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Natural Sciences�Grade 7

Term 1: Life and Living

Biodiversity

(PPT 4)

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Topic 2 �Biodiversity

Diversity of Animals: Invertebrates

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Invertebrates

  • Animals with no backbones.
  • There are many animals that belong to this group.
  • We will have a look at 2 phyla
    • arthropods
    • molluscs

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Invertebrates: Arthropods

  • All arthropods have jointed legs and an exoskeleton.
  • The exoskeleton contains chitin which makes it strong - it protects the soft tissues on the inside.
  • It provides a framework for muscles to attach to.
  • The body of arthropods are divided into segments.
  • 3 examples of classes of arthropods are insects, arachnids and crustaceans.

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Arthropods: Insects

  • This group is very diverse – more than a million different species have been identified.
  • Examples: beetles, locusts, mosquitoes, bees and ants.
  • Insects are found in nearly all the different environments on the Earth.

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Arthropods: Insects

Insects have –

  • 3 pairs of legs
  • 1 pair of antennae on the head
  • a body that is divided into 3 sections:
    • head with sense organs: eyes, antennae and a mouth
    • thorax with legs and wings
    • abdomen that contains intestines and reproductive organs.

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Arthropods: Insects

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Arthropods: Arachnids

  • Arachnids consist of over 100 000 different species.
  • Examples: spiders, scorpions, harvestmen, ticks and mites

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Arthropods: Arachnids

Arachnids have –

  • 4 pairs of legs
  • no antennae on the head
  • a body that is divided into 2 sections:
    • head and thorax (cephalothorax) which is joined into one section;
    • it carries sense organs, a mouth and legs.

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Arthropods: Arachnids (spider)

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Arthropods: Crustaceans

  • There are about 67 000 different species of crustaceans.
  • Examples: crabs, lobsters, crayfish, shrimp, krill and barnacles.
  • They look very different from each other, even though they belong to the same group.

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Arthropods: Crustaceans

Crustaceans have –

  • 5 or more pairs of legs
  • 2 pairs of antennae on the head
  • a body that is divided into 2 sections, but sometimes also 3 sections

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Arthropods: Crustaceans (crab)

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Invertebrates: Molluscs

  • Molluscs have soft bodies, for example snails.
  • They have a head and a foot region.
  • The body is covered by a hard shell.
  • The large majority of molluscs live in the sea.
  • Molluscs range from species that are

microscopically small to the giant squid.

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Invertebrates: Molluscs (land snail)

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Natural Sciences - Grade 7