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Chapter 1
Chapter 2
About 8,000 waves
strike the Big Sur
coastline every day.
How do organisms exchange energy
and nutrients in an ecosystem?
Introduction to
Earth’s Ecosystems
The Basic Process
of Life
Microscopic Organisms
on Earth
Earth’s Food Chains,
Webs, and Pyramids
Earth’s Cycles for Life
6 LS 5. Organisms in ecosystems exchange energy and
nutrients among themselves and with the environment.
ELA R 6.3.6.
Identify and
analyze features of
themes conveyed through
characters, actions, and
images. • ELA W 6.2.4.
Write responses to
ed. Lee Bennet Hopkins
by Natasha Wing
Redwood trees rise like skyscrapers
Fingering the clouds in search of moisture
Pulling down the fog and passing it
From limb to limb
Into the deep of the forest.
The fog blankets the forest
Blocking out light, movement, and sound
Like a curtain
Draped across a stage.
Yet behind the redwood curtain
Black bear walk and stalk their prey
Deer sleep and leap away
Slugs climb and slime on leaves
Birds sing and wing in the breeze.
The show must go on
As it has for thousands of years
Behind the redwood curtain.
Write About It
Response to Literature In this
poem the author describes a forest.
What is life like in this forest? What
plants and animals live there? Write an
essay explaining the main idea of the
poem. Use details from the poem to
show how the author makes her point.
-Journal Write about it online
Lesson 1
to Earth’s
California is home to one of the most diverse
collections of living things in the world. Why
do you think this is so?
6 LS 5.e. Students know the number and types of organisms an ecosystem
can support depends on the resources available and on abiotic factors, such
as quantities of light and water, a range of temperatures, and soil composition.
Do different ecosystems contain
different organisms?
Form a Hypothesis
Why do certain plants and animals live in certain
places? How does the amount of sunlight affect
different organisms? Write your answer as a
hypothesis in the form “If a plant needs lots of
sunlight, then . . .”
• trowel or spade
• 4 small stakes
Test Your Hypothesis
Experiment With your teacher select two
• meterstick
areas on or near your school grounds to study.
Choose one area that receives plenty of sunlight
and another that receives very little. Mark off
a 2-by-2-meter plot in each area with stakes
and string.
• string
Measure Measure the air temperature at
• safety goggles
ground level and at 1 meter above ground
level in each area.
• thermometer
• field guides
• graph paper
Record Data Using graph paper record the
locations of the living things in each area. What
kinds of organisms do you see? Use field guides
to help you identify the organisms.
Draw Conclusions
Compare your observations about the two areas.
How do the temperatures differ? Which area
contains more living things? What statement
can you make about the effect of sunlight on
an ecosystem?
Explore More
How do you think the amount of water in an
ecosystem affects living things? Make a prediction
about this, and design a procedure to test it. How
have people affected the ecosystem?
6 IE 7.a. Develop a hypothesis. • 6 IE 7.e. Recognize whether
evidence is consistent with a proposed explanation.
What Is an Ecosystem?
▶ Main Idea
6 LS 5.e
The number and types of
organisms in an ecosystem
depend on the resources
▶ Vocabulary
ecosystem, p. 26
biotic factor, p. 27
abiotic factor, p. 27
humus, p. 32
topsoil, p. 32
minerals, p. 32
acidity, p. 33
alkalinity, p. 33
ecology, p. 34
population, p. 34
community, p. 35
habitat, p. 36
niche, p. 36
▶ Reading Skill
Main Idea
Explore ecosystems
with a park ranger.
The living things in an area also work
together in systems. They all depend on the same
resources and are affected by changes that occur
around them. For example, a major change in
a nonliving part of an ecosystem, such as an
extreme drought, can affect all the organisms
in an ecosystem.
Living things are part of an ecosystem.
An ecosystem consists of the living and nonliving
things in an area that interact with one another.
An Ecosystem
A system is a group of things that work
together as a unified whole. There are systems all
around you. Our bodies contain organ systems
for breathing and for digesting food. Schools are
organized into school systems. Planets are part
of our solar system. Each system is made up of
parts that interact with one another closely.
Any living thing that is part of an
ecosystem is a biotic factor . This term
includes the root bio, which means
“living.” Living things include tiny
organisms, such as bacteria, as well as
the plants and animals people can see.
Any nonliving part of the ecosystem,
such as water, minerals, sunlight, air,
or soil, is an abiotic factor . This term
includes the prefix a-, which means
“not” or “without.”
How can you identify the abiotic
factors in an ecosystem? Abiotic factors
are the parts of the ecosystem that
help make life possible. For example,
sunlight provides warmth and energy.
Rocks provide shelter and, in time,
form soil. Water is so important to
living things that it is what scientists
look for first when searching for
signs of life on other planets. Other
abiotic factors include air, climate, and
altitude. All these factors influence the
number and types of organisms that
can live in an ecosystem.
Identifying the living things in an
ecosystem might seem to be easy. At the
beach you might see birds, fish, seals,
and seaweed. In contrast, think about
microscopic organisms inside your
mouth. The warm, moist environment
there supports millions of bacteria.
Quick Check
Main Idea What are five abiotic
factors in an ecosystem?
Critical Thinking How do biotic
and abiotic factors differ?
Reading Diagrams
How would the abiotic factors shown here
affect the organisms that live in the pond?
Clue: What are the nonliving things in the
Why are sunlight and
temperature important?
The amount of sunlight a
location receives directly affects
the temperature in that location.
Temperature, in turn, affects the
number and types of animals and
plants that can survive in a location.
Areas of Earth that receive greater
amounts of sunlight have higher
temperatures than other areas. The
equator is the part of Earth that
receives the most direct sunlight. Areas
around the equator that are not at
extremely high elevations are generally
known for their lush vegetation and
great diversity of living things.
The parts of Earth that receive the
least direct sunlight are the North
and South poles. Areas near the poles
have sparse or no vegetation and
fewer kinds of living things. For most
organisms, especially plants, sunlight
is an important abiotic factor.
Temperature change is another
factor that affects living things.
In some regions the temperature
changes very little.
◀ Parrots thrive in warm
climates, such as the
Amazon rain forest.
In tropical rain forests, for example,
the temperature stays around 80°F
(27°C) almost all the time. Many
animals and plants thrive in places
where the temperature does not change
much in a single day.
In other places, the temperature
may vary from day to night and
from season to season. In deserts the
temperature can vary from about 32°F
(0°C) to more than 100°F (38°C) in a
single day. The plants and animals in
a desert must be able to survive these
wide variations in temperature.
the seasons, some organisms migrate,
or travel to a different place. Others
become dormant, or less active, or
have other adaptations that enable
them to survive.
Quick Check
Main Idea How does temperature
affect organisms in rain forests?
Critical Thinking How does the
amount of direct sunlight affect
the plant growth in an area?
Changes in the seasons have similar
effects. Most organisms survive better
in warm, mild summers than in
cold, icy winters. In places where the
temperature changes a great deal with
▼ These penguins are adapted
to the temperatures in their
Antarctic surroundings.
Central Valley irrigation
Why is water important?
Without a steady supply of water, life would not exist on Earth.
Water helps living things in several ways. It keeps cells strong and healthy.
Cells are the basic units of life. Water dissolves and transports substances.
It also helps regulate the temperature of an organism.
Your Body’s Need for Water
Press your hands together, and they will seem
firm and solid. However, about 60% to 70% of
your body is made up of water. Some parts of your
body have an even greater percentage of water.
It is no wonder that water is so important to
your survival.
Water is the body’s main transportation
vehicle. Many substances dissolve in water.
This property of water is what makes it so
vital to life. Water carries nutrients, oxygen,
and other substances to various parts of your body.
Water also carries waste materials out of your body.
Water helps regulate your body’s temperature. It cools
your skin, making you feel cooler all over. It also helps
carry excess heat away from your cells.
Plants’ Need for Water
Plants, too, are made up mostly of
water. Some parts of a plant, such as
the leaves and stems, may be as much as
90% water. Water transports minerals
and nutrients throughout the plant.
Water keeps plant cells rigid. You
have probably seen what happens when
a plant does not receive enough water.
The leaves and stems become weak,
and the plant wilts.
Plants need water to grow. For this
reason, the amount of water in an
area affects the number and types of
plants that live there. Areas with little
rainfall, such as deserts, have fewer
plants. The plants that do grow there
have special adaptations that allow
them to conserve water.
Plants that grow in areas that receive
little rain have adapted to the dry
conditions. For example, the shape of
the barrel cactus enables it to expand
when rain falls and to shrink during
dry times. When it expands, this cactus
stores water in its spongy tissues.
Animals have adaptations for drought
and heat, too. The kit fox has large ears
with dense networks of veins. These
veins help the fox’s body shed heat.
One way that humans adapt to
dry conditions is to use irrigation. In
places where not enough rain falls to
grow crops, farmers water their fields.
Water taken from the Colorado River,
for example, irrigates almost 1 million
acres of land in Southern California.
This water helps crops such as lemons,
grapes, oranges, lettuce, and tomatoes
grow on land that would otherwise be
too dry for farming.
▲ barrel cactus, Anza-Borrego Desert
State Park, California
Quick Check
Main Idea Why do plants need
Critical Thinking Why is water
good for transporting substances
in plants and animals?
Why is soil important?
Soil is made up of weathered rock
and humus (HYEW•muhs). As rock
weathers it breaks down slowly into tiny
pieces. Humus is the material in soil
formed by the breakdown of plant and
animal remains. It mixes with the bits
of rock and adds nutrients to the soil.
Soil supplies the water, air, and
nutrients that plants need in order to
grow. By supporting the growth of
plants, soil helps living things survive.
Conservation of soil is important.
We can put plants on hillsides so the
soil will not erode. Farmers conserve
soil by rotating their crops and letting
fields lie fallow, or unplanted, every
few seasons.
The substances in soil affect the types
of organisms that can live in it. Some
compounds known as acids can harm
living things if they are present in high
Soil Layers
Topsoil is the upper layer
of soil, which is made
mostly of humus, minerals,
water, and air. The humus in
topsoil is spongy and holds
water very well. This makes
topsoil an ideal material for
plants to live in.
The layer below the topsoil is called
the subsoil. Some humus can be
found near the top of this layer. As
water seeps through the topsoil into
the subsoil, it brings particles of
minerals and clay with it.
Minerals are the
naturally occurring
solid materials of
Earth’s crust. They
include clay, sand,
and silt.
