Transcript Document

CO 7
Chapter 10
Photosynthesis
Name a plant you have
seen recently.
What is a plant anyway?
Photosynthetic Organisms
A. Photosynthesis transforms
solar energy
B. Organic molecules built by
photosynthesis provide both the
building blocks and energy for
cells.
Figure 7.1b
C. Plants use the raw materials:
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
Plants as Solar Energy Converters
A. Solar Radiation - Only 42% of solar radiation that hits the
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 sample
of pigments.
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 that chlorophylls
contribute to photosynthesis.
D. Photosynthetic Reaction
1. In 1930 C. B. van Niel showed that O2 given off by
photosynthesis comes from water and not from CO2.
2. The net equation reads:
E. Two Sets of Reactions in Photosynthesis
1. Light reactions cannot take place unless light is present.
They are the energy-capturing reactions.
b. Chlorophyl within thylakoid membranes absorbs solar energy
and energizes electrons.
c. Energized electrons move down the electron transport
system; energy is captured and used for ATP production.
d. Energized electrons are also taken up by NADP+, becoming
NADPH.
2. Calvin Cycle
Reactions
a. These reactions take
place in the stroma; can
occur in either the light or
the dark.
b. These are synthesis
reactions that use
NADPH and ATP to
reduce CO2.
What you should know by now..
1. The equation for photosynthesis. Write it!
2. The structure of a chloroplast. Sketch it!
3. Compare Absorption Spectrum to Action Spectrum. Sketch it!
4. Compare the two stages of photosynthesis and their
products. Chart it!
**Things are about to get much more difficult**
The Light Reactions
1. Two paths operate within the thylakoid membrane
noncyclic
*straight line
and
cyclic
*in a circle
2. Both paths produce ATP, but the noncyclic also produces
NADPH
3. PHOTOPHOSPHORYLATION = ATP production
1. Light hits photosystem II and exites an electron, H20
2. The primary electron acceptor passes the electron down the ETC and
generates ATP
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.
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
Light Reactions
A. Two Pathways
B. Noncyclic
C. Cyclic
D. ATP Production --> 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!
Yay! coloring!
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, probably since it is a slow enzyme.
Calvin Cycle Animation
C. Reduction of Carbon Dioxide
1. With reduction of
carbon dioxide, a
PGA
(3-phosphoglycerate [C3])
molecule forms.
2. Each of two PGA
molecules
undergoes
reduction to PGAL
in two steps.
3. Light-dependent
reactions provide
NADPH (electrons)
and ATP (energy) to
reduce PGA to
PGAL.
D. Regeneration of RuBP
1. Every three turns of
Calvin cycle, five
molecules of PGAL are
used to re-form three
molecules of RuBP.
2. Every three turns of
Calvin cycle, there is net
gain of one PGAL
molecule; five PGAL
regenerate three
molecules of RuBP.
Figure 7.8
E. The Importance of the Calvin Cycle
1. PGAL, the product of
the Calvin Cycle can be
converted into all sorts of
other molecules.
2. Glucose phosphate is
one result of PGAL
metabolism; it is a
common energy
molecule.
Figure 7.9
Factors the Affect Photosynthesis
1. Light Quality (color)
2. Light intensity
3. Light Period
4. Carbon Dioxide Availability
5. Water Availability
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 dry environments have a problem with water loss,
so they keep their stomata partly closed... this results in
CO2 deficit (Used in Calvin Cycle), and the level of O2
RISES
(as Light reactions Split Water Molecules).
Figure 7.10
C4 plants and CAM
plants use an
alternate pathway to
FIX carbon dioxide
from the air.
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 CO2 and fix 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.
Quick Practice
Quick Practice
grana
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)
The ABC's of Photosynthesis
1. Check out some these alphabet books for inspiration
The Absurd Alphabet | The Butterfly Alphabet
2. As a group create your own alphabet book. You can use
all letters or combine letters into groups [ A B ] [ C D
] etc. You should have at LEAST ten concepts with an
illustration and description.