Answers ws 2.1 Energy Flow in Ecosystems
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p. 56
What process produces carbohydrates and why are they important?
Photosynthesis, energy source for plants and
animals.
What is cellulose and what is unusual about it?
Chemical found in plant cell walls; can not be digested by most animals
What useful function does fungi do to cellulose?
Breaks down cellulose into usable nutrients that other organisms can use
How much cellulose is produced each year by plants? 28 000 000 000 000 kg
Define biomass. Total mass of living plants, animals, fungi, and bacteria in a given area
What are the typical units for biomass?
g/m2 or kg/m2
The 2 ways all organisms interact with it’s ecosystem are?
A) Obtains food energy from an ecosystem b)
contributes energy to the ecosystem
Define energy flow.
The flow of energy from an ecosystem to an organism and from one organism to another
What do the carbohydrates created by the producers during photosynthesis eventually become?
Energy sources for other life
forms
Define consumer and give an example.
An organism that does not undergo photosynthesis; is not a plant.
Ex: bee
Define decomposition.
The breakdown of organic wastes and dead organisms into simpler substances
Define biodegradation.
The action of decomposition by bacteria and fungi
Define decomposers.
Organisms that change wastes and dead organisms into usable nutrients
Fg 2.6 p. 60. Define food chain.
A single pathway starting with producers that point to the direction of where the energy goes
Define trophic level.
Each step (level) in a food chain
Define primary producer and give 3 examples.
1st trophic level in a food chain. All undergo photosynthesis. Ex: plants and
phytoplankton such as algae.
Phyto = plantlike plankton = microscopic ocean organism
Define primary consumer and give an example.
Organisms that are herbivores (eat plants)
Define secondary consumer.
Carnivores; organisms that eat primary consumers
ex: frogs and crabs
Fg. 2.7, define detrivore. Consumers that obtain energy and nutrients by eating the dead bodies of small animal, plant matter
and animal waste
Explain fg 2.8. Detrivores feed at every trophic level because everything dies
Carnivores that eat secondary consumers or higher are called 1 of the following 3 names, name them.
Top
carnivores, top consumers, top predators
Define omnivore and give an example.
Consumers that eat both plants and animals
ex: grizzly bear from fg 2.11
p. 62
Fg. 2.11, food chains are too simple too occur in nature. What is the difference between a food chain and a food web?
Since most organisms get their energy from more then 1 source, a food web is many chains interconnected
together.
Fg 2.12; The kJ (kilo joule) is an energy unit similar to the calorie. If an organism eats 100 kJ of food, give the % distribution of
how it is used the 3 ways.
A) 30 kJ (%) is lost as body heat due to chemical reactions occurring inside your cells called
cellular respiration,
B) 10 kJ (%) is used as growth and reproduction and repair of body parts,
C)
60 kJ (%) is lost as waste matter (poo) and death (body parts)
Fg 2.13. Define food pyramid.
A model that shows the loss of energy from trophic level to another. p. 64
How much energy is lost as you move up the food pyramid from trophic level to trophic level?
90%
Why are there so few top predators in any ecosystem?
As you move up each trophic level, 90% of the energy is lost from
the previous trophic level. Therefore there is very little energy left at the top trophic levels to feed these animals.
Why is maintaining he biodiversity of plants in an ecosystem essential for maintaining viable food webs? Most of the sun’s
energy is stored in different types of plants. Different types of plants allow different types of animals to get their energy.
CHAPTER 2 ANSWERS
Reading Check Answers, p. 59
1. Biomass refers to the total mass of living plants, animals, fungi, and bacteria living in an area. It can also refer to the mass
of organic matters such as trees, plant crops, manure, and organic material used to manufacture biofuels, such as biogas. It
is expressed in grams or kilograms per square metre.
2. Plants are called producers because they “produce” food in the form of carbohydrates during photosynthesis.
Carbohydrates become an energy source for other life forms.
3. A consumer is an organism that gets its energy from plants or the producers. An organism that gets energy from other
consumers is also known as a consumer.
