Chapter 20 Glossary, Summary, and Practice Questions

KEY TERMS

abyssal zone the deepest part of the ocean at depths of 4000 m or greater

acid rain a corrosive rain caused by rainwater mixing with sulfur dioxide gas as it fall through the atmosphere, turning it into weak sulfuric acid, causing damage to aquatic ecosystems

algal bloom a rapid increase of algae in an aquatic system

apex consumer an organism at the top of the food chain

aphotic zone the part of the ocean where photosynthesis cannot occur

arctic tundra a biome characterized by low average temperatures, brief growing seasons, the presence of permafrost, and limited precipitation largely in the form of snow in which the dominant vegetation are low shrubs, lichens, mosses, and small herbaceous plants

autotroph an organism capable of synthesizing its own food molecules from smaller inorganic molecules

benthic realm (also, benthic zone) the part of the ocean that extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor

biogeochemical cycle the cycling of minerals and nutrients through the biotic and abiotic world

biomagnification an increasing concentration of persistent, toxic substances in organisms at each trophic level, from the producers to the apex consumers

biome a large-scale community of organisms, primarily defined on land by the dominant plant types that exist in geographic regions of the planet with similar climatic conditions

boreal forest a biome found in temperate and subarctic regions characterized by short growing seasons and dominated structurally by coniferous trees

canopy the branches and foliage of trees that form a layer of overhead coverage in a forest

channel the bed and banks of a river or stream

chaparral a biome found in temperate coastal regions characterized by low trees and dry-adapted shrubs and forbs chemoautotroph an organism capable of synthesizing its own food using energy from inorganic molecules coral reef an ocean ridge formed by marine invertebrates living in warm shallow waters within the photic zone cryptofauna the invertebrates found within the calcium carbonate substrate of coral reefs

dead zone an area in a lake and ocean near the mouths of rivers where large areas are depleted of their normal flora and fauna; these zones can be caused by eutrophication, oil spills, dumping of toxic chemicals, and other human activities

detrital food web a type of food web that is supported by dead or decaying organisms rather than by living autotrophs; these are often associated with grazing food webs within the same ecosystem

ecosystem a community of living organisms and their interactions with their abiotic environment

ecosystem services the human benefits provided by natural ecosystems

emergent vegetation the plants living in bodies of water that are rooted in the soil but have portions of leaves, stems, and flowers extending above the water’s surface

equilibrium the steady state of a system in which the relationships between elements of the system do not change

estuary a region where fresh water and salt water mix where a river discharges into an ocean or sea

eutrophication the process whereby nutrient runoff causes the excess growth of microorganisms and plants in aquatic systems

fallout the direct deposition of solid minerals on land or in the ocean from the atmosphere

food chain a linear sequence of trophic (feeding) relationships of producers, primary consumers, and higher level consumers

food web a web of trophic (feeding) relationships among producers, primary consumers, and higher level consumers in an ecosystem

grazing food web a type of food web in which the producers are either plants on land or phytoplankton in the water; often associated with a detrital food web within the same ecosystem

gross primary productivity the rate at which photosynthetic producers incorporate energy from the Sun

hydrosphere the region of the planet in which water exists, including the atmosphere that contains water vapor and the region beneath the ground that contains groundwater

intertidal zone the part of the ocean that is closest to land; parts extend above the water at low tide

neritic zone the part of the ocean that extends from low tide to the edge of the continental shelf

net primary productivity

heat loss

the energy that remains in the producers after accounting for the organisms’ respiration and

non-renewable resource a resource, such as a fossil fuel, that is either regenerated very slowly or not at all oceanic zone the part of the ocean that begins offshore where the water measures 200 m deep or deeper pelagic realm (also, pelagic zone) the open ocean waters that are not close to the bottom or near the shore permafrost a perennially frozen portion of the Arctic tundra soil

photic zone the upper layer of ocean water in which photosynthesis is able to take place photoautotroph an organism that uses sunlight as an energy source to synthesize its own food molecules planktivore an animal that eats plankton

primary consumer the trophic level that obtains its energy from the producers of an ecosystem

producer the trophic level that obtains its energy from sunlight, inorganic chemicals, or dead or decaying organic material

resilience (ecological) the speed at which an ecosystem recovers equilibrium after being disturbed

resistance (ecological) the ability of an ecosystem to remain at equilibrium in spite of disturbances

savanna a biome located in the tropics with an extended dry season and characterized by a grassland with sparsely distributed trees

secondary consumer a trophic level in an ecosystem, usually a carnivore that eats a primary consumer

source water the point of origin of a river or stream

subduction the movement of one tectonic plate beneath another

subtropical desert a biome found in the subtropics with hot daily temperatures, very low and unpredictable precipitation, and characterized by a limited dry-adapted vegetation

temperate forest a biome found in temperate regions with moderate rainfall and dominated structurally by deciduous trees

temperate grassland a biome dominated by grasses and herbaceous plants due to low precipitation, periodic fires, and grazing

tertiary consumer a trophic level in an ecosystem, usually carnivores that eat other carnivores

trophic level the position of a species or group of species in a food chain or a food web

tropical rainforest a biome found near the equator characterized by stable temperatures with abundant and seasonal rainfall in which trees form the structurally important vegetation

wetland environment in which the soil is either permanently or periodically saturated with water

CHAPTER SUMMARY

Energy Flow through Ecosystems

Ecosystems exist underground, on land, at sea, and in the air. Organisms in an ecosystem acquire energy in a variety of ways, which is transferred between trophic levels as the energy flows from the base to the top of the food web, with energy being lost at each transfer. There is energy lost at each trophic level, so the lengths of food chains are limited because there is a point where not enough energy remains to support a population of consumers. Fat soluble compounds biomagnify up a food chain causing damage to top consumers. even when environmental concentrations of a toxin are low.

