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Name
CHAPTER 1
Class
Date
Interactions of Living Things
3 Types of Interactions
SECTION
National Science
Education Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
•
•
•
•
LS 3a, 3c, 4b, 4d
What determines an area’s carrying capacity?
Why does competition occur?
How do organisms avoid being eaten?
What are three kinds of symbiotic relationships?
How Does the Environment Control
Population Sizes?
Most living things have more offspring than will survive. A female frog, for example, may lay hundreds of
eggs in a small pond. If all of the eggs became frogs, the
pond would soon become very crowded. There would
not be enough food for the frogs or other organisms in
the pond. But in nature, this usually does not happen.
The biotic and abiotic factors in the pond control the frog
population so that it does not get too large.
Populations cannot grow without stopping because the
environment has only a certain amount of food, water,
space, and other resources. A resource that keeps a population from growing forever is called a limiting factor.
Food is often a limiting factor in an ecosystem.
All plants need sunlight.
In this forest, sunlight may
be a limiting factor. Not
all plants can get the
same amount of light.
STUDY TIP
Make a List As you read
this section, write down any
questions you may have.
Work with a partner to find the
answers to your questions.
STANDARDS CHECK
LS 4d The number of organisms
an ecosystem can support
depends on the resources available and abiotic factors, such as
quantity of light and water,
range of temperatures, and soil
composition. Given adequate
biotic and abiotic resources
and no disease or predators,
populations (including humans)
increase at rapid rates. Lack of
resources and other factors, such
as predation and climate, limit the
growth of populations in specific
niches in the ecosystem.
Word Help: resource
anything that can be used
to take care of a need
1. Define What is a
limiting factor?
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Interactions of Living Things
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Types of Interactions continued
What Is Carrying Capacity?
READING CHECK
The largest number of organisms that can live in an
environment is called the carrying capacity. When a
population grows beyond the carrying capacity, limiting
factors will cause some individuals to leave the area or to
die. As individuals die or leave, the population decreases.
The carrying capacity of an area can change if the
amount of the limiting factor changes. For example, the
carrying capacity of an area will be higher in seasons
when more food is available.
2. Explain Why can the
carrying capacity of an area
change?
How Do Organisms Interact in an Ecosystem?
READING CHECK
Populations are made of individuals of the same species.
Communities are made of different populations that interact.
There are four main ways that individuals and populations
affect one another in an ecosystem: in competition, as
predator and prey, through symbiosis, and coevolution.
3. List What are four
ways that organisms in an
ecosystem interact?
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Interactions of Living Things
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SECTION 3
Class
Date
Types of Interactions continued
Why Do Organisms Compete?
Competition happens when more than one individual
or population tries to use the same resource. There may
not be enough resources, such as food, water, shelter, or
sunlight, for all the organisms in an environment. When
one individual or population uses a resource, there is less
for others to use.
Competition can happen between organisms in the
same population. For example, in Yellowstone National
Park, elk compete with one another for the same plants.
In the winter, when there are not many plants, competition is much higher. Some elk will die because there is
not enough food. In spring, when many plants grow, there
is more food for the elk, and competition is lower.
Competition can also happen between populations. In
a forest, different types of trees compete to grow in the
same area. All of the plant populations must compete for
the same resources: sunlight, space, water, and nutrients.
Critical Thinking
4. Predict In a prairie
ecosystem, which two of the
following organisms most
likely compete for the same
food source: elk, coyotes,
prairie dogs, vultures?
How Do Predators and Prey Interact?
Another way organisms interact is when one organism
eats another to get energy. The organism that is eaten is
called the prey. The organism that eats the prey is called
the predator. When a bird eats a worm, for example, the
bird is the predator, and the worm is the prey.
PREDATORS
Predators have traits or skills that help them catch and
kill their prey. Different types of predators have different
skills and traits. For example, a cheetah uses its speed to
catch prey. On the other hand, tigers have colors that let
them blend with the environment so that prey cannot see
them easily.
READING CHECK
5. Identify What are two
traits different predators may
have to help them catch prey?
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Interactions of Living Things
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Date
Types of Interactions continued
PREY
Say It
Discuss In small groups,
talk about other animals that
escape predators in the four
ways described in the text.
Prey generally have some way to protect themselves
from being eaten. Different types of organisms protect
themselves in different ways:
1. Run Away When a rabbit is in danger, it runs.
2. Travel in Groups Some animals, such as musk oxen, travel
Critical Thinking
6. Infer Why do you think it
would be difficult for predators to attack animals in a
herd?
in herds, or groups. Many fishes, such as anchovies, travel
in schools. All the animals in these groups can help one
another by watching for predators.
When musk oxen sense danger, they move close together to protect their young.
3. Show Warning Colors Some organisms have bright
colors that act as a warning. The colors warn
predators that the prey might be poisonous. A brightly
colored fire salamander, for example, sprays a poison
that burns.
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Interactions of Living Things
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Types of Interactions continued
TAKE A LOOK
7. Color A fire salamander
has a black body with bright
orange or yellow spots. Use
colored pencils to give this
salamander its warning
colors.
