Unit 1 Classification of kingdom Animalia
Key unit competence: Classify animals into their main groups based on external features.
Key ideas
- Animals are multicellular eukaryotes with no cell wall and no chlorophyll. They are heterotrophs (they feed on ready-made food), most can move from place to place, they respond quickly to stimuli using nerves, and most reproduce sexually.
- Animals are divided into chordates (have a notochord at some stage of life) and non-chordates (no notochord). Most chordates are vertebrates: the notochord is replaced by a backbone (vertebral column).
- Features of all chordates at some stage: a notochord, a dorsal hollow nerve cord, gill slits (pharyngeal slits) and a post-anal tail. The five classes of vertebrates are Pisces, Amphibia, Reptilia, Aves and Mammalia.
- Pisces (fish): live in water, breathe with gills covered by an operculum (bony fish), have scales, fins and a lateral line that detects vibrations, and are poikilothermic (cold-blooded). A streamlined body, a swim bladder and a mucus-covered skin are adaptations to water. Example: tilapia.
- Amphibia: live part of their life in water and part on land; moist, scale-less skin used for gas exchange; tadpoles breathe with gills, adults with lungs and skin; external fertilisation, eggs laid in water; poikilothermic. Examples: frog, toad.
- Reptilia: dry skin with horny scales; lungs; lay eggs with a leathery shell on land; internal fertilisation; poikilothermic. Examples: lizard, snake, crocodile, tortoise, chameleon.
- Aves (birds): feathers, beak without teeth, forelimbs modified as wings, scaly legs, hollow light bones, air sacs, hard-shelled eggs, homeothermic (warm-blooded). Flight adaptations: streamlined body, keel for large flight muscles, light skeleton.
- Mammalia: mammary glands (feed young on milk), hair or fur, external ears (pinnae), a diaphragm, different types of teeth (heterodont: incisors, canines, premolars, molars), homeothermic, internal fertilisation. Subclasses: Prototheria (egg-laying, e.g. platypus), Metatheria (pouched, e.g. kangaroo), Eutheria (placental, e.g. human, cow, goat).
- Arthropoda is the largest phylum: jointed legs, a segmented body, an exoskeleton of chitin (they moult to grow) and an open blood system. Classes: Insecta (3 body parts, 6 legs, 1 pair of antennae, often wings), Arachnida (2 body parts, 8 legs, no antennae: spiders, ticks), Crustacea (2 pairs of antennae, many legs, mostly aquatic: crabs, crayfish), Chilopoda (centipedes, one pair of legs per segment) and Diplopoda (millipedes, two pairs per segment).
- Insect orders include Diptera (one pair of wings, halteres: housefly, mosquito), Coleoptera (hard fore wings: beetles, weevils), Hymenoptera (four membranous wings, narrow waist: bees, wasps, ants), Lepidoptera (scaly wings, coiled proboscis: butterflies, moths) and Dictyoptera (cockroach).
- Other phyla: Platyhelminthes (flat, mouth but no anus: tapeworm, liver fluke), Nematoda (round, unsegmented, tapering ends: Ascaris, hookworm), Annelida (segmented, chaetae: earthworm, leech), Mollusca (soft body, muscular foot, often a shell: snail, octopus), Cnidaria/Coelenterata (radial symmetry, tentacles, one opening: Hydra, jellyfish), Porifera (sponges, pores, no nervous system) and Echinodermata (spiny skin, five-part radial symmetry: starfish).
Common misconceptions
- "A spider is an insect." No: a spider has eight legs and two body parts and no antennae, so it is an arachnid.
- "Bats are birds because they fly." No: bats have fur, mammary glands and external ears, so they are mammals; their wings are skin, not feathers.
- "Whales and dolphins are fish." No: they breathe with lungs, feed young on milk and are warm-blooded, so they are mammals.
- "Cold-blooded animals always have cold blood." No: poikilothermic means body temperature changes with the surroundings; a lizard in the sun can be warm.
Worked examples
Example 1. A learner finds an animal with dry scaly skin, lungs, no legs and eggs with leathery shells. Name its class and give two reasons.
Solution
It is a reptile (class Reptilia), for example a snake. Reasons: dry skin with horny scales, and leathery-shelled eggs laid on land; it also breathes with lungs.
Example 2. Explain how a bird is adapted for flight.
Solution
Forelimbs are wings with feathers; the body is streamlined; bones are hollow and light; a large keel on the breastbone anchors strong flight muscles; air sacs supply plenty of oxygen; there are no teeth, which keeps the head light.
