ICSE Class 9 Biology Chapter 08 Five Kingdom Classification

Unit-4: Diversity in Living Organisms

Five Kingdom Classification

Syllabus: A brief outline of the five Kingdom classification:

Main characteristics of each kingdom with suitable examples Monera, Protista, Fungi, Plantae (Thallophyta, Bryophyta, Pteridophyta and Spermatophyta), Animalia - (Non-chordates from Porifera to Echinodermata and Chordates-all five Classes).

There are millions of different types of organisms starting from single-celled microorganisms like bacteria to large-sized plants like mango or pine trees and the huge-sized animals like elephants and whales. The range of size is not so surprising but it is the complexity of structure that is most significant (Fig. 8.1).

For studying diversity in living organisms, these are grouped according to the increasing similarity and from the less complex to more and more complex types.

Before we talk of Diversity in Organisms on a broad scale, we should first get familiar with the category levels of diversity, namely: Species, Genus, Family, Order, Class, Phylum and Kingdom.

Let us start with the lowest category i.e., species.

8.1 What is Species?

Species means an organism of a particular kind whose members can interbreed among themselves to produce fertile young ones.

All individuals of a species can normally breed among themselves. Individuals of a particular species differ from all other living beings. All house cats of the world belong to one species; they may have some differences among themselves such as colour, height and the length of tail, yet they can all interbreed. So, the house cat is one species (Felis domesticus). Similarly, there may be quite a few differences in the body features of the people of different countries or races, yet there can be a marriage between them with normal children. So, all mankind today belong to a single species (Homo sapiens). Similarly, all 'peepal' trees, and all mango trees belong to their respective species.

Horse and Donkey are two different species, and both have their numerous breeds. All breeds of a horse and those of a donkey can interbreed among themselves to produce fertile young ones but a cross between a horse and a donkey, though possible, does not produce a fertile "mule".

Mule (A living organism but not a species)

Mule is a cross (hybrid) between a donkey (male) and a mare (female horse). It resembles the male parent (donkey) in the size and shape of ears, legs and hooves, the shape of the tail and the shortness of the mane and is similar to the female parent (horse) in height, shoulder, etc.

Mule is sterile and cannot reproduce. (A cross between a horse (male) and a jenny (female donkey) produces HINNY which also is incapable of breeding)

Humans have been practising producing mules for centuries, but several new types of crosses have been successfully tried in modern times.

Some Other Examples of Crosses Between Two Different Species

Zebra mated with donkey produces "zenkey" with ears and back like those of donkey and striped legs and hips like the zebra. Zenkey is sterile.

Tiger mating with a female lion produces "Tigon" (sterile).

"Geep" is the product of a goat and a sheep, again sterile.

Pomato is a combination that produces potatoes underground and tomatoes above ground, but it produces no seeds.

Such crossing or interbreeding can occur only between two very closely related species, and the offspring are invariably sterile.

8.2 Categories Higher than Species

Genus. Similar species constitute the next higher category called genus (plural: genera). Let us take an example. We have crows around our homes. The hill crow (also called the jungle crow) is different from the crow found on the plains (the house crow) in many features-size, colour, beak, etc. The hill crow and the house crow are two different species (Fig. 10.2). They cannot interbreed; yet they are crows, easily made out from other birds. These two kinds of crows belong to the same genus Corvus.

Family. A group of genera with certain common characteristics form a family. Take an example. Lion (Panthera leo) and tiger (Panthera tigris) are different species but they belong to the same genus. This genus (Panthera) and another genus (Felis) which includes the domestic cat, also share some common characteristics. Therefore, there is the larger cat-family (Felidae) which includes the genus of lion and tiger, and the genus of the domestic cat.

Order. A group of related families make an order. For example, the cat family Felidae (lions, tigers and cats) and the dog family Canidae (dogs, foxes, jackals, etc.) possess some common features and so they make an order. In the example cited here the order is "Carnivora".

Class. Related orders make a class. For example, the orders of different animals like those of dogs, cats, bats, whales, monkeys and even humans, etc., have some common features such as hairy skin and milk-glands. The particular class of the animals mentioned here is "Mammalia".

Phylum. A phylum is the largest division in the classification of plants and animals. Related classes constitute a phylum. For example, the classes of different animals like the mammals, birds, reptiles, frogs, fishes, etc., together constitute the phylum Chordata which have a notochord or a backbone.

Kingdom. The kingdom is the largest division of living beings.

8.3 Drawbacks of the Old Two Kingdom Classification

According to the old classification as was given by Linnaeus (1707-1778) the entire world of living organisms was divided into two kingdoms: Kingdom Plantae (including all plants) and Kingdom Animalia (including all animals). But this scheme had several drawbacks. For example, how do we say that "Bacteria and fungi are plants" - they have no chlorophyll and do not carry out photosynthesis.

Some single-celled organisms such as Euglena cannot be exclusively called plant or animal - they have chloroplasts like the plants, have cell mouth to feed like animals and possess contractile vacuole for excretion.

Bread mould, etc., are multicellular, but they have nothing like roots, stem, and leaves and they do not bear any flowers or seeds and they have no chlorophyll.

