Chapter 7 Photosynthesis
Assignments
Read chapter 7 in textbook
Read pages 53-61 in Cliffs AP Bio book
Take sample test at the end of the Photosynthesis
chapter (page 62-65?)
Due Oct 12th
Read AP Investigation 5 Photosynthesis for Wed Oct
11th (Lab Bench also may help)
Mills AP Biology 2012
Chapter 7 Photosynthesis
• Topics
•
•
•
•
•
7.1 Photosynthetic Organisms
7.2 The Process of Photosynthesis
7.3 Plants as Solar Energy Converters
7.4 Plants as Carbon Dioxide Fixers
7.5 Other Types of Photosynthesis
Mills AP Biology 2012
7.1 Photosynthetic Organisms
• All life on Earth depends on solar energy
• Photosynthetic organisms (algae, plants, and
cyanobacteria) transform solar energy into the chemical
energy of carbohydrates
– Called autotrophs because they produce their own food.
• Photosynthesis:
– A process that captures solar energy
– Transforms solar energy into chemical energy
– Energy ends up stored in a carbohydrate
• Photosynthesizers produce food energy
– Feed themselves as well as heterotrophs
3
Photosynthetic Organisms
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
mosses
trees
kelp
Euglena
garden plants
cyanobacteria
diatoms
(Moss): © Steven P. Lynch; (Trees): © Digital Vision/PunchStock; (Kelp): © Chuck Davis/Stone/Getty Images; (Cyanobacteria): © Sherman Thomas/Visuals Unlimited; (Diatoms): © Ed Reschke/Peter Arnold; (Euglena): © T.E.
Adams/Visuals Unlimited; (Sunflower): © Royalty-Free/Corbis
4
Photosynthetic Organisms
• Photosynthesis takes place in the green portions of plants
– Leaf of flowering plant contains mesophyll tissue
– Cells containing chloroplasts are specialized to carry out
photosynthesis
• The raw materials for photosynthesis are carbon dioxide
and water
– Roots absorb water that moves up vascular tissue
– Carbon dioxide enters a leaf through small openings called
stomata and diffuses into chloroplasts in mesophyll cells
– In stroma, CO2 is combined with H2O to form C6H12O6 (sugar)
– Energy supplied by light
• Chlorophyll and other pigments absorb solar energy and energize
electrons prior to reduction of CO2 to a carbohydrate
5
cuticle
upper
epidermis
Leaf cross section
mesophyll
lower
epidermis
CO2
O2
leaf vein
stoma
outer membrane
inner membrane
stroma
stroma
granum
Chloroplast
37,000
thylakoid space
thylakoid membrane
Grana
independent thylakoid
in a granum
overlapping thylakoid
in a granum
Mills AP Biology 2012
Mills AP Biology 2012
Inside a chloroplast-movie
Hard drive.\..\Biology Clipart and
sounds\Biology movies and
animations\chloroplast journey
movie.mov
In this film, chloroplast migration in the moss,
Funaria, is shown at various intensities of strong
polarized light.
Migrating chloroplasts
microscopic
Hard drive..\..\Biology Clipart and
sounds\Biology movies and
animations\chloroplast migration dt
polarized and non polarized light.mov
Non-polarized strong light falling vertically on to the
moss leaf causes migration of the chloroplasts to the
the anticlinal cells walls (ie those perpendicular to
the leaf surface).
Conversely, strong polarized illumination transverse
to the long axis of the cell causes migration to the
anticlinal longitudinal walls of the cell.
Strong polarized light parallel to the longitudinal axis
of the cell walls provokes migration to the anticlinal
cross walls.
From:
http://www.cells.de/cellseng/medienarchiv/archiv/k124.htm
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
Photosynthesis is an energy transformation in which solar
energy is converted to chemical energy
Most life on earth would end without photosynthesis
Mills AP Biology 2012
Photosynthesis Overview
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
• What is the function of
photosynthesis?
– Captures energy (from the
sun)
– Energy is then used to
synthesize sugar, which the
cells can use for cell
respiration
• In the process, uses CO2 and
gives off O2
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
The process of photosynthesis is divided into light (light
dependent) and dark (light independent) reactions.
