Classification Of Living Things I SS1 Biology Lesson Note

Nature comprises millions of organisms, hence the need for identification, naming and classifying them in a meaningful manner. The present and widely accepted method of classification of organisms was introduced by Carolus Linnaeus. The study of the general principles of classification is called taxonomy or systematic.  

Classification is an arrangement of organisms into groups, each group is then split into smaller groups and the members of each group have certain features in common which distinguish them from other groups. The largest group of organisms is the kingdom.  The arrangement of living organisms from the highest to the lowest (with a decreasing variety of organisms) is as follows:

KINGDOM         

PHYLUM OR DIVISION        

CLASS          

ORDER        

FAMILY       

GENUS       

SPECIES

BINOMIAL NOMENCLATURE

This is the standard system of naming living organisms. Each type of organism is given two names:

The name of the genus (generic name) to which the organism belongs.

The name of the species (specific name) to which it belongs.

The generic name is always written first using an initial capital letter (underlined or italicized) e.g. Homosapiens is man’s scientific name.

MODERN CLASSIFICATION OF LIVING ORGANISMS

All organisms cannot be suitably classified as either plants or animals based on CarolusLinneaus classification. Therefore five kingdoms have been generally accepted for all living organisms, these include Monera, Protista, fungi, plantae and animalia.

 KINGDOM MONERA (Prokaryotes)

This group consists of the simplest living organisms (bacteria, blue-green anabaena).

•  They are microscopic single-celled.
• The cell wall does not contain cellulose. It is made up of protein and fatty materials.
•  They have no definite nucleus. The nucleus lacks nuclear membrane and DNA is scattered in the cytoplasm.
• They lack most cell organelles except the ribosome.
• Reproduction is asexual by binary fission. 

2. KINGDOM PROTISTA

•  They are unicellular organisms.
• The organisms are all eukaryotes i. e. cells have definite nuclei.
•  Most protists are aquatic organisms.
• They move either by cilia, flagella or pseudopodia.
• Some are free-living while few are parasitic. 
• Protists can be broadly divided into two groups;

1. Protozoa: animal-like protists e.g. amoeba, paramecium, plasmodium, trypanosome.
2. Protophyta: Plant-like protists e. g. Diatoms, chlorella, chlamydomonas.

Note: Euglena is a protist with plant and animal-like features.

 KINGDOM FUNGI 

•  They are non-green organisms which do not photosynthesize (lack chlorophyll).
• All fungi except slime moulds are non-motile.
•  They have rigid cell walls made up of chitin and polysaccharides.
• They reproduce asexually by producing spores and sexually as well.
• Most of them are saprophytes while some are parasites.
• They lack true roots, stems and leaves.
• Few are unicellular (yeast) while most are multicellular (rhizopus, mushroom).
•  Multicellular fungi have filamentous bodies that are made up of a network of fine, branching filaments called hyphae (singular: hypha). This mass of hyphae is known as mycelium (plural: mycelia).

KINGDOM PLANTAE

This consists of organisms with cellulose cell walls and chlorophyll for manufacturing their food. It consists of three major phyla i. e thallophyta, bryophyta and tracheophyta. 

 THALLOPHYTA (ALGAE)

 Examples include spirogyra, volvox, sargassum and kelp 

1. These are simple aquatic photosynthetic plants
2. They are non-vascular plants
3. They lack true roots, stems and leaves.
4. They are either unicellular or multicellular and may be green, brown or red.
5. They reproduce asexually (by cell division, fragmentation, spore) or sexually.
6. They exhibit alternation of generation.

 BRYOPHTA

These include hornworts, liverworts and mosses 

1. Bryophytes are multicellular, non vascular plants.
2. They also lack true roots, stems and leaves.
3. They have chlorophyll as the only photosynthetic pigment.
4. They are terrestrial but live in moist places.
5. They produce spores asexually and also reproduce sexually. Hence, they also show a distinct alternation of generation.

 TRACHEOPHYTA

1. They are green multicellular, terrestrial vascular plants i.e. they have tissues for conducting water and food. 
2. They have true roots, stems, and leaves.
3. It is the largest group of plants and can be subdivided into two i. e. pteridophytes and spermatophytes.

 PTERIDOPHYTA (FERNS)

 Examples include Dryopteris, Platycerium, ferns etc

• They are spore-bearing plants.
• They possess well-developed vascular tissues and chlorophyll
• Asexual and sexual reproductive organs are referred to as sori and prothallus respectively
• The stem grows horizontally and is referred to as rhizome

SPERMATOPHYTA

These are seed-bearing plants. They can be grouped into two

• GYMNOSPERMS

 Examples are cycads (whistling pine, fir), conifers and ginkgos

1. Their seeds are borne naked in special structures called cones. They don’t have flowers e.g. conifers, cycads. 
2. These are trees or shrubs with needle, broad or scale-like leaves.

