● Our living world is `color{violet}("fascinatingly diverse")` and `color{violet}("amazingly complex")`.

● We can try to understand its `color{violet}("complexity")` by investigating processes at various levels of biological organisation–`color{violet}("macromolecules, cells, tissues, organs")`, `color{violet}"individual organisms, population"`, `color{violet}("communities and ecosystems")` and `color{violet}("biomes")`.

● At any level of `color{violet}("biological organisation")` we can ask two types of questions….

● For example, when we hear the bulbul singing early morning in the garden, we may ask – `color{violet}("‘How does the bird sing?’")` Or, `color{violet}("‘Why does the bird sing?’ ")`

● The ‘how-type’ questions seek the mechanism behind the process while the `color{violet}("‘why type’")` questions seek the `color{violet}("significance of the process")`.

● For the first question in our example, the answer might be in terms of the `color{violet}("operation of the voice box")` and the `color{violet}("vibrating bone")` in the bird, whereas for the second question the answer may lie in the bird’s need to `color{violet}("communicate with its mate during breeding season")`.

● `color{violet}("Ecology")` is a subject which studies the `color{violet}("interactions among organisms")` and between the `color{violet}("organism")` and its `color{violet}("physical (abiotic) environment")`.

● `color{violet}("Ecology")` is basically concerned with four levels of `color{violet}("biological organisation – organisms, populations, communities")` and `color{violet}("biomes.")`

● Ecology at the organismic level is essentially `color{violet}("physiological ecology")` which tries to understand how `color{violet}("different organisms")` are adapted to their `color{violet}("environments")` in terms of not only `color{violet}("survival")` but also `color{violet}("reproduction")`.

● It is known that the rotation of our planet around the Sun and the tilt of its axis cause `color{violet}("annual variations")` in the `color{violet}("intensity")` and `color{violet}("duration of temperature, resulting in distinct seasons")`.

● These `color{violet}("variations")` together with `color{violet}("annual variation")` in `color{violet}("precipitation (precipitation includes both rain and snow)")` account for the formation of `color{violet}("major biomes")` such as `color{violet}("desert, rain forest")` and `color{violet}("tundra")` .



● On planet Earth, life exists not just in a few favourable habitats but even in extreme and harsh habitats – `color{violet}("scorching Rajasthan desert")`, `color{violet}"perpetually rain-soaked Meghalaya forests"`, `color{violet}"deep ocean trenches"`, `color{violet}"torrential streams"`, `color{violet}("permafrost polar regions")`, `color{violet}"high mountain tops"`, `color{violet}("boiling thermal springs"`, and `color{violet}("stinking compost pits")`, to name a few.

● Even our intestine is a unique habitat for hundreds of species of `color{violet}("microbes.")`

● There are some key elements that lead to so much `color{violet}("variation")` in the `color{violet}("physical and chemical conditions")` of `color{violet}("different habitats")`.

● The most important ones are `color{violet}("temperature, water, light and soil")`.

● It is important to note that the `color{violet}("physico-chemical (abiotic)")` components alone do not characterize the habitat of an `color{violet}("organism completely")`.

● The habitat includes `color{violet}("biotic components")` also – `color{violet}("pathogens, parasites, predators and competitors")` – of
the organism with which they interacts constantly.

● We assume that over a period of time, the organism had through natural selection, `color{violet}("evolved adaptations to optimise")` its `color{violet}("survival")` and `color{violet}("reproduction")` in its habitat.