Every inch of our planet is coated with life, and every living thing exists as part of a network of other living things and the physical environment.
This network is called an ecosystem, and most of them follow a fundamental framework.
An ecosystem’s physical environment provides sunlight, water, nutrients, shelter, and gasses like oxygen and carbon dioxide.
Elaborate multicellular structures called ‘plants’ filter the nutrients and gasses that flow past them (Technically organisms that fill this role are called ‘autotrophs’, as we needed a different word to try and cover all the variety and exceptions in the world’s diverse ecosystems).
Using the energy provided by sunlight, they chemically reconfigure these materials into their own structures for growth and reproduction, like roots, leaves, branches, sap, and flowers, honey, pollen, seeds, and nuts.
Plants who successfully grow to maturity use sexual reproduction; mixing their genes with other successful plants and passing them onto the next generation. This allows their population to rapidly adapt to a changing environment.
In many environments there is such an abundance of plants and the concentrated materials and energy they’ve collected, that they support populations of other, radically different creatures.
We know them as animals. They’re different types of elaborate multicellular structures, and they rely on putting plant matter through baths of stomach acid and a long digestive tract. This is a destructive process which extracts nutrition and energy from the plants and utilises them to build their own bodies.
Many animals eat other animals, sometimes instead of plants entirely, creating a multilevel ‘trophic pyramid’.
Each level on the tropic pyramid is supported by the levels below it. Just as the first level of animals are entirely dependent on plants to transform nutrients from their surrounding environment into digestible material they can use, so ‘higher’ levels depend on that level of plant eating animals, and so on. Ecosystems therefore depend on the theft of energy and materials.
This fundamental dynamic of the trophic (or food) web underscores every ecosystem. The availability of food creates niches that species evolve to exploit, often radically altering their bodies to better exploit that niche. It also creates interdependence between all of the 'players' in an ecosystem, but not just as predators and prey.
So most ecosystems are a more of a complex web than a simple hierarchy.
So every ecosystem is a kind of extremely elaborate flow of nutrients of which its creatures are entirely comprised. However, all of the fuss is not just for its own sake. Each creature has one single, overriding purpose in mind: to maximise its own genes in its species gene pool.
The Earth(Biosphere) is composed of organisms in just the same way organisms are composed of cells. Now, you might think, "They're all separate organisms, how could they be connected?". But the cells in your body are also not uniformly connected. And yet they flow together as one living thing. So also the biosphere is composed of seemingly separate things all dependent upon one another. The parts could not exist without the whole, and the whole could not exist without the parts. Animals exhale carbon dioxide, plants produce oxygen, and everything is intimately connected to everything else in a food web. Energy flows throughout the environment in a similar way as to how energy flows through the body. It's a magnificent symphony of interdependence.