4. Biodegradation is the action of living organisms, such as bacteria, to break down dead organic matter.
5. Decomposers change waste and dead organisms into usable nutrients.
Reading Check Answers, p. 64
1. Food chains are models that show the flow of energy from plant to animal and from animal to animal.
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2. Each step in a food chain is called a trophic level. Trophic levels in a food chain show the feeding and niche relationships
among organisms.
3. Herbivores take energy from producers while providing energy for carnivores in the food pyramid.
4. Food energy consumed is used to help the organism obtain and digest food, repair tissues, and more. Some food energy
is excreted as feces. Between 80 and 90 percent of the energy is used for chemical reactions in the body and eventually lost
to the ecosystem as heat. Very little food energy is used for growth or to increase biomass.
5. A food pyramid is a model that shows the loss of energy from one trophic level to another. It is often referred to as an
ecological pyramid.
CYU 2.1 p.67
1. To decompose leaves, fungi have finger-like projections that invade leaf tissue and break down the tissue by secreting
enzymes. After the cellulose in the dead leaf tissues is broken down into simpler nutrients, it is absorbed by the fungi.
2. Decomposition is the breaking down of organic waste and dead organisms into usable nutrients in soil and water.
3. Plants are called primary producers because they “produce” energy in the form of carbohydrates during photosynthesis.
This energy is made available to primary consumers that eat the plants.
4. In order from lowest trophic level to highest trophic level: grass, mouse, snake, eagle.
5. (a) Herbivores are primary consumers because they obtain their energy by eating plants, the primary producers.
(b) Carnivores are not primary consumers, because they obtain their energy by eating other consumers, so they are
secondary consumers. Primary consumers must obtain their food energy from primary producers.
6. Answers may vary but may include: (a) Snake (b) Wolf, eagle, or hawk (c) Bear
7. Ninety percent of energy is lost from producers to primary consumers. Ninety percent is lost again going from primary
consumers to secondary consumers. In total, 99 percent of energy is lost from primary producers to secondary consumers.
8.
(a) Producers: none
(b) Primary consumers: moose, elk, insects, bird, squirrel, mouse
(c) Secondary consumers: wolf, bird, fox, weasel, lynx
(d) Tertiary consumer: lynx
9. Answers will vary but may include: algae crustacean small fish large fish
10. The main difference between food chains and food webs is that a food web includes several interconnected food chains
since some animals eat more than one type of food.
11. Detrivores do not return energy to the ecosystem. The energy they obtain is lost as heat.
12. (a) A; (b) A; (c) B; (d) C or D; (e) E
13.
(a) 10 percent of 1 000 000 = 100 000 (b) 10 000
(c) 1000
14.
(a) Students’ answers will vary but may include grass, insect, snake, and hawk.
(b) Students’ answers will vary but may include grass–producer, insect–primary consumer, snake–
secondary
consumer, hawk–tertiary consumer
15. You do not gain weight every time you eat because, like the mouse in Figure 2.12 most energy goes into maintaining life
functions through chemical reactions and eventually is lost as heat.
16. There cannot be an unlimited number of trophic levels because 90 percent of the energy is lost at each trophic level.
Reading Check Answers, p. 71
1. Nutrients are important for plant and animal growth and for other life processes.
2. A nutrient store is the accumulation of nutrients for short or long periods of time in Earth’s atmosphere, oceans, and land
masses.
3. A nutrient cycle is the flow of nutrients in and out of nutrient stores. These flows are also known as exchanges.
4. Human activities can increase the amount of nutrients in the cycle faster than natural biotic and abiotic processes can
move them back to the nutrient stores. Some human activities reduce nutrient stores.
Reading Check Answers, p. 75
1. Carbon is stored short term in the plants on land, in the ocean, and in animal as well as in decaying soil. Carbon is also
found in the atmosphere as carbon dioxide gas. It is also stored in the ocean as carbonate, which can be incorporated into
marine shells.
2. Photosynthesis uses carbon dioxide from the atmosphere and reacts with water to produce carbohydrates and oxygen.
The energy from the Sun provides the energy for this reaction.
3. In cellular respiration, the carbon dioxide is returned to the atmosphere when plants and animals convert carbohydrates
and oxygen into carbon dioxide and water. In the process, energy is released within the cells to be used for growth, repair,
and reproduction.