Below the subsoil is partly weathered
parent rock. The parent rock is the
rock from which the soil is formed.
There is no humus at this depth.
Below this layer is solid rock, or bedrock.
concentrations. Acidity is the amount
of acid in a substance. Other compounds,
known as alkalis (AL•kuh•lighz), or bases,
may also be present in soil. Alkalinity
(al•kuh•LIN•uh•tee) is the amount of base
in a substance.
Testing Soil pH
The acidity or alkalinity of soil is
measured on a scale known as the pH
scale. The lower the pH, the more acidic
the soil is. The higher the pH, the more
basic or alkaline the soil is. The pH of
the soil in an area helps determine which
plants will grow there. If the pH of the
soil changes greatly, the plants there may
not be able to survive.
Put three different soil samples
in separate cups.
Using the soil-test kits provided
by your teacher, test the pH of
each sample. Record the pH
of each.
Predict What do you think would
happen if you added an antacid
to the soil samples? Design an
experiment to test your prediction.
Quick Check
Main Idea Why is soil important?
Critical Thinking Why should
people test soil before growing
crops in it?
The pH Scale
distilled water
(pH 7)
(pH 10)
(pH 11)
(pH 6)
(pH 13)
(pH 4)
(pH 2)
What lives in an ecosystem?
All the abiotic factors in an area,
including temperature ranges, sunlight,
water, and soil type, influence what
living things are found there. Every
organism in the ecosystem plays an
important role. The study of organisms
and how they interact in an ecosystem
is ecology (ee•KAHL•uh•jee). Scientists
who study this subject include ecologists,
zoologists, biologists, foresters, geologists,
and geographers.
In an ecosystem, all the organisms
of one species make up a population .
The millions of bacteria living in your
mouth make up a population. The
thousands of elephant seals living in
the waters off California are another
population. At one time, people hunted
elephant seals for their oil until only
about 100 remained. Today, there are
many elephant seals along California’s
coast. California sea lions are social
animals. The females recognize their
pups by their sounds and their smells.
Ecologists study populations,
looking at the role each population
plays in the ecosystem. They might
observe behaviors such as breeding
and feeding. Members of a population,
or species, breed with one another and
produce offspring. They also compete
for resources such as food, water, and
shelter. Almost all populations are
influenced by the human population.
California sea lions
Populations interact with other
plants and animals in their ecosystem.
Different species can compete with
each other and may even try to eat
each other. They can also help each
Tide-Pool Community
Populations and Communities
All the populations living in an area
make up a community . To understand
this think about an orchestra. All the
violins in the orchestra would make
up one population, the cellos another,
the clarinets another, and the trumpets
another. Each group of instruments
represents a population, and each
group makes a unique contribution
to the community, or the orchestra.
Communities are often named after
the locations in which they are found.
Cactuses, sagebrush, kangaroo rats,
and jackrabbits are part of a desert
community. Frogs, minnows, cattails,
and dragonflies live in a pond
community. Each community includes
a group of populations that can survive
in the conditions found there.
Tide-pool communities are found
where the ocean meets the land.
Organisms must be able to withstand
the changing tides and the motion of
the waves.
Reading Photos
Quick Check
Main Idea What is ecology?
Critical Thinking What is the
difference between a community
and an ecosystem?
What items in the photo
show that this is a tide-pool
Clue: What kinds of organisms
and land features do you see?
What roles do
organisms have?
The success of an ecosystem
depends on its ability to sustain life.
For life to thrive, there must be plenty
of resources, such as food and water.
In addition, the interactions among
living things must be in balance. To
achieve this balance, each member
of a community has a role to play.
A habitat is the place in which
a population lives. Your home is a
habitat. It provides you with the shelter
and food you need to survive. All of
an organism’s needs must be met by
its habitat. If you have ever set up an
aquarium, you know that fish require
water, the proper temperature, food,
and oxygen. Some types of fish and
other aquatic organisms can share a
habitat. In natural ecosystems several
populations may share the same habitat.
The role of an organism in an
ecosystem is called a niche (nitch).
A niche includes everything the
organism does and everything it
needs. Although organisms may share
habitats, they may not occupy the same
niche. Suppose everyone in your town
had the same job and tried to eat at
the same time in the same place. The
competition would become fierce.
Towns, and ecosystems, are successful
because individuals and groups make
different contributions.
Some populations occupy niches
of such importance that many other
organisms depend on them. These
populations are called keystone
species. For example, beavers build
dams that flood the surrounding area,
creating valuable wetlands. These
wetlands are a rich habitat for a wide
variety of living things.
Quick Check
Main Idea What is a habitat?
Critical Thinking Why can
populations share a habitat
but not a niche?
Wetlands help control flooding, filter
pollutants from water supplies, and serve
as habitats for many organisms.
Summarize the Main Idea
Ecosystems are
areas where living
things interact with
each other and with
nonliving things.
(pp. 26–27)
Sunlight and
temperature are
among abiotic factors
that influence the living
conditions in an area.
(pp. 28–33)
Populations include all
the organisms of one
species. Communities
include all populations
living in an area.
(pp. 34–35)
Make a
Study Guide
Make a layeredlook book (see pp.
487–490). Use the
titles shown. On
the inside of each
fold, write two
sentences about
the main idea of
the topic.
Writing Link
Think, Talk, and Write
Main Idea What determines the number
and types of organisms in an ecosystem?
Vocabulary In an ecosystem, all
organisms of one species make up
Main Idea What is the difference
between biotic and abiotic factors?
Critical Thinking If deserts had more
plant life, do you think that a greater
variety of animals would live there?
Why or why not?
Test Practice Which of these is
considered one of the layers of soil?
A alkalinity
B acidity
C bedrock
D humus
Test Practice Which of the following
an abiotic factor?
Math Link
Expository Writing
Monitor Population Growth
Research an endangered species (plant
or animal) in or near the ecosystem in
which you live. What biotic and abiotic
factors have contributed to the decline
of this species?
A state park contains 200 deer. If the
deer population doubles every year for
3 years, how many deer will live in the
park? Make a line graph to show how
the population changes over time.
-Review Summaries and quizzes online @ www.macmillanmh.com
When scientists compare they look for
similarities among objects, materials, and data. As
scientists study a particular ecosystem over time,
they can make comparisons. They can compare
the way the ecosystem functions in the present
with the way that it functioned in the past. With
this information they can predict what the
ecosystem might be like in the future.
Learn It
These hom
es in Lagun
were unaf f
ected by a Beach
When scientists study an ecosystem, they examine
every change they can. Scientists study changes
because one small change in an ecosystem can affect
many biotic and abiotic factors.
Charts and Venn diagrams are tools used to compare.
After you have collected and recorded data, you can see
at a glance whether the data, objects, or materials are
similar or not. Line graphs and bar graphs can also be
used to analyze changing conditions over time.
Try It
▶ Scientists monitor how sudden events such as floods
and mudslides affect an ecosystem. In this activity
you will compare a miniature landscape before and
after a “flood.” You will need a dishpan, soil, rocks,
small twigs, water, and a watering can.
▶ Build a hill landscape of soil, rocks, and
twig “trees” in a dishpan. Draw a picture of
your landscape on a chart like the one on
this page. Use the watering can to sprinkle
water gently on your hills. Record your
▶ Hold the can high, and continue to let
water fall down on the hills. Record
your observations. Pour the rest of the
water quickly over the hills. Record your
observations. Draw a picture of the way
your landscape looks now.
age d these
A landslide dam Beach.
homes in Lagun
Apply It
▶ Now use the information from your chart to create a Venn
diagram like the one on this page. Draw two overlapping
ovals. In one oval list the characteristics of your hill
ecosystem before the “flood.” In the other oval, list the
characteristics of your hill ecosystem after the “flood.” Write
the common characteristics in the area where the two ovals
▶ How did your hill ecosystem change?
▶ How did it stay the same?
▶ Next, choose an ecosystem near your school or home to
observe for a month. Note any changes in the ecosystem,
and make a chart or Venn diagram to compare its
characteristics at the beginning and at the end of the month.
6 IE 7.h. Identify changes in natural phenomena over time without manipulating
the phenomena (e.g., a tree limb, a grove of trees, a stream, a hillslope).
Lesson 2
The Basic
Process of Life
Energy from the Sun helps a plant grow.
A hummingbird gets food and energy from
a plant. How does sunlight produce energy?
6 LS 5.a. Students know energy entering ecosystems as sunlight is
transferred by producers into chemical energy through photosynthesis
and then from organism to organism through food webs.
How does light affect plants?
Form a Hypothesis
Plants need light to grow. What do you think will
happen to a plant’s leaves if you cover parts of them,
so that no light reaches those parts? Write your
answer as a hypothesis in the form “If parts of
a plant’s leaves do not receive any light, then . . .”
Test Your Hypothesis
Wrap small pieces of aluminum foil over parts of
several leaves. Wash your hands after handling
the plant.
• growing plant
(a large-leafed
plant will work
Use Variables Cover at least four different
leaves of the plant in the same way.
• aluminum foil
Place the plant in a window where it will get
lots of light. Water the plant with a measured
amount of water.
• paper clips
• water
Experiment After one day, carefully lift the
foil and check each leaf. Write down your
observations. Gently replace the foil in the same
position. Continue your observations each day for
one week. Replace the foil in the same position
each time. How did the areas covered by the foil
differ from the other parts of the leaves?
Draw Conclusions
Interpret Data How did the changes you
observed progress after one day? After two
days? After a week? How do light and darkness
affect the growth of leaves?
Explore More
Remove the foil from the leaves. Water the plant with
the same amount of water you used in the previous
week, and observe it each day for another week.
What happens when the leaves remain uncovered?
6 IE 7.a. Develop a hypothesis. • 6 IE 7.d. Communicate the steps and
results from an investigation in written reports and oral presentations.
▶ Main Idea
6 LS 5.a
Energy enters ecosystems
as sunlight, which is used
by plants to make food.
▶ Vocabulary
chloroplast, p. 43
chlorophyll, p. 43
photosynthesis, p. 43
roots, p. 44
stem, p. 45
transpiration, p. 48
respiration, p. 50
Why is photosynthesis
Every living thing needs energy to live and
grow. Some organisms, such as animals, get their
energy from eating plants. Where do the plants
get their energy from? Did you know that plants
store energy from the Sun in their cells?
▶ Reading Skill
Poppies use sunlight to make food.
Water + Carbon dioxide → Sugar + Oxygen
coleus plant
▶ chloroplast
seen through
a microscope
Almost all organisms on Earth
depend on the Sun for energy. The
Sun’s energy is stored by plants as
food during the food-making process.
