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7.7: Review

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    After completing this chapter you should be able to...

    • Differentiate between abiotic and biotic ecosystem components.
    • Describe the three main categories of ecosystems.
    • Explain the law of conservation of mass.
    • Discuss the biogeochemical cycles of carbon, nitrogen, phosphorus, and sulfur.
    • Explain how human activities have impacted these cycles and the potential consequences for Earth.
    • Explain how soil characteristics influence plant growth.
    • Identify and describe each component of soil.
    • Distinguish among sand, silt, and clay and explain how particle size influences soil texture.
    • Describe each horizon in a typical soil profile.
    • Explain how soils are formed, describing each of the five major factors that affect soil formation and composition.
    • Describe the major types and causes of soil degredation.

    Ecosystems consist of living (biotic) and nonliving (abiotic) components. They can be classified as freshwater, marine, or terrestrial. Resistance and resilience are measures of ecosystem health. 

    Matter is anything that occupies space and has mass. Pure forms of matter are called elements and the smallest units of an element are atoms. Atoms form molecules through ionic, covalent, or hydrogen bonding. Molecules that contain carbon and hydrogen covalent bonds are called organic. There are four main type of large organic molecules (biological macromolecules) in organisms: carbohydrates, lipids, proteins, and nucleic acids.

    The chemical elements that organisms need continuously cycle through ecosystems. Cycles of matter are called biogeochemical cycles, or nutrient cycles, because they include both biotic and abiotic components and processes. Examples of biogeochemical cycles include the carbon, nitrogen, phosphorus, and sulfur cycles, and each of these can be altered through human activities.

    Soil consists of organic and inorganic material as well as water and air. The organic material of soil is made of humus, which improves soil structure and provides nutrients. Soil inorganic material consists of rock slowly broken down into smaller particles that vary in size, such as sand, silt, and loam. Soils form slowly as a result of biological, physical, and chemical processes. Soil is not homogenous because its formation results in the production of layers called a soil profile. Most soils have four distinct horizons, or layers: O, A, B, and C. Their composition is influenced by the climate, presence of living organisms, topography, parent material, and time. The processes of erosion, compaction, and desertification degrade soils. While these processes occur naturally to an extent, they are exacerbated by certain agricultural practices, deforestation, and other human activities.


    Modified by Melissa Ha from the following sources:

    This page titled 7.7: Review is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha and Rachel Schleiger (ASCCC Open Educational Resources Initiative) .

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