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The Photosynthetic Process
Photosynthesis
Photo = light
synthesis = to make
Photosynthesis has been going on successfully for over 3 Billion years.
Chlorophyll a (Primary photosynthetic pigment) has been around unchanged for
about that long as well
An amazing system that uses building blocks (Water and Carbon dioxide) that are
abundant and cheap = requiring little energy to convert.
Also many complicated molecules can be toxic or unstable in large quantities,
however the starches made by photosynthesis are easily stored by the plant in large
quantities without any problems to be used during leaner times.
Light in the Wavelength Spectrum
In the electromagnetic wavelength spectrum visible light is just a small sliver of the
overall range. Plants operate using light from the infrared (IR) to the ultraviolet (UV) and
the visible spectrum in-between.
Photosynthesis Terms:
• Chloroplast
• Chlorophyll
• Photosynthetic pigments
• Accessory pigments
• Antioxidants
• Thylakoid
• Thylakoid Membrane
• Granna
• Stroma
• Lumen
• Electron transport chain
• ATP, (ADP)
• NADPH (NADP+)
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Calvin Cycle
Light reaction
Protons
Ions
G3P
Sucrose
Photorespiration
CAM plants
C4 Photosynthesis
Respiration
It is Not Just Plants
• Some photosynthetic protists, like euglena, contain
chloroplasts as do plants.
• Others, like the dinoflagellates, host endosymbiotic
organisms or obtain chloroplasts from prey they consume.
• Bacteria often contain bacteriochlorophyll. This compound
resembles chlorophyll but absorbs light of slightly longer
wavelengths.
• Unlike plants, many bacteria do not require water for
photosynthesis to occur. Because of this, they do not
produce oxygen.
Euglena
Dinoflagellate
Bacteria with
bacteriochlorophyll
Where in The Plant? - Chloroplast
The chloroplast is a triple membraned organelle
where photosynthesis takes place.
The thylakoid is the poker chip like structure
where the light reaction takes place.
The granum is simply a stack of thylakoids.
The thylakoid membrane is the center of
activity for the light reaction.
The lumen is the inside of the thylakoid (where
hydrogen ions build up).
The stroma is the fluid outside the thylakoids
where the Calvin Cycle takes place
Photosynthetic Pigments
There are several photosynthetic
pigments.
chlorophyll b, beta carotene and
xanthophylls are responsible for
absorbing and channeling light
energy to chlorophyll a where
that pigment is excited into a
higher energy potential.
Absorption Spectrum
Chromatography paper is used to separate out the
various light absorbing pigments in different
types of leaves or leaves at different times of the
year.
Leaves are typically ground up and the liquid
applied to the paper which separates out the
colors into bands across the paper.
Accessory pigments like the carotenoids are
thought to assist in absorption of different
wavelengths of light but more importantly help to
protect the plant from damage by too much light
Carrot with chromoplasts
Cells of the Bird of Paradise flower showing the bright chromoplasts
Chromoplasts which hold pigments that absorb light are used in
various parts of the plant like the fruit or flowers to make them more
attractive to pollinators or their fruit more attractive to the animal
world to help spread the seeds.
Red bell pepper with chromoplasts
Carotonoids
Carotonoids are Red, Orange, and
Yellow and are Considered Accessory
pigments.
Carotenoids are considered to perform two
major functions in photosynthesis. They
serve as accessory light harvesting pigments,
extending the range of wavelengths over
which light can drive photosynthesis, and
they act to protect the chlorophyllous
pigments from the harmful photodestructive
reaction which occurs in the presence of
oxygen
Anthocyanins
Anthocyanins are pigments that make up the
Blues and reds found often in berries
*Are not always produced in plants or in some
plants are not produced consistently depending
on things like weather conditions and how many
stored sugars are present.
*Most are water soluble and stored in the
vacuoles of the plant.
*Signal animals as to fruit ripening
*Used in leaves to gather up stored sugars
Xanthophylls
Xanthophyll - These are the yellow pigments of the leaves and are classified as
accessory pigments which absorb the wavelength of light that chlorophyll cannot
absorb.
They serve as protection to excessive
amount of sunlight to prevent damage
in the plant.
Three kinds of xanthophyll are known:
canthaxanthin, zeaxanthin and lutein.
Health Importance of the Various Plant Pigments
Many of the light absorbing and accessory pigments found in plants we have learned
have significant health benefits. Mostly as a form of antioxidant preventing the
onset of cancers
Photosynthesis
The most basic representation of the
photosynthetic chemical reaction
Light Reaction – Water and light energy (captured by the chlorophyll)
are used to create two sources of energy – ATP and NADPH
Calvin Cycle – Using the 2 energy sources, CO2 is introduced and used
to build 3 carbon molecules used as building blocks for food and other
products for the plant.
In Simplest Terms
The Light reaction uses water and
light energy to formulate 2 forms of
energy ATP and NADPH. The
byproduct of that part of the
process is oxygen.
The Calvin Cycle uses CO2 and the
energy sources built by the light
reaction to convert a 5 carbon
molecule into (2) 3 carbon
molecules PGAL which are the
building blocks for
Sugar, cellulose and other carbon
based molecules.
Molecules and Ions
In the Light Reaction
Sunlight energy splits
the water molecule
H2O into an oxygen
atom and 2 hydrogen
ions releasing 2
electrons to the
2
H
2O
system
Water molecules
This is now a
molecule of
Oxygen Gas
Sunlight Energy = 4H+ + 4eSplits water molecule
Hydrogen
ions
electrons
1. Using light energy the water
2. As the electron (e-) moves through the
molecule is split releasing electrons into
the system, hydrogen ions (H+) into the
lumen, and O2 into the atmosphere
electron transport chain, H+ ions are pulled
into the system from outside in the stroma
and deposited into the lumen
3. Finally the electron powered
again by light energy causes a
H+ Ion to connect with NADP+
and form a NADPH molecule to
use as energy in the Calvin
Cycle
4. As H+ Ions are being
pumped into the inside of the
thylakoid in the lumen the
concentration builds up and
the only exit is through a
protein called ATP synthase.
