Organisms and Environment
Easy Overview
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.
Ecosystem structure — who eats who
An ecosystem has biotic (living) and abiotic (non-living) components. Producers (plants) make food. Consumers eat them — primary (herbivores), secondary (carnivores), tertiary (top predators). Decomposers (bacteria, fungi) break down dead stuff and recycle nutrients. Energy flows one way (sun → plant → herbivore → carnivore), but nutrients cycle.
Food chains and food webs — the lunch lines
A food chain shows one path of energy flow: grass → deer → tiger. But real life is messier — a deer eats many plants, a tiger eats many animals. That's a food web. At each step, only about 10% of energy passes to the next level (10% law). The rest is lost as heat. That's why top predators are rare — there's just not enough energy.
Ecological pyramids — visualizing the ecosystem
Pyramid of numbers: how many individuals at each level. Pyramid of biomass: how much living matter at each level. Pyramid of energy: always upright because energy decreases at each step. Some pyramids can be inverted (like a tree feeding many insects), but the energy pyramid is always upright. Always.
Population interactions — it's complicated
Organisms interact in different ways. Mutualism (+/+): both benefit (bee and flower). Competition (-/-): both lose (two species fighting for the same food). Predation (+/-): one eats the other. Parasitism (+/-): one benefits, the other is harmed but not immediately killed (tapeworm in humans). Commensalism (+/0): one benefits, the other doesn't care (barnacles on a whale).
Pollution — the stuff we're doing to the planet
Air pollution (SO₂, NO₂) causes acid rain and respiratory disease. Water pollution (industrial waste, sewage) causes eutrophication — algae bloom, then oxygen depletion, then fish die. Soil pollution (pesticides, heavy metals) gets into our food. Noise pollution stresses us out. All of it comes back to haunt us — because we're part of the ecosystem too.
Biodiversity and conservation — why species matter
Biodiversity = variety of life on Earth. It matters because every species plays a role. Lose bees? No pollination. Lose vultures? Rabies spreads from rotting carcasses. India has biodiversity hotspots like the Western Ghats. Conservation: national parks, sanctuaries, biosphere reserves. In situ (in the wild) vs ex situ (zoos, seed banks). Both are needed.
Key Points
- •Ecosystem = biotic (living) + abiotic (non-living) components interacting as a system
- •10% law: only 10% of energy transfers to next trophic level; rest lost as heat
- •Food web is more realistic than a simple food chain
- •Ecological pyramids: numbers, biomass, energy; energy pyramid is always upright
- •Population interactions: mutualism, competition, predation, parasitism, commensalism
- •Eutrophication: excess nutrients → algal bloom → O₂ depletion → dead zones
- •Biodiversity hotspots in India: Western Ghats, Eastern Himalayas, Indo-Burma
- •Conservation: in situ (national parks, sanctuaries) and ex situ (zoos, botanical gardens, seed banks)
Practice Questions
- Explain the structure of an ecosystem with its biotic and abiotic components.
- What is the 10% law of energy transfer? Why can't a food chain have more than 4-5 trophic levels?
- Differentiate between food chain and food web with examples.
- Describe any three types of population interactions with examples.
- What is eutrophication? How does it kill aquatic life? Suggest ways to prevent it.