Download Ch. 8 Photosynthesis

Lesson Overview
Energy and Life
Lesson Overview
8.1 Energy and Life
Lesson Overview
Energy and Life
Chemical Energy and ATP
o Adenosine Triphosphate (ATP) – VERY IMPORTANT
ENERGY MOLECULE
o ATP consists of
1. adenine
2. 5-carbon sugar called ribose
3. three phosphate groups
Lesson Overview
Energy and Life
Using Biochemical Energy
o ATP is not good for storing energy
or for long term use
o cells keep small amount of ATP for
use
o
Cells can regenerate ATP by
using the energy in foods like
glucose
Lesson Overview
Energy and Life
Heterotrophs and Autotrophs
o Heterotrophs - obtain food by consuming other
living things; various types (herbivores, carnivores,
etc)
o Autotrophs - organisms that make their own food;
generally use sunlight to make food (photosynthesis)
Lesson Overview
Energy and Life
Lesson Overview
8.2 Photosynthesis:
An Overview
http://www.wwnorton.com/college/biology/discoverbio3/core/
content/index/animations.asp
Lesson Overview
Energy and Life
Light
Sunlight is a mixture of different wavelengths, many of
which are visible to our eyes and make up the visible
spectrum
Lesson Overview
Energy and Life
Pigments
Plants gather the sun’s energy with light-absorbing
molecules called pigments
chlorophyll – main pigment in plants
Lesson Overview
Energy and Life
Pigments
Two types of chlorophyll found in plants:
chlorophyll a and chlorophyll b
Another pigment found in plants
carotene
Lesson Overview
Energy and Life
Chloroplasts
Photosynthesis takes place inside chloroplasts
Chloroplast structure includes:
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double membrane
thylakoids (contain pigments)
grana (stacks of thylakoids)
stroma (fluid)
Lesson Overview
Energy and Life
Energy Collection
When chlorophyll absorbs light, the energy is transferred to
electrons
Lesson Overview
Energy and Life
High-Energy Electrons
•
Energy in electrons must be transferred to other
molecules to make food for the plant
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Electron carriers are used to transfer the energy to
another molecule
Lesson Overview
Energy and Life
High-Energy Electrons
NADP+ - a carrier molecule used in photosynthesis
NADPH - carry the high-energy electrons to chemical
reactions elsewhere in the cell
Lesson Overview
Energy and Life
An Overview of Photosynthesis
Photosynthesis uses the energy of sunlight to convert
water and carbon dioxide into high-energy sugars and
oxygen.
Lesson Overview
Energy and Life
PHOTOSYNTHESIS
Photosynthesis involves two sets of reactions:
1. light-dependent reactions
2. light-independent reactions
Lesson Overview
Energy and Life
Light-Dependent Reactions
The light-dependent reactions use sunlight & water to produce
ATP , NADPH (energy molecules), and oxygen
Take place within the thylakoid membranes
Lesson Overview
Energy and Life
Light-Independent Reactions
During light-independent reactions, ATP, NADPH, and carbon
dioxide are used to produce high-energy sugars
Light-independent reactions take place in the stroma (fluid)
Lesson Overview
Energy and Life
Lesson Overview
8.3 The Process of
Photosynthesis
Lesson Overview
Energy and Life
The Light-Dependent Reactions:
Generating ATP and NADPH
Photosystems (clusters of chlorophyll/proteins) absorb sunlight and
generate high-energy electrons that are then passed to a series of
electron carriers embedded in the thylakoid membrane
Lesson Overview
Energy and Life
Photosystem II
Light energy is absorbed in
the pigments within
photosystem II, “exciting”
electrons
These electrons are passed
to the electron transport
chain (ETC)
Lesson Overview
Energy and Life
Photosystem II
Enzymes of the inner surface of the
thylakoid break up water molecules
into 2 electrons, 2 H+ ions, and 1
oxygen atom:
2 electrons – go to PS II to replace
other electrons
Oxygen – released into atmosphere
H+ - create gradient to create ATP
***WATER IS A PRETTY IMPORTANT
PART OF THE EQUATION!!!
Lesson Overview
Energy and Life
Electron Transport Chain
Energy from the electrons used
to pump H+ from stroma into
thylakoid space
Electrons wind up at PS I
(chlorophyll/proteins); need to be
“recharged/re-energized” by
sunlight
Lesson Overview
Energy and Life
Photosystem I
At end of ETC, electrons combine with H+ and NADP+ to make NADPH
Lesson Overview
Energy and Life
Hydrogen Ion Movement and ATP
Formation
H+ ions accumulate within the thylakoid space during process,
creating a gradient
This gradient provides the energy to make ATP (using ATP
synthase to pump H+) - chemiosmosis
Lesson Overview
Energy and Life
Summary of Light-Dependent Reactions
The light-dependent reactions produce oxygen, ATP, and
NADPH
ATP and NADPH will be used in LIGHT-INDEPENDENT
REACTIONS to make sugar
Lesson Overview
Energy and Life
The Light-Independent Reactions:
Producing Sugars
Light-independent reactions, also known as Calvin
cycle, require CO2, ATP, and NADPH to make sugar
Takes place in stroma
Lesson Overview
Energy and Life
Carbon Dioxide Enters the Cycle
CO2 molecules enter the Calvin cycle from the atmosphere
An enzyme (rubisco) in the stroma combines carbon dioxide molecules
with 5-carbon compounds = CARBON FIXATION
Lesson Overview
Energy and Life
Carbon Dioxide Enters the Cycle
The 3-carbon compounds
use energy from ATP and
NADPH to change
throughout the cycle
Lesson Overview
Energy and Life
Sugar Production
2 3-carbon molecules leave the
cycle to become food for the
plant
The rest of the carbon
compounds are converted back
into the beginning 5 carbon
compounds to start cycle again
Lesson Overview
Energy and Life
Factors Affecting Photosynthesis
Among the most important factors that affect photosynthesis are
temperature, light intensity, and the availability of water.
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Average temp best (due to enzyme activity)
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high light intensity (up to a point)
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lack of water will slow or prevent photosynthesis
Lesson Overview
Energy and Life
Photosynthesis Under Extreme
Conditions
Most plants under bright, hot conditions close the small openings in their
leaves that normally admit carbon dioxide (to conserve water)
Carbon dioxide falls to very low levels, slowing down or even stopping
photosynthesis.
C4 and CAM plants have biochemical adaptations that minimize water
loss while still allowing photosynthesis to take place in intense sunlight
C4 plants – corn, sugarcane
CAM plants – pineapple, cacti