Develop accurate biological vocabulary, explain structure–function relationships, apply ideas to unfamiliar contexts, and use practical evidence.
Shared vertebrate feature
Vertebrates possess a vertebral column or backbone and an internal skeleton. The five main groups required are fish, amphibians, reptiles, birds and mammals. Classification questions often present an unfamiliar animal and ask for evidence, so identify the feature visible in the diagram rather than merely naming the group.
Fish and amphibians
Fish live in water, possess fins and gills, and usually have scales. Their eggs are commonly laid in water. Amphibians have moist, permeable skin; their larvae live in water and use gills, while adults usually breathe with lungs and skin. Their eggs lack a waterproof shell and are normally laid in water.
Reptiles and birds
Reptiles have dry skin covered with scales and usually lay leathery-shelled eggs on land. Birds have feathers, a beak and forelimbs modified as wings; they lay hard-shelled eggs and are endothermic. Wings alone are not a sufficient identifying feature because bats are mammals and some insects also fly.
Mammals
Mammals possess hair or fur and mammary glands that produce milk for young. They are endothermic and most give birth to live young, although this is not universal. The mammary gland is the defining feature represented by the group name.
Comparative answers
When comparing groups, use paired contrasts: fish have gills throughout life whereas adult amphibians normally have lungs; reptiles have dry scales whereas amphibians have moist skin. Do not rely on habitat alone, because whales are aquatic mammals and some reptiles spend much time in water.
Practical or data skill
Classify photographs of vertebrates and record the diagnostic evidence. Include one ‘misleading’ example, such as a whale or bat, to show why body structure is more reliable than habitat or movement.
Examination tip
Use features, not lifestyle alone. ‘Lives in water’ does not prove that an animal is a fish.
Review questions and suggested answers
Question 1
State two features of birds.
Suggested answer
Feathers and a beak; they also lay hard-shelled eggs.
Question 2
Why is a whale classified as a mammal?
Suggested answer
It has mammalian features such as mammary glands and hair at some stage, despite living in water.
Question 3
Which vertebrate group usually has moist skin?
Suggested answer
Amphibians.
