General Principles of Classification

  • Classification is the science that puts organisms into distinct groups to make their study easy and systematic.
  • Modern scientific classification is based on structure and functions.
  • Organisms with similar anatomical and morphological characteristics are placed in one group while those with different structures are grouped separately.
  • Modern studies in genetics and cell biochemistry are used to give additional help in classifying organisms.
  • There are seven major taxonomic groups.
  • The kingdom is the largest group.
  • Others are phylum (division for plants) class, order, family, genus and species, the smallest.

Binomial Nomenclature

  • Living organisms are named using Latin or Latinised names.
  • Every organism has two names.
  • This double naming is called binomial nomenclature.
  • This system of naming was devised by Carolus Linnaeus in the 18th Century.
  • The first name is the generic name – the name of the genus.
  • The second name is the name of the species.
  • The generic name starts with a capital letter while that of the species starts with a small letter.
  • The names are written in italics or are underlined in manuscripts.


Bean =Phaseolus vulgaris.

  • Phaseolus is the generic name,
  • vulgaris is specific name.

Dog =Canis familiaris.

  • Canis is the generic name
  • ,familiaris the specific name.

General Characteristics of Kingdoms

Organisms are classified into five kingdoms.

  • Monera,
  • Protoctista,
  • Fungi,
  • Plantae
  • Animalia 

Viruses do not fit neatly into any of the above kingdoms.

  • They are simple and not cellular.
  • They are metabolically inactive outside the host cell.
  • Most of them can be crystallised like chemical molecules.
  • Therefore they do not exhibit the characteristics of living organisms.

Examples of Organisms in Each Kingdom and Their Economic Importance

Kingdom Monera

General Characteristics

  • Unicellular and microscopic
  • Some single cells ,others colonial
  • Nuclear material not enclosed within nuclear membrane-prokaryotic
  • Have cell wall but not of cellulose.
  • Have few organelles which are not membrane bound
  • Mitochondria absent
  • Mostly heterotrophic, feeding saprotrophically or parasitically,some are autotrophic.
  • Reproduction mostly asexual through binary fission
  • Most of them are anaerobes but others are aerobes
  • Most move by flagella

  • Examples include  Escherichia coli, Vibrio cholerae and Clostridium tetani.
  • Spherical known as Cocci.
  • Rod shaped – e.g. Clostridium tetani
  • Spiral shaped  e.g. sprilla
  • Coma shaped- Vibrios -e.g., Vibrio cholerae.


Economic importance of bacteria Benefits to man include:

  • They are used in food processing e.g., Lactobacillus used in processing of cheese, yoghurt.
  • Involved in synthesis of vitamin Band K, in humans and breakdown of cellulose in herbivores.

Genetic Engineering

  • Bacteria are easily cultured and are being used for making antibiotics, aminoacids and enzymes e.g. amylase, and invertase e.g., Escherichia coli.

     Nutrient cycling:

  • Saprophytes
  • They are involved in decomposition of dead organic matter.
  • They are useful in the nitrogen cycle.
  • Nitrogen fixing and nitrifying bacteria.
  • They increase soil fertility.
  • Modem sewage works use bacteria in treatment of sewage.
  • Cleaning oil spills in oceans and lakes.

Harmful Effects

  • Bacteria cause disease:
  • To humans (e.g. Cholera).
  • To animals (e.g. Anthrax).
  • Bacteria cause food spoilage.
  • Others cause food poisoning e.g. Salmonella.
  • Denitrifying bacteria reduce soil fertility e.g., Pseudomonas denitrificans.

Kingdom Protoctista

Examples include ;

  • Algae such as spirogyra, Chlamydomonas, euglena, Sargassum
  • And protozoa such as amoeba, paramecium and Trypanosoma.

