A unicellular organism performs nutrition, metabolism, excretion, response, homeostasis, growth, and reproduction within one cell rather than distributing them among tissues.
Coverage 2012–2023 · Updated 15 Jul 2026
A unicellular organism must perform all essential life processes within one cell: homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli and reproduction.
| Need | One-cell solution |
|---|---|
| Nutrition and metabolism | Takes in materials and converts them through enzyme-controlled reactions |
| Homeostasis and excretion | Regulates internal conditions and removes wastes |
| Movement and response | Uses a flagellum, cilia, pseudopodia or directed growth where applicable |
| Growth and reproduction | Makes new cell material, copies genetic information and divides |
Paramecium uses cilia for movement and feeding, food vacuoles for digestion, and contractile vacuoles for water balance and excretion.
A unicellular organism is a complete living organism, not one specialized cell waiting for a tissue to perform the remaining life processes.
This objective is assessed through structured response, commonly using Identify / Outline / Compare.
Identify / Outline / Compare / Contrast
Build the answer around this relationship: One cell performs all functions required by a unicellular organism.
Including differentiation or meiosis among functions performed by every unicellular organism.
Representative question
Unicellular and multicellular organisms share the same functions of life. Outline four functions of life.
The SL core is a practical chain. First, understand cells as structural and functional units. Then use microscopes correctly: prepare, stain, calibrate, measure, and choose a method based on resolution and the detail needed. Finally, identify cell types from visible evidence and draw only what the micrograph shows. This is how the topic turns from definitions into exam performance.
