UNIT
B
Review
SUGGESTED ANSWERS
WHAT DO YOU REMEMBER?
1.
b
2.
d
3.
b
4.
d
5.
d
6.
c
7.
c
8.
c
9.
b
10.
d
11.
c
12.
d
13.
c
14.
b
15.
d
16.
b
17.
True
18.
True
19.
False. Some species can feed at many trophic levels.
20.
True
21.
False. Energy passes through ecosystems, but matter cycles within ecosystems.
22.
True
23.
False. Most of Canada’s habitat loss occurred in 19th and early 20th centuries when natural lands were
cleared for farmland.
24.
False. Introductions of species into an entirely new environment usually fail.
25.
False. Clear-cutting is a common method used by the forest industry.
26.
True
27.
False. Most of the food crops grown in Canada are non-native species.
28.
True
29.
tolerance range
30.
carrying capacity
31.
marine
32.
clearing and burning
33.
estuary
34.
biological control
35.
sulphur dioxide; nitrogen
36.
selective cutting
37.
thermal
38.
nitrogen; phosphorus; potassium
39.
tropical rainforest
40.
ecological footprint
41.
Matching: (a) (iv); (b) (ii); (c) (i); (d) (v); (e) (iii)
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WHAT DO YOU UNDERSTAND?
42.
The original source of energy in a food chain is the Sun.
43.
Sample answer: Three biotic factors you would find in a forest ecosystem are plants, deer, and ants. Three
abiotic factors you would find in a forest ecosystem are light, water, and soil.
44. Table 1
Problem
Alternative Farming Practice Solution
loss of soil nutrients, soil compaction, poor soil quality, erosion
no-tillage agriculture
too much fertilizer and pesticide use, nutrient poor soil
crop rotation
high-maintenance crops, variable growing conditions
crop selection suited to local conditions
45.
Sample answer: The effects of DDT on an ecosystem illustrate the interdependence of life on Earth by
showing how a single factor can affect many species in direct and indirect ways. For example, DDT was
intended to kill mosquitoes, but also killed a particular species of wasps. The lack of wasps lead to an
increase in the caterpillar population that the wasps previously fed upon. The caterpillars fed on thatched
roofs, and with more caterpillars, more roofs on houses were eaten, leaving people without shelter.
46.
Sample answer: Human activities that can alter the water, carbon, and nitrogen cycle include burning fossil
fuels and deforestation, which release more carbon dioxide to the atmosphere. Deforestation also decreases
the number of trees that can take in the carbon dioxide from the air. Farming can alter both the water and
the nitrogen cycle.
47.
Sample answer: It would be unlikely to find a food chain with 15 trophic levels because the number of
trophic levels in a food chain is limited because so much energy is lost at each trophic level. Typically, this
means that an ecosystem can support only 3–5 trophic levels.
48.
Sample answer: Matter and energy differ within a community because matter gets recycled in a
community, while energy flows through a community. Decomposers can break down matter and return it
to the soil. However, energy is used at each trophic level and is lost to the atmosphere as thermal energy.
49. (a)
Sample answer: Urban ecosystems can harm the environment because they are sources of air and
water pollution. In addition, urban ecosystems rely on resources from natural ecosystems outside their
boundaries. This depletes the resources of outside ecosystems.
(b)
Sample answer: Urban ecosystems can be helpful to the environment because people can save energy,
space, and resources by living closer together. Transportation can be more energy efficient if people
travel shorter distances and use public transportation.
50. (a)
Sample answer: Two examples of carnivores are weasels and goshawk.
(b)
Sample answer: Two examples of omnivores are black bears and humans.
(c)
Sample answer: Two examples of decomposers are bacteria and fungi.
(d)
Sample answer: Two examples of producers are pine trees and grass plants.
51. Table 2
52.
208
Natural Fertilizers
Synthetic Fertilizers
examples
manure, sludge, plant materials, compost, wood ashes
ammonia, manufactured urea, potash
advantages
release nutrients slowly, benefit nutrient cycling
act quickly, easy to apply
disadvantages
slower acting, harder to apply
production uses a lot of energy, can cause water
pollution, can cause imbalances in soil chemistry
and organisms
While grass is desirable in a lawn, grass can be a weed by competing with vegetable plants in a garden and
curbing their growth.
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53. (a)
54.
A marine ecosystem has a dissolved salt content averaging about 3 %, whereas a freshwater ecosystem’s
salt concentration is usually below 1 %.
(b)
An energy pyramid shows energy loss and transfer within food webs at each level, whereas a biomass
pyramid shows the total mass of all individuals at each level.
