Summary
Highlights
The nutrient cycle explains how nature recycles nutrients within an ecosystem, typically illustrated with three layers: biomass, litter, and soil. Nutrients are absorbed by plant roots from the soil (biomass), leaves fall and form a litter layer, which decomposes with rainfall, returning nutrients to the soil. Some nutrients are lost to surface runoff and leaching, while weathered rock adds to the soil.
Global ecosystems, or biomes, are areas with specific characteristics found around the world, such as tropical rainforests, deserts, and polar/tundra environments. Interdependence means that everything within an ecosystem relies on something else. In rainforests, climate, plants, soil, people, and animals are all interdependent. For example, humans cutting down trees impact soil protection, nutrient retention, and plant growth, creating a domino effect on the entire ecosystem.
Rainforests have distinct layers (forest floor, undercanopy, canopy, emergent) with plants and animals exhibiting unique adaptations. Plants have buttress roots for support, lianas to reach sunlight, and drip-tip leaves for water runoff. Animals adapt through camouflage, short wingspans, nocturnal habits, and sharp senses. The value of rainforests lies in being a source of products and medicines, offering long-term economic benefits like ecotourism, reducing the greenhouse effect, and regulating climate and water cycles. Management strategies include replanting, selective logging, ecotourism, education, conservation (national parks), debt reduction (conservation swaps), and international hardwood agreements to combat illegal logging.
Cold environments are categorized into polar and tundra. Polar environments are extremely cold with very low precipitation and few plants (mostly mosses/grasses), averaging -90°C, and are largely uninhabited. Tundra environments are also cold with low precipitation but have slightly more abundant plant life (shrubs, grasses, mosses), averaging -50°C, and can be inhabited by oil/gas workers and indigenous people. Both have very low biodiversity, making them vulnerable to environmental changes like global warming.
Plants in cold environments adapt with short growing seasons, small leaves to limit transpiration, shallow roots due to permafrost, and a low-lying growth habit for wind protection. Many plants also become dormant to survive cold, dark winters. Animals like polar bears adapt with thick fur for warmth, hibernation to conserve energy, migration to warmer areas, and white coats for camouflage in hunting and avoiding predators. Alaska is highlighted as a key case study for cold environments.