Download PHOTOSYNTHESIS: HARVESTING LIGHT ENERGY

PHOTOSYNTHESIS: HARVESTING LIGHT ENERGY Energy and Life u  Autotrophs are organisms that create their own energy molecules from inorganic molecules –  Plants are autotrophs since they convert sunlight into sugar molecules u  Heterotrophs are organisms that consume other organisms (dead or alive) to meet their energy needs Importance of Photosynthesis •  photosynthesis – uses the energy in sunlight to convert carbon dioxide to sugars •  provides usable chemical energy for life on earth, carbon building blocks, and oxygen •  food, clothing, and shelter Chemical Energy u  For most organisms, adenosine triphosphate (ATP) is the principle energy molecule –  Contains one adenine molecule, one ribose (sugar) molecule and three phosphate groups u  Adenosine diphosphate (ADP) has one less phosphate group than ATP and is the breakdown product of ATP Chemical Energy u  ATP is the basic energy source for most cells –  AcDve transport across membranes –  Movement within the cell u  ATP has a very short life span in cells and thus is not ideal for energy storage u  Cells store energy in the form of carbohydrates, lipids or protein –  One glucose molecules contains 90 Dmes the stored energy in a molecule of ATP Photosynthesis u 
Historical investigations of photosynthesis
–  Van Helmont (1600’s) determined that plant growth was not due to
soil…he thought it was due to water
–  Joseph Priestly (1700’s) determined that a substance in the
atmosphere was required for combustion and that plants produce
this substance
–  Jan Ingenhousz (1700’s) determined the substance produced by
plants only occurred when sunlight was present
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These investigations indicated that plants utilize CO2 &
H2O to grow and produce O2 as a by-product
Origin of Photosynthetic Organisms •  At first it is thought that only heterotrophs existed (heterotroph hypothesis) that fed on an organic soup. As the soup was depleted so did the heterotroph organisms. However, some of the heterotrophs were now capable of using light energy, they used the light energy and began to provide food for themselves and others. These were simple bacteria. •  Today similar bacteria exist, and it is thought that those simple bacteria became a part of the eukaryoDc cell Photosynthesis u  To carry out PS plants need chlorophyll –  Chlorophyll is a pigment that absorbs light –  Chlorophyll a and chlorophyll b are the two principle types found in plants Photosynthesis u  Chlorophyll a absorbs light in the red and violet region of the light spectrum u  Chlorophyll b absorbs light in the red and blue region of the light spectrum u  In both forms of chlorophyll, light energy raises the energy levels in electrons…these high-­‐energy electrons make PS work Photosynthesis u 
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In photosynthetic eukaryotes, PS takes place in chloroplasts
– Outer membrane – regulates substances into and out of
organelle
– Thylakoids: saclike membranes that are stacked into grana
which increase membrane surface area
u  Contain pigments and proteins that capture the energy in
sunlight
Stroma: region outside the grana– surrounds the thylakoids,
contains enzymes as well as its own DNA and RNA, and ribosomes
– evidence of bacterial origin for chloroplasts
Light dependent reactions take place in the thylakoids
– Energy fixing reactions
Light independent reactions (Calvin cycle) take place in the
stroma
– Carbon fixing reactions
OVERVIEW OF PS Chloroplast Structure Thylakoids •  Thylakoids •  Grana – stacked thylakoids oriented to have maximum sunlight absorpDon •  Light absorbing pigments are embedded in the thylakoids •  Chlorophyll a & Chlorophyll b •  Both absorb light in the violet/blue and orange/red regions and reflect green •  accessory pigments are available, their absorbed energy is given to special chlorophyll a •  cartenoids Chloroplast Anatomy
Chloroplast >
~ contains chlorophyll; makes plants green ~ performs Photosynthesis ~ makes Glucose to harness Energy
~ found only in plant cells
THE PROCESS OF PHOTOSYNTHESIS An Overview •  major steps in energy conversion •  absorpDon of light energy •  conversion of light energy into chemical energy •  storage of chemical energy in sugars •  light reacDons and the Calvin cycle (Calvin-­‐
Benson cycle or photosyntheDc carbon reducDon cycle) •  EquaDon: 3 CO2 + 3 H2O à C3H6O3 + 3 O2 Photosynthetic Pigment Absorptions
Photosynthesis
Two Phases of Photosynthesis
1.) Light-Dependent Reactions (Light reactions)
~ occurs in thylakoid membrane of chloroplast
~ needs light to start process
~ chlorophyll absorbs light, and water is split into O2 gas and H+
~ photolysis - process of water being split by light
~ H+ ions have a positive charge that powers the formation of ATP
~ final products = Oxygen, NADPH, and ATP
~ Light Reactions provide the ENERGY for next step (Calvin Cycle)
Light-Dependent Reactions
Photosynthetic ET and ATP synthase
The Light Reactions •  Light reac+ons convert visible light into chemical energy that powers sugar produc+on •  Chlorophyll absorbs light, water molecules split, chemical energy stored •  Photosystem I •  connected by electron transport system •  work together to absorb, concentrate, and transfer light energy to special chlorophyll a •  Photosystem II The Light Reactions Continued •  chlorophyll a -­‐ reacDon center •  in each photosystem the reacDon center loses energy–rich electrons which are carried on the electron transport •  PSI – loses electrons but they are replaced by electrons from PSII •  PSII – loses electrons but they are replaced by electrons removed from water •  EquaDon – H2O à 2 H+ + 2e+ + ½ O2 The Light Reactions Continued •  at end of flow the electrons from water combine with a hydrogen carrier, NADP+ -­‐ nicoDnamide adenine dinucleoDde phosphate •  forms NADPH – which transports the electrons needed for the Calvin cycle and other biosyntheDc reacDons in the chloroplast •  as they flow some of the energy is used in acDve transport of protons across the thylakoid membrane •  high [] of protons •  high [] of protons now diffuse down steep [] gradient through ATP synthtase forming ATP + P The Light Reactions Continued • 
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The first two events of photosynthesis occur AbsorpDon of light Conversion of light energy into chemical energy Three products formed: oxygen gas, ATP, and NADPH Light Reactions The Calvin Cycle •  powered by the light reac+ons •  Series of reacDons in which carbon dioxide is combined with the hydrogen split from water in the light reacDons •  Takes place in the stroma ` •  Products of the Calvin Cycle (G3P) •  The 3 carbon sugar produced can be used in many biosynthesis reacDons •  sucrose made in cytosol, and starch made in chloroplasts The Calvin Cycle (continued)
For each fixed carbon atom, 9 ATP
equivalents are required; thus 54 ATP are
needed to make one glucose molecule and to
complete the cycle
Even though there is an expenditure of energy in
the Calvin Cycle, recall that one glucose
molecule contains 90 times the stored
energy contained in a molecule of ATP
Photosynthesis
2.) Light-Independent Reactions (Dark Reactions AKA Calvin Cycle)
~ occurs in stroma of the chloroplast
~ happens with and without light
~ Uses energy, ATP and NADPH, from light reactions to make Glucose
Calvin cycle
Photosynthesis Song
Do Now
I Need a Little Light (Photosynthesis Song)
by Ross Durand
Use your notes on Photosynthesis to
explain the following lyrics. Please write
in complete sentences.
