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Chapter 10
Biology
Solar Energy
&
Photosynthesis
Origin of Solar System
Origin of Life Oxygen
Energy Atoms Electrons
Energy Fusion
The Earth Observing System (EOS)
ACRIMSAT
Active Cavity
Radiation Experiment
ERBE
Earth Radiation Budget Experiment
Photosynthesis
• 1. Photosynthesis uses sunlight as a
source of energy to produce
carbohydrates.
• 2. Photosynthetic organisms (algae,
plants and a few other organisms)
serve as ultimate source of food for
most life.
Photosynthesis2
A. Organisms Depend Upon
Photosynthesis
• 3. Most food chains start with
photosynthesizers.
• 4. Photosynthesis has produced most of
the oxygen in the atmosphere of our
planet.
CES Oxygen Production
Solar Radiation
• 1. Solar radiation is described in
terms of its energy content and its
wavelength.
• 2. Photons are discrete packets of
radiant energy that travel in waves.
Photosynthetic Pigments
• use primarily the visible light portion of
the electromagnetic spectrum.
• a. Two major photosynthetic pigments
are chlorophyll a and chlorophyll b.
• b. Both chlorophylls absorb violet, blue,
and red wavelengths best.
Photosynthetic pigments
• c. Very little green light is absorbed;
most is reflected back and is why leaves
appear green.
• d. Carotinoids are yellow-orange
pigments which absorb light in violet,
blue, and green regions.
Spectrophotometer
absorption = action spectrum
Absorption and action spectrum
• Photosynthesis produces oxygen;
• production of oxygen used to measure
rate of photosynthesis.
7.2. Photosynthesis Occurs in
Chloroplasts
Photosynthesis Leaf
O18 - Used to Track Oxygen
Photosynthesis Respiration
Photosynthesis Has Two Sets of
Reactions
• Light-dependent reactions takes place
in the thylakoids; cannot take place unless
light is present, traps energy.
• Light-independent reactions take place
in the stroma; can occur in either the light or
the dark, fixes carbon.
Photosynthesis Chloroplast
7.3. Solar Energy Is Captured
A. Light-dependent Reactions
• 1. Occur in the thylakoid membranes
• 2.
Photosystem I and Photosystem II;
a Photosystem is a pigment complex and
electron acceptor, chlorophyll a and
chlorophyll b molecules and orange and yellow
accessory pigments
• 3.
Cyclic and Non-Cyclic electron pathways
Cyclic Electron Pathway
• Some photosynthetic bacteria utilize
cyclic electron pathway only; pathway
probably evolved early.
• utilized only when CO2 is in limited supply
Photosynthesis
Carbohydrate Is Synthesized
by the Calvin Cycle
in the Stroma
A. Light-Independent Reactions
• 1. The second stage of photosynthesis;
light is not directly required.
• 2. Require CO2, which enters through leaf
and NADPH and ATP, which have been
produced by light-dependent reactions.
C. The Calvin Cycle Has
Three Stages
C14 Labeled
1. Fixing Carbon Dioxide
• a. CO2 fixation is the attachment of CO2 to
an organic compound.
• b. RuBP (ribulose bisphosphate) is a fivecarbon molecule that combines with
carbon dioxide.
2. Reducing PGA
• a. Six-carbon molecule immediately
breaks down, forms two PGA (3phosphoglycerate[C3]) molecules.
2. Reducing PGA
• b. Each of two PGA molecules undergoes
reduction to PGAL in two steps.
• c. Light-dependent reactions provide
NADPH (electrons) and ATP (energy) to
reduce PGA to PGAL.
3. Regenerating RuBP
• a. Every three turns of Calvin cycle, five
molecules of PGAL are used to re-form
three molecules of RuBP (ribulose
bisphosphate).
3. Regenerating RuBP
• b. Every three turns of Calvin cycle,
there is net gain of one PGAL molecule;
five PGAL regenerate RuBP.
• c. First molecule identified by Calvin
was PGA [C3], a three-carbon product;
Calvin cycle is also known as C3 cycle.