© 2013 Pearson Education, Inc. Lectures by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition – Eric J. Simon, Jean L. Dickey, and Jane B. Reece Chapter 7 Photosynthesis: Using Light to Make Food

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 © 2013 Pearson Education, Inc.

There are several types of biofuels. –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 –as a gasoline additive. –Cellulosic ethanol is a type of bioethanol made from cellulose in nonedible plant material such as wood or grass. –Biodiesel is made from plant oils or recycled frying oil. Biology and Society: Biofuels © 2013 Pearson Education, Inc.

THE BASICS OF PHOTOSYNTHESIS Photosynthesis –plants, algae (protists), and some bacteria, –transforms light energy into chemical energy, and –carbon dioxide and water as starting materials. The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules. Organisms that use photosynthesis are –photosynthetic autotrophs and –the producers for most ecosystems. © 2013 Pearson Education, Inc.

Chloroplasts: Sites of Photosynthesis 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. © 2013 Pearson Education, Inc.

The green color of chloroplasts is from chlorophyll, a light-absorbing pigment that plays a central role in converting solar energy to chemical energy. Stomata are tiny pores in leaves where –carbon dioxide enters and –oxygen exits. Chloroplasts: Sites of Photosynthesis © 2013 Pearson Education, Inc.

Figure Leaf cross section Stomata Vein CO 2 O2O2 Photosynthetic cells

Figure Interior cell LM Chloroplast Leaf cross section Stomata Vein CO 2 O2O2 Photosynthetic cells

Figure Interior cell LM Stroma Granum Thylakoid space Chloroplast Inner and outer membranes Colorized TEM Leaf cross section Stomata Vein CO 2 O2O2 Photosynthetic cells

Figure 7.2a Leaf cross section Stomata Vein (transports water and nutrients) CO 2 O2O2 Photosynthetic cells

Figure 7.2b Interior cell LM Stroma Granum Thylakoid space Chloroplast Inner and outer membranes Colorized TEM

Figure 7-UN01 Carbon dioxide 6 O 2 6 CO 2 6 H 2 O C 6 H 12 O 6 Water Glucose Photo- synthesis Oxygen gas Light energy

In the overall equation for photosynthesis, notice that the reactants of photosynthesis are the waste products of cellular respiration. In photosynthesis, –sunlight provides the energy, –electrons are boosted “uphill” and added to carbon dioxide, and –sugar is produced. The Simplified Equation for Photosynthesis © 2013 Pearson Education, Inc.

During photosynthesis, water is split into –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 Simplified Equation for Photosynthesis © 2013 Pearson Education, Inc.

A Photosynthesis Road Map Photosynthesis occurs in two multistep stages: 1.the light reactions convert solar energy to chemical energy and 2.the Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide. © 2013 Pearson Education, Inc.

A Photosynthesis Road Map 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: Photosynthesis © 2013 Pearson Education, Inc.

Figure Light H2OH2O O2O2 Chloroplast Light reactions NADPH ATP ––

Figure Calvin cycle CO 2 NADP + ADP P Sugar Light H2OH2O O2O2 Chloroplast Light reactions NADPH ATP  ––

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Chloroplasts –are chemical factories powered by the sun and –convert sunlight into chemical energy. © 2013 Pearson Education, Inc.

Figure 7-UN02 Light reactions CO 2 O2O2 H2OH2O NADPH Light Sugar ATP ADP P NADP  Calvin cycle – – +

The Nature of Sunlight Sunlight is a type of energy called radiation, or electromagnetic energy. The distance between the crests of two adjacent waves is called a wavelength. The full range of radiation is called the electromagnetic spectrum. © 2013 Pearson Education, Inc.