4. The importance of decomposition is that organic molecules, such as cellulose, are broken down and the carbon dioxide is
returned to the atmosphere.
Reading Check Answers, p. 78
1. Carbon is cycled from intermediate ocean depths by ocean currents.
2. Any two of: volcanic eruptions, decomposing trees, and forest fires
3. Burning fossil fuels reintroduces carbon, which was stored long ago, into the atmosphere.
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4. Other activities that have affected the carbon cycle include clearing land for agriculture and expansion of cities. The
amount of carbon dioxide returning to the atmosphere is reduced because there are fewer plants now.
Reading Check Answers, p. 80
1. Nitrogen fixation is the process where nitrogen gas is converted into ammonium.
2. Nitrogen fixation occurs in nitrogen-fixing bacteria within the soil and in bacteria attached to tree roots.
3. Organisms important to nitrogen fixation are Rhizobium and cyanobacteria.
4. In nitrification, ammonium is converted into nitrates, often in a two-step process where ammonium is converted into nitrite
and then nitrite is converted by other bacteria into nitrate.
5. The uptake of nitrates in plants benefits animals because the nitrogen is used to make proteins for the animal.
Reading Check Answers, p. 83
1. Denitrification is a process that returns nitrogen to the atmosphere and occurs when bacteria convert nitrates back to
nitrogen gas.
2. Humans contribute excess nitrogen to ecosystems by burning fossil fuels, clearing forest and grasslands, and using
chemical fertilizers.
3. Acid precipitation occurs when dissolved nitrogen compounds in the moisture in clouds falls back to Earth as nitric acid.
4. Nitrogen enters waterways by leaching from the soil by rain or irrigation water.
5. Eutrophication is the process by which excess nutrients result in increased plant production and decay.
Reading Check Answers, p. 86
1. Phosphorus is stored in ecosystems as phosphates in rock and in ocean floor sediments.
2. Weathering breaks down rock through chemical and mechanical processes.
3. Phosphorus enters ecosystems when it is taken in by land and water plants and then eaten by animals.
4. Humans contribute excess phosphate to ecosystems by using commercial fertilizers, detergents, industrial waste, livestock
farming, and untreated sewage.
CYU 2.2 p.91
1. (a) The abiotic components include the atmosphere, land, oceans, and marine and sedimentary rock.
(b) The biotic components include producers, consumers, and decomposers.
(c) Thicker arrows indicate the movement of greater amount of nutrients.
(d) Nutrients leave stores in rock by mechanical weathering and chemical weathering.
2. (a) Carbon is important to living organisms as it makes up molecules such as DNA, carbohydrates, and proteins.
(b) Nitrogen is important to living organisms as it makes up molecules found in proteins and DNA.
(c) Phosphorus is important to living organisms as it is found in the molecule that caries energy to plant cells and animal cells.
It aids in plant development and bone development in animals.
3. (a) Carbon is stored in the biosphere in plants and animals, in the atmosphere as carbon dioxide, in dissolved form in the
upper layers of the ocean, and in long-term stores in sedimentary rock.
(b) Nitrogen is stored in the biosphere as nitrogen gas in the atmosphere, in the ocean, and in land plants and animals.
(c) Phosphorus is stored in the biosphere as phosphate in rock and in ocean floor sediments.
4. Carbon is stored in the ocean as carbonates in marine organism shells and shell sediments on the ocean floor. This
sediment eventually forms limestone.
5. (a) Human activities that have influenced the carbon cycle include transportation, land clearing, agriculture, urban
expansion, burning fossil fuels, and clearing land for agriculture and buildings.
(b) Human activities have influenced the nitrogen cycle when nitrogen is added to the atmosphere by fossil fuel burning,
clearing forests and grasslands, and the use of chemical fertilizers.
(c) Human activities that have influenced the phosphorus cycle include the use of chemical fertilizers and detergents that
contain phosphates.
6. Geological uplift contributes to the phosphorus cycle as uplift exposes rock that then undergoes weathering.
7. (a) Rapidly; (b) Very slowly; (c) Very slowly; (d) Rapidly
8. Leaching is the removal by water of substances that have dissolved in moist soil.
9. Three ways plants influence the cycling of nutrients are through photosynthesis where carbon is stored and then released
in cellular respiration, through nitrogen and phosphorus storage in plants cells, and by uptake of nutrients into animals.
