Download Chapter 8 Notes Photosynthesis

Chapter 8
Biology: p 224-243
Biology 2009: Photosynthesis
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Vocabulary Terms:
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ATP and ATP Synthase
Heterotrophs
Autotrophs
Photosynthesis
Pigment
Chlorophyll
Thylakoid
Stroma
Granum
• NADP+
• Light- Dependent
reaction
• Light- Independent
reaction (Calvin Cycle)
• Photosystem
• Electron transport
chain
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Big Idea- Cellular Basis of Life
1. How do plants and other organism capture
energy from the sun?
a. How do organisms store energy?
b. What cellular structures and molecules are
involved in photosynthesis
c. How do photosynthetic organism convert the
sun’s energy into chemical energy?
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8.1 Energy and Life
Key questions:
1. What is ATP useful to cells?
2. What happens during the process of
photosynthesis?
Review: What is homeostasis?
Ones ability to regulate internal body conditions in
response to ones environment
What powers so much activity, and where does
that power come from?
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Chemical Energy and ATP
What is Energy?
- ability to do work
Cells use energy in the form of ATP- Adenosine
Triphosphate, which is made of adenine
(nitrogenous base), 5-carbon sugar (ribose),
and 3 phosphates
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What do we need energy for?
• Energy is the ability to do work.
• Your cells are busy using energy to build
new molecules, contract muscles, and
carry out active transport.
• Without the ability to obtain and use
energy, life would cease to exist.
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A. Storing Energy
• Adenosine diphosphate (ADP) looks almost
like ATP, except that it has two phosphate
groups instead of three. ADP contains some
energy, but not as much as ATP.
• When a cell has energy available, it can store
small amounts of it by adding phosphate
groups to ADP, producing ATP.
• ADP is like a rechargeable battery that
powers the machinery of the cell.
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B. Releasing Energy
– Cells can release the energy stored in
ATP by breaking the bonds between the
second and third phosphate groups.
– Because a cell can add or subtract these
phosphate groups, it has an efficient way
of storing and releasing energy as
needed.
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C. Using Biochemical Energy
1. One way cells use the energy provided by
ATP is to carry out active transport.
• Many cell membranes contain sodiumpotassium pumps. ATP provides the energy that
keeps these pumps working, maintaining a
balance of ions on both sides of the cell
membrane.
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Using Biochemical Energy
2. ATP powers movement, providing the energy
for motor proteins that contract muscle and
power the movement of cilia and flagella.
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Using Biochemical Energy
3. Energy from ATP powers the synthesis of
proteins and responses to chemical signals at
the cell surface.
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Using Biochemical Energy
- ATP is not a good molecule
for storing large amounts of
energy over the long term.
– It is more efficient for cells
to keep only a small supply
of ATP on hand.
– Cells can regenerate ATP
from ADP as needed by
using the energy in foods
like glucose.
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Heterotrophs Vs. Autotrophs
– What happens during the process of
photosynthesis?
– In the process of photosynthesis, plants
convert the energy of sunlight into chemical
energy stored in the bonds of carbohydrates
Photo- Light
Synthesis- to create
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Heterotrophs
– Organisms that obtain food by consuming other
living things are known as heterotrophs.
– Some heterotrophs get their food by eating
plants.
– Other heterotrophs, such as this cheetah,
obtain food from plants indirectly by feeding on
plant-eating animals.
– Still other heterotrophs, such as mushrooms,
obtain food by decomposing other organisms.
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Autotrophs
– Organisms that make their own food are
called autotrophs.
– Plants, algae, and some bacteria are able to
use light energy from the sun to produce food.
The process by which autotrophs use the
energy of sunlight to produce high-energy
carbohydrates that can be used for food is
known as photosynthesis.
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8.2 Photosynthesis Overview
KEY QUESTIONS:
1. What role do pigments play in the process of
photosynthesis?
a. Photosynthetic organisms capture energy from sunlight with
pigments.
2. What are electron carrier molecules?
a. An electron carrier is a compound that can accept a pair of highenergy electrons and transfer them, along with most of their energy, to
another molecule.
3. What are the reactants and products of
photosynthesis?
a. Photosynthesis uses the energy of sunlight to convert water and
carbon dioxide (reactants) into high-energy sugars and oxygen
(products).
