Ecology
Chapter 5 :
How Ecosystems Work
5.1 Energy Flow in Ecosystems
5.2 The Cycling of Matter
5.3 How Ecosystems Change
All information is from and/or adapted from :
1
Environmental Science Copyright 2013 Houghton Mifflin Harcourt Publishing Company
Pictures are cited within the picture and are from the Teacher DVD, unless otherwise noted in the picture’s citation
OBJECTIVES: Section 1
Energy Flow in ECOSYSTEMS

Describe how energy is transferred from the sun to
producers and then to consumers.

Describe one way in which consumers depend on
producers.

Identify two types of consumers.

Explain how energy transfer in a food web is more
complex than energy transfer in a food chain.

Explain why an energy pyramid is a representation
of trophic levels.
2
Section 1: Energy Flow in Ecosystems
Life Depends on the Sun
 Energy
from the sun enters an ecosystem
when plants use light energy to make sugar
molecules.
 This
happens through a process called
photosynthesis.
3
 Photosynthesis
is the process by which
plants, algae, and some bacteria use
sunlight, carbon dioxide, and water to
produce carbohydrates and oxygen.
4
Section 1: Energy Flow in Ecosystems
Life Depends on the Sun
** From Producers to Consumers
 Because plants make their own food, they
are called producers.
A
producer is an organism that can make
organic molecules from inorganic molecules.
 Producers
are also called autotrophs, or self-
feeders.
 Most
producers get their energy directly from
the sun by absorbing it through their leaves.
5
Section 1: Energy Flow in Ecosystems
Life Depends on the Sun
** From Producers to Consumers
 Organisms
that get their energy by eating
other organisms are called consumers.
 A consumer is an organism that eats other
organisms or organic matter instead of
producing its own nutrients or obtaining
nutrients from inorganic sources.
 Consumers are also called heterotrophs, or
other-feeders.
 Consumers get their energy indirectly by
eating producers or other consumers.
6
Section 1: Energy Flow in Ecosystems
Life Depends on the Sun
**An Exception: Deep-Ocean Ecosystems
 Deep-ocean
communities of worms, clams,
crabs, mussels, and barnacles exist in total
darkness on the ocean floor, where
photosynthesis cannot occur.
 The
producers in this environment are
bacteria that use hydrogen sulfide present in
the water.
 Other
underwater organisms eat the bacteria
or the organisms that eat the bacteria.
7
Check for Understanding
QUESTION:
RELATE:
How do producers and consumers get energy from the sun?
ANSWER:
Sample of an acceptable answer:

A producer gets energy from the sun through
photosynthesis.

A consumer get energy from the sun INDIRECTLY, by
eating other organisms that eat plants or organisms the
eat other organisms that have eaten plants.
8
Section 1: Energy Flow in Ecosystems
What Eats What
 Organisms
can be classified by what they
eat.
 Producers
– makes its own food using light
energy (photosynthesis) or chemical sources
(chemosynthesis)
Examples: grasses, ferns, cactuses, flowering
plants, trees, algae, some bacteria
 Consumers
– gets energy by eating producers
or other consumers
Examples: mice, starfish, elephants, humans
9
Section 1: Energy Flow in Ecosystems
What Eats What
 Types of Consumers:
 Herbivores - eat producers
Example: cows, sheep, deer, grasshopper
 Carnivores – eat other consumers
Examples: lions, hawks, snakes, sharks
 Omnivores – eat both producers and
consumers
Example: bears, pigs, gorillas, humans
 Decomposers – break down organic matter
from dead organisms
Example: fungi, bacteria
10
Section 1: Energy Flow in Ecosystems
Cellular Respiration: Burning the Fuel
 An
organism obtains energy from the food it
eats.
 This
food must be broken down within its
body.
 The
process of breaking down carbohydrates
to yield energy is called cellular respiration.
 Cellular
respiration occurs inside the cells of
most organisms.
11
Section 1: Energy Flow in Ecosystems
Cellular Respiration: Burning the Fuel
 During
cellular respiration, cells absorb
oxygen and use it to release energy from
food.
 Through
cellular respiration, cells use
glucose (sugar) and oxygen to produce
carbon dioxide, water, and energy.
12
Section 1: Energy Flow in Ecosystems
Cellular Respiration: Burning the Fuel
 Part
of the energy obtained through cellular
respiration is used to carry out daily
activities.
 Excess
energy is stored as fat or sugar.
13
Section 1: Energy Flow in Ecosystems
Energy Transfer
 Each
time an organism eats another
organism, an energy transfer occurs.
 This
transfer of energy can be traced by
studying food chains, food webs, and trophic
levels.
14
Section 1: Energy Flow in Ecosystems
Energy Transfer
** Food Chains
A
food chain is a sequence in
which energy is transferred
from one organism to the next
as each organism eats another
organism.
15
Section 1: Energy Flow in Ecosystems
Energy Transfer
** Food Webs
 Ecosystems,
however, almost
always contain more
than one food chain.
 A food web shows
many feeding
relationships that
are possible in an
ecosystem.
16
Section 1: Energy Flow in Ecosystems
Energy Transfer
** Trophic Levels
Each step in the transfer of energy through a
food chain or food web is known as a trophic
level.
 A trophic level is one of the steps in a food chain
or food pyramid; examples include producers
and primary, secondary, and tertiary consumers.
 Each time energy is transferred, some of the
energy is lost as energy in the form of heat.
 Therefore, less energy is available to organisms
at higher trophic levels.
 One way to visualize this is with an energy
pyramid.