Students may have other acceptable answers.
10. (a) iii; (b) ii; (c) i
11. Rhizobium lives in the root nodules and supplies the host plant with nitrogen in the form of ammonium. The plant supplies
sugar for the bacteria.
12. Lightning fixes nitrogen gas and converts it to nitrates and other nitrogen-containing compounds. These compounds fall in
acid rain.
13.
(a) Animals take up carbon by eating plants.
(b) Animals take up nitrogen by eating plants.
(c) Animals take up phosphorus by eating plants.
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14. (a) The process of photosynthesis during the daytime would reduce the amount of carbon dioxide, and the process of
cellular respiration at night would increase carbon dioxide levels.
(b) Carbon dioxide in Earth’s atmosphere is not only produced by cellular respiration. Human activities contribute to the levels
in the atmosphere.
15. (a) (b) (c) Refer to the diagrams in the text on pages 76, 81, and 85.
16. (a) Evidence that indicates that human activities are affecting the reproduction of animals is that sockeye populations are
smaller because of warmer river temperatures. This decline in salmon could also affect bear and eagle health and
reproduction.
(b) Evidence that indicates that human activities affect plant reproduction is that nitrogen-tolerant plants out-compete species
that cannot tolerate high nitrogen levels.
17. Sources of increased nitrogen levels on agricultural land are the application of excess fertilizer and animal waste.
18. Agricultural land is a major source of nitrogen fixation as crops such as peas, beans, clover, and alfalfa host Rhizobium
bacteria on their roots and these bacteria fix nitrogen.
19. (a) The effects of human interference in the carbon cycle result in climate change.
(b) The effect of human interference in the nitrogen cycle is the use of commercial fertilizers and agricultural practices
causing eutrophication.
(c) The effect of human interference in the phosphorus cycle includes the use of commercial fertilizers and detergents and the
build-up of animal and industrial waste, which overload the phosphate cycle and cause eutrophication.
Reading Check Answers, p. 96
1. Bioaccumulation is the gradual build-up of chemicals in living organisms.
2. Biomagnification is the process in which chemicals not only accumulate but become more concentrated at each trophic
level in a food pyramid.
3. A chemical bioaccumulates in an organism when the pollutants are stored in plant tissue and in the fat tissues of animals.
4. Persistent organic pollutants are carboncontaining compounds that remain in water and soil for many years.
5. The meaning of “ppm” is one part per million, or one particle of a given substance mixed with 999 999 other particles.
Reading Check Answers, p. 99
1. Heavy metals are metallic elements with a high density that are toxic to organisms at low concentrations.
2. Lead was introduced into ecosystems in the past as it was used in insecticides, paints, and as an anti-knock ingredient in
gasoline.
3. Cadmium enters the environment through rock weathering, volcanoes, forest fires, and the manufacture of plastics and
batteries.
4. Natural sources of mercury include volcanoes, geothermal springs, and rock weathering.
5. Mercury sulphide is converted into methyl mercury by bacteria in the soil.
CYU 2.3 p. 103
1. The disappearance of amphibians has been caused by prolonged drought, increased ultraviolet radiation, habitat loss,
pollution, overhunting, parasites, and diseases.
2. Synthetic chemicals become biomagnified in organisms when they become stored in plant tissue and the fat tissue of
animals.
3. A chemical bioaccumulates when the chemical is taken up faster than it is broken down and excreted.
4. PCBs are synthetic chemicals called polybiphenyls.
5. Sources of PCBs include paints, plastics, and lubricants for electrical transformers made between 1930 and 1970.
6. An example of a persistent organic pollutant (POP) is DDT.
7. DDT bioaccumulates because it has a long half-life. It enters plants and then the fatty tissue of fish, birds, and animals that
eat the plants.
8. Two ppm means two particles (such as of a pollutant) mixed with 999 998 other particles.
9. A chemical with a toxic level of 0.03 ppm is more toxic, as a smaller amount has a greater negative effect on the organism.
