Systems in Organisms
MYP Sciences — Life Science strand: Systems in Organisms
Every question in this unit rewards the same habit: linking a structure straight to its job. Examiners rarely want just 'the ribs protect organs' — they want you to say which organs, which bones are involved, and why the shape or arrangement makes that protection possible. The six systems below aren't six separate topics to memorise in isolation; they're one connected story of how your body supports itself, moves, reproduces, keeps its internal chemistry balanced, breaks down food, and moves oxygen and nutrients to every cell that needs them.
Overview: How the Body's Systems Fit Together
A 'system' in biology is a group of organs working together toward one job. This unit covers six of them, and almost every exam question tests the same skill: matching a structure (shape, position, material) to its function (what it does and why that shape helps).
- Skeletal & Muscular — support the body, protect soft organs, and produce movement at joints.
- Reproductive — produces gametes and allows fertilisation; the only system not needed for an individual's day-to-day survival.
- Excretion & Homeostasis — removes metabolic waste and keeps internal conditions (temperature, water) within a stable range.
- Interdependence — no system above works alone; each depends on at least one other to function.
- Digestive — mechanically and chemically breaks food into molecules small enough to absorb into the blood.
- Respiratory & Circulatory — exchange gases at the lungs and transport oxygen, nutrients, and waste around the body.
The shape of the chapter
Command terms this topic actually tests
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Identify | Give a specific name, value or answer with no explanation | Knowing | One correct word/number is full marks; adding explanation earns nothing extra |
| State | Give a short, precise factual answer | Knowing | A brief statement is enough unless the question also says 'and explain' |
| Describe | Give a detailed account naming relevant structures or steps | Knowing/Applying | Each structure or step named is usually worth a separate mark |
| Explain | Give the reason or mechanism — the 'why' or 'how' | Applying | Needs a cause-and-effect link, not a restated fact |
| Compare | Give similarities AND differences between two or more things | Applying | Must use comparative language ('whereas', 'both', 'unlike'); two separate lists lose marks |
| Suggest | Propose a scientifically reasonable idea, even if not stated in class notes | Applying/reasoning | Any plausible, scientifically sound reason earns credit — not only the 'expected' one |
Key point
Overview