17
Section 1: Energy Flow in Ecosystems
Energy Transfer
** Energy Pyramid
18
Section 1: Energy Flow in Ecosystems
Energy Transfer
** Energy Pyramid
 Each
layer of the pyramid represents one
trophic level.
 Producers
form the base of the energy
pyramid, and therefore contain the most
energy.
 The
pyramid becomes smaller toward the
top, where less energy is available.
19
Section 1: Energy Flow in Ecosystems
Energy Transfer
** How Energy Loss Affects an Ecosystem
 Decreasing
amounts of energy at each
trophic level affects the organization of
an ecosystem.
 Energy
loss affects the number of
organisms at each level.
 Energy
loss limits the number of trophic
levels in an ecosystem.
20
OBJECTIVES: TO BE COMPLETED
SECTION 1: ENERGY FLOW IN ECOSYSTEMS
Describe how energy is transferred from the sun to
producers and then to consumers.
____________________________________________
____________________________________________
____________________________________________
____________________________________________
 Describe one way in which consumers depend on
producers.
____________________________________________
____________________________________________
____________________________________________
____________________________________________

21
OBJECTIVES: TO BE COMPLETED
SECTION 1: ENERGY FLOW IN ECOSYSTEMS

(continued)
Identify two types of consumers.
1) ____________________________________
2) ____________________________________

Explain how energy transfer in a food web is more
complex than energy transfer in a food chain.
____________________________________________
____________________________________________
____________________________________________
____________________________________________
22
OBJECTIVES: TO BE COMPLETED
SECTION 1: ENERGY FLOW IN ECOSYSTEMS

(continued)
Explain why an energy pyramid is a representation
of trophic levels.
____________________________________________
____________________________________________
____________________________________________
____________________________________________
23
Ecology
Chapter 5 :
How Ecosystems Work
5.1 Energy Flow in Ecosystems
5.2 The Cycling of Matter
5.3 How Ecosystems Change
All information is from and/or adapted from :
24
Environmental Science Copyright 2013 Houghton Mifflin Harcourt Publishing Company
Pictures are cited within the picture and are from the Teacher DVD, unless otherwise noted in the picture’s citation
OBJECTIVES: Section 2
The Cycling of Matter

Describe the short-term and long-term process of
the carbon cycle.

Identify one way that humans are affecting the
carbon cycle.

List the three stages of the nitrogen cycle.

Describe the role that nitrogen-fixing bacteria play
in the nitrogen cycle.