So, the above three groups of organisms are now recognised as distinct kingdoms (Monera, Protista and Fungi), and these together with the two other kingdoms, the plants (Plantae) and animals (Animalia), now constitute what is called the Five Kingdom classification, as is given below.

8.4 Five Kingdom Classification

The five kingdoms under the recent scheme of classification are: 1. Monera, 2. Protista, 3. Fungi, 4. Plantae and 5. Animalia.

1. Kingdom Monera (unicellular and prokaryotic) - It mainly includes bacteria (Fig. 8.3), blue-green bacteria and some unicellular algae.

These are single-celled organisms

They have no organized nucleus.

The nuclear material (DNA) is distributed in the cell without being enclosed in a nuclear membrane. This condition of the cell is called prokaryotic (pro: primitive, karyon: nucleus).

They are also devoid of membrane-bound organelles like mitochondria and chloroplasts.

2. Kingdom Protista or more appropriately Protocista. (Unicellular and eukaryotic) - These are single-celled organisms having a well-defined nucleus with a nuclear membrane (eukaryotic). They include both the unicellular green autotrophic organisms (e.g. Chlamydomonas) as well as unicellular non-green heterotrophic organisms (e.g. Euglena, Amoeba, Paramecium) (Fig. 8.4), and also some of their multicellular photosynthetic descendants like Pandorina.

3. Kingdom Fungi (multicellular, eukaryotic and saprophytic) - Most fungi are made up of thread-like hyphae rather than cells, and there are many nuclei distributed in the continuous cytoplasm. Examples: Bread mould, Toadstool, Yeast, Penicillium (Fig. 8.5)

4. Kingdom Plantae (multicellular, eukaryotic and autotrophic) - These are made of many cells (multicellular). They all have chlorophyll and they make their own food by photosynthesis (autotrophic i.e. self nourishing). They include thallophyta (all algae), bryophyta (mosses), pteridophyta (ferns), gymnosperms (pine, etc.), and angiosperms (flowering plants).

Thallophyta: Includes all algae e.g. chlamydomonas, volvox etc. Thallophytes are autotrophic as they contain chlorophyll. They have a thallus like body, i.e. the plant body cannot be distinguished into roots, stem or leaves. They are primarily aquatic.

Bryophyta: e.g. mosses and liverworts plants belonging to this group have a plant body that has false root like structures called rhizoids.

Pteridophytes: Includes all ferns. Plants belonging to this group have a plant body that can be distinguished into root, stem, and leaves. The leaves are often made of leaflets bearing spores on the underside. They are non-flowering plants.

Gymnosperms: e.g. cycas, pine, fir etc. The plants belonging to this group bear naked seeds, i.e. the seeds are not enclosed in fruits. They may be either trees or shrubs. They bear both male and female flowers. They are of two types cycads and conifers.

Angiosperms: Includes all flowering plants. Plants belonging to this group have a highly developed plant body, which can be differentiated into root, stem, leaves, flowers and fruits. The seeds are enclosed in a fruit. They are further divided into monocots and dicots.

Monocots: The plant belonging to this group bear seeds having only one cotyledon, the leaves have parallel venation, and the root system is fibrous, e.g. maize, rice, grass etc.

Dicots: The plants belonging to this group bear seeds with two cotyledons, the leaves have reticulate venation, and a tap root system. e.g. pea, potato, apple, sunflower, rose etc.

5. Kingdom Animalia (Multicellular, eukaryotic and heterotrophic) - These are multicellular organisms without cell wall, without chlorophyll, usually mobile, and obtaining food by eating or sucking, etc. (heterotrophic i.e., differently nourished).

Of all the living organisms we are generally most familiar with plants (Plantae) and animals (Animalia). Therefore, it will be worth understanding the most distinct differences between these two (Table 8.1 page 77).

8.5 Naming an Organism (Extra Information, Useful to Know)

Common names are variable and sometimes confusing. We know animals and plants by the common names used for them in a particular locality. Can you think of any plant or animal which in India is known by several names? Pumpkin and custard apple could be good examples. Pumpkin in the local languages is known as, "sitaphal", "kashiphal", "kumhra," "petha", "kaddu" and so on.

Sometimes, a certain common name is not enough to indicate the particular species. There are different kinds of frogs, earthworms, or grasses. Talking of crows again, if you have to distinguish between the two kinds of crows, you have to use some adjectives such as the hill or jungle crow and

the plain or house crow. But it does not mean that the jungle crow cannot come to the plains and the plain crow cannot go to the hills. What is most important is that these two crows cannot interbreed, and so they are different species.

Scientific names. In science, people from different countries with different languages have to read about each other's research work. So, it was found necessary to eliminate any possible confusion in using local names by substituting them with names specially given in scientific language. The present practice is to use a two part name for each species. For example, our hill crow is Corvus macrorhynchos and the house crow is Corvus splenders. The first part in these names is the genus which is the same "Corvus" for both, and the second part is the name of the particular species of the genus. This method of naming the organisms is called the binomial nomenclature (bi: two, nomen: name), and was first introduced by Linnaeus (1707-1778).

Teacher's Note

Just as your full name (with surname) identifies you uniquely among billions of people, scientific names using genus and species help scientists worldwide communicate precisely about organisms without confusion caused by local language variations.

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