Classification is the placing of animals and plants in a series of increasingly specialized groups. This is based on their similarities and differences in structure and origin.Classification makes it possible to identify living organisms since similar organisms are grouped together while those which are different are grouped separately. It also makes it easy to study living organisms and even do research.Without classification, it would be difficult to deal with living organism since each organism would be treated as a separate entity. Carolus Linnaeus is credited with coming up with a universal system of classification.
The illustration below shows the major units used in classification of organisms.
State the general characteristics of each of the five kingdoms.
State the main characteristics of phyla Arthropoda, chordata and major divisions of the Kingdom Plantae.
Name the classes of division spermatophyta.
Describe the main characteristics of classes of phyla arthropoda and chordata
Use observable external features to construct simple dichotomous keys of plants and animals
Use already constructed dichotomous keys to identify organisms.
In form one, we covered classification I. We identified the major taxonomic units as: - Kingdom, Phylum/Division, Class, Order, Family, Genus and Species.We also named the five kingdoms as follows: - Monera, Protoctista, Fungi, Plantae and Animalia.The animation below shows the representatives of the five kingdoms that are used in classification of living organisms.
Click on the play button to view the animation.
In classification II we are going to look at the general characteristics of the members of these Kingdoms. We will also cover construction and use of Dichotomous key to identify living organisms.
This kingdom comprises of bacteria and blue green algae.
Their general characteristics are: -
Presence of a cell wall not made up of cellulose.
They are Unicellular and microscopic.
They have few organelles which are not membrane bound.
They are prokaryotic - this means that the nuclear material is not bound by a nuclear membrane.
Movement is by flagellum.
They reproduce asexually by binary fission.
Most respire anaerobically.
The illustration below shows the generalized structure of a bacterium
Members include: amoeba, paramecium, plasmodium, spirogyra, algae, Chlamydomonas and euglena.The animation shows examples of some members of kingdom Protoctista such as euglena, chlamydomonas and spirogyra.
Click on the play button to view the animation.
The illustration below shows the main parts of an amoeba.
Characteristics of members of kingdom Protoctista
Varied body forms: Some are unicellular while others live in colonies. The unicellular include amoeba, paramecium, euglena and chlamydomonas. The multicellular include spirogyras that are also thalloid in nature.
They are eukaryotic that is their nuclear material is bound by a nuclear membrane.
Protoctista has many organelles such as mitochondria, food vacuoles and contractile vacuoles.
Most are mobile, movement propelled by means of pseudopodia, cilia or flagella whereas others are sessile. The lashing of the flagellum in the chlamydomonas and the Euglena causes forward movement. The beating of cilia in the paramecium causes spiral movements.
Click on the play button below to see the movement in amoeba, paramecium and chlamydomonas.
Some of the Protoctista are heterotrophic while others are autotrophic.
Play the animation to see phagocytosis in amoeba.
The mode of reproduction is mainly asexual by fission, Fragmentation or sporulation depending on the species.
In some, specialized structures are used to perform specific functions such as contractile vacuoles for osmoregulation
This kingdom comprises of the mushrooms, toadstools, yeasts, bread moulds and Penicillia which are well known saprophytes. The parasitic ones cause animal and plant diseases such as ringworms in humans and wheat rust, tomato and potato blight in plants.The animation below shows Mushrooms, Bread moulds, yeast and toadstools which are examples of Kingdom Fungi.
Click on the play button to see the organisms .
General characteristics of members of kingdom fungi.
They are eukaryotic.
They lack chloroplasts.
Some are unicellular while others are multicellular. The unicellular ones are the simplest forms for example yeast while the multicellular forms have a basic unit called the hypha.
Hyphae appear as filaments which collectively make up the mycelium.
Fungi reproduce, both asexually and sexually. Asexual reproduction is by spores formation or budding as in yeast whereas sexual reproduction involves fusion of nuclei in hyphal branches.
The illustration below shows mycelium in a rhizopus
The general characteristics of kingdom Plantae are:
Eukaryotic and multicellular
Body differentiated into leaves, stem and roots
Have cells with cellulose cell wall
Have transport system
They are autotrophic
Reproduction is both asexual and sexual
They show alternation of generation
Divisions of the kingdom Plantae are:
Bryophyta for example moss plant
Pteridophyta for example fern plant
Spermatophyta for example maize plant
The following are the photographs of the moss, fern and the maize plants representing the three divisions of kingdom plantae.
Examples are moss and liverworts.
The members have the following general characteristics.
-They are terrestrial green plants which grow in humid or moist surfaces for example on the barks of trees, rocks, wall of buildings among others.