Explain how the excess use of fertilizer can affect
the nitrogen and phosphorus cycles.
25
Section 2: The Cycling of Matter
The Carbon Cycle
 The
carbon cycle is the movement of carbon
from the nonliving environment into living things
and back to the environment.
 Carbon
is the essential component of proteins,
fats, and carbohydrates, which make up all
organisms.
CHO-CHO-CHO (Carbohydrate 1:2:1)
CHO – (lipid/fat, no specific amounts)
CHOSN (protein)
CHOPN (nucleic acid)
26
Section 2: The Cycling of Matter
The Carbon Cycle
27
Section 2: The Cycling of Matter
The Carbon Cycle
 Carbon
exists in air, water, and living
organisms.
 Producers
convert carbon dioxide in the
atmosphere into carbohydrates during
photosynthesis. (carbohydrates- sugars)
 Consumers
obtain carbon from the
carbohydrates in the producers they eat.
(carbohydrates- sugars)
28
Section 2: The Cycling of Matter
The Carbon Cycle
 During
cellular respiration, some of the
carbon is released back into the atmosphere
as carbon dioxide.
 Some
carbon is stored in limestone, forming
one of the largest “carbon sinks” on Earth.
29
Section 2: The Cycling of Matter
The Carbon Cycle
 Carbon
stored in the bodies of organisms as fat,
oils, or other molecules, may be released into
the soil or air when the organisms dies.
 These
molecules may form deposits of coal, oil,
or natural gas, which are known as fossil fuels.
 Fossil
fuels store carbon left over from bodies of
organisms that died millions of years ago.
30
Section 2: The Cycling of Matter
The Carbon Cycle
** How Humans Affect the Carbon Cycle
 Humans
burn fossil fuels, releasing carbon
dioxide into the atmosphere.
 Increased
levels of carbon dioxide contribute to
climate change.
 Carbon
dioxide is a greenhouse gas along with
water vapor and other gases.
 Greenhouse
gases absorb and re-radiate infrared
energy, warming Earth.
31
Check for Understanding
QUESTION:
RELATE:
Explain how the carbon emission from an
18-wheeler truck, (such as the one pictured)
enters and exits producers such as the trees
in your local neighborhood.
ANSWER:
Sample of an acceptable answer:

Carbon dioxide emitted from the truck enters the trees
through photosynthesis.

Plants use carbon dioxide, water, and sunlight to produce
sugar and oxygen.
32
Section 2: The Cycling of Matter
The Nitrogen Cycle
 The
nitrogen cycle is the process in which
nitrogen circulates among the air, soil, water,
plants, and animals in an ecosystem.
 All
organisms need nitrogen to build
proteins, which are used to build new cells.
 Nitrogen
makes up 78 percent of the gases in
the atmosphere.
33
Section 2: The Cycling of Matter
The Nitrogen Cycle
 Nitrogen
must be altered, or fixed, before
organisms can use it. (N2)
 Only
a few species of bacteria can fix
atmospheric nitrogen into chemical
compounds that can be used by other
organisms.
 These
bacteria are known as nitrogen-fixing
bacteria.
34
Section 2: The Cycling of Matter
The Nitrogen Cycle
 Nitrogen-fixing
bacteria are bacteria that
convert atmospheric nitrogen into ammonia.
 These
bacteria live in nodules on the roots of
plants called legumes, which include beans,
peas, and clover.
 The
bacteria use sugar provided by the legumes
to produce nitrogen containing compounds such
as nitrates.
(nitrogen and oxygen)
 Excess
nitrogen fixed by the bacteria is released
into the soil.
35
Section 2: The Cycling of Matter
The Nitrogen Cycle
36
Section 2: The Cycling of Matter
The Nitrogen Cycle
** Decomposers and the Nitrogen Cycle
 Nitrogen
stored within the bodies of living things
is returned to the nitrogen cycle once those
organisms die.
 Decomposers
break down decaying plants and
animals, as well as plant and animal wastes.
 After
decomposers return nitrogen to the soil,
bacteria transform a small amount of the
nitrogen into nitrogen gas, which then returns
to the atmosphere to complete the nitrogen
cycle.
37
Section 2: The Cycling of Matter
The Phosphorus Cycle
 Phosphorus
is an element that is part of many
molecules that make up the cells of living
organisms.
 Plants
get the phosphorus they need from soil
and water, while animals get their phosphorus
by eating plants or other animals that have
eaten plants.
 The
phosphorus cycle is the cyclic movement of
phosphorus from the environment to organisms
and then back to the environment.
38
Section 2: The Cycling of Matter
The Phosphorus Cycle
39
Section 2: The Cycling of Matter
The Phosphorus Cycle

Phosphorus may enter soil and water when rocks
erode. Small amounts of phosphorus dissolve as
phosphate, which moves into soil, water, and
groundwater.