General Characteristics

  • They are said to be eukaryotic since their nucleus is bound by a membrane
  • Most are mobile, and use flagella, cilia and pseudopodia.
  • Some are sessile.
  • They reproduce mainly asexually, by binary fission, fragmentation and sporulation.
  • Some reproduce sexually by conjugation.
  • Some are heterotrophic e.g. paramecium.
  • Others are autotrophic e.g. spirogyra.

Economic importance of protoctista

  • Algae are the primary producers in aquatic food chains.
  • They release a lot of oxygen to the atmosphere.
  • Some cause human diseases like malaria and amoebic dysentry ,sleeping sickness
  • Some are source of food for humans e.g. sargassum is a source of iodine
  • Skeletons of diatoms used in paint making.

Spirogyra: They have spiral chloroplast.

  • They are green, thread-like filaments


  • This is a unicellular green algae and has a cup shaped chloroplast.
  • They move towards light using the flagella
  • Cilia assist the organism to move.
  • The shape is due to the presence of a thin flexible pellicle.

Kingdom Fungi

  • Multicellular fungi are made of thread-like structures called hyphae (singular hyphae) that form a mycelium.
  • .e.g.Saccharomyces cereviseae(bread yeast).
  • Others include Penicillium, Rhizopus, and edible mushroom

Economic Importance of Fungi

Beneficial Effects

  • Some fungi are used as food e.g. mushrooms.
  • Some are decomposers which enhance decay to improve soil fertility – recycling of nutrients e.g., toadstools.
  • Some are useful in brewing and bread making e.g., yeast. Yeast is used as food – a rich source of Vitamin B.
  • Some are useful in production of antibiotics e.g., Penicillium griseofulvin.
  • Used in sewage treatment e.g., Fusarium spp.

Harmful Effects

  • Some cause food poisoning by producing toxic compounds e.g. Aspergillus flavus which produces aflatoxins.
  • Some cause food spoilage, fabric and wood spoilage through decomposition.
  • Some cause diseases to humans e.g., athlete’s foot and ringworms.
  • Others cause diseases to plants e.g., potato blight (Irish potatoes) rust in tomatoes and smuts in cereals.


Kingdom Plantae

General Characteristics

  • They are multicellular and eukaryotic.
  • They are photosynthetic and have a pigment chlorophyll.
  • Their cells have cellulose cell walls.
  • They reproduce sexually, others asexually.
  • Kingdom Plantae has three major divisions:
  • Bryophyta,
  • Pteridophyta

Division Bryophyta

These include mosses and liverworts.

  • Plant body is not differentiated into root, stem and leaves.
  • They have simple structures which resemble leaves and stems.
  • They have rhizoids for absorbing water and anchoring the plant to substratum.
  • Life cycle consists of two morphologically different plants, the gametophyte and sporophyte.
  • The two alternate.
  • They show alternation of generations.
  • The gamete producing gametophyte is the persistent plant.
  • The sporophyte is attached to the gametophyte and is nutritionally dependent on it.
  • They lack vascular system.
  • Sexual reproduction is dependent on water.


Division Pteridophyta:

These include ferns and horsetails.

     General Characteristics

  • They have root and shoot system.
  • Leaves are compound known as fronds, they have a vascular system.
  • They show alternation of generations whereby the spore bearing sporophyte is the main plant.
  • Spores are borne in clusters on the underside of leaves making sari.
  • The gametophyte is an independent minute structure called prothallus which is short lived.
  • Sexual reproduction is dependent on water.


Division Spermatophyta

  • These are the seed bearing plants.

General Characteristics

  • Plant body is differentiated into root, stem and leaves.
  • Vascular tissue consists of xylem and phloem.
  • Sexual reproduction is independent of water.
  • Male gametophyte (pollen grain) germinates and grows to reach female gametophyte.
  • They are divided into two sub-divisions:




  • These are cone-bearing plants.
  • Naked seeds.
  • They are trees and shrubs.
  • Xylem consists of tracheids only.
  • Examples; pine, cypress and spruce.
  • They show xerophytic characteristics like having needle-like leaves.



