Download Photosynthesis Light-Dependent Reactions Calvin Cycle

Photosynthesis
Light-Dependent
Reactions
&
Calvin Cycle
Section 8.2
Fig. 10-2
• Photosynthesis occurs
in plants, algae, some
prokaryotes
• ENDERGONIC
PROCESS-stores
energy
• ANABOLIC
PROCESS-Builds up
molecules
BioFlix: Photosynthesis
(a) Plants
10 µm
(c) Unicellular protist
(e) Purple sulfur
bacteria
(b) Multicellular alga
(d) Cyanobacteria
40 µm
1.5 µm
Structures of Photosynthesis
• Leaves are the major
locations of
photosynthesis
• Chlorophyll - the green
pigment within
chloroplasts
• CO2 enters and O2 exits
the leaf through
microscopic pores called
stomata
Fig. 10-3a
Leaf cross section
Vein
• Chloroplasts
are found
mainly in cells
of the
mesophyll, the
interior tissue
of the leaf
Mesophyll
Stomata
Chloroplast
CO2
O2
Mesophyll cell
5 µm
Component of a Chloroplast
• Thylakoid – Saclike
photosynthetic
membranes
– Light-dependent
reactions occur here
• Granum – Stack of
thylakoids
• Stroma – Region
outside the thylakoid
membrane
– Reactions of the Calvin
Cycle occur here
DRAW THIS CHLOROPLAST
DIAGRAM IN YOUR NOTES
The Photosynthesis Equation
6 CO2 + 6 H2O + Light energy  C6H12O6 + 6 O2
The Two Stages of Photosynthesis: A Preview
• Photosynthesis consists of the Light Reactions
(the photo part) and Calvin Cycle (the synthesis
part)
• The light reactions (in the
thylakoids):
– Split H2O
– Release O2
– Reduce NADP+ to
NADPH
– Generate ATP from
ADP
• The Calvin cycle (in the
stroma) forms sugar from
CO2, using ATP and
NADPH
• The Calvin cycle begins
with carbon fixation,
incorporating CO2 into
organic molecules (most
importantly, glucose)
• LightDependent
reaction
– Occurs in
thylakoid
– Uses H2O
and light to
produce ATP,
NADPH, and
O2
– NADPH is an
electron
carrier
• Calvin cycle (Light-Independent
Reaction)
– Occurs in stroma
– uses carbon dioxide, ATP, and
NADPH to produce sugars (aka
food, glucose, carbohydrates, etc.)
Light-Dependent Reactions
Electron Transport Chain
• This stage of photosynthesis includes an electron transport chain
(ETC). The molecules of the electron transport chain use highenergy electrons to push H+ ions from the stroma into the inner
thylakoid space, producing ATP & NADPH in the process (Don’t
worry about the details of the ETC). The ATP & NADPH are then
used in the next stage, the light-independent reactions (Calvin
Cycle).
Calvin Cycle
Fig. 10-5-1
H2O
Light
NADP+
ADP
+ P
Light
Reactions
Chloroplast
i
Fig. 10-5-2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Fig. 10-5-3
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Calvin
Cycle
Fig. 10-5-4
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
Fig. 10-7
The light reactions convert solar (light) energy
to the chemical energy of ATP and NADPH
• Chloroplasts are
solar-powered
chemical
factories
– Their thylakoids
transform light
energy into the
chemical
energy of ATP
& NADPH
– ATP &NADPH
are then used
to power the
Calvin Cycle
(lightindependent
reactions)
Light
Reflected
light
Chloroplast
Absorbed
light
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Granum
Transmitted
light
The Nature of Sunlight
• Light is a form of electromagnetic energy
• The electromagnetic spectrum is the entire
range of electromagnetic energy, or radiation
• Visible light consists of wavelengths (including
those that drive photosynthesis) that produce
colors we can see
Wavelength is the
distance between
crests of waves
Wavelength
determines the type
of electromagnetic
energy
Fig. 10-6
10–5 nm 10–3 nm
103 nm
1 nm
Gamma
X-rays
rays
UV
106 nm
Infrared
1m
(109 nm)
Microwaves
103 m
Radio
waves
Visible light
380
450
500
Shorter wavelength
Higher energy
550
600
650
700
750 nm
Longer wavelength
Lower energy
Light and Pigments
• Pigments –
light
absorbing
chemicals
• Chlorophyll –
principle
pigment in
plants
–
–
–
–
Chlorophyll a
Chlorophyll b
Carotenoids
Xanthophyll
Why do leaves change colors?
• Chlorophyll
a
• Chlorophyll
b
Why Do Leaves Change Color?
Why Do Leaves Change Color?
• Leaves change color in the Fall because
chlorophyll begins to break down and
disappear, exposing the other pigments –
the carotenoids (orange, yellow, and reds)
and xanthophylls (yellows).
Factors Affecting Photosynthesis
• Water supply
• Amount of sunlight
• Temperature
Types of Photosynthesis
• C3 Photosynthesis
• C4 Photosynthesis
• CAM Photosynthesis
C3 Photosynthesis : C3 plants.
• Called C3 because the CO2 is first incorporated into a 3carbon compound.
• Stomata are open during the day.
• Photosynthesis takes place throughout the leaf.
• Adaptive Value: more efficient than C4 and CAM plants
under cool and moist conditions and under normal light
because requires less machinery (fewer enzymes and
no specialized anatomy)..
• Most plants are C3.
C4 Photosynthesis : C4 plants.
• Called C4 because the CO2 is first incorporated into a 4carbon compound.
• Stomata are open during the day.
Adaptive Value:
• Photosynthesizes faster than C3 plants under high light
intensity and high temperatures
• Has better Water Use Efficiency because they do not need
to keep stomata open as much (less water lost by
transpiration)
• C4 plants include several thousand species in at least 19
plant families. Examples: corn, sugar cane, grasses
CAM Photosynthesis : CAM plants. CAM stands for
Crassulacean Acid Metabolism
• Stomata open at night (when evaporation rates are
usually lower) and are usually closed during the day.
• Adaptive Value:
– Better Water Use under arid conditions due to opening
stomata at night when transpiration rates are lower (no
sunlight, lower temperatures, lower wind speeds, etc.).
• Examples: succulents such as cacti, pineapple, and
also some orchids and bromeliads