NDA Biology · Cell Biology
Cell Structure Fundamentals — What Every Cell Has
The cell is the smallest unit of life; every living cell — whether a bacterium or a human nerve cell — must have a plasma membrane, cytoplasm, ribosomes and genetic material, while only some have a cell wall or an organized nucleus.
Why this matters
Start here — this subtopic sets the vocabulary (cell, tissue, organ, organism) and the universal-vs-optional distinction the whole chapter leans on (6 PYQs). The bank's favourite trap is the word 'all': 'all cells have a cell wall' (false — animal cells don't) and 'all cells have a well-organized nucleus' (false — prokaryotes don't). All EASY or MODERATE — pure recall and careful statement-reading.
Concept 1 of 3: Levels of organization — molecules to organism
Definition
The structural hierarchy of life, simplest to most complex:
- Molecule — e.g. a protein, the chemical building block.
- Cell — the basic structural and functional unit of life.
- Tissue — a group of similar cells doing one job.
- Organ — different tissues working together (heart, leaf).
- Organism — the complete living individual.
Worked example
Practice this concept3 quick reps
Concept 2 of 3: The increasing-complexity sequence
Definition
The correct order of increasing complexity, with the trap distractors that scramble it:
- Correct: Protein → Tissue → Organ → Organism.
- A protein is a molecule; tissues are built from cells; organs from tissues; the organism is the whole.
- Any option that puts 'organism' before 'organ' or 'tissue' is wrong — the organism is always last.
| Step | Level | What it is |
|---|---|---|
| 1 (simplest) | Protein | A molecule — chemical building block |
| 2 | Tissue | Group of similar cells doing one job |
| 3 | Organ | Several tissues working together |
| 4 (most complex) | Organism | The whole living individual Organism is ALWAYS last — any option listing it earlier is a distractor. |
Practice this conceptself-check · 3 quick reps
The same idea in a real exam question:
Example 2 · Cell Biology · Cell Structure Fundamentals
Organism is the LAST rung, not an early one
Concept 3 of 3: Universal vs optional cell features
Definition
The universal-vs-optional split the bank tests:
- Universal (in all cells): plasma membrane, cytoplasm, ribosomes, genetic material (DNA).
- Optional (only some cells): cell wall (plants, fungi, bacteria — NOT animals), a membrane-bound nucleus (eukaryotes only — prokaryotes lack it), linear DNA (eukaryotes; prokaryotes have circular DNA).
- A living being also shows growth, repair and metabolism — non-living things do not.
| Feature | In all cells? | Note |
|---|---|---|
| Plasma membrane | Yes — universal | Outer boundary of every cell |
| Cytoplasm | Yes — universal | The cell's internal fluid |
| Ribosomes | Yes — universal | Even prokaryotes have them (70S) |
| Genetic material (DNA) | Yes — universal | Present in every cell |
| Cell wall | No — optional | Plants/fungi/bacteria have it; animal cells do NOT 'All cells have a cell wall' is FALSE — animal cells lack one. |
| Well-organized nucleus | No — optional | Eukaryotes only; prokaryotes have a nucleoid 'All cells have a well-organized nucleus' is FALSE — prokaryotes don't. |
Practice this conceptself-check · 4 quick reps
The same idea in a real exam question:
Example 3 · Cell Biology · Cell Structure Fundamentals
Beware the word 'ALL' in statement questions
Animal cell types: monocyte, basophil, lymphocyte, chondrocyte
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (2)
The increasing-complexity sequence4 rows
| Step | Level | What it is |
|---|---|---|
| 1 (simplest) | Protein | A molecule — chemical building block |
| 2 | Tissue | Group of similar cells doing one job |
| 3 | Organ | Several tissues working together |
| 4 (most complex) | Organism | The whole living individual Organism is ALWAYS last — any option listing it earlier is a distractor. |
Universal vs optional cell features6 rows
| Feature | In all cells? | Note |
|---|---|---|
| Plasma membrane | Yes — universal | Outer boundary of every cell |
| Cytoplasm | Yes — universal | The cell's internal fluid |
| Ribosomes | Yes — universal | Even prokaryotes have them (70S) |
| Genetic material (DNA) | Yes — universal | Present in every cell |
| Cell wall | No — optional | Plants/fungi/bacteria have it; animal cells do NOT 'All cells have a cell wall' is FALSE — animal cells lack one. |
| Well-organized nucleus | No — optional | Eukaryotes only; prokaryotes have a nucleoid 'All cells have a well-organized nucleus' is FALSE — prokaryotes don't. |
Watch out for (3)
- Organism is the LAST rung, not an early one→ The increasing-complexity sequence
- Beware the word 'ALL' in statement questions→ Universal vs optional cell features
- Animal cell types: monocyte, basophil, lymphocyte, chondrocyte→ Universal vs optional cell features
Test yourself on Cell Biology
15 past NDA questions from this chapter, timed at 15 minutes and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.