Open Systems
Open systems
Big idea: An <strong>{{open system|A system where both matter and energy can enter and leave across the system boundary.}}</strong> lets <strong>things ({{matter|Physical stuff that has mass and takes up space — water, air, nutrients, organisms, soil.}})</strong> and <strong>{{energy|The ability to do work or cause change — sunlight, heat, chemical energy. Cannot be held or contained.}}</strong> move in and out. If you can point to something entering and something leaving, it is probably an open system.
[Diagram: open-system] - Available in full study mode
First: what do we mean by "matter" and "energy"?
Students often find this confusing, so think of it this way:
Quick test: If you could trap it in a container, it is <strong>matter</strong>. If you cannot, it is <strong>energy</strong>.
So what is an open system?
An <strong>{{open system|A system where both matter and energy can enter and leave across the system boundary.}}</strong> is one where <strong>matter AND energy</strong> both move in and out across the {{system boundary|The imaginary line that separates a system from its surroundings. Inputs cross in, outputs cross out.}}.
Most things in nature are open systems because they are not sealed off from their surroundings.
Everyday examples (easy to picture)
If you can list at least one thing entering and one thing leaving, it is an open system.
Pond example (IB exam favourite)
A pond is a classic example used in IB exams because it clearly shows {{inputs|Matter or energy entering a system from outside (e.g., rain entering a pond).}} and {{outputs|Matter or energy leaving a system (e.g., water evaporating from a pond).}}. Tap each icon to explore:
[Diagram: pond-ecosystem] - Available in full study mode
<strong>{{Inputs|Matter or energy entering a system from outside (e.g., rain entering a pond).}} to a pond (things entering):</strong>
<strong>{{Outputs|Matter or energy leaving a system (e.g., water evaporating from a pond).}} from a pond (things leaving):</strong>
Because <strong>both matter and energy</strong> enter and leave, a pond is an <strong>open system</strong>.
Why are open systems always changing?
Because inputs and outputs are constantly happening, open systems are <strong>{{dynamic|Constantly changing over time. Open systems are dynamic because inputs and outputs keep happening.}}</strong> — they change over time.
If inputs and outputs are balanced, the system stays stable. If not, problems can occur.
Example: Too many nutrients entering a pond can cause {{algal blooms|A rapid overgrowth of algae in water, usually caused by too many nutrients (like fertiliser runoff). Turns water green and can kill fish by using up oxygen.}}.
Quick summary
Closed Systems
Closed systems
Big idea: A **{{closed system|A system where energy can enter and leave, but matter stays inside and is recycled.}}** is like a sealed jar sitting in sunlight. **{{Energy|The ability to do work or cause change — light, heat, movement, chemical energy in food.}}** can go in and out (the jar heats up or cools down), but **{{matter|Anything physical that has mass and takes up space — water, air, carbon, rocks, living things.}} stays trapped inside** — nothing physical enters or leaves.
The simple test: Is it closed or open?
[Diagram: closed-system] - Available in full study mode
Ask yourself two questions:
**Closed = sealed for matter, but not for energy.** Think of a greenhouse: sunlight enters, heat leaves, but the air and plants stay inside.
Why does this matter for exams?
IB loves to ask about Earth's cycles and whether they are open or closed. Here's the key:
If an exam asks why Earth's cycles are closed systems, say: <em>"Matter is recycled within the system and does not leave, but energy enters as sunlight and exits as heat."</em>
Picture it: The water cycle as a closed system
Imagine all the water on Earth in a giant sealed ball:
[Diagram: water-cycle] - Available in full study mode
The water you drink today contains the same water molecules that dinosaurs drank millions of years ago. That's a closed system in action!
Earth as a closed system
Planet Earth is considered a <strong>closed system</strong> because:
Yes, a few meteorites land and a few spacecraft leave, but these are so tiny compared to Earth's total mass that we ignore them.
Real-world example: Biosphere 2
**Biosphere 2** is a giant sealed greenhouse in Arizona, USA. Scientists built it to test if humans could survive in a closed system.
The experiment had problems (oxygen levels dropped, food ran short), showing how hard it is to maintain a closed system.
Earth's subsystems (they're all connected)
Earth contains smaller systems (<strong>{{subsystems|A smaller system operating within a larger system. Earth has many subsystems (atmosphere, hydrosphere, etc.).}}</strong>) that constantly exchange matter and energy with each other. Tap each one to learn more:
[Diagram: earth-subsystems] - Available in full study mode
Each subsystem is <strong>open</strong> (matter moves between them), but together they form a <strong>closed system</strong> (matter doesn't leave Earth).
Open vs Closed — quick comparison
Gaia hypothesis (bonus concept)
The <strong>{{Gaia hypothesis|The idea that Earth behaves like a self-regulating organism, maintaining conditions suitable for life.}}</strong> is the idea that Earth acts like a single living organism that regulates itself.
You don't need to memorise the Gaia hypothesis in detail. Just know it suggests <strong>Earth self-regulates</strong> through interactions between living and non-living parts.
Open vs closed (final exam check)
In exam answers, always say what enters and what leaves. That alone can earn full marks.