• Light (Dependent) Reactions
– Need light
– Occur in the membranes of the
choroplasts
– Photosystem II
• Generates ATP
– Photosystem I
• Generates NADPH
– ATP and NADPH are used to
power dark reactions
• Dark (light independent)
Reactions
– Can proceed with or without
light
– Occur in the stroma of
chloroplasts
– Carbon is “fixed” in the Calvin
Cycle (also called the C3 cycle)
to make glucose
– Uses energy from the light
reactions
– For most plants these occur in
the light – need the ATP and
NADPH from light rx, but don’t
depend directly on light.
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
• Equation Summarizing Photosynthesis
Carbon Dioxide
Reduced
6CO2 + 12 H2O + Energy  C6H12O6 + 6H2O + 6O2
Water Oxidized
Compare to - Cell Respiration
• C6H12O6 + 6H2O + 6O2  6CO2 + 12H2O + 36 ATP + heat
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
Mills AP Biology 2012
7.3 Plants as Solar Energy Converters
• Pigments:
– Chemicals that absorb certain wavelengths of light
– Wavelengths that are not absorbed are reflected/transmitted
• Absorption Spectrum
– Pigments found in chlorophyll absorb various portions of
visible light
– Graph showing relative absorption of the various colors of
the rainbow
– Chlorophyll is green because it absorbs much of the reds
and blues of white light
15
Photosynthetic Pigments and Photosynthesis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Increasing wavelength
chlorophyll a
chlorophyll b
carotenoids
Gamma
rays
X rays
UV
Infrared
Micro- Radio
waves waves
visible light
500
600
Wavelengths (nm)
a. The electromagnetic spectrum includes visible light.
750
Relative Absorption
Increasing energy
380
500
600
750
Wavelengths (nm)
b. Absorption spectrum of photosynthetic pigments.
16
Photosynthesis Overview
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
• Chloroplasts - structure
– Photosynthetic pigments are found in the photosynthetic membranes
of chloroplasts (recall that chloroplasts are organelles - a type of plastid) inside of
plant cells.
– Contain DNA and some ribosomes (like mitochondria)
Leaf Cell
Chloroplast – made up of
grana-(which are stacks of
thylakoids) and stroma –
(space between grana)
Mills AP Biology 2012
Granum (stacks of thylakoids)
Contain the pigment
chlorophyll as well as other
important proteins
Photosynthesis Overview
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.2 The Process of Photosynthesis
• Photosynthetic pigments
– Chlorophyll
(reflect green)
• Chlorophyll a (major pigment in most
plants)
• Chlorophyll b
– Carotenes (absorbs blue and green, reflects orange,
yellow or red)
– Xanthopylls (reflect yellow)
– Phycocyanins (reflect blue)
– Chlorophyll masks carotenes and
xanthophylls except in the fall when
chlorophyll starts to break down
Mills AP Biology 2012
Chromatography
More soluble
pigments travel
faster (carotene
fastest here)
7.3 Plants as Solar Energy Converters
• The light reactions consist of two alternate
electron pathways:
– Noncyclic pathway
– Cyclic pathway
• Capture light energy with photosystems
– Pigment complex helps collect solar energy like an
antenna
– Occur in the thylakoid membranes
• Both pathways produce ATP
• The noncyclic pathway also produces
NADPH
21
7.3 Plants as Solar Energy Converters
• Noncyclic pathway
–
–
–
–
Takes place in the thylakoid membrane
Uses two photosystems, PS I and PS II
PS II captures light energy
Causes an electron to be ejected from the reaction center
(chlorophyll a)
• Electron travels down electron transport chain to PS I
• Replaced with an electron from water, which is split to
form O2 and H+
• This causes H+ to accumulate in thylakoid chambers
• The H+ gradient is used to produce ATP
– PS I captures light energy and ejects an electron
• The electron is transferred permanently to a molecule of
NADP+
• Causes NADPH production
22
Chapter 7 Photosynthesis
7.3 Plants as Solar Energy Converters
• Solar energy is captured by the pigments in the
thylakoids for use in the light dependent reactions.
