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.
