CLASSIFICATION OF LIVING THINGS
The classification of living things based on shared characteristics is called Taxonomy. Taxonomy is the science dealing with the description, identification, naming, and classification of organisms. The modern taxonomic system was developed by a Swedish botanist Carolus Linneaeus (1707-1788) who provided scientists and students a way to sort and group organisms for easier study.
The first classification of living things is the kingdoms. The five kingdoms are:
- Animal Kingdom
- Plant Kingdom
- Fungi Kingdom
- Protist Kingdom
- Moneran Kingdom
Each Kingdom is then split into smaller groups, called Phyla. Each Phylum is split into smaller groups called Classes, each Class is split into Orders, each Order is split into Families, each Family is split into Genera, and each Genus is split into Species. A Species is a single organism, not a group. Some examples of species are Honey Mushroom or White Oak.
Hierarchy of Living Organisms
Sometimes intermediate levels are added, these are usually identified by prefixes such as sub- and super-, e.g. subphylum and superclass.
Meaning of Nomenclature
In science, Nomenclature is the devising or choosing of names for living organisms.
Binomial Nomenclature is used to name an organism, where the first word beginning with a capital is the genus of the organism and the second word beginning with lower-case letter is the species of the organism. For example, the scientific name of the maize plant is Zea mays and that of human is Homo sapiens.
A. Kingdom Monera
The microorganisms in Kingdom Monera are considered as the most ancient living forms on earth. The Kingdom Monera includes organisms that are single-celled. The kingdom is divided into two groups Archaebacteria and Eubacteria. All the organisms of this kingdom are prokaryotes. Prokaryotes are microscopic single-celled organisms that have neither a distinct nucleus with a membrane nor other specialised organelles. These include the bacteria and cyanobacteria. Cyanobacteria are a phylum of bacteria that obtain their energy through photosynthesis.
B. Kingdom Protista
Protists are eukaryotic organisms that cannot be classified as a plant, animal, or fungus. They are mostly unicellular, but some, like algae, are multicellular. Protists are single-celled and usually move by cilia, flagella, or by pseudopodia. There is usually no cell wall, although some forms may have a cell wall. They have organelles including a nucleus (i.e. Eukaryotes) and may have chloroplasts - some are green, others are not. They are small, although many are big enough to be recognised in a dissecting microscope or even with a magnifying glass. Nutrients are acquired by photosynthesis, ingestion of other organisms, or both. It has two main phyla:
- Protozoa–animal like nutrition (heterotrophic) examples are Paramecium, Amoeba etc.
- Algae–plant like nutrition (autotrophic) examples are Spirogyra, Chlamydomonas etc.
C. Kingdom Fungi
Fungi are multicellular, with a cell wall, organelles including a nucleus (eukaryotes), but no chloroplasts. They have no mechanisms for locomotion. Fungi range in size from microscopic to very large (such as mushrooms). Nutrients are acquired by absorption and they acquire nutrients from decaying material. The organisms in kingdom fungi include mushrooms, yeasts, molds, rusts, smuts, puffballs, truffles, morels, and molds.
D. Kingdom Plantae
Plants are multicellular and most of them don’t move, although gametes of some plants move using cilia or flagella. Organelles including nucleus, chloroplasts are present, and cell walls are present. Nutrients are acquired by photosynthesis (they all require sunlight). Plants have four main phyla:
- A) Thallophyta – This is a plant kingdom containing relatively simple plants, i.e. those with no leaves, stems, or roots. It includes the algae, bacteria, fungi, and lichens.
- B) Bryophyta — Bryophyte is a traditional name used to refer to all embryophytes that are non-vascular plants, namely the mosses, hornworts, and liverworts.
- C) Pteridophyta – These are vascular plants that reproduce and disperse via spores. Because they produce neither flowers nor seeds, they are referred to as cryptogams. "Cryptogamae" means hidden reproduction, referring to the fact that no seed is produced, thus cryptogams represent the non-seed bearing plants.
- D) Spermatophyta – These are seed-producing vascular plants. The seed plants are divided into gymnosperms and angiosperms.
- Gymnosperms are plants with naked seeds, they do not bear flowers.
- Angiosperms are flowering plants. The angiosperms are further grouped into dicotyledons and monocotyledons.
Differences between Monocotyledons and Dicotyledons
E. Kingdom Animalia
Animals are multicellular, and move with the aid of cilia, flagella, or muscular organs based on contractile proteins. They have organelles including a nucleus, but no chloroplasts or cell walls. Animals acquire nutrients by ingestion. All animals are motile, meaning they can move spontaneously and independently at some point in their lives. Kingdom Animalia has nine main phyla:
- Porifera (Sponges): are simple aquatic invertebrates that do not move about, but are attached to the rocks.
- Coelenterata: are aquatic animals, i.e. Hydra, Sea anemone, Jelly-fish and coral polyps.
- Platyhelminthes: are parasitic or aquatic animals in human being. It is made up of flatworms such as the planarians, flukes and tapeworms.
- Nematoda: are known as roundworms. Examples are hookworms, filarial worms and threadworms.
- Annelida: are segmented worms with long cylindrical bodies. Examples are earthworm, sea worm and leech.
- Mollusca: are soft unsegmented body organisms with a soft tissue called mantle covering the body. Examples are snails, octopuses, clams and squids.
- Arthropoda: It is the largest phylum in the animal kingdom. It is divided into the following classes:
- Crustacea – example includes crabs, prawns, lobsters and water fleas.
- Insecta – example includes ants, butterflies, beetles, aphids and grasshoppers.
- Miayrpodia – example includes millipedes and centipedes
- Arachnida – example includes spiders, scorpions, mites and ticks.
- Echinodermata : are the spiny-skinned animals. Examples are starfish, sea urchins and sea cucumbers.
- Chordata : are vertebrates ( animals with backbone ). They are divided into five classes :
- Pisces – are the fishes which are all aquatic.
- Amphibia – examples includes the frogs, toads, newts and salamanders.
- Reptilia – example includes the lizards, snakes, crocodiles and turtles.
- Aves – includes all types of birds, both flightless flying birds.
- Mammalia – is made up of the most advanced animals. Examples are rats, dogs, horses, whales and humans.