The following photograph shows moss plants growing on rocks and barks of trees.
-They are not differentiated into roots, stem and leaves.
-Instead they have rhizoids for anchoring and absorbing water and dissolved mineral salts.
The illustration shows capsule, seta and rhizoids of a moss plant.
-They show alternation of generations.
-The gametophyte is the gamete producing part and is dominant while the sporophyte is the spore producing part and is born on the gametophyte.
-They are non vascular.
These include the ferns and horsetails. The ferns show a wide variety from the small to giant tree ferns of more than ten metres tall.
A giant fern tree and a dwarf fern tree are shown on the photographs
They have chlorophyll so they can photosynthesis (are autotrophic).
They have roots, stems and leaves but no flowers.
The leaves are called fronds and grow from the stem.
On the illustration, roots, stem and fronds of a fern are shown.
On the lower surface of the fronds they bear spore producing structures called sori.
They posses clearly defined vascular tissue.
They show alternation of generation where the sporophyte is dominant.
Members of this division are the common green plants around us.
The photographs below show pine, palm, coffee, tea, coconut, Nandi flame, jacaranda and maize plants which are examples of members of division spermatophyta.
They are referred to as the seed bearing plants and share the following general characteristics;
1. Plant body differentiated into roots, stems, leaves and seed bearing structures.
The animation shows the different parts of a maize plant highlighting some of its features. Click on the play button to view the animation.
2. Vascular tissue is highly developed with xylem tissue containing both xylem vessels and tracheids.
3. Seeds are produced after fertilization
4. They contain chlorophyll for photosynthesis.
5. Reproduction is sexual and does not depend on water for fusion of gametes.
Sub-divisions of division spermatophyta
Division spermatophyta contains two main Subdivisions; gymnospermaphyta and angiospermaphyta.
Plant members in this group include pine, cyprus, and cedar.
The photographs below show the pine, cyprus and cedar plants.
General characteristics of gymnospermaphyta
Bear cones of two types; male and female cones The male and the female cones are also shown on the photograph below.
Show xerophytic characteristics e.g. rolled leaves, needle shaped leaves, sunken stomata, thick waxy cuiticle.
Xylem tissue which is mainly made of tracheids and phloem does not have companion cells
Seeds are borne on female cones and are not enclosed in a fruit wall (naked seeds)
Classes of Gymnospermaphyta
Sub-division gymnospermaphyta is divided into three main classes.
These are:- 1) Coniferales 2) cycadales and 3) Ginkoales
The photographs show the pine, cycad and ginko biloba which are members of sub - division gymnospermaphyta.
The member plants in this class include pine, cedar and Cyprus General characteristics of the class coniferales include; - Needle shaped leaves - Thick waxy cuticle - Female cones appear on lateral buds on young shoots while male cones are usually small and form clusters around the base of the terminal buds e.g. pinus.
-They have long compound leaves which are clustered at the apex of a thick usually short unbranched stems. -They have cones which are borne at the apex of the trunk among the leaves e.g. cycads
They are rare plants with fan like deciduous leaves. Representatives of this class are the Ginko biloba plant.
Play the animation to see, the needle-like leaves of the pine, the compound leaves of the cycad and the fan like leaves of ginko biloba.
Members include grasses such as bamboo, wheat, oat and maize; shrubs such as lantana camara and hibiscus species. Examples of herbs include black jack, persely and examples of trees are Croton, Eucalyptus species and the Nandi flame.
The photographs below show grasses like bamboo and wheat, shrubs like lantana camara and hibiscus and trees like eucalyptus and Nandi flame.
They have the following general characteristics
They produce flowers
They are Bisexual
They have seeds enclosed by a fruit wall
Their xylem tissues have tracheids and vessels while phloem has companion cells.
Classes of angiospermaphyta
Sub-division angiospermaphyta is divided into two classes i.e. dicotyledonae and monocotyledonae
Class dicotyledonae has the following general characteristics:
-Embryo of the seeds has two cotyledons
- Broad leaves with network of veins
-Have centrally placed star shaped xylem with phloem alternating at the arms of the xylem.
-Has vascular cambium
-Tap root system with a centrally placed xylem alternating with phloem
-Flowers have floral parts in fours or fives or their multiples.
-Have leaf petiole.
The diagram shows various parts of a bean plant (). Phaseolus vulgaris
Examples of class monocotyledonae are bamboo, maize among others.
The members of this class share the following general characteristics
Narrow leaves with parallel veins
Floral parts in threes or multiples of three
Leaf petiole modified to leaf sheath
Vascular bundles in the root are arranged in a ring and lack vascular cambium.
