Biology · Lesson 1

Characteristics of life & classification (kingdoms, binomial naming)

JAMBWAECNECO

What the syllabus asks

JAMB: characteristics of living things, classification of living things (Monera, Protista, Fungi, Plantae, Animalia), binomial system of naming, use of keys

WAEC: concept of living, characteristics of living things, differences between plants and animals, levels of organisation, classification of living things into kingdoms, binomial nomenclature, taxonomic hierarchy, simple dichotomous keys

NECO: concept of living, characteristics of living things, differences between plants and animals, levels of organisation, classification of living things into kingdoms, binomial nomenclature, taxonomic hierarchy, simple dichotomous keys

What you will learn

List and explain the characteristics of living things with examples.
Distinguish living from non-living things, and explain why viruses are borderline.
Compare plants and animals.
Describe levels of organisation from cell to organism with examples.
Explain the need for classification and list the taxonomic ranks in order.
Name the five kingdoms and give features and examples of each.
Write scientific names correctly and use a simple dichotomous key.

Key points

Living things show movement, respiration, sensitivity, growth, reproduction, excretion and nutrition, and they die.
Respiration is energy release in cells; it is not breathing.
Excretion removes metabolic waste; egestion removes undigested food.
Growth is a permanent increase in dry mass.
Plants: autotrophic, cellulose walls, grow throughout life, mostly fixed. Animals: heterotrophic, no walls, limited growth, mostly mobile.
Levels: cell → tissue → organ → system → organism.
Hierarchy: kingdom, phylum, class, order, family, genus, species; lower shared rank = closer relationship.
Binomial name: Genus capitalised, species small, italicised or underlined.
Five kingdoms: Monera (prokaryotes), Protista, Fungi (chitin, spores, saprophytes), Plantae, Animalia.
Viruses are not cells and sit on the border of life; a dichotomous key for n organisms needs n − 1 steps.

Start here: What does it mean to be alive?

Walk through Oyingbo market and you can sort what you see into two groups almost without thinking. The tomatoes, the goats, the trader, the flies, the mould on an old bread: living, or once living. The plastic bowls, the iron sheets, the radio, the stones in the gutter: non-living. But what exactly is the difference? Biology begins by answering that question carefully.

No single feature is enough. A car moves, a fire "feeds" on fuel and gives out carbon dioxide, a crystal of salt "grows" in a saturated solution. Yet none of these is alive. Biologists therefore use a set of characteristics: an object is alive only if it shows all of them at some stage of its life.

Living things (organisms) carry out movement, respiration, sensitivity (irritability), nutrition, growth, excretion and reproduction, and they eventually die.

A popular memory aid is MRS NERG or MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition. Nigerian teachers often add "D" for death. Use whichever you like; the important thing is to be able to explain each one, because WAEC asks you to.

There is also a third group worth naming: things that are dead (once living), such as firewood, dried fish or a leather bag. They contain the same chemicals as living things but no longer carry out the life processes.

Worked example 1.1

A student says "fire is alive because it moves, uses oxygen, gives out carbon dioxide and grows bigger". Explain why she is wrong.

Check every characteristic, not just some. We do this because an organism must show all of them.
Fire does not respond to stimuli in a controlled way, cannot reproduce itself from its own cells, has no cells at all and does not excrete metabolic wastes.
Its "growth" is just spreading to new fuel, not an increase in living material made from food.

Fire shows only some features by coincidence; it is non-living.

⚠️ Common mistake: choosing one feature (usually movement) as proof of life. Cars and clocks move. Always test against the full list.

Try it yourself. Is a seed of beans stored in a tin alive? Explain.

Show solution

Yes. It is dormant: it respires very slowly and will grow and reproduce when given water, air and warmth. It is living but inactive.

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Practice questions

1. Which of the following is NOT a characteristic of all living things?

Locomotion
Respiration
Excretion
Reproduction

Show answer

A: Locomotion
Plants do not move from place to place, but all living things respire, excrete and reproduce.

2. The correct order of classification from largest to smallest is

Kingdom, class, phylum, order, genus, family, species
Phylum, kingdom, class, family, order, genus, species
Species, genus, family, order, class, phylum, kingdom
Kingdom, phylum, class, order, family, genus, species

Show answer

D: Kingdom, phylum, class, order, family, genus, species
Memory tip: "King Philip Came Over For Good Soup".

3. The scientific name of man, Homo sapiens, is an example of

natural selection
trinomial classification
binomial nomenclature
taxonomy of kingdoms

Show answer

C: binomial nomenclature
Two names (genus + species) = binomial nomenclature, introduced by Linnaeus.

4. Which organism reproduces by binary fission?

Hydra
Amoeba
Spirogyra
Rhizopus

Show answer

B: Amoeba
Amoeba divides into two. Hydra buds; Rhizopus forms spores; Spirogyra conjugates.

5. Euglena is regarded as both plant-like and animal-like because it

has chloroplasts and can also feed heterotrophically
has a cell wall and cilia
reproduces sexually and asexually
lives in water and on land

Show answer

A: has chloroplasts and can also feed heterotrophically
Euglena photosynthesises in light but can absorb food in the dark.

Key words

Organism: Any individual living thing.
Irritability (sensitivity): The ability to detect and respond to changes (stimuli) in the environment.
Stimulus: A change in the surroundings that brings about a response.
Metabolism: All the chemical reactions going on in a living organism.
Excretion: Removal of waste products of metabolism from the body.
Egestion: Removal of undigested food (faeces); not excretion.
Autotroph: An organism that makes its own food from simple substances.
Heterotroph: An organism that depends on ready-made food.
Tissue: A group of similar cells performing the same function.
Organ: A structure made of different tissues working together for a function.
Taxonomy: The science of naming, describing and classifying organisms.
Binomial nomenclature: The two-name (genus + species) system of naming organisms, introduced by Linnaeus.

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