Living Creatures: Exploring their Characteristics · Lesson 1 of 8
What Makes Something Living?
“Investigate living and non-living things by testing familiar clues against difficult examples.”
• Sort familiar objects and organisms using reasons rather than appearance alone. • Explain why movement by itself cannot prove that something is alive. • Recognise several kinds of movement in plants without expecting them to walk. • Connect growth and nutrition with the lives of plants and animals.
A shell that seems still
Avadhi sees a shell on a walk and is surprised to hear that it may belong to a living snail. The hard shell does not look like a person or a bird, and it may not be moving when she sees it. But a moment of stillness does not tell the whole story of the creature inside. To decide whether something is living, we must ask what it does over time, not rely on a single glance.
Try looking around your classroom. A pencil, book, pigeon, car and plant are very different. Make an initial living or non-living guess for each and write a reason. Later, after studying more characteristics, return to the same record to see whether your reasons still hold. That is the purpose of the five-column classification table in the chapter: it makes a first prediction and a revised conclusion visible.
| Thing | First guess | A question worth asking |
|---|---|---|
| Pigeon | Living | Does it need food, grow and respond? |
| Pencil | Non-living | Does it carry out life processes? |
| Car | Non-living | Does being able to move make it alive? |
| Plant | Living | Can it move or grow without walking? |
Movement is more than travelling
A pigeon can fly from one place to another. A car also travels, but it does so because its machinery receives fuel and is operated; movement alone is therefore an unreliable test for life. A plant generally remains rooted in one place, yet parts of it can move and grow. The opening of a flower and a climber winding around a nearby support are movements worth observing over time.
Drosera is an insectivorous plant that obtains nutrition from trapped insects. Its leaves carry sticky, hair-like projections. When an insect enters the saucer-like leaf, the hairs can move inward and trap it. The plant does not chase the insect across the ground. Its movement occurs in a part of its body. Compare that with a car rolling on a road: the visible movement looks impressive, but it tells us little unless we ask what else the object does.
Problem
A child says that a car must be living because it can travel by itself. What should be checked before agreeing?
- 1.Movement is one possible clue, but a living thing is recognised from a combination of life processes.
- 2.Ask whether the car grows as an organism, needs nutrition in the biological sense, respires, responds as a living body and produces new cars of its own kind.
- 3.A car can move, but it does not carry out that collection of processes. The claim based on movement alone fails.
Growth and the need for food
Compare a photograph of yourself as a small child with your appearance now. Your body has grown, and an old set of clothes may no longer fit. Plants and other living beings also grow. Living beings obtain food or nutrition to support growth and development. A plant’s way of getting nutrition differs from an animal’s, but both need resources to remain alive and develop.
Growth is another useful clue that must be interpreted carefully. A pile of sand may become larger when someone adds more sand, but its grains have not developed into a living organism. A young plant grows as parts of its own body develop. The difference is in the process, not merely the final size.
A car moves without being alive, and a plant is alive without walking. Use several life characteristics together; the next lesson will build the fuller picture.
Quiz
What makes Avadhi’s motionless shell a difficult first example?
Why is a moving car not classified as living merely because it travels?
Which is a movement shown by a plant in the chapter?
What do sticky hairs on a Drosera leaf do when an insect enters?
Which observation best supports that a young plant is growing as a living organism?
Practice Problems
- Make a first-guess table for a pencil, pigeon, car, plant and snail shell. Give a reason and identify what further evidence you would seek.
- Explain why travelling from place to place is not required for every living being.
- Describe two different movements in plants and state what actually moves.
- Compare a young plant becoming larger with a pile of sand becoming larger. Why are these not the same kind of change?
- Write a response to a classmate who claims that a car is living because it moves and uses fuel.
Key Takeaways
• A still shell may belong to a living snail. • Movement alone is not a reliable test of life. • Plants show movements of parts even though they generally remain rooted. • Living beings grow and need nutrition for growth and development. • Classification improves when a first guess is tested against several characteristics.
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Start of chapter
Next · Lesson 2
Life Processes and Responses