CO 7
Photosynthesis
Name a plant you have
seen recently.
Photosynthesis
Brainstorm...
What are some careers or college
majors related to plants?
U of I - College of Agriculture
What is a plant anyway?
Photosynthetic Organisms
A. Photosynthesis transforms
solar energy into organic
molecules.
B. Organic molecules built by
photosynthesis provide both
the building blocks and energy
for cells.
Figure 7.1b
C. The raw materials are
carbon dioxide and water.
D. Chloroplasts carry out
photosynthesis.
Figure 7.1c
E. Chlorophylls and other
pigments involved in
absorption of solar energy
reside within thylakoid
membranes of chloroplasts
Figure 7.2
Two words that
sound alike but are
not at all similar:
Stroma
Stoma
Quick Check
1. Plant
2. Thylakoid
3. Photosynthesis
4. Organic Molecules
Plants as Solar Energy Converters
A. Solar Radiation - Only ~50% of solar radiation that hits
Earth’s atmosphere reaches surface; most is visible light.
B. Photosynthetic Pigments - Pigments found in chlorophyll absorb
various portions of visible light; absorption spectrum.
1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b.
2. Both chlorophylls absorb violet, blue, and red wavelengths best.
3. Most green is reflected back; this is why leaves appear green.
4. Carotenoids are
yellow-orange
pigments which
absorb light in violet,
blue, and green
regions.
5. When chlorophyll
breaks down in fall,
the yellow-orange
pigments in leaves
show through.
Fall Foliage Slideshow
C. Absorption and action spectrum –
A spectrophotometer measures the amount of light that
passes through a substance (pigment) by wavelength.
1) As different wavelengths are passed through, some
are absorbed.
2) Graph of percent of light absorbed at each
wavelength is absorption spectrum
.
3) Photosynthesis produces
oxygen; production of oxygen is
used to measure the rate of
photosynthesis.
4) Oxygen production and,
therefore, photosynthetic activity is
measured for plants under each
specific wavelength; plotted on a
graph, this produces an action
spectrum.
5) Since the action spectrum
resembles absorption spectrum,
this indicates…what?
 chlorophylls and carotenoids
contribute to photosynthesis.
Checkpoint
1. What is the relationship between the absorption spectrum and the
action spectrum?
2. How can we measure the rate of photosynthesis?
3. How is the wavelength of light related to the rate of
photosynthesis?
4. A radish plant is grown
using lights of different
colors.
Explain the data.
E. Two Sets of Reactions in Photosynthesis
1. Light reactions cannot take place unless light is present.
They are the energy-capturing reactions.
b. Chlorophyll within thylakoid membranes absorbs solar energy
and energizes electrons.
c. Energized electrons move down an electron transport system;
the energy is captured and used for ATP production.
d. Energized electrons are taken up by NADP+, becoming
NADPH.
2. Calvin Cycle
Reactions
a. These reactions take
place in the stroma; can
occur in either light or
dark conditions.
b. These are synthesis
reactions that use
NADPH and ATP to
reduce CO2 (add an eto it).
-- and make a
carbohydrate, sugar
D. Photosynthetic Reaction
1. In 1930 a Dutch-American microbiologist (Cornelius Bernardus Van
Niel) showed that O2 given off by photosynthesis comes from
water and not from CO2.
2. The net equation reads:
What you should know by now..
1. The equation for photosynthesis. Write it!
2. The structure of a chloroplast. Sketch it!
3. The two reactions of photosynthesis.
**Things are about to get much more difficult**
7.3 The Light Reactions
1. Two electron paths operate between two photosystems within
the thylakoid membrane
•
linear electron flow, and cyclic electron flow
2. Both paths use ATP, but only the noncyclic also produces
NADPH to be used in the Calvin Cycle
3. PHOTOPHOSPHORYLATION = ATP production by sunlight
• Due to the movement of ions (H+) across a selectively
permeable membrane, down their electrochemical
gradient (CHEMIOSMOSIS).
1. Light hits photosystem II and excites an electron in the pigment
(chlorophyll, etc.)…initial electron supplied by splitting water
(photolysis  energy from photons, assisted by enzymes)
2. The primary electron acceptor passes the electron down the ETC and
generates ATP via chemiosmosis
3. Light is required for PSI, but not water, it generates NADPH
Something trivial....
Photosystem I and Photosystem II are
named based on when they were discovered,
PSI was established first.
Cyclic Electron Flow:
- many prokaryotes, including purple-sulfur bacteria, and mutant plants
Q: Can you think of the
environmental conditions
in which this would be a
major advantage?
