SPI Biology · Free notes
Cell Biology: SPI Biology
Cell Biology has 8 questions in the SPI bank, seven of them EASY, all from the SPI practice paper and the LWS mocks. They come straight from the Class 9 chapter on the cell: a part and its job, a feature only plant cells have, and which way water moves in osmosis. The wrong options are usually real cell parts that belong to both kinds of cell or do a different job, so learn each part with what makes it different.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Cell Structure
6 questionsEvery living thing is made of cells, and each cell has a membrane around it, cytoplasm inside it and small parts called organelles that each do one job.
Diffusion and Osmosis
2 questionsOsmosis is the movement of water through a selectively permeable membrane from the weaker solution to the stronger one.
Formula & revision sheet
0 formulas · 4 reference tables · 7 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 4 reference tables · 7 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (3)
The cell as the unit of life, plant and animal cells5 rows
| Part | Plant cell | Animal cell |
|---|---|---|
| Cell wall | Present (cellulose) | Absent The cell wall is the surest feature that tells a plant cell from an animal cell. |
| Chloroplasts | Present in green parts | Absent |
| Vacuole | One large central vacuole | Small or none |
| Centrosome | Absent | Present |
| Cell membrane, nucleus, mitochondria | Present | Present |
The cell membrane4 rows
| Feature | Cell membrane | Cell wall |
|---|---|---|
| Found in | All cells | Plant cells (also fungi and bacteria) |
| Made of | Lipids and proteins | Cellulose (in plants) |
| Lets substances through | Selectively: it controls entry and exit | Freely The membrane controls traffic both ways, not just one way. |
| Nature | Thin, flexible, living | Rigid, gives shape and support |
Cell organelles and their jobs5 rows
| Organelle | Job | Nickname |
|---|---|---|
| Nucleus | Controls the cell, holds DNA | Control centre |
| Mitochondria | Release energy | Powerhouse of the cell |
| Lysosome | Digests worn out parts and germs | Suicidal bag Lysosomes, not vacuoles, are the suicidal bags. |
| Ribosome | Makes proteins | Protein factory |
| Chloroplast | Photosynthesis | Kitchen of the cell |
Watch out for (5)
- Picking a part both cells share→ The cell as the unit of life, plant and animal cells
- Thinking a big animal starts as many cells→ The cell as the unit of life, plant and animal cells
- Only entry, or only exit→ The cell membrane
- Carbohydrates as the main material→ The cell membrane
- A vacuole as the suicidal bag→ Cell organelles and their jobs
Reference tables (1)
Hypotonic, isotonic and hypertonic solutions3 rows
| Solution outside | Compared with the cell | Water moves | The cell |
|---|---|---|---|
| Hypotonic (for example pure water) | Weaker | Into the cell | Swells |
| Isotonic | Same | No net movement | Stays the same |
| Hypertonic (for example strong salt or sugar solution) | Stronger | Out of the cell | Shrinks Hyper means more: more salt outside, so water leaves. |
Watch out for (2)
- Swapping hypo and hyper→ Hypotonic, isotonic and hypertonic solutions
- Water following the weaker side→ Hypotonic, isotonic and hypertonic solutions
Question weightage by concept
5 concepts · 8 questions — where the marks actually sit, so you know what to drill first
Question weightage by concept
5 concepts · 8 questions — where the marks actually sit, so you know what to drill first
| Concept | Qs | Share |
|---|---|---|
| The cell as the unit of life, plant and animal cells | 3 | 38% |
| The cell membrane | 2 | 25% |
| Cell organelles and their jobs | 1 | 13% |
| Concept | Qs | Share |
|---|---|---|
| Hypotonic, isotonic and hypertonic solutions | 2 | 25% |
| Diffusion: from more to lessfoundation | — | — |
Test yourself on a real paper
Sit a past SPI paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.