Download 2 Flow of Energy

9th Grade Ecology &
Environmental Science
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Kevin Ketler
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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AUTHORS
Kevin Ketler
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: May 23, 2016
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Contents
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Contents
1
Ecosystems
1
2
Flow of Energy
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3
Food Chains and Food Webs
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C ONCEPT
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Concept 1. Ecosystems
1
Ecosystems
Define ecology and ecosystem.
Distinguish between abiotic and biotic factors.
Describe a niche and habitat.
Explain the competitive exclusion principle.
What lives in the forest?
Take a close look at this ecosystem. Obviously there are deer and many types of plants. But there are organisms that
live there that cannot be seen in the picture. Many other animals, such as rabbits, mice, and countless insects. There
are also bacteria and fungi. Add in the nonliving aspects of the area, such as the water, and you have an ecosystem.
The Ecosystem
Ecology is the study of how living things interact with each other and with their environment. It is a major branch
of biology, but has areas of overlap with geography, geology, climatology, and other sciences. The study of ecology
begins with two fundamental concepts in ecology: the ecosystem and their organisms.
Organisms are individual living things. Despite their tremendous diversity, all organisms have the same basic
needs: energy and matter. These must be obtained from the environment. Therefore, organisms are not closed
systems. They depend on and are influenced by their environment. The environment includes two types of factors:
abiotic and biotic.
1. Abiotic factors are the nonliving aspects of the environment. They include factors such as sunlight, soil,
temperature, and water.
2. Biotic factors are the living aspects of the environment. They consist of other organisms, including members
of the same and different species.
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An ecosystem is a unit of nature and the focus of study in ecology. It consists of all the biotic and abiotic factors in
an area and their interactions. Ecosystems can vary in size. A lake could be considered an ecosystem. So could a
dead log on a forest floor. Both the lake and log contain a variety of species that interact with each other and with
abiotic factors. Another example of an ecosystem is pictured in Figure 1.1.
FIGURE 1.1
A desert ecosystem. What are some of
the biotic and abiotic factors in this desert
ecosystem?
When it comes to energy, ecosystems are not closed. They need constant inputs of energy. Most ecosystems
get energy from sunlight. A small minority get energy from chemical compounds. Unlike energy, matter is not
constantly added to ecosystems. Instead, it is recycled. Water and elements such as carbon and nitrogen are used
over and over again.
Niche
One of the most important concepts associated with the ecosystem is the niche. A niche refers to the role of a
species in its ecosystem. It includes all the ways that the species interacts with the biotic and abiotic factors of the
environment. Two important aspects of a species’ niche are the food it eats and how the food is obtained. Look at
Figure 1.2. It shows pictures of birds that occupy different niches. Each species eats a different type of food and
obtains the food in a different way.
Habitat
Another aspect of a species’ niche is its habitat. The habitat is the physical environment in which a species lives
and to which it is adapted. A habitat’s features are determined mainly by abiotic factors such as temperature and
rainfall. These factors also influence the traits of the organisms that live there.
Competitive Exclusion Principle
A given habitat may contain many different species, but each species must have a different niche. Two different
species cannot occupy the same niche in the same place for very long. This is known as the competitive exclusion
principle. If two species were to occupy the same niche, what do you think would happen? They would compete
with one another for the same food and other resources in the environment. Eventually, one species would be likely
to outcompete and replace the other.
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Concept 1. Ecosystems
FIGURE 1.2
Bird Niches. Each of these species of
birds has a beak that suits it for its niche.
For example, the long slender beak of the
nectarivore allows it to sip liquid nectar
from flowers. The short sturdy beak of the
granivore allows it to crush hard, tough
grains.
Summary
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•
•
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Ecology is the study of how living things interact with each other and with their environment.
The environment includes abiotic (nonliving) and biotic (living) factors.
An ecosystem consists of all the biotic and abiotic factors in an area and their interactions.
A niche refers to the role of a species in its ecosystem.
