- 5.1: Ecosystem Types and Dynamics
- An ecosystem is a community of organisms and their nonliving environment. Ecosystems may be freshwater, marine, or terrestrial. Some ecosystems are more resistant to disturbances than others. Resilience refers to how quickly an ecosystem returns to equilibrium following a disturbance. Foundation species have great influence on community structure.
- 5.2: Matter
- At its most fundamental level, life is made of matter. Matter is something that occupies space and has mass. All matter is composed of elements, substances that cannot be broken down or transformed chemically into other substances. Each element is made of atoms, which can bind together to form molecules. The four biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.
- 5.3: Biogeochemical Cycles
- Biogeochemical cycles represent the movement of chemical elements through water, air, soil, rocks, and organisms. Carbon cycles slowly between the ocean and land, but it moves quickly from the atmosphere to organisms (through photosynthesis) and back to the atmosphere (through cellular respiration). The nitrogen cycle and phosphorus cycles are other key biogeochemical cycles. Excess nutrients can disrupt aquatic ecosystems through eutrophication.
- 5.4: Fresh Water Supply and the Water Cycle
- Despite the abundance of water on Earth, only about 0.01% is available for human use. Most of Earth's water is in the oceans, and much of the freshwater is trapped in ice caps and glaciers. The water cycle describes the movement of water among bodies of water, the atmosphere, organisms, and the ground. This drives the availability of water resources, including precipitation, surface water, and groundwater.
- 5.5: Soils
- Soil is the outer loose layer that covers the Earth's surface and is the foundation for agriculture and forestry. Soils consist of organic material, inorganic material, water and air, and they differ in proportions of clay, silt, and sand. A soil profile is characterized by horizontal layers called horizons. Climate, organisms, topography, parent material, and time influence soil composition and formation.
- 5.6: Soil Degradation
- Erosion, compaction, salinization, and desertification are interacting processes that degrade soil (lower its quality).
Rachel Schleiger (CC-BY-NC)
Thumbnail image - This sage thrasher’s diet, like that of almost all organisms, depends on photosynthesis.