N
AME:
C
HAPTER7
Photosynthesis: Using Light to
Make Food
Chapter Objectives
Opening EssayExplain how plants can be used as a renewable energy source. Explain why this is better than burning fossil fuels.
An Overview of Photosynthesis
7.1 Define autotrophs, heterotrophs, producers, and photoautotrophs.
7.2 Describe the structure of chloroplasts and their location in a leaf. Identify specifically where most light energy is converted to chemical energy.
7.3 Explain how plants produce oxygen. Describe the experiments that revealed the source of the oxygen produced during photosynthesis.
7.4 Describe the role of redox reactions in photosynthesis and cellular respiration.
7.5 Compare the reactants and products of the light reactions and the Calvin cycle. Explain how photosynthesis relates to these reactions.
The Light Reactions: Converting Solar Energy to Chemical Energy
7.6 Describe the properties and functions of the different photosynthetic pigments.
7.7 Explain how photosystems capture solar energy.
7.8–7.9 Explain how the electron transport chain and chemiosmosis generate ATP, NADPH, and oxygen in the light reactions.
7.9 Compare photophosphorylation and oxidative phosphorylation.
The Calvin Cycle: Reducing CO2 to Sugar
7.10 Describe the reactants and products of the Calvin cycle. Explain why this cycle is dependent upon the light reactions.
7.11 Compare the mechanisms that C3, C4, and CAM plants use to obtain and use
carbon dioxide. Note examples of plants that use each of these systems.
Photosynthesis Reviewed and Extended
7.12 Review the overall process of the light reactions and the Calvin cycle, noting the products, reactants, and locations of every major step.
7.13 Describe the greenhouse effect. Explain how deforestation and the use of fossil fuels contribute to global warming.
Key Terms
1.
Autotroph-2. C3
plant-3. C4
plant-4. Calvin
cycle-5. CAM
plants-6. carbon
fixation-7. chlorophyll
a-8. electromagnetic
spectrum-9. global climate
change-10. grana (singular,
granum)-11. greenhouse
effect-12.
heterotrophs-13. light
14.
mesophyll-15. NADP
+-16.
Photon-17.
Photophosphorylation-18.
Photorespiration-19.
Photosynthesis-20.
Photosystem-21. stomata (singular,
stoma)-22.
stroma-23.
thylakoids-24.
wavelength-Lecture Outline
A.Plants, algae, and certain prokaryotes
1.
2.
a.
b.
B.Algae farms can be used to produce
1.oils for biodiesel or
2.
II. An Overview of Photosynthesis
A.7.1 Autotrophs are the producers of the biosphere
1.Autotrophs
a.
b.sustain themselves, and
c.
2.
Photoautotrophs-3.
Chemoautotrophs-4. Heterotrophs are consumers that feed on
a.
b.
5.Photosynthesis in plants
a.
b.
c.
B.7.2 Photosynthesis occurs in chloroplasts in plant cells
1.
Chloroplasts-2. Chlorophyll
a.
b.is responsible for the green color of plants, and
c.
3.Chloroplasts are concentrated in the cells of the the green tissue in the
interior of the leaf.
4. Stomata
-a.
b.
5.Veins in the leaf deliver water absorbed by roots.
6.Chloroplasts consist of an envelope of two membranes, which
a.enclose an inner compartment filled with a thick fluid
called-7.Thylakoids
a.are often concentrated
in-b.have an internal compartment called the , which has functions analogous to
the intermembrane space of a mitochondrion.
c. Thylakoid membranes also house much of the
machinery-8.Chlorophyll molecules
a.
b.
C.7.3 SCIENTIFIC DISCOVERY: Scientists traced the process of photosynthesis using isotopes
1.Scientists have known since the 1800s that plants produce O2. But does this oxygen come from
car-bon dioxide or water?
a.For many years, it was assumed that oxygen was
extracted-b.However, later research using a heavy isotope of oxygen, 18O,
confirmed-D.7.4 Photosynthesis is a redox process, as is cellular respiration
1.Photosynthesis, like respiration, is a redox (oxidation-reduction) process.
a.
2.Cellular respiration uses redox reactions to harvest the chemical energy stored in a
glucose molecule.
a.
b.The electrons lose potential as they travel down the electron transport chain to O2.
c.
3.In photosynthesis,
a.light energy is captured
by-b.light energy is converted
to-c. chemical energy is stored
in-E.7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH
1.Photosynthesis occurs in two metabolic stages.
a.The occur in the thylakoid membranes. In these reactions
i.
ii. ATP is
generated-iii.light energy is absorbed by the chlorophyll molecules to
drive-iv. NADPH produced
i. The Calvin cycle is a cyclic series of
reactions-ii. During the Calvin cycle, CO2 is incorporated
into-iii.After carbon fixation, enzymes of the
cycle-iv. The Calvin cycle is often called
the-III. The Light Reactions: Converting Solar Energy to Chemical Energy
A.7.6 Visible radiation absorbed by pigments
drives-1.Sunlight contains energy called electromagnetic energy or electromagnetic radiation.
a.Visible light is only a small part of the , the full range of
electro-magnetic wavelengths.
b.Electromagnetic energy travels in waves, and the is the distance
between the crests of two adjacent waves.