  • Seeds are enclosed within a fruit.
  • They comprise trees, shrubs and herbs.
  • Xylem consists of vessels of tracheids.
  • These are the most advanced plants.
  • Angiosperms has two classes;



Economic Importance of Spermatophyta

  • They are a source of food for humans and other animals.
  • Source of fue1- wood fuel and charcoal.
  • Source of timber for building and for paper.
  • Ornamental plants.
  • Useful in textile industry.


Kingdom Animalia

  • Most animals move from place to place in search of food.

Major phyla are:

  • Platyhelminthes (Tapeworm).
  • Nematoda (Ascaris).
  • Annelida (Earthworm).
  • Mollusca (Snails).
  • Arthropoda
  • chordata


Phylum Arthropoda

Distinguishing Characteristics

  • They have jointed appendages, which are specialised for various functions.
  • Their body is covered by a hardened exoskeleton made of chitin.
  • It is shed at intervals to allow for growth.
  • They have jointed body parts.
  • Most are divided into head, thorax and abdomen.
  • Some have two body parts,

General Characteristics

  • Body is segmented.
  • They have bilateral symmetry.
  • Gaseous exchange is through tracheal system, book lungs or gills which opens to the outside through spiracles.
  • Aquatic forms use gills.
  • Reproduction is mainly sexual.
  • They have an open circulatory system.


Phylum Arthropoda divided into five classes;

  • Crustacea,
  • Arachnida,
  • Chilopoda,
  • Diplopoda
  • Insecta

This division is based on:

  • The number of limbs.
  • Presence and number of antennae.
  • Number of body parts.

Class Crustacea

  • Most of them are aquatic, a few are terrestrial found in moist places e.g., woodlouse.


Distinguishing Characteristics

  • Two body parts head and thorax are fused to form cephalothorax and an abdomen .
  • They have two pairs of antennae; one is small and branched, the other is long.
  • They have five or more parts of limbs.
  • Some of these are modified for other functions e.g., locomotion, feeding and defence.
  • Exoskeleton hardened with deposits of calcium carbonate i.e. carapace.

Other Characteristics

  • Mouthparts include a pair of mandibles and two pairs of maxillae.
  • Gaseous exchange is through gills.
  • They have a pair of compound eyes.
  • Most crustaceans are free-living but a few are parasitic e.g., barnacles.
  • Examples are cray-fish and crab.


Class Arachnida

  • Members are carnivorous and paralyse prey using poison produced from poison claws.

 Distinguishing Characteristics

  • The body has two parts: cephalothorax and abdomen.
  • Cephalothorax is head fused to thorax.
  • A pair of chelicerae, on ventral side of cephalothorax.
  • They have four pairs of walking legs.
  • They have no antennae.
  • Instead they have a pair of short pedipalps which are sensitive to touch.
  • Most arachnids use book lungs for gaseous exchange.
  • Other characteristics include simple eyes.
  • Examples include garden spider, ticks, scorpions.


Class Chilopoda

 e.g. Centipede

Distinguishing Characteristics

  • The body has 2 body parts, a head and trunk.
  • The body is elongate, and has 15 or more segments.
  • Has a pair of legs on each segment.
  • The body is dorso-ventrally flattened.

Other characteristics include:

  • Head has a pair of antennae.
  • Gaseous exchange through tracheal system.
  • Are carnivorous.

Class Diplopoda e.g. Millipede

Distinguishing Characteristics

  • Has two parts: head, short thorax and a trunk .
  • Body elongate with 9-100 segments.
  • Has two pairs of legs on each segment.
  • They have a cylindrical body.
  • Gaseous exchange is by tracheal system.


Other characteristics:

  • Head has a pair of antennae.
  • Are herbivorous.


Class Insecta

Distinguishing Characteristics

  • Body is divided into three body parts head, thorax and abdomen.
  • They have three pairs of legs ..
  • Most insects have a pair or two of wings.

