Samacheer Class 9 Social Science - Biosphere

Loss of biodiversity refers to the decline in the number and variety of species, genetic diversity, and ecosystems over time. This loss occurs when species become extinct or their populations decline significantly, when genetic variation within species decreases, and when entire ecosystems are destroyed or degraded. The primary causes of biodiversity loss include habitat destruction from deforestation and urbanization, pollution from industrial and agricultural sources, overexploitation of species through hunting and overfishing, climate change, and the introduction of invasive species. Biodiversity loss is a critical environmental concern because it reduces the resilience of ecosystems, diminishes the services that nature provides to humans such as pollination and water purification, and eliminates species that may have potential medicinal or agricultural value. Once a species becomes extinct, that genetic and biological diversity is lost forever, making conservation efforts essential to prevent further decline.

Terrestrial biomes are large geographic regions characterized by distinct climate patterns, vegetation types, and animal communities. The major terrestrial biomes include tropical rainforests, which are hot and wet year-round with dense vegetation and high biodiversity; tropical deciduous or monsoon forests, which experience distinct wet and dry seasons and shed their leaves seasonally; savannas, which are grasslands with scattered trees found in tropical and subtropical regions; deserts, which are arid regions with minimal rainfall and specialized drought-resistant plants and animals; temperate grasslands, which have moderate rainfall and are dominated by grasses with few trees; temperate deciduous forests, which experience four distinct seasons and trees that lose their leaves in winter; Mediterranean biomes, characterized by mild wet winters and hot dry summers; taiga or boreal forests, which are found in high northern latitudes with coniferous trees and long cold winters; tundra, the coldest biome with permafrost and minimal vegetation; and alpine or mountain biomes, which occur at high elevations and have conditions similar to tundra despite lower latitudes. Each biome supports unique plant and animal communities adapted to its specific climate and environmental conditions.

Terrestrial biomes are ecosystems that occur on land and are classified primarily by their vegetation type and climate characteristics. Major terrestrial biomes include forests, deserts, grasslands, and tundra regions. Each terrestrial biome supports distinct plant and animal communities adapted to specific temperature and precipitation patterns. Aquatic biomes are ecosystems that occur in water environments and are classified by salinity, depth, water flow, and nutrient levels. These include freshwater biomes such as lakes, rivers, and ponds, and marine biomes such as oceans and seas. Aquatic biomes also include transitional zones like estuaries, wetlands, coral reefs, and intertidal zones. The organisms in aquatic biomes are specially adapted to their specific water conditions, whether freshwater or saltwater, still or flowing, shallow or deep.

Tropical vegetation is characterized by dense, multilayered forests with high biodiversity and a wide variety of plant and animal species. Tropical forests contain both evergreen trees that retain their leaves year-round and deciduous trees that shed leaves seasonally. These forests thrive in regions with high rainfall and consistently warm temperatures throughout the year, creating ideal conditions for rapid plant growth and decomposition. Desert vegetation, by contrast, is sparse and consists primarily of xerophytic plants such as cacti, succulents, and hardy shrubs that have evolved special adaptations to conserve water and survive in extremely arid conditions. Desert biomes have very low biodiversity compared to tropical forests, with fewer species but those species are highly specialized for survival. Deserts experience very low rainfall, often less than 25 centimeters annually, and extreme temperature fluctuations between day and night. The vegetation in deserts has adaptations like thick waxy leaves, deep root systems, and the ability to store water to cope with prolonged drought and harsh environmental conditions.

Savannas are tropical and subtropical grasslands characterized by scattered trees and shrubs interspersed among grasses. These biomes experience distinct wet and dry seasons, with moderate rainfall concentrated during the wet season. Savannas have warm temperatures year-round and are found in regions of Africa, Australia, and South America. The vegetation is adapted to periodic fires and grazing by large herbivores. Savannas support diverse wildlife including lions, elephants, zebras, and antelopes. Tundra is a cold, treeless biome found in high latitudes near the Arctic and Antarctic regions, as well as at high altitudes on mountains. Tundra experiences extremely low temperatures for most of the year and is characterized by the presence of permafrost, a layer of permanently frozen soil beneath the surface. Vegetation in tundra is limited to low-growing plants such as mosses, lichens, and dwarf shrubs that can survive the harsh conditions. Tundra has very low biodiversity and short growing seasons, with most biological activity concentrated in the brief summer months when temperatures rise slightly above freezing.