1.  “I need a little light so I can store
energy. I need a light like so I can make
ATP”
2.  “I’m sitting here in this chloroplast
feeling green the whole day through.”
Photosynthesis Song
3.  “The ATP and NADPH are going to
make a cycle go round.”
I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I’m gunna make some food.
It’s out of sight, and I need a little light.
I’m sitting here in this chloroplast
feeling green the whole day through.
You add a little thylakoid just
a-waiting for something to do.
I’m going to move some electrons through a
chain
And pump some Hydrogen in
But its been dark all night,
and you can see the state I’m in.
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I’m gunna make some food.
It’s out of sight, and I need a little light.
When the electrons leave that chain
They’re going to join NADP
And that high concentration of hydrogen
Is gunna walk outside of me
It’s gunna go through a special protein,
It’s gunna kick some ATP out
But that’s what moving these elections is really
all a-bout
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I’m gunna make some food.
It’s out of sight, and I need a little light.
The ATP and NADPH are going to make
a cycle go round.
At the end of the Calvin cycle, glucose can
be found.
You gotta put in 6 pieces of CO2 to make
that precious food.
And use up the products of the thylakoid darn this systems good
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I’m gunna make some food.
It’s out of sight, and I need a little light.
There’s one other thing I need besides
light – it’s good old water.
And see that chlorophyll, that loses its
electrons, needs to get some back - and
that’s what the water does
But the whole reason that electron moved
is because of the light
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I’m gunna make some food.
It’s out of sight, and I need a little light.
Photosynthesis Summary u  PS is the process plants use to turn the energy in sunlight into chemical energy u  Plants are autotrophs u  There are two major steps in PS: –  Light reacDons = fix energy –  Light Independent ReacDons (Dark reacDons) = fix carbon into G3P Photosynthesis Summary u  The light reacDons have two parts: –  PS system II: occurs in thylakoids, absorbs light (P680), creates high energy electrons and H+, forms ATP, splits water and releases O2 –  PS I: occurs in thylakoids, absorbs light (P700), makes the electron carrier NADPH Photosynthesis Summary u  The dark reacDons occur as the Calvin Cycle –  CO2 is removed from the air –  One of every three carbon atoms fixed in the Calvin cycle is used to make glucose…the rest are used to replenish chemicals used in the cycle –  Nine ATP equivalents are required to fix each carbon to complete the cycle Rate of Photosynthesis •  environment effects photosynthesis •  rate – acDvity per unit of Dme •  measure CO2 absorbed, or O2 given off •  four environmental factors •  light intensity -­‐ levels off at certain point, can determine what plant grows there and then what ecosystem can exist •  Temperature -­‐ opDmum temperature is necessary, or freezing or denaturing of Calvin cycle enzymes may occur •  [] of CO2 -­‐ as CO2 increases so does the rate of photosynthesis, to a certain point before leveling off •  [] of O2-­‐ an increase of O2 reduces the rate of photosynthesis •  the environmental factors play together, some are opDmum while others are minimum so they have a combined effect •  limiDng factors Photorespiration and Photosynthesis •  PhotorespiraDon – light-­‐dependent process involving the uptake of oxygen and release of carbon dioxide that occurs along with photosynthesis in all plants •  CounterproducDve to photosynthesis •  Prevents incorporaDon of CO2 in the Calvin cycle and results in the loss of previously incorporated CO2 •  When rubisco binds with oxygen in the chloroplast, no new carbon dioxide is fixed, and RuBP is converted to Carbon dioxide •  Photosynthesis slows, photorespiraDon interferes with Calvin cycle Special Adaptations •  C-­‐4 plants, carbon dioxide is first incorporated in a 4-­‐carbon acid (that’s where the name comes from) •  Low CO2, high light and temp •  sugarcane, corn, crabgrass •  special features keep CO2 low in an area so it diffuses quickly keeping photosynthesis running •  And CAM plants (crassulacean acid metabolism) – open stomates at night, desert plants – cactus and jade plants