Name
Sectioii
Date
2i
Energy Iow n Ecosystems
Summary
Textbook pages 56-6 7
Before You Read
In this section, you will explore food chains and food webs, as well as food pyramids.
What are the main differences between a chain and a web? Record your ideas below.
Mark the Text
How does energy flow in an ecosystem?
Energy flow is the transfer of energy from one organism to
In Your Own Words
Define the bold terms in this
summary in your own words.
another in an ecosystem. Every organism interacts with its
ecosystem in two ways:
1. the organism obtains food energy from the ecosystem
2. the organism contributes energy to the ecosystem
How are energy flow and feeding relationships in
ecosystems modelled?
Ecologists use three models to illustrate energy flow and
feeding relationships in an ecosystem:
Reading Check
1 What are the different
steps in a food chain
called?
1. Food chains: Food chains show the flow of energy from
plant to animal and from animal to animal. Plants are
called producers because they “produce” food in the form
of carbohydrates during photosynthesis. Consumers eat
plants and other organisms. Each step in a food chain is
called a trophic level.
Trophic
Type of Organism
Energy Source
Example
1 St
primary producer
obtain energy from
the Sun
grass, algae (plants)
5d
2
primary consumer
obtain energy from
primary producers
grasshoppers, krill
(herbivores)
rd
3
secondary
consumer
obtain energy from
primary consumers
frogs, crabs
tertiary consumer
obtain energy from
secondary
consumers
hawks, sea otters
(top carnivores)
th
4
14
MHR • Section 2.1
Energy Flow in Ecosystems
(carnivores)
© 2008 McGraw-HUI Ryerson Limited
Section
Name
2.1
Date
Summary
continued
2. Food webs: Many animals are part of more than one
food chain in an ecosystem because they eat or are eaten
by several organisms. Interconnected food chains are
illustrated in a model called a food web. Animals that eat
plants and other animals are called omnivores.
3. Food pyramids: A food pyramid (or ecological pyramid)
is a model that shows the loss of energy from one trophic
level to another. When one organism consumes another,
the energy stored in the food organism is transferred to the
consumer. However, not all of this energy is incorporated
into the consumer’s tissues. Between 80 and 90 percent of
it is used for chemical reactions and is lost as heat. This
means ecosystems can support fewer organisms at higher
trophic levels, as less energy reaches these levels.
DReading Check
1. What does a food pyramid
demonstrate?
lII[IIIIi great horned
long-tailed
weasel
jackrabbit
-.
grasses
Food pyramid
How do dead organisms contribute to energy flow?
Decomposition describes the breakdown of organic wastes
and dead organisms. Energy is released in decomposition.
When living organisms carry out decomposition, it is called
biodegradation.
• Detrivores, such as small insects, earthworms, bacteria,
and fungi, obtain energy and nutrients by eating dead
plants and animals, as well as animal waste.
• Decomposers, such as bacteria and fungi, change wastes
and dead organisms into nutrients that can once again be
used by plants and animals.
Detrivores and decomposers feed at every trophic level.
© 2008 McGraw-Hit Ryerson Limited
Section 2.1
Energy Flow in Ecosystems
•
MHR
15
Sectioi
Date
Name
22
Nutrient Cycles in cosystems
Summary
Textbook pages 68-91
Before You Read
Like other organisms, your body relies on nutrients to stay healthy. Based on your
current understanding, create a definition of what you think a nutrient is. Write your
definition in the lines below.
How are nutrients cycled in the biosphere?
Mark the Text
Check for Understanding
As you read this section, be
sure to reread any parts you
do not understand. Highlight
any sentences that help you
improve your understanding.
Reading Check
1. Name the three main
nutrient cycles.
Nutrients are chemicals required for plant and animal growth
and other life processes. They are constantly recycled within
Earth’s biosphere. Nutrients spend different amounts of time
in stores within the atmosphere, oceans, and land. Nutrients
are stored for short periods of time in short-term stores, such
as living organisms and the atmosphere. Nutrients can also
be incorporated into longer-term stores, such as Earth’ s crust.