Practice questions
State four general characteristics of animals.
Show answer
Multicellular eukaryotes; no cell wall and no chlorophyll; heterotrophic nutrition; most move from place to place; respond quickly using nerves (and muscles); most reproduce sexually.
Common mistake: Saying all animals have a backbone.
Name the five classes of vertebrates and give one example of each.
Show answer
Pisces (tilapia), Amphibia (frog), Reptilia (lizard/snake), Aves (chicken/eagle), Mammalia (cow/human).
Common mistake: Putting the bat in Aves.
Give three ways in which a fish is adapted to life in water.
Show answer
Streamlined body reduces resistance; gills absorb dissolved oxygen; fins for movement and balance; swim bladder controls buoyancy; lateral line detects vibrations; mucus and overlapping scales reduce friction.
Common mistake: Saying fish breathe air dissolved in the gills without water flow.
State four characteristics of mammals.
Show answer
Mammary glands; hair or fur; external ears (pinnae); diaphragm; different types of teeth; homeothermic; most give birth to live young.
Common mistake: Saying all mammals give birth to live young (monotremes lay eggs).
Give three differences between an insect and a spider.
Show answer
Insect: three body parts, six legs, one pair of antennae, often wings, compound eyes. Spider: two body parts, eight legs, no antennae, no wings, simple eyes.
Common mistake: Counting the spider's pedipalps as antennae.
State two ways in which arthropods are useful and two ways in which they are harmful to humans.
Show answer
Useful: bees pollinate crops and make honey; silkworms make silk; crabs and prawns are food; some insects eat pests. Harmful: mosquitoes spread malaria; ticks spread diseases to cattle; locusts and weevils destroy crops; termites damage wood.
Common mistake: Giving only harmful examples.
Name the phylum of each animal: (a) Ascaris; (b) liver fluke; (c) octopus; (d) starfish.
Show answer
(a) Nematoda; (b) Platyhelminthes; (c) Mollusca; (d) Echinodermata.
Common mistake: Putting the octopus in Cnidaria because of its tentacles.
Explain why classification of animals is important.
Show answer
It makes the huge variety of animals easier to study, helps to identify unknown animals, gives every animal one scientific name understood worldwide, and shows relationships between groups.
Common mistake: Saying classification is only for naming.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The duck-billed platypus is an unusual mammal because it: a. Crustacea 2. Crabs and crayfish belong to the class: b. A notochord 3. Which feature is present in all chordates at some stage of life? c. two pairs of legs on each segment 4. A millipede differs from a centipede because it has: d. lays eggs Show answer
1 → d (lays eggs) · 2 → a (Crustacea) · 3 → b (A notochord) · 4 → c (two pairs of legs on each segment)
- It belongs to the egg-laying Prototheria.
- They have two pairs of antennae and live mostly in water.
- The notochord defines the phylum Chordata.
- Diplopoda means double legs.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
Arthropoda (insects) · feathers · spiracles · Cnidaria (Coelenterata)- A feature found only in birds is .
- Insects breathe through openings called .
- An animal has one opening to its gut, tentacles and radial symmetry. It belongs to .
Show answer
1: feathers · 2: spiracles · 3: Cnidaria (Coelenterata)
- Other animals also have lungs, backbones or eggs.
- Spiracles open into tracheae.
- Hydra and jellyfish have a sac-like gut and tentacles.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The tapeworm belongs to the phylum: a. chitin 2. Animals whose body temperature stays constant are called: b. homeothermic 3. The exoskeleton of arthropods is made of: c. Platyhelminthes 4. Animals obtain their food by: d. feeding on ready-made food (heterotrophs) Show answer
1 → c (Platyhelminthes) · 2 → b (homeothermic) · 3 → a (chitin) · 4 → d (feeding on ready-made food (heterotrophs))
- It is a flatworm.
- Birds and mammals are homeothermic (warm-blooded).
- Chitin is tough and waterproof.
- Animals lack chlorophyll, so they are heterotrophs.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
vibrations and pressure changes in water · internal, inside the female · external, in water · marsupials (Metatheria)- Fertilisation in most frogs is .
- Kangaroos belong to the group of mammals called .
- The lateral line of a fish detects .
Show answer
1: external, in water · 2: marsupials (Metatheria) · 3: vibrations and pressure changes in water
- The male releases sperm over eggs laid in water.
- Their young develop in a pouch.
- It is a sense organ along the side of the body.