Develop accurate biological vocabulary, explain structure–function relationships, apply ideas to unfamiliar contexts, and use practical evidence.
General arthropod features
Arthropods have a segmented body, jointed appendages and a hard external skeleton. The exoskeleton supports and protects the body but must be shed during growth. The required groups are insects, arachnids, crustaceans and myriapods.
Insects and arachnids
Insects have three body regions, three pairs of legs and one pair of antennae; many have one or two pairs of wings. Arachnids have two main body regions, four pairs of legs and no antennae. Spiders, scorpions and mites are arachnids.
Crustaceans and myriapods
Crustaceans commonly have more than four pairs of legs and two pairs of antennae. Many are aquatic and breathe with gills. Myriapods have many similar body segments and many legs, with one pair of antennae. Centipedes generally have one pair of legs per body segment, while millipedes appear to have two pairs on many segments.
Ferns and flowering plants
Ferns have vascular tissue, true roots, stems and fronds, but reproduce by spores rather than seeds and do not produce flowers. Flowering plants form seeds within ovaries and are divided into monocotyledons and dicotyledons using seed leaves, leaf veins, root systems and flower-part numbers.
Monocot and dicot features
Monocotyledons have one cotyledon, parallel leaf veins, fibrous roots and flower parts usually in multiples of three. Dicotyledons have two cotyledons, branching net-like veins, a tap-root system and flower parts usually in fours or fives. Use more than one feature when a specimen is incomplete.
Practical or data skill
Examine photographs or specimens of arthropods and leaves. Construct a comparison table and then hide the names, using only the features to re-identify each group.
Examination tip
Count pairs of legs carefully. Insects have three pairs; arachnids have four pairs.
Review questions and suggested answers
Question 1
State three features of an insect.
Suggested answer
Three body regions, three pairs of legs and one pair of antennae.
Question 2
How do ferns reproduce?
Suggested answer
By spores.
Question 3
Give one feature that distinguishes a monocotyledon leaf from a dicotyledon leaf.
Suggested answer
Monocot leaves usually have parallel veins; dicot leaves usually have net-like veins.