Nutrient cycles describe the flow of nutrients in and out of
stores as a result of biotic and abiotic processes. Without
human interference, nutrient cycles are almost perfectly
balanced. There are three main cycles that move nutrients
through terrestrial and aquatic ecosystems:
1. the carbon cycle
2. the nitrogen cycle
3. the phosphorus cycle
How does the carbon cycle work?
Carbon is an essential component of cells and life-sustaining
chemical reactions. Carbon is cycled through living and
decaying organisms, the atmosphere, bodies of water, and
soil and rock. Carbon moves between stores via six main
processes:
1. Photosynthesis: Photosynthesis is a chemical reaction that
converts solar energy and atmospheric carbon dioxide gas
) into chemical energy.
2
(C0
2. Cellular respiration: During cellular respiration, plants
and animals obtain energy by converting carbohydrates
and oxygen (On) into carbon dioxide and water.
© 2008 McGraw-Hill Ryerson Limited
Section 2.2
Nuirent Cvces ir Ecosvsternc
MHR
2
Date
Name
3. Decomposition: Decomposers release carbon dioxide into
the atmosphere through the decomposition of carbon-rich
organic matter in soil.
4. Ocean processes: Dissolved carbon dioxide is stored in
oceans. Marine organisms store carbon-rich carbonate
-) in their shells, which eventually form sedimentary
2
3
(CC
rock.
5. Volcanic eruptions
6. Forest fires
How do human activities affect the carbon cyc’e?
Human activities, such as fossil fuel combustion and land
clearance, quickly introduce carbon into the atmosphere
from longer-term stores. These actions increase the levels of
carbon dioxide, a greenhouse gas that contributes to global
climate change.
How does the nitrogen cycle work?
Nitrogen is an important component of DNA and proteins.
Most nitrogen is stored in the atmosphere, where it exists as
). It is also stored in bodies of water, living
2
nitrogen gas (N
organisms, and decaying organic matter. Most organisms
cannot use atmospheric nitrogen gas. The nitrogen cycle
involves four processes, three of which make nitrogen
available to plants and animals.
1. Nitrogen fixation: Nitrogen gas is converted into nitrate
j, compounds that are
4
j and ammonium (NH
3
(N0
usable by plants. Nitrogen fixation occurs mainly through
nitrogen-fixing bacteria, and when lightning strikes in the
atmosphere.
2. Nitrification: Ammonium is converted into nitrate and
j through the work of nitrifying bacteria.
2
nitrite (N0
3. Uptake: Useable forms of nitrogen are taken up by
plant roots and incorporated into plant proteins. When
herbivores and omnivores eat plants, they incorporate
nitrogen into their own tissues.
4. Denitrification: Denitrifying bacteria convert nitrate.
back into atmospheric nitrogen.
22
MHR
•
Section 2.2
Nutrient Cyc’es jr osvsterns
© 2008 Mc3raw-HW Rverson Limited
_
Section
Name
2.2
Date
Summary
cortnued
How do human activities affect the nitrogen cycle?
Fossil fuel combustion and burning organic matter release
nitrogen into the atmosphere, where it forms acid rain.
Chemical fertilizers also contain nitrogen, which escapes
into the atmosphere or leaches into lakes and streams. High
levels of nitrogen cause eutrophication (too many nutrients)
and increased algal growth in aquatic ecosystems, depriving
aquatic organisms of sunlight and oxygen.
How does the phosphorus cycle work?
Phosphorus carries energy to cells. It is found in phosphate
-) rock and sediments on the ocean floor. Weathering—
3
4
(P0
through chemical or physical means—breaks down rock,
releasing phosphate into the soil from longer-term stores.
Organisms take up phosphorus. When they die, decomposers
return phosphorus to the soil. Excess phosphorus settles on
floors of lakes and oceans, eventually forming sedimentary
rock. It remains trapped for millions of years until it is
exposed through geologic uplift or mountain building.
