vit
acti ies
36&37 Decomposers
(Sessions I and II)
BROWARD COUNTY ELEMENTARY SCIENCE BENCHMARK PLAN
Grade 3—Quarter 4
Activities 36 & 37
SC.B.1.2.1
The student knows how to trace the flow of energy in a system (e.g., as in an ecosystem).
SC.B.2.2.1
The student knows that some source of energy is needed for organisms to stay alive and
grow.
SC.G.1.2.1
The student knows ways that plants, animals, and protists interact.
SC.G.1.2.4
The student knows that some organisms decompose dead plants and animals into simple
minerals and nutrients for use by living things and thereby recycle matter.
SC.G.1.2.5
The student knows that animals eat plants or other animals to acquire the energy they need
for survival.
SC.G.1.2.6
The student knows that organisms are growing, dying, and decaying and that new
organisms are being produced from the materials of dead organisms.
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SC.H.1.2.1
The student knows that it is important to keep accurate records and descriptions to provide
information and clues on causes of discrepancies in repeated experiments.
SC.H.1.2.2
The student knows that a successful method to explore the natural world is to observe and
record, and then analyze and communicate the results.
SC.H.1.2.3
The student knows that to work collaboratively, all team members should be free to reach,
explain, and justify their own individual conclusions.
SC.H. 1.2.4
The student knows that to compare and contrast observations and results is an essential
skill in science.
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ACTIVITY ASSESSMENT OPPORTUNITIES
The following suggestions are intended to help identify major concepts covered in the activity
that may need extra reinforcement. The goal is to provide opportunities to assess student
progress without creating the need for a separate, formal assessment session (or activity) for
each of the 40 hands-on activities at this grade level.
1. Session I—Activity 36: Have students list the ways that the petri dish is a model for what
happens in real life. (Answers might include: It is a small sample. It is like the real thing
but simple to manage.) Ask students to name one way the model is not like the real thing
besides its size or scope. (The model is in a sealed container.)
2. Session II—Activity 37: Ask, What do you think the first step of all decomposing is? (The
early stages of decomposing involve breaking down large pieces into smaller pieces.)
Continue, Do you think soil is living or dead (Soil is made up of both living and dead
things. It is a mixture of things that were never alive, such as bits of rocks, things that
were once alive, and things that are now alive, such as earthworms, ants, mold, and
bacteria.)
3. Use the Activity Sheet(s) to assess student understanding of the major concepts in the
activity.
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activities 36 & 37 Decomposers
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In addition to the above assessment suggestions, the questions in bold and tasks that
students perform throughout the activity provide opportunities to identify areas that may
require additional review before proceeding further with the activity.
vit
acti ies
36&37
Decomposers
1
petri dish
1 pair tweezers
OBJECTIVES
Students observe the role of dead
organisms in enriching the soil, and
determine that even dead organisms have a
valuable role in the cycles of life.
For the class
2
bags, disposal kit (for petri dishes)
food samples (bread, cheese,
vegetable peelings, fruit slices,
and so on)*
newspaper*
soil, local (containing pebbles,
leaf fragments, small twigs, dead
organisms, and so on but no live
organisms)*
1 roll tape, masking
2 rolls tape, transparent
6
water sprinklers
water, tap*
Delta Science Readers Plant and
Animal Life Cycles and Food Chains
and Webs
The students
predict what will happen as organisms
decay
observe the decomposition of dead
organisms
infer that in nature the decomposition of
dead organisms enriches the soil
SCHEDULE
Session I—Activity 36 About 50 minutes
Session II—Activity 37 About 40 minutes,
approximately 4 days after completing
Session I (once a significant amount of mold
begins to form on the food samples)
For the teacher
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VOCABULARY
bacteria
decay
mold
nutrients
Activity Sheet 36, Parts A and B
2 prs gloves, disposable*
safety goggles*
For each team of two
1
1
1 pr
tweezers
PREPARATION
For each student
1 pr
container, clear, with lid, for live
organisms*
*provided by the teacher
MATERIALS
1
1
cup, paper, 8-oz
magnifier
Session I—Activity 36
1 Gather and bring to class in sealed plastic
bags samples of food that will readily
decompose (such as bread, cheese,
vegetable peelings, and slices of apples or
bananas).