2.Light behaves as discrete packets of energy
called-a.A photon
-b.The shorter the
a.
absorb-b.are built into
the-4.Plant pigments
a.absorb
some-b.reflect or
transmit-5.We see the color of the wavelengths that are transmitted. For example, chlorophyll transmits green
wavelengths.
6.Chloroplasts contain several different pigments,
which-a. Chlorophyll a
-b. Chlorophyll
b-c. Carotenoids
i. broaden the spectrum of colors that can drive photosynthesis and
ii. provide photoprotection, absorbing and dissipating excessive light energy that would
otherwise damage chlorophyll or interact with oxygen to form reactive
oxidative molecules.
B.7.7 Photosystems
a.increases the
potential-b.sends the
electrons-c. These unstable electrons
i. drop back down to their “ground state,” and as they do,
ii. release their excess energy
as-2.Within a thylakoid membrane, chlorophyll and other pigment molecules
a.
absorb-b.
transfer-3.In the thylakoid membrane, chlorophyll molecules are organized along with other
pigments and proteins
into-4.A consists of a number of light-harvesting complexes surrounding a
reaction-center complex.
5.A light-harvesting complex contains various pigment molecules bound to proteins.
6.Collectively, the light-harvesting complexes function as a light-gathering antenna.
7.The light energy is
passed-a.Finally, it reaches the reaction center where a primary electron acceptor accepts these electrons
and consequently becomes reduced.
b.This solar-powered transfer of an electron from the reaction-center pigment to the primary
elec-tron acceptor is the first step
9.Each type of photosystem has a characteristic reaction center.
a.Photosystem II, which functions
first,-c. Photosystem I, which functions
second,-C.7.8 Two photosystems connected by an electron transport chain
generate-1.In the light reactions, light energy is transformed into the chemical energy
of-2.To accomplish this, electrons are
a.
removed-b.passed from photosystem II
to-c. accepted by NADP+, reducing
it-3.Between the two photosystems, the electrons
a.move
down-b.provide energy for the synthesis
of-4.The products of the light reactions are
a.
b.
c.
1.Interestingly, chemiosmosis is the mechanism that
a.is involved in oxidative phosphorylation in mitochondria and
b.
generates-2.ATP is generated because the electron transport chain produces a concentration gradient of hydrogen
ions across a membrane.
3.In photophosphorylation, using the initial energy input from light,
a.the electron transport chain pumps H+
-b.the resulting concentration gradient drives H+ back through ATP
synthase,-4.How does photophosphorylation compare with oxidative phosphorylation?
a.Mitochondria use oxidative phosphorylation to transfer chemical energy from food into the
chem-ical energy of ATP.
b.Chloroplasts use photophosphorylation
to-IV. The Calvin Cycle: Reducing CO2 to Sugar
A.7.10 ATP and NADPH
power-1.The Calvin cycle
makes-2.To produce sugar, the necessary ingredients are
a.
b.
4.A plant cell may then use G3P to make glucose and other organic molecules.
5.The steps of the Calvin cycle include
a.
b.
c.
d.regeneration of the starting
molecule-B.7.11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry
cli-mates
1.Most plants use CO2 directly from the air, and carbon fixation occurs when the
enzyme-2.Such plants are called because the first product of carbon fixation is a
three-carbon compound, 3-PGA.
3.In hot and dry weather, C3 plants
a.close
their-b.prevent CO2 from
entering-c. As O2 builds up in a leaf, rubisco adds O2 instead of CO2 to RuBP, and a
two-carbon product of this reaction is then broken down in the cell.
d.This process is called
4. C4 plants have evolved a means of
a.carbon
fixation-b.optimizing the Calvin cycle.
5.C4 plants are so named because they
first-6.When the weather is hot and dry, C4 plants keep their stomata
mostly-7.Another adaptation to hot and dry environments has evolved in the CAM plants, such as pineapples
and cacti.
8. CAM
plants-9.CO2 is fixed into a four-carbon compound,
a.which
banks-b.releases it to the Calvin
cycle-V.Photosynthesis Reviewed and Extended
A.7.12 Review: Photosynthesis
uses-1.Most of the living world depends on the food-making machinery of photosynthesis.
2.The chloroplast
a.
b.
3.About half of the made by photosynthesis are consumed as fuel for
4.Sugars also serve as the starting material for making other organic molecules, such as proteins,
lipids, and cellulose.
5.Excess food made by plants is stockpiled
as-B.7.13 CONNECTION: Photosynthesis may moderate global climate change
1.The greenhouse
effect-a.Solar radiation includes visible light that penetrates the Earth’s
atmosphere-b.Heat radiating from the warmed planet is absorbed by gases in the
atmosphere,-d. Without the warming of the greenhouse effect, the Earth
would-2.The gases in the atmosphere that absorb heat radiation are called greenhouse gases. These include
a.
b.
c.
3.Increasing concentrations of greenhouse gases have been linked to (also called
global warming), a slow but steady rise in Earth’s surface temperature.
4.Since 1850, the atmospheric concentration of CO2 has increased by about 40%, mostly due to the
combustion of fossil fuels including
b.
c.
5.The predicted consequences of continued warming include
a.
b.
c.
d.
e. increased extinction rates, and
f. the spread of tropical disease.
6.Widespread deforestation has aggravated the global warming problem by reducing an effective CO2
sink.
7.Global warming caused by increasing CO2 levels may be reduced by
a.
b.
