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.
Examples of Binomial Nomenclature
a) Bean =
Phaseolus vulgaris
- Phaseolus is the generic name
- vulgaris is the specific name.
b) Dog =
Canis familiaris
- Canis is the generic name
- familiaris the specific name.
c) Human =
Homo sapiens
d) Potato =
Solanium tuberosum
e) Maize =
Zea mays
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. The reasons are:
- 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.
General characteristics of kingdom
Kingdom Monera
Characteristics of Kingdom Monera
- 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 of Kingdom Monera
- 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.
Importance of Bacteria
- They are used in food processing e.g., Lactobacillus used in processing of cheese, yoghurt.
- Involved in synthesis of vitamin B and 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 by Bacteria
- Bacteria play an essential role of organic matter degradation in nutrient cycling
- Saprophytes (Fungus) are found on dead or decaying organic matter such as decaying tree logs.
- 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.
- Modern sewage works use bacteria in treatment of sewage.
- Cleaning oil spills in oceans and lakes.
Harmful Effects of Bacteria
- 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 Kingdom Protoctista
- Algae such as spirogyra, Chlamydomonas, euglena, Sargassum.
- Protozoa such as amoeba, paramecium and Trypanosoma.
General Characteristics of Kingdom Protoctista
- 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 (Plant that have no stalk. Organisms that stay in one place).
- 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.
Importance of Kingdom 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 dysentery ,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.
Benefits 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.
Harmful Effects of Fungi
- 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
Characteristics Kingdom Plantae
- 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:
Divisions of Kingdom Plantae
- Bryophyta
- Pteridophyta
- Spermatophyta
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 of Division Pteridophyta
- 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 of Division Spermatophyta
- 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
1. 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.
2. 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
Dicotyledonae vs Monocotyledonae
| Dicotyledonae |
Monocotyledonae |
| Embryo has two cotyledons |
Embryo has one cotyledon |
| Leaves are broad and have network of veins |
Leaves are long with parallel veins (have leaf sheath) |
| Transverse section of root has no pith |
Transverse section of root has pith |
| Have tap root system |
Have fibrous root system |
| Cross section of stem reveals vascular bundles arranged in a ring. |
Cross section of stem reveals vascular bundles scattered all over. |
| Vascular cambium present and have secondary growth. |
Vascular cambium absent and do not have secondary growth. |
| Flower parts in four, five or multiples of these |
Flower parts in four, five or multiples of these |
| Examples: herbs e.g. tomato; shrubs e.g. tea, hibiscus, lantana. |
Examples: grass, wheat, sugar-cane. |
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
1. Phylum Arthropoda
Characteristics of Phylum Arthropoda
- 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, 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.
a. Class Crustacea
- Most of them are aquatic, a few are terrestrial found in moist places e.g., woodlouse.
Characteristics of Class Crustacea
- 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.
b. Class Arachnida
- Members are carnivorous and paralyse prey using poison produced from poison claws.
Characteristics of Class Arachnida
- 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.
c. Class Chilopoda
e.g. Centipede
Characteristics of Class Chilopoda
- 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.
- Head has a pair of antennae.
- Gaseous exchange through tracheal system.
- Are carnivorous.
d. Class Diplopoda
e.g. Millipede
Characteristics of Class Diplopoda
- 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.
e. Class Insecta
Characteristics of Class Insecta
- 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.
- 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.
- e.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).
2. 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.
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
a. 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.
Characteristics of Class Pisces
- 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.
b. Class Amphibia
- Larval forms are aquatic while adults are terrestrial.
- Adults return to water for breeding e.g. frogs, toads, newts, salamanders.
Characteristics of Class Amphibia
- 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).
c. Class Reptilia
- Examples are snakes, crocodiles, lizards, chameleons, tortoises and turtles.
Characteristics of Class Reptilia
- 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.
d. Class Aves
- These are birds.
- They are terrestrial and arboreal and others are aquatic.
- e.g. flamingo, goose, ostrich, penguin, hawk, dove.
Characteristics of Class Aves
- 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).
e. Class Mammalia
- They are arboreal e.g. tree-squirrels,
- Others terrestrial e.g. humans .
- Others are aquatic e.g. dolphins and whales.
Characteristics of Class Mammalia
- 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).
Examples of Class Mammalia
- 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 of 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, orangutang, 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.
Common Features Used in Identification of plants
Leaves
Type of 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.
Inflorescence
- 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.
Common Features Used for Identification in Animals
Features used to identify animals include:
- 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 eyes.