This activity goes on in plant cells that
have chloroplasts (KLOR•uh•plasts),
structures found in the cells of leaves
and stems of green plants. Chloroplasts
contain a substance called chlorophyll
(KLOR•uh•fil), a green substance in plants
that absorbs energy from sunlight.
When sunlight falls on a leaf, the
chlorophyll traps energy from the Sun.
Photosynthesis (foh•toh•SIN•thuh•sis)
is the process of making food by
using sunlight. Plants, and some other
organisms, take in carbon dioxide from
the air and water from the environment.
The plant or other organism then
changes these two raw materials into
two products. The products are sugar,
or food, and oxygen.
Inside the chloroplasts the energy
from the Sun is used to split the water
molecules into hydrogen and oxygen.
The hydrogen and oxygen combine
with carbon atoms to produce food
in the form of sugars. Oxygen, which
is given off by the plant as a waste
product, enters the atmosphere.
Photosynthesis helps sustain life on
Earth. In addition to producing oxygen,
which animals breathe, plants also take
in carbon dioxide to make food. This
helps our environment, because plants
act as natural air scrubbers. They absorb
carbon dioxide that would otherwise
pollute the air. Then they turn it into
oxygen that other living things need.
Quick Check
Summarize Where do plants
store energy from the Sun?
Critical Thinking What is
What do roots and stems do?
When you think of photosynthesis, which part of the
plant do you think of first? Most people think of the leaves.
However, other plant structures play important roles in
photosynthesis as well.
Most roots hold plants in the soil
and take in water and minerals to feed
the plants. There are two kinds of
roots: taproots and fibrous roots.
Taproots are thick and straight with
a few root hairs along the sides.
If you have ever tried to pull a
dandelion out of the ground, you
know that taproots grow very
deep and strong.
Fibrous roots do not grow as
deep, but they branch out into
a network of thin, hairy roots.
These roots can form thick mats.
Plants such as marigolds and
grass have fibrous root systems.
Some plants, such as orchids, have
aerial roots. Aerial roots do not anchor
the plant to the ground or absorb
minerals from the soil. Instead they
reach out above the ground for water
and sunlight to nourish the plant. To
get the sunlight and water they need,
plants with these roots grow high in
the branches of rain-forest trees.
Their green aerial roots are actually
able to carry out photosynthesis.
Roots also store some of the food that
the plant produces. This is why edible
roots such as carrots, sweet potatoes, and
sugar beets have such high nutritional
value. When animals eat these roots,
energy from the Sun passes along to them.
Parts of a Root
Root Hairs Secondary
roots that are
threadlike tissues on
the surface of the root
through which water
and minerals enter
Xylem Tissue
through which
water and
minerals flow up
through the plant
Phloem Tissue
through which
food from the
leaves moves
down through
the plant
Epidermis The
outermost layer
of the root
Root Cap A thin covering,
made up of cells, that
protects the root tip as
it grows into the soil
Parts of a Stem
Soft Stem
Woody Stem
Reading Diagrams
How are the xylem, the phloem, and the
cambium arranged differently in a woody
stem and in a soft stem?
Stems are the parts of a plant
that support leaves and flowers. The
stem also transports water and other
substances between the roots and
leaves. Why do you think plants need
to hold their leaves up to the Sun? They
need to do this so they can receive as
much sunlight as possible to carry out
Look at the diagram on this page.
Inside the stem are tubes called xylem
(ZIGH•luhm) and phloem (FLOH•uhm).
Xylem carries water and minerals up
from the roots through the plant to
the leaves. Phloem carries food from
the leaves to other parts of the plant.
Xylem and phloem may be separated
by another layer of cells called the
Stems also help store energy. Like
roots some stems store energy in the
form of food. Sugarcane is an example
Clue: Compare the drawings of the two
types of stems. How are they alike? How
are they different?
of an edible stem. Some plants, such as
asparagus, have photosynthetic cells in
their stems that can help make food.
Other plants use stems as a reservoir
for water. In what environment do you
think it is very important for plants to
store large amounts of water? You are
correct if you said, “The desert.” Some
kinds of cactuses can store enough
water to get through several days or
even several years without rainfall!
Quick Check
Summarize What functions do
roots and stems share?
Critical Thinking How do roots,
which are not green, contribute
to photosynthesis?
What are leaves?
Look at a leaf from a tree or
a shrub. You might have difficulty
accepting the fact that the leaf is such
a powerful food-making machine.
Inside the thin blade of the leaf are
the structures that provide Earth with
food, oxygen, and clean air. Leaves
with only one blade are simple leaves.
Leaves with two or more blades are
compound leaves.
The parts of a leaf work together
to help keep the plant alive. The
outermost part of a leaf is its epidermis
(ep•i•DUR•mis). Cells of the epidermis
secrete a waxy coating called a cuticle
Parts of a Leaf
(KYEW•ti•kuhl). This waxy covering
helps prevent water from leaving the
plant. The leaf makes food in cells
between the layers of the epidermis.
These cells contain chloroplasts. The
epidermis on the lower surface of a
leaf contains many tiny pores called
stomata (STOH•muh•tuh) (singular,
stoma). Stomata open and close to
let gases, such as carbon dioxide and
oxygen, in and out. These openings
also control the amount of water
that leaves the plant. Guard cells
surrounding the stomata regulate
when the stomata open and close.
How Leaves Work
The veins that run through the
leaf blade bring water and minerals
to the last stop on their journey from
the roots. When carbon dioxide enters
through the stomata and sunlight is
captured by the chlorophyll in the
chloroplast, all the ingredients are
in place to produce food.
Some leaves, such as those of
spinach or lettuce, store food. Others
are designed to protect the plant. The
spines on a cactus are actually the
leaves. They do a good job of protecting
the plant from being eaten, and their
small size and pointed shape minimize
water loss in the dry environment of
a desert.
Collect a variety of leaves.
Observe Examine each leaf with
a hand lens, and write down each
structure that you can identify.
Place a piece of white paper over
the leaf, and rub back and forth
with a crayon, making a print of
the leaf.
Identify On the rubbing, identify
the leaf as simple or compound,
and label each structure.
Using two different-color crayons,
trace the flow of water and food
through the veins.
In some areas of the world
where there are seasonal changes in
temperature, plants shut down their
food-making factories at certain times
of year. During the winter months, they
live off the food they have stored. Green
chlorophyll disappears from the leaves.
When this happens people can see the
other colors, such as yellow and orange,
that are usually masked by the green
pigment. Maple trees, as well as some
other plants, store sugar in their leaves.
The stored sugars trigger the formation
of a red pigment, giving these plants
their vibrant autumn colors.
Quick Check
Summarize What do leaves do
for a plant?
Critical Thinking What is the
difference between a simple leaf
and a compound leaf?
How does water move through plants?
Roots absorb water and minerals from the soil. The stems
and leaves transport the water and minerals throughout the
plant. This might not seem like a huge task in a small plant,
but how can water reach the top of a 90-meter (295-foot)
giant sequoia?
Several forces work together to move water through a
plant. Pressure builds up in the roots and forces water to
move upward into the stems. In small plants root pressure
alone can move water all the way through the plant. However,
in most plants root pressure is not enough to push water
through tall stems and into leaves. Forces that pull the water
upward are needed as well.
Capillary action is one force that pulls water up into plants.
Water molecules stick to one another and to other substances,
such as glass, cloth, cells, and soil. You can observe capillary
action by dipping the corner of a paper towel into a glass of
water. The water will appear to climb up the paper towel.
The other force that pulls water upward through a plant
is caused by evaporation. Transpiration (trans•puh•RAY•shuhn)
is the loss of water from plant leaves. The water in the
plant travels up through the veins of the leaves, and then it
evaporates into the atmosphere through the stomata. As the
plant loses water, more water moves into the plant cells to
take the place of the water that has been lost.
These three forces—root pressure, capillary action,
and transpiration—work together to keep water moving
through the parts of the plant. These forces help the plant
carry out photosynthesis and keep it from wilting.
Quick Check
Summarize What three forces move water upward
through a plant?
Critical Thinking What would happen to the plant if
it did not have stomata on the bottoms of its leaves?
◀ A huge tree can move more than 1,800 liters (476 gallons)
of water from the ground to its leaves each day. Most
people drink about 2 liters (4 pints) of water each day.
sequoia tree, Sequoia National Park, California
How Water Moves Through a Plant
Almost 99% of the water
that enters the roots is
given off into the air by
transpiration through
the leaves’ stomata.
Water moves up the stem,
through a leaf’s petiole,
and into the leaf’s veins.
The veins carry the water
to the leaf’s cells.
The water is pushed upward
into the xylem and travels
up the stem. Capillary
action pulls water up
through the xylem.
Reading Diagrams
What causes water to travel from a plant’s
roots to its stem?
Loss of water through
transpiration in the leaves
helps pull the water upward
through the xylem toward
the top of the plant.
Water and dissolved
minerals enter the plant’s
root hairs from the soil.
Pressure builds up in the
roots as water moves in.
Clue: Follow the path of the blue arrows in
the diagram, and read the text on page 48.
Watch how plants
transport water @ www.macmillanmh.com
Apples contain energy stored
during photosynthesis.
What happens during
When food is eaten, energy passes from
organism to organism. Every time energy
is passed along, some energy is lost. Each
organism uses some of the energy for its own
daily activities. How does a plant or animal
use the energy that is stored in the food it eats?
When an organism needs fuel, its cells can
use oxygen to break apart food molecules. The
release of energy in plants and animals from
food is called respiration (res•puh•RAY•shuhn).
In respiration, which occurs in plants and
animals, sugars and oxygen join to produce
water, carbon dioxide, and energy.
Water + Carbon dioxide → Sugar + Oxygen
happens only in cells with chloroplasts
needs sunlight
stores energy
turns energy to a sugar
produces oxygen
uses water to make food
uses carbon dioxide
Sugar + Oxygen → Carbon dioxide + Water + Energy
happens in most cells
happens in light or dark
releases energy
turns a sugar to energy
uses oxygen
produces water
Quick Check
Summarize What role does
respiration play in cells?
Critical Thinking Why can
photosynthesis and respiration
be considered reverse processes?
produces carbon dioxide
Summarize the Main Idea
Photosynthesis is the
process in which plants
convert energy from the
Sun into usable chemical
energy stored as food.
(pp. 42–43)
Roots and stems
transport water and
other substances
between the roots
and the leaves.