• Light dependent reactions are composed of two
systems
– Photosystem 2 (PS II)
– Photosystem 1 (PS I)
– Named in order they were discovered
Mills AP Biology 2012
• Photosystem 1 and 2 Overview
Mills AP Biology 2012
H2O
CO2
solar
energy
Noncyclic Pathway:
Photosystem II
ADP+ P
NADP+
sun
Light
reactions
Calvin
cycle
NADPH
ATP
electron
acceptor
thylakoid
membrane
energy level
O
e–
• Light Dependent Reactions
CH2O
– Energy from light excites antennae
complex electrons in pigments
(chlorophyll a , b and carotenoids) of
thylakoid.
– Energy from antennae complex funneled
to a reaction center (a special chlorophyll a
pigment molecule).
– Reaction center electrons are passed to an
electron transport chain.
– Energy from ETC used to make ATP
– Electron passed to photosystem I
e–
reaction center
pigment
complex
e–
Photosystem II
H 2O
2H+
1
– O2
2
25
H2 O
CO2
solar
energy
• Light Dependent
Reactions
Photosystem II
ADP+
NADP+
sun
– Energy from light
excites antennae
complex electrons in
pigments (chlorophyll a
, b and carotenoids) of
thylakoid.
– Energy from antennae
complex funneled to a
reaction center (a
special chlorophyll a
pigment molecule).
– Reaction center
electrons are passed to
an electron transport
chain.
– Energy from ETC used
to make ATP
– Electron passed to
photosystem I
P
Calvin
cycle
Light
reactions
NADPH
ATP
thylakoid
membrane
electron
acceptor
CH2O
energy level
O
e–
ATP
e–
reaction center
pigment
complex
e–
Photosystem II
H2O
2H+
CO2
1
– O2
2
CH2O
Calvin cycle
reactions
Chapter 7 Photosynthesis
7.3 Solar Energy Capture – Electron Pathways
• Light Dependent Reactions
– Photosystem I
• Energy from light excites
electrons in antennae complex
(also receives electron from PS II)
• Energy from antennae complex is
funneled to the reaction center
• Reaction center electron is
passed to an electron transport
chain
• Energy from ETC used to form
NADPH + H+ (actual reaction
NADP+ + 2H -> NADPH + H+ )
– This use of PS I and PS II
together is called non cyclic
photophosphorilation because
electrons are passed from PS II to
PS I.
Mills AP Biology 2012
Noncyclic Electron Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H2O
CO2
solar
energy
ADP+ P
NADP+
Light
reactions
sun
Calvin
cycle
sun
NADPH
ATP
thylakoid
membrane
electron
acceptor
electron
acceptor
energy level
O
CH2O
e–
e–
e–
NADP+
H+
ATP
e–
e–
NADPH
e–
reaction center
reaction center
pigment
complex
pigment
complex
Photosystem I
e–
Photosystem II
CO2
H2O
CH2O
Calvin cycle
reactions
2H+
1
– O2
2
28
Mills AP Biology 2012
Mills AP Biology 2012
7.3 Plants as Solar Energy Converters
• Summary
– PS II:
• Consists of a pigment complex and electron acceptors
• Receives electrons from the splitting of water
• Oxygen is released as a gas
– Electron transport chain:
• Consists of cytochrome complexes and plastoquinone
• Carries electrons between PS II and PS I
• Also pumps H+ from the stroma into the thylakoid space
– PS I:
• Has a pigment complex and electron acceptors
• Adjacent to the enzyme that reduces NADP+ to NADPH
– ATP synthase complex:
• Has a channel for H+ flow
• H+ flow through the channel drives ATP synthase to join ADP and Pi
31
7.3 Plants as Solar Energy Converters
• The thylakoid space acts as a reservoir for hydrogen
ions (H+)
• Each time water is oxidized, two H+ remain in the
thylakoid space
• Transfer of electrons in the electron transport chain
yields energy
– Used to pump H+ across the thylakoid membrane
– Protons move from stroma into the thylakoid space
• Flow of H+ back across the thylakoid membrane
– Energizes ATP synthase, which
– Enzymatically produces ATP from ADP + Pi
• This method of producing ATP is called
chemiosmosis
32
Chemiosmosis
Mills AP Biology 2012
Photosynthesis: H+ are pumped from stroma of chloroplast into thylakoid, then
diffuse back out into stroma.
