N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t – 3 r d G r ad e S ci en c e
Needs of Living Organisms
Unit 2 Clarifying Statements
Rev. May 2006
Needs of Living Organisms
A system is a collection of cycles, structures, processes and things that interact.
The things can be almost anything including objects, organisms, machines, or
processes. Learning about systems requires understanding how parts relate to and
influence one another. Systems often contain other systems that may interact.
There is interdependency of the components within a system and therefore
systems may not work when a change occurs such as a part being removed. Systems
should be emphasized as students investigate the roles of various organisms within
an ecosystem.
All living things need a place in which to live, an environment. An environment is
everything in an area including things such as food, air, water, and shelter. These
things are the basic needs that an organism requires in order to live. In an
environment the living and nonliving things that affect each other, or interact,
form an ecosystem. An ecosystem contains many habitats or places where many
organisms live with all of their basic needs being met. For example a student’s
habitat may be their neighborhood: where they live, play, and go to school.
In this unit 3rd grade students need to observe and describe habitats of
organisms in an ecosystem. As students study different habitats, they begin to
identify that organisms have similar needs, and may compete with one another for
resources such as food, water, air, light and space. Additionally, living organisms
need a way to dispose of waste. Students should understand that organisms may
interact with each other in ways that may harm (a tick spreading disease when it
bites another organism) or help (a sea anemone providing protection to a clown fish
in exchange for bits of food) each other. Another way organisms interact is
predation, a feeding relationship, where an animal that is eaten is the prey and the
animal eating the prey is the predator. Predator-prey relationships help to keep
ecosystems in balance.
In earlier grades, students learned that organisms need energy to live and are
divided into two main groups (producers and consumers) based on how they get
their energy. It is appropriate to review the interactions between these groups at
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t – 3 r d G r ad e S ci en c e
Needs of Living Organisms
Unit 2 Clarifying Statements
Rev. May 2006
this time. Students need to recall that the movement of energy through an
environment from one living thing to another forms a food chain. An ecosystem may
have many food chains that overlap because most organisms are part of more than
one food chain; therefore, the focus in this unit of study is on food webs. Food
webs contain producers and consumers that are used as food by more than one
living organism and show a more complete picture of the flow of energy in an
ecosystem. Arrows in a food chain and a food web show the direction of the flow
of energy and should always point away from the organism being consumed and
toward the organism doing the consuming.
Food Web Example
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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N o r t h E a st I n d ep en d e nt S c h o o l D i st ric t – 3 r d G r ad e S ci en c e
Needs of Living Organisms
Unit 2 Clarifying Statements
Rev. May 2006
Students should understand that the source of energy in most ecosystems is the
Sun. Because energy in an ecosystem begins with the Sun, producers are almost
always the starting point of a food chain and a food web.
Students may now begin to examine the survival needs of different organisms and
conclude how conditions in particular habitats can limit what kind of living
organisms can survive. For any particular environment, some kinds of plants and
animals thrive (prosper), may become ill, or perish (die off.) Different species may
live in the same habitat, but each one has a specific role. The interaction of these
organisms, each with its specific role, is one factor that contributes to the overall
health of the system. Environmental changes in an organism’s habitat are
sometimes beneficial and sometimes harmful. Changes caused by nature such as
storms and floods can kill organisms and destroy habitats. These changes can also
bring a new rich layer of soil to a riverbank so that new plants can grow and fallen
trees may provide a new home for some animals. Students should also gain
understanding that organisms modify their environment to meet their needs.
Some examples include birds building a nest, prairie dogs digging burrows, or
spiders building a web. Sometimes one organism’s modification may be harmful to
another organism. For example, factories run by humans can dump waste into water
sources contaminating the water and killing organisms. In some cases, the
destruction of habitats can cause a species to completely disappear.
Clarifying statements are intended to deepen teachers’ understanding of science concepts and serve as a guide for
instructional design. They are not intended to serve as student instructional materials.
This publication is the property of North East Independent School District. Duplication in whole or in part, outside of NEISD, is
prohibited without express written permission from NEISD.
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