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Chapter 4: Energy
From the sun to you in two easy steps
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
Objectives
Both organisms and machines need energy to
work
When we burn gasoline, we break the bonds
between carbon and hydrogen atoms, releasing
CO2, H2O, and a lot of energy.
The activities of living things is also fueled by
breaking the chemical bonds in food molecules
and harnessing the 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
Photosynthesis: the process by which plants
capture energy from the sun and store it in the
chemical bonds of sugars and other food
molecules they make
Cellular respiration: the process by which all living
organisms release the energy stored in the
chemical bonds of food molecules and use it to
fuel their lives.
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.
What is energy?
Definition of energy: The capacity to do work.
Work is anything that involves moving matter
against an opposing force.
4.2
Energy has two forms.
Kinetic and Potential
Kinetic Energy
The energy of moving objects
Kinetic energy examples
Heat energy: lots of molecules moving rapidly
Light energy: moving photons of light
Mechanical energy: turning wheels, gears, levers, etc.
Electrical energy: moving electrons through a conductor.
Potential Energy
Stored energy. A capacity to do work that results from the location or
position of an object.
Examples of Potential Energy
Mechanical energy: A wound-up spring
Electrical energy: a charged battery.
Food also is potential energy in the form of stored
chemical energy.
Chemical Energy
Briefly…
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 can never be created or destroyed.
It can only change from one form to another.
All the energy now present in the universe has been there since the
universe began.
This energy can be transformed from one form of energy into another.
In all our eating and growing, driving and sleeping, we are simply
transforming energy.
The energy stored in the gasoline is chemical energy. When it is ignited in the engine, it
combusts, and the explosion drives the piston which turns the wheels. It also creates
heat in the engine. So chemical energy is changed to two other forms, mechanical
and heat energy.
In automobiles, for example, about three-quarters of the energy in
gasoline is lost as heat.
Thus, for every $10 spent on gas, only about $2.50 goes toward moving
the car!
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 as a form of
fuel for their cells.
The second law of thermodynamics tells us that although the quantity
of energy in the universe is not changing, its quality is.
Little by little, the amount of energy that is available to do work
decreases.
Summarizing
Energy is neither created nor destroyed but can change forms.
Each conversion of energy is inefficient and some of the usable
energy is converted to less useful heat energy.
Now that we understand that organisms on earth cannot capture every
single bit of energy released by the sun—and that energy conversions
are inefficient—we can look at the chief energy currency of the cell:
ATP.
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).
ATP acts like a rechargeable battery that temporarily
stores energy that can then be used for cellular work in
plants, animals, bacteria, and all the other organisms
on earth.
The three phosphate groups in ATP make it effective in carrying and storing
energy for a short time.
The bonds between the phosphate groups contain a large amount of energy.
These bonds are also unstable. With the slightest push, one of the phosphate
groups will pop off, releasing a little burst of energy that the cell can use.
Adenosine Triphosphate
Pop off the third phosphate group
ATP ADP + Phosphate group + energy release
This energy is used to drive chemical reactions necessary for
cellular functioning.
Building muscle tissue
Repairing a wound
ATP Molecules
Cells cannot use light energy directly to do work.
First, the energy has to be converted into chemical energy (energy
stored in chemical bonds), a type of potential energy in ATP
molecules.
An organism can then use ADP, a free-floating phosphate, and an input
of kinetic energy to rebuild its ATP stocks.
Recycling in the Cell
ADP + phosphate group + energy = ATP
In a Nutshell…
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 can be converted to the potential
energy of the energy-rich but unstable bonds in the ATP molecule.
In five years a tree in a big planter can increase its weight by 150
pounds as it grows .
From a seed to a tree: Where does the mass come from?
Plants aren’t the only photosynthesizers.
Some bacteria and many other unicellular organisms are also capable of using the
energy in sunlight to produce organic materials.
