Download Bio113Photo-Energy 03.ppt

Biology 113
Photosynthesis:Transformation of Energy
History of Photosynthesis; Light and Color
OBJECTIVES:
To understand the basic concepts associated with energy transformations,
including the Laws of Thermodynamics that govern energy transformations.
To understand the chemical nature of photosynthesis.
To understand the history of our understanding of photosynthesis.
To master basic concepts associated with the nature of light
To understand how pigments work.
To understand how photosynthesis evolved.
Energy
potential energy vs. kinetic energy
kinds of energy - thermal, light, electrical, mechanical, chemical
First Law of Thermodynamics (Law of the Conservation of Energy)
Second Law of Thermodynamics (Law of Entropy)
exergonic vs. endergonic chemical reactions; enzymes, coenzymes and cofactors
energy in open vs. closed systems
Chemical Nature of Photosynthesis
Oxidation - Reduction Reactions in General
chlorophyll
6CO2 + 12H2O ---------> C6H12O6 + 6O2 + 6H2O ; Equation for Photosynthesis
light
Enzymes, cofactors and coenzymes
energy of activation
ATP/ADP – the universal energy exchange system in living organisms
coupled reactions: endergonic rxn + ATP + ATPase --> exergonic reaction
History of Photosynthesis
van Helmont's willow tree experiments (1648?)
Priestley's method of "restoring air" (1771)
Ingenhousz experiments - light are green plants are necessary for “restoring air” (1778)
Englemann's experiment (1882)
van Niel's observations (1920's):
6CO2 + 12 H2S --------=> C6H12O6 + 12S + 6H2O purple sulfur bacteria
light
Hill Reaction – isolated chloroplasts if given an electron acceptor will generate 02
Ruben and Kamen - verify that the O2 in photosynthesis comes from water (1941)
Light
electromagnetic spectrum = radiant energy
gamma - X-rays - UV - violet - blue - green - yellow - orange - red - infrared - radio
10
380 nm
500 nm
750 nm
10
visible light - 380-750 nm - biologically active (some use infrared & some use UV)
light as a wave phenomenon; velocity (speed of light) = wavelength X frequency
light as a particle; energy = Planck’s constant X speed of light / wavelength
photons and quanta of light
Chlorophyll and light absorption
pigment - a substance that absorbs visible light
porphyrin ring (conjugated bonds uniting 4 pyrole rings around a central chlorophyll
molecule, with a long insoluble carbon-hydrogen chain which anchors the molecule)
light absorption -->heat or heat and light (fluorescence) or resonance energy transfer or
transfer of a high-energy electron (leaving an electron “hole”)
absorption spectrum for chl. a, chl. b, and carotenoids (carotenes and xanthophylls)
action spectrum for photosynthesis
accessory pigments in Kingdom Plantae - chl. b, carotenes, xanthophylls
motile aquatic bacteria, bacteriorhodopsin and evolution of photosynthesis
color