2
3
4
Make a copy of Activity Sheet 36, Part A,
for each student.
Fill the water sprinklers with tap water.
Choose a warm location where all petri
dishes may rest, undisturbed, for
approximately 4 days after Session I.
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3
Session II—Activity 37
1 Begin this session once a significant
amount of mold has formed on the food
scraps.
2 Obtain enough samples of fresh, local,
nonpackaged soil (containing pebbles,
dead organisms, and decaying organic
matter) so that each team of two will
have a sample to study. Examine the
soil carefully and remove all live
organisms (earthworms, ants and other
insects, spiders, and so on) with
tweezers. Put the live organisms in a
clear container so students can examine
them without handling them. Make sure
the lid is on tightly. Punch holes in the
lid if needed to allow air into the
container. Fill a paper cup with soil for
each team of two.
Activity Sheet 36, Part A
Decomposers
Session I—Activity 36
1. Record the date that you put food scraps into your petri dish.
Then draw a picture of your petri dish. Label what you see.
Date:
Drawings and labels will vary.
Make a copy of Activity Sheet 36,
Part B, for each student.
2. Predict what you think might happen to your petri dish.
Answers will vary. Possible answer: They will get
moldy.
CONTINUED
BACKGROUND INFORMATION
Each generation of plants and animals goes
through a normal process of birth, growth
and development, and death.
Activity Sheet 36, Part B
Decomposers
Session II—Activity 37
3. Record the date of your observation of your petri dish. Then draw a new
When plants and animals die, bacteria and
fungi in the air and soil cause them to
decay, or decompose. A minute fungi that is
commonly seen is known as mold. When
plants and animals are buried in the soil,
elements such as carbon, nitrogen,
phosphorus, calcium, iron, and zinc are
released into the soil as decomposition
occurs. These useful substances, called
nutrients, enrich the soil and are “recycled”
as they are taken in through the water
absorbed by the roots of new plants.
384
activities 36 & 37 Decomposers
picture. Label what you see. Show any changes that occurred.
Date:
Drawings and labels will vary.
Answers will vary. Possible answer:
The food is covered by a fuzzy substance. There are
black dots on the tips of the substance.
4. Changes I observed:
5. Write a conclusion about what happens to dead material. How does this affect
the life cycles of other plants and animals?
Sample answer: Remains of dead organisms are broken
down by bacteria. The once-living material has
nutrients that can be used again by plants and animals
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Even in death, plants and animals continue
to have an important role in the cycles of
life. Many plants are eaten by animals, and
many animals are killed and eaten by other
animals, thus insuring the survival of new
generations of plants and animals in the life
cycle. Some animals, such as vultures and
many types of insects, eat dead animals.
Guiding the Activity
Additional Information
Session I—Activity 36
1
On the board, draw the flowchart shown in
Figure 36-1.
birth
growth and
development
death
Figure 36-1. The stages in a generation.
Ask, What does this diagram show?
If students do not identify the diagram properly,
explain that it shows the process that each
generation of living things passes through.
Ask, What do you think happens to a
plant’s or an animal’s body when it dies?
At this point, accept all reasonable
responses.
Tell students that in this activity, they will
learn what happens to the bodies of living
things when they die.
Display the food scraps. Ask, Are these
living, nonliving, or dead objects?
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2
Demonstrate the process of putting three or
four samples of food scraps into the bottom
of a petri dish. Then divide the class into
teams of two. To each team, distribute a petri
dish, a strip of masking tape, and an
assortment of food scraps. Monitor students
as they complete the task of putting food
scraps into their petri dishes. Have team
members write their names on the strip of
masking tape, and affix it to the lids of their
petri dishes. Then have students place their
open petri dishes, with the lids next to them
for identification purposes, in an undisturbed
place for approximately 30 minutes.
If necessary, point out that they are parts
of, or made from, things that were once
alive. Therefore, they are dead things.
The 30-minute period will allow bacteria to
settle on the food scraps, thus hastening
decomposition.
