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The Process that feeds the Biosphere (The Nature of Sunlight (Wavelength:…
The Process that feeds the Biosphere
The Two Stages of Photsynthesis
Light Reactions
the light reactions are the steps of photosynthesis that convert solar energy to chemical energy.
Light absorbed by chlorophyll drives a transfer of electrons and hydrogen ions from water to an acceptor.
NADP+ (nicotinamide adenine dinucleotide phosphate)
First Cousin to NAD+
The light reactions use solar energy to reduce NADP+ molecule to NADPH
the "
Photo
" part of photosyntheis
Photophosphorylation: the light reactions also generate ATP using chemiosmosis to power the addition of a phosphate group to ADP
Calvin Cycle
Carbon Fixation; the intitial incorporation of carbon into organic compounds.
rubisco
; the enzyme that catalyzes this first step is RuBP carboxylase-oxygenase.
Phase 3 of the Regeneration of the CO2 acceptor
C
3
plants the first organic product of carbon fixation.
Wheat
Soy Beans
Rice
C
4
plants are the preface of Calvin cycle with an alternate mode of carbon fixation that forms a four carbon compound as its first product.
sugarcane
corn
members of the grass family
Bundle sheath cells
: are arranged into tightly packed sheaths around the veins of the leaf.
PEP carboxylase
the first step by an enzyme present only in mesophyll cells.
Calvin Cycle named after Melvin Calvin, to begin elucidate its steps in the late 1940s
The "
synthesis
" part of photosynthesis
The reducing power is the "
second phase
" provided by NADPH, which acquired its cargo of electrons in the light reactions.
The Calvin Cycle begins in most plants occurs during the Daylight that only the light reactions provide the NADPH and ATP that the Calvin Cycle requires.
The
carbohydrate
produced directly from the Calvin cycle is not glucose.
Glyceraldehyde
3-Phosphate (G3P; three carbon sugar
Photorespiration
; it occurs in the light (photo) and consumes O2 while producing CO2 (respiration)
Photosynthesis
: sun light converted into chemical energy that is stored in sugar and other organic molecules.
Chloroplasts
: Plants and other photosynthetic organisms contain cellular organelles.
All green parts of a plant, including green stems and unripened fruit, have chloroplasts
Thylakoids
: suspended within the stroma is a third membrane system made up of sacs
Thylakoid membrane is populated by two types of photosystems that cooperate in the light reactions of photosynthesis.
Photosystem II (PS II)
known as "
P680
" because of the pigment best absorbing light having a wavelength of 680nm
linear electron flow
; the energy transformation is a flow of electrons through the photosystems and other molecular components built into the thylakoid membrane.
Photosystem I (PS I)
known as "
P700
" because of the pigment best absorbing light having a wavelength of 700nm
cyclic electron flow
; photoexcited electrons can take an alternative path, the electrons cycle back from ferredoxin to the cytochrome complex via a plastocyanin molecule.
Chlorophyll
: the green pigment that gives leaves their color.
Chlorophyll molecules are organized along with other small organic molecules and proteins into complexes called
Photosystems
.
Photosystem
: composed of a reaction center complex surrounded by several light harvesting complexes.
Primary electron acceptor
: molecule capable of accepting electrons and becoming reduced.
light harvesting complex
chlorophyll b
multiple carotenoids
chlorophyll a
Mesophyll
: the tissue in the interior of the leaf
Chloroplasts are chemical factors powered by the sun.
Chloroplasts and mitochondria generate ATP by the same basic mechanism.
Heterotrophs
: "Biosphere- Consumers"
Consume remains of other organisms by decomposing and feeding on organic litter.
Feces
Fallen leaves
Dead organisms
Obtain organic material by the second major mode of nutrition.
All heterotrophs, including humans are completely dependent on photoautotrophs for food and also oxygen.
Autotrophs
: "Self-Feeders"
All plants are autotrophs
Photoautotrophs
, organisms that use light as a source of energy to synthesize organic substances.
"Producer" of the Biosphere
Produce organic moleclues from CO2 and other inorganic raw materials obtained from the environment.
Photosynthesis: Scientific Inquiry
The use of Glucose (C6H12O6) can simplify the relationship between photosynthesis and respiration.
Using Molecular formulas, the complex series of chemical reactions in photosynthesis.
C. B. van Niel investigated photosynthesis in bacteria that make their carbohydrate from CO2 but do not release O2.
His conclusion is at least in these bacteria CO2 is not split into carbon and oxygen. One group of bacteria used hydrogen sulfide rather than water for photosynthesis.
The Nature of Sunlight
Electromagnetic spectrum
: the entire range of radiation
Protons
: the model of light as waves explains many of light's properties but in certain respects light behaves as though it consists of discrete particles.
Wavelength
: the distance between the crests of electromagnetic wave.
The most important to life is the narrow band from about 380nm to 750nm in wavelength.
Visible Light
: can be detected as various colors by the human eye.
Electromagnetic Waves
are disturbances of electric and magnetic fields rather than disturbances of a material medium.
Pigments
: substances that absorb visible light
Spectrophotometer
: the ability of a pigment to absorb various wavelenghths of light can be measured with an instrument.
Absorption spectrum
: a graph plotting a pigments light absorption versus wavelength. Three types of pigments are shown from the absorption spectra
Chlorophyll
a
: the key light capturing pigment that participates directly in the light reactions
Chlorophyll
b
: the accessory pigment and separate group of accessory pigment called carotenoids
Carotenoids: hydrocarbons that are various shades of yellow and orange because they absorb violet and blue green light.
Action spectrum
: prepared by illuminating chloroplasts with light of different colors and then plotting wavelength against some measure of photosynthetic rate.
