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					Science 10                          Sustainability of Ecosystems
Answer Key                              End of Unit Test Review


Indicate whether each statement is true or false. Correct each false statement.

1.    Plants add carbon dioxide to the atmosphere through the process of
      cellular respiration.


2.    Organisms require nitrogen to make proteins.


3.    Decomposers are an essential part of all nutrient cycles.


4.    Green plants occupy the second trophic level in food chains.

      False. Green plants occupy the first trophic level in food chains.

5.    The biomass of herbivores in an ecosystem is generally greater than the
      biomass of plants.

      False. The biomass of herbivores in an ecosystem is generally
      smaller than the biomass of plants.

6.    The process of biomagnification tends to increase the concentration of
      chemical pollutants in organisms at the bottom of the food chain.

      False. The process of biomagnification tends to increase the
      concentration of chemical pollutants in organisms at the top of the
      food chain.

Complete each statement with the correct term or phrase.

7.    The build-up of nitrogen in lakes produces eutrophication.

8.    The process of cellular respiration uses oxygen and produces carbon

9.    The process of photosynthesis combines water with carbon dioxide gas
      to produce carbohydrates.

10.   Denitrifying bacteria convert nitrates into nitrogen gas.

11.   Lichen is a pioneer species in this type of succession primary


12.   Primary consumers are animals that eat plants.

13.   There is a loss of energy at each trophic level.

14.   The largest population of a species that an environment can support over

      the long term is called the carrying capacity of the environment for this


15.   Competition among members of the same species is called intraspecific

Match each description in column A with the correct term in column B. Place the
letter for the term beside the description.

      A                                              B
      16. process used by green plants to make
 C                                             (a) consumers
 B    17.   role of green plants in an ecosystem     (b) producers

 A    18.   role of animals in an ecosystem          (c) photosynthesis
      19. network of links that channel energy
 E     and materials through the organisms in an     (d) decomposers
      20. continual    movement     of  elements
 G     between the living and non-living parts of    (e) food web
       the environment
      21. process by which pollutants become
                                                     (f) biological
 F     more concentrated as they move along a
       food chain
      22. something captured by producers from
 H                                                   (g) nutrient cycle
       the Sun
      23. organisms that help to recycle valuable
 D                                                   (h) energy

Multiple Choice

Circle the correct answer.

24.   Which process removes carbon dioxide from the air?

      (a)    respiration
      (b)    photosynthesis
      (c)    acid precipitation
      (d)    eutrophication

25.   Which process removes nitrogen from the air?

      (a)    nitrogen fixation
      (b)    denitrification
      (c)    photosynthesis
      (d)    nitrification
26.   The amount of usable energy that is used for growth and reproduction of
      organisms at each link in a food chain is about

      (a)    10 percent
      (b)    30 percent
      (c)    50 percent
      (d)    90 percent

27.   Which of the following is NOT a result of a change in the nitrogen cycle?

      (a)    eutrophication
      (b)    acid precipitation
      (c)    global warming
      (d)    increased crop production

Short Answer

Write a sentence or two to answer each of the following questions.

28.   Explain why a nutrient cycle on Earth is called a closed system.

      A nutrient cycle on Earth is called a closed system because there is
      little or no input of new nutrients from outside the cycle, which is
      maintained through continual recycling of nutrients.

29.   Write an equation that summarizes the process of photosynthesis.

      6 CO2 + 6H2O + energy  C6H12O6 + 6O2

30.   Do the materials that make up a tree come mainly from the soil, water,
      or air? Explain.

      The biomass of a tree comes from all three sources. As a plant, a
      tree adds to its biomass chiefly through photosynthesis, which
      requires carbon dioxide from the air and water drawn up from the
      soil. A tree’s growth is also increased by nitrogen from the air and
      soil (through compounds that are absorbed by the roots) and
      phosphorous, from the soil.
31.   How does the combustion of fossil fuels affect the carbon cycle?

      The combustion of fossil fuels adds to the air large amounts of
      carbon that have been stored for millions of years below the
      Earth’s surface. Such excessive amounts of carbon cannot be
      recycled as rapidly as it is being added to the biosphere. In this
      way, the carbon cycle has been disrupted.

32.   Why might an organic farmer add manure to a field?

      Animal manure, which contains nitrogen compounds, can be used
      as a natural plant fertilizer. The manure is broken down by
      decomposers in the soil to release ammonia, which can be used
      directly by some plants as a source of nitrogen. The ammonia can
      be converted by nitrifying bacteria back into nitrates, which can be
      absorbed by plants that use nitrogen in this form. Because this
      fertilizer contributes to natural recycling, it does not release
      excess nitrates into the soil or adjacent waterways, as artificial
      fertilizers do. An organic farmer would prefer to use a fertilizer
      that supports the agricultural ecosystem without causing harm to
      it or neighbouring ecosystems.

33.   Why do food webs require a continual input of energy from the Sun?

      Food webs require a continual supply of energy from the Sun
      because so much is lost through consumption from producers to
      other organisms. About ten percent of energy produced by plants
      from the Sun’s energy transfers to organisms at each successive
      trophic level. Some energy is used by consumers to support life
      functions; much of it is lost as heat given off as a result of such
      functions. This lost energy is continually replaced, so that plant
      growth can continue and consumers can continue to acquire

34.   Give an example of a way in which technology affects sustainability.

      Biotechnology can support the production of new types of food, as
      well as disease and pest resistant see varieties, by altering or
      adding genes in animals or plants. This technology could increase
      the sustainability of human populations by increasing the
      reliability of food supply. It is also possible that the sustainability
      of natural ecosystems could be reduced by this technology through
      competition or predation by genetically modified organisms, or
      through expansion of agricultural ecosystems.

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