Chapter 7 Photosynthesis: Using Light to Make Food 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 Lectures by Edward J. Zalisko 2013 Pearson Education, Inc.
THE BASICS OF PHOTOSYNTHESIS Photosynthesis is used by plants, algae (protists), and some bacteria, transforms light energy into chemical energy, and 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 and the producers for most ecosystems. 2013 Pearson Education, Inc.
Figure 7.1 LM Plants (mostly on land) PHOTOSYNTHETIC AUTOTROPHS Photosynthetic Protists (aquatic) Photosynthetic Bacteria (aquatic) Forest plants Kelp, a large, multicellular alga Micrograph of cyanobacteria
Chloroplasts: Sites of Photosynthesis Chloroplasts are the site of photosynthesis and found mostly in the interior cells of leaves. Inside chloroplasts there 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 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. 2013 Pearson Education, Inc.
Figure 7.2-3 LM Colorized TEM Photosynthetic cells Vein Chloroplast Inner and outer membranes Stroma Thylakoid space Granum CO 2 O 2 Stomata Leaf cross section Interior cell
The Simplified Equation for Photosynthesis In the overall equation for photosynthesis, notice that the. reactants of photosynthesis are the waste products of cellular respiration Light energy 6 CO 2 6 H 2 O C 6 H 12 O 6 Photo- Carbon dioxide Water synthesis Glucose 6 O 2 Oxygen gas 2013 Pearson Education, Inc.
The Simplified Equation for Photosynthesis In photosynthesis, sunlight provides the energy, electrons are boosted uphill and added to carbon dioxide, and sugar is produced. 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. 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. The initial incorporation of carbon from the atmosphere into organic compounds is called carbon fixation. 2013 Pearson Education, Inc.
THE LIGHT REACTIONS Light H 2 O CO 2 Chloroplasts are chemical factories powered by the sun and convert sunlight into chemical energy. Light reactions O 2 NADP ADP + P ATP NADPH Calvin cycle Sugar
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 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 7.5 Light Chloroplast Reflected light Absorbed light Transmitted light (detected by your eye)
Animation: Light and Pigments Right click slide / select Play 2013 Pearson Education, Inc.
Number of bacteria Figure 7.6 Light Prism Microscope slide Bacteria Bacteria Algal cells 400 500 600 700 Wavelength of light (nm)
Chloroplast Pigments Chloroplasts contain several pigments: Chlorophyll a absorbs mainly blue-violet and red light Chlorophyll b absorbs mainly blue and orange light Carotenoids absorb mainly blue-green light. The spectacular colors of fall foliage are due partly to the yellow-orange light reflected from carotenoids. 2013 Pearson Education, Inc.
How Photosystems Harvest Light Energy Light behaves as photons, fixed portions of light energy. Chlorophyll molecules absorb photons. Electrons in the pigment gain energy. Excited state Absorption of a photon excites an electron. e The electron falls to its ground state. Light Heat Photon Chlorophyll molecule Light (fluorescence) Ground state (a) Absorption of a photon (b) Fluorescence of a glow stick
How Photosystems Harvest Light Energy 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 lightgathering antenna. 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. Trapped energy then used to make ATP and NADPH. 2013 Pearson Education, Inc.
Figure 7.9 Chloroplast Cluster of pigment molecules Photon e Electron transfer Primary electron acceptor Reactioncenter chlorophyll a Reaction center Thylakoid membrane Transfer of energy Photosystem Pigment molecules
How the Light Reactions Generate ATP and NADPH Two types of photosystems cooperate in the light reactions: 1. the water-splitting photosystem 2. the NADPH-producing photosystem. 2013 Pearson Education, Inc.
Figure 7.12 e ATP e e NADPH e e e e Water-splitting photosystem NADPH-producing photosystem
Figure 7.10-3 Primary electron acceptor 2 Energy to make ATP Primary electron acceptor 2e 2e 3 NADP NADPH 2e Light Light 1 Reactioncenter chlorophyll H 2 O 1 2 2 H O 2 2e Reactioncenter chlorophyll Water-splitting photosystem NADPH-producing photosystem
How the Light Reactions Generate ATP and NADPH The light reactions take place in the thylakoid membrane. An electron transport chain releases energy that the chloroplast uses to make ATP. 2013 Pearson Education, Inc.
Figure 7.11 To Calvin cycle Light H Light NADPH NADP ADP P H ATP 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 Thylakoid membrane
THE CALVIN CYCLE Light H 2 O CO 2 The Calvin cycle functions like a sugar factory within a chloroplast and regenerates the starting material with each turn. Light reactions O 2 NADP ADP + P ATP NADPH Calvin cycle Sugar
Figure 7.13-4 CO 2 (from air) P 1 RuBP sugar ADP P ATP 4 P Calvin cycle P Three-carbon molecule ATP ADP P NADPH G3P sugar 3 P P NADP G3P sugar 2 G3P sugar P Glucose (and other organic compounds)
Evolution Connection: Solar-Driven Evolution C 3 plants use CO 2 directly from the air and are very common and widely distributed. C 4 plants close their stomata to save water during hot and dry weather and still can carry out photosynthesis. CAM plants are adapted to very dry climates and open their stomata only at night to conserve water. 2013 Pearson Education, Inc.
Figure 7.14 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 Sugar C 4 plant Sugar CAM plant Day
Figure 7-UN04 Light energy 6 CO 2 6 H 2 O C 6 H 12 O 6 Photosynthesis Carbon dioxide Water Glucose 6 O 2 Oxygen gas
Figure 7-UN05 Chloroplast Light H 2 O CO 2 Stack of thylakoids Light reactions NADP ADP P ATP Calvin cycle Stroma NADPH O 2 Sugar Sugar used for cellular respiration cellulose starch other organic compounds
Figure 7-UN06 ADP ATP e acceptor 2e NADP e acceptor 2e 2e NADPH Photon Photon Chlorophyll H 2 O 2e Chlorophyll NADPH-producing photosystem 2 H + 1 2 O 2 Water-splitting photosystem
Figure 7-UN07 CO 2 ATP NADPH Calvin cycle ADP NADP P G3P P Glucose and other compounds (such as cellulose and starch)