2.2
Food Chains and Food Webs
Page 33
PRESCRIBED LEARNING OUTCOMES
Time
• analyze the roles of organisms as part of interconnected food webs,
populations, communities, and ecosystems
• assess survival needs and interactions between organisms and the
environment
• assess the requirements for sustaining healthy local ecosystems
KNOWLEDGE
• 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
45–60 min
Key Ideas
The Sun is the source of all
the energy in most
ecosystems.
Energy flows through
ecosystems.
A model can be used to show
how energy flows through an
ecosystem.
Vocabulary
• food chain
• food web
Skills and Processes
ICT OUTCOMES
• use a variety of information technology tools to create, modify, explore,
and present electronic documents that express ideas or concepts
• apply predetermined search criteria to locate and retrieve information
using information technology tools
• synthesize information from a variety of electronic sources for
presentations
Classifying
Making Inferences
Program Resources
SM 2.2 Food Chains and Food
Webs
BLM 0.0-9 Chapter Key Ideas
Nelson Science Probe 7
Web site
www.science.nelson.com
SCIENCE BACKGROUND
• The Sun is the main source of
energy for life on Earth. There is a
brief write-up of another source of
energy for life—chemosynthesis—in
Awesome Science.
• Decomposers form the nutrient base
for food webs. This will be explained
further in Section 2.5.
TEACHING NOTES
Related Resources
Ecology: Food Chains
(video, VHS). BC: Magic
Lantern Communications,
1992. ISBN/Order No:
23022
Nelson Science Probe 7
Web site
www.science.nelson.com
1 Getting Started
• Check for Misconceptions
– Identify: Students may think that animals will eat whatever is
available, especially if the bulk of their experience with animals is
with urban scavengers, such as raccoons.
– Clarify: Explain to students that certain animals eat certain types
of food to give them the energy they need to live. Explain,
referring to the food chain model, that an organism depends on
the organisms before it in the food chain for food energy. No
matter how hungry they may be, a deer would not consider eating
a mouse and an eagle would not consider eating grass.
– Ask What They Think Now: Ask students if all animals would eat
insects. Ask why or why not.
NEL
Chapter 2
Energy flows and matter cycles in ecosystems.
53
• Ensure that students understand that the word chain is used because
it denotes living things linked together.
• Students may need reminding that the energy discussed in this
section originates with the Sun.
• Challenge students to predict what would happen if the Sun’s rays
were somehow blocked and could not reach Earth. What would it
affect? (It would affect more than just the plants, as organisms are
connected in food chains and webs. Ultimately, it would affect all
life on Earth.)
2 Guide the Learning
• Refer students to the question from Figure 1, and encourage
answers. Students should understand that the original source of
energy for each food chain, and almost every food chain on Earth, is
the Sun. Ensure that students recognize that one food chain is landbased and the other is marine-based.
• Ensure that students are able to trace the food chains within food
webs. Have students take turns calling out items in each food chain
visible in Figure 2. For example, Sitka spruce, red squirrel, marten.
Then, have them identify each organism as a producer, herbivore,
carnivore, or omnivore.
• In Figure 3, students may question where the decomposers come in.
This will be further explained in Section 2.5, but students could
think about what happens to plants and animals when they die or
are eaten. They may suggest that bodies rot or decompose and that
an animal excretes waste after it consumes things.
• For students who need additional support with the reading in this
section, use SM 2.2 Food Chains and Food Webs.
• Assign the Try This activity.
TRY THIS: DRAW A LUNCH FOOD CHAIN
Purpose
• Students will illustrate the food chain for items in their lunch and see how energy
moves from the Sun to other organisms that make up their lunch.
Notes
• Ask students to identify any producers in the lunch item. For example, there may
be lettuce in a sandwich or beans in a burrito, or even tomatoes in the chili
sauce.
• Students may need to make several chains to illustrate some food items, such as
a burrito, completely.
• If students’ lunches are too simple (such as an apple), provide them with
alternatives to work with. A slice of pizza, a hamburger, a wrap, a cheese-andtomato sandwich.
• Ask students which ingredient has the longest food chain.
Suggested Answers
• A sample food chain for a burrito:
– cheese: Sun, grass, cow, human
– refried beans: Sun, bean plants, human
54
Unit A: Ecosystems
NEL
– vegetable toppings: Sun, tomato, onion, pepper plants, human
– sour cream or yogurt: Sun, grass, cow, human
– meat filling: Sun, field of grain, chicken, human
– tortilla: Sun, corn or wheat, human
• Food chains should begin with the Sun and have arrows from one item to the
next.