An ecosystem is composed of two main categories of components that interact together. Biotic components include all living organisms within the ecosystem, which are classified into three functional groups: producers such as plants that manufacture food through photosynthesis, consumers including herbivores, carnivores, and omnivores that feed on other organisms, and decomposers such as bacteria and fungi that break down dead organic matter and recycle nutrients. Abiotic components are the non-living physical and chemical factors that influence life in the ecosystem, including sunlight which provides energy for photosynthesis, water which is essential for all life processes, air containing oxygen and carbon dioxide, soil which provides nutrients and support for plants, and temperature which affects metabolic rates and organism distribution. Energy flows through the ecosystem from the sun through producers to consumers and finally to decomposers, while nutrients cycle between biotic and abiotic components through biogeochemical cycles. The interaction between biotic and abiotic components creates a balanced system where energy is transferred and nutrients are continuously recycled, allowing the ecosystem to sustain life and maintain stability over time.

Ecosystems provide essential functions such as production of organic matter (primary productivity), nutrient cycling, decomposition, habitat provision, regulation of climate and water, and support for food chains and biodiversity.

Aquatic biomes cover most of Earth's surface and are diverse ecosystems adapted to water environments. Freshwater biomes include lakes, rivers, ponds, and streams that contain water with low salinity. Marine biomes encompass oceans and seas with high salinity and are the largest biomes on Earth. Estuaries are transitional zones where freshwater from rivers meets and mixes with saltwater from the ocean, creating unique conditions with varying salinity levels. Wetlands are areas where water covers the soil for at least part of the year, supporting specialized vegetation and serving as nurseries for many aquatic species. Coral reefs are highly productive marine ecosystems found in shallow tropical waters, characterized by symbiotic relationships between corals and algae and supporting exceptional biodiversity. Intertidal zones are areas along coastlines that are alternately covered and exposed by tides, experiencing extreme environmental changes. Aquatic biomes differ primarily in their salinity levels, water depth, water flow patterns, temperature, and nutrient availability. These varying conditions create distinct ecological niches that support communities of organisms specially adapted to their specific aquatic environment, whether freshwater or marine, still or flowing, shallow or deep.

Tundra biomes are located in high northern latitudes across the Arctic region, forming a continuous band around the North Pole. These include northern Canada, Alaska, Greenland, northern Scandinavia (Norway, Sweden, Finland), and northern Russia or Siberia. The tundra extends southward from the Arctic Ocean and is characterized by permafrost, low temperatures, and sparse vegetation. Additionally, alpine tundra occurs on high mountain tops worldwide, such as the Himalayas, Rocky Mountains, and Andes, where similar cold conditions and low vegetation exist despite lower latitudes. When marking on a world outline map, shade these polar regions and identify major mountain ranges with alpine tundra zones.

Equatorial biomes occur in a narrow band along the equator where warm temperatures and high rainfall support dense tropical rainforests. The major equatorial biome regions include the Amazon Basin in northern South America, which is the world's largest tropical rainforest; the Congo Basin in central Africa, containing the second-largest rainforest; and equatorial Southeast Asia, including Indonesia, Malaysia, and Papua New Guinea. These regions are characterized by evergreen broadleaf forests with high biodiversity, abundant wildlife, and complex layered vegetation. On a world outline map, mark these three primary equatorial biome zones by shading the areas around the equator in South America, Africa, and Asia-Pacific regions.

The Arctic Tundra food web begins with producers—lichen, grasses, and arctic wildflowers—which use sunlight to manufacture food through photosynthesis. These producers form the base of the food chain and are consumed by primary consumers, which are herbivores including lemmings, arctic hares, caribou, and musk oxen. Energy then flows to secondary consumers and top predators such as wolves, hawks, and polar bears, which feed on the various herbivores depending on their hunting preferences and prey availability. Different predators target different herbivores, creating multiple feeding pathways within the web. The overall energy flow follows the path: Sun → producers → herbivores → carnivores. Decomposers, though not always shown in simplified diagrams, play a crucial role by breaking down dead plants and animals, recycling nutrients back into the soil, and supporting the growth of new producers. This cyclical process maintains the balance and sustainability of the Arctic Tundra ecosystem.