IGCSEBiologyCambridge (CIE)Revision Notes1. Characteristics & Classification of Living OrganismsCharacteristics, Classification & Features of OrganismsFeatures of Organisms

Features of Organisms (Cambridge (CIE) IGCSE Biology): Revision Note

Exam code: 0610 & 0970

Written by: Lára Marie McIvor

Reviewed by: Jenna Quinn

Updated on 28 August 2026

Kingdoms: animals & plants

All living organisms share characteristics. Organisms can be grouped together based on common features they share
All living organisms can be grouped into one of five kingdoms
Animals and plants are both kingdoms within this grouping system
Main features of all animals:
- they are multicellular
- their cells contain a nucleus but no cell walls or chloroplasts
- they feed on organic substances made by other living things

Diagram of a typical animal cell labelled with nucleus, cell membrane, cytoplasm, mitochondria and ribosomes on rough endoplasmic reticulum — **A typical animal cell**

Main features of all plants:
- they are multicellular
- their cells contain a nucleus, chloroplasts and cellulose cell walls
- they all feed by photosynthesis

Diagram of a typical plant cell labelled with cell wall, cell membrane, chloroplasts, nucleus, mitochondria, cytoplasm, vacuole and rough ER with ribosomes — **A typical plant cell**

The animal kingdom

Several main features are used to place organisms into groups (opens in a new tab) within the animal kingdom

Vertebrates

All vertebrates have a backbone
- There are five classes of vertebrates

Vertebrate table

Class	Main features	Examples
Mammals	Fur/hair on skin Have a placenta Young feed on milk from mammary glands External ears (pinna) visible Endothermic	Horse, dog, squirrel, human
Birds	Skin covered in feathers Have 2 legs and 2 wings instead of forelimbs Lay eggs with hard shells on land Have a beak Endothermic	Parrot, blue tit, eagle
Reptiles	Dry, fixed scales on skin Lay eggs with rubbery shells on land	Snake, turtle, iguana
Amphibians	Smooth, moist skin Adults usually live on land (and so have lungs) Larvae live in water (and so have gills) Lay eggs without shells in water	Frog, toad, newt
Fish	Loose, wet scales on skin Use gills to breathe Lay eggs without shells in water	Flounder, grouper

Diagram showing vertebrate groups—reptiles, fish, amphibians, birds and mammals—with simple notes on skin, eggs, blood temperature and example animals — **Vertebrate classification**

Invertebrates

Invertebrates do not possess a backbone
One of the morphological characteristics used to classify invertebrates is whether they have legs or not
All invertebrates with jointed legs are part of the arthropod phylum
All arthropods share the following visible features:
- They have an exoskeleton
- They have a segmented body
- They have jointed legs

They are classified further into the following groups:

Arthropod groups table

Class	Main features	Examples
Myriapods	Body consists of many segments Each segment contains at least one pair of jointed legs One pair of antennae	Centipede
Insects	Three-part body: head, thorax and abdomen Adults have six jointed legs Two pairs of wings (one or both pairs may be vestigial, meaning non-functional and undeveloped) One pair of antennae	Butterfly
Arachnids	Two-part body: cephalothorax and abdomen Four pairs of jointed legs No antennae	Spider
Crustaceans	More than four pairs of jointed legs Chalky exoskeleton formed from calcium Use gills to breathe Two pairs of antennae	Crab

Diagram showing classification of arthropods into arachnids, crustaceans, insects and myriapods, with simple drawings and key features of each group. — **Arthropod classification**

Examiner Tips and Tricks

Make sure that you are aware of the distinction between the main features of a group of organisms and the defining features of a group:
An exam question might ask you to state the main features of a group of organisms; these are given above, and some of these main features are shared between the groups
- E.g. all of the vertebrates have a backbone, and all of the arthropods have segmented bodies
It is also possible that an exam question might ask you to give a defining visible feature of any one of these groups, i.e. a feature that sets a group apart from the other groups
- E.g. mammals have fur while the other vertebrates do not, and crustaceans have two pairs of antennae while this is not the case for the other groups of arthropods
It is common for students to confuse arachnids with crustaceans, and to not be able to state a visible feature identifying an organism as an arthropod, any one of "exoskeleton, jointed legs or segmented body" would be an appropriate answer

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