Diversity of Plant Life | What is Classification in Biology

Table of Contents


Earth is perhaps the only planet known to suport life forms. The land, water and air of the planet are inhabited by innumerable organisms. Plethora of organisms occurring on the earth is unique to this planet. The presence of life all over the eath makes it a very special place. These organisms are so varied that each one of them has its own distinciveness. Each form is different from the other in its external appearance, internal structure, metabolism and other characters. Besides this organisms also differ in their habitat, the natural habit, life span, etc. to establish their individuality. The earth has, therefore, inconceivable number Or variants of seemingly similar organisms. Such diversity of life forms within the group and amongst the individuals forms a major fascinating study.

The variety of life forms is referred to as the bio diversity. It is the natural biological wealth 0f the earth. It includes the whole range oi mammals, birds, reptiles, amphibians, fishes, insects and other invertebrates, plants, fungi and
variety of microorganisms such as protists, bacteria and viruses.

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what is classification in science?

Biodiversity is recognized at three levels genetic level, species level and ecosystem level. Genetic diversity is defined as variation in genetic composition of individuals within or among species. Scientists estimate that a unicellular organism has genes ranging between a hundred to few hundreds. The magnitude of genetic diversity
harboured by 13-14 million species is beyond imagination. Genetic differences between the individuals of a species provide the basis for the diversity that is found between species. Although studies in genetic diversity are not yet very widespread and sharply focussed, yet in genetic diversity of some wild crop relatives and domesticated animals have been studied in some detail.

Species diversity pertains to the variety of species. So far 1.7 million species of organisms have been recorded. India’s contribution to this record stands at 7%; it includes 49,000 species of plants and over 81,000 species of animals. As of now, only 70% of the area has been surveyed. Thus the flora and fauna already identified are only part of what actually occur in India. The list is being constantly revised especially in the case of lower plants and invertebrate animals.

What is the meaning of Ecosystem diversity?

Ecosystem diversity

Ecosystem diversity refers to the diversity of ecosystems and habitats. The wide variety in physical features and climatic situations have resulted in a diversity of ecological habitats like forests, grasslands, wet lands, coastal and marine ecosystems, and desert ecosystems. These ecosystems harbour and sustain the immense biodiversity.

Biodiversity is dynamic at all the three levels. The genetic composition of species changes over time in response to natural and human induced selection pressures. Occurrence and relative abundance of species in ecological communities change as a result of ecological and physical factors and ecosystems respond strongly to external dynamics and internal pressures. Ecological systems do not exist as discrete units but represent different parts of a natural continuum.

As per Global Biodiversity Assessment Report (1995) so far 3,92,700 species of flowering and non-flowering plants have been identified in the world. Of these, 49,000 species representing about 12% of the recorded world’s flora have been identified in India. Table 2 shows comparative
number of recorded species.

In the following pages diverse life forms in relation to the habitat, habit and duration of life have been described briefly.

What is Habitat?


Angiosperms occur in a variety of habitats. Plants like Nymphaea lotus (water lily), Nelumbo nucifera (lotus), Utricularia (bladder wort), Pistia stratoites (water lettuce), Wolffia, Lemna (duck weed), Hydrilla, Vallisneria, etc., grow in fresh water ponds and pools. They possess an extensive system of air cavities in roots, stem and leaves and their roots grow well in saturated soil and absorb water from it. These plants are called hydrophytes.

The other extreme are plants like Opuntia, Aloe, Agave, Calotropis, etc., which grow in very dry places. These are known as xerophytes. Unlike hydrophytes, roots of xerophytes are not able to absorb water from saturated soil. In order to survive in dry habitats some xerophytes complete their life-cycle in a very short span of time (often within only few weeks) when the soil is moist. Such xerophytes are called ephemerals Solanum mexicana, Argemone (e.g.,xanthocarpum, Suaeda fruiticosa). During the period of their growth, ephemerals have only as much drought resistance as typical mesophytes. Some other xerophytes accumulate water in their fleshy stems or leaves and are called succulents (e.g, Aloe, Agave, Opuntia). Xerophytes growing on sandy soils are called psammophytes and those on the exposed rocks are called lithophytes.

