Explanations
10.1 Populations
 
10.2 Communities
 
10.3 Food Relationships
 
10.4 Ecological Succession
 
 
10.5 Ecosystems
 
10.6 Biomes
 
10.7 Review Questions
 
10.8 Explanations
 
Explanations

1.      B      

Individual organisms occupy particular niches (geographical locations as well as roles). Populations consist of individuals of an interbreeding species. Many coexisting populations constitute a community, and many communities coexist within a biome.

2.      D     

Only 10 percent of energy moves between trophic levels, because it is lost to sustain respiration and metabolic processes. Saprophytic activity does not explain the loss of energy as you move up a food pyramid. Biomass decreases because energy is lost, not the other way around. While it is true that secondary consumers eat primary consumers, this scenario does not affect the change in energy capacity between trophic levels.

3.      D     

All of the listed organisms are involved in the nitrogen cycle. Decaying (saprophytic), nitrifying (chemosynthetic), denitrifying, and nitrogen-fixing bacteria all play roles in the nitrogen cycle. Decaying bacteria produce ammonia (NH3), which is transformed into nitrites (NO2) and nitrates (NO3) by nitrifying bacteria. Denitrifying bacteria convert ammonia into free N2 in the atmosphere.

4.      C     

Asexual reproduction such as parthenogenesis takes greatest advantage of unlimited space and resources in a stable environment. This mode of reproduction facilitates rapid population growth. Although species diversity created through sexual reproduction is sacrificed, it is not necessary in a noncompetitive atmosphere. Organisms (no matter how similar) in an environment without limitations do not compete with one another.

5.      D     

Depleted resources, competition for food and space, predation, and disease all slow population growth. These factors shape carrying capacity for populations in any given community.

6.      B     

The first answer is a bit of a trick: symbiosis refers to a number of different relationships between organisms, including a mutually beneficial relationship, but it does not refer specifically to that sort of relationship. Mutualism does refer to a relationship beneficial to both organisms. Commensalism helps one organism and does not harm the other, while parasitism benefits one organism and harms the other. Competition refers to a battle for resources and survival between populations.

7.      A     

As an ecosystem moves through the stages of succession, it is characterized by an increase in total biomass, a decrease in net productivity relative to biomass, a greater capacity to retain nutrients within the system, increasing species diversity, increasing size of organisms, increasing life spans, and complex life cycles. Climax communities will not shift unless there is a cataclysmic event.

8.      C     

Beech, maple, and oak populate the temperate deciduous forest. High biodiversity is not a characteristic of the barren tundra. The desert exhibits short growing seasons immediately after precipitation.

9.      D     

Carbon dioxide in the atmosphere is directly produced by bacterial decay of waste and dead organic material. (Respiration also produces CO2, but it is not listed among the answer choices.) Photosynthesis and the animal consumption of producers contribute to the carbon cycle but are not directly responsible for the production of CO2. Chemosynthesis is not involved in the carbon cycle.

10.      D     

Biomass decreases from producers up through each level of consumers. Grasses, the only producer in the group, must have the largest biomass.

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