1.3Characteristics and Classification of Living Organisms

Features of organisms — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

5 min read 10 parts Lesson 3 of 6 1 quiz

📚 Cambridge IGCSE Biology 0610 Hub / Topical Revision

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Lesson summary

1.3 Features of organisms — IGCSE BIOLOGY notes: State the main features used to place organisms into kingdoms and into groups within the animal and plant kingdoms.Five kingdoms — All living organisms are placed in one of animals, plants, fungi, protoctists or prokaryotes.Animals…

Vertebrates
Arthropods
Defining feature
Arthropod identification
Invertebrate
Endothermic

Part 1 of 8Animal and plant kingdoms

Fern as an example of a non-flowering plant

Spore-producing structures on the underside of a fern frond

Sunflower as an example of a flowering plant

Five kingdoms

All living organisms are placed in one of animals, plants, fungi, protoctists or prokaryotes.

Animals

Multicellular organisms whose cells have a nucleus but no cell wall and no chloroplasts.
They feed on organic substances made by other living things.
Carbohydrate is stored as glycogen.

Plants

Multicellular organisms whose cells have a nucleus, chloroplasts and cellulose cell walls.
They feed by photosynthesis.
Carbohydrate is stored as starch or sucrose.

Part 2 of 8Fungi, protoctists and prokaryotes

Fungi

Usually multicellular, with a nucleus and cell walls that are not made of cellulose.
They do not photosynthesise; they feed saprophytically on dead material or parasitically on living material.
Moulds, mushrooms and yeast are examples.

Protoctists

Mostly unicellular organisms whose cells always have a nucleus.
Some have cell walls and chloroplasts, so some photosynthesise and others feed on organic matter.
Amoeba, Paramecium and Plasmodium are examples.

Prokaryotes

Often unicellular organisms with a cell wall (not cellulose) and cytoplasm but no nucleus and no mitochondria.
Bacteria and cyanobacteria are examples.

Part 3 of 8Five kingdoms compared

Kingdom	Nucleus	Cell wall	Chloroplasts	Nutrition
Animals	Yes	No	No	Take in organic substances
Plants	Yes	Cellulose	Yes	Photosynthesis
Fungi	Yes	Not cellulose	No	Saprophytic or parasitic
Protoctists	Yes	Some	Some	Photosynthesis or feeding
Prokaryotes	No	Yes, not cellulose	No	Varied

Part 4 of 8Vertebrate classes

Vertebrates
- Animals with a backbone, divided into five classes: mammals, birds, reptiles, amphibians and fish.

Class	Main features
Mammals	Fur or hair on skin; placenta; young fed on milk from mammary glands; external ears (pinnae); endothermic
Birds	Skin covered in feathers; two legs and two wings; hard-shelled eggs laid on land; beak; endothermic
Reptiles	Dry, fixed scales on skin; rubbery-shelled eggs laid on land
Amphibians	Smooth, moist skin; adults usually on land with lungs; larvae in water with gills; eggs without shells laid in water
Fish	Loose, wet scales on skin; gills for breathing; eggs without shells laid in water

Part 5 of 8Arthropod features

Arthropod features

Invertebrates

Animals without a backbone.

Arthropods

All invertebrates with jointed legs belong to the arthropod phylum.
They have an exoskeleton.
They have a segmented body.
They have jointed legs.

Part 6 of 8Arthropod classes

Spider showing the body regions and eight legs of an arachnid

Class	Main features	Example
Myriapods	Many body segments; at least one pair of jointed legs per segment; one pair of antennae	Centipede
Insects	Head, thorax and abdomen; six jointed legs; two pairs of wings (may be vestigial); one pair of antennae	Butterfly
Arachnids	Cephalothorax and abdomen; four pairs of jointed legs; no antennae	Spider
Crustaceans	More than four pairs of jointed legs; chalky calcium exoskeleton; gills; two pairs of antennae	Crab

Part 7 of 8Main features and defining features

Main features and defining features

Main features

Features that describe a group but may be shared with other groups, such as a backbone in all vertebrates.

Defining feature

A feature that sets one group apart from the others.
Mammals alone have fur.
Crustaceans alone have two pairs of antennae.

Arthropod identification

Any one of exoskeleton, jointed legs or segmented body shows an organism is an arthropod.

Part 8 of 8More from the specification

Species and Genus

In the binomial classification system, the genus represents closely related organisms while the species designates individuals capable of interbreeding to produce fertile offspring.

Molecular Phylogeny

DNA base sequences and amino acid sequences are used to classify organisms with greater accuracy than purely morphological characteristics.

Monocotyledonous vs Dicotyledonous Leaves

Monocots exhibit narrow leaves with parallel vein systems, whereas dicots possess broad leaves with branching network systems of veins.

Binomial

A two-part Latin name of genus then species.

Dichotomous

Branching into two.

Binomial system

An internationally agreed system naming each organism with a genus and a species in Latin.

Multiple choice

Section I, 60 questions in 90 minutes.

Species

A group of organisms that can reproduce to produce fertile offspring.

Classification

Grouping organisms by shared features and relationships.

Sequence

The order of bases in DNA or amino acids in a protein.

Monocotyledon

A flowering plant with one cotyledon, parallel leaf veins and petals in threes.

Dicotyledon

A flowering plant with two cotyledons, reticulated leaf veins and petals in fours or fives.

Key terms

Term	Meaning
Vertebrate	An animal with a backbone.
Invertebrate	An animal without a backbone.
Arthropod	An invertebrate with an exoskeleton, a segmented body and jointed legs.
Endothermic	Able to keep a constant body temperature using heat made by the body.
Saprophytic	Feeding on dead or decaying material.
Prokaryote	An organism whose cells have no nucleus.
Protoctist	A mostly unicellular organism whose cells have a nucleus.

Avoid these mistakes

Giving habitat as a classification feature — whales live in water but are mammals because they have fur or hair and feed milk.

Confusing arachnids with crustaceans — arachnids have four pairs of legs and no antennae, crustaceans have two pairs of antennae.

Saying fungi photosynthesise — they have no chloroplasts and feed saprophytically or parasitically.

Saying reptiles lay eggs in water — reptile eggs have rubbery shells and are laid on land.

Last updated: 24 October 2026