10. DDT affects the nervous system and immune system and causes reproductive disorders.
11. The effect of biomagnification is so great in killer whales (orcas) because the toxins such as PCBS are stored in blubber
and, when blubber is burned for energy the chemical is released into the whale’s bloodstream, reducing immune system
activity.
12. Methyl mercury affects nerve cells, damages the heart, kidneys, and lungs, and suppresses the immune system.
13. (a) Cadmium poisoning is caused by smoking.
(b) Cadmium can harm the human body when it accumulates in lung tissue, causing cancer. Cadmium can also be taken into
the body in certain foods, where it accumulates and leads to infertility and damage to the central nervous system, immune
system, and DNA.
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14. Bioremediation is the use of living organisms to clean up the environment. Scientists have extracted the enzymes from
chemical-eating bacteria and have used them to clean up the environment.
15. Scientists use frogs to evaluate the health of an ecosystem since amphibians live in both land and aquatic environments.
Their egg casings are permeable and sensitive to harmful chemicals in the water. Their skin, which is partly used for
breathing, is sensitive to air and water pollutants.
16. Sample answer:
Heavy
Natural Sources
Metal
Lead
Soil
Human-made
Sources
Insecticide, paints,
gasoline ingredient
Effects on Plants and
Animals
Very toxic at 0.0012
ppm
Toxic to earthworms
and soil organisms at
very low levels, high
death rates in fish
Bioaccumulates in
brain, heart, kidneys of
vertebrates
Cadmium
Earth’s crust, trees
burning
Plastics, batteries,
mining
Mercury
Released from
volcanoes,
geothermal springs,
rock
Burning fossil
fuels, mining,
battery
manufacture,
Effects on Humans
Anemia, nervous system damage,
sterility in men, low fertility rates in
women, brain damage and kidney
failure
Accumulates in lung tissue and
causes cancer, stores in liver and
kidney, infertility, damage to
central nervous system, immune
Affects nerve cells, heart, kidneys,
and lungs and suppresses the
immune system
17. A chemical with a long half-life stays for decades in the environment where it may bioaccumulate and biomagnifying.
18. The amount of chemical left from 3 tonnes after 120 years would be 3/16 of a tonne. This is calculated by 3 tonnes ½4
(since 120/30 = 4)
19. The chemical could be picked up in the atmosphere and be carried by wind currents 1000 km away and deposited back
down with precipitation.
20. Plants can be used for bioremediation as they can trap the waste in the soil and then take in the heavy metal into their
tissues. They can act as stabilizers, reducing wind and soil erosion to reduce the spreading of the contaminant.
21. To test the effect of the insecticide on geraniums, you would require many geranium plants. For example, apply a very
low concentration of the insecticide on 100 plants, then apply a slightly higher concentration of insecticide on another 100
plants. Continue to increase the concentration of insecticide on other geranium plants until the lethal dosage is found.
Chapter 2 Review p. 104
1. Decomposers break down waste and dead organisms and make the usable nutrients available for the rest of the
ecosystem.
2. Plants change solar energy into chemical energy in the form of carbohydrates. A primary consumer, such as a deer, eats
the grass, and some of the energy is stored in its body. A secondary consumer, such as a wolf, eats the deer to obtain
energy. Ninety percent of the energy is lost between the grass and the deer, and 90 percent of the energy is lost between the
deer and the wolf.
3. Most of the energy from the Sun that is trapped by plants is lost as heat to the environment.
4. The two major life processes that involve both carbon and oxygen are photosynthesis and cellular respiration.
5. The process of cellular respiration can be represented by the following equation:
C6H12O6 (carbohydrates) + 6O2 6CO2 + 6H2O
6. (a) The nutrient cycle shown in the illustration is the carbon cycle.
(b) A: cellular respiration; B: photosynthesis; C: decomposition; D: sea surface gas exchange
7. Nitrogen is fixed by bacteria and by lightning.
8. (a) The product formed as a result of nitrification is nitrate.
(b) The product formed as a result of denitrification is nitrogen gas.
9. Weathering releases phosphate from rock through chemical processes and mechanical processes.
10. (a) The photograph shows land being cleared for agriculture.