Plants absorb phosphates in the soil through their
roots.
40
Section 2: The Cycling of Matter
The Phosphorus Cycle

Some phosphorus washes off the land and ends up
in water bodies.

Because many phosphate salts are not soluble in
water, they sink to the bottom and accumulate as
sediment.
41
Section 2: The Cycling of Matter
The Phosphorus Cycle
** Fertilizers: Nitrogen & Phosphorus Cycles
 Fertilizers,
which people use to stimulate
and maximize plant growth, contain both
nitrogen and phosphorus.
 Excessive
amounts of fertilizer can enter
terrestrial and aquatic ecosystems through
runoff.
42
Section 2: The Cycling of Matter
The Phosphorus Cycle
** Fertilizers: Nitrogen & Phosphorus Cycles
 Excess
nitrogen and phosphorus can cause
rapid growth of algae.
 Excess
algae can deplete an aquatic
ecosystem of important nutrients such as
oxygen, on which fish and other aquatic
organisms depend.
43
Check for Understanding
QUESTION:
RECOGNIZE
How do algal blooms harm aquatic ecosystems ?
ANSWER:
Sample of an acceptable answer:

Algal blooms can harm aquatic ecosystems by depleting
their nutrients, such as oxygen.
44
OBJECTIVES: TO BE COMPLETED
SECTION 2: The Cycling of Matter

Describe the short-term and long-term process of
the carbon cycle.
____________________________________________
____________________________________________
____________________________________________
____________________________________________

Identify one way that humans are affecting the
carbon cycle.
____________________________________________
____________________________________________
____________________________________________
____________________________________________
45
OBJECTIVES: TO BE COMPLETED
SECTION 2: The Cycling of Matter

(continued)
List the three stages of the nitrogen cycle.
1) ___________________________________________
2) ___________________________________________
3) ___________________________________________

Describe the role that nitrogen-fixing bacteria play in
the nitrogen cycle.
____________________________________________
____________________________________________
____________________________________________
____________________________________________
46
OBJECTIVES: TO BE COMPLETED
SECTION 2: The Cycling of Matter

(continued)
Explain how the excess use of fertilizer can affect
the nitrogen and phosphorus cycles.
____________________________________________
____________________________________________
____________________________________________
____________________________________________
47
Ecology
Chapter 5 :
How Ecosystems Work
5.1 Energy Flow in Ecosystems
5.2 The Cycling of Matter
5.3 How Ecosystems Change
All information is from and/or adapted from :
48
Environmental Science Copyright 2013 Houghton Mifflin Harcourt Publishing Company
Pictures are cited within the picture and are from the Teacher DVD, unless otherwise noted in the picture’s citation
OBJECTIVES: Section 3
How Ecosystems Change

List two types of ecological succession.

Explain how a pioneer species contributes to
ecological succession.

Describe how lichens contribute to primary
succession.

Explain what happens during old-field succession.
49
Section 3: How Ecosystems Change
Ecological Succession
 Ecosystems
are constantly changing.
 Ecological
succession is a gradual process of
change and replacement of the types of
species in a community.
 Each
new community that arises often makes
it harder for the previous community to
survive.
50
Section 3: How Ecosystems Change
Ecological Succession
** Primary Succession
 Primary
succession is a type of succession that
occurs on a surface where no ecosystem existed
before. It begins in an area that previously did
not support life.
 Primary succession can occur on new islands
created by volcanic eruptions, in areas exposed
when a glacier retreats, or any other surface
that has not previously supported life.
 Primary succession is much slower than
secondary succession. This is because it begins
where there is no soil.
51
Section 3: How Ecosystems Change
Ecological Succession
** Primary Succession
A
pioneer species is a species that colonizes an
uninhabited area and that starts an ecological
cycle in which many other species become
established.
 Over time, a pioneer species will make the new
area habitable for other species.
 The first pioneer species to colonize bare rock
are usually bacteria and lichens, which can live
without soil.
 The growth of lichens breaks down the rock,
which with the action of water, begins to form
soil.
52
Section 3: How Ecosystems Change
Ecological Succession
** Secondary Succession
 Secondary
succession occurs on a surface
where an ecosystem has previously existed.
It is the process by which one community
replaces another community that has been
partially or totally destroyed.
 Secondary
succession can occur in
ecosystems that have been disturbed or
disrupted by humans, animals, or by natural
process such as storms, floods, and
earthquakes.
53
Section 3: How Ecosystems Change
Ecological Succession
** Secondary Succession
A
climax community is the final, stable
community in equilibrium with the
environment.
 Even
though a climax community may change
in small ways, this type of community may
remain the same through time if it is not
disturbed.
54
Check for Understanding
QUESTION:
COMPARE:
How is secondary succession different from primary succession?
ANSWER:
Sample of an acceptable answer:

Primary succession occurs where no ecosystem existed
before.

