Animals: Structure, Life Activity and Classification
Animals are eukaryotic, heterotrophic, motile (at least in some stage) organisms with nervous tissue and, in most, specialised organ systems. Classification: kingdom → phylum → class → order → family → genus → species. Key invertebrate groups: sponges, coelenterates (radial symmetry, two layers, gastrovascular cavity), flatworms, roundworms, annelids (segmented, closed circulation), molluscs (soft body, mantle, shell), arthropods (jointed limbs, exoskeleton; insects, crustaceans, arachnids). Vertebrates: fish, amphibians, reptiles, birds, mammals - distinguished by skin, respiration, circulation, thermoregulation and reproduction.
Understand life activity: nutrition (heterotrophic, digestive systems), respiration (gills, lungs, skin, tracheae), circulation (open in molluscs and arthropods, closed in annelids and vertebrates), excretion, nervous regulation and reproduction (external vs internal fertilisation, oviparity, viviparity, metamorphosis).
Traps
Questions swap open and closed circulation, confuse amphibian and reptile eggs (amphibians need water, reptiles have amniotic eggs), and mislabel arthropods as vertebrates. Also remember insects have tracheae, not lungs.
Rule of thumb
Match the environment to the respiratory organ: water → gills; land → lungs/tracheae; moist skin supplements respiration in amphibians.
Worked example
"Which animal has a closed circulatory system, segmented body and no limbs?" Options: snail, earthworm, spider, frog. The segmented annelid with closed circulation is the earthworm.