2.5
The Role of Decomposers in
Recycling Matter
Page 44
Time
PRESCRIBED LEARNING OUTCOMES
45–60 min
• analyze the roles of organisms as part of interconnected food webs,
populations, communities, and ecosystems
Key Ideas
A model can be used to show
how energy flows through an
ecosystem.
Matter cycles within
ecosystems.
Program Resources
BLM 2.5-1 Decomposer and
Detrivore Daily Log
SM 2.5 The Role of
Decomposers in
Recycling Matter
BLM 0.0-9 Chapter Key Ideas
Nelson Science Probe 7
Web site
www.science.nelson.com
KNOWLEDGE
• organisms interact with each other and use and recycle chemicals from
the environment
• living things need energy to carry out their activities; the flow of
energy from one organism to another is part of an energy web
• producers of food such as plants are related to consumers
(e.g., animals) and decomposers (e.g., bacteria and fungi) in webs of
interdependence called food chains and food webs
• food webs are individual food chains that are linked
ICT OUTCOMES
• work cooperatively using information technology tools
• access information using a variety of on-line information tools
• use a variety of information technology tools to create, modify,
explore, and present electronic documents that express ideas or
concepts
• synthesize information from a variety of electronic sources for
presentations
• apply the principles of good design when developing electronic
documents
SCIENCE BACKGROUND
• Decomposers are mainly bacteria
and fungi that convert dead matter
into gases such as carbon and
nitrogen to be released back into the
air, soil, or water.
• Moulds, mushrooms, and bracket
fungi are examples of a saprophyte,
which is a type of organism that
feeds as it breaks down dead
organic matter.
• There are about 100 000 species of
decomposers.
• Salmon migrate back to the streams
where they were born; fall is a good
time to observe them as water
levels are often low. The nutrients
released into the stream from the
decomposed salmon feed
microscopic organisms that become
food for larger organisms. In the
66
Unit A: Ecosystems
spring, many salmon species’ eggs
hatch, and the young fish, or fry, will
thrive in a nutrient-rich water system
of streams and lakes. Most species
of salmon will feed for an entire year
before heading down the network of
streams, lakes, and rivers that make
up their journey to the sea. They will
go out to sea to feed and grow, and
return, depending on the species, in
three to four years to their birth
stream.
• Scientists are finding certain
nutrients in forest soil samples that
they know come only from the
ocean.
• Decomposers, then, play an
important role in a complex nutrient
network that connects ecosystems
thousands of miles apart.
NEL
TEACHING NOTES
Related Resources
1 Getting Started
• Check for Misconceptions
– Identify: Students may think that when an organism dies, its
matter disappears or is removed from the cycle.
– Clarify: Explain to students that matter and energy flow from one
organism to another, but that matter remains on Earth and will be
recycled though decomposition.
– Ask What They Think Now: Ask students to think about what
happens to the leaves in a forest. (They slowly rot or decompose
into smaller pieces, adding to the buildup of items on the forest
floor. The leaf is no longer in the shape of a leaf, but its bits and
pieces will be added to the ground thereby making soil, which
provides a nutritious place for new plants to grow.)
• Display a common fruit or vegetable that can be grown locally—for
example, a carrot or cucumber. Ask students to describe where this
food may end up if it is not eaten. Ask students to think about a way
that this food may be recycled as they go through the section.
LeBox, Annette. Salmon
Creek. Toronto:
Groundwood Books,
2004.
Lynch, Wayne. The Scoop
on Poop. Calgary: Fifth
House Publishers, 2001.
Pascoe, Elaine, and Dwight
Khun. The Ecosystem of
a … (series: garden,
grassy field, fallen tree,
milkweed patch, stream,
apple tree). New York:
Powerkids Press, 2003.
Wakeman, Dan, and
Wendy Shymanski.
Fortress of the Grizzlies:
The Khutzeymateen
Grizzly Bear Sanctuary.
Surrey, BC: Heritage
House Publishing
Company, 2003.
2 Guide the Learning
• Have students draw or write what happens to the common food
item (from the Getting Started section) when it is discarded at this
point, or use the example as a starting point for a class discussion.
• After reading the Composting subsection and viewing the compost
food web (Figure 4), ask students to think about a rotting log. Ask,
How is this an example of matter being reduced and nutrients being
recycled? (The log will be eaten by insects and other decomposers,
which will break it down into microscopic bits. The bacteria and
fungi will decompose the log as well. This will return the matter to a
soil form.)