Cell Respiration: H+ are pumped from matrix into intermembrane space, then
diffuse back out into matrix.
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.3 Solar Energy Capture –Thylakoid Membrane
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Chemiosmosis and the Light Dependent Reactions
Mills AP Biology 2012
•
http://www.sirinet.net/~jgjohnso/photosynthesis.html
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Photosynthesis- Electron and ATP Synthesis
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Chapter 7 Photosynthesis
7.3 Solar Energy Capture – Electron Pathways
• Cyclic photophosphorylation
– Some primitive bacteria have only one photosystem and the electron moves in a
cyclical fashion = cyclic photophosphorilation (creates only ATP)
– Plants can use cyclic and non cyclic
Photosynthetic bacteria –
Cyanobacterium Anabaena
Mills AP Biology 2012
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.3 Solar Energy Capture – Electron Pathways
• Read AP Lab #4 for Oct 21st
– Plant pigments and photosynthesis
http://www.phschool.com/science/biology_place/labbench/lab4/intro.html
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Plants as Carbon Dioxide Fixers
• Light Independent (Dark)
Reactions
– ATP and NADPH made in
the light dependent
reactions are used to
reduce carbon dioxide,
forming a carbohydrate
– Cycle of reactions called
the Calvin cycle (also
called C3 cycle)
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Plants as Carbon Dioxide Fixers
• Light Independent (Dark) Reactions
– Carbon dioxide (that has diffused in from the
atmosphere through stomates) is used to form
glucose (a carbohydrate)
– Incorporating carbon, from carbon dioxide, into an
organic compound (RuBP) = carbon fixation
– Process involves a series of chemical reactions
called the Calvin Cycle (or C3 cycle)
Melvin Calvin 1911-1997
Nobel Prize in Chemistry 1961
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Plants as Carbon Dioxide Fixers
• Calvin Cycle
– RuBP (ribulose biphosphate)
is both the starting and
ending compound of the
cycle
– CO2 reacts with RuBP 
PGA (a 3 carbon compound
–phosphoglyceric acid)
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Plants as Carbon Dioxide Fixers
– PGA  PGAL
=(phosphoglyceraldehyde)
• Uses the energy from ATP
and NADPH (that came from
light reactions) to form bonds
– Most of PGAL  RuBP
• Uses energy from ATP
produced in light reactions
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Plants as Carbon Dioxide Fixers
Only one out of every
6 PGALs is used to
make glucose.(PGAL
sometimes called
G3P)
Mills AP Biology 2012
Calvin Cycle Animation
Starts w 3 RuBP’s to net 1 PGAL
..\..\Biology\Biology Clipart Movies Animations
Sounds\Biology movies\Calvin Cycle in 3 steps animation.swf
Mills AP Biology 2012
Calvin cycle – starts w 1 RuBP to net 1 PGAL after 3
turns..\..\Biology\Biology Clipart Movies Animations Sounds\Biology animations\Calvin[1].swf
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Chapter 7
Photosynthesis
G3P
7.4 Plants as Carbon
Dioxide Fixers
• What is PGAL
(glyceraldehyde-3phosphate = G3P)
used for?
– Starting point
for metabolism
of many organic
compounds
glucose
phosphate
fatty acid
synthesis
amino acid
synthesis
+
fructose
phosphate
Sucrose (in leaves,
fruits, and seeds)
Mills AP Biology 2012
Starch (in roots Cellulose (in trunks,
and seeds)
roots, and branches)
Chapter 7 Photosynthesis
7.4 Other Types of Photosynthesis
• Three known modes of photosynthesis
– C3 – Calvin Cycle
– C4
– CAM
• Modes vary by the way they “fix” carbon
• In hot, dry climates
•
– Stomata must close to avoid wilting
– CO2 decreases and O2 increases
– O2 starts combining with RuBP, leading to the production of CO2
– This is called photorespiration
To understand why different methods may be advantageous – must first
understand photorespiration
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Other Types of Photosynthesis
• Photorespiration
– Need to understand
photorespiration to understand why
C4 photosynthesis is beneficial.
