Biology is the study of life. But what exactly makes something alive? Scientists agree that all living things share a set of characteristics. These characteristics are summarised in the acronym MRS GREN (or MRS NERG), and you must be able to list and explain each one for WAEC.
The Seven Characteristics of Living Things
| Characteristic | Meaning | Example |
|---|---|---|
| Movement | The ability to change position or place | A lizard running; plants turning towards light |
| Respiration | Release of energy from food | Glucose broken down in cells to release energy |
| Sensitivity | Responding to stimuli (changes in the environment) | Withdrawing a hand from a hot object |
| Growth | Permanent increase in size and complexity | A seedling becoming a mature tree |
| Reproduction | Producing offspring of the same kind | A hen laying eggs; plants producing seeds |
| Excretion | Removal of metabolic waste products | Removing carbon dioxide and urea |
| Nutrition | Obtaining and using food for energy and growth | Plants photosynthesising; animals feeding |
Remember: Egestion (removing undigested food) is NOT excretion. Excretion is the removal of waste produced by metabolism inside the body, such as carbon dioxide, urea and excess water.
Distinguishing Living from Non-Living Things
A living thing shows all the characteristics of life, while a non-living thing shows none (or only some, temporarily). For example:
- A car moves and uses fuel, but it does not grow, reproduce, excrete or respond on its own — so it is non-living.
- A seed appears inactive but is alive because it respires slowly and will germinate (grow) under the right conditions.
Key Points
- All living things share the same basic life processes.
- Use MRS GREN to recall all seven characteristics.
- Excretion ≠ egestion: excretion removes metabolic waste.
- A living thing performs all characteristics; non-living things perform none permanently.
Summary
To be classified as living, an organism must show movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. Memorise these seven processes — they form the foundation of every other topic in Biology.
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