Biology 1202B Chapter Notes - Chapter 7: Pyruvic Acid, Iron Fertilization, Carboxylation

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Kaden VanHelden
Biology 1202B: Chapter 7 – Photosynthesis
7.1 Photosynthesis: An Overview
Photosynthesis – the use of light energy to convert carbon dioxide into organic
compounds such as carbohydrates
oOrganic compounds have one or more C-H bonds
Autotrophs “self-feeding” – organisms that produce its own food using CO2 and other
simple inorganic compounds from the environment and energy from the Sun
oThe ones that use light can also be called photoautotrophs
Photoautotrophic organisms are known as earth’s primary producers
oPrimary producers generate the organic compounds that are used by other
7.1a Photosynthesis is an Oxidation-Reduction Process
CO2 and O2 are consumed and produced in equal molar amounts during photosynthesis
oThus one can measure rate of reaction at rate CO2 is consumed or at rate O2 is
In the reaction water is oxidized to oxygen (this requires energy)
In the reaction CO2 reduced to carbohydrate
The two previously mentioned parts of the reaction occur separately within the
7.1b Photosynthesis Can Be Divided into the Light Reactions and the Calvin Cycle
Light reactions and the Calvin cycle are required to convert carbon dioxide into
Light reactions include:
oCapturing of light
oUtilization of energy to synthesize NADPH and ATP
oElectrons used to reduce NADP+ to NADPH come from oxidization of H2O
In Calvin cycle
oElectrons and protons carried by NADPH and energy of ATP hydrolysis are used
to convert CO2 into carbohydrate
Carbohydrates are used for energy, but also for carbon skeletons used in biosynthesis of
lipids, amino acids, and nucleotides
7.1c In Eukaryotes, Photosynthesis Takes Place in Chloroplasts
Both light reactions and the Calvin cycle take place within the chloroplast, an organelle
that is comprised of 3 membranes
oOuter membrane – covers surface
oInner membrane – just inside outer membrane separated by aqueous
intermembrane space
Stroma – the aqueous environment within the inner membrane
oThylakoid membrane – flattened, closed sacs
Thylakoid lumen is space within these sacs
Stack of thylakoids is called a granum
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Kaden VanHelden
Embedded in thylakoid membrane are the components that carry out the light reactions
of photosynthesis: proteins, pigments, electron transport carriers, and ATP synthase
Enzymes are found within the stroma to catalyze reactions of the Calvin cycle
7.1d Photosynthesis from a Global Perspective
Half of carbon is fixed by unicellular photosynthetic algae called phytoplankton that
inhabit marine environments
The nutrient that limits phytoplankton growth in temperate regions of the oceans is iron
oExperiments with iron fertilization saw rapid phytoplankton growth
Increased photosynthesis from the ocean could potentially draw in some of the excess
CO2 being released as a result of climate change
7.2 The Photosynthetic Apparatus
Photosynthetic apparatus is a series of large protein complexes found in the thylakoid
membrane that are responsible for the light reactions
Photosystems – large complex into which the light absorbing pigments for
photosynthesis are organized with proteins and other molecules
oLead the conversion of light energy into chemical energy in the initial reactions of
7.2a Electrons in Pigment Molecules Absorb Light Energy
Photosynthesis requires the capture and utilization of light energy
When light interacts with matter it is best to look at light in terms of particles, not waves
oThese particles of energy are referred to as photons
oShorter wavelength of photon = greater energy
Photons energy can only be used when absorbed by pigment molecules
Absorption occurs when energy of photon is transferred to an electron within a molecule,
exciting it to a higher energy level
When an photon is absorbed 1 of 3 things can occur:
1. It goes back to ground state, releasing energy has heat or light of a longer
2. Energy of electron is transferred to a neighboring molecule (not the electron
itself), this is an efficient process
3. Excited electron is transferred to a nearby electron-accepting molecule
7.2b Chlorophylls and Carotenoids Cooperate in Light Absorption
Light absorbed by green pigments are called chlorophylls
Light absorbed by yellow-orange pigments are called carotenoids (think carrots =
An absorption spectrum can be measured using a spectrophotometer and a pure sample
of the pigment
An absorption spectrum is a plot of the absorption of light as functions of wavelength
Chlorophyll has really only 2 excited states: one that matches the energy of a blue
photon and one that matches that of a red photon
Photosynthesis depends on absorption done by carotenoids and chlorophylls acting
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