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
7th Grade Science
Unit 6
Ecology
Spring 2006
ECOLOGY
Ecology is the study of the interactions between organisms and their environment.
This is a large unit at 7th grade and covers many key concepts.
Ecological Succession
Ecological succession is the natural and orderly process by which an ecosystem
changes as it develops or re-grows. Seventh grade is the first year in which
students are introduced to this concept. There are two types of ecological
succession: primary succession and secondary succession. The difference between
these two is the presence or absence of soil. In primary succession there may be
little or no soil as when a glacier retreats or when lava flow covers an area.
If a glacier retreats and leaves behind a barren environment, the first living
organisms to move in are called pioneer species. They are usually moss and lichens.
These pioneer species break apart the rock which erodes and weathers over time.
Decaying lichens and moss add nutrients to the forming soil. As time progresses,
new plant life moves into the area. This supports a variety of animal life, including
insects, birds and rodents. Over time the soil will be thick enough to support
larger trees and animals. Another example of primary succession can be seen in
the formation of a barrier island, such as Padre Island on the Texas coast:
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
7th Grade Science
Unit 6
Ecology
Spring 2006
Secondary succession is the normal re-growth of organisms into an area where soil
already exists. Examples of secondary succession would be plants and animals
returning to an area after a fire, flood or human activity. Secondary succession
occurs much faster than primary succession. At some point the area reaches a
stable point where very few new plants or animals are introduced. This type of
community is known as a climax community.
In discussing ecological succession, it is important for students to understand the
importance of ecological succession in restoring equilibrium to an ecosystem.
Ecological succession allows an ecosystem to recover from a disturbance in this
return to equilibrium. If an area is disturbed but organisms from the original
community remain nearby, they may repopulate the original area again as succession
progresses.
Photosynthesis
The 7th grade student should be familiar with the process of photosynthesis. This
concept was introduced in 4th grade and revisited in 5th grade. Students should
know that photosynthesis is the process by which radiant energy from the Sun is
transferred into chemical energy as an organism containing chlorophyll, such as
plants and algae, makes food for itself. This is also an example of how an organism
is responding to the external stimulus of light. The sunlight stimulates the
chloroplasts in the cells to begin glucose (sugar/food) production. Food production
is the job of the green pigment chlorophyll, contained in the chloroplasts. In
plants, this occurs in the cells of leaves. Carbon dioxide and water are required
for this reaction. Glucose is produced as is oxygen, which is released as waste.
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
7th Grade Science
Unit 6
Ecology
Spring 2006
Components of an Ecosystem & How they Interact
An ecosystem includes all the living organisms (biotic) and all the non-living things
(abiotic) found in a community. Biotic factors include producers, consumers and
decomposers. Abiotic factors include soil, rock, water, landforms, light and
temperature. Organisms in the environment are constantly receiving stimuli from
other organisms as well as from abiotic factors. These would be external stimuli.
A stimulus may elicit a response. Stimuli may be direct, such as when a predator
approaches its prey, triggering a fight or flight response. Stimuli may also occur
as part of a larger system, such as the length of sunlight in a day triggering the
response of migration. External stimuli in the environment that affect plants are
called tropisms. Plants grow up away from the ground. This is a response to the
earth’s gravity, or gravitropism. Plants grow toward the light, a response called
phototropism. Some plants respond to touch. If the plant encounters an obstacle,
this response allows the plant to bend and keep growing around the object.
The living organisms of a community are the producers, consumers, and
decomposers. A producer is a plant or chlorophyll bearing organism that has the
ability to absorb sunlight and make food for itself. A consumer is an organism that
eats other organisms. A decomposer is an organism (such as bacteria) that has the
ability to break down a dead organism and return its nutrients to the soil. In this
way, all the nutrients in the environment are recycled.
One way to examine how these organisms interact is with the use of models,
including food chains, food webs and energy pyramids. The elementary student
first studied food chains and food webs. The 6th grade student described energy
flow through food chains and webs. Plants are always the first organism to appear
in a food chain because they are producers that obtain energy directly from the
sun. An animal that eats the plant is called a primary consumer. The energy now
has passed from the sun to the plant and on to the animal that ate the plant. If
another animal eats the primary consumer, that animal is called a secondary
consumer. The original energy from the sun has now been passed on again. If
there is another animal in the chain, it will be called a tertiary consumer. All food
chains contain arrows which point in the direction of energy flow and not in the
direction of “who eats who.”