• ANGIOSPERMS 

1. They form the largest group in the plant kingdom and are adapted to almost every kind of habitat. Examples are oil palm trees, water leaves, maize plants etc.
2. They bear true flowers for sexual reproduction.
3. They have more abundant water-conducting vessels than gymnosperms.
4. They bear seeds enclosed in fruits. 
5. They show more specialized and complex reproductive mechanisms involving pollination and fertilization.
6. Angiosperms are grouped into two, monocotyledons and dicotyledons.

 MONOCOTYLEDONOUS PLANTS 

1. Examples include maize, guinea grass, rice, oil palm etc.
2. They have seeds with one seed leaf (cotyledon).
3.  They are generally herbs with scattered vascular bundles in their stem.
4. They have leaves with parallel venation and fibrous root systems.
5. They undergo hypogeal germination (i.e. their cotyledons remain below the ground at germination.)
6. They do not undergo secondary growth.

 DICOTYLEDONOUS PLANTS 

1. Examples include orange, hibiscus plants etc.
2. They are more primitive angiosperms having seeds with two seed leaves
3. They have a tap root system
4. They usually undergo secondary growth
5. The leaves have veins arranged in a branched network
6. They undergo epigeal germination (i.e. the cotyledons are borne above the soil).

KINGDOM ANIMALIA

This consists of multicellular organisms with no cell wall; they have no chloroplasts in their cell therefore they feed heterotrophically. Animals can be classified into two main groups:

1. Invertebrates – animals without backbones. 
2. Vertebrates – animals with backbones.

These two groups can further be divided and subdivided based on body symmetry, body design and body cavity.

1. INVERTEBRATES

 Phylum Porifera (sponges): 

a) They are primitive multicellular, aquatic animals (colonies of cells)

b) They lack true tissues and nervous system

c) Reproduce asexually and sexually (hermaphrodites

 Phylum Coelenterata (Cnidaria: Hydra, jellyfish, sea anemones): 

a) They have two layered bodies surrounding a central hollow cavity called an enteron. 

b) They have tentacles and most of them are marine

c) Possession of stinging cells called nematocysts 

c) There is only one opening called the mouth. d) No anus.

 Phylum Platyhelminthes (Flatworms: Tapeworm, planaria, liver fluke)

a) They have soft, flat, unsegmented elongated bodies

b) They lack body cavities. 

c) They are bilaterally symmetrical and mainly parasites in man and other animals

d) They possess an alimentary canal. No anus

Phylum Nematoda (roundworm, hookworm, guinea worm)

a) They have a thread-like, cylindrical, unsegmented body with no body cavity. 

b) They are bilaterally symmetrical. 

c) They have an alimentary canal with a mouth and anus

d) Some are parasitic, while others are free living 

Phylum Annelida (earthworm, leeches) 

a) They have internal and external segmented bodies which are long and cylindrical. 

b) They have true body cavities (ceoloma). 

c) The appendages (setae) are not jointed

Phylum Mollusca (snail, squid, octopus)

a) They have soft unsegmented bodies

b) Tentacles are present in most members

c) Some have shells e.g snails, squid etc while others have no shells e. g. octopus, slug 

 Phylum Echinodermata (starfish, brittle star, sea lily)

a) They possess tough, spiny and calcareous exoskeletons

b) The head is not usually distinct

c) They are all marine

d) Most of them are stay shaped

e) Examples are brittle stars, starfish, sea urchins, sea lilies etc

 Phylum Arthropoda (the largest group in the animal kingdom) 

a) They have segmented bodies

b) They have exoskeletons made up of chitin

c) Their appendages are jointed. 

d) They have body divisions

e) They are bilaterally symmetrical.

f) They can be subdivided into four classes 

• Insectae. g cockroach, housefly, grasshopper etc.

• Arachnida e.g. spider, scorpion, tick etc.
• Crustaceans e.g. crab, crayfish, prawns etc.
• Myriapoda e.g. centipedes and millipedes.

ASSIGNMENT:

1. Angiosperms and gymnosperms belong to the plant group known as    scizophyta     B. bryophyta     C. pteridophyta     D. spermatophyte

2. Sting cells are normally found in    Flatworms    B. Hydra   C. Snails    D. Paramecium

3. Which of the following are differentiated into true roots, stems and leaves?                              Schizophyta     B. Bryophyta     C. Pteridophyta     D. Algae

4. Each of the following is an arthropod EXCEPT   crab  B. millipede  C. spider  D. snail

5. In which of the following groups of animals are flagella and cilia found    Flatworms     B. Protozoa    C. Nematodes   D. Coelenterates
6. State two distinguishing features of each of the four classes of the phylum Arthropoda

7. In a tabular form, state four differences between monocot and dicot plants