Chapter 4: Energy
From the sun to you in just two steps
Lectures by Mark Manteuffel, St. Louis Community College
Learning Objectives
Understand and be able to explain the following:

How energy flows from the sun and through all life
on earth

How photosynthesis uses energy from sunlight to
make food
Learning Objectives
Understand and be able to explain the following:

How cellular respiration converts food molecules into
ATP, a universal source of energy

Alternative pathways to energy acquisition
Energy flows
from the sun and
through all life
on earth.
4.1 Cars that run on french fry oil?
Organisms and machines need energy to
work.
What are biofuels?
Q
Humans can get energy from
food. Can machines?
Biofuels and Fossil Fuels
 Chains
of carbon and hydrogen atoms
• Energy is stored in the bonds
 Animal
fats and oils
How do fuels provide energy?
 The
activities of living organisms are
fueled by breaking chemical bonds and
harnessing the released energy.
Energy Conversions
 All
life depends on capturing energy from
the sun and converting it into a form that
living organisms can use.
 Two
key processes
• Photosynthesis
• Cellular respiration
Take-home message 4.1
 The
sun is the source of the energy that
powers all living organisms and other
“machines.”
 The
energy from sunlight is stored in the
chemical bonds of molecules.
Take-home message 4.1
 When
these bonds are broken, energy is
released, regardless of whether the bond
is in a molecule of food, of a fossil fuel or
of a biofuel such as the oil in which french
fries are cooked.
4.2 Energy has two forms.
Kinetic and Potential
What is energy?
 The
capacity to do work
 Work
• Moving matter against an opposing
force
Kinetic Energy
 The
energy of
moving objects
• Heat energy
• Light energy
Potential Energy
A
capacity to do work that results from the
location or position of an object
 Concentration
energy
 Food
gradients and potential
has potential energy 
Chemical Energy
Take-home message 4.2
 Energy,
the capacity to do work, comes in
two forms.
Take-home message 4.2
 Kinetic
energy is the energy of moving
objects.
 Potential
energy, such as chemical energy,
is stored energy that results from the
position or location of an object.
4.3 As energy is captured and
converted, the amount of energy
available to do work decreases.
Energy Conversions
Only ~1% of the energy released by the sun that
earth receives is captured and converted by plants.
• Converted into chemical bond energy
 What happens to the other 99%?

Thermodynamics
The study of the transformation of energy
from one type to another
First Law of Thermodynamics
 Energy
 It
can never be created or destroyed.
can only change from one form to
another.
Energy Tax!


Every time energy is converted from one form to another the
conversion isn’t perfectly efficient.
Some of the energy is always converted to the least usable
form of kinetic energy: heat.
Second Law of Thermodynamics
 Every
conversion of energy includes the
transformation of some energy into heat.
 Heat
is almost completely useless to living
organisms
Take-home message 4.3
 Energy
is neither created nor destroyed
but can change form.
 Each
conversion of energy is inefficient,
and some of the usable energy is
converted to less useful heat energy.
4.4 ATP molecules are like
free-floating rechargeable
batteries in all living cells.
How do cells directly fuel their
chemical reactions?
 None
of the light energy from the sun can
be used directly to fuel cellular work.
 First
it must be captured in the bonds of a
molecule called adenosine triphosphate
(ATP).
Structure of ATP
ATP Molecules
 Cells
cannot use light energy directly to do
work.
 First,
the energy has to be converted into
chemical energy in ATP molecules.
Adenosine Triphosphate
 Pop off the third phosphate group
• ATP  ADP + Phosphate group + energy release
 Release
a little burst of energy!
 Use
this energy to drive chemical
reactions necessary for cellular
functioning.
• Building muscle tissue
• Repairing a wound
• Growing roots
Recycling in the Cell
ADP + phosphate group + energy = ATP
Take-home message 4.4

Cells temporarily store energy in the bonds of
ATP molecules.

This potential energy can be converted to kinetic
energy and used to fuel life-sustaining chemical
reactions.

