Systems within systems
A cell, an excavator, an eye and a river basin have little in common, except that each is a system: parts with jobs, working together for one purpose, and each part a system of smaller parts. Seeing them that way is how you understand one quickly, and how you find what went wrong when it fails.
Why think in systems?
Because most things worth understanding are too complicated to take in all at once. A body has trillions of cells; a car has thousands of parts. Nobody understands them part by part. You understand them level by level: what the whole does, what its few big subsystems do, and only then what is inside each one.
The idea also tells you where to look when something goes wrong. Every part serves the whole, so a failure anywhere shows up as trouble for the whole, and tracing the trouble back down through the levels leads to the part that failed.
Where it turns up
- The Hubble Space Telescope — launched in 1990 with its main mirror ground very slightly the wrong shape, so every picture came back blurred; in 1993 astronauts fitted corrective optics, in effect a pair of glasses, and the whole telescope worked
- Medicine — a family doctor looks at the whole person, while specialists each look after one system: a cardiologist the heart and blood vessels, a neurologist the brain and nerves
- A car's dashboard — each warning light belongs to one subsystem, such as the brakes, the engine oil or the battery charging, so a driver or mechanic knows where to look first
- A river basin — in 2016 a pipeline leaked oil into the North Saskatchewan River in Saskatchewan, and North Battleford and Prince Albert, downstream, had to stop drawing drinking water from the river for weeks
- 1. The words, first
- 2. A living thing: cells to systems
- 3. A machine: subsystems and simple machines
- 4. An optical system: the eye
- 5. A drainage basin: everything upstream matters
- 6. The same four questions in every unit
The words, first
The idea: Whether something is a system, a subsystem or a component depends on the level you are looking at: the heart is a component of the circulatory system, and a system of tissues in its own right.
| Word | What it means |
|---|---|
| System | A group of parts that work together to do one job. |
| Subsystem | A system that is one part of a bigger system. |
| Component | A single part of a system. |
| Function | The job a part does for the whole. |
| Input / output | What goes into a system, such as energy, materials or information / what comes out. |
| Level of organization | How big a view you take: cell, tissue, organ, organ system, organism. |
| Hydraulic cylinder | A tube with a piston inside, moved by liquid pumped in under pressure. |
| Drainage basin | All the land that drains into one river system. |
A living thing: cells to systems
The idea: Cells make tissues, tissues make organs, organs make systems, and systems make an organism. Each level does something none of its parts can do alone.
| Level | Example | What it can do that its parts cannot |
|---|---|---|
| Cell | A heart muscle cell | Contract |
| Tissue | Heart muscle | Contract all together, in step |
| Organ | The heart | Pump blood, using muscle, nerve and other tissues |
| Organ system | The circulatory system | Carry oxygen and food to every cell |
| Organism | You | Stay alive |
Worked: when one part fails. In an asthma attack, the airways narrow. That is a problem in one system, the respiratory system, but the whole body feels it. Less air gets through to the lungs' air sacs, so less oxygen gets into the blood; the heart beats faster to deliver what there is, and the muscles tire quickly. A problem at one level shows up at every level above it.
Spares. Some systems have a backup built in. You have two kidneys, and a person can live a normal life with one, which is why a living person can donate a kidney.
A machine: subsystems and simple machines
The idea: Take a machine apart from the top down: its overall job, the subsystems that share that job, and the simple machines inside each one.
Worked: an excavator. Its overall job is to dig and lift. Five subsystems share the work:
| Subsystem | Its job | Components |
|---|---|---|
| Power | Supplies the energy | A diesel engine turning a hydraulic pump |
| Hydraulic | Carries force to where it is needed | Pump, hoses, valves and hydraulic cylinders |
| Arm and bucket | Digs and lifts | The boom, arm and bucket are levers, moved by cylinders; the bucket's teeth are wedges |
| Tracks | Moves the machine | Driven wheels turning the tracks |
| Controls | Lets the operator choose what happens | Joysticks and pedals that open and close valves |
Following the energy. Fuel → engine → pump → liquid under pressure → cylinder → arm. Each arrow is one part handing energy to the next, and at each one friction turns a little into heat. That is why the whole machine is less efficient than any one of its parts.
Tracing a failure. The arm will not lift, though the engine runs. The engine and pump work, so the problem is further along: in the hydraulic subsystem, where a split hose is leaking. A mechanic works the same way every time: from the symptom, to the subsystem, to the component.
An optical system: the eye
The idea: In the eye, every part has one job in getting a sharp image onto the retina. Most vision problems are one part doing its job slightly wrong, and often an added lens can correct it.
| Component | Its function | When it goes wrong |
|---|---|---|
| Cornea | Does most of the bending of light | An unevenly curved cornea blurs the image; laser surgery can reshape it |
| Iris and pupil | Control how much light gets in | In bright light, a pupil that stays wide lets in glare |
| Lens | Fine-tunes the focus by changing shape | It stiffens with age, making close reading hard; if it clouds over, a cataract, it can be replaced with a plastic one |
| Retina | Turns light into nerve signals | Damage leaves blank patches that no lens can fix |
Adding a subsystem. Glasses, microscopes and telescopes are lenses or mirrors added in front of the eye's own system. Looking through a microscope, the light passes the objective lens, the eyepiece, then the cornea and lens, and lands on the retina: one optical system of five parts. Like Hubble's fix, glasses do not repair the eye. They add a part that makes the whole system work.
A drainage basin: everything upstream matters
The idea: A drainage basin is a system joined by flowing water. Whatever enters it anywhere upstream ends up downstream, so the whole basin, not one town, is what has to be looked after.
Inputs, parts and outputs. The inputs are rain and snowmelt, including meltwater from glaciers. The parts are small streams joining into larger rivers, lakes, wetlands that soak up floods and filter the water, and groundwater that keeps streams flowing in dry months. The outputs are the river's flow to the sea, and the water people, animals and plants take out along the way.
Worked: tracing one change. Trees are logged from a steep hillside upstream. Without the forest to slow it, rain runs off faster instead of soaking in. The stream rises faster after storms and carries more mud. Downstream, the water turns cloudy, stonefly nymphs disappear from the riverbed, and a town's treatment plant has to work harder to clear its water. One change in one place is felt all the way down the basin.
Why it matters in Alberta. Alberta's major rivers begin in the Rocky Mountains, so what happens to the glaciers, forests and snowpack there affects the water of cities hundreds of kilometres away.
The same four questions in every unit
The idea: Four questions take apart any system in the course: what is its job, what are its parts, what flows between them, and what happens if one fails.
- What is the whole system's job?
- What are its subsystems or components, and what does each one do?
- What flows between them: matter, energy or information?
- What happens to the whole if one part fails?
| Unit and system | A part that fails | What the whole loses |
|---|---|---|
| A · Fluids: an oil pipeline — pumps, pipe, valves | A pump station shuts down | The oil beyond it slows or stops |
| B · Cells: the circulatory system | A heart valve leaks | Some blood flows backwards, and the heart has to work harder |
| C · Light: a camera | The lens is smudged | Every picture is blurred, though the sensor works perfectly |
| D · Machines: a bicycle | The chain comes off | Pedalling no longer moves the bike |
| E · Water: a drainage basin | A wetland is drained | Floods downstream come faster and higher |
The pattern. In every row, the part that failed was working for the whole, not for itself. That is what makes something a system, and it is why a good answer about any part of it says what the part does for the whole.