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THINK ABOUT IT
– How would you design a system to capture
the energy of sunlight and convert it into a
useful form?
– Plants have solved these issues—and
maybe we can learn a trick or two from them.
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Light
– Energy from the sun travels to Earth in the
form of light.
– Sunlight is a mixture of different
wavelengths, many of which are visible to our
eyes and make up the visible spectrum.
– Our eyes see the different wavelengths of the
visible spectrum as different colors: red,
orange, yellow, green, blue, indigo, and violet.
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Pigments
• Plants gather the sun’s energy with light-absorbing
molecules called pigments.
• The plants’ principal pigment is chlorophyll.
• The two types of chlorophyll found in plants, chlorophyll
a and chlorophyll b, absorb light very well in the blueviolet and red regions of the visible spectrum, but not in
the green region, as shown in the graph.
• Leaves reflect green light, which is why plants look green.
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Pigments
• Plants also contain red and orange pigments such as
carotene that absorb light in other regions of the
spectrum.
• Most of the time, the green color of the chlorophyll
overwhelms the other pigments, but as temperatures
drop and chlorophyll molecules break down, the red and
orange pigments may be seen.
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Chloroplasts
• Photosynthesis takes place inside organelles called
chloroplasts.
• Chloroplasts contain saclike photosynthetic membranes
called thylakoids, which are interconnected and arranged in
stacks known as grana.
• Pigments are located in the thylakoid membranes.
• The fluid portion outside of the thylakoids is known as the
stroma.
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Energy Collection
• Because light is a form of energy, any compound that
absorbs light absorbs energy. Chlorophyll absorbs visible
light especially well.
• When chlorophyll absorbs light, a large fraction of the
light energy is transferred to electrons. These highenergy electrons make photosynthesis work.
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High-Energy Electrons
• The high-energy electrons produced by chlorophyll are
highly reactive and require a special “carrier.”
• Think of a high-energy electron as being similar to a hot
potato. If you wanted to move the potato from one place to
another, you would use an oven mitt—a carrier—to
transport it.
• Plants use electron carriers to transport high-energy
electrons from chlorophyll to other molecules.
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High-Energy Electrons
• NADP+ (nicotinamide adenine dinucleotide phosphate) is a
carrier molecule.
• NADP+ accepts and holds two high-energy electrons, along
with a hydrogen ion (H+). In this way, it is converted into
NADPH.
• The NADPH can then carry the high-energy electrons to
chemical reactions elsewhere in the cell.
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An Overview of Photosynthesis
• Photosynthesis uses the energy of sunlight to convert
water and carbon dioxide into high-energy sugars and
oxygen.
In symbols:
6 CO2 + 6 H2O  C6H12O6 + 6 O2
In words:
Carbon dioxide + Water  Sugars + Oxygen
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An Overview of Photosynthesis
• Plants use the sugars generated by
photosynthesis to produce complex
carbohydrates such as starches, and to
provide energy for the synthesis of other
compounds, including proteins and lipids.
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An Overview of Photosynthesis
Has two major Reactions: (Test Questions)
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You must know where each one takes place
What goes in and out of each one
Reactions:
1. Light Dependent RXNGoes in: water, light, (ADP, NADP+)
Comes out: oxygen (ATP, NADPH)
Takes place in: thylakoid membranes
2. Light Independent RXN ( dark rxn, Calvin Cycle)
Goes in: CO2 (NADPH, ATP)
Comes out: Sugar (ADP, NADP+)
Takes place in: Stroma
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1. Light-Dependent Reactions
• light-dependent reactions- because they require the
direct involvement of light and light-absorbing pigments.
• The light-dependent reactions use energy from sunlight
to produce ATP and NADPH.
• These reactions take place within the thylakoid
membranes of the chloroplast.
• Water is required as a source of electrons and hydrogen
ions. Oxygen is released as a byproduct.
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Light-Independent Reactions
• Plants absorb carbon dioxide from the atmosphere and complete the
process of photosynthesis by producing sugars and other
carbohydrates.
• During light-independent reactions, ATP and NADPH molecules
produced in the light-dependent reactions are used to produce highenergy sugars from carbon dioxide.
• No light is required to power the light-independent reactions.
• The light-independent reactions take place outside the thylakoids, in
the stroma.
