Transcript Chapter 9 Pictures

PHOTOSYNTHESIS
Photosynthesis
• process by which green
plants & some organisms
– seaweed, algae & certain
bacteria
• use light energy to convert
CO2 + water glucose
• all life on Earth, directly or
indirectly, depends on
photosynthesis as source of
food, energy & O2
Autotrophs
• self feeders
– organisms that
make their own
organic matter from
inorganic matter
– producers
• use inorganic
molecules such as
CO2, H2O & minerals
to make organic
molecules
Heterotrophs
• consumers
– other feeders
• depend on glucose
as energy source
– cannot produce it
• obtained by eating
plants or animals
that have eaten
plants
Carbon and Energy Flow
CO2 + H2O
Photosynthesis
Carbs
Proteins
Lipids + O2
Cellular (Aerobic)
Respiration
(ATP Produced)
Food Chain
• byproduct of
photosynthesis is O2
• humans & other
animals breathe in
oxygen
• used in cellular
respiration
Other Benefits of Photosynthesis
• humans also dependent on
ancient products of
photosynthesis
• fossil fuels
– natural gas, coal & petroleum
• needed for modern industrial
energy
• complex mix of hydrocarbons
• represent remains of
organisms that relied on
photosynthesis millions of
years ago
Photosynthesis
• plants produce more
glucose than can use
• stored as starch &
other carbohydrates
in roots, stems &
leaves
• can draw on these
reserves for extra
energy or building
materials as needed
Sites of Photosynthesis
• leaves & green stems
• in cell organelles
– chloroplasts
• concentrated in green
tissue in interior of leaf
• mesophyll
• green due to presence
of green pigment
chlorophyll
Chloroplasts
• each cell has 40-50 chloroplasts
– oval-shaped structures with
double membrane
• inner membrane encloses
compartment filled with stroma
• suspended in stroma are diskshaped compartmentsthylakoids
– arranged vertically like stack
of plates
• one stack-granum (plural,
grana)
• embedded in membranes of
thylakoids are hundreds of
chlorophyll molecules
Chlorophyll
• light-trapping
pigment
• other light-trapping
pigments, enzymes &
other molecules
needed for
photosynthesis are
also found in
thylakoid membranes
How Photosynthesis Works
• Requires
–CO2
–Water
–Sunlight
• Makes
–O2
–Glucose
How Photosynthesis Works
• CO2 enters plant via
pores- stomata in leaves
• water-absorbed by roots
from soil
• membranes in
chloroplasts provide sites
for reactions of
photosynthesis
• chlorophyll molecules in
thylakoids capture energy
from sunlight
• chloroplasts rearrange
atoms of inorganic
molecules into sugars &
other organic molecules
Photosynthesis
• redox reaction
• 6CO2 + 12H2OC6H12O6
+ 6O2 + 6H2O in presence
of light
• must be an oxidation & a
reduction
• water is oxidized
– loses electrons &
hydrogen ions
• carbon dioxide is
reduced
– gains electrons &
hydrogens
Photosynthesis
• 2 stages
• light-dependent reactions
– chloroplasts trap light
energy
– convert it to chemical
energy
– contained in nicotinamide
adenine dinucleotide
phosphate-(NADPH) &
ATP
– used in second stage
• light-independent reactions
– Calvin cycle
– formerly called dark reactions
– NADPH (electron carrier) provides
hydrogens to form glucose
•
ATP provides energy
Light Energy for Photosynthesis
• sun energy is radiation
– electromagnetic energy
• travels as waves
• distance between 2 waveswavelength
• light contains many colors
• each has defined range of
wavelengths measured in
nanometers
• range of wavelengths is
electromagnetic spectrum
• part can be seen by
humans
– visible light
Pigments
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light absorbing molecules
built into thylakoid membranes
absorb some wavelengths & reflect others
plants appear green because
chlorophyll-does not absorb green light
– reflected back.