(b) This activity affects the phosphorus cycle as phosphates are released from the trees in the form of ash, which
accumulates in the soil. The phosphate then leaches from the ash and runs off into the water supply to settle on the bottom of
lakes and is now unavailable for organisms.
11. An example in which carbon moves from the abiotic to the biotic part of an ecosystem is photosynthesis.
12. Shelled marine organisms contribute to the carbon cycle when their shells form into sedimentary rock, which traps carbon
in stores.
13. (a) Carbon enters long-term stores in the form of carbonate in shells, which eventually forms sedimentary rock, and in the
form of hydrocarbon compounds forming fossil fuels.
(b) Carbon leaves long-term stores as carbon dioxide when fossil fuels are burned.
14. (a) The phosphorus cycle differs from the carbon cycle because no phosphorus is stored in the atmosphere.
(b) The phosphorus cycle differs from the nitrogen cycle since phosphorus is not in the atmosphere.
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15. (a) Green plants would contain the greatest biomass since a large amount is needed for energy as there is a 90 percent
energy loss to the consumers.
(b) The organisms in this food web that would contain the least biomass would be the top carnivore, the hawk, as there has
been a loss of energy moving up the energy pyramid.
16. Bacteria enable plants to take up nitrogen as they convert ammonia into nitrates which the plants can take up in their
roots.
17. (a) The two largest stores of carbon are sedimentary rock and fossil fuels.
(b) These carbon stores have become substantial as dead marine and land organisms have accumulated over time.
18. Heavy metals are harmful to the environment because they are toxic at low concentrations.
19. PCBs harm orcas because the chemical bioaccumulates in blubber and is released when the organism uses the fat for
energy.
20. Effects of persistent organic pollutants on organisms are that they cause nervous system, immune system, and
reproductive disorders.
21. The flow of energy through an ecosystem differs from the cycle of nutrients in an ecosystem because energy flows out of
the ecosystem as heat but nutrients are retained and recycled within the ecosystem.
22. (a) The species most likely to consist of herbivores is species A because they are at the second trophic level and they
have obtained energy from the largest biomass source plants.
(b) The species most likely to consist of carnivores is species B because they are secondary consumers and require many
organisms to support their energy requirements as there is a 90 percent loss of energy between trophic levels.
23. You would not gain 450 g if you were to eat a 450 g meal as the energy in the meal is used to fuel cellular respiration for
body growth and repair. Most of the energy in the 450 g is lost as heat.
24. An increase in agricultural activity might affect a local fishery as chemical fertilizers might leach into the watershed.
Animal waste may also leach chemicals into the watershed. Eutrophication may occur, which may kill fish.
25. (a) Volcanic activity is involved in the carbon cycle as carbon dioxide can be released from an active volcano.
(b) Volcanic activity is involved in the nitrogen cycle as ash containing ammonia can be released from an active volcano.
26. The role of decomposers in the carbon cycle is to convert organic molecules, such as cellulose, back into carbon dioxide.
27. Farmers often add nitrogen and phosphorus to their crops but not carbon since carbon is obtained from the atmosphere
in the form of carbon dioxide while nitrogen and phosphorus enter through plant roots.
28. Organisms are most affected by biomagnification at higher trophic levels as the chemicals bioaccumulate in the tissues of
producers and lower consumers.
29. (a) If the secondary consumers in a food chain use 4200 kcal of energy, the amount of energy used by the producers in
that food chain was 42 000 kcal.
(b) The amount of energy available to the tertiary consumers would be 420 kcal.
30. Zooplankton and phytoplankton in a water ecosystem can contain low levels of a chemical while adult fish living in the
same ecosystem contain levels high levels because the chemicals bioaccumulate and biomagnify up the food chain.
31. (a) The evidence that cadmium bioaccumulates in humans is that it is found in the lungs and kidneys.
(b) Individuals exposed to second-hand smoke are at risk since the small particles released into the air from a smouldering
cigarette are very high in cadmium.
(c) If a person smoked 15 cigarettes per day and 50 percent of the cadmium in each cigarette was absorbed, the cadmium
intake would be between 7 to 15 micrograms per day.
(d) Since cadmium has a half-life of 30 years, the person will never be rid of the cadmium.
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