• Have pairs of students trace with one finger a food chain within the
compost food web (Figure 4) to understand the process. For
example, students could trace apple to bacteria to earthworm to
robin.
• Start students with BLM 2.5-1 Decomposer and Detrivore Daily Log.
• After reading the Dying Salmon subsection, refer back to the chapter
introduction questions. Ask students where the materials that make
up an orca’s body come from. Ask students where these materials go
if the orca dies of disease or old age. (For the orcas that consume
salmon as a large part of their diet, this recycling of nutrients is
critical. The salmon are only present because their needs are met in
the freshwater part of their lives. When the orca dies, it will
decompose and the nutrients will feed other organisms, which will
in turn feed salmon, which will ultimately feed other orcas.)
• For students who need additional support with the reading in this
section, use SM 2.5 The Role of Decomposers in Recycling Matter.
NEL
Chapter 2
Energy flows and matter cycles in ecosystems.
67
3 Consolidate and Extend
• Review with students how decomposers break down their food,
using the last of the energy in the food chain. Look at the compost
food web on page 46 to help review the key idea about how a model
can be used to show how energy flows through an ecosystem. Ask
students to work with a partner to determine if and how the
questions in the introductory paragraph were answered. Have
students consider, How much do we depend on the recycling of matter?
What is the role of living things in the recycling of matter?
• Refer back to the food web shown in Section 2.2, Figures 2 and 3.
Ask students where they might add the decomposers here.
• Use the Reading and Thinking Strategies to guide students’
reading of the Dying Salmon subsection.
Technology Connections
Have students create a
food web, or modify a
previously created one,
to show the range of
organisms from
decomposers to
predators. Students could
use the Internet to find
images of organisms and
a computer graphics
program to organize and
present their food web.
Text boxes may also be
used to explain
relationships throughout
the food web.
• Using the Dying Salmon subsection, have students draw a diagram
and add details. The diagram will be a visual representation of the
two paragraphs in the Dying Salmon subsection. Students should
start by making a quick sketch of a river and a forest area on a sheet
of paper. They should then insert details noted while reading
through the subsection, such as the salmon moving up the river, or
certain animals eating the salmon or moving them into the forest.
• Have students add details and examples to BLM 0.0-9 Chapter Key
Ideas.
• Plan a field trip to anywhere with large-scale decomposition. This
may include a fall salmon run, an orchard, a pumpkin patch, or a
district composting depot.
• If the class is able to visit a local wastewater treatment facility, then
read the Tech.Connect feature prior to the visit.
• Assign the Check Your Understanding questions.
At Home
Have students make
observations about
decomposers and
detrivores around their
homes, and write their
observations in BLM 2.5-1
Decomposer and
Detrivore Daily Log.
68
Unit A: Ecosystems
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. Decomposers link the living and non-living parts of an ecosystem by reducing
dead plant and animal matter into a form so small or liquid-like that it can get
into the soil, water, or air.
2. If there were no decomposers in an ecosystem, then no nutrients would be put
back into the ecosystem, and organisms would have nothing to feed on. Life
would eventually cease. There also would be a large amount of plant and animal
matter piled up everywhere.
NEL
Reading and Thinking Strategies: Visualize
• Read the paragraph between Figures 2 and 3 to
students. Read slowly, sentence by sentence,
explaining that you want them to make quick sketches
of the images that come to mind as they listen. Read
the paragraph again as they complete their sketches.
Have students share their sketches with a partner.
Figure 2
These bracket fungi are decomposers.
The importance of decomposers in an ecosystem should not
be underestimated based on their small size. Imagine what your
schoolyard would look like with years of accumulated leaves and
grass clippings still in their original forms. Without decomposers,
nutrients would remain locked in the tissues of dead plants and
animals. Decomposers break down matter and turn it into the
nutrients that living things need every day (Figure 3).
Figure 3
Moulds and bacteria spoil food, but by doing so they recycle nutrients within the
ecosystem.
NEL
2.5
The Role of Decomposers in Recycling Matter
45
Meeting Individual Needs
ESL and Extra Support
• Have students complete a diagram showing a cycle of what happens to
a common fruit or vegetable as it decomposes.
• For students who need additional support with the reading in this
section, use SM 2.5 The Role of Decomposers in Recycling Matter.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Suggestions for Teaching Students Who Are Having Difficulty
Evidence that students can
• explain how decomposers link the living and
non-living parts of an ecosystem
Identify something in their daily life that can decompose. Draw a diagram (including
labels) to how it is cycled through the ecosystem.
NEL
Chapter 2
Energy flows and matter cycles in ecosystems.
69