The diagram below shows various parts of a maize plant (Zea mays).
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This is a group of living organisms with distinct characteristics which include;
-They are eukaryotic and multicellular
-No cell wall
-All are heterotrophic
-Most reproduce sexually while a few reproduce asexually
-Most show locomotion but a few are sessile
-Kingdom Animalia is made up of many phyla but in this course, we will learn the characteristics of only two phyla; namely:- Phylum arthropoda and Phylum chordata.
Below are photographs of members of phylum arthropoda (centipede, millipede and grasshoppers) and phylum chordata (frog, lizard, fish, bird and man).
Members of this phylum have segmented bodies, jointed appendages and an exoskeleton.
This phylum is divided into five classes based on;
Number of limbs
Number of body parts
Number of antennae
The classes are: - Crustacea, Chilopoda, Diplopoda, Insecta and Arachnida.
The photographs below show some members of phylum arthropoda; crayfish, centipede and grasshopper.
Click on the play button to view the animation
The main characteristics of the phylum arthropoda include: -
Jointed appendages-some paired and specialized for various functions.
Body covered with hardened exoskeleton made of chitin and is shed off periodically in a process called moulting.
They have segmented bodies.
Body of most members divided into three body parts namely the head, thorax and abdomen some have two body parts with the head and thorax fused to form a cephalothorax and abdomen.
The photographs highlight various features of members of phylum arthropoda.
Members are bilaterally symmetrical.
Have open circulatory system where blood flows in open cavities with a tubular dorsal heart.
Well developed head with eyes, sensory structures and fairly well developed brain.
Gaseous exchange is through the tracheal system though a few aquatic forms use gills
Sexes are separate with reproduction being sexual.
The animation below shows the various characteristics of members of the phylum arthropoda. Click on the play button to view the animation.
The name crustacean is derived from Crusta which means a hardy shiny coat. Members include lobsters, crayfish, shrimps, crabs and water fleas.
The photographs represent some members of class crustacea such as lobsters, crayfish, shrimps, crabs and water fleas.
They share the following characteristics: -
Head fused with thorax to form a cephalothorax.
Covered by a shiny coat the carapace.
Two pairs of antennae
A pair of compound eyes
Three pairs of mouth parts that is open pair mandible and two pairs maxillae
Five to twenty pairs of limbs modified for locomotion, feeding and defense located on cephalothorax and abdomen.
The animation shows the different parts of a crayfish (crustacean).
Play the animation to see the parts.
These are arthropods with a pair of walking legs on each segment. This class is comprised of centipedes.
The illustration below shows the various parts of a centipede
General characteristics of chilopoda are;
Body divided into two parts head and trunk
Body comprising of up to 15 or more segments
A pair of walking legs in each segment
A pair of simple eyes on the head.
A pair of antennae
Posses poison claws on the head which secrete poisonous substances.
Gaseous exchange is through a tracheal system
Have separate sexes.
The animation outlines some of the characteristics of class chilopoda. Play the animation to view the characteristics
This class comprises the millipedes
The illustration below shows the various parts of a millipede
The following are the general characteristics
Diplopods have three body parts, the head short thorax consisting of four segments and a body trunk
The body has numerous segments each bearing two pairs of walking legs except for the first thoracic segment.
The head has a pair of antennae and mandibles
Members have cylindrical body
They have two clumps of many simple eyes
Each body segment has a pair of spiracles for breathing
Millipedes have no poison claws
Play the video to see the movement of a millipede
This class includes, the spiders, scorpions, ticks and mites.
Photographs of a spider, scorpion, tick and a mite which are members of class arachnida are shown below.
They have the following general characteristics.
The body has two parts; the cephalothorax and abdomen
The cephalothorax consists of a fused head and thorax
The ventral side of cephalothorax has two chelicerae each having a claw-like structure which produces poison that paralyses prey.
The cephalothorax has four pairs of walking legs each having seven joints Each leg ends in two toothed claws
Have no antenna.
The cephalothorax commonly has eight simple eyes
Others are parasitic and have specially adapted mouth parts for piecing and sucking blood.
Most arachnids have book lungs for gaseous exchange
Some members are carnivorous and are able to paralyze the prey using the poison produced.
The illustration shows the various parts of members of class arachnida
Examples of members of this class include: Butterfly, grasshopper, termites and cockroach.
Examples of members of class insecta, that is, Butterfly, grasshopper, termite and cockroach are shown in the Photographs below.
The general characteristics of class insect are:
The body is divided into three parts, head, thorax and abdomen.
