Cells and Living Systems
Every living thing you can name — sponge, footballer, elephant, you — is built from the same basic unit: the cell. This unit is really one big argument stacked on itself: cells specialise, specialised cells group into tissues and organs, and that's why complex organisms can't just be one giant blob doing everything at once. Keep asking 'why does this structure look the way it does?' and most exam answers write themselves.
Overview — How This Topic Fits Together
Cells are the smallest units that can carry out all the processes of life on their own — getting energy, removing waste, growing, responding, reproducing. Everything in this unit builds from that single idea: simple organisms are made of few cell types living independently; complex organisms have hundreds of cell types, grouped into tissues, organs and systems, none of which can survive alone.
- Structure always matches function — a cell's shape and internal parts exist because of the specific job it does. Examiners test this link directly, not just the fact.
- As organisms get bigger and more complex, they need more different cell types and more levels of organisation — this is the sponge → jellyfish → human trend you'll see tested.
- Microscopes are the tool that makes all of this visible — magnification and field of view trade off against each other, and that trade-off is a favourite data-based question.
The shape of the chapter
Command terms that appear on every cells paper
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| State | Give a short, factual answer — no reasoning needed. | Criterion A | One correct word or short phrase earns full marks; writing extra reasoning wastes time and earns nothing more. |
| Identify | Select and name the correct answer from information already given. | Criterion A | Must be picked from the data provided (e.g. the table) — a correct general-knowledge answer that isn't in the data loses the mark. |
| Describe | Give a detailed account of what something is or does — no 'why' required. | Criterion C | Marks are lost if you explain causes instead of describing features — 'describe' wants the WHAT, not the WHY. |
| Explain | Give reasons, showing understanding of a cause-and-effect link. | Criterion A | Needs a linking word like 'because' or 'so that' — stating two true facts with no connection between them scores zero. |
| Compare | Identify similarities and differences between two things. | Criterion C | Must give both a similarity AND a difference — giving only differences caps the mark even if both are correct. |
| Suggest | Propose an idea or explanation for an unfamiliar situation. | Criterion A | Any scientifically reasonable answer is accepted even if it wasn't directly taught — don't leave this blank because you 'haven't learned it'. |
Key point
Overview