4. Use Camouflage Some organisms can hide from
predators by blending in with the background. This
is called camouflage. A rabbit’s natural colors, for
example, may help it blend in with dead leaves or
shrubs so that it cannot be seen. Some animals may
look like twigs, stone, or bark.
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What Is Symbiosis?
Some species have very close interactions with other
species. A close association between two or more species
is called symbiosis. Each individual in a symbiotic relationship may be helped, hurt, or not affected by another
individual. Often, one species lives on or in another species. Most symbiotic relationships can be divided into
three types: mutualism, commensalism, and parasitism.
READING CHECK
8. List List the three types of
symbiotic relationships.
MUTUALISM
When both individuals in a symbiotic relationship are
helped, it is called mutualism. You can see mutualism in
the relationship between a bee and a flower.
Organism hurt?
Organism helped?
Example
No one
both organisms
A bee transfers pollen
for a flower; a flower
provides nectar to a bee.
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Interactions of Living Things
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Types of Interactions continued
In a mutualistic relationship, both species benefit.
Critical Thinking
9. Compare How does
mutualism differ from
commensalism?
COMMENSALISM
When one individual in a symbiotic relationship
is helped but the other is not affected, this is called
commensalism.
Organism hurt?
Organism helped?
Example
No one
one of the organisms
A fish called a remora
attaches to a shark
and eats the shark’s
leftovers.
The remoras get a free meal, but the shark is not harmed.
PARASITISM
READING CHECK
10. Define In parasitism, is
the host helped or hurt?
A symbiotic relationship in which one individual
is hurt and the other is helped is called parasitism.
The organism that is helped is called the parasite. The
organism that is hurt is called the host.
Organism hurt?
Organism helped?
Example
Host
parasite
A flea is a parasite on
a dog.
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Interactions of Living Things
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SECTION 3
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Types of Interactions continued
TAKE A LOOK
11. Infer How do you think
the caterpillar helps the wasps?
This tomato hornworm is being parasitized by young wasps. Their
cocoons are on the caterpillar’s back.
What Is Coevolution?
Relationships between organisms change over time.
Interactions can even be one reason that organisms
change. When a long-term change happens in two species
because of their close interactions, the change is called
coevolution.
One example of coevolution can be seen in some flowers and the organisms that pollinate them. A pollinator
is an organism, such as a bird, insect, or bat, that carries pollen from one flower to another. Flowers need
to attract pollinators to help them reproduce. Different
flowers have evolved different ways to attract pollinators.
Some use colors or odors. Others use nectar as a food
reward for the pollinator.
Some plants can use a variety of pollinators. Others
have coevolved with certain pollinators. For example, the
bat in the picture below has a long sticky tongue. It uses
its tongue to get nectar from deep inside the flower. Only
an organism with a way to reach the nectar could be a
pollinator for this flower.
.
Say It
Investigate With a partner,
look up the meaning of the
suffix co-. Discuss how the
meaning of this suffix can
help you remember what
coevolution means. Think
of some other words that
have co-.
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Interactions of Living Things
Name
Class
Section 3 Review
Date
NSES
LS 3a, 3c, 4b, 4d
SECTION VOCABULARY
carrying capacity the largest population that an
environment can support at any given time
coevolution the evolution of two species that is
due to mutual influence, often in a way that
makes the relationship more beneficial to both
species
commensalism a relationship between two
organisms in which one organism benefits and
the other is unaffected
mutualism a relationship between two species
in which both species benefit
parasitism a relationship between two species
in which one species, the parasite, benefits
from the other species, the host, which is
harmed
predator an organism that kills and eats all or
part of another organism
prey an organism that is killed and eaten by
another organism
symbiosis a relationship in which two different
organisms live in close association with each
other
1. Identify What are two resources for which organisms are likely to compete?
2. Explain What happens to a population when it grows larger than its carrying capacity?
3. Infer Do you think the carrying capacity is the same for all species in an
ecosystem? Explain your answer.
4. Summarize Complete the chart below to describe the different kinds of symbiotic
relationships.
Example
organisms
Type of
symbiosis
Organism(s)
helped
Flea and dog
Bee and flower
Organism(s)
hurt
host (dog)
mutualism
Remora and
shark
none
5. Apply Concepts The flowers of many plants provide a food reward, such as nectar,
to pollinators. Some plants, however, attract pollinators but provide no reward.
What type of symbiosis best describes this relationship? Explain your answer.
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Interactions of Living Things
E
Environmental Science Answer Key
Chapter 1 Interactions of
Living Things
4. Labels go on sun, grasses, prairie dog, coyote, vulture, and bacteria, in that order.
5. Most organisms eat more than one type of
food.
SECTION 1 EVERYTHING IS CONNECTED
6. Without producers, consumers would have
no food. None of the animals would live.
7. about 90%
8. The middle level—deer are herbivores like
the prairie dogs.
9. Wolves were at the top of the food chain and
controlled the populations of herbivores.
1. Biotic factors are living; abiotic factors are
nonliving.
2. Individuals make up a population. Both levels
include organisms of only one species.