The thorax is made up of three segments with three pairs of legs.
Some insects have one or two pairs of wings on the thorax.
The head has a pair of antennae, a pair of compound eyes and several simple eyes.
The illustration shows the various parts of members of class insecta.
The mouth parts consist of mandibles, maxillae and labium.
The mouth parts are modified according to their feeding habits. E.g. chewing, piercing and sucking.
The abdomen is made up of eleven or fewer segments with terminal parts modified for reproduction.
They breath through spiracles; gaseous exchange is through the tracheal system.
Excretion is through malphigian tubules, which remove uric acid.
The insects undergo complete or incomplete metamorphosis. In complete metamorphosis The egg hatches into the larva which changes into the pupa and then into the adult. In the incomplete metamorphosis The egg hatches into the larvae which are called the nymph. These grow from the 1st instar 2nd instar 3rd instar and 4th instar. The nymph are similar to the adult but lacks wings and is sexually immature.
Play the animation below to see some of the characteristics of members of this class
This phylum consists of the fish, amphibians, reptiles, birds and mammals.
Below are photographs showing organisms belonging to different classes of phylum chordata.
They include tilapia (fish), frog (amphibians), crocodile (reptiles), domestic fowl (aves) and cow (mammals).
Members of this phylum have the following general characteristics.
Notochord present at some stage in the lifetime which persists in some organisms but changes to vertebral column in higher animals.
Have an endoskeleton made of cartilages and bones
Have a post anal tail
Have a dorsal and hollow nerve cord situated in the vertebral column.
The illustration shows the vertebral column in human
They are bilaterally symmetrical
Have segmented muscle blocks called myotomes on either side of the body.
Have limbs that are formed from more than one body segment e.g. fins in fish, walking legs in frogs and wings in birds
Have a ventrally located heart with closed circulatory system.
Have openings into the pharynx called pharyngeal or visceral clefts at some stage in their life cycle.
Play the animation to see the various characteristics of members of phylum chordata
All members of this class live in water and include tilapia, sharks, Nile perch, Sardines and dolphin.
The photograph shows the various parts of a fish.
They have the following general characteristics
Are all aquatic
Most have their bodies covered with scales
Have gills for gaseous exchange
Have fins for locomotion
Have a streamlined body to facilitate movement in water.
Have a lateral line which acts as a sensory organ
Are poikilothermic / ectothermic.
Reproduce sexually with fertilization being internal.
Play the video to see the role of fins and streamlined body in fish locomotion.
This class comprises of the toads, frogs, salamanders and the newts.
Below are photographs of a toad, frog, salamander and the newt which are members of class amphibia
They spend part of their life in water and land. Adult amphibians go to water for reproduction; and the earlier stages of development take place in water (eggs and tadpoles).
They have the following general characteristics
Soft and moist skin
Four well developed pentadactyl limbs for locomotion
Gaseous exchange occurs through the gills in tadpoles; and lungs, buccal cavity and moist skin in adults
Closed circulatory system
Reproduction is sexual with external fertilization. The females lay eggs in water as the male sprays the eggs with sperm.
Play the video to view the process of reproduction in frogs
The word reptilia come from a word reptilis which means crawl because they move by creeping or crawling. Animals in this class include snakes, turtles, tortoises, crocodiles and lizards.
The photographs of a snake, turtle, tortoise, crocodile and a lizard are shown below.
Main Characteristics include
Have a dry scaly skin which in a tortoise is hardened to form a shell.
Two pairs of limbs except the snake
Fertilization is internal with most laying eggs covered in a leathery shell to reduce desiccation. In a certain species of chameleon the fertilized egg is retained within the oviduct and gives birth to live young ones.
Mostly terrestrial and a few being partially aquatic
Double circulatory system with most members having a three chambered heart; two atria and a partially divided ventricle.
Note: A crocodile has a four chambered heart Well developed lungs for gaseous exchange
They are poikilothermic or ectothermic.
They have an internal auditory meatus
They have lungs for gaseous exchange
They are endothermic
They have a double circulation with a four chambered heart
The illustrations show various characteristics of members of class reptilia.
Four chambered heart
Scaly skin of a snake and snake eggs
Two pairs of limbs of a lizard
Scaly skin of a crocodile
These are birds. They are terrestrial and arboreal while some have adapted to aquatic life. Examples include: Chicken, weaverbird, hawks, eagle and turkeys.
The photographs show some members of class aves which include; Chicken, weaverbird, eagle and vulture.
