Transcript Chapter 7
Chapter 10
Biology
Solar Energy
& Photosynthesis
Origin of Solar System
Origin of Life Oxygen
Energy Atoms Electrons
Energy Fusion
The Earth Observing System (EOS)
ERBE Earth Radiation Budget Experiment ACRIMSAT Active Cavity Radiation 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 planet.
of our
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, and red wavelengths best.
blue,
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 CO 2 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 CO 2 , 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. CO 2 fixation is the attachment of CO 2 an organic compound.
to b. RuBP (ribulose bisphosphate) is a five carbon molecule that combines with carbon dioxide.
2. Reducing PGA
•
a. Six-carbon molecule immediately breaks down, forms two PGA (3 phosphoglycerate[C
3
]) 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
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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 [C 3 ], a three-carbon product; Calvin cycle is also known as C 3 cycle .