-
Avoids both photosystem II, release of O2, and donation of
electrons to NADP+ --> diverts more capture photons to
produce ATP
-
Fd = ferrodoxin protein, & Pc = plastocyanin protein
Figure 7.5
Indicate which system
(PS1 or PS2 or BOTH)
____1. Splits water
____2. Produces NADPH
____3. Has an electron transport chain
____4. Requires light
____5. Utilizes a primary electron acceptor
____6. Occurs in the thylakoid
____7. Requires the input of H20
____8. The cyclic path
____9. Uses chlorophyll
____10. Releases oxygen
Are you still confused? This is pretty
hard to visualize, but through the magic
of technology, we can watch these
processes as animations
McGraw Hill Animation
Forest Biology - The Light Reactions
DB Post Assignment:
Summarize the 8 Steps of Linear Electron Flow (pg. 194)
7.3 Light Reactions
A. Two Pathways
B. Noncyclic
C. Cyclic
D. ATP Production --> Photophosphorylation
(CHEMIOSMOSIS)
When H20 is split, two H+ remain
These H+ are pumped from the stroma into the thylakoid
This creates a gradient used to produce ATP from ADP
ATP is the whole point of Photosystem II and will be
used to power the Light Independent Reactions (Calvin
Cycle)
Figure 7.7
Chemiosmosis is difficult to visualize.
So... you get to color it!
The Calvin Cycle
Also called
*The Light Independent Reactions
*The Dark Reactions
*Named after Melvin Calvin, who
used a radioactive isotope of
carbon to trace the reactions.
The Calvin Cycle
is a series of reactions producing carbohydrates.
carbon dioxide fixation, carbon dioxide reduction,
and regeneration of RuBP.
FIXATION
REDUCTION
REGENERATION
B. Fixation of Carbon Dioxide
1. CO2 fixation is the attachment of CO2 to an organic
compound called RuBP.
2. RuBP (ribulose bisphosphate) is a five-carbon molecule
that combines with carbon dioxide.
3. The enzyme RuBP carboxylase (rubisco) speeds this
reaction; this enzyme comprises 20–50% of the protein
content of chloroplasts
Calvin Cycle Animation
Mainly this is a reshuffling of
carbons using ATP and NADPH
as energy
G3P can be
converted into
other things
Fortunately....
AP Biology no longer requires the
memorization of every step of the Calvin
Cycle, but you should understand the
beginning and the end and what it's
purpose is.
Summary Statements:
What is the purpose of the Calvin Cycle?
Where does the cell get its energy to perform these reactions?
What is the final product?
What factors affect photosynthesis?
1. Light Quality (color)
2. Light intensity
3. Light Period
4. Carbon Dioxide Availability
5. Water Availability
Photosynthesis
Simulation
Waterweed
Simulator
*Design an experiment to test ONE of the above factors*
Some Plant Taxonomy
In order for photosynthesis to occur, plants must open tiny
pores on their leaves called STOMATA.
Opening these pores can lead to loss of water.
Alternative Pathways
The Calvin Cycle is the MOST Common Pathway for Carbon
Fixation. Plant Species that fix Carbon EXCLUSIVELY through
the Calvin Cycle are known as C3 PLANTS.
Plants in hot and/or dry environments have a problem with
water loss, so they keep their stomata partly closed...
…this results in a CO2 DEFICIT (Used in Calvin Cycle), and the
level of O2 RISES (as Light reactions Split Water Molecules).
Figure 7.10
In the presence of high O2,
Rubisco combines O2 with
RuBP instead of CO2.
 only one molecule of G3P is
produced and a toxic 2C
molecule
called phosphoglycolate is
produced.
C4 plants and CAM plants
bypass this by using an
alternate pathway to FIX
carbon dioxide from the air.
C4 PATHWAY uses PEP
carboxylase to transfer CO2
to bundle sheath cells
where there is little to no
O2.
Figure 7.11
THE CAM PATHWAY - Plants that use the
CAM Pathway open their stomata at night and
close during the day.
At night, CAM plants take in and use PEPC to
fix CO2 into organic compounds. During the
day, CO2 is released from these compounds
and enters the Calvin Cycle. Because they
have their stomata open only at night, they
grow slow.
CARBON FIXER:
C4/Cam  PEP Carboxylase
C3  RuBisCo
Quick Practice
Quick Practice
granum
thylakoid
stroma
O2
Pg 129b
Light & H2O
CO2
ADP
NADP
ATP
NADPH
O2
glucose
A = photosystem II
B = photosystem I
C = H20
D = Electron Transport Chain
E = ATP Synthase
AB = ATP
AC = phospholipids
AD = light (energy)
Finito
Photosynthesis Activities
1. Elodea photosynthesis rate (lab)
2. Photosynthesis alphabet book
3. Chromatography of a spinach leaf
4. Viewing elodea cells chloroplasts
5. Fall colors observation