Figure 7.4 Visible light Wavelength (nm) Radio waves Wavelength  580 nm Micro- waves Gamma rays Infrared UV X-rays 10 –5 nm 1 nm 1 m1 m Increasing wavelength –3 nm10 3 nm 10 6 nm 10 3 m

Figure 7.5a Light Chloroplast Absorbed light Transmitted light (detected by your eye) Reflected light

The Process of Science: What Colors of Light Drive Photosynthesis? Observation: In 1883, 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. © 2013 Pearson Education, Inc.

Experiment: Engelmann –laid a string of freshwater algal cells in a drop of water on a microscope slide, –added oxygen-sensitive bacteria to the drop, and –used a prism to create a spectrum of light shining on the slide. The Process of Science: What Colors of Light Drive Photosynthesis? © 2013 Pearson Education, Inc.

Results: Bacteria –mostly congregated around algae exposed to red- orange and blue-violet light and –rarely moved to areas of green light. Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum. Animation: Light and Pigments The Process of Science: What Colors of Light Drive Photosynthesis? © 2013 Pearson Education, Inc.

Figure 7.6 Light Microscope slide Prism Bacteria Algal cells Bacteria Wavelength of light (nm) Number of bacteria

Chloroplast Pigments Chloroplasts contain several pigments: 1.Chlorophyll a –absorbs mainly blue-violet and red light and –participates directly in the light reactions. 2.Chlorophyll b –absorbs mainly blue and orange light and –participates indirectly in the light reactions. © 2013 Pearson Education, Inc.

Carotenoids –absorb mainly blue-green light, –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. Chloroplast Pigments © 2013 Pearson Education, Inc.

Figure 7.7

How Photosystems Harvest Light Energy Light 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. © 2013 Pearson Education, Inc.

Figure 7.8 Light (b) Fluorescence of a glow stick Photon Heat Light (fluorescence) Ground state Chlorophyll molecule Excited state e–e– (a) Absorption of a photon The electron falls to its ground state. Absorption of a photon excites an electron.

Figure 7.8a Light Photon Heat Light (fluorescence) Ground state Chlorophyll molecule Excited state e–e– (a) Absorption of a photon The electron falls to its ground state. Absorption of a photon excites an electron.

In the thylakoid membrane, chlorophyll molecules are organized with other molecules into photosystems. A photosystem is a cluster of a few hundred pigment molecules that function as a light- gathering antenna. How Photosystems Harvest Light Energy © 2013 Pearson Education, Inc.

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. Another team of molecules built into the thylakoid membrane then uses that trapped energy to make –ATP and –NADPH. How Photosystems Harvest Light Energy © 2013 Pearson Education, Inc.

Figure 7.9 Chloroplast Thylakoid membrane Cluster of pigment molecules Pigment molecules Primary electron acceptor Reaction- center chlorophyll a Electron transfer Reaction center Photosystem Transfer of energy Photon e–e–

Figure 7.9b Pigment molecules Primary electron acceptor Reaction- center chlorophyll a Electron transfer Reaction center Photosystem Transfer of energy e–e– Photon

How the Light Reactions Generate ATP and NADPH Two types of photosystems cooperate in the light reactions: 1.the water-splitting photosystem and 2.the NADPH-producing photosystem. © 2013 Pearson Education, Inc.

Figure Primary electron acceptor Water-splitting photosystem Light H2OH2O 2 H  Reaction- center chlorophyll O2O2  2e2e – 2e2e – 1

Figure Primary electron acceptor Water-splitting photosystem Light H2OH2O 2 H  Reaction- center chlorophyll O2O2  Electron transport chain Energy to make ATP 2e2e – 2e2e – 12

Figure Primary electron acceptor Water-splitting photosystem Light H2OH2O 2 H  O2O2  Electron transport chain Energy to make ATP Primary electron acceptor 2e2e – Light NADPH-producing photosystem Reaction- center chlorophyll 2e2e – NADPH NADP  2e2e – 2e2e – 123 –– Reaction- center chlorophyll

The light reactions are located in the thylakoid membrane. An electron transport chain –connects the two photosystems and –releases energy that the chloroplast uses to make ATP. How the Light Reactions Generate ATP and NADPH © 2013 Pearson Education, Inc.