At other times, inputs of kinetic energy are
converted to the potential energy of the energyrich but unstable bonds in the ATP molecule.
Photosynthesis
uses energy
from sunlight
to make food.
4.5 Where does plant matter come from?
Photosynthesis: the big picture.
From a seed
to a tree:
Where does
the mass
come from?
Photosynthetic Organisms
Photosynthesis: The Big Picture
3
inputs
2
products
Take-home message 4.5
 Through
photosynthesis, plants use water,
the energy of sunlight, and carbon dioxide
gas from the air to produce sugars and
other organic materials.
 In
the process, photosynthesizing
organisms also produce oxygen, which
makes all animal life possible.
4.6 Photosynthesis take place in
the chloroplasts
Organelles found in plant cells
A Closer Look at Chloroplasts
Take-home message 4.6
 In
plants, photosynthesis occurs in
chloroplasts, green organelles packed in
cells near the plants’ surfaces, especially
in the leaves.
4.7 Light energy travels in waves:
plant pigments absorb specific
wavelengths
Light Energy

A type of kinetic energy

Made up of little energy packets called photons
Light Energy

Different photons carry different amounts of
energy, carried as waves.

Length of the wave = amount of energy the
photon contains.
Electromagnetic Spectrum

Range of
energy that is
organized into
waves of
different
lengths.

Shorter the
wavelength,
higher the
energy.
Visible Spectrum
 Range
of energy humans see as light
 ROYGBIV
 Pigments
= molecules that absorb light
Chlorophyll
 Plant
pigment
 Absorbs
certain wavelengths of energy
(photons) from the sun
 Absorbed
energy excites electrons
Plant Pigments
 Plant
pigments can only absorb specific
wavelengths of energy
 Therefore,
plants produce several
different types of pigments
Plant Pigments
 Chlorophyll
a
 Chlorophyll
b
 Carotenoids
Take-home message 4.7
 Photosynthesis
is powered by light energy,
a type of kinetic energy made up from
energy packets called photons.
Take-home message 4.7
 Photons
hit chlorophyll and other lightabsorbing molecules in cells near the
green surfaces of plants.
 These
molecules capture some of the light
energy and harness it to build sugar from
carbon dioxide and water.
4.8 Photons cause electrons in
chlorophyll to enter an excited state.
Electron Excitation
 Conversion
of electromagnetic energy into
chemical energy of bonds between atoms
 Photons
of specific wavelengths bump
electrons up a quantum level into an
excited state
Two Potential Fates of Excited
Electrons
(1) Electrons return to their resting,
unexcited state.
(2) Excited electrons are passed to other
atoms.
The Passing of Electrons
in Their Excited State
 Chief
way energy moves through cells
 Molecules
that gain electrons always carry
greater energy than before receiving them
• Can view this as passing of potential energy from
molecule to molecule
Take-home message 4.8
 When
chlorophyll gets hit by photons, the
light energy excites an electron in the
chlorophyll molecule, increasing the
chlorophyll’s potential energy.
 The
excited electrons can be passed to
other atoms, moving the potential energy
through the cell.
4.9 Photosynthesis in detail:
the energy of sunlight is
captured as chemical energy.
FOLLOW THE ELECTRONS!
The “Photo” Part



Sunlight
ATP
A high-energy electron carrier
Electrons That Leave the
Photosystem Are Replenished
Where does oxygen come from?
An Electron Transport Chain
Connects the two photosystems
Product #1 of the “Photo” Portion
of Photosynthesis:
ATP
The Second Photosystem
 Follow
the electrons
Product #2 of the “Photo” Portion
of Photosynthesis:
NADPH
Products from the “Photo”
Portion
 ATP
and NADPH
 Time
for the “synthesis” part!
Take-home message 4.9
 There
 The
are two parts of photosynthesis.
first is the “photo” part, in which light
energy is transformed into chemical energy,
while splitting water molecules and
producing oxygen.
Take-home message 4.9
 Sunlight’s
energy is first captured when an
electron in chlorophyll is excited.
 As
this electron is passed from one molecule
to another, energy is released at each
transfer, some of which is used to build the
energy-storage molecules ATP and NADPH.
“SYNTHESIS”
4.10 Photosynthesis in detail:
the captured energy of
sunlight is used to make food.
The Calvin Cycle

