Download Photosynthesis and Energy

Photosynthesis and Energy
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Photosynthesis reaction solar energy
chemical energy.
LIGHT
CO2 + 2H2A  (CH2O) + H2O +2A
LIGHT
CO2 + 2H2S
 (CH2O) + H2O + 2S LIGTH
3CO2 + 6H2O  C3H6O3 + 3O2 + 3H2O
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Why is photosynthesis important?
•  Photosynthesis is arguably the
most important biological
process on earth. •  Production of sugars
•  Liberation of oxygen
•  Responsible for removal of ~
200 billion tons of C from the
atmosphere yearly.
•  Leaves, flowers, seeds, roots,
fruits, bark, pollen, etc.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Thylacoid: Minimum unit inside
the chloroplast containing
chlorophyll Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Electromagnetic Spectrum
high energy
short wavelength
gamma
rays
x-rays
low energy
long wavelength
ultraviolet
infrared
microwaves
radiowaves
visible
light
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Figure 8.2
A substance that absorbs light
is known as a pigment.
Color is associated with the
concept of light absorption.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Primary photosynthetic pigment : chlorophyll a Accessory pigments: chlorophyll b, chlorophyll c,
carotenoids, (carotens and xanthophylls) and phycobilins
(phycoerythrin and phycocyanin).
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carotens and xanthophylls
A big number of plants drop their
leaves and twigs and go dormant
during dry spells.
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phycobilins
Abundant red algae and cianobacteria
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Electrons (ē) are boosted
As the ē to the ground state the energy released would be:
a)  Converted completely or partially to heat (fluorescence)
b)  The energy can pass from one excited chlorophyll to another…
c)  A high energy ē is transferred to an ē receptor chain.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stages of Photosynthesis
•  There are two primary stages to photosynthesis.   light-dependent reactions: Energy-transduction reactions
  light-independent reactions: Carbon fixation reactions
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stage 1: The Steps of the Light Reactions
• In the first stage, called the
light reactions, electrons
derived from water are
energetically boosted by the
power of sunlight. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stage
1: The
the Light
Reactions
Stage
1:Steps
The of
Steps
of the
Light
Reactions
sunlight
photosystem I
photosystem II
Water is split, yielding both electrons and oxygen.
The electrons move through the light reactions.
The oxygen is what organisms such as ourselves breathe in. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Photosystem II is located in the grana
Photosystem I and ATP Synthase are located mainly stroma
tylakoids and outer portions of the grana
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stage 2: The Calvin Cycle
•  In this second stage, the
Calvin cycle, the electrons are
brought together with carbon
dioxide and a sugar.
Carbon + ATP +NADPH ----------Glucose and other derivatives
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stage 2: The Calvin Cycle
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
G3P
•  G3P can be used for
energy or for plant
growth. •  Everything in the
plant ultimately is
derived from this
sugar, in association
with minerals and
water that the plant
absorbs through its
roots.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Photorespiration
C4 plants
 Saturate CO2 into mesophyll
cells Oxaloacetate
 C4 = oxaloacetate
 PEP carboxylase (PEPCase)
 Requires additional energy corn
sugarcane
PEPCase
PEP + CO2
Oxaloacetate
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Different metabolic pathways C3 vs. C4
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C4 plants efficiency
Photosynthesizes faster than C3 plants under high light intensity and high temperatures • CO2 is delivered directly to RUBISCO.
• Oxygen don’t undergo photorespiration.
Has better water use efficiency • PEP Carboxylase brings in CO2 faster.
• Not need to keep stomata open as much.
• Less water lost by transpiration for the same amount of CO2 gain
for photosynthesis.
C4 plants include several thousand species in at least 19 plant families.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
CAM (crassulacean-acid metabolism)
Called CAM after the plant family in which it was first found (Crassulaceae) and
because the CO2 is stored in the form of an acid before use in photosynthesis.
CO2
malate
PEP-case
The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released to RUBISCO for
photosynthesis
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Crassulaceae tissue
★ Substomatal chamber
Protected stoma
Compact mesophyll
Tissue for water storage
Deep cuticule
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CAM Plants
CAM plants include many succulents such as cactuses and agaves
and also some orchids and bromeliads
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
CAM efficiency
Commonly, stomata are open at night when transpiration rates are lower
CAM plants can just leave their stomata closed night and day.
• Oxygen given off in photosynthesis is used for respiration
• CO2 given off in respiration is used for photosynthesis.
The plant to survive dry spells, and it allows the plant to recover very quickly
when water is available.
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Attendance
Where does the oxygen come from that is released during the process
of photosynthesis?
Why is water necessary for the overall process of photosynthesis?
Why are the light-dependent reactions necessary for photosynthesis?
What is the function and characteristics of peroxisomes?
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.