Eukaryotic cells contain a nucleus, 80S ribosomes, and membrane-bound organelles such as mitochondria, endoplasmic reticulum and Golgi apparatus. However, the exact organelles present vary among animal, plant and fungal cells.
Core Organelles and Their Functions
Organelles are discrete subunits of cells adapted to perform specific functions. Compartmentalization allows enzymes and metabolites to be concentrated and separates incompatible biochemical processes.
Organelle | Main function |
|---|---|
Nucleus | Stores chromosomes; site of transcription. Its double membrane contains nuclear pores. |
80S ribosomes | Synthesize polypeptides by translation; may be free or attached to rough endoplasmic reticulum. |
Rough endoplasmic reticulum | Synthesizes and transports proteins destined for secretion or movement within the cell. |
Smooth endoplasmic reticulum | Synthesizes lipids and performs other metabolic functions. |
Golgi apparatus | Modifies, sorts and packages proteins into vesicles. |
Mitochondria | Produce ATP during aerobic cell respiration. |
Lysosomes | Contain hydrolytic enzymes for intracellular digestion. |
Vesicles | Transport or store materials within cells. |
Vacuoles | Store substances; the large sap vacuole in plant cells supports turgor. |
Chloroplasts | Carry out photosynthesis in plants and some other eukaryotes. |
Differences Between Eukaryotic Cell Types
Cell type | Distinguishing structures |
|---|---|
Animal | No cell wall or chloroplasts; typically has centrioles and small vesicles. |
Plant | Cellulose cell wall, chloroplasts and a large permanent sap vacuole. |
Fungus | Chitin cell wall; no chloroplasts; vacuoles may be present. |
A common misconception is that every eukaryotic cell contains every organelle. Specialized cells may lack particular structures: mature human red blood cells lack a nucleus and mitochondria, while phloem sieve tube elements lack a nucleus.
Exam Technique
For IB Biology A2.2, be ready to identify eukaryotic cells and organelles in electron micrographs. If asked to distinguish cell types, state paired differencesfor example, “plant cells have a cellulose cell wall, whereas animal cells do not”rather than listing unrelated features.