(c)
Organic methods use no pesticides or artificial fertilizers; integrated pest management uses all methods
of crop management including organic methods.
(d)
Natural ecosystems are self-sustaining for long periods of time, but engineered ecosystems are created
and must be maintained by human actions.
Human activities affect soil in urban environments in many ways. For example, in an urban environment, many
soils are paved over. Many soils are compacted by human activity. Some soils are over-treated with fertilizer.
SOLVE A PROBLEM
55. (a)
(b)
Recycling water from urine helps the space station crew to survive longer without resupply of water
from Earth.
Biogeochemical cycles play a similar role by converting wastes and important chemicals in sinks and
deposits into nutrients, oxygen, and water.
56. (a)
Calcium levels have declined far enough to begin affecting the survival of the microscopic herbivores.
(b)
The loss of a source of energy in a lower level of a food chain can severely reduce the carrying capacity
of the ecosystem for organisms higher in the food chain.
57. (a)
The population will increase greatly.
(b)
The lion fish will consume many prey organisms and perhaps extirpate them. The loss of the prey
organisms will upset the food web.
(c)
The spines could protect the lion fish from predators, making their survival and rapid spread more likely.
(d)
Sample answer: To reduce their numbers, lion fish could be hunted or natural enemies could be brought
in. Boats could be checked to make sure that lion fish are not brought to new places. Introducing
enemies could be tricky because the enemies themselves could cause problems in local ecosystems.
58. (a)
Increased human population will mean more pollution, waste, energy demand, and monoculture agriculture.
(b)
If people live close together in efficiently designed communities, they will use less energy for heating
dwellings and transportation to and from work; natural ecosystems will also remain less fragmented.
(c)
Sample answer: Pollution can be the root cause of many environmental problems including habitat
loss and endangerment of species so I would focus on controlling that first.
59. (a)
When fat tissue in a mother’s body becomes a part of her breast milk, any pesticides stored in the fat
will be consumed by a nursing infant.
(b)
Pesticides, especially DDT, can cause predatory birds to lay eggs with thin shells, resulting in poor
hatching rates and population declines.
(c)
Organic foods are grown without pesticide use. There is no danger of pesticides spreading into the
environment, and people eating the organic foods will not be exposed to pesticides.
60.
Sample answer: I would tell him that the fertilizer is running off into his pond. The nutrients in the fertilizer
are causing excessive algal growth in the pond (also called an algal bloom). As the algae die, decomposers
begin to break them down, using oxygen in the process. Because the amount of algae is so high, the number
of decomposers is high as well and over time, the decomposers use up most of the oxygen in the pond. As a
result, the other organisms in the pond, such as fish, cannot live.
61.
Sample answer: Eating locally reduces air pollution because food does not have to be transported as far, so
less fossil fuels are burned during transport. Also, keeping local farmers in business ensures that farms and
pastures are not taken over and used for urban development.
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62. (a)
(b)
Sample table:
Benefit
Cost
no danger to pets or humans
yards less attractive
no pesticide leaching in water system
more weeds and insects
less pesticide in ecosystem
more money spent on weeding
Sample answer: Dear Editor, I would like to express my support for the recent legislation banning the use of
pesticides for cosmetic use. Although some might consider the increase in weeds to be a problem; I would
like to point out the many benefits of this legislation. A reduction in the use of pesticides will avoid a danger
to pets and humans, will reduce the amount of chemicals in our water supply, and will prevent unintended
damage to natural ecosystems. In conclusion, a few weeds are a small price to pay for these benefits.
CREATE AND EVALUATE
63. (a)
(b)
64. (a)
65.
The most striking difference between the two ecosystems is that the bog biomass pyramid narrows
toward the top, whereas the marine biomass pyramid widens.
The biomass of the primary consumers in the English Channel, a marine ecosystem, is much greater
than the biomass of the primary producers. This can only occur if the primary producers are able to
replenish themselves very rapidly.
Sample answer: The walruses may have been heavily hunted by people.
(b)
The loss of one species usually has an affect on other species in an ecosystem through a food web,
recycling of nutrients, habitat changes or other factors. The loss of walruses probably increased
populations of fish and other things walruses ate. This in turn may have influenced the prey of the fish.
(c)
Sample answer: If the walruses were hunted out of the region, they should still be able to survive there
and should be reintroduced. However, doing so could be very expensive and may not be practical.
(d)
Sample answer: People do not have the right to eliminate animal populations for their own interests.
The extirpation or extinction of animal species harms ecosystems and reduces biodiversity on Earth,
negatively affecting all organisms.
