Chapter 4: Energy
From the sun to you in two easy 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
How cellular respiration converts food
molecules into ATP, a universal source of
energy
Alternative pathways to energy acquisition
4.1 Cars that run on french fry oil?
Organisms and machines need energy to
work.
What are biofuels?
One-year-old Willow Trees growing in an “energy
plantation” in upstate New York
Renewable Energy Source! Plants are Fuel and Food!
Where does
ethanol
come from?
How much
energy does
it take to
produce
ethanol fuel?
Where do
fossil fuels
come from?
Chemical Energy for food and fuel
Living cells
and
automobile
engines
use the
same basic
process to
make
chemical
energy
available
for work.
Chains of carbon and hydrogen atoms
Energy is stored in the bonds
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
These two processes are
cyclical.
How is photosynthesis related to the
Greenhouse Effect and Global Warming?
Photosynthesis
draws CO2 out of
the atmosphere
reducing its
ability to absorb
infrared energy
and generate
heat.
What is energy?
The capacity to do work
 Work = Moving matter against an opposing
force

Kinetic = energy
of motion, light
and heat
Potential = stored
energy that
results from the
location or
position of an
object
Chemical Energy
Food Calorie =
the amount of
energy that raises
the temperature
of 1 gram of water
by 1 degree
Celsius.
Calories on food
packages are
actually
kilocalories (1,000
calories).
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%?

First Law of Thermodynamics

Energy can never be created or destroyed.

It can only change from one form to another.

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.
4.4 ATP molecules are like
free-floating rechargeable
batteries in all living cells.
 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
Pop off the third phosphate group:
ATP  ADP + Phosphate group +
energy release
ATP
energizes
other
molecules
in cells by
transferring
phosphate
groups to
them.
Recycling in the Cell
ADP + phosphate group + energy = ATP
The ATP Cycle:
A working
muscle cell
recycles all of
its ATP once
each minute!
Plants do move! They move towards light.
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
“Photo” and “Synthesis”
3
inputs/reactants
2
outputs/products
How important are plants to human survival?
4.6 Photosynthesis takes place in the
chloroplasts
Chlorophyll
 Plant
pigment
 Absorbs
certain
wavelengths
of energy
(photons)
from the sun
 Absorbed
energy excites
electrons
Light energy is kinetic energy
made of particles called photons.
This
electron
is now
“excited”
This is the
chief way
energy moves
through cells,
as the
passing of
potential
energy from
molecule to
molecule.
4.9 Photosynthesis in detail:
the light “photo” and dark
“synthesis” (Calvin Cycle)
reactions
Focus on the big picture:
FOLLOW THE ELECTRONS!
An Electron Transport Chain
Is important to both photosynthesis and cellular respiration.
Excited electrons pump H+ ions across
the membrane, like water behind the
dam. The ATP Synthase enzyme is like
the hydroelectric generator making
electricity – makes ATP.
Some excited electrons are used to make
ATP and some are passed on to a highenergy electron carrier (NADPH).
The Calvin Cycle (Dark reactions)

Series of chemical
reactions

Occurs in stroma

Enzymes and
starting material
(5 carbon
molecule) are
recycled
Summary
of Photosynthesis
4.11 The battle against world hunger
can use plants adapted to water scarcity.
Stomata
Pores for gas exchange
The side effect is water loss!
How to get CO2 when stomata are shut?
•C3 photosynthesis uses a
3-carbon sugar as it’s
building block for glucose.
•C4 plants use a 4-carbon
sugar and produce a
“CO2-sticky tape” enzyme
to supplement CO2
uptake while stomata are
partially closed.
CAM plants 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
Even plants that are adapted for dry heat are suffering from
global warming.
The photosynthesis and cellular respiration equations
are opposites… if you know one you know the other.
The only difference is the type of energy.
Cellular Respiration:
1 Glucose (C6H12O6) + 6 O2
6 CO2 + 6 H2O + ATP
Photosynthesis:
4.12 How do living organisms fuel
their actions? Cellular respiration:
the big picture.
ATP is the powerhouse molecule!
Cellular Respiration


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Requires (1) fuel and
(2) oxygen.
Potential energy stored
in chemical bonds of
sugar, protein, and fat
molecules.
Breaks bonds to release
the high-energy
electrons captured in
ATP.
Oxygen is electron
magnet.
Three-Step
Process
Biggest ATP
“payoff” (90%)
occurs during the
electron transport
chain.
4.13 The first step of cellular
respiration: glycolysis is the universal
energy-releasing pathway.
Glycolysis: the universal energy-releasing
pathway
4.14 The second step of cellular
respiration: the Krebs cycle
extracts energy from Acetyl-CoA
in the form of ATP and highenergy electron carriers.
The product of glycolysis (pyruvate) is modified
using an Coenzyme A so that it can enter the
mitochondria and be used in the Krebs cycle
(Acetyl-CoA)
This is also the step where CO2 is released
(exhaled).
Input: Acetyl-CoA from Pyruvate
Outputs: CO2, ATP, and electron carriers.
4.15 The third step
in cellular respiration: ATP is built in
the electron transport chain.
Follow the Electrons,
as We Did in Photosynthesis
This proton concentration gradient
represents a significant source of
potential energy! Oxygen is the electron
magnet.
Summary of Cellular Respiration.
The 3 stages:
1. Glycolysis
2. Krebs
cycle
3. Electron
transport
4.16 Beer,
wine, and
spirits are
by-products
of cellular
metabolism
in the
absence of
oxygen.
Aerobic = presence of
oxygen
Anaerobic = absence of
oxygen – no electron
transport chain.
Fermentation produces a
different byproduct.
4.17 Eating a
complete diet:
cells can run
on protein and
fat as well as
on glucose.