As it passes through the H+
combines with ADP Molecule
and forms ATP to use in the
Calvin Cycle
Light Reaction
• Photons of light are used to power the movement of electrons (From water molecule
splitting) through an electron transport chain. (Pathway)
• Water enters and splits into O2 molecule and hydrogen protons donating the electron
to the system and pumping positively charged ions to the inside of the thylakoid
membrane (lumen)
• O2 becomes a by product but Hydrogen ions from the original water molecule
congregate in the inside of the membrane creating a positive charge buildup
• As the ions move to exit the only hole is a protein (called ATP synthase) . As the
Hydrogen ions pass through that protein, it converts ADP into ATP which is an energy
source needed in the Calvin cycle
• As the electrons move through the system they create 2 forms of energy: NADPH and
ATP. These now are in the Stroma outside the Thylakoid membrane and ready to fuel
the Calvin Cycle which occurs there.
ATP is used twice and NADPH
once during one revolution of the
Calvin Cycle to push the cycle
along.
3. 1 of the G3P is used and
combined with (2) CO2
molecules to regenerate the 5
carbon molecule (RuBP) to use
at the beginning of the cycle
again.
1. CO2 is brought in and
added to 5 carbon
molecule to make larger 6
carbon molecule
(temporary).
2. The 6 Carbon
molecule is split into
(2) 3 Carbon
molecules G3P that
become building
blocks for food or
other products for
the plant
Calvin Cycle - Light Independent Reaction
• ATP and NADPH from the light reaction are used as an energy source
to convert Carbon From CO2 and a 5 carbon molecule 1st into a 6
carbon molecule and then into (2) 3 carbon molecules.
• These 3 carbon molecules (G3P)are used by the plant as building
blocks to make sucrose and other products like cellulose that the
plant needs.
• Some of the molecules are used to rebuild the 5 carbon molecule
used at the beginning of the Calvin cycle so they return to the cycle.
• ATP is now ADP and NADPH is now NADP+ and is returned to the
light reaction
Photosynthesis – In Simplest Terms
What you
have to
know
This
Respiration
PHOTOSYNTHESIS
6CO2 + 6H2O
Energy
C6H12O6 + 6O2
RESPIRATION
C6H12O6 + 6O2
6CO2 + 6H2O + ENERGY
Photorespiration
• Photoresiration happens when there is a shortage of CO2 available to use
in the Calvin Cycle of photosynthesis
• Often O2 will fill in where CO2 entered before and another molecule instead
of the normal 3 carbon building blocks is manufactured.
• This new molecule has yet to prove to have any use to the plant and has to
then be broken down again by the plant.
• This is a part of C3 Photosynthesis which is the system of most plants and
happens usually when stomata have to close on a hot day.
Crassulacean Acid Metabolism (CAM) Plants
CAM was first discovered in the Crassulaceae family of plants and are
plants that have another way to carry out photosynthesis.
Members of many other plant families are CAM plants:
Euphorbiaceae
Cactaceae
Orchidaceae
Liliaceae
Bromiliadaceae
Agavaceae
Crassulacean Acid Metabolism
Night - Stomata Open
• CO2 brought into leaf cells used to
make an acid – Malic acid
• Malic acid is stored in the cells
Day - Stomata Closed
• Acid Broken down
CO2
Photosynthesis
• 6H2O + 6CO2
C6H12O6 + 6O2
By having stomata open at night water loss from the leaves is less than if
stomata were open during the day giving the plant an advantage in hot
dry areas
Some Examples of CAM Plants
Some Cactus
Some Orchids
Some bromeliads like pineapple
Crassulaceae family “Jade Plants”
C4 Photosynthesis
• In C4 photosynthesis Stomata are open during the day
• CO2 diffuses into the leaf
• C4 plants are able to store CO2 in the leaf cells as an acid to use as
a later source of CO2
• If water stress occurs during the afternoon, the stomata will close
to protect the plant from water loss.s
• C4 plant continues to photosynthesize using stored CO2
Warm season grasses are C4 plants. They use less water and even under
water stress conditions, continue to photosynthesize and grow.
Corn
Examples of C4 Plants
Bermudagrass
C4 plants are typically
able to endure
challenging warm
temperatures that might
stress most (C3) plants.
Sorghum
The C4 Photosynthesis Advantage in Southern
California For Warm Season Grasses
Tall Fescue ‘Marathon II” - Cool Season
Common Bermudagrass – Warm season
We have no native turf grasses in California. We live in the middle of a
transitional zone that doesn’t grow cool season grasses very easily. Our
long dry Summers set the stage for competition between cool season
grasses and warm season warm season grasses.
Kikuyugrass – Warm season
OCC Horticulture department lawn with Cool season Tall fescue
being challenged by Common Bermudagrass - A weed
Regional Grass Map of the United
States showing the transitional area of
Southern California being right on the
edge of transitional and Warm Season
grasses.
What you need to know
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What part of the electromagnetic scale do plants use
What are the parts of the chloroplast
What happens in the light reaction - What powers it? - What is produced?
What happens in the Calvin Cycle. What powers it. What molecule used as
a building block is formed.
• What is photorespiration? What causes it to happen? Why is it bad?
• What is Crassulacean Acid Metabolism?(CAM) What types of plants are
cam plants how does CAM photosynthesis method help these plants?
• How does C4 photosynthesis work?