Other characteristics include:

  • A pair of antennae.
  • They breathe through spiracles, and gaseous exchange is through tracheal system.


 The class is divided into several orders based on:

  • Mouth parts- – type e.g. biting or piercing.
  • Position of mouthparts – ventral or anterior.
  • Wings – presence or absence; number of wing types, structure, texture.
  • Size of legs.

Order Orthoptera

  • Have biting and chewing mouthparts.
  • Hind legs longer than other legs e.g. fore wings, leathery and longer than hind legs .
  • g. locusts and grasshoppers .
  • Swarming – locusts are a menace to farmers and the environment as they destroy crops and vegetation.

Order Diptera

  • True flies e.g. houseflies, and mosquitoes have sucking and piercing mouthparts, 1 pair of wings.
  • The second pair is vestigial- acts as balancer.
  • Mouthparts are ventral.
  • These are disease vectors e.g., female anopheles mosquito transmits malaria.


Order Lepidoptera

  • Butterflies and moths have sucking mouthparts,
  • Two pairs of wings covered by scales.
  • This group is important to farmers in pollination.


Order Hymenoptera

  • Bees ,wasps, ants.
  • They have sucking mouthparts, two pairs of wings which are membranous.
  • Some are non-winged e.g. some ants.
  • Bees are important in pollination i.e. in production of honey.

Order Isoptera – Termites

  • They have biting mouthparts which are anterior.
  • Most are wingless,
  • Those with wings they are membranous and of the same size.
  • They are important in nutrient cycling as they feed on cellulose.


Order Coleoptera – Beetles

  • Have biting mouthparts,
  • Two pairs of wings,
  • Fore wing hardened enclosing membranous wings.
  • Destruction of stored grains and legumes (pulses)


Phylum Chordata

  • This name is derived from the term notochord.
  • This is a long flexible rod-like structure.
  • The more familiar chordates are known as vertebrates.
  • In vertebrates the notochord exists only in embryonic stages of development which in later stages is replaced by a vertebral column.

Main Characteristics of Vertebrates

  • Members of the phylum have a notochord in early stages of development.
  • They have visceral clefts – which are slits perforating the body wall at the pharynx.
  • In fish these slits become gills while in higher chordates these slits are only present in embryo.
  • They have a dorsal, hollow nerve cord.
  • It develops into a brain at the anterior and spinal cord at the posterior end.
  • The spinal cord is enclosed within the vertebral column.
  • They have segmented muscle blocks known as myotomes on either side of the body.
  • They possess a post-anal tail although rudimentary in some.
  • They have a closed circulatory system.
  • The heart is ventrally located.
  • They possess an internal skeleton.

   The main classes of phylum chordata are;

  • Pisces,
  • Amphibia,
  • Reptilia,
  • Aves
  • Mammalia.

Class Pisces

  • These are the fishes.
  • Some fish have a skeleton made of cartilage e.g. the shark.
  • Others like Tilapia have a bony skeleton.

     Distinguishing Characteristics

  • They are aquatic.
  • Movement is by means of fins.
  • They have a streamlined body.
  • They have a lateral line for sensitivity.
  • Their heart has two chambers, the auricle and ventricle – simple circulatory system.

  Other Characteristics

  • Their body temperature changes according to the temperature of the environment.
  • They are ectothermic (poikilothermic).
  • Body covered with scales.
  • They have gills for gaseous exchange.
  • Exhibit external fertilisation.

Class Amphibia

  • Larval forms are aquatic while adults are terrestrial.
  • Adults return to water for breeding e.g. frogs, toads, newts, salamanders.

Distinguishing Characteristics

  • Skin is soft and without scales.
  • They have four well developed limbs.
  • The hind limbs are longer and more muscular than forelimbs.
  • The limb can be used for walking, jumping and swimming
  • Gaseous exchange is through the skin, gills and lungs.
  • Middle ear is present.