Series of
chemical
reactions

Occurs in
stroma

Enzymes are
recycled
The Processes in the Calvin Cycle
Occur in Three Steps:
Take-home message 4.10
 The
second part, or “synthesis” part, of
photosynthesis is the Calvin cycle, and it
occurs in the stroma of the chloroplast.
Take-home message 4.10
 During
this phase, carbon from CO2 in the
atmosphere is attached (fixed) to
molecules in chloroplasts, sugars are built,
and molecules are regenerated to be used
again in the Calvin cycle.
 The
fixation, building, and regeneration
processes consume energy from ATP and
NADPH (the products of the “photo” part
of photosynthesis).
4.11 The battle against world
hunger can use plants adapted to
water scarcity.
Evolutionary Adaptations
 Some
plants thrive in hot, dry conditions
 Adaptations
that reduce evaporative water
loss
• How do plants use water?
Stomata
Pores for gas exchange
How to get CO2 when stomata are shut?
C4 Photosynthesis
• C4 plants produce ultimate “CO2-sticky
tape” enzyme.
• C4 photosynthesis adds an extra set of
steps.
CAM Photosynthesis
 Close
stomata during hot dry days
 At
night, stomata open, CO2 let in and
temporarily bound to a holding molecule
 During
day, CO2 gradually released and
used while stomata are closed
All Three Photosynthetic Pathways
Take-home message 4.11
 C4
and CAM photosynthesis are
evolutionary adaptations at the
biochemical level that, although more
energetically expensive than regular (C3)
photosynthesis, allow plants in hot, dry
climate to close their stomata and
conserve water without shutting down
photosynthesis.
Cellular respiration
converts food
molecules into
ATP,
a universal source
of energy for living
organisms.
4.12 How do living organisms
fuel their actions?
Cellular respiration: the big
picture.
Cellular
Respiration
The big picture
A Human Example
Eat food
 Digest it
 Absorb nutrient molecules into bloodstream
 Deliver nutrient molecules to the cells


At this point, our cells can begin to extract
some of the energy
• stored in the bonds of the food molecules
Take-home message 4.12
 Living
organisms extract energy through a
process called cellular respiration, in which
the high-energy bonds of sugar and other
energy-rich molecules are broken, releasing
the energy that went into creating them.
Take-home message 4.12
 The
cell captures the food molecules’ stored
energy in the bonds of ATP molecules.
 This
process requires fuel molecules and
oxygen, and it yields ATP molecules, water,
and carbon dioxide.
4.13 The first step of cellular
respiration: glycolysis is the universal
energy-releasing pathway.
Glycolysis: the universal energy-releasing
pathway
Glycolysis
Three of the ten steps yield energy
– quickly harnessed to make ATP.
High-energy electrons are transferred to NADH.
Net result:
 each
glucose molecule broken down into two
molecules of pyruvate
 ATP molecules produced
 NADH molecules store high-energy electrons
Take-home message 4.13
 Glycolysis
is the initial phase in the
process by which all living organisms
harness energy from food molecules.
 Glycolysis
occurs in a cell’s cytoplasm and
uses the energy released from breaking
chemical bonds in food molecules to
produce high-energy molecules, ATP and
NADH.
4.14 The second step of
cellular respiration: the Krebs
cycle extracts energy from
sugar.
The
Preparatory
Phase to the
Krebs Cycle
Payoff from the Krebs cycle:



