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Energy Conversions
Photosynthesis
Cellular Respiration
Energy Conversion
• Energy: The ability to do work or cause
motion
– Potential E: “Stored Energy”; Energy of
position
– Kinetic Energy: Energy of motion
– Chemical Energy: Potential
Kinetic
Exothermic Vs Endothermic
• Exothermic: Gives off heat
– Examples: Fire
• Endothermic: Absorbs heat
– Examples: Cold Pack, Photosynthesis
Photosynthesis
Light Reaction
Light-Dependent Reactions
Calvin Cycle
Fig. 10-2
• Photosynthesis:
–
–
–
–
BioFlix: Photosynthesis
in plants
algae,
Some protists
some prokaryotes
(a) Plants
10 µm
(c) Unicellular protist
(e) Purple sulfur
bacteria
(b) Multicellular alga
(d) Cyanobacteria
40 µm
1.5 µm
Structures of Photosynthesis
• Chloroplasts are structurally similar to
photosynthetic bacteria
• Leaves are the main area
of Photosynthesis
• Their green color is from
chlorophyll, the green
pigment
• CO2 enters and O2 exits
the leaf through pores
called stomata
Fig. 10-3a
Leaf cross section
• Chloroplasts
are found in
cells of the
mesophyll, the
interior tissue
of the leaf
– A typical
mesophyll cell
has 30–40
chloroplasts
• Thylakoid
• Grana
• Stroma
Vein
Mesophyll
Stomata
Chloroplast
CO2
O2
Mesophyll cell
5 µm
Component of a Chloroplast
• Thylakoid –
– Saclike photosynthetic
membranes
– Light-dependent
reactions occur here
• Granum / Grana:–
– Stack of thylakoids
• Stroma –
– Region outside the
thylakoid membrane
– Reactions of the Calvin
Cycle occur here
The Photosynthesis Equation
6 CO2 + 6 H2O (light energy)  C6H12O6 + 6 O2 (water given off also)
• Lightdependent
reactions
– Occurs in
Thylakoid
– Used H2O and
light to produce
ATP, NADPH,
and O2
– NADPH is an
electron carrier
• Calvin cycle
– Occurs in stroma
– uses carbon dioxide, ATP, and
NADPH to produce sugars
Photosynthesis Goal? – What is it?
• Needs Energy:
– Photophosphorylation –
– The production of ATP using energy from an
electron transport chain.
Photosynthesis
• Photosynthesis:
– Light reactions (the photo part)
– Calvin cycle (the synthesis part)
• The light reactions:
– (in the thylakoids):
– Split H2O
– Release O2
– Reduce NADP+ to
NADPH
– Generate ATP from
ADP by
photophosphorylation
• The Calvin cycle
– (in the stroma) forms
sugar from CO2, using
ATP and NADPH
– The Calvin cycle
begins with carbon
fixation, CO2 into
organic molecules
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 energy to the
chemical energy of ATP and NADPH
Light
• Chloroplasts
are solarpowered
chemical
factories
– Their thylakoids
transform light
energy into
chemical
energy:
Reflected
light
Chloroplast
Absorbed
light
• ATP
• NADPH
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Granum
Transmitted
light
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BIOFLIX: Photosynthesis
• PEARSON:
http://media.pearsoncmg.com/bc/bc_0med
ia_bio/bioflix/bioflix.htm?9apphotosynthesi
s
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
–
–
–
–
Chlorophyll a
Chlorophyll b
Carotenoids
Xanthophyll
Why do leaves change colors?
• Chlorophyll
a
• Chlorophyll
b
NADP+ + e- + Energy  NADPH
• NADP+
– (Nicotinamide adenine
dinucleotide phosphate)
– Electron, hydrogen,
and energy carrier
Light-Dependant
Reactions
1. Photosystem II
• Chlorophyll absorbs light
• Electrons on a chlorophyll molecule (p680)
absorb energy (become excited) are
“energized”
• High-energy electrons are passed on to
the electron transport chain
• Chlorophyll’s electrons are replenished
by the breakdown of H2O
2. Electron Transport Chain
• The molecules of the electron transports
chain use high-energy electrons to push
H+ ions from the stroma into the inner
thylakoid space.
3. Photosystem I
• Chlorophyll absorbs light-energy and reenergized the electrons from
photosystem II.
• NADP+ picks up these high-energy
electrons and H+ to become NADPH.
4. Hydrogen Ions
• Chemiosmosis = Electrochemical
Gradient
• Hydrogen ions build up inside the thylakoid
membrane.
– High concentration of H+ inside the
membrane (Strong Positive Charge)
– Low concentration of H+ outside the
membrane (Negative Charge)
– Provides the energy to form ATP
5. ATP formation
• H+ try to reach equilibrium.
• Pass through the ATP synthase
• Movement of H+ ions through the ATP
synthase powers ATP production
Calvin Cycle
The Calvin Cycle / Dark Reaction
1. 6 CO2 molecules enter the cycle.
2. Enzyme “rubisco” (RuBP) forms 3carbon molecules
3. ATP and NADPH form the High energy
3-Carbon molecules (G3P)
4. 2 (G3P)are combined to form a 6-carbon
sugar
Calvin Cycle
Factors Affecting Photosynthesis
• Water supply
• Amount of sunlight
• Temperature
LAB: Plant Pigments
Types of Photosynthesis
• C3 Photosynthesis
• C4 Photosynthesis
• CAM Photosynthesis
C3 Plants (Most Plants)
• Called C3 because the CO2 is first
incorporated into a 3-carbon 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)
C4 plants
• Called C4 because the CO2 is first joined to make
a 4C compound.