Photosynthetic Organisms
Photosynthetic Organisms
Photosynthesis: The Big Picture
3 inputs or raw materials:
Sunlight
Water
Carbon dioxide
2 outputs or end products:
Oxygen
Sugar
“Photo” and “Synthesis”
Photosynthesis is two separate events: a “photo” segment, during which light is
captured, and a “synthesis” segment, during which sugar is synthesized.
Take-home message
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,
the light-harvesting organelles of plant cells.
The chloroplast is filled with a fluid called the stroma.
Floating in the stroma is an elaborate system of interconnected membranous
structures called thylakoids.
The conversion of light energy to chemical energy—the “photo” part of
photosynthesis—occurs inside the thylakoids. (This is also called the
“light” reaction because light energy is needed.)
The production of sugars—which are made in the “synthesis” part of
photosynthesis—occurs within the stroma. (This is also called the
“dark reaction” or light independent reaction because light is not
needed here.)
Take-home message 4.6
In plants, photosynthesis occurs in chloroplasts, a green organelle
packed in cells near the plants’ surfaces.
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
Shorter the wavelength, higher the energy of the photon.
Visible Spectrum
Visible Spectrum: Range of energy humans see as light
ROYGBIV (colors of the rainbow from longest wavelengths to
shortest).
Humans (and some other animals) can see colors because our eyes
contain light-absorbing molecules called pigments.
Chlorophyll
Plant pigments are in the thylakoid membrane. They also make
use of the visible spectrum.
These pigments absorbs certain wavelengths of energy.
Absorbed energy excites electrons in the pigments, and is
converted to kinetic energy.
Plant Pigments
Plant pigments can only absorb specific wavelengths of energy
Therefore, plants produce several different types of pigments to
maximize absorption.
Plant Pigments
Chlorophyll a:
Chlorophyll b:
Carotenoids:
Chlorophyll is essential for photosynthesis to take place,
especially chlorophyll a.
Photosynthesis is powered by light energy, a
type of kinetic energy made up from energy
packets called photons.
In summary 4.7
Photons hit chlorophyll and other light-absorbing
molecules near the green surfaces of plants.
These molecules capture the light energy and
harness it to build sugar from carbon dioxide and
water.
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
Or excited electrons pass on the energy, causing
other electrons to be excited.
Excited electrons can be passed to other atoms.
The passing of electrons from molecule to molecule is one of the chief
ways that energy moves through cells.
The “Photosystem Machine”:
Photosystems are arrangements of light-capturing pigments in the
thylakoids. They capture and store light energy in an ATP molecule
and another molecule called NADPH.
The electrons in ATP and NADPH
sugar molecules.
are later used to build
Why must plants get water for photosynthesis to occur?
Photosystem pigments loose their electrons when
they pass them along. The replacement electrons
come from water, when water is split into
hydrogen and oxygen.
The splitting of water produces the free oxygen that makes
up 20% of the atmosphere.
Summary
There are two parts of photosynthesis.
The first is the “photo” part, in which light energy is transformed
into chemical energy while splitting water molecules and
producing oxygen.
Summary
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.
Products from the “Photo” Portion
ATP and NADPH
Time for the “synthesis” part!
“SYNTHESIS”
The “synthesis part of photosynthesis takes place in a
series of chemical reactions called the Calvin cycle.
The Calvin Cycle
Series of chemical reactions
Occurs in stroma
The enzyme rubisco plucks carbon atoms from carbon dioxide
molecules in the air. The carbon atoms are used to make sugar.
NADPH and ATP supply the energy.
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.
Carbon dioxide and an enzyme rubisco are used to build sugar,
using energy from NADPH and ATP.
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 include
Closing pores on their leaves to reduce evaporation of water.
These pores are called stomata
Pores for gas exchange
How to get CO2 when stomata are shut?
Closing the stomata solves one problem for plants (too much water
evaporation) while it creates another: with the stomata shut, carbon
dioxide cannot enter them, nor oxygen leave.
If there are no carbon molecules for sugar production, the Calvin cycle
tries to fix carbon but instead finds only oxygen.
Plant growth comes to a standstill and crops fail.