(pp. 44–49)
During respiration,
plants and animals
release energy from
(p. 50)
Make a
Study Guide
Make a three-tab book
(see pp. 487–490).
Use the titles shown.
On the inside of each
tab, summarize how
that topic can help you
understand how plants
make food.
Writing Link
Think, Talk, and Write
Main Idea How does energy enter
Vocabulary The process by which
plant leaves lose water is
Summarize How does root pressure
differ from transpiration?
Critical Thinking Explain
the relationship between plants
and an atmosphere suitable for
sustaining life.
Test Practice In addition to carbon
is one of the
products of respiration.
A sugar
B oxygen
C chlorophyll
D energy
Test Practice What is the process
of making food by using sunlight?
A photosynthesis
B xylem
C transpiration
D chloroplast
Math Link
Write a Narrative
Calculate Oxygen Released
Describe the journey of a water
molecule through a plant. How does
it enter the plant? How does it move
through the plant? How does it exit
the plant?
A forest produces 56 liters of oxygen
in 1 week. A single plant can produce
1 liter per week. How long will it take
the forest to produce enough oxygen
to fill a 10,000-liter tank?
-Review Summaries and quizzes online @ www.macmillanmh.com
Life in the
Good expository writing
▶ introduces the main idea
and develops it with facts
and supporting details.
▶ gives important information
about a topic.
▶ summarizes information
from a variety of sources.
▶ uses transition words, such
as therefore and then, to
connect ideas.
▶ draws a conclusion based
on the facts and information
Until recently scientists thought that
all life on Earth depended on sunlight.
In the 1970s they made a startling
discovery. They found creatures on the
ocean floor that did not need sunlight
to live. The question, then, was how
these creatures could survive on the
cold, dark ocean floor.
Earth’s mantle contains hot,
melted rock called magma. When
breaks in Earth’s crust occur on the
ocean floor, magma wells up, fills in
the spaces, and gushes forth as a hot
liquid called lava.
These worms live near
hot-water vents on the
ocean floor. They eat
bacteria that live on
chemicals in the water.
galatheid crab
ELA W 6.1.2. Create multiple-paragraph expository compositions: a. Engage the interest
of the reader and state a clear purpose. b. Develop the topic with supporting details and
precise verbs, nouns, and adjectives to paint a visual image in the mind of the reader.
c. Conclude with a detailed summary linked to the purpose of the composition.
The lava contains large amounts
of various chemicals that bacteria
feed on. These hot spots are called
hydrothermal vents. Scientists found
worms, clams, crabs, mussels,
and fish living near these vents.
The animals survive in this dark
environment by eating these bacteria.
Most life on Earth depends on
sunlight and on photosynthesis—but
not all life does! Nature is full of
Write About It
Expository Writing Write a report
telling how sunlight helps support your
life. Engage your reader right away, and
clearly state your purpose for writing.
Introduce the main idea, and develop it
with facts. Use supporting details and
precise verbs, nouns, and adjectives to
describe and explain your subject. Do
print and online research. Summarize
your findings at the end of the report.
-Journal Write about it online
Lesson 3
on Earth
Did you ever think about where some of the most
amazing and beautiful organisms can be found? Look at
several drops of pond water through a microscope. The
paramecium shown here is one part of the fascinating
world of microscopic organisms.
6 LS 5.b. Students know matter is transferred over time from one organism to
others in the food web and between organisms and the physical environment.
What can you see through
a microscope?
Make a Prediction
What do you think you will see if you look at an
onion skin, sand, or yeast under a microscope? Write
your prediction in the form “If I look at an onion skin,
sand, or yeast under a microscope, then . . .”
• microscope
Test Your Prediction
• 4 microscope
Observe Place a piece of newspaper on a
• dropper
microscope slide. Place the slide on the stage
of the microscope, and observe it under
low power. Draw what you see. Look at the
newspaper again under high power. Record
your observations.
• water
• toothpick
• small pieces
of newspaper
Observe Select your own samples. Repeat
step 1 for each sample. Record what you see.
• onion skin
Record Data Make a data table to record
• sand
the details of what you observed. How many
organisms did you observe? How big were
they? What colors were they?
• yeast
Draw Conclusions
Observe What did you learn about the
way objects appear when viewed through a
microscope? What happened to your observations
as you changed from low power to high power?
Observe Describe the appearance of each
of the samples you observed.
Explore More
Did you see any differences among the samples
under the microscope? Research the types of cells
you looked at. Analyze and present your results.
6 IE 7.b. Select and use appropriate tools and technology
(including calculators, computers, balances, spring scales,
microscopes, and binoculars) to perform tests, collect data,
and display data.
▶ Main Idea
What are microscopic
6 LS 5.b
Microscopic organisms are found everywhere.
They live and grow on every surface in the
world. Some are producers, which can make
their own food by photosynthesis. Others are
consumers, which eat other organisms for food.
Some are decomposers, which break down and
consume dead organisms. Microorganisms are
an important part of Earth’s ecosystems. They
provide larger organisms with some of the food
and oxygen they need to survive. They help
enrich the environment by breaking down
dead organisms.
Energy and matter are
transferred from one
organism to another at
the microscopic level.
▶ Vocabulary
microscope, p. 57
electron microscope, p. 57
prokaryote, p. 58
eukaryote, p. 58
protist, p. 59
▶ Reading Skill
Classify and Categorize
Compound Microscope
Reading Diagrams
What parts of the microscope would
you use to change the focus?
Clue: Look at the diagram, and read
the labels.
Studying Microscopic Organisms
A microscope is an instrument
that produces an enlarged image of
an object. Anton van Leeuwenhoek
(AN•ton•vahn•LAY•ven•hook), a Dutch
merchant, used a microscope to study
microscopic organisms in the 1600s.
His tool was very simple, but scientists
today have more-powerful microscopes
that enable them to see microscopic
organisms in much greater detail.
Scientists study living and nonliving
microscopic organisms with an
instrument called a compound light
microscope. A compound light
microscope uses two or more lenses
and a light source to magnify
objects. The lens on the bottom of
the microscope’s body tube is the
objective lens. The lens at the top
of the body tube, nearest your eye,
is called the ocular lens.
Samples placed on the stage of the
microscope are first magnified by the
objective lens. The image that reaches
the ocular lens is then magnified
again. For example, the objective
lens of a microscope magnifies an
object 200 times (200x) and the
ocular lens magnifies it 10 times
(10x). If these two magnifications are
multiplied together, then the overall
magnification is 2,000 times (2,000x)
(200 × 10 = 2,000). Images begin to
get blurry at magnifications higher
than 2,000x.
Scientists study very small, nonliving
organisms and other objects with
an electron microscope . This is
a powerful microscope that uses a
beam of electrons, rather than a light
▲ Scanning electron microscopes produce
magnified images, such as this picture
of bacteria found on the human tongue.
source, to magnify samples. Electron
microscopes cannot be used on living
samples, because the stream of electrons
and the preparation process would
kill them. The most commonly used
electron microscope is called a scanning
electron microscope, or SEM. The SEM
can magnify as much as 300,000 times
(300,000x). It scans the surfaces of
nonliving samples and gives detailed
three-dimensional images of them.
Quick Check
Classify and Categorize Describe
the different kinds of microscopes.
Which do scientists use to study
living organisms?
Critical Thinking Explain why
scientists do not use electron
microscopes to study human
What are microscopic organisms
that make their own food?
Microscopic organisms are
classified in two ways: by their cell
structure and by what they eat. The
cell structure determines whether they
are prokaryotes (pro•KEH•ree•ohtz)
or eukaryotes (yoo•KEH•ree•ohtz).
Prokaryotes have a simple cell
structure without a nucleus in each
cell. Eukaryotes are more complex
organisms that do have a nucleus in
each cell. Within each of these two
groups, there are organisms that eat
other organisms (consumers) and
those that can make their own food
Producers make food by using the
energy in sunlight for photosynthesis.
Green plants use photosynthesis to
make their own food and release
oxygen. However, green plants are not
the only organisms that carry out
photosynthesis. Many microscopic
producers make their own food and
give off oxygen.
Microscopic organisms that
produced the oxygen that first
made Earth inhabitable for other
living things were prokaryotic
producers, such as cyanobacteria
(SIGH•an•oh•bak•teer•ee•uh). They can
be found in many places, including
fresh and salt water, hot springs, and
the Arctic. Today cyanobacteria and
other photosynthetic microscopic
producers produce about half of our
oxygen supply. Without these
organisms plants and trees alone
would not be able to support life
on Earth.
▼ Cyanobacteria often form a
chain of cells called a filament.
These chains can produce
different kinds
of algae.
Another kind of microscopic
organism is a protist. A protist is a
single-celled, eukaryotic organism that
cannot be clearly classified as animal
or plant. Many protists are capable
of producing their own food through
photosynthesis, like plants. Others eat
microscopic organisms.
One example of a photosynthetic
protist is a diatom. Diatoms live in
either salt water or fresh water. These
protists are very small and have
shapes such as straight lines, circles,
or squares. Because there are so many
diatoms living in lakes and oceans,
they are some of the most important
producers of oxygen and are a major
food source for many other organisms.
Another kind of protist is a
dinoflagellate (dighn•uh•FLAJ•uh•luht) .
A dinoflagellate has characteristics
of both plants and animals. Some
species of dinoflagellates can light up
like fireflies. When stirred up, they give
off light and make the ocean appear
to glow in the wakes of passing boats.
Most dinoflagellates are photosynthetic
and make up a significant part of the
phytoplankton, or photosynthetic
microorganisms that float in oceans
and lakes. They are also important
oxygen producers and a major food
Quick Check
Classify and Categorize How
do scientists classify microscopic
organisms that have characteristics
of both plants and animals?
Critical Thinking How are
cyanobacteria different from
plantlike protists?
What are microscopic organisms
that cannot make their own food?
Some microscopic organisms
are not able to make their own food.
Instead, they need to find food in
their environment. They must be able
to move to where food is. To do this
they have developed structures on the
outsides of their cells that help them
move and eat.
One protist of this type is a
protozoan. Protozoans have no cell
walls and can find and eat food.
Examples of protozoans include
flagellates (FLAJ•uh•latz) and ciliates.
Flagellates are protozoans that have
flagella (fluh•JEL•uh), or long, hairlike
structures that whip and lash to help
them swim. Some flagellates live in
ponds and lakes, feeding on smaller
organisms. Many others are parasites,
which means that they feed off and
harm other organisms.
