CBSE Class 10 Biology Our Environment Notes Set 09

Ecosystem and Its Components

An ecosystem is a community of living organisms interacting with each other and with their non-living surroundings. Biotic components are producers (green plants), consumers (herbivores, carnivores, omnivores) and decomposers (bacteria and fungi). Abiotic components are the lithosphere (soil and rocks), hydrosphere (water) and atmosphere (gases) along with light, temperature, humidity and wind.

Terrestrial Biomes

1. Tropical rain forest: near the equator, rainfall above 200 cm, warm all year, tall evergreen trees in layers, greatest diversity.
2. Savannah: tropical grassland with scattered trees and a dry season.
3. Desert: less than 25 cm rainfall, sparse xerophytic plants, animals active at night.
4. Temperate grasslands: prairies (North America), steppes (Eurasia), pampas (South America), veldt (South Africa).
5. Taiga (coniferous forest): cold northern forest of pine, fir and spruce with long winters.
6. Tundra: very cold treeless region with mosses and lichens and frozen subsoil.

Aquatic Biomes

Freshwater biomes are lentic (still water: ponds, lakes, swamps, with plants such as Pistia and Eichhornia) and lotic (running water: rivers, streams). The marine biome has littoral, neritic, oceanic and deep-sea zones. Small drifting organisms are plankton (phytoplankton as producers and zooplankton as consumers); strong swimmers such as fish are nekton.

Food Chain, Food Web and Pyramids

A food chain shows the transfer of food and energy from producers to consumers, for example grass → grasshopper → frog → snake → eagle. Interlinked chains form a food web, which makes the ecosystem more stable. Only about 10% of the energy of one trophic level reaches the next, so food chains are short.
Ecological pyramids show numbers, biomass or energy at each level. The pyramid of energy is always upright; the pyramid of numbers or biomass can be inverted in some ecosystems.

Biogeochemical Cycles

1. Carbon cycle: plants fix atmospheric CO₂ in photosynthesis; respiration, decay and burning return it to the air.
2. Oxygen cycle: photosynthesis releases oxygen; respiration and combustion use it.
3. Nitrogen cycle: nitrogen-fixing bacteria (Rhizobium) and lightning convert N₂ to usable forms, nitrifying bacteria produce nitrates which plants absorb, and denitrifying bacteria return nitrogen to the air.

Natural Resources and Conservation

Resources are renewable (water, forests, wind, solar energy) or non-renewable (coal, petroleum, minerals). Wildlife is protected through national parks, sanctuaries and biosphere reserves, laws against hunting and trade, captive breeding of endangered species and public education. Over-use, deforestation and pollution threaten species, and pearl culture, aquaculture and social forestry are examples of using resources sustainably.