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PHOTOSYNTHESIS
Chapter 8
8-1: Energy & Life
• Energy is supplied to some things in the form
of gasoline or electricity
• Cells need energy too!
• Where do plants gets the energy they need to
produce food?
• What is the role of ATP in cellular activities?
Autotrophs & Heterotrophs
• Living things get their energy from food
• The energy in most food comes from the sun
• Organisms that can make their own food are
called autotrophs
• Heterotrophs obtain energy from the food they
consume (by eating plants directly, eating animal
that ate autotrophs, or by decomposing other
organisms)
• All organisms must release the energy stored in
sugars and other compounds in order to survive
Autotrophs use light energy from the sun to produce food.
These impalas get their energy by eating grass. In contrast, a
leopard gets its energy by eating impalas and other animals.
Impalas and leopards are both heterotrophs.
Chemical Energy & ATP
• Cells use ATP (Adenosine triphosphate) to store
and release energy
• ATP consists of adenine, ribose, and three
phosphate groups
• ADP (Adenosine diphosphate) is like ATP, but
with 2 phosphates instead of three
• The energy is stored with the addition of the third
phosphate
• Energy is released by breaking the bonds that holds
the third phosphate – used for active transport,
protein synthesis, muscle contraction, etc.
Chemical Energy & ATP
ATP Formation
Using Biochemical Energy
• Cells use ATP to move sodium ions (Na+) out of
the cell and potassium ions (K+) into the cell with
sodium-potassium pumps
• ATP is also used to move organelles throughout
the cell
• ATP is also used for:
– Making proteins & nucleic acids, response to chemical
signals, & even the light in a firefly
• There is very little ATP in a cell, only enough for
a few seconds.
• ATP is not useful for long-term storage – glucose
can store 90 times more chemical energy
The SodiumPotassium pump
uses ATP
8-2: Photosynthesis: An Overview
• In the process of photosynthesis, plants use the
energy of sunlight to convert water and carbon
dioxide into high energy carbohydrates (sugars
and starches) and oxygen (a waste product)
– What did the experiments of van Helmont, Priestley,
and Ingenhousz reveal about how plants grow?
– What is the overall equation for photosynthesis?
– What is the role of light and chlorophyll in
photosynthesis?
Investigating Photosynthesis
• When a tiny seedling grows into a tall tree with
a mass of several tons, where does the tree’s
increase in mass come from?
• Van Helmont, Priestley, and Ingenhousz
performed experiments to find out
Three additional slides accompany this section
* Van Helmont’s Experiment
• Van Helmont carefully measured the mass
of soil and a small plant
• After 5 years, the mass of the plant
increased significantly, but the mass of the
soil did not change
• He concluded that the mass of the plant
came from the water he added
• This conclusion was partially correct
* Van Helmont’s
Experiment
* Priestley’s Experiment
• Priestley sealed a candle in a jar and noticed it
slowly went out
• This was due to the consumption of all the
oxygen
• He noticed that if he placed a sprig of mint in
the jar, the candle could be relighted after a few
days and would remain lit for a while
• He concluded that the plant was supplying the
material that the candle needed to burn (oxygen)
* Priestley’s
Experiment
* Ingenhousz Experiment
• Ingenhousz experiment showed that Priestley’s
experiment would only work if the plant was
exposed to light
• Therefore, they showed that light is necessary
to produce oxygen
• These (and other) experiments showed that in
the presence of light, plants transform carbon
dioxide and water into carbohydrates and
release oxygen
The Photosynthesis Equation
• Photosynthesis uses the energy of sunlight
to convert water and carbon dioxide into
high-energy sugars and oxygen
Light and Pigments
• In addition to water and carbon dioxide,
photosynthesis requires light and chlorophyll, a
molecule in chloroplasts
• Plants gather the energy in light with molecules
called pigments
• Chlorophyll absorbs light very well in the blueviolet and red regions of the visible spectrum
• Plants do not absorb green light very well
• When chlorophyll absorbs light, the energy raises
the energy levels of the electrons which allows
photosynthesis to work
8-3: The Reactions of Photosynthesis
• Describe the structure of a
chloroplast
• What factors may affect
the rate of photosynthesis?
Inside a Chloroplast
• In plants and other photosynthetic
eukaryotes, photosynthesis takes place
inside the chloroplasts
• Chloroplasts contain saclike membranes
called thylakoids, which are arranged in
stacks called grana
• The two parts of photosynthesis include the
light-dependent reactions (in thylakoid
membranes) and light-independent reactions
(Calvin Cycle) in the stroma (region outside
the thylakoid membrane)
Factors Affecting Photosynthesis
• Since water is needed for
photosynthesis, a shortage
of water can slow or stop
the process
• Photosynthesis works best
at temperatures between 0
and 35 degrees C due to
enzyme activity
• Increasing light intensity
increases photosynthesis