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.
- 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.
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
- 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.
- Bacteria are easily cultured and are being used for making antibiotics, aminoacids and enzymes e.g. amylase, and invertase e.g., Escherichia coli.
- 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.
- 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.
Examples include ;
- Algae such as spirogyra, Chlamydomonas, euglena, Sargassum
- And protozoa such as amoeba, paramecium and Trypanosoma.
- 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.
- 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
- 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.
- 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.
- 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:
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.
These include ferns and horsetails.
- 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.
- These are the seed bearing plants.
- 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.
- Most animals move from place to place in search of food.
Major phyla are:
- Platyhelminthes (Tapeworm).
- Nematoda (Ascaris).
- Annelida (Earthworm).
- Mollusca (Snails).
- 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,
- 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;
This division is based on:
- The number of limbs.
- Presence and number of antennae.
- Number of body parts.
- Most of them are aquatic, a few are terrestrial found in moist places e.g., woodlouse.
- 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.
- 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.
- Members are carnivorous and paralyse prey using poison produced from poison claws.
- 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.
- 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
- 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.
- Head has a pair of antennae.
- Are herbivorous.
- 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.
- 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)
- 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;
- These are the fishes.
- Some fish have a skeleton made of cartilage e.g. the shark.
- Others like Tilapia have a bony skeleton.
- 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.
- 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.
- Larval forms are aquatic while adults are terrestrial.
- Adults return to water for breeding e.g. frogs, toads, newts, salamanders.
- 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.
- They have a three-chambered heart with two atria and one ventricle.
- Fertilisation is external.
- They are ectothermic (poikilotherms).
- Examples are snakes, crocodiles, lizards, chameleons, tortoises and turtles.
- 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.
- They are ectothermic (poikilothermic).
- Have 2 pairs of limbs.
- They use lungs for gaseous exchange.
- These are birds.
- They are terrestrial and arboreal and others are aquatic
- g. flamingo, goose, ostrich, penguin, hawk, dove.
- 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 ).
- They are arboreal e.g. tree-squirrels,
- Others terrestrial e.g. humans
- Others are aquatic e.g. dolphins and whales.
- 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.
- 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.
- 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.:
- Flowers scented.
- 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.:
- plants above 1m tall.
- plants below 1m tall.
Some Common Features Used for Identification
- Type of leaf Leaf
Type of venation.
- Simple leaf
- 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.
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.
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.
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.
- Type of teeth.