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8.3 The Process of Photosynthesis
Key Questions:
1. What happens during the light-dependent
reactions?
a. use energy from sunlight to produce oxygen and convert
ADP and NADP+ into the energy carriers ATP and NADPH.
2. What happens during the light-independent
reactions?
a. ATP and NADPH from the light are used to produce
high-energy sugars
3. What factors affect photosynthesis?
a. Among the most important factors that affect
photosynthesis are temperature, light intensity, and
the availability of water.
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THINK ABOUT IT
Why do chloroplasts contain so many membranes?
• When most pigments absorb light, they eventually lose
most of that energy as heat. Chloroplasts avoid such
losses. Membranes are the key to capturing light energy
in the form of high-energy electrons.
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The Light-Dependent Reactions:
Generating ATP and NADPH
• Thylakoids contain clusters of chlorophyll and proteins
known as photosystems.
• Photosystems absorb sunlight and generate high-energy
electrons that are then passed to a series of electron
carriers embedded in the thylakoid membrane.
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Summary of Light-Dependent
Reactions
• The light-dependent reactions produce oxygen gas and
convert ADP and NADP+ into the energy carriers ATP
and NADPH.
• ATP and NADPH provide the energy needed to build
high-energy sugars from low-energy carbon dioxide.
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The Light-Independent
Reactions: Producing Sugars
• During the light-independent reactions, commonly referred
to as the Calvin cycle, plants use the energy that ATP and
NADPH contains to build stable high-energy carbohydrate
compounds (sugar/starch) that can be stored for a long
time.
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Summary of the Calvin Cycle
1.
2.
3.
4.
The Calvin cycle uses 6
molecules of carbon dioxide to
produce a single 6-carbon
sugar molecule.
The energy for the reactions is
supplied by compounds
produced in the light-dependent
reactions.
The plant uses the sugars
produced by the Calvin cycle to
meet its energy needs and to
build macromolecules needed
for growth and development.
When other organisms eat
plants, they can use the energy
and raw materials stored in
these compounds.
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The End Results
• The two sets of photosynthetic reactions work together
—the light-dependent reactions trap the energy of
sunlight in chemical form, and the light-independent
reactions use that chemical energy to produce stable,
high-energy sugars from carbon dioxide and water.
• In the process, animals, including humans, get food and
an atmosphere filled with oxygen.
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Factors Affecting
Photosynthesis
1. Temperature
2. Light
3. Water
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1. Temperature and 2. Light
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The reactions of photosynthesis are made possible by enzymes that
function best between 0°C and 35°C.
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Temperatures above or below this range may affect those enzymes, slowing
down the rate of photosynthesis or stopping it entirely.
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High light intensity increases the rate of photosynthesis.
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After the light intensity reaches a certain level, however, the plant reaches
its maximum rate of photosynthesis, as is seen in the graph.
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3. Water
• Because water is one of the raw materials in
photosynthesis, a shortage of water can slow or
even stop photosynthesis.
• Water loss can also damage plant tissues.
• Plants that live in dry conditions often have waxy
coatings on their leaves to reduce water loss.
They may also have biochemical adaptations
that make photosynthesis more efficient under
dry conditions.
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Photosynthesis Under Extreme
Conditions
– In order to conserve water, most plants under
bright, hot conditions close the small openings in
their leaves that normally admit carbon dioxide.
– This causes carbon dioxide within the leaves to
fall 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.
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C4 Plants
CAM Plants
• specialized chemical
pathway that allows them to
capture even very low levels
of carbon dioxide and pass
it to the Calvin cycle.
• The name “C4 plant” comes
from the fact that the first
compound formed in this
pathway contains 4 carbon
atoms.
• The C4 pathway requires
extra energy in the form of
ATP to function.
• corn, sugar cane, and
sorghum.
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Crassulacae family, such as cacti
and succulents, incorporate
carbon dioxide into organic acids
during photosynthesis in a
process called Crassulacean Acid
Metabolism (CAM).
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admit air into their leaves only at
night, where carbon dioxide is
combined with existing molecules
to produce organic acids,
“trapping” the carbon within the
leaves.
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During the daytime, when leaves
are tightly sealed to prevent water
loss, these compounds release
carbon dioxide, enabling
carbohydrate production.
•
pineapple trees, many desert
cacti, and “ice plants”.
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