Sample letter:
Dear Member, I think you should consider allowing natural pesticides to be used in organic farming. These
pesticides are natural products, so they must be similar to what plants actually produce. Thank you.
66. (a)
The whale sharks likely arrive just after the red crab migration because the red crabs have already
released their eggs into the ocean and some have hatched and then are consumed by the sharks.
(b)
Yellow crazy ants are reducing the population of red crabs. The whale sharks depend on newly hatched
red crabs for food, so a reduction in red crab numbers could cause a reduction in whale shark numbers.
(c)
Sample food web: Tree seedlings are eaten by red crabs; red crabs are eaten by whale sharks and yellow
crazy ants; yellow crazy ants have no predators.
yellow
crazy ants
whale sharks
red crabs
tree seedlings
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(d)
67. (a)
By preying on red crabs, yellow crazy ants threaten the sustainability of the rain forest ecosystem on
Christmas Island. Because fewer red crabs might mean fewer whale sharks, the yellow crazy ants also
affect the whale sharks. This affects the sustainability of aquatic ecosystems.
When the lemming population is high for a while, the owl population then begins to increase.
(b)
The owl population tends to increase after an increase in the lemming population.
(c)
The owl population is a limiting factor for the lemming population because when the owl population
is high it limits the lemming population.
68. (a)
Sample food web:
hawks
mice
snakes
grasshoppers
Deer
rabbits
grasses
(b)
The producers are the grasses. They are important as producers because they provide the energy for the
consumers in the ecosystem. Without the grasses, there would be no way to create chemical energy
from light energy and the food web would collapse.
(c)
A carnivore is the snake. An herbivore is the rabbit.
(d)
Snakes and hawks compete for rabbits.
(e)
Sample energy pyramid of the food web:
tertiary consumers
hawks
arrows ⫽ energy lost
secondary consumers
mice, snakes
primary consumers
grasshoppers, rabbits,
and deer
producers
grasses
energy pyramid
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REFLECT ON YOUR LEARNING
69.
A forest is crucial to life because its trees are major suppliers of oxygen to the planet. A river is crucial to
life on Earth because it is a key part of the water cycle. It brings run-off to the oceans where the cycle of
evaporation, precipitation, and liquid water flow can begin again.
70.
Sample answer: The sustainable measures I will now employ to reduce my ecological footprint are
composting, recycling, and using public transportation whenever possible.
71.
Sample answer: No, such ecosystems can only be made more sustainable by “green practices,” but they are
not fully sustainable. I do not feel that humans should try to live without engineered ecosystems; without
engineered ecosystems, many humans could not obtain the resources they need to survive. Humans
demand too many resources for engineered farming and urban centres to become less common.
72.
Sample answer: I could conserve water by taking shorter showers and turning the faucet off while brushing
my teeth. I could eat lower on the food chain by consuming less meat. I could conserve energy around the
house by turning off lights and keeping the thermostat at a cooler temperature during the winter. Each of
these actions uses fewer resources, which in turn makes the environment more sustainable.
73. (a)
(b)
Sample answer: I found the concept of energy flow through an ecosystem the most difficult to
understand.
Sample answer: I plan to talk to my teacher who could explain this concept further or could suggest
reading material that would help to explain it further.
WEB CONNECTIONS
74.
Sample answers will include green roofs, public transportation, support of high mileage vehicles, use of
solar panels for electricity, waste recycling programs, promotion of organic foods and local produce, and
tax breaks for use of energy-saving features in homes. Students’ reports should summarize the results of
their research.
75. (a)
(b)
76.
212
Sample answer: The loggerhead shrike is a bird that is on the endangered species list. The main events
leading to its endangered status are loss of habitat, use of pesticides and collisions with automobiles.
Steps being taken to protect it include population and habitat monitoring, landowner education, and a
captive breeding and release program.
The liquid-filled cavity of a pitcher plant could be considered an ecosystem because:
(a)
the cavity contains both biotic (the plant, prey, such as flies, ants, spiders, moths, mosquitos, bacteria)
and abiotic factors (rainwater). The abiotic and biotic factors interact with each other in the cavity.
Mosquitos feed on the prey and bacteria break the prey down into nutrients for the plant.
(b)
The interactions described in (a) form a food web within the cavity of the plant.
(c)
The movement of matter through the biotic and abiotic environment (i.e. biogeochemical cycles) also
indicates that the cavity of the plant pitcher is an ecosystem. The prey is broken down into nutrients
for the plant; when the plant dies and decomposes, these nutrients are returned to the environment.
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