Download Photosynthesis

Photosynthesis
The Sun
The Ultimate Energy Source
For Life on Planet Earth
Pyramid of Biomass
Trophic Levels
Consumers
Heterotrophs
The Sun
Photosynthesis (P/S)
Producers
Autotrophs
The Equation
This carbon came from CO2
Note that there is carbon in CO2
Photosynthesis
6CO2 + 6H2O
Light
Chlorophyll
C6H12O6 + 6O2
CO2: Carbon Dioxide

Air

78% N2

21% O2

.04% CO2
H2 O
Exits
2 Guard Cells
surrounding a
pore
CO2 Enters
Open Stomate
Transpiration
The evaporative water
loss by a plant – primarily
through open stomata
Closed Stomate
How Does Water Get In The Plant?
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Roots
Water enters through the __________
Most water is lost from the plant
Leaves (Actually the stomates on the leaf surface)
through the _________
To reduce water loss leaves are covered
with a waxy cuticle (plant “chapstick”)
The Leaf is Covered with a Waxy
Cuticle: “Plant Chapstick”
If water cannot get out of
the leaf through the waxy
cuticle what cannot get
into the leaf for P/S?
CO2 Enters
H2O Exits
Mesophyll cell or photosynthetic cell: Note the chloroplasts
Transpiration

The evaporative water loss by a plant,
primarily through stomata
Note that this part of the graph shows that the more the
stomates are open the greater the water loss via transpiration.
Transpiration
Rate
Closed
Partially
Open
Fully
Open
Degree of Stomatal Opening
Photosynthesis and Transpiration

High Rates of P/S are associated with
high transpiration rates
Note that this part of the graph shows that the more the
stomates are open the faster the rate of photosynthesis.
Rate of
P/S
Closed
Partially
Open
Fully
Open
Degree of Stomatal Opening
An Open Stomate
Guard cells
Pore
A Partially Closed Stomate
Notice the waxy
cuticle on the
leaf surface
Light:
Light Energy is inversely
proportional to
wavelength
This means the smaller
the wavelength the
higher the energy!
Chlorophyll:
The Primary P/S Pigment


Pigments absorb light energy
The color you see is the color that is
reflected

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White
versus
Black
Why is chlorophyll green? It reflects green light
Would you expect green light to be an
effective color of light for P/S?
No. Green light is reflected. For light to be used on P/S it must be absorbed!
Structure of a Chloroplast
Chlorophyll Reflects Green Light

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Chlorophyll absorbs
blue and red light
Accessory pigments
such as carotenoids
absorb green light
and pass the energy
to chlorophyll
Absorption Spectra
Amount
Of Light
Absorbed
Notice that this part of the graph
indicates not much green light is
absorbed. Thus green light is
reflected.
This part of the
graph shows blue
light is absorbed
Wavelength of Light (nm)
This part of the graph shows
red light is absorbed
Accessory Pigments

Absorb colors of light that chlorophyll
cannot (Yep – that means they absorb green light)

Pass the energy to chlorophyll

Example: Carotenoids -
Absorption Spectra
Amount
Of Light
Absorbed
Notice that carotenoids
can absorb some colors of
green
Wavelength of Light (nm)
Carotenoids
Accessory Pigments
Accessory Pigments
These quacking aspen trees are winter
deciduous. This means that they drop
their leaves in winter. Before they drop
their leaves, chlorophyll is reabsorbed, and
their accessory pigments become
visible. The visible accessory pigments are
responsible for “fall color”.
The light reactions require water
The dark reactions require
carbon dioxide
Photosynthesis
is a two step
process:
•The light
reactions
Stroma
Notice that the
light reactions
produce oxygen
The dark
reactions
produce
glucose
• The dark rxns
or the Calvin
cycle
Photosynthesis is a Two Step Process
The Light Reactions

6CO2 + 6H2O
The Dark Reactions
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The Light Reactions: Light Dependant
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Photochemical


C6H12O6 + 6O2
Convert light energy into chemical energy
The Light Independent or Dark Reactions
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Temperature Dependant
Use the chemical energy created in the light
reactions to convert CO2 to glucose
The Light and Dark Reactions
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The Light Reactions
occur on the grana
The Dark Reactions
take place in the
stroma
The Light Reactions are Light Dependent
Light Saturation
Rate of
P/S
Can you think of a habitat
or ecosystem where P/S might
be limited by light?
When light saturation is reached
photosynthesis is going as fast
as it can. Turning up the light
beyond this point has no
effect on the rate of P/S.
Low Med
High
Light Intensity
The Dark Reactions are Temperature Dependent
Rate of
P/S
This part of the graph says
that if you increase the
temperature you increase
rate of photosynthesis
Low Med High
What is beginning to happen here?
The temperature is so high,
enzymes begin to denature
and the plant dies
Extreme
Temperature
Can you think of a habitat or ecosystem where P/S
might be limited?
High Potential Energy Molecules
NADP+
+
2e-
(2H)
Energy Required
Low P.E.
NADPH
High P.E.
NADPH
+
H+
High P.E.
+
H+
Energy Released
NADP+
Low P.E.
+
2e-
Does the formation of NADPH require or release energy?
It requires energy
NADP is made in the light reactions.
ATP: The Universal Energy Molecule
Energy from the
sun is used to
make ATP
ATP is cellular
gasoline.
ATP is made in the light reactions
The Light Reactions

