Photosynthesis
Sections 4.2-4.3
The overall process of
photosynthesis produces
sugars that store chemical
energy.
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Overview
• All energy on earth comes from the sun.
• We depend on:
– Plants
– Algae (underwater plants)
– Cyanobacteria (photosynthetic bacteria)
• To provide this energy to us!
Overview
Overview
• Photosynthetic organisms are producers.
• Producers make their own source of
chemical energy.
• Plants use photosynthesis and are
producers.
• Photosynthesis captures energy from
sunlight to make sugars.
Overview
• Carbon dioxide and water are taken in by
plants
• Plants absorb light energy and convert it to a
usable form.
– ATP
• Energy is used to “fix” carbon dioxide into
sugar molecules
– Chemical energy
• Sugar is converted to starch and stored for
use by the plant, and by animals when they
eat plants.
Chlorophyll
• Chlorophyll is a
molecule that
absorbs light
energy.
• In plants,
chlorophyll is
found in organelles
called
chloroplasts.
chloroplast
leaf cell
leaf
Plants are green because of the
pigment chlorophyll.
(which absorbs light energy)
• During the fall, the green chlorophyll
pigments are greatly reduced revealing
the other pigments, this is the reason
leaves turn brown in the fall.
• Carotenoids are pigments that are
either red or yellow.
• Photosynthesis
takes place in two
parts of
chloroplasts.
–grana
(thylakoids)
–stroma
grana (thylakoids)
chloroplast
stroma
Chloroplasts
• Have TWO
membranes
– A “bi-bilayer!”
• The inner membrane is
called the thylakoid.
• The thylakoid is folded
and looks like stacks of
coins called granum
(grana=singular).
• The stroma is the
space surrounding the
granum.
Image source: http://www.daviddarling.info/encyclopedia/C/chloroplasts.html
Chloroplasts
• Chlorophyll
molecules are
embedded in the
thylakoid membrane
• Act like a light
“antenna”
• These molecules
can absorb sunlight
energy.
Image from Biology 11: College Preparation. Pg 73. Nelson,
Toronto. 2003.
Light (dependent)Reactions
•
Happen ONLY in sunlight
– Hence they depend on light!
– Water is also required
1. Light energy is absorbed by chlorophyll
molecules in the thylakoid
2. The energy generates molecules of ATP
(ADP converted to ATP)
3. Convert NADP+ to NADPH (Electron
Carriers)-Energy then goes to Light
Independent reaction
4. Produce Oxygen (O2) gas
Light (dependent)Reactions
Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto. 2003.
Light (dependent)Reactions
Light Independent Reactions
(formerly the “dark reactions”)
•
Happen in sunlight, and in the dark.
–
–
1.
2.
3.
4.
Hence “independent of light”
Makes sugars
Takes place in the stroma.
CO2 enters from the atmosphere
ATP generated by sunlight drives the Calvin Cycle.
Monosaccarides (eg. glucose) are manufactured in the
cycle.
5. Monosaccarides are used to “build” polysaccharides (eg.
Starch).
Light Independent Reactions
(formerly the “dark reactions”)
Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto. 2003.
Light Independent Reactions
(formerly the “dark reactions”)
Overall Reaction
What is the equation for photosynthesis?
carbon dioxide + water  glucose + oxygen + energy
6CO2 + 6H2O  C6H12O6 + 6O2 + energy
granum (stack of thylakoids)
1
chloroplast
6H2O
6O2
2
thylakoid
energy
stroma (fluid outside the thylakoids)
6CO2
1 six-carbon sugar
C6H12O6
3
4
Factors that affect the rate
of Photosynthesis are…
• Availability of Water
• Temperature
• Intensity of Light
• Concentration of CO2
H2O
CO2
S
u
n
L
I
G
H
T
Light
Dependent
Reactions
Calvin Cycle
CHLOROPLAST
O2
Sugars