Photosynthesis and Energy
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Why is photosynthesis important?
•  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
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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).
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
carotens and xanthophylls
A big number of plants drop their
leaves and twigs and go dormant
during dry spells.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
phycobilins
Abundant red algae and cianobacteria
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stages of Photosynthesis
•  There are two primary stages to photosynthesis. ü  light-dependent reactions: Energy-transduction reactions
ü  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 in the
stroma, tylakoids and outer portions of the grana
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stage 2: The Calvin Cycle
•  electrons + carbon dioxide +
sugar.
Carbon + ATP +NADPH ----------à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
ü Saturate CO2 into mesophyll
cells Oxaloacetate
ü C4 = oxaloacetate
ü PEP carboxylase (PEPCase)
ü Requires additional energy corn
sugarcane
PEPCase
PEP + CO2
Oxaloacetate
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Different metabolic pathways C3 vs. C4
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
C4 plants efficiency
Photosynthesizes faster than C3 plants under high light intensity and high
temperatures C4 metabolism has better water use efficiency • 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
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
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.