Photochemical: Light energy is converted to
chemical energy in the form of two high
potential energy molecules. (ATP and
NADPH)
ATP
H2O
½ O2
2eNADPH
Two electrons are transferred
from water to NADP
When electrons are removed
from water oxygen is produced
The Light Reactions

The Two High Potential Energy
Molecules Produced are:
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ATP
__________
NADPH (NADPH2)
__________
Water
The Electron Source is?__________
When water gives up electrons what
waste product is produced? Oxygen
A model for the
light reactions
A Model For The Light Reactions
High P.E.
Low P.E.
The Light Independent or “Dark” Reactions
The Light Independent Reactions or the “Dark Reactions”
High P.E
Low P.E.
ATP
ADP + P
6CO2 ---------------------------------------------------- C6H12O6
High P.E.
Low P.E.
NADPH2
NADP + 2e-
What is the “fuel” that drives the dark reactions?__________
Chemical energy (ATP and NADPH2)
The light reactions
Where was this “fuel” produced?_______________________
Carbon dioxide diffuses into the
open stomates into intercellular air
spaces. From the air spaces it then
diffuses into a P/S cell.
C3 Photosynthesis: The Normal Pathway
(Air space between cells)
Chloroplast (green): Any cell with chloroplasts is a
photosynthetic cell.
Photosynthetic (P/S) cells)
Diffusion is the driving force that gets CO2 into
the leaf and into a P/S cell
6 Turns to Make
____
One Glucose
Plants with Kranz Anatomy have the P/S
cells in the center of the leaf around the
leaf veins.
C4 Photosynthesis: Kranz Anatomy
Photosynthetic (P/S) cells
Nonphotosynthetic (non P/S) cells
(They lack chloroplasts)
The C4 acid is analogous
to a taxi with
a passenger
The C4 acid
drops off a
CO2 for the
dark reaction i.e.,
the passenger has
been dropped off
into the P/S cell.
Fast Reaction
3C PEP is a taxi without a passenger
It will pick up
a passenger
called CO2
The taxi called PEP will return to the non P/S cell
to pick up another passenger (CO2)
(P/S Cell)
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CO2 diffuses through the open
stomate into a nonphotosynthetic cell
Fast Reaction

Note that the dark reaction in the
photosynthetic cell is the exact
same dark reaction that occurs
in C3 plants. In C4 plants the
only place this occurs is in cells
in the middle of the leaf that
surround the leaf veins.

CO2 is quickly grabbed by 3
carbon PEP and converted into a
4 carbon acid. This reaction
occurs so fast that the
concentration of CO2 leaf below
the open stomate is so low that
there is a very high diffusional
pull for CO2 from the atmosphere
into the leaf. This means that C4
plants suck in CO2 better than C3
plants.
Since C4 plants have a greater
diffusional pull for CO2, they can
partially close their stomates to
conserve water and still have
fast rates of photosynthesis!!
Tidestroma oblongifolia
The common name of this
plant is “mouse ears”. It is
the plant featured in the
article High Efficiency
Photosynthesis.
This is a C4 Plant with _______
anatomy
Desert Holly – A C4 Plant
Desert holly
can live in
salty soils since
it has salt
glands
Kranz Anatomy – C4 Plants
Note that the
chloroplasts
are in the
center of the
leaf
CAM Photosynthesis:
Cacti and Other Succulents
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Stomata closed during the day and open at night
Take in CO2 at night and convert it into a 4C acid
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The 4C acid is a storage form of CO2
It is analogous to filling up your pantry with CO2 at night
During the day, when the stomata are closed, the 4C acid
releases CO2 to the Calvin-Benson Cycle (dark reaction)
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This is analogous to using CO2 from the pantry for P/S since the
stomates are closed and the plant can’t get CO2 from the air
What is the advantage of having the stomata open at night and closed
during the day?
The stomates are only open when the temperature is low and humidity is high.
This reduces the transpiration rate and allows the plant to conserve water.
Pancake Cactus – A Stem Succulent
CAM P/s
Green
Stem
Question #28 in Worksheet II
Would you expect plants in Death Valley to be
actively photosynthesizing in August? Explain
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There are 3 possible right answers:
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If it is a C3 plant – No. The plant would be water
stressed. When plants are water stressed the stomates
are closed and CO2 cannot get into the leaf.
If it is a C4 plant – Maybe. C4 plants have a very high
water use efficiency. They can partially close their
stomates to reduce water loss and still do fairly fast
photosynthesis.
If it is a CAM plant – Yes. CAM plants are the most water
use efficient plants. In addition they are succulents and
store water in their tissues. This stored water is used
during periods of drought.