How do human activities affect the phosphorus
9
cycle
Commercial fertilizers and phosphate-containing detergents
enter waterways and contribute additional phosphate to the
phosphorus cycle. Slash-and-burn forest clearance reduces
phosphate levels, as phosphate in trees enters soil as ash. It
leaches out of the soil and settles on lake and ocean bottoms,
unavailable to organisms. ®
© 2008 McGraw-HW Rverson Limited
Section 2.2
Check
1. List a human activity that
can cause changes to a
flIJtflnt cycle.
Nutrient Cycles in Ecosystems
•
MHR
23
Section
Date
Name
ffects of Diooccumulotion on Ecosystems
23
Siininry
Textbook pages 92-103
Before You Read
Everyday activities, such as driving or heating your home, often pollute ecosystems. In
your opinion, which human activity is the most harmful to the environment? Explain.
Mark the Text
Summarize
As you read this section,
highlight the main points in
each paragraph. Then write a
short paragraph summarizing
what you have learned.
DReading Check
1. What is the difference
between bioaccumulation
and biomagnification?
How can pollutants affect food chains and
ecosystems?
Human activity creates many harmful pollutants. These build
up in the environment when decomposers are unable to break
them down. Plants take up these pollutants. The pollutants
are then transferred along the food chain until they reach the
highest trophic level. Bioaccumulation refers to the gradual
build-up of pollutants in living organisms. Biomagnilication
refers to the process in which pollutants not only accumulate,
but also become more concentrated at each trophic level.
Organisms at lower trophic levels may be affected by the
pollutant, but primary, secondary, and tertiary consumers
will be more affected, because levels will build up in their
tissues as they consume contaminated food. An example
of this is the PCB concentrations in the orca’ s food web.
When orcas consume food contaminated with PCBs, they
store some of the PCBs in their blubber. When salmon (their
primary food) is not available, orcas use their blubber for
energy. This releases PCBs into their system. Pollutants can
build up to toxic levels in organisms at the top of the food
chain. They can also affect entire ecosystems when keystone
species, species that greatly affect ecosystem health, or the
reproductive abilities of species are harmed.
What are some human-made compounds that bioac
cumulate and biomagnify?
PCBs (polychlorinated biphenyls)
• PCBs were once widely used in industrial products but
are now banned in North America. They interfere with
normal functioning of the body’s immune system and
cause problems with reproduction.
30
MHR
•
Secton 2.3
Effects of Bioaccumuation on Ecosystems
© 2008 McGraw-Hill Ryerson Limited
• PCBs have a long half-life (time it takes for the amount
of a substance to decrease by halt). They stay in the
environment for a long time. Aquatic ecosystems are
most sensitive to PCBs. Organisms at high trophic levels,
like the orca, retain high levels of the pollutant.
POPs (persistent organic pollutants)
• POPs are harmful, carbon-containing compounds that
remain in water and soil for many years.
• DDT (dichioro-diphenyl-trichioroethane) is a toxic POP
that was used as a pesticide in the past to control disease
carrying mosquitoes.
• Accumulation is measured in parts per million (ppm).
This refers to one particle of a given substance mixed
with 999 999 other particles. DDT is harmful at 5 ppm.
© 2008 McGraw-Hill Ryerson Limited
Section 2.3
Effects of Bioaccumuation on Ecosystems
•
MHR
31
Heavy metals
Once heavy metals enter the biosphere, they do not degrade,
and they can not be destroyed.
• Heavy metals, such as lead (Pb), cadmium (Cd), and
mercury (Hg), are toxic at low concentrations; however,
small amounts are naturally present in soil. For humans,
the most serious source of cadmium poisoning is
smoking.
• Human activities can cause these metals to build up in
ecosystems. In the past, use of lead-based insecticides,
batteries, and paints, increased lead to harmful levels.
Despite reductions, lead still enters ecosystems through
improperly disposed electronic waste.
Reading Check
1. Provide an example of how
the effects of chemical
pollution can be reduced.
32
MHR
•
Section 2.3
How can the effects of chemical pollution be
reduced?
Some harmful chemical pollutants can be removed from
the environment by bioremediation, a process where
micro-organisms or plants help clean them up. Reacting
contaminants with certain chemicals can also make them less
harmful.
Effects of Bioaccumulation on Ecosystems
© 2008 McGraw-Hill Ryerson Limited