Photosynthesis
Bio 391 – Ch4
How Exactly is Sunlight captured
and converted into Food?
Light Reaction
http://vcell.ndsu.edu/animations/photosynthesis/movie.htm
Calvin-Benson Cycle
http://www.youtube.com/watch?v=mHU27qYJNU0
What are autotrophs?
Obtains energy from nonliving sources
Photoautotrophs
Photosynthesis
Sun energy converts CO2 into sugars
Enzymes convert sugars into amino acids
and other needed compounds
Chemoautotrophs
Specialized bacteria
No sunlight – use energy of inorganic
substances (Fe, S, etc.)
Review Question #1
Photoautotrophs have adapted to take
advantage of…
A. the energy of radio waves.
B. sulfur and other inorganic materials
.
C. an inexhaustible energy source.
D. fungi, bacteria, and other one-celled
organisms.
Nature of Light
Light is a form of electromagnetic
radiation. How does it travel?
A. Rays
B. Photons
C. Waves
D. Electricity
Waves
What is the highest point of a wave called?
A.
B.
C.
D.
Crest
Trough
Peak
Frequency
Waves 2
What is the distance between two waves
called?
A. Frequency
B. Wavelength
C. Waveheight
D. Amplitude
Electromagnetic Spectrum
Wide range of energy types
λ = wavelength
Visible Light
ROYGBIV
Excites pigment molecules which trap energy
Wavelength & Energy
What is the connection between
wavelength and energy of the waves?
A. The higher wavelengths have lower
energy.
B. The higher wavelengths have higher
energy.
C. The lower wavelengths have lower
energy.
D. There is no connection between
wavelength and energy.
Wavelength & Energy 2
Which color light has the highest
wavelength and lowest energy?
A. Red
B. Violet
C. Green
D. Blue
Electromagnetic Radiation
Structure
Thylakoids &
pigment
Granum
Stroma
Own DNA & RNA
Chloroplasts
Video 3
Light-Dependent Reactions, Part 1
• Click the image to play the video segment.
Chlorophyll
Chlorophyll absorbs light …
A. In the violet/blue and orange/red range.
B. In the black/white and orange/yellow
range.
C. Of all visible wavelengths.
D. Primarily in the green range.
Chlorophyll & Accessory Pigments
Two types – “a” and “b”
Absorbs violet-blue and orange-red
colors
~ 350-500 nm & 650-700 nm
Reflects green  plants have green color
Accessory Pigments
Absorb other colors of light and transfer Σ to
chlorophyll-a
Most noticeable in the fall months
EX: carotenoids
Simplified Photosynthesis
Light Reactions
Pigments in thylakoids absorb light
Light converted into chemical Σ
Calvin Cycle (a.k.a. “Dark Reactions”)
Chemical Σ used to make 3 carbon sugars
from CO2
Used to make more complex sugars or other
biochemical molecules
Overall Reaction
3CO2 + 3H2O  C3H6O3 + 3O2
6CO2 + 6H2O C6H12O6 + 6O2
Video 4
Light-Dependent Reactions, Part 2
• Click the image to play the video segment.
Light Reactions
In the chloroplast, light energy causes…
A. Electrons to flow from water to NADP+
B. Hydrogen and oxygen bond to produce
water
C. Sulfur particles to bond to water
molecules
D. Electrons to diffuse across the Calvin
membrane
Light Reaction Products
The products of the light reactions are…
A.
B.
C.
D.
H2O, CO2, ATP
O2, NADPH, ATP
NADPH, H2O, ADP
O2, ATP, CO2
Review #3
During photosynthesis what happens to
the oxygen atoms in water molecules?
A. They help form carbohydrates
B. They act as hydrogen-acceptor
molecules
C. They end up as oxygen gas
D. They help form both carbohydrates and
water.
LIGHT REACTION
Review : What just happened?
1. Make a list of steps from sun to ATP
2. Summarize the main points
Cyclic v. Noncyclic
Photophosphorylation
http://highered.mcgraw-hill.com/olc/dl/120072/bio12.swf
Talking textbook
Simple vs. Complex Autotrophs
Generates ATP but not NADPH. Why?
Calvin Cycle Summary
Video 5
Calvin Cycle
• Click the image to play the video segment.
Calvin Cycle
Keys to understanding….
It’s all about rearrangement
6 (1) + 6(5) = 12 (x)
What makes that statement true?
6 (CO2) + 6 (RuBP) = 12(PGA)
10 (3) = 6 (x)
10 (PGA) = 6 (RuBP)
Calvin Cycle Summary
Each turn fixes 1C
3 turns = 1 PGAL
PGAL is a carbon skeleton
Lipids
Amino acids  proteins
Glucose, sucrose, starch
Rubisco
Catalyzes CO2 fixation
Activated by light thus Calvin cycle requires some
level of light to occur
“C3 plants” – those that fix CO2 into 3C PGAL
Concept Map
Section 8-3
Photosynthesis
includes
use
to produce
takes place in
take place in
of
uses
to produce
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
takes place in
use
NADPH
Stroma
of
O2
Chloroplasts
uses
ATP
NADPH
to produce
High-energy
sugars
Factors Effecting the Rate of
Photosynthesis
Sections 4.5 – 4.6
Light Intensity
More light = higher rate
Reaches saturation point
Enzymes of light reaction going
as fast as possible
Higher than saturation point
 PS declines
Chlorophyll accumulates light
faster than it can transfer it to
ETS
Extra energy goes to oxygen
producing OH- when reaction
w/H2O
OH- or H2O2 damages
chloroplasts
PHOTOINHIBITION
CO2 Concentration
Similar to light
intensity
Hits a saturation
point
Does not decline
after saturation
Temperature
Optimal temperature
range
If too high…
Proteins denature
If too low…
Molecular movement is
slower
High Temps =
Stomata close
Prevents water loss
Increases
photorespiration
C4 and CAM adaptations
O2 Concentration
Rubisco binds CO2 and O2
equally as well
Molecular shapes are similar
Halves productivity of PGA
production
Gycolate broken down to CO2
Benefits?
Occurs when stomates close
Evolutionary Adaptations:
C4 and CAM plants
Leaf Anatomy
2 cell types:
Mesophyll & bundle sheath
No rubisco in mesophyll cells
2 fixation enzymes
RuBP carboxylase
PEP carboxylase
Fix CO2 as 4-C acid
Then fix it again as 3-C
C4 Plants:
Reducing
Photorespiration
Reducing Photorespriation:
CAM plants
Crassulacean acid metabolism
Open stomates at night, close during the day
CO2 + 3C  4C saved until morning
4C  3C + CO2  Calvin Benson cycle
Grow very slowly
1. Which graph represents an increasing light intensity before saturation?
2. Which light intensity graph represents photorespiration if the x axis is relabeled as
oxygen?
3. Which unlabeled graph represents increasing CO2 on the x axis?
Match Outcomes (Left) with
Process (Right)
Releases O2
Stores energy
Releases CO2
Uses CO2
Releases energy
Produces sugar
Uses sugar
Uses O2
Photosynthesis
Cell respiration
Both
Neither
Match Outcomes (Left) with Organisms
(Right)
Releases O2
Stores energy
Releases CO2
Uses CO2
Releases energy
Produces sugar
Uses sugar
Uses O2
Plants
Animals
Both
Neither
Rainbows are separated white light