• Stomata are open during the day
• Adaptive Value:
– Photosynthesizes faster than C3 plants
– Can take HEAT and intense sunlight
– Better water use enzymes brings in CO2 faster and so
does not need to keep stomata open as much (less water lost
by transpiration) for the same amount of photosynthesis.
– Examples: four-wing saltbush, corn, and many of
our summer annual plants.
CAM Plants:
• CAM stands for Crassulacean Acid Metabolism
• Stomata open at night (when evaporation rates are
usually lower)
• During the day, the acid is broken down and the CO2
is released to RUBISCO for photosynthesis
• Adaptive Value:
– Better Water Use Efficiency than C3 plants under dry conditions due
to opening stomata at night when transpiration rates are lower (no
sunlight, lower temperatures, lower wind speeds, etc.).
• Examples: CAM plants include many succulents
such as cactuses and agaves and also some
orchids and bromeliads
Cellular Respiration
Cellular Respiration
• Transforming the “potential” energy in food
into chemical energy cells can use: ATP
• CR = same way in plants and animals.
• Overall Reaction:
– C6H12O6 + 6O2 → 6CO2 + 6H2O
Cellular Respiration Overview
• Breakdown of glucose starts in the
cytoplasm:
• At this point life diverges into two forms
and two pathways
– Anaerobic respiration = fermentation
– Aerobic cellular respiration = High amounts of
ATP
C.R. Reactions
• Glycolysis
– Glucose molecule broken down into two 3carbon molecules called pyruvate
– Process is ancient / all organisms from
simple bacteria to humans perform it the
same way
– Yields 2 ATP molecules for every one
glucose molecule broken down
– Yields 2 NADH per glucose molecule
Anaerobic Cellular Respiration
• Some organisms thrive in environments with little or no
oxygen
– Marshes, bogs, gut of animals, sewage treatment ponds
• No oxygen used = anaerobic
• Results in no extra ATP
– ONLY to regenerate NAD+ so it can return to pick up more electrons
and hydrogens
• End products: Alcohol or Lactic Acid:
– YEAST & PLANTS:
– MUSCLE CELLS:
Ethanol and CO2 in beer/bread
Lactic Acid
Aerobic Cellular Respiration
• Oxygen required = aerobic
• 2 more sets of reactions which occur in a
specialized structure within the cell called
the mitochondria
– 1. Kreb’s Cycle
– 2. Electron Transport Chain
Kreb’s Cycle
• Completes the breakdown of glucose
– Pyruvate 3-C broken down, the carbon and
oxygen atoms end up in CO2 and H2O
– Hydrogens and electrons are stripped and
loaded onto NAD+ and FAD to produce NADH
and FADH2
• Production of only 2 more ATP but
loads up the coenzymes with H+ and
electrons which move to the 3rd stage
Electron Transport Chain
• Electron carriers loaded with electrons and
protons from the Kreb’s cycle move to this
chain-like a series of steps (staircase).
• As electrons drop down stairs, energy
released to form a total of 32 ATP
• Oxygen waits at bottom of staircase, picks
up electrons and protons and in doing so
becomes water
Energy Tally
• 36 ATP for aerobic
– vs.
• 2 ATP for anaerobic
– Glycolysis
– Kreb’s
– Electron Transport
2 ATP
2 ATP
32 ATP
36 ATP
• Anaerobic organisms can’t be too energetic but are important for
global recycling of carbon
• http://ideastream.pbslearningmedia.org/re
source/tdc02.sci.life.cell.mitochondria/thepowerhouse-of-the-cell/ (5:53)
Cellular Respiration Song 
• http://www.youtube.com/watch?v=3aZrkdz
rd04
Review – Compare / Contrast
• Photosynthesis & Cellular Respiration
Comparing
Photosynthesis & Respiration
Photosynthesis
Cellular
Respiration
Function
Energy Storage
Energy Release
Location
Chloroplasts
Mitochondria
Reactants
CO2 and H2O
C6H12O6 and O2
Products
C6H12O6 and O2
CO2 and H2O
Equation
6CO2 + 6H2O 
C6H12O6 + 6O2
C6H12O6 + 6O2
6CO2 + 6H2O
Redox Reactions
• A chemical reaction involving the transfer of
one or more elections from one reactant to
another; also called oxidation/reduction
reactions
• In oxidation, a
substance loses
electrons, or is
oxidized
• In reduction, a
substance gains
electrons, or is
reduced (the
amount of
positive charge
is reduced)
Fig. 9-UN1
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
Fig. 9-UN2
becomes oxidized
becomes reduced
Reverse Process of Each Other
• Oxidative phosphorylation O2 reduced to
H2O using electrons donated by NADH or
FADH2 (Respiration)
• Photophosphorylation just the reverse,
H2O oxidized to O2 with electrons
accepted (Photosynthesis)
The Light-Dependent Reactions
• Photophosphorylation is the process of
creating ATP using a Proton gradient
created by the Energy gathered from
sunlight.
• Chemiosmosis is the process of using
Proton movement to join ADP and P.
• What is the function of NADPH?
• How is light energy converted into
chemical energy during photosynthesis?
• Can the complete process of
photosynthesis take place in the dark?
Explain your answer.