Some plants, including corn and sugarcane, have evolved a process that minimizes
water loss but still enables them to make sugar when the weather is hot and
dry.
These plants use C4 Photosynthesis
C4 plants produce ultimate “CO2-sticky tape” enzyme. It can bind
to CO2 even if concentrations are low. The stomata need only
be open a tiny bit.
A third and similar method of carbon fixation, called CAM (for
crassulacean acid metabolism), is also found in hot dry areas.
In this method, the plants close their stomata during the hot dry days.
At night, they open the stomata and let CO2 into the leaves, where it binds
temporarily to a holding molecule. Cactus and pineapple are examples.
Both C4 and CAM photosynthesis is a little more energetically
expensive than C3 photosynthesis for a plant, so they are only
an adaptive advantage in hot dry climates.
All Three Photosynthetic Pathways
Summary
C4 and CAM photosynthesis are evolutionary adaptations at the
biochemical level that, although being more energetically
expensive than C3 photosynthesis, allow plants to close their
stomata and conserve water without shutting down
photosynthesis.
4.12 How do living organisms fuel their
actions? Cellular respiration.
All living organisms extract energy from the
chemical bonds of molecules (which can be
considered “food”) through a process called
cellular respiration.
This process is a bit like photosynthesis in reverse. In cell respiration,
plants and animals break down the chemical bonds of sugar and
other energy-rich food molecules to release the energy. The simple
equation for breaking down sugar.
Oxygen + Sugar
carbon dioxide + water + ATP
Cellular Respiration
Remember ATP Molecules?
ATP supplies energy in the form of electrons to biochemical
reactions in the cell.
To generate energy as ATP, fuels such as glucose and other
carbohydrates, proteins, and fats are broken down in cellular
respiration in three steps:
(1) glycolysis,
(2) the Krebs cycle, and
(3) the electron transport chain.
Cellular Respiration
The big picture
4.13 The first step of cellular respiration: glycolysis is
the universal energy-releasing pathway.
Glycolysis: literally means the splitting of glucose.
Glycolysis
Glucose is broken down to yield two molecules of a substance called pyruvate in
the cytoplasm of the cell.
4.14 The second step of cellular respiration:
the Krebs cycle extracts energy from sugar.
Pyruvate is transformed to a large molecule called acetyl-Co-A.
Acytyl Co-A enters the Krebs cycle in the mitochondria, binding to
an enzyme.
The Krebs cycle tears the molecule apart, yielding carbon dioxide
and some high energy molecules of ATP, NADH and FADH2.
Payoff from the Krebs cycle:
ATP
NADH
FADH2
These will be used in the 3
rd
step.
4.15 The third step
in cellular respiration: ATP is
built in the electron transport chain in large
quantities. Water is also generated here.
In the Three-Step Process
Glycolysis breaks down glucose to pyruvate.
Pyruvate is transformed to acetyl-CoA and enters
the Krebs cycle.
The Krebs cycle breaks down Acetyl Co-A to make ATP,
NADH, and FADH2
These three molecules plus oxygen enter the next step. The electron
transport chain generates lots of ATP and some water.
If you run or swim as fast as you can, you soon feel a burning sensation in your
muscles. This is caused by lactic acid buildup.
The mitochondria cannot complete normal cell respiration without oxygen.
Instead cells have a back-up method for breaking down sugar.
In the absence of oxygen pyruvate forms lactic acid in animals.
Yeast use a special form of glycolysis called fermentation
to produce ethanol.
Yeast produce alcohol only in the absence of oxygen. That is why the
fermentation tanks used in producing wine, beer, and other spirits
are built specifically to keep oxygen out.
Take-home message 4.17
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.
Review questions
Define the following terms:
Cellular respiration
Energy
First law of thermodynamics
Photosynthesis
Second law of thermodynamics
Potential energy
Kinetic energy
Review questions
In text 2nd edition.
Do multiple choice questions at end of chapter:
all except 7 and 16.