All protists that have small, hairlike
projections, or cilia, extending from
the outsides of their cells are called
ciliates. These organisms use the cilia
as oars to move themselves through
water. Ciliates also use their cilia to
direct bacteria and other food from
their environment into a food vacuole.
A food vacuole is a structure inside
a cell that stores food.
▶ Scientists use scanning
electron microscopes to
study microorganisms.
Other Traveling Protists
Another group of protists has
pseudopods (SOO•doh•podz), or “false
feet.” This group of protists includes
hundreds of species of amoebas.
Found in fresh water, salt water,
and soil, amoebas use their pseudopods
to pull themselves in the direction
in which they want to move. They
also use their pseudopods to eat. An
amoeba will extend a false foot and
wrap it around what it wants to eat.
When the end of the pseudopod meets
the amoeba’s body, both the foot and
the food become part of the body.
Once the food is inside the amoeba,
it gets wrapped in a food vacuole to
be digested.
paramecium magnified 100 times
Observing Protists
Slide a metric ruler onto the stage
of your microscope, and focus on
it, using the highest power. Measure
the field of view, and record your
measurement in millimeters.
Obtain a pond-water
sample from your
teacher. Put a drop of
the water in the center
of a microscope slide.
Gently place a coverslip
over it.
▲ The most common example of a ciliate
is the paramecium. Tiny surface hairs
enable it to move.
euglena magnified 130 times
Observe Starting with
the lowest power, focus
the microscope until
you find microorganisms.
Switch to high power, and
focus. Draw what you see.
▲ A euglena can make its own food or eat
food from the environment. A flagellum
helps it move.
amoeba magnified 30 times
Measure Estimate how much
area one microorganism you are
observing takes up. Multiply that
number by the size of your field
of view to estimate the size of
the organism in millimeters. For
example, 1 × 1 mm = 1 mm.
Quick Check
Classify and Categorize How are
microscopic consumers grouped?
Critical Thinking How do
microscopic consumers get to
their food?
Reading Photos
▲ An amoeba moves by forming thick
extensions, or pseudopods. As a
pseudopod is thrust forward, the
rest of the amoeba flows with it.
Which protozoan is the smallest?
The largest?
Clue: Read the label that tells
how many times each protozoan
was magnified.
lake ecosystem
What roles do microscopic
organisms have in ecosystems?
Microscopic producers make their own food through
photosynthesis. As a result of that process, they give
off about half of the oxygen in our atmosphere. However,
microscopic consumers cannot make their own food.
As a result they eat other microscopic organisms.
Both microscopic producers and microscopic consumers
are the main food source for larger consumers. There are
also microscopic organisms that feed on dead organisms
of all sizes. These organisms are called decomposers,
and their job is to recycle organic materials back into
the food chain. This cycle of what eats what becomes
the first set of links in a food chain that extends
from the tiniest organisms all the way to humans.
Quick Check
Classify and Categorize What are the
three roles of microscopic organisms?
Critical Thinking What would happen if
all organisms could make their own food?
▼ These mushrooms
help recycle
the log.
Summarize the Main Idea
Microscopes are tools
that produce enlarged
images of objects.
(pp. 56–57)
Think, Talk, and Write
Main Idea Matter and
are transferred from one organism
to another at the microscopic level.
Vocabulary A(n)
an enlarged image of an object.
Classify and Categorize What is the
Microscopic organisms
that produce food
include cyanobacteria,
diatoms, dinoflagellates,
and euglenas.
(pp. 58–61)
Microscopic producers
form the foundation
for most food chains
in the oceans and in
freshwater ecosystems.
(p. 62)
Make a
Study Guide
Make a three-tab book
(see pp. 487–490).
Use the titles shown.
On the inside of each
tab, write several
sentences that classify
and categorize each of
the topics.
Writing Link
major difference between eukaryotes
and prokaryotes?
Critical Thinking Why are protists
hard to identify as plants or animals?
Test Practice Which organisms use
pseudopods to move?
A amoebas
B euglenas
C cyanobacteria
D diatoms
Test Practice Which organisms live
either salt water or fresh water?
Math Link
Write a Narrative
Determine Magnification
Write about one of the microorganisms
that you have learned about. Describe
what its life is like. What does it look
like? How does it move? Does it have
any enemies?
If the objective lens on a microscope
magnifies an object 100 times (100x),
and the ocular lens magnifies it
10 times (10x), what is the overall
-Review Summaries and quizzes online @ www.macmillanmh.com
What do museums do when their artwork and
other cultural artifacts are being slowly eaten by
organisms they can’t even see? They turn to scientists
like Maria Pia Di Bonaventura at the American
Museum of Natural History. Maria Pia is not a
detective, but she knows how to unlock mysteries like
these, where the main suspects are microorganisms
such as fungi and bacteria.
Maria Pia helped an art museum take a
microscopic look at several paintings. Paintings
made of wood, ink, oils, and canvas can be perfect
environments for some microorganisms to grow in.
You may not be able to
see them with your eyes,
but they give themselves
away by their green, blue,
and yellow tints and the
black markings they leave
▶ Maria Pia is a microbiologist.
That’s a scientist who
studies microorganisms
and their effects on other
ELA R 6.2.3. Connect and clarify main ideas by identifying
their relationships to other sources and related topics.
Meet a Scientist
To study the microorganisms
that are making their home in the
art, Maria Pia first takes a sample
of them. Back in the lab, Maria Pia
focuses on the fungi. She grows
them to find out more about their
DNA. The DNA provides the
information that Maria Pia uses to
determine the species of the fungi.
The different species respond to
different treatments, so after she
identifies a species, she can figure
out the best way to protect the
paintings from its damage.
Fungi don’t just live on
paintings. They live in all kinds
of environments on our planet,
in the tropical rain forests and
the cold tundras, in the rivers
and the oceans, and even in
deserts! Maria Pia is interested
in investigating their amazing
diversity—there are over 100,000
▲ Fungi grew on and damaged
this artwork.
species of fungi, and more are
being discovered all the time. In
fact, the world’s largest known
organism is thought to be a fungus
weighing over 100 tons, about the
weight of an adult blue whale!
Write About It
Main Idea
1. Why do museums ask for help
from scientists like Maria Pia
Di Bonaventura?
2. How does Maria Pia’s work help protect
works of art and other artifacts?
Main Idea
▶ Look for the question or
problem being discussed.
▶ Think about how the details
relate to each other.
-Journal Write about it online
Lesson 4
Earth’s Food
Chains, Webs,
and Pyramids
Whales are among the largest animals ever to have lived
on Earth. What do such large animals eat? Surprisingly,
many of them eat some of the smallest organisms in the
ocean: tiny shrimplike animals called krill. A humpback
whale eats as much as 1,360 kilograms (3,000 pounds)
of krill, plankton, and small fish each day.
6 LS 5.b. Students know matter is transferred over time from one
organism to others in the food web and between organisms and the physical
environment. • 6 LS 5.c. Students know populations of organisms can be
categorized by the functions they serve in an ecosystem.
How can you model a food chain?
Make a Prediction
What would a food chain of 20 organisms look
like? Would it be linear? Write your answer as a
prediction in the form “If 20 animals were made
into a food chain, then it would look like . . .”
Test Your Prediction
Cut construction paper into 20 rectangles. Write
the names of eight producers, six animals that
eat the producers, four animals that eat the plant
eaters, and two animals that eat the animals
that eat the plant eaters. Make a hole in each
• top half of empty
soda bottle
• yarn
• construction
Make a Model Cover the top of the soda
bottle with construction paper. This will be the
Sun. Punch eight holes around the rim. Attach
a piece of yarn to each of the eight producers.
Attach the other ends to the soda bottle. Using
yarn, link each plant-eating animal to a producer.
Continue by linking the animals that eat the plant
eaters to the plant-eating animals. Only one animal
may be attached to a food source.
• hole punch
• scissors
Draw Conclusions
Observe How many levels are in your model?
What happens to the number of organisms in
each level as you move away from the Sun?
Predict What would happen to the number of
plant eaters if a drought destroyed the plants?
What happens to the animal populations?
Explore More
What changes might occur in an ecosystem into
which the predators move? Make a prediction and
test it. Then analyze and present your results.
6 IE 7.d. Communicate the steps and results from an
investigation in written reports and oral presentations.
▶ Main Idea
6 LS 5.b
Energy and matter are
transferred from one
organism to another
in food chains and
food webs.
▶ Vocabulary
producer, p. 69
consumer, p. 69
decomposer, p. 69
food chain, p. 70
primary consumer, p. 71
secondary consumer, p. 71
tertiary consumer, p. 71
food web, p. 72
herbivore, p. 72
carnivore, p. 72
omnivore, p. 73
predator, p. 73
prey, p. 73
scavenger, p. 73
energy pyramid, p. 76
▶ Reading Skill
Compare and Contrast
cattle grazing,
Big Sur, California
▲ These cattle get their energy directly from
the grass, which is a producer. How would
you classify the cattle? They are consumers.
What are producers, consumers,
and decomposers?
Think about how food is arranged at the
grocery store. There are sections for baked
goods, meats, produce, and dairy products. How
do you think each of the food groups would fit
into an ecosystem? Energy in many ecosystems
begins with the Sun and is transferred from one
organism to another. Each living thing has a role
in this process.
Explore food webs
with a park ranger.
Explore energy
pyramids with
a farmer.
Think of the last time you went to the grocery
store. What did you see in the produce section?
You saw producers—fruits and vegetables. The
grains used to make the bread in the bakery aisle
are producers, too.
Producers , such as plants and
algae, are organisms that use energy
from the Sun to make their own
food. They also produce oxygen
and food that other living things need
to survive. Most producers on Earth
live near the surface of the ocean,
where tiny photosynthetic organisms
carry out more than 70% of the
photosynthesis that occurs on Earth.
Green plants are among the producers
that live on land.
If an organism cannot create
its own food, it must directly or
indirectly consume, or eat, other
organisms. Consumers get energy
by feeding directly on producers
or by eating animals that feed on
producers. If you eat fish, chicken,
or beef, you are indirectly getting
energy from a producer. The steer
that is now a steak either grazed on
grass or was fed a mixture of grains.
▼ These mushrooms are
returning important
substances to the
environment by
breaking down
the stump of
a maple tree.
Decomposers break down dead
organisms into simpler substances.
Some of these substances are absorbed
by the decomposers. Others are
returned to the environment. This
is one reason why decomposers are
an important part of an ecosystem.
Elements that are essential to life,
such as oxygen, nitrogen, and carbon,
are building blocks of living things.
