VMBO Year 3 · Classification · Section 4.4

Plants and animals

Classifying plants by structure and reproduction

Biologists use plant structure and reproduction to distinguish groups. Many land plants have roots, stems and leaves. Flowering plants also form flowers. Vascular plants have tissues transporting water, minerals and sugars. They include seed plants and seedless vascular plants such as ferns and horsetails.

Seed plants, spore-producing plants and algae

Seed plants reproduce using seeds. They have vascular tissues, roots, stems and leaves. Examples include beech trees and dandelions.

Spore-producing plants reproduce without seeds. Ferns and horsetails have vascular tissues. Mosses also reproduce by spores but lack true vascular tissues and true roots. They therefore do not belong to the vascular plants.

Algae can be single-celled or multicellular. They lack the true roots, stems and leaves of land plants. Depending on the group, reproduction may involve division, spores or sex cells.

Classifying animals by symmetry and skeleton

Symmetry describes how body parts are arranged. In a simplified model:

• Bilateral symmetry: one plane divides the body into corresponding left and right halves, as in humans and beetles.
• Radial symmetry: body parts are arranged around a central axis, as in adult starfish or sea anemones.
• Asymmetry: no plane produces corresponding halves, as in many sponges.

Different skeletons

An exoskeleton is outside the body, such as an insect's outer covering or a snail's shell. An endoskeleton is inside, as in humans. Some animals lack a hard skeleton and use fluid pressure or soft tissues for support.

Seven groups used in this course

• Sponges: usually asymmetrical, attached aquatic animals; supported by fibres, mineral spicules or both.
• Cnidarians: usually radially symmetrical, with tentacles bearing stinging cells; many lack a hard skeleton, although corals form one.
• Worms: an informal grouping of elongated, bilaterally symmetrical animals, generally without a hard skeleton.
• Molluscs: soft-bodied animals, usually based on bilateral symmetry; many have a shell.
• Arthropods: bilaterally symmetrical animals with an exoskeleton and jointed legs.
• Echinoderms: adults usually have radial symmetry and an internal skeleton of calcareous plates; marine animals such as starfish.
• Vertebrates: bilaterally symmetrical animals with an internal skeleton and a backbone.

These are useful school groups, but they do not all represent the same formal taxonomic rank.