– Uses the energy of light(photo), but
produces oxygen(respiration) as a
product, not CO2
– If too much oxygen builds up in
leaves, the plant will use
photorespiration instead of
photosynthesis.
– How can too much oxygen build
up? (see next slide)
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Other Types of Photosynthesis
• Photorespiration
– Stomates open and close to regulate
water and O2 exit, and CO2 entry
– Hot and dry  close to conserve
water, but then less CO2 available
and O2 builds up
– RuBP carboxylase (rubisco)
combines with O2and then with
RuBP (for respiration), instead of
CO2 (for carbon fixation)
– Produces one molecule of PGA and
releases (eventually) CO2
• This CO2 exits the chloroplast and is
no longer usable by the Calvin cycle.
– Does not produce any usable energy
– Only occurs in C3 plants
Stomate Movement Movie
Hard drive ..\..\Biology Clipart and
sounds\Biology movies and
animations\stomatal movement movie.mov
Mills AP Biology 2012
CO2 produced in
photorespiration is not
available to the Calvin
cycle.
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Other Types of Photosynthesis
• C 3 (“regular”) Photosynthesis
– Mesophyll cells arranged in parallel
layers
– Mesophyll cells have well formed
chloroplasts (bundle cells don’t)
– Only mesophyll cells carry out
photosynthesis
– Bundle sheath cells do not have
chloroplasts
– Use enzyme RuBP carboxylase
(rubisco) to fix carbon dioxide to
RuBP first detectable molecule
is PGA
– Wheat, rice, oats
– Photorespiration can reduce yield
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Other Types of Photosynthesis
• C 4 Photosynthesis
–
–
–
Isolates rubisco from atmospheric oxygen
by moving calvin cycle into bundle sheath
cells.
Mesophyll cells not parallel, instead
arranged concentrically around bundle
sheath cells
Mesophyll cells and bundle cells have
chloroplasts
•
•
•
–
–
Mesophyll cells use enzyme PEPcase (has
little attraction to oxygen)to fix carbon dioxide
to PEP  first detectable molecule
oxaloacetate, a 4 C molecule (as opposed to
a 3 C compound).
CO2 passed to bundle cells (takes energy)
where it enters the Calvin cycle – Calvin cycle
only occurs in bundle cells
Process keeps concentration of CO2 high in
the bundle sheath cells – rubisco binds more
CO2 and less O2
In hot, dry climates have a rate of
photosynthesis 2-3X higher than C3 plants –
no photorespiration
Corn, sugarcane, Bermuda grass
Mills AP Biology 2012
Mills AP Biology 2012
Chapter 7 Photosynthesis
7.4 Other Types of Photosynthesis
• CAM Photosynthesis
– Crassulacean acid metabolism
– Happens in most succulent plants
– During night use PEPCase, forming
C 4 molecules  which are stored in
mesophyll cells
– During day (when ATP and NADPH are
available)– C 4 molecules are released
to the Calvin cycle
– Open stomates only at night,close
during day (opposite of most plants),
conserving water, but limits CO2
available  less photosynthesis
– Similar to C4 cycle in that it makes
an intermediary C compound to be
used by the calvin cycle
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Partitioning in space.
Partitioning in time.
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7.4 Other Types of Photosynthesis
• Each method of photosynthesis has advantages
and disadvantages
– Depends on the climate
• C4 plants most adapted to:
– High light intensities
– High temperatures
– Limited rainfall
• C3 plants better adapted to
– Cold (below 25°C)
– High moisture
• CAM plants are better adapted to extreme aridity
– CAM occurs in 23 families of flowering plants
– Also found among nonflowering plants
60
Read Connecting the Concepts with the Big Ideas pg 131
The End
Mills AP Biology 2012