ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Chapter Outline		AP BIOLOGY: Chapter Twenty-Seven Review Answers 1. A biome is an assemblage of organisms that has a characteristic appearance and that occurs over a wide terrestrial geographical area. The two key physical factors that effect the distribution across the earth of biomes are (1) amounts of heat that reach the earth and its seasonal variation and (2) global atmospheric and resulting oceanic circulation patterns. 2. Most deserts are located at these latitudes because the air is falling and being warmed; since warm air holds more moisture than cool air, there is less precipitation. It is more likely that a desert will form at the interior of a continent due to the distance from the sea. The windward side of a mountain generally is moister because as the air rises on this side, it is cooled and loses its moisture-holding capacity, causing precipitation. On the leeward side the air descends, is warmed, and holds more moisture, blocking precipitation. 3. There is a wider variety on the land as a result of the sharper barriers between terrestrial habitats; ocean variation is less distinct and there is less variety of available niches, resulting in less evolutionary diversity. 4. The three major oceanic habitats are (1) the neritic zone-shallow zones along the continental coasts with a large number of species; (2) the surface zone-upper layers of the open sea with diverse species; and (3) the abyssal zone-deep-water areas shown to have more diversity than was thought as sampling techniques have improved. 5. Plankton are microscopic organisms, algae, and cyanobacteria. Nekton are fish and other larger organisms that feed on the nekton. The photosynthetic plankton are important because 40% or more of the earth's photosynthesis occurs in them. The level is slow and there is a rapid turnover of nutrients in the surface zone; most of the nutrients are tied up in the organisms. 6. The abyssal zone would appear to be quite inhospitable, with its intense pressure, low temperature, and complete lack of light (and therefore photosynthesis). Sulfur-spewing hydrothermal vents provide chemoautotrophs with a metabolite (sulfur), and therefore can support a surprisingly diverse community around the vents, including tube worms that can reach over a meter in length, large clams, acorn worms, and a host of other unusual organisms. 7. Almost 2% of the earth's water is fresh. The three zones are (1) littoral zone-shallow water along the edges; (2) limnetic zone-upper layer of open water; and (3) profundal zone-water below the limit of light penetration. 8. Organic and inorganic nutrients are supplied to lakes chiefly from the terrestrial environments. Rain, of course, adds to lakes, and oxygen can also diffuse directly through the surface. "Nutrient richness" of healthy lake systems tends to be cyclical, being greatest in the thermal-induced fall and spring overturns. 9. Eutrophic lakes are organic and abundant in minerals; the action of decomposers makes the hypolimnion stagnant during the summer. Oligotrophic lakes are characterized by scarce organic matter and nutrients; they are generally deep with an abundant supply of oxygen in the hypolimnion. Oligotrophic lakes are more susceptible to the effects of pollution because the excess phosphorus from fertilizers increases productivity, which ultimately depletes the lake of oxygen. 10. The seven most prominent biomes are tropical rain forests, savannas, deserts, temperate grasslands, temperate deciduous forests, taiga, and tundra. The stratification is imitated in changes in elevation at a given latitude in that lower elevations are more similar to the equator and the highest elevations are more similar to the poles. 11. The key characteristics are a great variety of species, highly specialized, tremendous rainfall, poor soil nutrition, and most nutrients in living organisms-especially the trees. Slash-and-burn agriculture is damaging because burning destroys the nutrients rather than putting them back in the soil. 12. The key characteristics are extremely low precipitation, sparse vegetation, large daily temperature fluctuations, extreme heat in summer, and deciduous and evergreen vegetation. The adaptations necessary include (1) succulent plants store water and exhibit CAM photosynthesis and (2) animals may limit activity to moist periods and are nocturnal; they are also able to store large quantities of water in their tissues. 13. The key characteristics are extremely rich soil, long cold winters, and relatively abundant rainfall. They resemble savannas in that they have large quantities of perennial grasses which support herds of large grazing mammals. 14. The key characteristics are long cold winters, short summers, winters that are very dry, greatest precipitation in summer, short days in winter and long ones in summer, infertile soils, coniferous trees, and limited variability of species. The tundra contains virtually no trees, only scrubby plants, open grassland that can get boggy at times, and an underlying layer of permafrost-ground that never thaws.