Organisms and Environment

You don't exist in a bubble. You're part of a giant web of life — eating, being eaten, breathing what trees exhale, drinking water that dinosaurs drank. This chapter zooms way out. It's about how organisms interact with each other and their environment: ecosystems, food chains, pollution, and why biodiversity matters. An ecosystem includes biotic (living) and abiotic (non-living) components interacting as a system. Producers (plants, algae) capture solar energy through photosynthesis and make food. Consumers eat them — primary consumers (herbivores), secondary consumers (carnivores), tertiary consumers (top predators). Decomposers (bacteria, fungi) break down dead matter and recycle nutrients. Energy flows in one direction (sun to producer to consumer), but nutrients cycle. The 10% law (Lindeman's trophic efficiency law) states that only about 10% of energy at one trophic level passes to the next. The rest is lost as heat through respiration. This is why food chains rarely have more than 4-5 trophic levels — there's just not enough energy at the top. It's also why top predators are rare. A food chain is a single path of energy flow (grass to deer to tiger). But real ecosystems are more complex — a food web shows multiple interconnected food chains. Ecological pyramids visualize trophic structure. The pyramid of numbers shows how many individuals at each level. The pyramid of biomass shows the total living matter. The pyramid of energy is always upright because energy decreases at each step. Some pyramids (numbers, biomass) can be inverted — for example, one tree can feed thousands of insects. But the energy pyramid is always upright. Biogeochemical cycles move nutrients through ecosystems. The carbon cycle: CO2 is fixed by photosynthesis into organic compounds, returned by respiration, decomposition, and burning. Carbon dioxide acts as a greenhouse gas — too much causes global warming. The nitrogen cycle involves fixation (N2 to NH3 by Rhizobium, lightning, or industrial process), nitrification (to NO3-), assimilation by plants, ammonification (decay back to NH4+), and denitrification (back to N2). The phosphorus cycle is slower — phosphorus is released by weathering of rocks, taken up by plants, and returned through decomposition. Unlike carbon and nitrogen, phosphorus has no atmospheric component. Water cycles through evaporation, condensation, precipitation, and runoff. Population interactions are how species relate. Mutualism (+/+): both benefit — bees and flowers, Rhizobium and legumes. Competition (-/-): both lose — two species fighting for the same food source. Predation (+/-): one eats the other — lion and zebra. Parasitism (+/-): one benefits, the other is harmed but not immediately killed — tapeworm in humans, ticks on dogs. Commensalism (+/0): one benefits, the other neither benefits nor is harmed — barnacles on a whale, orchids on a tree. Amensalism (-/0): one is harmed, the other unaffected — a large tree shading out smaller plants. Pollution is the introduction of harmful substances into the environment. Air pollution (SO2, NO2, particulate matter) causes acid rain and respiratory diseases. Water pollution (industrial waste, sewage, agricultural runoff) causes eutrophication — excess nutrients cause algal blooms, which deplete oxygen when they decompose, creating dead zones. Soil pollution (pesticides, heavy metals) gets into the food chain. Noise pollution causes stress and hearing loss. The greenhouse effect (CO2, methane, CFCs, nitrous oxide) traps heat, causing global warming and climate change. Ozone depletion (by CFCs) increases UV radiation reaching Earth, causing skin cancer and cataracts. The Montreal Protocol (1987) successfully phased out CFCs. Biodiversity is the variety of life on Earth — genetic diversity, species diversity, and ecosystem diversity. India has four biodiversity hotspots: Western Ghats, Eastern Himalayas, Indo-Burma, and Sundaland. Biodiversity is valuable for ecosystem services (pollination, water purification, climate regulation), medicine (many drugs come from plants), and intrinsic worth. Threats include habitat destruction, overexploitation, pollution, invasive species, and climate change. Conservation: in situ (national parks, wildlife sanctuaries, biosphere reserves) and ex situ (zoos, botanical gardens, seed banks, gene banks). India has 106 national parks, 573 wildlife sanctuaries, and 18 biosphere reserves. Project Tiger (1973) brought tigers back from near extinction. The Chipko movement showed community-based conservation in action.