IB Biology Topic C4.2.1: Ecosystems Notes

Ecosystems: Open Systems Where Energy Flows Through but Matter Cycles Within

1. An ecosystem is an open system in which both energy and matter can enter and exit across its boundary.
2. Energy flows through the ecosystem, entering mainly as light and leaving as heat, while matter cycles internally and can also cross the boundary.

Open and Closed Systems Differ in What Can Cross Their Boundary

1. Open system: both energy and matter can be exchanged with the surroundings.
   1. An ecosystem takes in energy from the sun and nutrients from the soil, and it releases heat, oxygen, water vapour, and organic waste.

1. Closed system: only energy can cross the boundary, while matter stays contained within the system.
   1. A sealed terrarium is close to a closed system because its plants absorb light and release oxygen while its water and nutrients are recycled inside.

Energy Crosses the Boundary but Never Returns to Be Reused

1. Energy enters the ecosystem across its boundary, mostly as sunlight captured by producers.
2. At each step energy is lost as heat that leaves the ecosystem and cannot be recovered, so a continuous external supply is needed.

Matter Cycles Within the Ecosystem and Can Also Cross the Boundary

1. Unlike energy, matter such as carbon, nitrogen, and water is recycled internally within the ecosystem.
2. Matter can still cross the boundary, entering as minerals from weathered rock or leaving as material washed or blown away.

The Open System Idea Reaches Beyond Biology