3. No, different populations must interact in an
ecosystem.
4. A single alligator or bird should be circled
in red, the three alligators in blue, all the
animals and plants in brown, and the whole
picture in green.
5. 28,000 m
Review
1. Producers use energy from the sun to make
their own food. Producers are the base of
the food chain. All consumers depend on
producers.
Review
1. A community is all the populations that
interact in the same area. An ecosystem is
the community plus the abiotic factors in
the environment.
2. Level
Description
Individual
a single organism
Population
a group of organisms of
the same species that live
in the same area
Community
all of the populations of
species that live in the
same habitat and interact
with one another
Ecosystem
a community of
organisms and their
abiotic environment
Biosphere
the part of Earth where
life exists
2. Grass (Producer)
Mouse (Primary consumer)
Snake (Secondary consumer)
3. Answers will vary but should include at least
one of the organisms from question 2.
4. No, energy is lost as it moves through a food
chain. After a few steps in the chain, there isn’t
enough energy left to support more organisms.
SECTION 3 TYPES OF INTERACTIONS
1. a resource that keeps a population from
growing forever
2. if the amount of the limiting factor changes
3. in competition, as predator and prey,
through symbiosis, and coevolution
4. elk and prairie dogs
5. speed, colors that let them blend with the
environment
3. An organism depends on biotic factors
(other organisms) and abiotic factors (water,
rocks, light, temperature, air).
4. No, only organisms of one species make up
a population. There are usually more than
one species of bird in an area.
6. Possible answer: It may be difficult for the
predator to see individual animals in the group.
7. Any combination of black and orange
patches is acceptable.
8. mutualism, commensalism, parasitism
9. In mutualism, both species benefit. In commensalism, only one species benefits.
10. The host is hurt.
11. The wasps can use the caterpillar for food.
SECTION 2 LIVING THINGS NEED ENERGY
1. Producers use energy from sunlight to make
their own food.
2. Tigers: carnivores
Deer: herbivores
Humans: omnivores
3. Decomposers break down dead matter into
nutrients for other organisms to use.
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Environmental Science
E
Environmental Science Answer Key continued
SECTION 2 ECOLOGICAL SUCCESSION
Review
1. Possible answers: food, water, sunlight,
2.
3.
4.
5.
1. 34%
2. the first species to live or grow in an area
3. Lichens don’t have roots. They get their
shade, shelter
Individuals will die or will have to move to a
new area. This will cause the population to
decrease.
No, some species may use more resources
than others. Some species may be more
affected than others by a limiting factor.
First row, left to right: parasitism, parasite (flea)
Second row, left to right: both, none
Third row, left to right: commensalism
Commensalism; the pollinator is not
harmed, but the plant still benefits.
4.
5.
6.
7.
Review
1. Abiotic factors are the nonliving parts of the
2.
Chapter 2 Cycles in Nature
SECTION 1 THE CYCLES OF MATTER
3.
1. Water vapor cools and changes into drops of
2.
3.
4.
5.
6.
7.
liquid water. The water drops form clouds.
Photosynthesis uses carbon dioxide from
the air. When the sugars that a plant makes
during photosynthesis are broken down, carbon returns to the environment.
photosynthesis
respiration, combustion, decomposition
Animals need to get nitrogen from plants or
other animals. Plants get their nitrogen from
nitrogen fixation.
decomposition
They are recycled in the environment or
reused by other organisms.
4.
5.
6.
7.
Review
1. energy from the sun
2. There should be arrows from air to plants
3.
4.
5.
6.
water from the air, so they do not need soil.
tall trees
in places where living things already exist
weeds
conifers
environment. They include water, light, and
space.
Primary succession is the change from bare
rock to a community of organisms. Secondary
succession is a change in a community where
other living things already exist.
In secondary succession, there is already
soil for new plants to use. In primary
succession, soil has to develop before
species other than lichens can grow.
There is little grass in a mature forest,
because the tall trees prevent the light from
reaching the ground. Nuts grow on many
kinds of trees. Therefore, there would be
more nut eaters than grass eaters.
Tall trees need deep soil. Pioneer species are
the first species to live or grow in an area.
There usually would not be soil in an area
where no living things had been before.
the variety of species that live in an area
pieces of rock that have been broken down
and remains of dead lichens
Chapter 3 The Earth’s
Ecosystems
to animals to decomposers to air, and from
plants to decomposers.
Matter on Earth is limited, so it needs to be
used over and over again.
Living things are made mostly of water.
Water carries nutrients to cells and carries
wastes away. Water also helps organisms
regulate their body temperatures.
Nitrogen fixation is the process in which
bacteria in soil change nitrogen gas into a
form that plants can use.
molecules that contain carbon
SECTION 1 LAND BIOMES
1. Biomes are made of many related
2.
3.
4.
5.
6.
ecosystems.
Africa, South America
plenty of rain, moderate temperatures
deciduous trees and shrubs
in cones
The evergreen conifers shade the forest
floor, but the deciduous trees of the temperate forest allow light to reach the ground.
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Environmental Science