A habitat is the physical environment in which a species lives and to which it is adapted.
Two different species cannot occupy the same niche in the same place for very long.
_________________________________________________________________________
Review
1. Define ecology.
2. Define biotic and abiotic factors of the environment. Give an example of each.
3. How do ecologists define the term ecosystem? What makes up an ecosystem?Define population and community.
4. Compare and contrast the ecosystem concepts of niche and habitat.
5. Determine if each of the following are biotic or abiotic factors.
1. soil
2. light
3. grass
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4. water
5. bacteria
References
1. Jon DeJong. An example of a desert ecosystem . CC BY 2.0
2. Jodi So. An illustration of different bird beak types adapted for its niche . CC BY-NC 3.0
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C ONCEPT
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Concept 2. Flow of Energy
2
Flow of Energy
Describe energy flows through ecosystems.
Distinguish photoautotrophs from chemoautotrophs.
Distinguish herbivores from carnivores and omnivores.
Explain the role of decomposers.
Compare scavengers to detritivores and to saprotrophs.
What is happening inside each leaf and blade of grass?
Photosynthesis. Maybe the most important biochemical reaction of Earth. As sunlight shines down on this forest,
the sunlight is being absorbed, and the energy from that sunlight is being transformed into chemical energy. That
chemical energy is then distributed to all other living organisms in the ecosystem.
Flow of Energy
To survive, ecosystems need a constant influx of energy. Energy enters ecosystems in the form of sunlight or
chemical compounds. Some organisms use this energy to make food. Other organisms get energy by eating the
food.
Producers
Producers are organisms that produce food for themselves and other organisms. They use energy and simple
inorganic molecules to make organic compounds. The stability of producers is vital to ecosystems because all
organisms need organic molecules. Producers are also called autotrophs. There are two basic types of autotrophs:
photoautotrophs and chemoautotrophs.
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1. Photoautotrophs use energy from sunlight to make food by photosynthesis. They include plants, algae, and
certain bacteria (see Figure 2.1).
2. Chemoautotrophs use energy from chemical compounds to make food by chemosynthesis. They include
some bacteria and also archaea. Archaea are microorganisms that resemble bacteria.
FIGURE 2.1
Different types of photoautotrophs are important in different ecosystems.
Consumers
Consumers are organisms that depend on other organisms for food. They take in organic molecules by essentially
“eating” other living things. They include all animals and fungi. (Fungi don’t really “eat”; they absorb nutrients
from other organisms.) They also include many bacteria and even a few plants, such as the pitcher plant shown in
Figure 2.2. Consumers are also called heterotrophs. Heterotrophs are classified by what they eat:
• Herbivores consume producers such as plants or algae. They are a necessary link between producers and
other consumers. Examples include deer, rabbits, and mice.
• Carnivores consume animals. Examples include lions, polar bears, hawks, frogs, salmon, and spiders.
Carnivores that are unable to digest plants and must eat only animals are called obligate carnivores. Other
carnivores can digest plants but do not commonly eat them.
• Omnivores consume both plants and animals. They include humans, pigs, brown bears, gulls, crows, and
some species of fish.
Decomposers
When organisms die, they leave behind energy and matter in their remains. Decomposers break down the remains
and other wastes and release simple inorganic molecules back to the environment. Producers can then use the
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Concept 2. Flow of Energy
FIGURE 2.2
Pitcher Plant. Virtually all plants are producers. This pitcher plant is an
exception. It consumes insects. It traps them in a sticky substance in
its “pitcher.” Then it secretes enzymes that break down the insects and
release nutrients. Which type of consumer is a pitcher plant?
molecules to make new organic compounds. The stability of decomposers is essential to every ecosystem. Decomposers are classified by the type of organic matter they break down:
• Scavengers consume the soft tissues of dead animals. Examples of scavengers include vultures, raccoons, and
blowflies.
