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Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz
Biology for a
Changing World
SECOND EDITION
Lecture PowerPoint
CHAPTER 5
Energy Flow and Photosynthesis
Copyright © 2014 by W. H. Freeman and Company
Stuff to understand
1. What things do photosynthesis
2. Why is photosynthesis important to ecosystems
3. List the types of energy & what types are involved
in photosynthesis
4. How does photosynthesis convert energy from
sunlight into energy stored in energy filled
molecules
Energy basics
• Energy = capacity to do work
– Making molecules
– Moving stuff in and out of cells
• Without a constant source of energy, all life on Earth would
stop (new energy always being added to system)
Types of Energy
• Kinetic energy - the energy of motion or
movement (e.g. photons of light moving)
– Heat - the kinetic energy generated by random movement of
molecules or atoms
• Potential energy - stored energy in the
chemical bonds
Energy basics
• Autotrophs don’t create energy, they convert it
Light reactions convert sunlight
To chemical energy
kinetic energy
potential energy
• Chemical energy
– potential energy stored in chemical bonds
– break bonds to release energy
potential energy
Energy basics
• Humans and other animals obtain energy by
eating food (we’re heterotrophs)
• Chemical energy
potential energy is stored in bonds of biological
molecules
break bonds to release – and use – energy
Two kinds of reactions
• Anabolic uses energy to Add atoms (build molecules)
• Catabolic reactions Cut bonds & release energy
Energy basics
• Algae and plants get energy from sun
• Trap energy and store it in molecules
• lots of biofuel stuff in this chapter.
will discuss @ end of powerpoint
Sunlight energy
Light energy is the
energy of the
electromagnetic
spectrum of
radiation
Sunlight energy
• Light energy is made
of particles called
photons, or packets
of light energy
• Photons of different
wavelengths
contain different
amounts of energy
Photosynthesis: a closer look
• Chlorophyll is a
pigment present
in the green parts
of plants
• It absorbs
photons of light
energy
Photosynthesis Overview
Sun’s energy  chemical energy used to
make complex molecules (anabolic RX)
Energy transformation is
not efficient
• With each energy
transformation, some
energy is lost as heat
• Every transformation
looses some energy
• This is why we need to
keep supplying energy
to any system
Nutrients cycle, energy passes through
Photosynthesis (one of two opposite paths)
Next powerpoint
Energy: two major paths
Photosynthesis:
Cellular
Respiration:
• Most producers (autotrophs) do both
• Most consumers (Heterotrophs) don’t use
photosynthesis
• BOTH PATHS USE ELECTRON TRANSPORT
CHAINS
Where do we find
photosynthesis
Most common in these three kingdoms
1. Bacteria
2. Plants
3. Protists
Biology always has weird exceptions
 pea aphids!!
Photosynthesis (producers)
• most ecosystems based on photosynthesis
• Photosynthesizers are producers
• Consumers must eat
Producers (autotrophs)
• Take energy from the environment, store it in
molecules they make
Chemosynthesis – less common
Photosynthesis = uses light to make sugar (it is G3P!!!)
• Photosynthesis Overview:
Inputs
Outputs
• Use own sugars for their OWN respiration
Eukaryotes use mitochondria for respiration
Molecular Energy Carriers: ATP
Adenosine triphosphate (ATP)
ATP is the main energy source of cell
• Requires energy
– Photosynthesis
– Respiration
Molecular Energy Carriers
• ATP (used for MANY types of reactions)
• NADPH (some energy for anabolic
reactions)
• NADH (absorbs energy released in
catabolic)
NADPH & NADH
– NADPH: electrons & hydrogen to anabolic
react.
– NADH: picks up electrons and hydrogen
released from catabolic reactions
Leaves
• Stomata – how plants
“breath”
Take in CO2, release O2
(opposite of respiration)
carbon dioxide to make sugars
• Many cells full of
Chloroplasts
Photosynthesis organelle
Calvin Cycle (sugar
production) happens
here
Light: energy to make Carbohydrates
• Chloroplast – photosynthesis organelles
for plant/algae
• Have chlorophyll to absorb light energy
Light reactions – make energy molecules
Calvin cycle – make sugars
Photosynthesis: a two stage process
You must know “light reactions” and “Calvin Cycle”
Photosynthesis: Two Stages
Photosynthesis stages:
1. Light reactions
Use light energy to make ATP, NADPH, and
break water
broken water molecules: source of oxygen
2. Calvin cycle
CO2  sugar using energy from ATP and NADPH
Entire ecosystem depends on this sugar!!!
