2.1 Cell structure
- Syllabus
- 0610–2026–2027
- Topic
- 2.1
- Level
- —
Learning objectives
2.1.1Structure of a plant cell• Describe and compare the structure of a plant cell with an animal cell, limited to: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria, vacuoles2.1.2Structure of a bacterial cell• Describe the structure of a bacterial cell, limited to: cell wall, cell membrane, cytoplasm, ribosomes, circular DNA, plasmids2.1.3Identify cell structures• Identify the cell structures listed in 2.1.1 and 2.1.2 in diagrams and images of plant, animal and bacterial cells2.1.4Functions of cell structures• Describe the functions of the structures listed in 2.1.1 and 2.1.2 in plant, animal and bacterial cells2.1.5Cell division makes new cells• State that new cells are produced by division of existing cells2.1.6Specialised cell functions• State that specialised cells have specific functions, limited to: (a) ciliated cells – movement of mucus in the trachea and bronchi (b) root hair cells – absorption (c) palisade mesophyll cells – photosynthesis (d) neurones – conduction of electrical impulses (e) red blood cells – transport of oxygen (f) sperm and egg cells (gametes) – reproduction2.1.7Meaning of the terms: cell, tissue• Describe the meaning of the terms: cell, tissue, organ, organ system and organism as illustrated by examples given in the syllabus
Compare plant and animal cell structures
Plant and animal cells both contain a cell membrane, cytoplasm, nucleus, ribosomes and mitochondria.
| Structure | Plant cell | Animal cell |
|---|---|---|
| cell membrane | present | present |
| cytoplasm, nucleus, ribosomes, mitochondria | present | present |
| cellulose cell wall | present outside membrane | absent |
| chloroplasts | present in photosynthetic cells | absent |
| vacuole | usually one large permanent vacuole | small temporary vacuoles may occur |
The cell wall often gives plant cells a regular outline, while animal cells may have an irregular outline. Chloroplasts occur in green photosynthetic tissues, not in every plant cell.
Do not call the cell wall a second membrane. Both cell types have a membrane, and absence of visible chloroplasts does not prove that a cell is animal.
Describe the structure of a bacterial cell
A bacterial cell has a cell wall, cell membrane and cytoplasm containing ribosomes. Its genetic material is circular DNA, and it may also contain plasmids.
| Structure | Description |
|---|---|
| cell wall | surrounds and supports the cell |
| cell membrane | boundary controlling movement of substances |
| cytoplasm | site of cell reactions |
| ribosomes | small structures in the cytoplasm |
| circular DNA | main genetic material, free in the cytoplasm |
| plasmids | small additional loops of DNA |
Bacteria have no nucleus: their circular DNA is not enclosed by a nuclear membrane. They also lack mitochondria and chloroplasts.
A plasmid is a loop of DNA, not a whole bacterial cell, gene or protein. Ribosomes are present even though bacteria lack membrane-bound organelles.
Identify cell structures in diagrams and images
Identify a cell structure from its position, outline and internal pattern, then check that it is possible in that cell type.
| Visual clue | Likely structure |
|---|---|
| rigid outer boundary outside a thinner membrane | cell wall |
| thin boundary around cytoplasm | cell membrane |
| large dark body in a eukaryotic cell | nucleus |
| many small dots | ribosomes |
| oval with folded internal membrane | mitochondrion |
| oval with stacked internal membranes in a plant cell | chloroplast |
| large clear central region in a plant cell | vacuole |
| diffuse large loop plus small DNA rings in a bacterium | circular DNA and plasmids |
In a micrograph, structures may not match textbook colours or perfect shapes. Use scale, boundary relationships and repeated internal features rather than colour.
Do not identify an organelle from darkness alone. Confirm its location and cell type: a chloroplast cannot be in an animal cell and bacterial DNA is not a nucleus.
Link cell structures to their functions
Each listed cell structure contributes a specific function to the cell.
| Structure | Function |
|---|---|
| cell membrane | controls movement of substances into and out of the cell |
| cell wall | supports the cell and prevents bursting |
| nucleus | contains genetic material and controls cell activities |
| cytoplasm | site of many chemical reactions |
| chloroplast | photosynthesis; contains chlorophyll |
| ribosome | protein synthesis |
| mitochondrion | aerobic respiration and energy release |
| vacuole | contains cell sap and helps maintain plant-cell turgidity |
| circular DNA | carries the main bacterial genetic information |
| plasmid | small additional DNA loop that can carry genes |
Cells with high energy requirements contain many mitochondria; cells making much protein contain many ribosomes. Structure abundance can therefore provide evidence about function.
Mitochondria release energy by respiration; they do not ‘make energy’. Cell walls provide support, whereas membranes control exchange.
State how new cells are produced
New cells are produced by the division of existing cells.
An existing cell divides to form daughter cells. In plant tissue, new cell membrane and cell wall material form between the daughter nuclei as the two cells separate.
Cell division increases cell number for growth, replacement and repair. The new cells do not arise spontaneously from non-living material.
This objective requires the source of new cells, not the detailed stages or chromosome behaviour of mitosis.
Match specialised cells to their functions
Specialised cells have particular structures suited to specific functions.
| Specialised cell | Specific function | Helpful feature |
|---|---|---|
| ciliated cell | moves mucus in trachea and bronchi | cilia beat together |
| root hair cell | absorption of water and mineral ions | long extension gives large surface area |
| palisade mesophyll cell | photosynthesis | many chloroplasts |
| neurone | conduction of electrical impulses | long axon and branched connections |
| red blood cell | transport of oxygen | haemoglobin; biconcave shape; no nucleus when mature |
| sperm cell | male role in reproduction | flagellum for movement and nucleus with genetic material |
| egg cell | female role in reproduction | large cell with nutrient-rich cytoplasm and nucleus |
Identify the function first, then choose the feature that makes that function more effective. A root hair increases absorption area; cilia move material over a cell surface.
Do not swap cilia with the sperm flagellum: cilia move mucus across tissue, while a flagellum moves the sperm cell.
Build the levels of biological organisation
Biological organisation builds from cells to tissues, organs, organ systems and a complete organism.
| Level | Meaning | Example |
|---|---|---|
| cell | smallest unit of a living organism | palisade mesophyll cell |
| tissue | group of similar cells working together for a shared function | palisade mesophyll tissue |
| organ | group of tissues working together for specific functions | leaf or heart |
| organ system | group of organs working together | digestive or circulatory system |
| organism | complete living individual | a plant or a human |
Palisade cells form palisade tissue; this tissue contributes to the leaf organ; leaves work with stems and roots in the plant; together they form the organism.
Ask what the structure contains: one cell, similar cells, several tissues, or several organs. A leaf contains several tissues, so it is an organ—not a tissue.
Size alone does not decide the level. A large single cell remains a cell, and an organ can belong to more than one organ system.