Fill in the blank or multiple choice:
Part 1 Introduction to Energy:
Stored energy is __________________. The energy of motion is
__________________. Food is a form of ________ energy.
Energy is (definition)_____________________________. Energy can change form but
is not lost is the _______________ law of thermodynamics. When energy changes
form, some heat is released. This is the ___________ law of thermodynamics. The
least usable form of energy to life is __________________.
Burning gasoline for energy is similar to getting energy from food because
in both activities we must _______________ in molecules to get the
energy.
The _____ is the source of energy to power living things. (Hint, a celestial
object)
Life is dependent on energy from _______. The two key processes life
uses to convert energy are ______ and ______.
Cells temporarily store energy in the bonds of what “battery” molecule?
_______
An overview of Cellular Respiration:
In the breakdown of sugar, what molecules are the input? ________ and
________.
The output molecules are _____, _______, and ________.
The three steps of cellular respiration.
The first step in cellular respiration is called ______________________.
The input for it is ___________________________.
The output is __________________
The growth in mass of a tree over time can be accounted for mostly from its intake of A) water B) carbon
dioxide gas C) minerals from the ground.
What are the 3 inputs into photosynthesis?
______, _______, and _________.
What are the two outputs? ______, _____.
The kinetic energy to power photosynthesis comes from light “particles” called ________.
The “photo” or light reaction part of photosynthesis takes place in what part of the chloroplast? ________.
Name three light absorbing pigments in the leaf?
Why does a plant have more then one light absorbing pigment? Which one is absolutely essential for it to
have?
At which of the above steps is water split and oxygen produced as a waste
product? __________________. A) “Photo” or light reaction B)
“Synthesis” or dark reaction
At which step is carbon dioxide used to build glucose?
__________________ A) “Photo” or light reaction B) “Synthesis” or dark
reaction
At which step is G3P produced? _____________________.A) Krebs cycle
B) Calvin cycle. G3P is used to build _________.
In cellular respiration, the input or raw materials are ___________________________.
The output or end products are _________________________________.
The first step in cellular respiration is called ______________________.
The raw material for it is __________________.
The end product is __________________
At what step is cell respiration is carbon dioxide produced? ________________
At what step in cell respiration is oxygen used and water produced? _________
The “battery molecule” in which cells temporarily store energy is called ________.
All of the steps in cell respiration produce some ATP, but which step of cell respiration produces most of
the ATP? _____________.
True or false? Only glucose can participate in cellular respiration. Proteins and fats cannot provide raw
materials to make ATP in cell respiration. Justify your answer.
Why might oxygen be considered a “waste product” of photosynthesis? Why is this important to life on
earth?
In the absence of oxygen, cell respiration in yeast produces via glycolysis the byproduct ________. In the
absence of oxygen, cell respiration in your muscles produces the byproduct ________ which makes
your muscles sore.
In what ways are C3, C4, and CAM plants different regarding how they use their stomates? What is the
adaptive value of C4 and CAM photosynthesis over that of C3? What adaptive value does C3
photosynthesis have over the other two?
Multiple choice
. What are the raw materials of photosynthesis?
A) water and carbon dioxide
B) glucose, water, and oxygen
C) glucose and carbon dioxide
D) water and oxygen
E) water, carbon dioxide, and oxygen
A necessary pigment for photosynthesis to occur is
A) anthocyanin
B) carotene
C) xanthophylls
D) chlorophyll
e) chloroplast
Glucose is split into two three-carbon pyruvates in what stage of cellular respiration?
A) Kreb’s cycle
B) Chemiosmosis
C) chemosynthesis
D) Glycolysis
E) Electron Transport Chain
. Glycolysis occurs
A) inside the mitochondrion
B) inside the chloroplast
C) outside the mitochondrion
D) inside the nucleus
E) inside the Golgi
. Carbon dioxide is generated out of which step in cellular respiration?
A) Calvin cycle
B) Krebs cycle
C) Glycolysis
D) Electron Transport Chain
E) Chemiosmosis