Features of Organisms (Cambridge International IGCSE Biology)

The five kingdoms

Spec point — 1.3.1 · State the main features used to place animals and plants into the appropriate kingdoms

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

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

A typical plant cell

The animal kingdom

Spec point — 1.3.2 · State the main features used to place organisms into groups within the animal kingdom, limited to: (a) the main groups of vertebrates: mammals, birds, reptiles, amphibians, fish (b) the main groups of arthropods: myriapods, insects, arachnids, crustaceans Classify organisms using the features identified

The animal kingdom

• Several main features are used to place organisms into groups within the animal kingdom

Vertebrates

• All vertebrates have a backbone

  • There are five classes of vertebrates

Vertebrate table

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

Arthropod classification

Exam Hint

• 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