ATP
NADH
FADH2
Take-home message 4.14
A
huge amount of additional energy can
be harvested by cells after glycolysis.
 First
the end-product of glycolysis,
pyruvate, is chemically modified.
 Then,
in the Krebs cycle, the modified
pyruvate is broken down step-by-step.
Take-home message 4.14
 This
breakdown process releases carbon
into the atmosphere (as CO2) as bonds are
broken, and captures some of the
released energy in two ATP molecules and
numerous high-energy electron carriers
for every glucose molecule.
4.15 The third step
in cellular respiration:
ATP is built in the electron
transport chain.
Mitochondria
 Two
key features of mitochondria are
essential to their ability to harness energy
from molecules:
• Feature 1: mitochondrial “bag-within-a-bag”
structure
• Feature 2: electron carriers organized within the
inner “bag”
The
“bag-withina-bag”
Follow the Electrons… (just as we did
in photosynthesis)
#2) This proton concentration
gradient represents a significant
source of potential energy!
Proton Gradients
and Potential Energy
The force of the flow of H+ ions fuels the
attachment of free-floating phosphate
groups to ADP to produce ATP.
Take-home message 4.15
 The
largest energy payoff of cellular
respiration comes as electrons from NADH
and FADH2 produced during glycolysis and
the Krebs cycle move along the electron
transport chain.
Take-home message 4.15
 The
electrons are passed from one carrier
to another and energy is released,
pumping protons into the intermembrane
space.
 As
the protons rush back to the inner
mitochondrial matrix, the force of their
flow fuels the production of large amounts
of ATP.
4.16 THIS IS HOW WE DO IT
Can we combat the fatigue
and reduced cognitive
functioning of jet lag with
NADH pills?
Pure or Basic Science
and Applied Science
• What is jet lag and why is it of
scientific interest?
• How is jet lag related to cellular
respiration?
Why should NADH alleviate
symptoms of jet lag?
• If levels of NADH could be increased by
taking the molecule in pill form, this might
lead to increased production of usable
energy through the electron transport
chain.
• Testable prediction:
– “Supplementing NADH should counteract
some of the effects of jet lag, including
reduced cognitive functioning and fatigue.”
Experimental Setup
• The researchers used a randomized,
controlled, double-blind experimental
design.
• 2 groups: Placebo or NADH
• Battery of tests
• Overnight “red-eye” flight
• Retesting
Did NADH reduce the
symptoms of jet lag?
1. Vigilance
 Placebo: 37% of subjects made
omission errors.
 NADH: 14% of subjects made omission
errors.
Did NADH reduce the
symptoms of jet lag?
2. Working memory
 Placebo: Subjects answered 6.8 more
problems per minute than in the
baseline test.
 NADH: Subjects answered 13.2 more
problems per minute than in the
baseline test.
Did NADH reduce the
symptoms of jet lag?
3. Multi-tasking
 Placebo: Subjects increased performance by
19.2 points over baseline.
 Subjects’ reaction time was slower than
baseline by 0.44 seconds.
 NADH: Subjects increased performance by
77.5 points over baseline.
 Subjects’ reaction time was faster than
baseline by 0.15 seconds.
Did NADH reduce the
symptoms of jet lag?
4. Visual perception
 Placebo: Subjects completed 1.4 more
items per minute than at baseline.
 NADH: Subjects completed 5.4 more
items per minute than at baseline.
Did NADH reduce the
symptoms of jet lag?
5. Sleepiness
 Placebo: 75% of subjects reported
increased sleepiness.
 NADH: 25% of subjects reported
increased sleepiness
What conclusions can we draw
from these results?
• The researchers’ conclusion, supported by
the evidence, was that “NADH appears to
be a suitable short-term countermeasure
for the effects of jet lag on cognition and
sleepiness.”
Take-home message 4.16
• The symptoms of jet lag—including
fatigue, memory loss, and reductions in
cognitive performance—can impair the
performance of people in many
professions today.
Take-home message 4.16
• The results of a randomized, controlled,
double-blind study support the hypothesis
that an NADH supplement may be a
suitable short-term countermeasure for
these effects.
There are
alternative
pathways to
energy
acquisition.
4.17
Beer, wine, and
spirits are byproducts of
cellular
metabolism in
the absence of
oxygen.
Take-home message 4.17
 Oxygen
deficiency limits the breakdown of
fuel because the electron transport chain
requires oxygen as the final acceptor of
the electrons generated during glycolysis
and the Krebs cycle.
Take-home message 4.17
 When
oxygen is unavailable, yeast resort
to fermentation, in which they use a
different electron acceptor, pyruvate, and
in the process generate ethanol, the
alcohol in beer, wine, and spirits.
4.18
Eating a
complete diet:
cells can run
on protein and
fat as well as
on glucose.
Take-home message 4.18
 Humans
and other organisms have
metabolic machinery that allows them to
extract energy and other valuable
chemicals from proteins, fats, and
carbohydrates in addition to the simple
sugar, glucose.
Learning Objectives
Understand and be able to explain the following:




How energy flows from the sun and through all life
on earth
How photosynthesis uses energy from sunlight to
make food
How cellular respiration converts food molecules into
ATP, a universal source of energy
Alternative pathways to energy acquisition