Systems in Organisms
MYP Year 3 Sciences — Systems in Organisms
Every system in this unit does one job, but examiners only give marks when you connect the STRUCTURE of a part to the FUNCTION it performs and the CONSEQUENCE if it changes. A bone's calcium phosphate percentage, a forearm's lever arms, a villus's shape — none of it is worth memorising as an isolated fact. Read every diagram and data table as a clue about function first.
Overview: How This Unit Fits Together
Every organism keeps itself alive by running several systems at once, and none of them work in isolation. A bone only makes sense once you connect its structure to what it has to survive (impact, load, growth); a stomach only makes sense once you see it as one stage in a continuous processing line that hands off to the small intestine, liver and bloodstream. Questions on this unit almost always reward you for making that link explicitly — structure → function → consequence — rather than just naming parts.
- The six systems split into three jobs: STRUCTURE & MOVEMENT (skeletal-muscular), CONTINUITY of the species (reproductive), and INTERNAL BALANCE & PROCESSING (excretion/homeostasis, digestive, respiratory-circulatory) — interdependence threads through all of them.
- Command terms decide how much you write: 'Identify' wants a word pulled straight from the given data/diagram; 'Explain' wants a mechanism or reason, not a repeated observation.
- Exam data almost always comes as a table, graph or diagram of a real body part or a real medical scenario — you're marked on reading it correctly as much as on recalling facts.
The shape of the chapter
Command terms that decide your mark
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| State | Give a specific fact/name/answer, no justification needed | — | One correct word or short phrase = full mark; adding unnecessary explanation wastes time, not marks |
| Identify | Pick out the correct feature from the given diagram, table or scenario | — | The answer must reference the given stimulus specifically — a correct but generic fact not tied to the source loses the mark |
| Describe | Give a detailed, structured account of a structure or process | — | Needs multiple linked points; a single unexplained word never scores full marks |
| Explain | Give reasons — show cause and effect, answer 'why', not just 'what' | — | The mark sits on the causal link ('...because...'), not on restating the observation |
| Calculate | Produce a numerical answer with working shown | — | Method marks are awarded for correct substitution even if the final arithmetic slips; a bare final number with no unit can lose the mark |
| Suggest/Analyse | Apply your knowledge to an unfamiliar context and propose a reasoned answer | — | Marks go to a reasoned answer grounded in the given evidence, not an unsupported opinion |
Key point
Overview