At Home
3 Consolidate and Extend
Have students draw a
food chain for parts of a
meal.
• Add details and examples to BLM 0.0-9 Chapter Key Ideas.
• Post some of the food chains students produced for the Try This
activity to compare how long the food chain is for the average
ingredient.
• Assign the Check Your Understanding questions.
Technology Connections
CHECK YOUR UNDERSTANDING—SUGGESTED ANSWERS
1. A food chain always begins with plants, because the animals that we eat have
eaten something that ate a plant, which grew using the Sun’s energy.
2. Answers will vary. Here are some examples:
– a pet bird: Sun, sunflower and millet plants, bird OR Sun, apple tree, bird
– a pet dog: Sun, rice plants, corn plants, wheat plants, dog OR Sun, hay, lamb,
dog
– a pet snake: Sun, hay (with seedy heads), mouse, snake
3. Food chains are parts of a food web. An animal’s diet actually involves several
different food chains, which can be linked together in a food web.
Have students work
independently or with a
partner to create an
annotated food web.
Students could locate and
download images of
various organisms from
the Internet and organize
them into a food web
using a graphics program.
Students could include
text boxes with
information regarding
relationships and other
factors affecting the food
web.
TRY THIS: DRAW A LUNCH FOOD CHAIN
Skills Focus: classifying, inferring
1. Write down everything that you had for lunch, either yesterday or today.
2. List all the organisms that were required to produce your lunch.
For example, a sandwich may require wheat and yeast for the bread,
and meat or cheese for the filling. Did your lunch include products
from both plants and animals?
3. Choose several items from your lunch. Draw a food chain for each item,
with you at the top in each case. Which is the longest food chain?
Consumers do not usually rely on only one source of food. For
example, a coyote eats rabbits, but it will also eat mice, grouse and
their eggs, and many other animals. The mice that the coyote eats
consume the seeds, inner bark, and shoots of many different plants.
Thus, most organisms are part of several food chains. A model that
shows several different food chains, and the connections between
them, is called a food web (Figures 2 and 3).
LEARNING TIP
Evaluate the food web in
Figure 2 by comparing it
to what you have learned
about the Khutzeymateen
Valley. Do you think that all
of the organisms in the
valley have been shown?
Marten
Grizzly bear
Human
Salmon
Red
Squirrel
Porcupine
Skunk
cabbage
Stinging
nettle
Sitka
spruce
Grasses and
sedges
Deer
Mouse
Reading and Thinking Strategies: Synthesize,
Interpret Visuals and Graphics
• Making notes: Invite pairs of students to demonstrate
their understanding of food chains and food webs by
describing the chains and webs in words.
• Analyzing diagrams: For each of the food chains and
food webs (Figures 1, 2, and 3), have students examine
the diagrams systematically. Have them begin by
reading the caption and looking at the overall diagram to
get a sense of what it is about. Then, have them
consider each section or element closely, beginning
with the largest element. Ask them what clues in the
diagram help them understand the ideas (its shape, and
graphics such as arrows that show how the parts fit
together).
Red
elderberry
Figure 2
This food web shows some of the organisms in the Khutzeymateen Valley ecosystem. It
is made up of many food chains.
34
NEL
Unit A
Ecosystems
NEL
Chapter 2
Energy flows and matter cycles in ecosystems.
55
Meeting Individual Needs
ESL
• Group ESL students with language-competent classmates, or use a
resource team to help them complete the tasks.
Extra Support
• For students who need additional support with the reading in this
section, use SM 2.2 Food Chains and Food Webs.
ASSESSMENT FOR LEARNING
What To Look For in Student Work
Suggestions for Teaching Students Who Are Having Difficulty
Evidence that students can
• draw and label a food chain, and describe
how organisms get food energy
• create models (e.g., to illustrate how energy
flows through an ecosystem)
• make inferences based on observations
(e.g., infer the links between organisms)
• use technical language correctly (food
chain, food web)
• describe the effects of removing an
organism from a food web
• create products that are complete
(e.g., food web)
Provide students with a list of possible lunches to consider for Try This:
Draw a Lunch Food Chain. (Try to make this culturally sensitive.)
Have students work in pairs on the same lunch example.
56
Unit A: Ecosystems
NEL