Download Unit 4 Photosynthesis

UNIT 5
PHOTOSYNTHESIS
ENERGY & MATTER
Energy
In – Sunlight
Out – Bonds between Biomolecules
Matter
In – H2O(Soil; van Helmont), CO2 (Air),
Inorganic
Inorganic – No Carbon
Organic - Carbon
Out
O2; Other Biomolecules (Sugars, ETC.)
QUESTION…
Where does photosynthesis
occur?
ANATOMY OF
PHOTOSYNTHESIS
Leaf- Major site of photosynthesis; although
can occur all over Plant
Mesophyll – tissue in interior of leaf
Stomata – Pores; take in CO2 release O2
Vein – Transport water absorbed by roots
Chloroplasts
Organelle of photosynthesis
2 membranes;
Thylakoids – houses light absorbing pigments
thylakoid sacs are stacked – named Granum
Stroma & thylakoid space
CHLOROPHYLL & PIGMENT
Chlorophyll are BOUND DIRECTLY to
thylakoid membrane
Provide thylakoid with its “green” color
What is a pigment?
Substances that absorb visible light
- Different pigments absorb different
wavelengths of light
Light can be reflected, transmitted, absorbed
PHOTOSYNTHESIS
Complex set of reactions that convert light
energy into chemical energy.
1.Absorption of Light Energy
2.Conversion of Light Energy into Chemical
Energy
3.Storage of Chemical Energy as sugars
- 1 & 2 are the Light (dependent)
Reactions
-
Convert light to usable energy
- 3 is the Light Independent (Dark)
Reactions or The Calvin Cycle
-
Build biomolecules
DIAGRAM – LIGHT REACTION
Two clusters of light absorbing pigments:
Photosystem II & Photosystem I
Named in order discovered
Regions of Concentrated Chlorophyll
What is evidence that red and blue light is
absorbed in plants?
In absorbing light, what change does this
cause?
Energized electrons leave chlorophyll
Move down proteins in thylakoid membrane
called Electron Transport Chain
OVERVIEW QUESTIONS
What do we know about the structure of a
leaf?
What are the names of the reactions that
occur during photosynthesis?
How would you describe what occurs in the
Light Reactions?
How would you describe what occurs in the
Light Independent Reactions/Calvin Cycle?
Any time molecule ACCEPTS electrons
Reduced or Oxidized?
REDUCED
Oxidation
Reduction
Is
Is
Loss (e-)
Gain (e-)
Rapid shift down proteins: Reduced 
Oxidized  Reduced…
REDOX REACTION
This process is how electrons move down
proteins of Electron Transport Chain
When pigment molecule absorbs a photon,
photon is passed from protein to protein
Electron Transport Chain
Think of “The Wave”
Series of protein molecules embedded in
thylakoid membrane
@ Each protein
Redox reactions – pass e-
Small amount of energy is released from each
Redox reaction
Certain proteins serve only to pass eOthers have specific function
When e- passes through a specific protein in
ETC
Causes the ACTIVE TRANSPORT
(LowHigh) of H+ into Thylakoid space
Like PSII & PSI, proteins in ETC are
embedded in thylakoid membrane
Surplus of protons (H+) develop within the
interior of Thylakoid – Set up HUGE
Concentration Gradient
More H+ on the interior than on the exterior
Is the movement of H + this active or passive
transport?
Do we need a transport protein?
Is this energy requiring or energy releasing?
How does this energy change our system?
Helps form ATP!!!
PHOTOLYSIS
Specific enzyme is attached to PSII that
breaks H2O down
Occurs simultaneously as photons are
hitting PSII
Light splits H2O
4 H+
4 eO2
What are the functions of all of the above?
ATP
Adenosine Triphosphate- usable cellular
energy
ATP broken into Adenosine Diphosphate
ATP  ADP + Pi + Energy
Which is energy storing?
Energy releasing?
