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Classification of vertebrates

Your guide: Miss AimanThinks the human body is the best-designed machine in the syllabus.

Classification of vertebrates

A shark, a frog, a snake, a pigeon and a cat all have a backbone.

Let us sort them into five groups.

Five groups, from fish to mammals.

1 · Fishes

Pisces are aquatic vertebrates. The body is streamlined. Breathing is by gills. The heart has two chambers. Blood circulation is single and incomplete.

Jawless fishes: Myxini (hagfish) and Cephalaspidomorphi (lamprey). Jawed fishes: Chondrichthyes (cartilage; sharks, skates) and Osteichthyes (bone; lungfish).

2 · Amphibia and Reptilia

Amphibia: moist skin without scales. Three-chambered heart. Gills in larvae, lungs and skin in adults. External fertilisation. Ectothermic.

Reptilia: first group with the amniotic egg. The egg has amnion, allantois and chorion. Dry scaly skin. Internal fertilisation. Oviparous.

3 · Aves and Mammalia

Aves: feathers, wings, light bones, a bill, a keel on the sternum. Four-chambered heart. Endothermic and homeothermic. Air sacs and a syrinx.

Mammalia: mammary glands and hair. Sebaceous and sweat glands. Pinna and three middle-ear bones. Four-chambered heart and a muscular diaphragm.

Three groups: monotremes (egg-laying: platypus, echidna), marsupials (pouch: kangaroo, opossum), placentals (placenta, viviparous: dolphin, rat, bat, human).

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Notes, short questions and MCQs

Read the full notes: key terms, model answers and MCQs with answers

Classification of vertebrates

A shark, a frog, a snake, a pigeon and a cat all have a backbone.

Let us sort them into five groups.

Five groups, from fish to mammals.

1 · Fishes

Pisces are aquatic vertebrates. The body is streamlined. Breathing is by gills. The heart has two chambers. Blood circulation is single and incomplete.

Jawless fishes: Myxini (hagfish) and Cephalaspidomorphi (lamprey). Jawed fishes: Chondrichthyes (cartilage; sharks, skates) and Osteichthyes (bone; lungfish).

2 · Amphibia and Reptilia

Amphibia: moist skin without scales. Three-chambered heart. Gills in larvae, lungs and skin in adults. External fertilisation. Ectothermic.

Reptilia: first group with the amniotic egg. The egg has amnion, allantois and chorion. Dry scaly skin. Internal fertilisation. Oviparous.

3 · Aves and Mammalia

Aves: feathers, wings, light bones, a bill, a keel on the sternum. Four-chambered heart. Endothermic and homeothermic. Air sacs and a syrinx.

Mammalia: mammary glands and hair. Sebaceous and sweat glands. Pinna and three middle-ear bones. Four-chambered heart and a muscular diaphragm.

Three groups: monotremes (egg-laying: platypus, echidna), marsupials (pouch: kangaroo, opossum), placentals (placenta, viviparous: dolphin, rat, bat, human).

Key terms

Ectotherm
Gets heat from outside.
Endotherm
Makes heat inside the body.
Amniotic egg
An egg with amnion, allantois and chorion.
Placenta
Organ that feeds the foetus and removes its waste.

Short questions with model answers

  1. Q1. Which class first had the amniotic egg? What do the membranes do?

      Reptilia. The membranes protect the embryo from drying out, feed it, and let it develop on land.

    Common mistakes

    • ✗ “Mammals all give birth to live young.”

      ✓ Monotremes lay eggs. The book names the platypus and echidna.

    MCQs

    1. 1. How many heart chambers do amphibians have?

      1. (a) 3
      2. (b) 2
      3. (c) 4
      4. (d) 1
      Show answer

      (a) Two atria and one ventricle.

    2. 2. Which mammals have a pouch?

      1. (a) Marsupials
      2. (b) Monotremes
      3. (c) Placentals
      4. (d) Bats
      Show answer

      (a) Kangaroo and opossum are examples.

    3. 3. Which vertebrate group is endothermic?

      1. (a) Aves
      2. (b) Amphibia
      3. (c) Reptilia
      4. (d) Pisces
      Show answer

      (a) Birds (and mammals) make their own heat.

    4. 4. The skeleton of sharks is:

      1. (a) cartilaginous
      2. (b) bony
      3. (c) made of chitin
      4. (d) absent
      Show answer

      (a) Class Chondrichthyes.

    Quick revision

    • Five groups: fishes, amphibians, reptiles, birds, mammals.
    • Heart chambers: 2, 3, then 4 in birds and mammals.

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