CLASSIFICATION II

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 18^th 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.

Examples:

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

Chlamydomonas:

• 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:

Gymnosperms

Angiosperms

Gymnosperms

• 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.

 

Angiosperms

• 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;

Monocotyledonae

Dicotyledonae.

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

Leaves

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.

Stem

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

Infloresence

• 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?

 

Roots

• 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.