Characteristics of living things
FoundationLiving things share seven characteristics: nutrition, respiration, sensitivity, growth, reproduction, excretion and movement.
- Seven traits: nutrition, respiration, sensitivity, growth, reproduction, excretion, movement
- All are needed to be called living
- Movement alone is not enough
§Text Passage
1Walk into a park or down to the seashore and you will find cats, birds, trees and grasses everywhere. They look very different, yet they share the same signs of life. After long observation, scientists grouped what all organisms have in common into life processes such as nutrition, respiration, excretion, growth, reproduction, sensitivity and movement, and used them as the basic test for telling living things from non-living things.
2These processes work together and support an organism throughout its life. An animal takes in food and digests it into nutrients; through respiration the nutrients are broken down to release energy for movement and other body activities, while metabolic wastes are removed from the body. Surplus nutrients are used for growth, and once an individual matures it can reproduce and pass life on to the next generation.
3Examples appear all around us in daily life: mould slowly spreads over a piece of bread, a mimosa folds its leaflets when touched, and a roadside banyan keeps stretching towards the sunlight. Plants cannot move about the way animals do, yet growing towards the light and sending roots deeper into the soil show sensitivity and movement just as clearly.
4Understanding the characteristics of life goes far beyond the classroom. Doctors judge a patient's condition from breathing and heartbeat, farmers water and fertilise crops according to their growth needs, and scientists apply the same criteria when they look for signs of life in Martian soil. It helps us tell living things from non-living things, classify species, and lays the basis for studying disease, conserving ecosystems and even searching for life beyond Earth.
1Summary 重點摘要
Living things share seven characteristics: nutrition, respiration, sensitivity, growth, reproduction, excretion and movement.
2Vocabulary cards Vocabulary
Taking in food or nutrients to obtain energy and materials for growth.
Releasing energy by breaking down nutrients — happens in every cell.
Responding to changes around them, e.g. mimosa leaves closing.
The process by which an organism increases in size and complexity over time.
The life process of producing offspring to continue the species.
Removing waste, e.g. carbon dioxide, urine.
Moving the whole body or parts of it, as animals do.
The sum of all chemical reactions inside an organism, including building up and breaking down substances.
3Step by step Steps
- Check one by oneTo decide whether something is living, the most reliable method is to check the seven life processes one by one: does it take in nutrients? Can it respire? Does it excrete waste? Can it grow and reproduce? Does it sense and respond to changes around it? For example, an apple left out for a while slowly rots. The change looks life-like, but rotting is only the work of microbes breaking it down; the apple itself cannot reproduce, so it is not a living thing. A stone lacks all seven processes outright and is clearly non-living.
- All seven countThe seven characteristics need not all be obvious at a glance, but an organism must have every one of them. Plants sense things slowly: seedlings grow towards the light, and the leaflets of a mimosa fold together when touched. Their movement often shows as a change in the direction of growth, with roots reaching down into the soil and shoots stretching upwards. These subtle signs are the easiest to miss, so observe with extra care and verify trait by trait before drawing a conclusion.
- Watch the trapsBeing able to move or to grow bigger does not prove life. A car can be driven along and a cloud keeps swelling, but neither takes in nutrients, excretes metabolic waste, nor reproduces, so neither is living. All seven characteristics must be present; if any one is completely absent, the object cannot be classed as living. In written answers, list the seven processes first and check the object against each one, rather than rushing to a conclusion from a single sign.
- Test in the fieldPractising in a park or at the beach makes judgement quick and accurate. Hong Kong's common banyan trees grow towards the light, flower, fruit and reproduce; black kites hunt small animals, respire and raise chicks — both are living. A shell on the sand comes from a living animal, but once the animal dies every life process has stopped: no growth, no reproduction — so the shell itself is non-living. Applying classroom knowledge in a real setting, item by item, leaves a much deeper impression.
- Respiration and excretionRespiration and excretion are easy to mix up and must be told apart. Respiration is the process by which cells break down nutrients to release energy for the body, and it goes on inside every cell day and night. Excretion specifically means removing the waste produced by metabolism: the carbon dioxide from cell respiration leaves through the lungs, while nitrogenous waste is removed as urine. Faeces are only undigested food residue, not metabolic waste, so never list them as excreted waste in answers, or marks will be lost.
- The boundary of growthTrue growth must be driven by cell division and an increase in the material making up the body from within. Sugar crystals growing ever larger and stalactites slowly lengthening are merely matter piling up on a surface, not biological growth. The boundary case is the virus: it can reproduce, yet it has no cellular structure and cannot carry out any life process once outside a host cell, so scientists generally do not class viruses as complete living things. Such borderline cases show exactly why checking the characteristics one by one matters.
4Diagrams Diagrams
5Worked example Example
Example: a seed looks completely still. Is it living?
- A seed germinates → growth
- The plant can reproduce
- It also respires and excretes
- It responds to changes in its surroundings
- Answer: Yes, it is living. A seed looks quiet but still respires, using stored food; given water it germinates and grows, later flowers and reproduces, and responds to changes such as light and gravity. All seven characteristics are present. Never judge by surface stillness alone — verify trait by trait before concluding.
6Common mistakes Mistakes
7Quick check Quick check
Q1Which is a characteristic of living things? A. rusting B. reproducing C. melting
Q2A car moves. Is it living? Why?
Q3Name any three characteristics of living things.
Q4A shell on the beach came from a living thing. Is it living? Why?
Q5Plants cannot run. How do they show movement and sensitivity?
8Recap Recap
- Seven traits: nutrition, respiration, sensitivity, growth, reproduction, excretion, movement
- All are needed to be called living
- Movement alone is not enough
- Plants are living too: they grow towards light and sense their surroundings
- Telling living from non-living underpins classification and the study of ecosystems