When decomposers do their jobs,
they recycle these and other important
substances back into the environment.
In the process they clean up the
environment by ridding it of waste
matter. Earth’s decomposers include
worms, bacteria, fungi, and insects.
Quick Check
Compare and Contrast What are
the main differences among producers,
consumers, and decomposers?
Critical Thinking How do consumers
get the energy they need to survive?
What is a food chain?
A food chain shows how energy
flows from one organism to another in
an ecosystem. In a food chain, producers
absorb the Sun’s energy before passing
it on to consumers and decomposers.
The path by which the energy travels can
be short and simple or long and complicated.
What does a food chain look like? Is it arranged
by size, from the largest organism to the smallest?
Do larger organisms always consume organisms of
a slightly smaller size? This is not always the case.
Remember the humpback whale? It eats krill, some
of the smallest animals in the sea. Cougars, on the
other hand, sometimes prefer to prey on animals
larger than themselves, such as moose and elk.
▲ The zebra and
the lion are part
of a food chain.
Forest Food Chain
Reading Diagrams
What is the path of energy
in this forest food chain?
Clue: Follow the arrows.
Your Food Chain
Keep a log of everything you eat
for one day.
Classify For each food, determine
whether it is a producer or a
Classify Which foods did you list
as producers?
Links in the Food Chain
Consumers can be classified by
where they fall on the food chain.
Primary consumers , which are
organisms that eat producers, are the
second link in a food chain after
producers. On land, primary consumers
include insects, mice, rabbits, horses,
and elephants. The size of the animal
does not always determine its diet or
its location on the food chain.
The organisms that get their energy
by eating primary consumers are
called secondary consumers .
Secondary consumers make up the
third link in a food chain. Many birds,
for example, are secondary consumers,
because they eat insects that feed on
plants. A snake that eats such a bird
is a tertiary consumer . A tertiary
consumer is usually the top predator
in a food chain. There are usually many
producers and few tertiary consumers.
What happens to an organism
that is not eaten? If an organism
is not eaten, it will eventually die.
Decomposers are present throughout
the food chain to break down the
remains of dead plants and animals.
Classify Which foods did you list
as consumers?
Communicate Select two foods
from the consumer group, and
draw a possible food chain for
each. Do not forget to include
yourself. Did you include
decomposers in your food
chain? Where do they fit?
The remains of these plants and
animals break down into nutrients that
producers use. This completes the cycle
and allows another food chain to begin.
The amount of energy present decreases
as it travels through each organism, but
it never completely disappears. Some of
the energy is used for life processes, and
some is given off as heat, but it never
completely disappears.
Quick Check
Compare and Contrast How do
people fit into the food chain?
Critical Thinking Compare primary,
secondary, and tertiary consumers.
What is a land food web?
Do you eat only one kind of food?
If you are like most people, you enjoy
a variety of foods. In nature most
organisms would not survive if they
fed on only one type of food.
A food chain represents only one
thing that each consumer may eat. It
shows only one path that the energy
follows from the Sun through the food
chain. A food web shows all the food
chains in an ecosystem and shows how
they overlap. Food webs also show the
roles and relationships among all the
species in an ecosystem.
Just like food chains, all food webs
begin with producers. Herbivores are
primary consumers, or animals that
eat producers. On land, herbivores
have flat-edged teeth in the fronts
Land Food Web
A food web is a series of overlapping
food chains. It is a more accurate
representation of the feeding
relationships in an ecosystem
than a food chain,
because most
animals eat more
than one thing.
of their mouths for tearing plant
material. Their flattened back teeth
are perfect for grinding the plants
to a pulp. Many ocean-dwelling
animals are filter feeders. Some filter
feeders use modified teeth, called
baleen, to filter out small organisms
from huge mouthfuls of water.
Carnivores are secondary and
tertiary consumers, animals that eat
other animals. Some carnivores rip
into prey with their sharp incisors
and canine teeth or with their beaks.
They typically eat more than one kind
of animal. For example, coyotes eat
a variety of small mammals as well as
birds and snakes. Cats will eat fish and
other animals. The golden eagle preys
upon a variety of animals, including
prairie dogs, rabbits, and ground
Animals that eat both producers
and consumers are omnivores . Many
animals, including humans, are
omnivores. Raccoons will eat fruits,
nuts, grains, birds’ eggs, young rabbits,
rodents, fish, turtles, and even scraps
from your garbage.
Living things that hunt and kill other
living things for food are predators .
The animals they hunt are prey . Most
animals, at one time or another, will be
both predator and prey. A snake can eat
a mouse one day and find itself as prey
for a hawk the next day.
Reading Diagrams
▲ The California condor
is a large scavenger.
Which of these animals are
predators? Which are prey?
Clue: Follow the arrows on
the diagram to see which
animals prey on others.
Have you ever been on a scavenger
hunt? It is a game in which you have to
find items. In the same way, scavengers
seek out the remains of dead animals
to eat. They eat meat without hunting
or killing the prey. Jackals, vultures,
and crows are scavengers. Fungi are
another type of scavenger. Fungi such
as mushrooms get their energy from
decaying plants and animals.
Quick Check
Compare and Contrast What
is the difference between a food
chain and a food web?
Critical Thinking Which roles in
a food web could people play?
What is a marine food web?
Just like land food webs, marine
food webs begin with producers.
In the ocean, phytoplankton are
the primary producers. Because
phytoplankton depend on sunlight
to carry out photosynthesis, the size
of their populations depends on the
amount of sunlight that penetrates
the water. Oceans are divided into
different areas depending on the
amount of sunlight they receive
and the temperature of the water.
Intertidal Zone
The intertidal (in•tur•TIGH•duhl)
zone is the area of the ocean at the
edge of the land. This area is affected
by changes in high and low tides.
Despite the harsh conditions found at
the ocean’s edge, the intertidal zone
supports a variety of living things. Each
time the tide comes in, the plants and
animals that live there are submerged in
water. At low tide they are exposed to
air and sunlight.
Some parts of the intertidal zone
are covered by water only during the
highest tides. Only a few species of
algae and mollusks are found there.
Areas that are underwater during high
tide contain algae and animals such as
snails, crabs, sea stars, and small fish.
These are food sources for many land
and sea creatures as well as shorebirds.
red knots
Ocean Zones
From just beyond the low-tide
line to the point where the open
ocean begins is an area where
sunlight penetrates and waters are
calmer. There you will find
some of the world’s most
magnificent underwater
habitats. For example,
the giant kelp forests
off the California coast
provide food and shelter
to hundreds of species
of fish, invertebrates,
marine birds, and marine
mammals. This is a region
of complex food webs with
predators such as sea lions and
harbor seals and many types of
prey at every feeding level.
In the open ocean, most organisms
live in three main zones. The top, or
sunlight, zone reaches from the surface
down to about 200 meters (656 feet).
Plankton live near the surface, where
the sunlight penetrates the water.
Squid, octopuses, whales, fish, and
many other organisms feed on the
Between about 200 meters (656
feet) and 1,000 meters (3,280 feet)
there is little light. This zone, the
twilight zone, is dark and cold, with
little food available. Animals that live
in this zone have adaptations for these
harsh conditions. The third zone down
has no light and is called the midnight
zone. No photosynthetic organisms
grow here, and some animals are
▲ Sea otters find shelter and food in
the diverse kelp-forest community.
Quick Check
Compare and Contrast What are
the differences among the three
main zones in the open ocean?
Critical Thinking What do land
food webs and marine food webs
have in common?
How are populations
Food chains and food webs
show how energy flows through an
ecosystem. What they do not show
is how energy is lost as it passes
from producers to consumers to
decomposers. Energy pyramids are
models that show how energy moves
through a food chain. Producers always
make up the base of the pyramid.
At each feeding level above the base,
energy is lost. When animals eat, they
cannot absorb all the energy their food
contains. Organisms also lose energy
when they perform their daily activities.
Think about the energy you use each
day. As energy is used, it is transferred
to the environment as heat.
Energy decreases from the base
of the pyramid to the top. About
10% of the energy at one level can
be used by animals at the next level.
With less and less energy available at
higher levels, fewer animals can survive.
Are there more producers or consumers
in the world? The decrease in energy
limits the number of consumers on the
food chain, so there are more producers.
▶ ocean energy pyramid
Anything that happens in an
ecosystem can upset the balance of
food and energy. As long as populations
in a community can obtain the food,
water, and shelter they need, they can
reproduce and grow as a species. If
something happens to decrease any
of these resources, competition may
increase within the community. This
can cause the population of a species
to decrease or even to become extinct.
On the other hand, the species might
adapt to change or migrate to new
areas. Knowing about food chains and
food webs helps scientists predict how
communities will be affected by change.
Quick Check
Compare and Contrast What do the
layers of an energy pyramid show?
Critical Thinking What would
happen if resources decreased
in a location?
Summarize the Main Idea
Producers use energy
from the Sun to
make their own food.
Consumers get their
energy from producers.
(pp. 68–69)
A food chain shows the
flow of energy from
one organism to
another in an ecosystem.
(pp. 70–71)
A food web shows all
the food chains in an
ecosystem and how
they overlap.
(pp. 72–75)
Make a
Study Guide
Make a three-tab book
(see pp. 487–490).
Use the titles shown.
On the inside of each
tab, compare and
contrast the role of
each topic with others
in the lesson.
Writing Link
Think, Talk, and Write
Main Idea Food chains show how
Vocabulary A(n)
the remains of dead animals it finds.
Compare and Contrast How is a
scavenger different from a decomposer?
Critical Thinking Explain why a food
web tells us more about an ecosystem
than a food chain.
Test Practice Which of the following
is not a group into which organisms
are classified in an ecosystem?
A producers
B decomposers
C consumers
D energy pyramids
Test Practice What are living things
that hunt and kill other living things
for food?
A herbivores
B predators
C fungi
D scavengers
Math Link
Persuasive Writing
Use Percents
Research an issue that affects Earth’s
ecosystems. Then write and record a
public-service announcement to state
your position on the issue.
An energy pyramid shows that
90% of the energy is lost from one
level to the next. If you start with
100,000 units of energy, how much
energy does the next level get?
-Review Summaries and quizzes online @ www.macmillanmh.com
Why Are They
at the Top
of Their
Food Chain?
Have you ever seen an eagle, a hawk, or an owl swoop
down and capture its food? These birds of prey, or
raptors, are at the top of their food chain, because they
have few predators. Their bodies are amazing flying
machines that enable them to attack quickly and fly
away with their prey.