They have the following general characteristics: -
Body covered with feathers for insulation and flight
They have beaks
The sternum is enlarged to form a keel for attachment of flight muscles
The illustration below shows the skeleton in birds
The hind limbs have scaly skin
The hind limbs are for walking or swimming.
The forelimbs are modified into wings for flight. However some birds cannot fly e.g. ostrich and the emu.
They have an internal auditory meatus.
They have lungs for gaseous exchange
They are endothermic (Homoiothermic).
Fertilization is internal.
They lay yolky eggs with calcareous shells.
They have a double circulation with a four chambered heart.
Click on the play button to see movement of various types of birds.
This class consists of the most advanced forms of animals. Examples include mice, cats, dogs, cattle, gazelles, giraffes, elephants, monkeys and human beings.
Examples of mammals are shown in the photographs below.
They have the following general characteristics
Body covered with fur or hair
Have external ear lobes
Females have mammary glands for milk production.
Have well developed lungs for gaseous exchange
Have a highly developed brain
Have a well developed closed circulatory system with a four chambered heart.
Are Homoiothermic / endothermic.
Have sweat glands
They have muscular diaphragm separating the thoracic and abdominal cavities
The illustrations outline various characteristics of mammals such as four chambered heart and highly developed brain.
Four chambered heart
Highly developed brain
Well developed breathing system
The term dichotomous key comes from a word dichotomy meaning divide in two parts.
A dichotomous key consist of a series of part contrasting statements that describe characteristics of a particular organism. It only uses inheritable observable features.
Common features used for identification of organisms when constructing a dichotomous key are: -
Features used in animals
Number of body parts for example in insects the ant has 3 body parts.
Feeding structures for example beaks in birds and duck.
Presence and type of eyes e.g. millipede simple eyes & housefly compound eyes
Presence & number antennae e.g. one pair of antennae in insects.
Structures on body surface such as fur, hair, feathers and scales.
Locomotory structures for example fins, legs and wings.
The illustrations below outlines the common features used for identification of animals when constructing a dichotomous key.
They include the following: -
Number of body parts, exoskeleton, compound eyes, segments and antennae in arthropods; fins and scale in fish; beaks and feathers in birds and fur or hair in mammals.
Three body parts in insects and beak in birds
Exoskeleton in a crab and endoskeleton in man
Compound eyes in housefly and simple eyes in centipede
Antennae in a butterfly
Fins in fish
Fur in bear and feathers in bird
Features used in Plants.
Leaf venation is either parallel veins or Network veins.
Leaf lamina is either narrow or broad
The tip of the leaf may be pointed as in the bean or could be ovate as in the oxalis or lobbed as in geranium.
Plants root system may be fibrous as in maize or tap root as in bean.
In plants flowers are borne on stems as solitary e.g. hibiscus or in cluster called inflorescence as in the sun flower
In plants may have various stems types e.g. woody stem as in fig tree, Herbaceous stem as in black jack or succulent/ fleshy as in sugar cane.
Most stem are cylindrical but a few may be rectangular e.g. lantana camara.
Leaves may be green e.g. commelina or colored e.g. purple color of tradescantia.
leaves are attached to the stem by either petiole or leaf stalk e.g. cassava leaf or a sheath as in the napier grass.
The following are photographs outlining the main features used in identification of plants:
- Leaf arrangement (alternate or opposite), leaf type (simple or compound), leaf colour (green or not green), leaf venation (parallel or net work), leaf shape (broad or narrow) and leaf margin (serrated or dentate).
Play the animations below to view the common features used in identification of plants.
a) Leaf arragement
b) Compound leaves
c) Leaf colour
d) Leaf venation
e) Leaf shape
f) Leaf margin
g) Leaf attachment to the stem
h) Shape of the leaf tip
i) Plant root systems
j) Flower type ( solitary e.g. hibiscus or inflorescence eg in sun flower)
k) Stems types
l) Rectangular stem of lantana camera.
CONSTRUCTING A DICHOTOMOUS KEY
First step involves looking at the organisms and picking a single distinguishing characteristic that separates the organisms into two groups. Label the two groups as 1a and 1b. Then continue picking a new distinguishing characteristic to separate organism in 1a until each organism has its own separate set of characteristics and is fully identified then repeat the same procedure to1b.
Let us demonstrate how to construct a dichotomous key using the following organisms.
Plants: Tradescantia,Cassia siamea,Zea mays,Beans and Jacaranda.
Animals: Spider, dragon fly, Termite, Millipede and centipede.
The photographs below show plants and animals to be used in the construction of the dichotomous key.
Play the animations to see the identification of living organisms using the dichotomous key.
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