Other Characteristics

  • They have a three-chambered heart with two atria and one ventricle.
  • Fertilisation is external.
  • They are ectothermic (poikilotherms).


Class Reptilia

  • Examples are snakes, crocodiles, lizards, chameleons, tortoises and turtles.

     Distinguishing Characteristics

  • The skin is dry and is covered by horny scales.
  • Fertilisation is internal.
  • Some species eggs contain a lot of yolk and have either leathery or calcareous shells.
  • They have a double circulatory system.
  • The heart has three chambers – two atria and a partly divided ventricle.
  • However crocodiles have a four chamber heart.


Other Characteristics

  • They are ectothermic (poikilothermic).
  • Have 2 pairs of limbs.
  • They use lungs for gaseous exchange.


Class Aves

  • These are birds.
  • They are terrestrial and arboreal and others are aquatic
  • g. flamingo, goose, ostrich, penguin, hawk, dove.

     Distinguishing Characteristics

  • Body is covered by feathers and legs with horny scales.
  • They have two pairs of limbs.
  • Fore limbs modified to form wings for flight.
  • Hind limbs are for walking or swimming.
  • The mouth is a protruding beak.
  • They have hollow bones.
  • They have double circulation with a four-chambered heart (2 atria, 2 ventricles).
  • They have lungs for gaseous exchange.
  • Lungs are connected to air sacs in bones.
  • Fertilisation is internal.
  • They lay eggs with calcareous brittle shell.
  • They have constant body temperatures hence are homoiotherms (endothermic ).


Class Mammalia

  • They are arboreal e.g. tree-squirrels,
  • Others terrestrial e.g. humans
  • Others are aquatic e.g. dolphins and whales.

    Distinguishing Characteristics

  • They have mammary glands hence name of the class.
  • Body is covered with fur or hair.
  • Their teeth are differentiated into four types (heterodont dentition).
  • They have external ear-pinna.
  • Most have sweat glands.
  • They have a diaphragm that separates the body cavity into thoracic and abdominal.

    Other Characteristics

  • Internal fertilisation – most give birth.
  • They have a double circulatory system with a four-chambered heart.
  • They are endothermic (homoiotherms) .

 Eg   Duck-billed Platypus (egg-laying mammal)

Eg.Kangaroo (pouched mammal)

  • The young are born immature and are nourished in a pouch with milk from mammary glands.

Placental Mammals

  • They give birth to fully developed young ones which are fed on milk from mammary glands.
  • Some are aquatic. e.g. dolphins, whale,
  • Others are flying e.g, bat;
  • Most are terrestrial e.g. rabbits, elephants, buffalo, giraffe, antelope, cow, human being. 

Placental mammals are divided into various orders:

  • Rodentia: e.g. rats, mice – have one pair 9f upper incisors.
  • Insectivora: e.g. mole-they are like rodents:
  • Carnivora: e.g. dog; lion – flesh eaters, they have long pointed canines.
  • Cetacea: e.g. whales and dolphins ­Aquatic mammals. Forelimbs are flippers.
  • Chiroptera: e.g. bats – Forelimbs form wings.
  • Artiodactyla: e.g. antelopes, cattle – they are even toed with split hooves.
  • Perissodactyla: e.g. horse, donkey – they are odd toed with hooves.
  • Proboscidea: e.g. elephant – upper lip and nose elongated to form trunk.
  • Lagomorpha: e.g. rabbit, hare – mammals with upper and lower incisors. Have larger hind legs than forelegs.
  • Primata: e.g. gorilla, orang utang, chimpanzee, monkeys – some are arboreal, with hand and foot for grasping.
  • Human – Homo sapiens – upright gait, opposable thumb hence use of tools.