During the 30-minute period, distribute to
each student a copy of Activity Sheet 36,
Part A. Instruct students to work
independently to complete it. When they have
finished, allow time for them to share their
predictions.
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385
Guiding the Activity
3
Additional Information
When the 30-minute period has elapsed,
direct students’ attention to the petri dishes.
Distribute the water sprinklers for teams to
share, and have students use them to add a
slight amount of moisture to their food
scraps. Then have them close the petri
dishes. Distribute the rolls of transparent
tape for teams to share, and instruct them to
secure the lids in place by encircling them
with strips of the tape, as shown in Figure
36-2. Tell them that they will not open the
petri dishes again.
Safety Note: Caution students not to put
any of the foods in their mouths.
Have them place the dishes in a warm, dark
place, such as a closet. Explain that in
approximately 4 days they will have the
opportunity to check on the predictions they
have made.
Figure 36-2. A closed petri dish, secured with tape.
Session II—Activity 37
4
Have each team of two retrieve their petri
dishes and a magnifier. Caution them not to
open the dishes. Have them examine their
food scraps, using the magnifiers. Ask, What
changes do you observe?
Students should note a white, pink, or blue
fuzzy or powdery substance growing on the
food scraps.
Write the word decay on the board. Explain
that decay describes what is happening to
the food. It means “break down.” Ask, Why
do you think the food scraps have begun to
decay?
Write the word bacteria on the board. Explain
that bacteria are tiny organisms that help to
break down, or decay, dead organisms.
Ask, How do you think the bacteria got into
your petri dishes?
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activities 36 & 37 Decomposers
Accept all reasonable answers at this point.
Lead students to understand that during
the 30 minutes that the petri dishes were
left open, many bacteria carried in the air
had the opportunity to enter the dishes.
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Encourage students to observe the petri
dishes of others, noting how different foods
may have undergone different changes.
Guiding the Activity
Write the word mold on the board. Ask, What
does this word mean, and do you see any
mold in your petri dishes?
Additional Information
Accept all reasonable responses.
If necessary, identify the fuzzy or powdery
growth on the food scraps as mold and remind
students that mold is a tiny organism that
feeds off of other organisms—dead or alive.
Ask, How do you think mold got into your
petri dishes?
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5
During the 30-minute period that the food in
the petri dishes was exposed to the air, mold
particles in the air settled on the food.
Distribute to each student a copy of Activity
Sheet 36, Part B. Have students complete
question 3, including the drawing and the
description of the changes they observed.
Ask, What conditions helped the food
decay?
Students should suggest that moisture,
warmth, and bacteria and mold helped the
food decay.
Ask, If we had put some food scraps
outside, in a more natural setting, like a
field or a playground, would those
conditions also be present?
Yes.
Ask, What would have happened to food
scraps left in a natural setting?
They probably would have begun to decay.
Ask, What do you think would happen to
food scraps if they were buried in the soil?
At this point, accept all reasonable
responses. Students may speculate that the
food scraps would continue to decay until
they became tiny pieces of the soil itself.
Have teams return their petri dishes to the
closet. Distribute a few sheets of newspaper
to each team, and have them cover their
desks with it. Then distribute to each team a
pair of tweezers and a paper cup filled with
the fresh, nonpackaged soil sample you
collected and prepared. Instruct students to
dump their soil sample onto the newspaper
and examine it with their tweezers. Ask, What
is contained in your sample of soil? Show
students the container with live organisms
and let students examine them. Explain that
you removed the live organisms from the soil.
Students should be able to observe twigs,
pebbles, bits of dead leaves, dead insects,
and the like. Encourage students to observe
the findings of others.
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On the board, make a three-column chart
with the column headings Living, Nonliving,
and Dead. As students report on their
observations, work with them to classify each
observed item by writing it in the correct
column on the chart. Then encourage
students to use their magnifiers to examine
the soil more closely. Ask them to describe
what other elements they observe, and add
any new items to the chart. Then ask, Based
on your observations, what three types of
things are found in soil?
6
Point out that the nonliving substances—
various types of rocks and minerals—are
basic elements in Earth’s surface. Ask, Why
were there so many living organisms in the
soil?
