Holt Chapter 9
Photosynthesis
and
Respiration
9-1: Energy and Living Systems
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What type of energy is used in cells, and what is
the ultimate source of this energy?
How is an organism’s metabolism related to the
carbon cycle?
How is energy released in a cell?
Plants convert sunlight into chemical energy.
This chemical energy can be used for
biological processes in nearly all living
things.
Chemical Energy
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Organisms use and store energy in chemical
bonds
Specifically in the C-C, C-H bonds of organic
compounds
All of this energy originally comes from the sun
Photosynthesis is the process used by living
organisms to use solar energy to create C-C
bonds in organic compounds
 Autotrophs
(like plants) are able to make their own
organic compounds (like carbs/’sugar’ and amino
acids for proteins and fatty acids for lipids, etc.)
 Heterotrophs (everything else) must get their energy
and their supplies in a pre-made form. (sugar, protein,
fat and even DNA)
Metabolisms and the Carbon Cycle

Metabolism is the sum of an organisms chemical
reactions
 Catabolic
reactions are used to break down
molecules
 Anabolic reactions are used to build molecules
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Photosynthesis
 Energy
from the sun drives reactions that create
organic compounds like sugar, starch, amino acids
and nucleic acids
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Respiration
 Organisms
“burn” organic compounds to release the
energy in them
Review of Carbon Cycle
CO2
RESPIRATION
combustion
H2O
sunlight
PHOTOSYNTHESIS
Glucose
or fuel
decomposition
or organic compound
Oxygen
Transferring Energy
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You wouldn’t put a whole tree into a wood stove
Cells need to release energy in “steps”
 Not
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too much; usable amounts; less heat
Steps of the process are directed by enzymes
 These
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are found in membranes of the mitochondria
Small pieces of energy are called ATP
 Adenosine
tri-phosphate
 “currency” of the cell
 Used to do work
 ATP
ADP + Pi
 Energy rich compound used to store enegy
9-2: Photosynthesis
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What is the role of pigments in photosynthesis?
What are the roles of electron transport chains?
How do plants make sugars and store extra
unused energy?
What are three environmental factors that affect
photosynthesis?
Nearly all of the energy of life processes
comes from the sun
and is stored in organic molecules
during the process of photosynthesis.
Harvesting Light Energy
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1 % of solar energy is
captured by plants
Solar energy is
converted to chemical
bond energy
Happens in
chloroplasts, with
chlorophyll
Light Energy
Light is electromagnetic radiation
 Travels through space as waves
 Solar energy is both light and heat
 Different wave lengths (l) or colors
have different amounts of energy
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Pigments
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Pigments are chemical compounds that absorb
specific wavelengths of light. Other colors of light
are reflected.
Chlorophyll absorbs RED and BLUE and reflects
green – so the leaves look green.
Chlorophyll (chemical) in embedded in the inner
portions of the chloroplasts membranes (called
thylakoid membranes)
Many other accessory pigments in most plants,
in addition to chlorophyll a and chlorophyll b
Electron carriers
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Light hits thylakoid
membrane
Electrons are excited
(gain energy)
Energy is used to split
water molecules
H+ and e- flow through
electron transport chain
Generate NADPH and
Oxygen
H2O  H+ + e- + O2
Equation for Photosynthesis
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“to make using light”
sunlight
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6CO2 + 6H2O
chlorophyll
C6H12O6 + 6O2
 You should know this equation for all future quizzes, tests
and the final exam
Light and Dark Reactions
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Light reactions need light
(solar energy)
They also need
chlorophyll and water
They occur on the
thylakoid membrane
They involve an ETC
They generate O2 and an
energy storing compound
called NADPH
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Dark reactions do not need
light
They are also called the
Calvin cycle and the Carbon
fixing reactions.
They use NADPH to link
carbons from CO2 into
‘sugars’
Use CO2 and generate
organic compounds
Happen in the stroma
Chloroplast details
Factors Affecting Photosynthesis
1.
2.
3.
Light intensity (longer days, brighter
sunlight, closer to equator = more photo.)
Carbon dioxide (CO2) concentration (lots
of available CO2 diffuses into stomata
and spongy mesophyll of leaves
Temperature (lots of enzymes directing
these reactions, all enzymes are proteins
that function best in specific temperature
ranges)