Transcript Chapter 5 - SchoolRack

Michèle Shuster • Janet Vigna • Gunjan Sinha • Matthew Tontonoz
Biology for a
Changing World
FIRST EDITION
Intro to Biology
Dr. Steve Schwendemann
CHAPTER 5
Energy Flow and Photosynthesis
Copyright © 2012 by W. H. Freeman and Company
Chapter 5
Mighty Microbes
Copyright © 2012 by W. H. Freeman and Company
U.S. Energy Consumption
• The United States is the largest consumer
of fossil fuels.
Energy Basics
• Energy is the capacity to do work.
Cellular work includes processes such as
building complex molecules and moving
substances in and out of the cell.
• Without a source of energy, all life on
earth would stop.
Energy Basics
• Energy cannot be created, so organisms
must obtain it from an outside source.
Humans and other animals obtain the energy
they need by eating food.
• Food contains chemical energy – potential
energy stored in the bonds of biological
molecules. Breaking these bonds releases
that stored energy, making it available to
power cell functions.
Energy Basics
• Algae are very
efficient
energy
converters –
the oil they
produce is rich
in chemical
energy. All
they need to
make this oil is
sunlight,
carbon
dioxide, water,
nitrogen, and
phosphorus.
Energy is conserved
• Energy cannot
be created or
destroyed.
When energy
is transferred
from food or
fuel to the
organisms or
products that
use it, that
energy
changes form.
This principle is
known as the
“conservation
of energy.”
Energy is conserved
• A cereal bar
contains potential
energy (stored
energy) in the
chemical bonds
that hold the
molecules of that
bar together.
Energy is conserved
• When a
cyclist eats
and digests
the bar,
digestion
breaks those
chemical
bonds, and
the stored
potential
energy is
released.
Energy is conserved
• As the cyclist
climbs a hill, his
body converts this
potential energy
into the kinetic
energy (the energy
of motion or
movement) of
muscle contraction
and heat (the
kinetic energy
generated by
random movement
of molecules or
atoms).
Energy is conserved
• At the top of the
hill, the cyclist
relies on
potential
energy to get
him downhill.
His relatively
higher position
means that he
has “positional”
potential
energy.
Energy is conserved
• As the cyclists
coasts down
the hill, the
friction of the
wheels on the
ground
converts his
positional
potential
energy into the
kinetic energy
of moving
wheels and
heat.
Energy is conserved
• From the
cereal bar to
the spinning
wheels,
energy is
converted
from one
form into
another.
With every
conversion,
some energy
is lost as
heat.
Energy transformation is not
efficient
• The conversion of
energy from one
form to another
isn’t 100% efficient.
With each energy
transformation, a
bit of energy is lost
to the environment
as heat.
• This inefficiency is
the reason we
need to keep
supplying energy to
any system.
Capturing energy:
Photosynthesis
• For almost all living things on earth, the
ultimate source of energy is the sun.
• Autotrophs are organisms such as plants,
algae, and certain bacteria that capture
the energy of sunlight by photosynthesis.
• Heterotrophs are organisms that obtain
energy by eating other organisms.
Capturing energy:
Photosynthesis
• Photosynthesis is the process by which
plants and other autotrophs use the
energy of sunlight to make energy-rich
molecules using carbon dioxide and water
Capturing energy:
Photosynthesis
• The process of photosynthesis can be
summarized in the following equation:
Sunlight + Water + Carbon dioxide  Oxygen + Glucose
Capturing energy:
Photosynthesis
• Plants and other
photosynthesizers
use the energy of
sunlight to make
the molecule
glucose using
carbon dioxide as a
source of carbon.
In the process,
water molecules
are split and
oxygen is given off
as a by-product.
Capturing energy:
Photosynthesis
• Photosynthesis occurs in chloroplasts – organelles
present in leaves and algae.
Capturing energy:
Photosynthesis
• Photosynthesis has two
parts: a “photo” part
and a “synthesis” part.
• During the “photo” part,
light energy is captured
in chemical form.
• During the “synthesis”
part, chemical energy
is used to generate
glucose molecules
using the carbon atoms
of carbon dioxide.
Sunlight
• Light energy is the
energy of the
electromagnetic
spectrum of
radiation.
• Light energy travels
to the earth in
particles called
photons, or
packets of light
energy. Photons of
different
wavelengths
contain different
amounts of energy.
Carbon fixation
•
•
Photosynthesis
captures carbon
dioxide gas from the
air and incorporates
those carbon atoms
into sugar, a process
called carbon
fixation.
By converting
inorganic gaseous
carbon into an
organic form that can
be eaten by animals
or used by plants to
grow and increase
their biomass, carbon
fixation is ultimately
the way carbon
enters the global
energy chain.
Photosynthesis: A closer look
• Chlorophyll is the
pigment present in
the green parts of
plants that
absorbs photons
of light energy
during the light
reactions of
photosynthesis.
Photosynthesis: A closer look
• When red and blue photons of sunlight hit
chlorophyll during the light (“photo”) reactions, the
electrons in its atoms become excited. These
excited electrons are used to generate an energycarrying molecule known as adenosine
triphosphate (ATP), which is used in the
“synthesis” part of photosynthesis to make sugar.