Construction and Use of Dichotomous Keys

  • Biological keys are sets of statements that act as clues leading to the identification of an organism.
  • By following the keys we can be able to place an organism in its group.
  • The most common key is the dichotomous key.
  • This is a biological tool for identification of unknown organisms.
  • The word dichotomous means branching into two.
  • A single characteristic is considered at a time.
  • Two contrasting statements are put forward to describe the characteristics in such a way as to separate the organisms.
  • This continues until all the organisms have been identified.

Rules Used to Construct a Dichotomous Key

  • Use morphological characteristics as far as possible e.g. type of leaf – simple or compound.
  • Select a single characteristic at a time and identify it by number. 1. Type of leaf. .
  • Use identical forms of words for two contrasting statements e.g.:
  1. Flowers scented.
  2. Flowers not scented.
  • Start with a major characteristic that divide the organisms into two large groups then proceed to lesser variations that would separate the organisms   further into smaller groups.
  • Use positive statements especially the first one.
  • Avoid generalizations e.g. short plants. Be specific in your description e.g.:
  1. plants above 1m tall.
  2. plants below 1m tall.


Some Common Features Used for Identification

In Plants


  1. Type of leaf Leaf

Compound leaves.

Type of venation.

  • Simple leaf
  • Trifoliate
  • Pinnate
  • Type of leaf margin.
  • Type of leaf arrangement on stem.
  • The colour of leaf.
  • The texture of leaf; whether hairy or smooth.
  • Shape of the leaf e.g. palmate.


  • Type of stem – woody or herbaceous.
  • Shape of stem – cylindrical or rectangular.
  • Texture of stem smooth or spiny.


  • Are flowers terminal or lateral
  • For each flower:
  • Is the flower regular or irregular?
  • Number of floral parts for each whorl.
  • Are floral parts free or fused?



  • Type of root system- Taproot or fibrous?
  • Function of the root.

In Animals

Features used to identify animals:

  • Type of mouthparts.
  • Type of skeleton.
  • Presence or absence of antennae.
  • Body segmentation.
  • Body covering: scales, fur, hair or feathers.
  • Number of body parts.
  • Locomotory structures: legs, wings and fins.
  • Presence or absence of vertebral column.
  • Presence and type of eves.


Practical Activities

To examine Bryophyta

  • A mature moss plant is obtained.
  • The specimen is observed using a hand -lens.
  • A labelled drawing showing structures is made: rhizoids, set a capsule, gametophyte, sporophyte ..

To examine Pteridophyta

  • A mature fern plant is obtained.
  • It is observed using a hand lens.
  • Sori can be seen on the lower side of fronds.
  • A labelled drawing showing: frond, pinna, sorus, rhizome and adventitious roots.

To examine Spermatophyta

A mature twig of either cypress or pinus with cones is obtained.

  • Observation of Male and female is made using a hand-lens.
  • The naked seeds are noted.
  • The leaves show xerophytic characteristics e.g. they are rolled, or needle-like.


   A mature bean plant with pods is obtained,

  • Observation of the leaves, stem and roots is made.
  • Leaves are compound, broad arid have network of veins.
  • The Ieaf-has a leaf stalk.
  • They have a tap root system.
  • Floral parts are in five e.g. 5 petals.
  • A bean seed has two cotyledons.

   A mature maize plant is obtained.

  • Observation of the leaves, stems and roots is made.
  • Leaves are simple, narrow and long with parallel veins ..
  • The petiole is modified to form a leaf sheath.
  • They have a-fibrous root system.
  • Floral parts are in threes.
  • A maize gram has one cotyledon,

Examination of Arthropoda

  • Specimens of crayfish, millipede, centipede grasshopper and spider are obtained.
  • Where specimens are not available photographs are used.
  • External features of the specimens are observed.

     The differences in the following are noted:

  • Body parts.
  • Other appendages.
  • Eyes.

 Examination of Chordata

  • The following specimens are obtained:
  • Tilapia, frog, Lizard, bird and rabbit.
  • Using observable features each specimen is placed into its class.

Features used include:

  • Body covering.
  • Limbs.
  • Type of teeth.
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