• Detritivores consume detritus—the dead leaves, animal feces, and other organic debris that collects on the
soil or at the bottom of a body of water. On land, detritivores include earthworms, millipedes, and dung beetles
(see Figure 2.3). In water, detritivores include “bottom feeders” such as sea cucumbers and catfish.
• Saprotrophs are the final step in decomposition. They feed on any remaining organic matter that is left after
other decomposers do their work. Saprotrophs include fungi and single-celled protozoa. Fungi are the only
organisms that can decompose wood.
FIGURE 2.3
Dung Beetle. This dung beetle is rolling a
ball of feces to its nest to feed its young.
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Summary
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•
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•
Ecosystems require constant inputs of energy from sunlight or chemicals.
Producers use energy and inorganic molecules to make food.
Consumers take in food by eating producers or other living things.
Decomposers break down dead organisms and other organic wastes and release inorganic molecules back to
the environment.
Review
1.
2.
3.
4.
5.
6.
What is the ultimate source of most energy in most ecosystems?
How does most energy enter ecosystems?
What is the role of a producer? Give an example of a producer.
What do primary consumers eat?
How much energy does an organism pass to the organism that eats it?
If a plant captures 1000 calories of solar energy, how much energy is passed to the bird that ate the bug that
ate the plant?
References
1. Tree: User:Haabet/Wikimedia Commons; Grass: User:Polishname/Wikipedia; Diatoms: Gordon T. Taylor/Stony Brook University/NOAA; Seaweed: User:Flyingdream/Wikipedia; Cyanobacteria: Barry H. Rosen/USGS;
Purple bacteria: Janice Carr/CDC. Photoautotrophs include plants, algae, and bacteria and can be found in
terrestrial and aquatic ecosystems . Public Domain
2. Tim Mansfield. A pitcher plant is different from other plants because it is not a producer, it is a consuemer .
CC BY 2.0
3. Amy Goldstein. A dung beetle is an example of a detritivore . CC BY 2.0
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C ONCEPT
Concept 3. Food Chains and Food Webs
3
Food Chains and Food
Webs
• Describe a typical food chain.
• Explain how food chains and webs model feeding relationships.
Who eats whom?
Describing the flow of energy within an ecosystem essentially answers this question. To survive, one must eat. Why?
To get energy. Food chains and webs describe the transfer of energy within an ecosystem, from one organism to
another. In other words, they show who eats whom.
Food Chains and Food Webs
Food chains and food webs are diagrams that represent feeding relationships. Essentially, they show who eats whom.
In this way, they model how energy and matter move through ecosystems.
Food Chains
A food chain represents a single pathway by which energy and matter flow through an ecosystem. An example
is shown in Figure 3.1. Food chains are generally simpler than what really happens in nature. Most organisms
consume—and are consumed by—more than one species.
Food Webs
A food web represents multiple pathways through which energy and matter flow through an ecosystem. It includes
many intersecting food chains. It demonstrates that most organisms eat, and are eaten, by more than one species.
Examples are shown in Figures 3.2 and 3.3.
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FIGURE 3.1
This food chain includes producers and
consumers. How could you add decomposers to the food chain?
FIGURE 3.2
Food Web.
This food web consists of
several different food chains. Which organisms are producers in all of the food
chains included in the food web?
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Concept 3. Food Chains and Food Webs
FIGURE 3.3
Examples of food webs.
Summary
• Food chains and food webs are diagrams that represent feeding relationships.
• Food chains and webs model how energy and matter move through ecosystems.
Review
1.
2.
3.
4.
What is a food chain?
Describe the role of decomposers in food webs.
Why is a food web more realistic than a food chain?
Draw a terrestrial food chain that includes four feeding levels.
References
1. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. An example of a food chain that includes pro
ducers and consumers . CC BY-NC 3.0
2. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. An example of a foodweb . CC BY-NC 3.0
3. Mariana Ruiz Villarreal (LadyofHats) for CK-12 Foundation. Two more examples of food webs . CC BY-NC
3.0
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