Secondary succession occurs where an ecosystem
previously existed.
55
Section 3: How Ecosystems Change
Ecological Succession
** Old Field Succession
 Old-field
succession is a type of secondary
succession that occurs when farmland is
abandoned.
 When
a farmer stops cultivating a field,
grasses and weeds quickly grow and cover
the abandoned land.
 Over
time, taller plants, such as perennial
grasses, shrubs, and trees take over the
area.
56
Section 3: How Ecosystems Change
Ecological Succession
** Secondary Succession
57
Check for Understanding
QUESTION:
INFER:
Why do you think smaller plants disappear after pine trees begin to grow?
ANSWER:
Sample of an acceptable answer:

Shade from the pine trees keeps smaller plants from
receiving the sunlight they need to grow.
58
Section 3: How Ecosystems Change
Ecological Succession
** Fire and Secondary Succession
 Natural
fires caused by lightning are a necessary
part of secondary succession in some
communities.
 Minor
forest fires remove accumulations of
brush and deadwood that would otherwise
contribute to major fires that burn out of
control.
 Some
animal species also depend on occasional
fires because the feed on the vegetation that
sprouts after a fire has cleared the land.
59
Check for Understanding
QUESTION:
IDENTIFY:
List two ways that fire can be beneficial to a forest community.
ANSWER:
Sample of an acceptable answer:

Two benefits include the removal of accumulated brush
and the return of nutrients to the soil.
60
OBJECTIVES: TO BE COMPLETED
SECTION 3: The Cycling of Matter

List two types of ecological succession.
1) ___________________________________________
2) ___________________________________________

Explain how a pioneer species contributes to ecological
succession.
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
61
OBJECTIVES: TO BE COMPLETED
SECTION 3: How Ecosystems Change

(continued)
Describe how lichens contribute to primary succession.
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________

Explain what happens during old-field succession.
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
62
Vocabulary to Know:
Section 1 – – Energy Flow in Ecosystems

Photosynthesis – the process by which plants, algae, and some bacteria use sunlight, carbon dioxide,
and water to reproduce carbohydrates and oxygen.

Producer – an organism that can make organic molecules from inorganic molecules; a photosynthetic or
chemosynthetic autotroph that serves as the basic food source in an ecosystem.

Consumer – an organism that eats other organisms or organic matter instead of producing its own
nutrients or obtaining nutrients from inorganic sources.

Decomposer – an organism that feeds by breaking down organic matter from dead organisms; examples
include bacteria and fungi.

Cellular Respiration – the process by which cells produce energy from carbohydrates; atmospheric
oxygen combines with glucose to form water and carbon dioxide.

Food Chain – the pathway of energy transfer through various stages as a result of the feeding patterns
of a series of organisms.

Food Web – a diagram that shows the feeding relationships between organisms in an ecosystem.

Trophic Level – one of the steps in a food chain or food pyramid; examples include producers and
primary, secondary, and tertiary consumers.
63
Vocabulary to Know:
Section 2 – The Cycling of Matter

Carbon Cycle – the movement of carbon from the non-living environment into living things and back.

Nitrogen-Fixing Bacteria – bacteria that convert atmospheric nitrogen into ammonia.

Nitrogen Cycle – the process in which nitrogen circulates among the air, soil, water, plants, and animals
in an ecosystem.

Phosphorus Cycle – the cyclic movement of phosphorus in different chemical forms from the
environment to organism and then back to the environment.
Section 3 – SECTION TITLE

Ecological Succession – a gradual process of change and replacement in a community.

Primary Succession – succession that begins in an area that previously did not support life.

Secondary Succession – the process by which one community replaces another community that has
been partially or totally destroyed.

Pioneer Species – a species that colonizes an uninhabited area and that starts an ecological cycle in
which many other species become established.

Climax Community – a final, stable community in equilibrium with the environment
64