Ask, What do you think they eat?
Point out that the fragments of leaves that
the students observed in the soil had broken
into very small pieces. Ask, Why do you
think this happens? How did the large
pieces become small pieces? If necessary,
remind students what they have learned
about the role of bacteria and mold in
promoting decay.
Ask, Do you think the same thing would
happen to pieces of fruit or vegetables that
were buried in the soil?
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activities 36 & 37 Decomposers
Additional Information
living, nonliving, and dead things
Such living organisms as ants, beetles, and
worms burrow into the soil and live there.
Lead students to understand that some eat
other living organisms that they kill, and
others eat dead and decaying plants and
animals.
Students should speculate that the leaves
decay, breaking down into tiny fragments
that become part of the soil itself.
Yes.
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Guiding the Activity
Guiding the Activity
7
Ask, How might the decaying parts of dead
plants help new plants to grow?
Additional Information
Accept all reasonable responses.
Lead students to understand that particles
from decaying plants in the soil will mix with
the water that the new plants take in through
their roots.
Write the word nutrients on the board. Point
out that many dead organisms contain
nutrients—helpful materials that living things
need to grow and survive. When the tiny
particles of decayed plants and animals mix
with the soil, and the water that is in the soil,
the nutrients feed the new plants and help
them to grow.
8
Ask, How do dead plants and animals help
in the life cycles of living plants and
animals?
They enrich the soil; they pass nutrients from
one generation to another.
Based on their observations, have students
complete questions 4 and 5 on Activity Sheet
36, Part B. Then summarize by discussing
their answers.
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9
As appropriate, read or review page 13 of the
Delta Science Reader Plant and Animal Life
Cycles and pages 4–9 of the Delta Science
Reader Food Chains and Webs.
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Have students work together to research
compost—what it is made of, how it
improves garden soil, and why it generates
heat as it ripens.
SCIENCE JOURNALS
Have students place their completed activity
sheets in their science journals.
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activities 36 & 37 Decomposers
CLEANUP
Have students roll up their dirt samples on
the newspapers and dispose of them. Then
have them wash their hands and return the
paper cups, magnifiers, transparent tape,
masking tape, and tweezers to the kit.
Return all live organisms to the outdoor
area where you collected the soil.
Collect all petri dishes in one of the
disposal bags. Seal the bag and affix the
contaminated material tag before disposing
of it, in order to ensure that no one will
open it.
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REINFORCEMENT
Connections
Science Extension
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Ask students to find out what compost is
(the decomposed remains of food scraps
and other dead materials such as leaves
and grass clippings) and how it improves
soil. You may want to have students create
a class compost bin on school grounds,
following instructions they have found in
science activity books such as Botany: 49
Science Fair Projects by Robert L. Bonnet
and G. Daniel Keen. Students could
investigate the effectiveness of compost by
growing identical plants in three different
pots—one containing sand, the second
ordinary soil collected from outdoors, and
the third a mixture of equal parts soil and
compost. Also encourage students to find
out why a compost pile heats up as the
materials decompose.
Tell students that earthworms, snails,
mites, sowbugs, and many other small
animals living in soil also help decay dead
material by breaking it down into smaller
pieces. Without the action of these
animals, it would take a much longer time
to break down dead material.
Science, Technology, and Society
Have students examine the labels from
different types of plant fertilizers and list all
the nutrients they contain. Ask volunteers to
compile a master list from the individual lists.
(See the Science and Health connection.)
Encourage students to research the purpose
of different “blends” of nutrients. Also ask
them to find out how different types of
fertilizers are manufactured.
Science and Health
Suggest that students research the names of
the nutrients that humans need
(carbohydrates, fats, proteins, vitamins,
minerals, and water), the role of each nutrient
in maintaining good health, and its dietary
sources. Ask volunteers to compile the
findings into a master list. Then have
students compare this list with the master list
of plant nutrients from the Science,
Technology, and Society connection. Which
nutrients are needed by both humans and
plants? (water and certain minerals, primarily
phosphorus and potassium)
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activities 36 & 37 Decomposers