3.
4.
2.
5.
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.
True.
Organisms require nitrogen to make proteins.
True.
Decomposers are an essential part of all nutrient cycles.
True.
Green plants occupy the second trophic level in food chains.
False. Green plants occupy the first trophic level in food chains.
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.
8.
The build-up of nitrogen in lakes produces eutrophication.
The process of cellular respiration uses oxygen and produces carbon dioxide.
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
succession
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 species.
15. Competition among members of the same species is called intraspecific competition.

Match each description in column A with the correct term in column B. Place the letter for the term beside the description.
B
C
A
16.
process used by green plants to make carbohydrates
(a) consumers
B 17.
role of green plants in an ecosystem (b) producers
A 18.
role of animals in an ecosystem (c) photosynthesis
E
G
F
H
D
19.
network of links that channel energy and materials through the organisms in an ecosystem
20.
continual movement of elements between the living and non-living parts of the environment
21.
process by which pollutants become more concentrated as they move along a food chain
22.
something captured by producers from the Sun
23.
organisms that help to recycle valuable nutrients
Circle the correct answer.
(d) decomposers
(e) food web
(f) biological magnification
(g) nutrient cycle
(h) energy
24. Which process removes carbon dioxide from the air?
(a)
(b)
(c) respiration photosynthesis 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)
(b)
10 percent
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)
(b)
(c)
(d) eutrophication acid precipitation global warming increased crop production
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 CO
2
+ 6H
2
O + energy  C
6
H
12
O
6
+ 6O
2
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 energy.
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.