Living and Non-Living Things: How Do We Tell Them Apart?

Introduction

Every day, you interact with two broad categories of objects: things that are alive and things that are not. A dog barking in the street, a mango tree in your compound, and even the bacteria you cannot see are all living things. On the other hand, a stone by the roadside, a plastic chair, and the water in a cup are non-living things. Learning to tell living things and non-living things apart is one of the very first and most important skills in the study of Basic Science, because it forms the foundation for topics such as classification, ecology, and the study of the human body.

What Are Living Things?

Living things, also called organisms, are things that possess life. They are born (or hatch, or germinate), they grow, they carry out life processes, and eventually they die. Examples of living things include human beings, animals such as goats, birds and fish, plants such as maize, orange trees and grass, and microorganisms such as bacteria and fungi that are too small to see with the naked eye.

What Are Non-Living Things?

Non-living things are things that do not have life. They cannot grow on their own, they do not reproduce, and they do not carry out any of the life processes that living things carry out. Examples of non-living things include a table, a bicycle, a rock, a book, water, air, and a mobile phone. Some non-living things, like a car or a robot toy, may appear to "move" or "make sounds," but this does not mean they are alive — they only respond because a human being designed them to do so using batteries, engines or electricity.

The Characteristics of Living Things

Scientists use a set of characteristics, often remembered with the mnemonic MRS GREN, to decide whether something is truly alive. Every living thing must show all of these characteristics, not just one or two.

• Movement: Living things can move all or part of their body. Animals walk, swim or fly, while plants show slower movements such as leaves turning toward sunlight (this is called tropism).
• Respiration: Living things release energy from food through a chemical process called respiration, which happens inside their cells.
• Sensitivity: Living things can detect and respond to changes in their surroundings, called stimuli. For example, you blink when dust flies into your eye, and a plant's roots grow toward water.
• Growth: Living things increase in size and mass over time as a permanent change, from a baby to an adult, or from a seed to a full-grown tree.
• Reproduction: Living things can produce new individuals of their own kind, ensuring their species continues to exist.
• Excretion: Living things remove waste products that are produced inside their bodies as a result of chemical reactions, such as sweat, urine and carbon dioxide.
• Nutrition: Living things take in food or make their own food to obtain energy and materials needed for growth and repair.

A useful way to remember these seven characteristics is the phrase Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition — MRS GREN.

Why Non-Living Things Do Not Qualify

A non-living thing may show one characteristic of life but never all seven at once. For example, a river moves, but it does not respire, grow, reproduce or excrete waste, so it is non-living. A candle flame produces heat and seems to "grow" as it burns, but it does not feed, reproduce or respond to stimuli in the way a living organism does. This is why scientists insist that all seven characteristics must be present together before something can be classified as a living thing.

Once-Living (Dead) Things

It is important to note a special group of objects called "once-living things." These are materials that came from living things but are no longer alive, such as a wooden table (which came from a tree), a leather bag (which came from an animal's skin), or firewood. Although their raw material was once part of a living organism, once they have been cut off, processed or the organism has died, they no longer show the characteristics of life and are therefore classified as non-living.

Grouping Objects Around Us

In our environment, we can sort almost every object into one of these three groups:

• Living things: humans, animals, plants, and microorganisms that are currently alive.
• Non-living things: things that have never been alive, such as rocks, metals, water, air, and man-made items like desks and phones.
• Once-living things: things that came from a living organism but are now dead or processed, such as paper, wood, wool, leather and cotton cloth.

Practical Activity

Look around your classroom or home and list ten objects you can see. For each object, decide whether it is living, non-living, or once-living, and give a reason for your answer using the MRS GREN characteristics. This activity helps you apply what you have learned rather than just memorising definitions.

Why This Topic Matters

Understanding the difference between living and non-living things is the starting point for many other topics you will study in Basic Science and Biology, including classification of living things into kingdoms, ecosystems, nutrition, and body systems. It also helps you appreciate and care for the environment, since living things need protection and proper care to continue their life processes, while non-living resources need to be used wisely because many of them, like minerals and fossil fuels, cannot be replaced once they are used up.

Summary

Living things are things that possess life and show all seven characteristics summarised as MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion and Nutrition. Non-living things lack these characteristics entirely, while once-living things are materials derived from organisms that are no longer alive. Being able to correctly classify objects in your environment as living, non-living or once-living is a fundamental skill that prepares you for deeper study in the sciences.

Common Mistakes to Avoid

Many students confuse "moving" with "being alive." Remember that movement alone does not prove life — a toy car, a flowing river, and smoke rising into the air all move, yet none of them are alive because they cannot carry out the other six life processes. Likewise, some students assume that anything soft or anything that grows in size must be alive; however, materials like a rising cake batter or a growing crystal only appear to grow through purely physical or chemical changes, not through the biological process of nutrition and cell division that living organisms use to grow permanently.

Living and Non-Living Things in Our Nigerian Environment

In a typical Nigerian community, you will find many clear examples to practise this classification. In the market, yams, tomatoes and live chickens are living or were recently living things, while the weighing scale, the wheelbarrow and the money used to pay for goods are non-living. On a farm, the cassava plants, earthworms in the soil, and the farmer's goats are living things, while the cutlass, hoe and irrigation pipes are non-living tools that the living farmer uses to carry out farming activities. Recognising these examples in your everyday surroundings makes the concept easier to remember than only reading it from a textbook.

Revision Questions to Discuss in Class

• Is fire a living thing? Explain your answer using the MRS GREN characteristics.
• Give three examples of once-living things you can find in your school bag.
• Explain why a growing crystal of salt is not considered a living thing even though it increases in size.
• List five living things and five non-living things found in your school compound.