Raptors have strong, sharp beaks and
Finding ratios
large wings. Their wings help them soar
and swoop down on their prey, which they
To find the ratio of body
capture in their talons, or claws. Raptors’
length to wingspan,
wingspans (the distance from the tip of one
▶ divide the body length
extended wing to the tip of the other) are far
by the wingspan.
longer than their bodies.
The table on the next page shows the
bald eagle: 80 ÷ 200 = 0.40
lengths of some raptors’ bodies and their
(expressed as a fraction:
corresponding wingspans. Look at the data,
= 8 =2
and complete the table by finding the ratio
200 20 5
of body length to wingspan in decimal form.
expressed as a percent:
Then place these decimals on a number line
to determine which bird has the smallest
body in relation to its wingspan.
Body length
(in centimeters)
(in centimeters)
Ratio of body
to wingspan
Bald eagle
White-tailed hawk
Gray hawk
Swainson’s hawk
Sharp-shinned hawk
Long-eared owl
Golden eagle
Cooper’s hawk
Number Line
Solve It
1. Which bird’s body length is half of its wingspan?
2. If a raptor’s wingspan were 112 centimeters, how long
would its body have to be for it to have a body-towingspan ratio of 0.45?
3. Use a tape measure to determine the ratio of your arm
span to your body length. Will everyone in your class
have the same ratio? Why or why not?
MA NS 6.1.2. Interpret and use ratios in different contexts (e.g.,
batting averages, miles per hour) to show the relative sizes of
two quantities, using appropriate notations (a/b, a to b, a:b).
Lesson 5
Earth’s Cycles
for Life
Water covers about 75% of Earth’s surface.
Did you ever wonder where all this water comes
from? Could the water in your shower be from
the same stream that a lion once drank from?
6 LS 5.b. Students know matter is transferred over time from one organism to
others in the food web and between organisms and the physical environment.
How does water recycle itself?
Make a Prediction
All living things rely on water, yet there is a limited
supply of water on Earth. Water is recycled so that it
can be used again and again. What will happen to soil
if it is moistened with water and then placed under a
heat source? Write your answer as a prediction in the
form “If moistened soil is allowed to sit under a heat
source, then the water in the soil will . . .”
• empty soda bottle
with cap (cut into
Test Your Prediction
Place about 4 inches of soil in the bottom half
of the soda bottle.
• soil
Spray the soil with water so that it is moist
but not wet.
• lamp or window
with sunlight
Secure the top half of the soda bottle over
the bottom half. Use tape if necessary.
• water spray bottle
Observe Place the bottle under a lamp or in
direct sunlight. Observe it every 10 minutes for
a class period. Write down your observations.
Observe the bottle again on the second day.
Write down your observations.
Draw Conclusions
What did you see the first day? What did you
see the second day?
Infer What was the source of the water? What
was the source of the energy that caused
changes in the bottle?
Observe What happened to the water?
Explore More
What might happen if you added some small plants to
the bottle? Some small rocks? What might happen if
you added more heat or placed the bottle in the shade?
6 IE 7.e. Recognize whether evidence is consistent with a proposed explanation.
▶ Main Idea
6 LS 5.b
Earth recycles water and
other substances, such as
carbon and nitrogen.
▶ Vocabulary
water cycle, p. 83
evaporation, p. 83
condensation, p. 83
precipitation, p. 83
carbon cycle, p. 84
nitrogen cycle, p. 86
nitrate, p. 87
nitrite, p. 87
composting, p. 88
How does Earth have enough
air and water to keep us alive?
You know that people recycle bottles, cans,
and newspapers to help the environment. Did you
know that the environment recycles itself, too?
The air people breathe and the water people
drink do not run out, because the planet is
always recycling them.
▶ Reading Skill
Main Idea
The Water Cycle
Golden Gate Bridge, San Francisco, California
The Water Cycle
A cycle is a series of events that
happen one after another, in the same
order, over and over again. Think
about a bicycle. Why do you think it
is called that? It has two wheels (bi-)
that go around and around (-cycle).
The water cycle is the continuous
movement of water between Earth’s
surface and the air. The water cycle
works because water can change
from a solid to a liquid to a gas and
back again. The energy from the Sun
powers the water cycle.
The Sun heats the water in oceans,
lakes, rivers, ponds, and puddles. This
causes evaporation , the process in
which a liquid changes into a gas. As
the water vapor moves higher into the
atmosphere, it cools and condenses
into tiny water droplets. Condensation
is the process in which a gas changes
into a liquid. Condensation causes
water to form on the outside of a cold
glass of lemonade on a hot day.
Droplets of condensed water
accumulate in clouds. When the
droplets become too heavy, they fall
to Earth’s surface. Precipitation is
any form of water—rain, snow, sleet,
or hail—that falls to Earth.
When water hits Earth’s surface,
it may soak into the ground and be
stored as groundwater, in a process
called collection. It may also run across
the surface and be collected in streams,
ponds, lakes, oceans, or other bodies
of water. Some of this collected water
evaporates back into the atmosphere.
About 85% of the water that
evaporates on Earth comes from the
ocean. Most of this water quickly
condenses and falls back into the
ocean. Water evaporates from both
freshwater and saltwater sources.
However, all of the precipitation that
falls on Earth is fresh water. The salt is
left behind when salt water evaporates.
Quick Check
Main Idea What form of water does
condensation produce, a liquid,
a solid, or a gas?
Critical Thinking What is the order
of the four parts of the water cycle?
What is the carbon cycle?
Carbon is one of the elements that make up all living
things. Plants and animals (including people) need carbon
to live. There is not a lot of carbon in the atmosphere,
so it must be recycled. Otherwise it would be used up too
quickly. The process in which carbon is recycled between
the atmosphere and living things is called the carbon cycle .
There is evidence that a buildup of gases such as carbon
dioxide, nitric oxide, and methane trap heat that normally
would escape from Earth’s atmosphere. Called the greenhouse
effect, this buildup raises temperatures and leads to global
Since 1850 the average temperature on Earth has risen
about 1.8°F (1°C ). Some scientists predict it will rise 3.5°F
(2°C) by the year 2100. They believe this rise will lead to
many problems, such as the melting of the polar ice caps,
which would cause sea levels to rise and flood coastal areas.
The Carbon Cycle
Carbon enters the air in three ways: when plants
and animals decay; when animals breathe out
(exhale); and when fossil fuels such as coal, oil,
gasoline, and natural gas are burned.
Plants During photosynthesis,
plants use the carbon from carbon
dioxide to make sugars, starches,
and proteins. They also give off
oxygen, which is used by animals.
Death and decay When living things
die, the carbon in them goes into the
air and the ground. Some of it is turned
into carbon dioxide by the organisms
that feed on dead organisms.
Carbon and Life
Carbon is stored in molecules of
living and dead organisms, in organic
matter in soil, in the air as carbon
dioxide, and in fossil fuels. Dissolved
carbon dioxide is also found in the
ocean and in the shells of some marine
Plants and other photosynthetic
organisms take in carbon dioxide
and water and use them to make
food. During this process, oxygen is
released into the atmosphere as a waste
product. When living things need to
use the energy that has been stored in
food, they use oxygen to break apart
the molecules during respiration. The
final products are energy, water, and
carbon dioxide. The carbon dioxide is
returned to the atmosphere, continuing
the cycle.
Quick Check
Main Idea Why is the carbon
cycle important to living things?
Critical Thinking Where does
the carbon that has been stored
in an animal’s body go when the
animal dies?
Reading Diagrams
What happens to carbon when
living things die?
Clue: Read the text boxes.
Storage Some carbon is
stored as fossil fuels. This
is the carbon left behind
by certain organisms that
died millions of years ago.
Animals Animals eat plant
sugars, starches, proteins, and
other substances. The animals
use the carbon in these foods to
make their own body chemicals.
The Nitrogen Cycle
nitrogen gas
nitrites with
What is the nitrogen cycle?
All living things must have nitrogen
to develop and grow. Nitrogen is
needed to make proteins, which are
the building materials for muscles,
skin, bones, blood, plants’ cell walls,
and internal organs. Just like water
and carbon, nitrogen is cycled through
the environment.
The nitrogen cycle is the
continuous trapping of nitrogen gas
into compounds in the soil and the
returning of nitrogen gas to the air.
Earth’s atmosphere is 78% nitrogen.
You would think this would be
enough to supply living things with
the nitrogen they need. However,
plants and animals cannot use nitrogen
in this form. Plants must get nitrogen
from nitrogen compounds in the soil
that have been made usable. Animals
then get nitrogen in the same way they
get energy—by eating plants or by
eating the animals that eat the plants
that absorb the nitrogen.
Uses of Nitrogen
Lightning can change the nitrogen
found in the atmosphere into a watersoluble compound that dissolves in
rainwater to form nitric acid. A small
amount of nitrogen is absorbed into
soil this way.
The rest of the nitrogen in soil
comes from bacteria. Certain bacteria,
called nitrogen-fixing bacteria, live in
Fill two plastic cups with pond
water or water from an aquarium.
Add a few water plants, such as
elodea, to each cup.
Add a teaspoon of houseplant
food to one cup, and label the
Be Careful. Always wear
protective gloves when handling
plant foods.
nitrogen compounds
Reading Diagrams
What role do decomposers
play in the nitrogen cycle?
Observe Place both cups in a
sunny window, and observe them
each day for a week. Record your
Interpret Data What effect did
the plant food have on the plant
growth in the cups? What is the
independent variable in this lab?
What is the dependent variable?
Clue: Where do plants
obtain nitrogen from?
the roots of beans, peas, and peanuts
and can extract nitrogen from the air.
Other bacteria convert this nitrogen
into usable compounds called nitrates
and nitrites . Plants absorb the nitrates
and nitrites and use them to make
proteins. These proteins are passed
along when animals eat plants and
one another.
When plants and animals die,
nitrogen from their remains returns
to the soil when bacteria break it down
into nitrogen gas. These bacteria return
about the same amount of nitrogen to
the air as other bacteria take from the
air, keeping nature in balance.
Quick Check
Main Idea What is the nitrogen
Critical Thinking Why do some
people use manure, or raw animal
wastes, in their gardens?
How are plants recycled?
Plants are necessary to each
of nature’s cycles. Plants continue
their work even after they die. Think
of a giant tree falling in a forest.
Right away it becomes a habitat for
many different animals, including
birds, frogs, and insects. Soon after
it falls, the tree begins to break down.
