Chapter 7 Photosynthesis: Using Light to Make Food Lectures by Chris C. Romero, updated by Edward J. Zalisko 2010 Pearson Education, Inc. PowerPoint Lectures for Campbell Essential Biology, Fourth Edition Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition Eric Simon, Jane Reece, and Jean Dickey
THE BASICS OF PHOTOSYNTHESIS Photosynthesis: Is used by plants, some protists, and some bacteria Transforms light energy into chemical energy Uses 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 The producers for most ecosystems 2010 Pearson Education, Inc.
LM Plants (mostly on land) PHOTOSYNTHETIC AUTOTROPHS Photosynthetic Protists (aquatic) Photosynthetic Bacteria (aquatic) Forest plants Kelp, a large alga Micrograph of cyanobacteria Figure 7.1
Chloroplasts: Sites of Photosynthesis Chloroplasts are: The site of photosynthesis Found mostly in the interior cells of leaves Inside chloroplasts are 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. Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits. 2010 Pearson Education, Inc.
TEM LM Vein Chloroplast Inner membrane Outer membrane Granum Stroma Thylakoid CO 2 Stomata O 2 Leaf cross section Interior cell Figure 7.2-2
The Overall Equation for Photosynthesis In the overall equation for photosynthesis, notice that: The reactants of photosynthesis are the waste products of cellular respiration. 2010 Pearson Education, Inc.
Light energy In photosynthesis: - Sunlight provides the energy - Electrons are boosted uphill and added to carbon dioxide - Sugar is produced 6 6 H2O C6H12O6 CO2 Photo- Carbon Water synthesis Glucose dioxide 6 O2 Oxygen gas Figure 7.UN1
During photosynthesis, water is split into: Hydrogen Oxygen Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar. Oxygen escapes through stomata into the atmosphere. 2010 Pearson Education, Inc.
A Photosynthesis Road Map Photosynthesis occurs in two stages: The light reactions convert solar energy to chemical energy The Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide 2010 Pearson Education, Inc.
Light H 2 O Chloroplast Light reactions ATP NADPH O 2 Figure 7.3-1
Light H 2 O Chloroplast CO 2 Light reactions NADP + ADP P Calvin cycle ATP NADPH O 2 Sugar (C 6 H 12 O 6 ) <> Figure 7.3-2
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Chloroplasts: Are chemical factories powered by the sun Convert solar energy into chemical energy 2010 Pearson Education, Inc.
The Nature of Sunlight Sunlight is a type of energy called radiation, or electromagnetic energy. The full range of radiation is called the electromagnetic spectrum. 2010 Pearson Education, Inc.
Increasing wavelength 10 5 nm 10 3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 3 m Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light 380 400 500 600 700 750 Wavelength (nm) Wavelength = 580 nm Figure 7.4
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. 2010 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 Used a prism to create a spectrum of light shining on the slide 2010 Pearson Education, Inc.
Results: Bacteria: Mostly congregated around algae exposed to red-orange and blue-violet light Rarely moved to areas of green light Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum. 2010 Pearson Education, Inc.
Number of bacteria Light Prism Microscope slide Bacterium Algal cells 400 500 600 700 Wavelength of light (nm) Figure 7.5
Chloroplast Light Reflected light Absorbed light Transmitted light Figure 7.6
Chloroplast Pigments Chloroplasts contain several pigments: Chlorophyll a: Absorbs mostly blue-violet and red light Participates directly in the light reactions Chlorophyll b: Absorbs mostly blue and orange light Participates indirectly in the light reactions 2010 Pearson Education, Inc.
Carotenoids: Absorb mainly blue-green light Participate indirectly in the light reactions 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. 2010 Pearson Education, Inc.
How Photosystems Harvest Light Energy Light behaves as photons, discrete packets of 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. 2010 Pearson Education, Inc.