Figure 7.11 Light H2OH2O Thylakoid membrane 2e2e – O2O2 ATP NADP  Light Stroma Inside thylakoid Photosystem Electron transport chain NADPH ADP  P HH ATP synthase To Calvin cycle HH Electron flow HH HH HH HH HH Thylakoid membrane ––

O2O2 Figure 7.11a H2OH2O Thylakoid membrane 2e2e – Stroma Inside thylakoid Photosystem Electron transport chain HH Thylakoid membrane HH

Figure 7.11b Light ATP NADP  Photosystem Electron transport chain NADPH ADP  P HH ATP synthase To Calvin cycle HH Electron flow HH HH HH HH HH – –

Figure 7.12 Water-splitting photosystem Photon ATP NADPH e – Photon NADPH-producing photosystem – – e – e – e – e – e – e –

THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE The Calvin cycle –functions like a sugar factory within a chloroplast and –regenerates the starting material with each turn. © 2013 Pearson Education, Inc. Blast Animation: Photosynthesis: Light-Independent Reactions

Figure 7-UN03 Light reactions CO 2 O2O2 H2OH2O NADPH Light Sugar ATP ADP P NADP  Calvin cycle – – +

Figure P P P Three-carbon molecule RuBP sugar CO 2 (from air) Calvin cycle 1

Figure ATP NADPH ADP  P NADP  P P P P G3P sugar Three-carbon molecule RuBP sugar CO 2 (from air) Calvin cycle –– 21

Figure ATP NADPH ADP  P NADP  P P P P P P G3P sugar Three-carbon molecule G3P sugar RuBP sugar CO 2 (from air) Calvin cycle Glucose (and other organic compounds) –– 231

Figure ATP NADPH ADP  P NADP  P P P P P P G3P sugar Three-carbon molecule G3P sugar RuBP sugar CO 2 (from air) Calvin cycle Glucose (and other organic compounds) –– 2314 ATP ADP  P

Evolution Connection: Solar-Driven Evolution C 3 plants - use CO 2 directly from the air –are very common and widely distributed. C 4 plants - close their stomata to save water during hot and dry weather –can still carry out photosynthesis. CAM plants - are adapted to very dry climates –open their stomata only at night to conserve water. © 2013 Pearson Education, Inc.

Figure 7.14 Sugar C 4 Pathway (example: sugarcane) C 4 plant CAM plant Sugar Calvin cycle Calvin cycle Day Cell type 1 Four-carbon compound Night Four-carbon compound Cell type 2 CAM Pathway (example: pineapple) ALTERNATIVE PHOTOSYNTHETIC PATHWAYS CO 2

Figure 7.14a Sugar C 4 Pathway (example: sugarcane) C 4 plant Calvin cycle Cell type 1 Four-carbon compound Cell type 2 CAM plant Sugar Calvin cycle Day Four-carbon compound Night CO 2 CAM Pathway (example: pineapple) CO 2

Figure 7-UN04 Carbon dioxide 6 O 2 6 CO 2 6 H 2 O C 6 H 12 O 6 WaterGlucose Photosynthesis Oxygen gas Light energy

Figure 7-UN05 Light H2OH2O O2O2 Chloroplast Light reactions NADPH ATP Calvin cycle CO 2 NADP  ADP P Sugar Stack of thylakoids Stroma – – Sugar used for cellular respiration cellulose starch other organic compounds

Figure 7-UN06 acceptor Water-splitting photosystem Photon H2OH2O 2 H  Chlorophyll 2e2e – O2O2 + Electron transport chain ATP NADPH-producing photosystem Chlorophyll NADPH NADP  e – 2e2e – 2e2e – e – acceptor ADP Photon 2 1 – – 2e2e –

Figure 7-UN07 NADPH Calvin cycle ADP P NADP  P ATP G3P CO 2 Glucose and other compounds (such as cellulose and starch) – –