Decomposers are organisms that
break down dead plants and animals
into useful things such as minerals
and rich soils. Plants need these in
order to grow. As you can see, each
kind of organism has a role that
helps others survive. Worms, crickets,
cockroaches, bacteria, and fungi are
decomposers. These organisms help
plants survive.
▼ The yellow coral
fungus helps break
down this fallen tree.
What happened to the fallen tree
also applies to your yard and some
of the food scraps around your home.
Certain kinds of scraps from the food
you eat or cuttings from your yard still
contain nutrients and other substances
that can be recycled. Composting is
the process in which decomposers
break down organic matter so it can
be used as a natural fertilizer for
gardening or farming. You can make
compost by mixing three parts dry
leaves and plant material, one part
fresh grass clippings, and one part
vegetable food scraps. Decomposers
soon go to work, breaking down these
materials into nitrogen and other
elements that make the soil rich.
Quick Check
Main Idea What is the role of
decomposers in an ecosystem?
Critical Thinking What is the
first thing that happens when
a tree dies and falls down?
Summarize the Main Idea
The water cycle is the
continuous movement
of water between
Earth’s surface and
the atmosphere.
(pp. 82–83)
The carbon cycle is
the process in which
carbon moves between
the atmosphere and
living things.
(pp. 84–85)
The nitrogen cycle
is the movement of
nitrogen among air, soil,
plants, and animals.
(pp. 86–87)
Make a
Study Guide
Make a three-tab folded book (see
pp. 487–490). Use the titles shown.
On the inside of each tab, write two
sentences about
the main idea of
the topic.
Writing Link
Think, Talk, and Write
Main Idea Earth
carbon, and nitrogen.
Vocabulary The process in which a
gas changes into a liquid is
Main Idea What happens to the
nitrogen compounds that are not
absorbed by plants?
Critical Thinking What would happen
if Earth became much warmer?
Test Practice Which of the following
objects would most likely take the
longest to decompose?
A plastic bottle
B eggshell
C paper bag
D schoolbook
Test Practice What is the process
which a liquid changes into a gas?
Math Link
Expository Writing
Estimate Fresh Water
Research a local environmental
problem that is related to water or air.
How does this problem result from
human activities?
Of Earth’s fresh water, 69% is polar
ice, 30% is groundwater, and 0.9%
is permafrost. What percent of
Earth’s fresh water is available for
use by people?
-Review Summaries and quizzes online @ www.macmillanmh.com
Inquiry Structured
What factors affect the carbon,
water, and nitrogen cycles?
Form a Hypothesis
small cup
The carbon cycle is a series of events that recycles carbon through
the environment. Carbon exists in many forms and can be found
in the air and in plants and animals. Plants take in carbon dioxide
from the air and convert it into food and oxygen. The amount
of carbon found in the air is affected by air pollution, especially
pollution from the burning of fossil fuels. What role do plants play
in the carbon cycle? Write your answer as a hypothesis in the form
“If carbon dioxide is added to a system containing a plant, then . . .”
Be Careful. Wash your hands with soap and water after the
investigation. Immediately wash any area of skin that comes in
contact with bromothymol blue.
Test Your Hypothesis
Use a straw to blow slowly into a small
cup of bromothymol blue. Record
your observations in your journal.
test tube
with cap
Be Careful. Be sure to breathe out
through the straw. Do not breathe in.
Do not drink the liquid in the cup.
Measure Pour 10 milliliters of
bromothymol blue into a test tube.
Record the color of the liquid in
your journal.
Experiment Use a straw to blow
gently into the test tube until the
liquid turns light green. Place one
piece of elodea in the test tube, and
put the cap on the tube.
Place the test tube in a rack near a
window, and check the color of the
bromothymol blue every 30 minutes
for 2 hours. Record the color of the
liquid at each interval.
6 IE 7.a. Develop a hypothesis.
Draw Conclusions
Explain What made the bromothymol blue change color
in step 1?
Analyze If you had continued blowing into the test tube
instead of capping it, what do you think would have happened
during the 2-hour experiment?
Infer What part of the carbon cycle did you represent when
you blew into the test tube?
Inquiry Guided
What factors affect the water cycle?
Form a Hypothesis
Does temperature affect the water cycle? Write your answer as
a hypothesis in the form “If the average air temperature changes
over a long period of time, then the water cycle will . . .”
Test Your Hypothesis
Design an experiment to investigate how temperature affects the
water cycle. Write out the materials you need and the steps you
will follow. Record your results and observations.
Draw Conclusions
Did your results support your hypothesis? Why or why not? What
do you think would happen to the water cycle in a large land area
if volcanic ash blocked the Sun’s rays for a few months?
Inquiry Open
What can you learn about the nitrogen cycle? For
example, does pollution affect it? Come up with a
question to investigate. Then design an experiment to
answer your question, and carry out your experiment.
Organize your experiment to test only one variable,
or one item being changed. Write down the steps so
that another group could complete the experiment by
following your instructions.
Remember to follow the
steps of the scientific process.
Ask a Question
Form a Hypothesis
Test Your Hypothesis
Draw Conclusions
CHAPTER 1 Review
Summarize the Main Ideas
An ecosystem consists of
the living and nonliving
things in an area that
interact with each other.
(pp. 24–37)
Fill each blank with the best term
from the list.
abiotic factor, p. 27
nitrogen cycle, p. 86
pyramid, p. 76
omnivore, p. 73
eukaryote, p. 58
Photosynthesis is the
process of making food
by using sunlight.
(pp. 40–51)
Microscopic producers,
consumers, and
decomposers are parts
of the food chain.
(pp. 54–63)
Food chains, webs,
and pyramids show
how energy flows
within an ecosystem.
(pp. 66–77)
Water, carbon, and
nitrogen cycle through
the living and nonliving
parts of the environment.
(pp. 80–89)
Make a
Study Guide
transpiration, p. 48
water cycle, p. 83
niche, p. 36
1. Energy from sunlight is a(n)
. 6 LS 5.e
2. Everything an organism does
and everything it needs make up its
. 6 LS 5.e
3. A complex organism that has
a nucleus in each cell would be
classified as a(n)
. 6 LS 5.b
4. A(n)
would eat both
producers and consumers. 6 LS 5.b, c
5. The term
describes the
loss of water from leaves. 6 LS 5.a
6. A model showing how energy
moves through a food chain is
. 6 LS 5.b
7. Evaporation, condensation, and
precipitation are parts of the
. 6 LS 5.b
8. Denitrifying bacteria are an important
part of the
. 6 LS 5.b
Take a sheet of paper
and tape your lesson
study guides as
shown. Use the study
guides to answer the
questions on these
-Review Summaries and quizzes online @ www.macmillanmh.com
Answer each of the following
in complete sentences.
9. Cause and Effect What effect would
over-logging of trees have on the
amount of carbon dioxide in the
atmosphere? 6 LS 5.a
Save the Trees
Suppose a kind of insect is destroying all
the Joshua trees. Your goal is to convince
state officials that funding must be made
available to save the Joshua trees.
What to Do
10. Critical Thinking How does the
angle at which the Sun’s rays strike
Earth affect the number and types
of organisms found in different areas
of the world? 6 LS 5.b, e
11. Predict What two effects might
occur if most of the phytoplankton
living in the world’s oceans were
destroyed? 6 LS 5.a
12. Infer Explain why Earth is probably
the only planet in our solar system
that has soil. 6 LS 5.b
13. Explanatory Writing Be a teacher
for the day. How would you explain
the nitrogen cycle to your students?
6 LS 5.b
1. Find out what niche the Joshua
trees occupy. In what ways do
other organisms living in the same
ecosystem depend on these trees?
2. Prepare a display to show officials
how the destruction of the Joshua
trees could disrupt the food chains
in the ecosystem.
Analyze Your Results
▶ Explain how a disruption in one
part of an ecosystem can have
far-reaching effects.
▶ Would the benefits of saving the
Joshua tree outweigh the risks of
spraying to prevent insect damage?
How do organisms exchange
energy and nutrients in an
What do microscopic organisms
provide to larger organisms? 6 LS 5.b
fresh water
composing organisms
increased sunlight
Which of the following types of
organisms turns energy from the
Sun into chemical energy? 6 LS 5.a
eat the bacteria in the soil
store carbon for the plants
break down plant proteins
turn nitrates into nitrogen gas
5 5 Why are organisms such as
earthworms and fungi called
decomposers? 6 LS 5.c
A They break down very quickly
after they die.
B They break down other organisms
into simpler substances.
C They are the only organisms that
cannot make their own food.
D They break down carbon dioxide
into oxygen through respiration.
Look at the table below.
Category A
Category B
tomato plant
humpback whale
willow tree
field mouse
These organisms are grouped
into 6 LS 5.c
A decomposers and tertiary
B primary consumers and
C producers and consumers.
D omnivores and producers.
4 4 What is the role of a decomposer
when plants die? 6 LS 5.b
Which of the following best
describes the role of roots
and stems in a plant? 6 LS 5.a
A Roots and stems transport water
and minerals to the leaves so that
photosynthesis can occur.
B Roots and stems help the plant
move and keep cool in hot weather.
C Roots and stems transport water
and minerals to the flowers to
attract bees so that pollination
can occur.
D Roots and stems are where
photosynthesis takes place.
The diagram below shows an
ocean energy pyramid.
10 0 The energy in a community
flows from producer to primary
consumer and from primary
consumer to 6 LS 5.c
tertiary consumer.
secondary consumer.
top predator.
11 1 A scientist observes a crow eating
both insects and grass. What can
she conclude about crows? 6 IE 7.e
A Crows will never eat higher-level
B The crow will always eat only
Which organism in the
energy pyramid is a secondary
consumer? 6 LS 5.b
8 8 What adaptations do plants have to
live in desert environments? 6 LS 5.e
A They reflect light from the Sun.
B They migrate during the day to
cooler areas.
C They store water in spongy tissues.
D They do not grow in desert
9 9 Microscopic organisms that recycle
organic materials back into the food
chain are 6 LS 5.b
insects or grasses.
C The crow is the only organism
that eats insects and grasses.
D Crows will eat both insects
and grasses.
12 2 Some populations occupy niches
of such importance that many other
organisms depend on them. These
populations are called keystone
species. Which of the following
is an example of a keystone
species? 6 LS 5.e
A Venus’s-flytraps catching flies
in the garden
B moles digging in the soil, creating
long tunnels under grass
C beavers building a dam, creating
a valuable wetland
D birds building a nest high up
in a tree
Materials prepared by PASS at