Biogeochemical Cycles

Mineral nutrients are cycled through ecosystems and their environment. Of particular importance are water, carbon, nitrogen, phosphorus, and sulfur. All of these cycles have major impacts on ecosystem structure and function. As human activities have caused major disturbances to these cycles, their study and modeling is especially important. Ecosystems have been damaged by a variety of human activities that alter the natural biogeochemical cycles due to pollution, oil spills, and events causing global climate change. The health of the biosphere depends on understanding these cycles and how to protect the environment from irreversible damage.

Terrestrial Biomes

Earth has terrestrial and aquatic biomes. Aquatic biomes include both freshwater and marine environments. There are eight major terrestrial biomes: tropical rainforests, savannas, subtropical deserts, chaparral, temperate grasslands, temperate forests, boreal forests, and Arctic tundra. The same biome can occur in different geographic locations with similar climates. Temperature and precipitation, and variations in both, are key abiotic factors that shape the composition of animal and plant communities in terrestrial biomes. Some biomes, such as temperate grasslands and temperate forests, have distinct seasons with cold and hot weather alternating throughout the year. In warm, moist biomes, such as the tropical rainforest, net primary productivity is high as warm temperatures, abundant water, and a year-round growing season fuel plant growth. Other biomes, such as deserts and tundra, have low primary productivity due to extreme temperatures and a shortage of water.

Aquatic and Marine Biomes

Aquatic biomes include both saltwater and freshwater biomes. The abiotic factors important for the structuring of aquatic biomes can be different than those seen in terrestrial biomes. Sunlight is an important factor in bodies of water, especially those that are very deep, because of the role of photosynthesis in sustaining certain organisms. Other important factors include temperature, water movement, and salt content. Oceans may be thought of as consisting of different zones based on water depth, distance from the shoreline, and light penetrance. Different kinds of organisms are adapted to the conditions found in each zone. Coral reefs are unique marine ecosystems that are home to a wide variety of species.

Estuaries are found where rivers meet the ocean; their shallow waters provide nourishment and shelter for young crustaceans, mollusks, fishes, and many other species. Freshwater biomes include lakes, ponds, rivers, streams, and wetlands. Bogs are an interesting type of wetland characterized by standing water, a lower pH, and a lack of nitrogen.

ART CONNECTION QUESTIONS

• 4
  Figure 20.12 Which of the following statements about the nitrogen cycle is false?
• 
  Ammonification converts organic nitrogenous matter from living organisms into ammonium (NH +).

• Denitrification by bacteria converts nitrates (NO -) to nitrogen gas (N ).
• 
  The aphotic zone, the neritic zone, the oceanic zone, and the benthic realm.

32

• 3
  2
  Nitrification by bacteria converts nitrates (NO -) to nitrites (NO -).
• Nitrogen fixing bacteria convert nitrogen gas (N₂) into organic compounds.
• Figure 20.28 In which of the following regions would you expect to find photosynthetic organisms?

REVIEW QUESTIONS

• Decomposers are associated with which class of food web?
• grazing
• detrital
• inverted
• aquatic
• The producer in an ocean grazing food web is usually a

.

• plant
• animal
• fungi
• plankton
• Which term describes the process whereby toxic substances increase along trophic levels of an ecosystem?

• biomassification
• biomagnification
• bioentropy
• heterotrophy
• The majority of the water found on Earth is:
• ice
• water vapor
• fresh water
• salt water
• The process whereby oxygen is depleted by the growth of microorganisms due to excess nutrients in aquatic systems is called .
• dead zoning
• eutrophication
• retrophication

CRITICAL THINKING QUESTIONS

• Compare grazing and detrital food webs. Why would they both be present in the same ecosystem?
• Why are drinking water supplies still a major concern for many countries?
• The extremely low precipitation of subtropical desert biomes might lead one to expect fire to be a major disturbance factor; however, fire is more common in the
• 
  The photic zone, the intertidal zone, the neritic

zone, and the oceanic zone.

• The photic zone, the abyssal zone, the neritic zone, and the oceanic zone.
• The pelagic realm, the aphotic zone, the neritic zone, and the oceanic zone.

d. depletion

• Which of the following biomes is characterized by abundant water resources?
• deserts
• boreal forests
• savanna
• tropical wet forests
• Which of the following biomes is characterized by short growing seasons?
• deserts
• tropical wet forests
• Arctic tundra
• savanna
• Why is the tundra treeless?
• lack of sufficient water
• permanently frozen ground
• winters too harsh
• too many fires
• Where would you expect to find the most photosynthesis in an ocean biome?
• aphotic zone
• abyssal zone
• benthic realm
• intertidal zone
• A key feature of estuaries is
• low light conditions and high productivity
• salt water and fresh water
• frequent algal blooms
• little or no vegetation

temperate grassland biome than in the subtropical desert biome. Why is this?

• In what ways are the subtropical desert and the Arctic tundra similar?
• Describe the conditions and challenges facing organisms living in the intertidal zone.