as light is absorbedenergy is absorbed
chloroplasts contain several kinds of
pigments
different pigments absorb different
wavelengths of light
red & blue wavelengths are most effective
in photosynthesis
other pigments are accessory pigments
absorb different wavelengths
enhance light-absorbing capacity of a leaf
by capturing a broader spectrum of blue &
red wavelengths along with yellow and
orange wavelengths
Pigment Color & Maximum
Absoption
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Violet: 400 - 420 nm
Indigo: 420 - 440 nm
Blue: 440 - 490 nm
Green: 490 - 570 nm
Yellow: 570 - 585 nm
Orange: 585 - 620
nm
• Red: 620 - 780 nm
Chlorophylls
• Chlorophyll A
– absorbs blue-violet & red
light
– reflects green
– participates in light reactions
• Chlorophyll B
– absorbs blue & orange light
– reflects yellow-green
– does not directly participate
in light reactions
– broadens range of light plant
can use by sending its
absorbed energy to
chlorophyll A
Carotenoids
• yellow-orange pigments
• absorb blue-green
wavelengths
• reflect yellow-orange
• pass absorbed energy to
chlorophyll A
• have protective function
– absorb & dissipate
excessive light energy
that would damage
chlorophylls
Photosynthesis
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Pigments
Absorb light
Excites electrons
Energy passed to
sites in cell
• Energy used to
make glucose
Photosystems
• chlorophyll & other
pigments clustered
next to one another in a
photosystem
• when photon strikes
one pigment molecule
• energy jumps from
pigment to pigment
until arrives at reaction
center
Reaction Center
• electron acceptor traps
a light excited electron
from reaction center
chlorophyll
• passes it to electron
transport chain which
uses energy to make
ATP & NADPH
Photosystems
• two photosystems
participate in light
reactions
• photosystems II & I
Light Reactions
• make ATP & NADPH
• electrons are removed from
molecules of water
• oxygen escapes to air
• electrons are passed from
photosystem II to
photosystem I to NADP+
• light drives electrons from
H2O to NADP+ which is
oxidized NADPH which is
reduced
Photosystem II
• water is split
• oxygen atom combines
with oxygen from
another split water
forming molecular
oxygen-O2
• each excited electron
passes from
photosystem II to
photosystem I via
electron transport chain
Photosystem I
• electron acceptor captures an
excited electron
• excited electrons are passed
through a short electron
transport chain to NADP+
reducing it to NADPH
• NADP+ -final electron
acceptor
• electrons are stored in high
state of potential energy in
NADPH molecule
• NADPH, ATP and O2 are
products of light reactions
ATP Formation-Chemiosmosis
• uses potential energy of
hydrogen ion
concentration gradient
across membrane
• gradient forms when
electron transport chain
pumps hydrogen ions
across thylakoid
membrane as it passes
electrons down chain
that connects two
photosystems
ATP Formation-Chemiosmosis
• ATP synthase (enzyme)
uses energy stored by H
gradient to make ATP
• ATP is produced from
ADP & Pi when hydrogen
ions pass out of thylakoid
through ATP synthase
• photophosphorylation
Calvin Cycle/Dark Reactions
• light independent reactions
• depend on light indirectly for
inputs-ATP & NADPH
• occurs-stroma of chloroplast
• each step controlled by
different enzyme
• cycle of reactions
• makes sugar from CO2 &
energy
• ATP provides chemical energy
• NADPH provides high energy
electrons for reduction of CO2
to sugar
Steps of Calvin Cycle
• starting material-ribulose
bisphosphate (RuBP)
• first step-carbon fixation
• rubisco (an enzyme) attaches
CO2 to RuBP
• Next-reduction reaction takes
place
• to do this cycle uses carbons
from 3 CO2 molecules
• to complete cycle must
regenerate beginning
component-RuBP
• for every 3 molecules of CO2
fixed, one G3P molecule
leaves cycle as product of
cycle
• remaining 5 G3P molecules
Calvin Cycle
• regenerated RuBP is used
to start Calvin cycle again
• process occurs repeatedly
in each chloroplast as long
as CO2, ATP & NADPH are
available
• thousands of glucose
molecules are produced
• used by plants to produce
energy in aerobic
respiration
• used as structural materials
• stored