390 ■ CHAPTER 21 Ecosystems
REVIEWING THE SCIENCE
● (^) An ecosystem consists of
communities of organisms
and the physical environment
in which those communities
live. It is the sum of all biotic
elements interacting with
all abiotic elements. Energy,
materials, and organisms can
move from one ecosystem to
another.
● (^) An energy pyramid
represents the amount of
energy available to each
trophic level of a food chain in
an ecosystem.
● (^) Energy enters an ecosystem
when producers capture
it from an external source,
such as the sun. A portion
of the energy captured by
producers is lost as metabolic
heat at each trophic level.
As a result, energy flows in
only one direction through
ecosystems.
● (^) Nutrients are the chemical
elements required by living
organisms. Unlike energy,
nutrients are recycled and
reused within and across
ecosystems. Earth has a
fixed amount of nutrients.
● (^) Decomposers break down
the dead bodies of other
organisms, both consumers
and producers, releasing the
nutrients in the bodies of
dead organisms back to the
physical environment.
● (^) Four ecosystem processes
link the biotic and abiotic
worlds in an ecosystem:
nutrient cycling, energy flow,
water cycling, and succession.
● (^) Ecosystems depend on
energy capture, the trapping
of solar energy by producers
via photosynthesis, and the
storage of that energy as
chemical compounds in their
bodies.
● (^) Earth is categorized into
10 major biomes, regions
defined by their climatic and
ecological features.
● (^) Net primary productivity
(NPP) is the energy acquired
through photosynthesis that
is available for growth and
reproduction to producers in an
ecosystem. NPP is estimated
by the amount of biomass
produced in a given area during
a specified period of time.
THE QUESTIONS
The Basics
(^1) The movement of nutrients between organisms and the
physical environment is called
(a) nutrient cycling.
(b) ecosystem services.
(c) net primary productivity.
(d) decomposition.
(^2) How much energy is transferred up the energy pyramid from
one trophic level to the next?
(a) 90%
(b) 50%
(c) 10%
(d) 10%–50%
(^3) Which organisms are considered the “recyclers” of our planet?
(a) consumers
(b) producers
(c) phytoplankton
(d) decomposers
(^4) The terrestrial biome that receives the most consistent year-
round rainfall is
(a) wetland.
(b) boreal forest.
(c) tropical forest.
(d) chaparral.
(^5) Link each term with the correct definition.
BIOME 1.^ The energy acquired through
photosynthesis by producers of an
ecosystem.
ECOSYSTEM 2. A group of communities interacting
with one another and with the
physical environment they share.
NET PRIMARY
PRODUCTIVITY
- A large, distinct region defined by
its unique climatic and ecological
features.
ECOLOGICAL
COMMUNITY- The populations of different species
that live and interact with one
another in a particular place.
Challenge Yourself
(^6) Select the correct terms:
The biome characterized by shrubs and nonwoody plants that
grow in regions with cool, rainy winters and hot, dry summers is
(tundra / chaparral). Another biome with few trees, but in this
case dominated by grasses and nonwoody plants, is (grassland /
tundra). The most productive aquatic biome is (freshwater /
estuaries).
(^7) Which of the following is a component of an ecosystem but not
of an ecological community?
(a) a producer
(b) water
(c) a secondary consumer
(d) a primary consumer