This whole process has a specific name:
Movement of protons within the thylakoid
space due to the redox reactions that move
electrons down the Electron Transport
Chain
H+ Gradient develops
Ion Channel/Enzyme – ATP Synthase
moves H+ out of the thylakoid
Provides energy for the formation of ATP
from ADP + P + Energy
Chemiosmosis
PHOTOSYSTEM I
95% of what we know about PSII are the
same for PSI
Photons hit chlorophyll A & B
Excite electrons to a higher energy state
Electrons are accepted by proteins in
ETC, “jump” from protein to protein
Cause influx of H+ into thylakoid space
Will help “power” ATP Synthase
5 % DIFFERENCE
1. Electrons from PS II are refilling
electrons lost at PS I
Refilling e- lost at PS I
2. Electrons from PSI reduce
NADP+
NADP+ is the final “resting place” of
electrons
Final electron acceptor
VERY High affinity for electrons
PHOTOSYSTEM I
At end of the reaction:
NADP+ + H+ + 2e-  NADPH
NADPH is known as a Coenzyme
“Electron shuttle”
Pick up electrons and Hydrogen ions, transfer
them to Calvin Cycle, return to Light Reaction
3CO2
(3) 5-Carbon
Ribulose
BiPhosphate
RuBP
3 ADP
(3)
6-Carbon
Intermediate
- Unstable
3 ATP
(6) 3-Carbon
PGA
(5) 3-Carbon
PGAL
6 ATP
6 ADP
(6) 3-Carbon
PGAL
(1) 3- Carbon
PGAL
6 NADPH
6 NADP+
(3)
(3) 5-Carbon
Ribulose
BiPhosphate
PGA
6-Carbon
Intermediate
- Unstable
(6) 3-Carbon
(5) 3-Carbon
PGA
PGAL
(6) 3-Carbon
PGAL
GOALS
1. Compare and contrast the advantages
and disadvantages of the following:
C3, C4 & CAM
2. Explain how limiting factors (CO2, O2,
Light intensity, H2O) may affect
photosynthesis and be able to
draw/explain graphs that detail various
limiting factors
3. Predict how photosynthesis will change
when environmental factors change
ENVIRONMENTAL EFFECTS
OF PHOTOSYNTHESIS
Goal is to examine various
environmental effects that have
implications on the rate of
photosynthesis
Exchange in Leaves
How do plants move CO2 & H20 in and O2
out of the plant?
Stomata
pores on the underside of leaves
Exchange CO2 & H20 in and O2
Has the ability to close - Guard Cells
PHOTOINHIBITION
In high light intensity, there will be more
energy than can be absorbed by
chlorophyll
Excess energy beyond the saturation
point will cause O2 molecules to react
with H+ ions to make OH- ions and
H 2O 2.
These products are harmful to the
chloroplast and must be broken down
Rate of photosynthesis is reduced
PHOTORESPIRATION
When RUBISCO binds to O2 instead of CO2
Although RUBISCO is efficient of binding
inorganic carbon (CO2) – it also attracts O2
to binding site
O2 and CO2 have SIMILAR SHAPE
Non-specific active site
4x higher binding affinity for CO2 than O2
Running photorespiration lowers
photosynthetic output
Takes in O2, Releases already fixed CO2
Only one PGAL per cycle
Half as efficient!
PGA
PGA
EVOLUTIONARY RELIC
At point of origin of photorespiration, there
was NO O2 in the atmosphere
Why should we consider this?
2.5 to 3 BILLION years ago – environment
was almost all CO2
Unnecessary for plants to worry about O2
binding
Not much O2 in the atmosphere,
no need for enzyme to differentiate between
O2 and CO2
Inefficient? Adaptation to address the
inefficiency? C4
C3 STRUCTURE VS.
C4 STRUCTURE
C4 PLANTS
What do we need to address the inefficiency
of Rubisco?
A different enzyme to avoid O2 binding.
We got it –PEP Carboxylase
Fixes CO2 to 3-C structure PEP to form 4-C
OAA - Oxaloacetic Acid
Various Enzymes convert OAA into 4-C Malic
Acid
Malic Acid “sneaks” CO2 into Bundle Sheath
Cells
CO2 Breaks off –Run Calvin Cycle as normal
C4
EXTREMELY IMPORTANT
THE BUNDLE SHEETH CELLS ARE
IMPERMEABLE TO CO2!!
Why is this important?
Carbons are really stow-aways
Move 4th Carbon into bundle sheath cell
Separate from Malate – Malate leaves –
NOT CO2
Once in, cannot leave
Thus C4 concentrates CO2 in Sheath Cells
Examples of C4 Plants:
Rice, Soybeans, Sugar Cane, Corn, Warm
Season Grasses
C4 ADVANTAGE
C4 more effective in High Temperatures or
High O2 environments
What happens in environments w/ high
temp.?
Stomates Close
Mesophyll cells “pump” CO2 into the bundle
sheath cells, keeping CO2 concentration
high
Avoid possibility for Photorespiration
C4 plants are successful in hotter/drier
climates –
C4 DISADVANTAGE
More ATP required to convert 3-Carbon
in Sheath cell back into PEP
Spend extra energy to run this reaction.
Need PEP to bind CO2 to OAA
Must spend energy to convert pyruvate
into PEP
How does the carbon fixation of C3 differ
from C4? (aside from process…)
LOCATION, LOCATION,
LOCATION!!!
CAM
CAM – Crassulacean Acid Metabolism
Adaptation for intense arid conditions
Many succulent plants, cacti, pineapples,
Jade
Water conservation adaptation
Plants open stomata at night
Take up CO2 & incorporate into organic acids
Close stomata during the day
Prevent massive water loss
But, no CO2 can enter
CAM
During the day, when light is plentiful
CO2 is released from Organic Acids
Breaks off of Malic Acid
CO2 moves to Calvin Cycle
Organic Acid returns to bind more CO2
at night
So, how do C4 and CAM pathways of
carbon fixation differ?
C4 Separates Calvin Cycle in LOCATION!
CAM separates Calvin Cycle in TIME!