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
7th Grade Science
Unit 6
Ecology
Spring 2006
A food web is more complicated but more realistic. A web shows how chains
may overlap as some animals eat more than one food source. The 2005 TAKS
information booklet states the study of food webs should “include examples
from Texas or the southwestern United States in addition to global examples.”
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
7th Grade Science
Unit 6
Ecology
Spring 2006
As one organism consumes another, energy is lost. Organisms at each level in a
food chain use the energy to carry out life processes. As this occurs, some energy
is lost to the environment as heat. As a result, there is a decrease in available
energy at each level of a food chain. This concept is modeled by an energy pyramid
which illustrates a decrease in the amount of available energy and a decrease in
the number of organisms from producer to top consumer.
Students should understand that every organism in a community has an impact on
every other organism. An increase or decrease in one organism will impact the food
supply for another organism. Abiotic factors also impact the interactions within
the environment. For example, a decrease in rainfall may destroy the producers in
a food web, affecting all the dependent consumers.
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
7th Grade Science
Unit 6
Ecology
Spring 2006
Different Environments and the Organisms they Support
The primary objective while teaching biomes is for students to understand that
different environments support different varieties of organisms. A biome is a
large region characterized by a distinct climate and specific types of plant and
animal life. Major biomes include the tundra, forests, grasslands, deserts,
freshwater and marine ecosystems.
Tundra
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climate is very cold with little rainfall
ground remains frozen almost all year; has permafrost
shallow layer of soil above permafrost supports some grasses but primary
producers are mosses and lichens
animals include the snowshoe hare, artic fox, mice, caribou and wolves;
there are no amphibians or reptiles
animal adaptations include thick fur coats, white camouflage, shorter or
more compact appendages for heat conservation
Forests
forest type depends on location/latitude but all forests are located
where temperatures are mild and there is plenty of rain
Temperate Deciduous Forest
 have trees that lose their leaves in the fall, an adaptation for water and
energy conservation
 many animals migrate or hibernate in winter; migration is an adaptation
that provides the animal with a warm climate and plentiful food sources;
hibernation is an adaptation for energy conservation
Tropical Rain Forest
 near the equator; warm with abundant rainfall
 many vertical layers in trees provides for multiple niches and great
biodiversity
Coniferous Forest
 there are cold, long winters
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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
7th Grade Science
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Unit 6
Ecology
Spring 2006
trees have thick, waxy needles for leaves, an adaptation that prevents
damage in winter
many animals migrate or hibernate in winter
some animals have camouflaged coats that change color in winter
Grasslands
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climate is dry and windy with little rainfall
main plants include different varieties of grasses, adapted to have long
roots to reach water; some have underground stems that allow them to
grow back after a fire; thick tangled roots that hold the soil and don’t
get blown away; winds help spread pollen
animals include prairie dogs, mice, and animals like antelope that graze
animals adapted to eat grass or seeds; animals that can burrow to get
out of the heat; animals that live in herds or colonies for protection in
open environment
Deserts
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climate is very dry and hot during the day but cool at night
main plants include cacti, short bushes, and small flowering plants
plants are adapted to flower quickly and produce seeds after a rain; can
store water in their stems and roots; many have thorns to keep the
animals away, an adaptation for water conservation as well as protection
many plants have well developed roots that go deep or are well spread out
to absorb water when it does come; many plants grow far apart from one
another to avoid competition for water sources
animals include kangaroo rat, snakes, lizards, insects, rabbits, vultures
animals are adapted to take cover under rocks or be active at night; many
animals can burrow; some animals get the water they need through the
food they eat
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
7th Grade Science
Unit 6
Ecology
Spring 2006
Marine Ecosystem
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marine environments are salt water / oceans
climate is determined by temperature, depth in water and salinity content
sunlight penetration determines what plants and animals are present
plankton are ocean’s main producers
animals adapted to anchor themselves to land or rock, such as clams and
barnacles, occur in areas nearest the shore where waves are a factor
animals in the open ocean live further apart from one another since
resources are more limited
Freshwater Ecosystem
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includes rivers, streams, springs, lakes, etc.
plants and animals that live in moving water have adaptations that allow them
to cling to rock
producers include plankton, moss and algae but trees, vines, grasses reeds,
etc. are also abundant in some of these environments, such as in a swamp
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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