Transcript Bio113Photo-Energy 03

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
nm
380 nm
750 nm
500
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 carbonhydrogen 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