Photosynthesis
Energy and Life
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Nearly every activity in modern society
depends on Energy…think about it.
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Driving a car!
Typing a paper!
Using your IPOD!
Talking on your cell phone!
Living things also require ENERGY!
Where does that Energy come from?
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Autotrophs (AKA: Producers)
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Use the sunlight as their
ENERGY source.
Heterotrophs (AKA: Consumers)
 Obtain energy from the plants
or other organisms that they
consume.
Chemical Energy
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Candles burn
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What does that mean?
Wax molecules store
energy in the bonds
between the hydrogens
and carbons
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Electrons move
from higher energy
levels to lower
energy levels.
Heat and light
energy are
released.
Living things use and
store energy
Plants store energy as sugar or starch
Animals store energy as glycogen
(animal starch)
Or as fat
ATP: Adenosine Triphosphate
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Adenine
Ribose:5 carbon sugar
3 phosphate groups
Storing Energy
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ADP (adenosine diphosphate) is a
compound that looks like ATP except it
Phosphate group.
is lacking a __________
This one difference is the key to the
way in which living things store energy.
Storing Energy (cont.)
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When a cell has energy available, it can
store small amounts of it by adding a
phosphate group to ADP, producing ATP.
Think of ATP as a fully charged battery
and ADP as only a partially charged
battery. http://www.biologyinmotion.com/atp/index.html
Now that we have Energy stored…how
do we release it?....
Releasing Energy
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Energy that is stored in ATP is released
by breaking the chemical bond between
the second and third phosphates.
What the energy in ATP can do
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Active transport
Protein synthesis
Muscle contraction
What the energy in ATP can do
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Synthesis of nucleic acids
Move organelles throughout the cell
Responds to chemical signals of cell
Fireflies!
Question?????
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Do you think cells have an abundant
amount of ATP?
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Answer: Most cells have only a small
amount of ATP, enough to last them for a
few seconds of activity.
Why?
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Answer: ATP is great for transferring
Energy, not for storing Energy.
ATP Wrap-UP
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Long term storage is done by other
molecules, such as glucose, glycogen,
starch
ATP can be regenerated by the cell
over and over again
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ADP + Energy + P → ATP
Required energy comes from food molecules
8-2:Overview of Photosynthesis
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Van Helmont’s Experiment
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Priestley
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Plants gain mass from water
Plants produce oxygen
Jan Ingenhousz
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Light is necessary
8-2:Overview of Photosynthesis
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Photosynthesis converts light energy
into the chemical energy of sugar and
other organic compounds.
Light energy drives the reactions
O2- byproduct and is released into atmosphere
The Photosynthetic Equation
Light and Pigments
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Pigments: light absorbing molecules
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Chlorophyll absorbs blue-violet and red light
When a pigment absorbs light, it absorbs the
energy from that light
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Energy excites electrons
8-3: The Reactions of Photosynthesis
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Where does photosynthesis take place?
Parts of the chloroplasts
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Thylakoids-Proteins in the thylakoid
membrane organize chlorophyll and other
pigments into clusters known as
photosystems.
Parts of the chloroplasts
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Photosystems-light collecting units
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Reactions of photosystems in 2 parts:
Light-dependent reactions (take place in
thylakoid membrane)
 Light-independent reactions (take place
in the stroma)
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Light-Dependent Reactions
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The light-dependent reactions produce oxygen
gas and convert ADP and NADP+ into ATP
and NADPH.
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Occur in the thylakoid
Calvin Cycle (light-independent)
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The Calvin Cycle uses ATP and NADPH from
the light-dependent reactions to produce highenergy sugars.
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It takes carbon dioxide from the atmosphere
and converts it into high-energy sugars that
can be used to meet the plant’s energy needs
and to build more complex molecules.
What does all of that mean?
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The two sets of photosynthetic reactions work
together…
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The light-dependent reactions trap the energy of
sunlight in chemical form
The light-independent (Calvin cycle) uses that
chemical energy to produce stable, high-energy
sugars from carbon dioxide and water.
Factors Affecting Photosynthesis
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Shortage of water can slow down or stop
photosynthesis
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Plants have adaptations to reduce water loss: waxy
coating on plants in dry areas.
Temperature
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Plants have enzymes that work best from 32-95
degrees F. Temperatures above or below can
damage these enzymes which can slow down or
stop photosynthesis.
Factors Affecting Photosynthesis
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Intensity of light
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Increasing light intensity increases the rate of
photosynthesis. (It will reach a max level)