(a) Absorption of a photon e Excited state Light Photon Chlorophyll molecule Heat Ground state Light (fluorescence) (b) Fluorescence of a glow stick Figure 7.8
A photosystem is a group of chlorophyll and other molecules that function as a light-gathering antenna. 2010 Pearson Education, Inc.
Chloroplast Figure 7.9-1
Chloroplast Pigment molecules Thylakoid membrane Figure 7.9-2
Chloroplast Pigment molecules Photon Electron transfer Primary electron acceptor Reactioncenter chlorophyll a Reaction center Antenna pigment molecules Thylakoid membrane Transfer of energy Photosystem <> Figure 7.9-3
How the Light Reactions Generate ATP and NADPH Two types of photosystems cooperate in the light reactions: The water-splitting photosystem The NADPH-producing photosystem 2010 Pearson Education, Inc.
Primary electron acceptor 2e Light H 2 O Reactioncenter chlorophyll 2e 2 H + + 1 2 O 2 Water-splitting photosystem Figure 7.10-1
Primary electron acceptor Energy to make ATP 2e Light H 2 O Reactioncenter chlorophyll 2e 2 H + + 1 2 O 2 Water-splitting photosystem Figure 7.10-2
Primary electron acceptor Energy to make ATP Primary electron acceptor 2e 2e NADP NADPH 2e Light Light H 2 O Reactioncenter chlorophyll Reactioncenter chlorophyll NADPH-producing photosystem 2e 2 H + + 1 2 O 2 Water-splitting photosystem Figure 7.10-3
The light reactions are located in the thylakoid membrane. An electron transport chain: Connects the two photosystems Releases energy that the chloroplast uses to make ATP 2010 Pearson Education, Inc.
To Calvin cycle Light Light NADPH H + ATP H NADP ADP P Stroma Thylakoid membrane Inside thylakoid H 2 O 1 2 Electron transport chain Photosystem Photosystem 2e O 2 H H H H ATP synthase Electron flow H + Figure 7.11
To Calvin cycle Light Light NADPH H ATP H NADP ADP P Stroma Thylakoid membrane Photosystem Electron transport chain Photosystem ATP synthase Inside thylakoid Electron flow H 2 O 1 2 2e O 2 H H H H H Figure 7.11a
e ATP e e NADPH e e e e Water-splitting photosystem NADPH-producing photosystem Figure 7.12 <>
THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE The Calvin cycle: Functions like a sugar factory within the stroma of a chloroplast Regenerates the starting material with each turn 2010 Pearson Education, Inc.
CO 2 (from air) P RuBP sugar Three-carbon molecule P P Calvin cycle Figure 7.13-1
CO 2 (from air) P RuBP sugar Three-carbon molecule P Calvin cycle P ATP ADP P NADPH P NADP G3P sugar Figure 7.13-2
CO 2 (from air) P RuBP sugar Three-carbon molecule P Calvin cycle P ATP ADP P NADPH G3P sugar P P NADP G3P sugar G3P sugar P Glucose (and other organic compounds) Figure 7.13-3
CO 2 (from air) P RuBP sugar Three-carbon molecule ADP P ATP P Calvin cycle P ATP ADP P NADPH G3P sugar P P NADP G3P sugar G3P sugar P Glucose (and other organic compounds) Figure 7.13-4
Evolution Connection: Solar-Driven Evolution C 3 plants: Use CO 2 directly from the air Are very common and widely distributed: wheat, oats, rice 2010 Pearson Education, Inc.
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 2010 Pearson Education, Inc.
ALTERNATIVE PHOTOSYNTHETIC PATHWAYS C4 Pathway (example: sugarcane) CAM Pathway (example: pineapple) Cell type 1 CO 2 CO 2 Night Four-carbon compound Four-carbon compound Cell type 2 CO 2 CO 2 Calvin cycle Calvin cycle 2010 Pearson Education, Inc. Sugar C 4 plant Sugar CAM plant Day Figure 7.14