1. What Makes an Ecosystem?

An ecosystem is all the living things in an area together with the nonliving things they interact with. The living parts are biotic factors — plants, animals, fungi, bacteria. The nonliving parts are abiotic factors — sunlight, temperature, water, air, soil, and rocks.

Scientists describe nature in levels of organization, from small to large:

• Organism — a single individual.
• Population — all the individuals of one species in an area.
• Community — all the different species living and interacting there.
• Ecosystem — the community plus its nonliving surroundings.
• Biosphere — all of Earth's ecosystems together.

The key idea is interaction: organisms depend on resources, compete for what's limited, and change their surroundings. A change in one part can ripple through the rest — if rainfall drops, plants grow less, then plant-eaters have less food, and so on.

⚠️ Common misconception: an ecosystem is not only the living organisms. The nonliving environment (sun, water, soil, air) is part of the system too.

💡 Tip: biotic = living; abiotic = nonliving. Order of levels: organism → population → community → ecosystem.