Photosynthesis
Sunlight as an Energy Source Photosynthetic organisms use pigments to capture the energy of sunlight Photosynthesis The synthesis of organic molecules from inorganic molecules using the energy of light
Properties of Light Visible light is part of an electromagnetic spectrum of energy radiating from the sun Travels in waves Organized into photons Wavelength The distance between the crests of two successive waves of light (nm)
Electromagnetic Spectrum of Radiant Energy
The Rainbow Catchers Different wavelengths form colors of the rainbow Photosynthesis uses wavelengths of 380-750 nm Color you see are the wavelengths not absorbed why the ocean is blue!!! Pigment An organic molecule that selectively absorbs light of specific wavelengths Chlorophyll (a & b) The most common photosynthetic pigment Absorbs violet and red light (appears green)
Photosynthetic Pigments Collectively, chlorophyll and accessory pigments absorb most wavelengths of visible light Certain electrons in pigment molecules absorb photons of light energy, boosting electrons to a higher energy level Energy is captured and used for photosynthesis
Fig. 7-4c, p. 110
Key Concepts: The Rainbow Catchers The flow of energy through the biosphere starts when chlorophylls and other photosynthetic pigments absorb the energy of visible light http://www.youtube.com/v/ijcv g9m-7s0
Overview of Photosynthesis Chloroplast An organelle that specializes in photosynthesis in plants and many protists Stroma A semifluid matrix surrounded by the two outer membranes of the chloroplast Sugars are built in the stroma
Overview of Photosynthesis Thylakoid membrane Folded membrane that make up thylakoids Contains clusters of light-harvesting pigments that absorb photons of different energies Photosystems (type I and type II) Groups of molecules that work as a unit to begin the reactions of photosynthesis (network of pigments) Convert light energy into chemical energy Where photosynthesis begins
Overview of Photosynthesis Light-dependent reactions Light energy is transferred to ATP and NADPH Water molecules are split, releasing O2 Light-independent reactions Energy in ATP and NADPH drives synthesis of glucose and other carbohydrates from CO2 and water
Visual Summary of Photosynthesis
Summary: Photosynthesis http://www.youtube.com/v/c1_u ez5wx1o
Sites of Photosynthesis in Plants
Light-Dependent Reactions In the first stage of photosynthesis, light energy drives electrons out of photosystems The electrons may be used in a noncyclic pathway of ATP formation (there s a cyclic pathway too, but you don t need to worry about that pathway for this course! Yay!!!)
Capturing Energy for Photosynthesis Photons boost electrons in pigments to higher energy levels Electrons are released from special pairs of chlorophyll a molecules in photosystems
Cyclic and Noncyclic Pathways Electrons from photosystems take noncyclic or cyclic pathways, forming ATP Worry about this pathway! FYI, more primitive photosynthesizers use this pathway!
Replacing Lost Electrons Electrons lost from photosystem II are replaced by photolysis of water molecules, which dissociate into hydrogen ions and oxygen Photolysis Process by which light energy breaks down a molecule such as water
Electron Flow in a Noncyclic Pathway Electrons lost from a photosystem enter an electron transfer chain in the thylakoid membrane Electron transfer chains Organized arrays of enzymes, coenzymes, and other proteins that accept and donate electrons in a series
Harvesting Electron Energy Light energy is converted to chemical energy Entry of electrons from a photosystem into the electron transfer chain is the first step in lightdependent reactions ATP forms in the stroma Electron energy is used to build up a H+ gradient across the membrane H+ flows through ATP synthase, which attaches a phosphate group to ADP
Noncyclic Pathway of Photosynthesis
Animation: Noncyclic pathway of electron flow http://www.youtube.com/v/ey1r eqiywys
Key Concepts: Making ATP and NADPH Photosynthesis proceeds through two stages in the chloroplasts of plants and many types of protists In the first stage, sunlight energy is converted to the chemical bond energy of ATP The coenzyme NADPH forms in a pathway that also releases oxygen
Light-Independent Reactions: The Sugar Factory The cyclic, light-independent reactions of the Calvin-Benson cycle are the synthesis part of photosynthesis Calvin-Benson cycle Enzyme-mediated reactions that build sugars in the stroma of chloroplasts
Carbon Fixation Carbon fixation Extraction of carbon atoms from inorganic sources (atmosphere) and incorporating them into an organic molecule Builds glucose from CO2 Uses bond energy of molecules formed in lightdependent reactions (ATP, NADPH)
The Calvin-Benson Cycle Enzyme rubisco attaches CO2 to RuBP Forms two 3-carbon PGA molecules PGAL is formed PGAs receive a phosphate group from ATP, and hydrogen and electrons from NADPH Two PGAL combine to form a 6-carbon sugar Rubisco is regenerated
Inputs and Outputs of the Calvin-Benson Cycle
The Calvin-Benson Cycle
Animation: Calvin-Benson cycle http:// www.youtube.com/v/mhu27qyjnu0
Key Concepts: Making Sugars The second stage is the synthesis part of photosynthesis, in which sugars are assembled from CO2 The reactions use ATP and NADPH that form in the first stage of photosynthesis
3-D Video!!!! OOOOOOOHHHHHHHH!!! AAAAAAAAHHHHHHHH!!!
Photosynthesis and the Atmosphere The evolution of photosynthesis dramatically and permanently changed Earth s atmosphere
Different Food Sources Autotrophs Organisms that make their own food using energy from the environment and inorganic carbon Heterotrophs Organisms that get energy and carbon from organic molecules assembled by other organisms
Earth With and Without Oxygen Atmosphere
Effects of Atmospheric Oxygen Selection pressure on evolution of life Oxygen radicals Development of ATP-forming reactions Aerobic respiration Formation of ozone (O3) layer Protection from UV radiation
Key Concepts: Evolution and Photosynthesis The evolution of photosynthesis changed the composition of Earth s atmosphere New pathways that detoxified the oxygen by-product of photosynthesis evolved Photosynthesis by autotrophs removes CO2 from the atmosphere; metabolism by all organisms puts it back in Human activities have disrupted this balance, and contribute to global warming
Homework Assignment!!! Due 10/31 Send to me by e-mail! 5 pts. Question: What Causes Global Warming? Answer: Scientists have determined that a number of human activities are contributing to global warming by adding excessive amounts of greenhouse gases to the atmosphere. Greenhouse gases such as carbon dioxide accumulate in the atmosphere and trap heat that normally would exit into outer space. Your assignment: What are the ramifications of global warming on the process of photosynthesis? How does that affect the process of photosynthesis? Write ½ - ¾ of a page answer that expresses your opinions using what you know about the process of photosynthesis discussed in this chapter.