63 Cell type C C Night Four-carbon compound Four-carbon compound Cell type CO CO Night Cell type C C Cell type Four-carbon compound CO Four-carbon compound CO Sugar C4 plant Sugar CAM plant Day Sugar C 4 plant Sugar CAM plant Day Figure 7.4b 64 Figure 7.4c 65 C 4 athway (example: sugarcane) CAM athway (example: pineapple)
Figure 7-UN04 66 Figure 7-UN05 67 Chloroplast H O C energy 6 C 6 H O C 6 H O 6 hotosynthesis Carbon dioxide Water Glucose 6 Oxygen gas Stack of thylakoids reactions NAD + AD AT NADH Sugar Stroma Sugar used for cellular respiration cellulose starch other organic compounds Figure 7-UN06 68 Figure 7-UN07 C 69 AD AT e acceptor NAD + hoton e acceptor NADH hoton AT NADH AD NAD + Chlorophyll H O H + + Chlorophyll Water-splitting photosystem NADH-producing photosystem G3 Glucose and other compounds (such as cellulose and starch)