Download Answers to 2.5 pg 47 #1-8

Unit Task Bookmark
Students can employ the
knowledge they gained
learning about food webs
in cataloguing different
species for the Unit Task.
CHECK
Extend and Assess
• To consolidate the learning, ask, Why don’t ecological pyramids for energy,
biomass, and numbers all have the same basic shape? Point out that biomass and
energy are closely related—the more biomass, the more energy. here must
always be more energy available at each lower trophic level. At each step up
the trophic ladder energy is used and lost. So it takes a very large mass/energy
of producers and primary consumers to support a small mass of secondary
and tertiary consumers. However, biomass and energy are not always related
to numbers. A single large tree—a producer at the lowest trophic level—can
support thousands of insect consumers at the next higher trophic level.
herefore a pyramid of numbers in a forest ecosystem may be “inverted”
as we saw in Figure 8(a).
• Ask, How does the shape of these pyramids afect what you see when you take a
walk in the forest? Students should recognize that during a walk in the forest
they are certain to see a very large mass of producers—even though this
may be in the form of a relatively small number of trees. he consumers
have a much lower biomass and are not as obvious. However they are very
abundant. Primary consumers (insects, squirrels) will be more common than
secondary consumers (spiders, salamanders). You would be much less likely to
see top consumers (foxes, hawks).
• Have students complete the Check Your Learning questions on page 47 of
the Student Book.
YOUR LEARNING
Suggested Answers
1. Sample answer: The term ecological niche refers to the function that a species plays in an ecosystem, including
what it eats and how it behaves.
• Humans eat plants and animals. They also interact with their environment to plant and harvest food. They have
few predators, but for example, they do supply food to bacteria living in their digestive system, biting insects,
and sometimes parasites such as head lice.
• Moose eat plants. They have a few predators (humans and wolves), and may be fed on by blood-feeding insects
and are a host to some parasites.
• A snake eats small animals such as mice and frogs. It is preyed upon by some birds and larger mammals.
• Flies feed on decaying animals and plant materials. In turn, larger animals, such as turtles, frogs, snakes, birds,
and raccoons may eat lies.
2. A food chain is a simple, idealized version of a food web. A food chain does not show all of the interactions in an
ecosystem. A food web is complex. It shows many of the possible interactions in an ecosystem.
3. If a species is added to an ecosystem, the new species may have no natural predators, so it will prey on the other
species in the ecosystem and perhaps crowd out other animals. If a species is removed from an ecosystem, other
animals that depend on that species for food may be harmed and could even die out.
4. As you move up to higher trophic levels, the amount of stored energy decreases because some energy is used to
produce energy to move, grow, reproduce, and stay warm. When an animal eats another animal, it does not eat
the entire animal. The energy in these parts does not move up to the next trophic level.
5. The lowest trophic levels contain the greatest biomass because there are many more producers or fewer but larger
producers (irst trophic level) than carnivores (third or fourth trophic levels). This occurs simply because the organisms
at a higher trophic level can only exist if there is an adequate supply of energy from lower trophic levels—this requires
more biomass/energy below. Therefore, although a forest might be full of trees, it cannot be full of wolves, too.
6. Carnivores occupy the third and fourth trophic levels. The irst level is occupied by producers. The second level is
occupied by herbivores. The third and fourth levels are occupied by animals that eat herbivores or other carnivores.
For example, a carnivore, such as a hawk, might eat another carnivore, such as a snake, which eats rodents, which
eats seeds. A carnivore, such as a spider, might eat insects, which might eat plant nectar.
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Unit B: Sustainable Ecosystems
NEL
7. Bison, zebra, and kangaroos are all grass eaters. They cannot be shown on the same food web, however, because they
live in different ecosystems on different continents. Bison live in North America, zebra live in Africa, and kangaroos live in
Australia.
8. (a) If the red fox were killed off by rabies, rabbit, mouse, and squirrel populations would increase because foxes
would no longer eat them. However, more rabbits, mice, and squirrels might eat up the grasses and berries and
seeds needed to support their population. Hawk populations would be expected to increase because they would
have more prey. So over time, the numbers of the remaining species would reach a new balance that could be
supported by the plant life. (b) rabbit, mouse, squirrel (c) grasses, berries, tree seeds
DIFFERENTIATED INSTRUCTION
At Home
• Students may have diiculty understanding the many possible paths in a food
web. Have students determine each path in the food web in their own way.
his may help students understand how to “read” a food web, and how to
appreciate its complexity. For example, verbal/linguistic learners may beneit
from writing each food chain and using arrows as well as the phrase “is eaten
by” (e.g., grass → (is eaten by) snowshoe hare → (is eaten by) lynx).
• Challenge logical/mathematical learners to investigate food chains/webs
for food products such as beef cattle or pigs. Students should address such
questions as: How many kilograms of feed (e.g., corn) go into producing a single
livestock animal? How many other types of resources (water, fertilizer, fossil fuels)
go into the raising of this animal? Students should consult local government
or environmental groups. Students could post their indings on a class blog,
wiki, or website.
• Visual/spatial and bodily/kinesthetic learners may want to develop a food
web diagram for a local ecosystem. Students can work together to explore
and catalogue diferent species that live in a limited local area, such as a ield,
stream, or log. Students should try to include as many plant, animal, fungi,
and other species as possible. Urge students to create a graphic, or threedimensional model showing their food web.
ENGLISH LANGUAGE LEARNERS
• Review words that are used to describe shape, beginning with pyramid. Have
a volunteer deine pyramid, draw the shape, and use the word in a sentence.
Ensure students realize that shapes can be oriented in diferent ways. Move
on to other shape words: square, rectangle, circle, sphere, cylinder, etc. Have
students deine each word, draw the shape, and use the word in a sentence.
NEL
Have students look in
their refrigerator and
cupboards and make a
list of all the foods their
family consumes. Ask,
What percentage of these
foods is plant based? What
percentage is meat based?
Have students draw a pie
chart that shows these
percentages.
Math Connection
Assuming the irst trophic
level of an energy pyramid
has one million joules,
how many joules will exist
at each level above that?
(100 000, 10 000, 1000,
100, 10, 1)
Have students express
each number as a power
of 10. Ask, What kind of
mathematical relationship
do you see? (105, 104,
103, 102, 101, 100; Some
students may recognize
this as an exponential
relationship.)
Chapter 2 Understanding Ecosystems
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