Chloroplasts
• Light reactions in Thylakoids
• The Calvin cycle (CO2  sugar) in
stroma
Thylakoid space = where we put the hydrogen
First Stage: the light reactions
This is where we make ATP
Light Reaction: 1st Part
• Photons of light are
absorbed by chlorophyll
• Electrons in the chlorophyll
atoms become “excited”
• Excited electrons help
generate an energycarrying molecule known
as adenosine triphosphate
(ATP)
• ATP will be used in the
Calvin Cycle to make sugar
Light Reactions:
energy from light excites electrons
Electron  electron transport chains
PS II happens 1st!!
Chloroplast: Light Reactions
• Light-absorbing molecules in thylakoid
membrane collect energy from sunlight
• Absorbed light gives energy to electron
• Chloroplast ETC plays “hot potato” with electron
• Uses energy to pump protons (hydrogen ions)
Chloroplast: Light Reactions
Thylacoid membranes full of hydrogen ions
1.
2.
From splitting water
From chloroplast electron transport chain
Making ATP : movment of H+ ions
Thylacoid membranes full of hydrogen ions
H+ wants to move: high concentration 
low
H+ movement = energy (like water wheel)
The movment of hydrogen
ions powers the production
of ATP (“ATP synthesis”) and
NADPH
Making Oxygen: byproduct
Splitting water frees Oxygen
Two broken H20 molecules
Two free oxygens combine
O + O  O2
Oxygen Gas
Needed for all life on earth!!!
Chloroplasts
1. Light reactions in Thylacoids
2. The Calvin cycle (CO2  sugar) in
stroma
Uses ATP made by
light reactions!!!
Calvin Cycle: 2nd Part
• Photosynthesis
captures carbon
dioxide gas from
the air
• Incorporates
carbon atoms into
sugar (G3P!!!)
• “Carbon fixation”
Carbon fixation
• Conversion of
inorganic gaseous
carbon into an
organic molecule
• Sugars used by
autotrophs and
heterotrophs
• Main way carbon
enters the global
energy chain
Calvin Cycle: making sugars
• Part 2 of photosynthesis
• Happens in Stroma
• Uses carbon dioxide from air
“carbon fixation”
• Makes a three carbon sugar
glyceraldehyde 3-phosphate (G3P)
• Depends on an enzyme nickname “Rubisco”
Rubisco picks up the incoming CO2
Calvin Cycle: making sugars
• Calvin Cycle needs energy
• Fixes one carbon each cycle
3 cycles to make each 3 carbon sugar (G3P)
• G3P is the building block of all
carbohydrates
G3P: building block of sugars
• G3P is the building block of glucose and
all the other carbohydrates
• Leaves chloroplast, fuel chemical
reactions
• In plants, G3P can be stored as starch for
use at night
Photosynthesis: a two stage process
You must know “light reactions” and “Calvin Cycle”
Hot or try conditions stress plants
Heat and low humidity increase water loss
Plants will die if they don’t have enough water
Closing the Stomata can
reduce water loss…
…but CO2 down & O2 up
Plants need to take in
CO2 to make sugars!!!
Oxygen messes up RUBISCO
ATP used to make sugar
ATP used to fix RUBISCO!!
Photorespiration wastes the plant’s energy, makes it
harder to grow in hot or dry conditions
Other ways to do photosynthesis
keep the oxygen away from the rubisco!!!
Using algae to make fuel
• Algae are best known for the green, red, or brown
hues
• Also have ability to capture energy of sunlight and
convert it into usable forms of energy
• Much is in the form of oils ideally suited to making
fuel
costs, benefits, and sustainability?
Copyright © 2014 by W. H. Freeman and Company
Fossil fuels are limited
• Demand for oil will increase over next 25 years
• Sources of oil are finite
• Takes millions of years to replenish
U.S. energy consumption
• The United
States is the
largest
consumer of
fossil fuels
• New energy
sources being
developed to
reduce our
demand
Energy basics
Biofuels
• Renewable fuels made from living organisms
• In 2012, more than 150 companies were
dedicated to making fuel from algae
How green are biofuels?
Summary
• All living organisms require energy to live and grow. The ultimate
source of energy on Earth is the sun.
• Energy is neither created nor destroyed, but converted from one
form to another. Kinetic energy is the energy of motion and
includes heat energy and light energy. Potential energy is stored
energy and includes chemical energy.
• Photosynthesis is a series of chemical reactions that captures the
energy of sunlight and converts it to chemical energy in the form
of sugar and other energy-rich molecules.
• Photosynthetic organisms are known as autotrophs. MOST
animals do not photosynthesize; they are known as heterotrophs.
Not Happy with your grade?
Not understanding the material?
Remember that the TLCC has
Free Biology Tutoring