PHOTOSYNTHESIS
Photosynthesis
• Anabolic (small molecules combined)
• Endergonic (stores energy)
• Carbon dioxide (CO2) requiring process
that uses light energy (photons) and
water (H2O) to produce organic
macromolecules (glucose).
SUN
photons
6CO2 + 6H2O  C6H12O6 + 6O2
glucose
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Question:
Where does
photosynthesis
take place?
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Plants
• Autotrophs – produce their own food
(glucose)
• Process called photosynthesis
• Mainly occurs in the leaves:
a. stoma - pores
b.mesophyll cells
Mesophyll
Cell
Chloroplast
Stoma
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Stomata (stoma)
Pores in a plant’s cuticle through
which water vapor and gases (CO2
& O2) are exchanged between the
plant and the atmosphere.
Stoma
Carbon Dioxide
(CO2)
Guard Cell
Oxygen
(O2)
Guard Cell
Found on the underside of leaves
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Mesophyll Cell of Leaf
Nucleus
Cell Wall
Chloroplast
Central Vacuole
Photosynthesis occurs in these cells!
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Chloroplast
Organelle where photosynthesis
takes place.
Stroma
Outer Membrane
Inner Membrane
Thylakoid
Granum
Thylakoid stacks are connected together
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Function of the Stroma
• Light Independent reactions
occur here
• ATP used to make
carbohydrates like glucose
• Location of the Calvin Cycle
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Thylakoid
Thylakoid Membrane
Granum
Thylakoid Space
Grana make up the inner membrane
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Question:
Why are
plants
green?
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Chlorophyll Molecules
• Located in the thylakoid membranes
• Chlorophyll have Mg+ in the center
• Chlorophyll pigments harvest energy
(photons) by absorbing certain
wavelengths (blue-420 nm and red660 nm are most important)
• Plants are green because the green
wavelength is reflected, not absorbed.
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Wavelength of Light (nm)
400
500
600
700
Short wave
Long wave
(more energy)
(less energy)
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Absorption of Light by
Chlorophyll
Chlorophyll absorbs blue-violet & red light best
Absorption
violet
blue
green yellow
wavelength
orange
red
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Question:
During the fall,
what causes the
leaves to change
colors?
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Fall Colors
• In addition to the chlorophyll
pigments, there are other pigments
present
• During the fall, the green
chlorophyll pigments are greatly
reduced revealing the other pigments
• Carotenoids are pigments that are
either red, orange, or yellow
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Question:
What do
cells use
for energy?
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Energy for Life on Earth
• Sunlight is the ULTIMATE
energy for all life on Earth
• Plants store energy in the
chemical bonds of sugars
• Chemical energy is released as
ATP during cellular respiration
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Structure of ATP
• ATP stands for adenosine
triphosphate
• It is composed of the nitrogen base
ADENINE, the pentose (5C) sugar
RIBOSE, and three PHOSPHATE
groups
• The LAST phosphate group is bonded
with a HIGH ENERGY chemical bond
• This bond can be BROKEN to release
ENERGY for CELLS to use
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Removing a Phosphate from ATP
Breaking the LAST PHOSPHATE bond
from ATP, will --– Release ENERGY for cells to use
– Form ADP
– Produce a FREE PHOSPHATE GROUP
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High Energy Phosphate Bond
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FREE PHOSPHATE can be re-attached to
ADP reforming ATP
Process called Phosphorylation
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Parts of
Photosynthesis
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Light Reaction Summary
Reactants:
• H2O
• Light Energy
Energy Products:
• ATP
• NADPH
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Light Independent Reaction
• ATP & NADPH from light
reactions used as energy
• Atmospheric C02 is used to
make sugars like glucose and
fructose
• Six-carbon Sugars made
during the Calvin Cycle
• Occurs in the stroma
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Two Parts of Photosynthesis
Two reactions make up
photosynthesis:
1.Light Reaction or Light
Dependent Reaction Produces energy from solar
power (photons) in the form of
ATP and NADPH.
SUN
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Two Parts of Photosynthesis
2. Calvin Cycle or Light
Independent Reaction
• Also called Carbon Fixation
or C3 Fixation
• Uses energy (ATP and
NADPH) from light reaction
to make sugar (glucose).
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Chloroplast
Outer Membrane
Inner Membrane
STROMA– where Calvin Cycle occurs
Thylakoid
Granum
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Photorespiration
•
•
•
•
Occurs on hot, dry, bright days
Stomates close
Fixation of O2 instead of CO2
Produces 2-C molecules instead of
3-C sugar molecules
• Produces no sugar molecules or no
ATP
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Photorespiration
Because of photorespiration, plants
have special adaptations to limit
the effect of photorespiration:
1. C4 plants
2. CAM plants
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C4 Plants
• Hot, moist
environments
• 15% of plants
(grasses, corn,
sugarcane)
• Photosynthesis
occurs in 2 places
• Light reaction mesophyll cells
• Calvin cycle - bundle
sheath cells
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CAM Plants
• Hot, dry environments
• 5% of plants (cactus and ice
plants)
• Stomates closed during day
• Stomates open during the night
• Light reaction - occurs during
the day
• Calvin Cycle - occurs when CO2 is
present
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Question:
Why do CAM
plants close
their stomata
during the day?
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Cam plants close
their stomata in
the hottest part
of the day to
conserve water
Cellular
Respiration
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Cellular Respiration
• A catabolic, exergonic, oxygen (O2) requiring
process that uses energy extracted from
macromolecules (glucose) to produce energy
(ATP) and water (H2O).
C6H12O6 + 6O2  6CO2 + 6H2O + energy
ATP
glucose
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Question:
• In what kinds organisms does cellular
respiration take place?
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Plants and Animals
• Plants - Autotrophs: self-producers.
• Animals - Heterotrophs: consumers.
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Mitochondria
• Organelle where cellular respiration takes
place.
Outer
membrane
Inner
membrane space
Matrix
Cristae
Inner
membrane
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