Photosynthesis
Chapter 7
Photosynthesis
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Almost all plants are photosynthetic autotrophs
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As are some bacteria and protists
Generate their own organic matter through photosynthesis
Photosynthesis
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Occurs in chloroplasts
Energized electrons are added to carbon dioxide to make
sugar
Converts solar energy into the chemical energy of a
carbohydrate
Sunlight provides the energy
Anatomy of a Plant
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Carried out by the green
portions of plants
Leaves contain mesophyll
tissue specialized for
photosynthesis
Water taken up by roots and
transported to leaves by
veins
Anatomy of a Plant
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Carbon dioxide enters
through openings in the
leaves called stomata
Light energy absorbed
by chlorophyll and other
pigments in thylakoids
of chloroplasts
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Main organelle that
carries out
photosynthesis!!!!
Chloroplasts
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Are found in the interior cells of leaves
Contain stroma, a thick fluid
Contain thylakoids, membranous sacs
Photosynthetic Reaction
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Glucose and oxygen are the products of photosynthesis
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Oxygen given off comes from water
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CO2 gains hydrogen atoms and becomes a carbohydrate
Reaction written as:
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Two Steps…..
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1. Light reactions convert
solar energy to chemical
energy
 Light-dependent
reactions
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take place only in presence
of light
produce ATP and NADPH
2. Calvin cycle makes sugar
from carbon dioxide
 Light-independent
reactions
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do not need light to occur
result in the formation of
organic molecules
Light Reactions
An Overview of Photosynthesis
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Photosystem
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Starting point of photosynthesis
Network of pigments in the membrane of the
thylakoid
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molecules that absorb light energy
primary pigment of a photosystem is chlorophyll
pigments act as an antenna to capture energy from
sunlight
individual chlorophyll pigments pass the captured energy
between them
How Plants Capture Energy from Sunlight
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Light comprised of packets of energy called
photons
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Sunlight has photons of varying energy levels
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possible range of energy levels is represented by an
electromagnetic spectrum
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Human eyes only
perceive photons of
intermediate energy
levels
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this range of the
spectrum is known as
visible light
Chloroplasts absorb
select wavelengths of
light that drive
photosynthesis
The light reactions of photosynthesis
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Two types of photosystems
cooperate in the light
reactions
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Photosystem II
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captures a photon of light
and releases an excited
electron to the electron
transport system (ETS)
Photosystem I
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absorbs another photon of
light and releases an
excited electron to another
ETS
Electron transport chain
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Connects the two photosystems
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Releases energy that the chloroplast uses to
make ATP
Calvin Cycle
Calvin Cycle
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Light-independent
These reactions are the second stage of
photosynthesis
Functions like a sugar factory within a chloroplast
Regenerates the starting material with each turn
NADPH and ATP produced in light reactions used to
reduce carbon dioxide to a carbohydrate
Overview of Photosynthesis
Photosynthesis Versus Cellular Respiration
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Both plant and animal cells carry out cell respiration
Only plant cells photosynthesize
Both processes utilize an electron transport chain
and chemiosmosis for ATP production
Photosynthesis reduces CO2 to carbohydrates and
releases O2
Respiration utilizes O2 and gives off CO2
Photosynthesis and Respiration Compared
Environmental Impacts
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Photosynthesis has an enormous
impact on atmosphere.
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Greenhouses used to grow plant
indoors
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Trap sunlight that warms the air
inside
The greenhouse effect
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swaps O2 for CO2
Warms the atmosphere
Caused by atmospheric CO2
Greenhouse gases are the most
likely cause of global warming
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Slow but steady rise in the Earth’s
surface temperature
Destruction of forests may be
increasing this effect