A vast majority of angiosperms, however,grow in places of moderate water supply; they are known as mesophytes. These plants cannot survive for long either in water saturated or moisture deficient soil. In nature there are forms of plants showing transition among hydrophytes, mesophytes and xerophytes. It is however, possible to observe Some features characteristic of each type.

Besides above, there are some special plants which grow in saline soil with high concentration of salts like NaCl, MgCl2 and MgSO4. Such plants are called halophytes. Most of them grow in salt marshes along coasts and have characteristic called negatively breathing geotropic roots pneumatophores. These commonly inhabit sea-shores and form mangrove vegetation. Some halophytes (eg. Rhizophora mangle) do not absorb salt but actively exclude it form their roots,
while others (e.g., Aleuropus litoralis) take up the
salt and excrete it through their specialized glands.

What is Habit?


Angiosperms show a considerable variation in their habit, i.e., shape, size and form. These characters mainly depend upon the nature of the stem, its branching and height. Plants like Pisum (pea), (gram), Brassica (mustard),Cicer arietinum Zingiber officinale (ginger), Canna, etc., have soft and delicate stems reaching a height of few centimeters or at the most a meter. They are called

What is herbs?


Some plants have profusely branched hard and woody stem, giving a bushy appearance (e.g.China rose, cotton, etc.). These are known as shrubs.Plants like Mangifera indica (mango), Acacia arabica (gum tree), Ficus elastica (India rubber banyan), plant), Ficus benghalensis (great Eucalyptus, etc., have a distinct hard and woody stem which may reach several meters in height. These are called trees.

What is the Duration of Life?

Duration of Life?

Angiosperms differ greatly in their span of life. There are annuals (e.g., rice, wheat, maize, pea, marigold, mustard) with a life-span of few months or at the most a year.

Plants like beet, cabbage, radish, turnip, carrot, etc.. are biennials. They usually remain in vegetative state in the first year and produce flowers and fruits only in the second year. Shrubs and trees are perennials with life-span extending from few to several hundred years. Shorea (sal), Tectona (teak), etc., are known to live for about 100-150 years. Ficus benghalensis (great banyan) in the Indian Botanic Garden (Kolkata) is more than 200 years old and the girth of its main trunk is more than 35 meters.

Eucalyptus is estimated to live for about 300 years. The famous Bodhi tree (Ficus religiosa) at Gaya is about 2500 years old.

Most of the perennials (e.g.. mango, guava,neem) flower and fruit in a particular season each year. They are called polycarpic. Some plants like bamboos are monocarpic; they bear fruits only once in life time and then die.


The size of angiosperms varies from nearly duck microscopic to giant trees. Wolfia punctata (duck weed) is the smallest angiosperm on record with fronds measuring only 1/35 of an inch in length. Montezuma Cypress-Taxodium mucronatum is the thickest known three with a diameter of 11.62 m (38.1 ft).

Coast Redwood of California-Sequoia sempervirens is the tallest tree, that reaches a height of 115.56 m (379.1 ft). Eucalyptus regnans is a tall tree reaching a height upto 99.6 meters.


Most of the angiosperms are autotrophs, i.e., they are green and make their own food. A few derive their nutrition from the stem (e.g., Cuscuta) or roots (e.g. Rafflesia, Orobanche) of the other living plant and are called parasites. Monotropa (Indian pipe) found in the dense forests of Himachal Pradesh, gets food from the dead and decaying organic matter. Such plants are known
as saprophytes.

Many mosses, ferns and orchids (e.g., Vanda) grow on the stems or branches of other plants but do not absorb food from them. These are called epiphytes. They are autotrophic. They obtain carbon dioxide and some moisture from the humid air, and their roots absorb minerals which from the debries, and water Some accumulates in the crevices of the bark on which they grow. The hanging roots of epiphytic orchids have a special tissue called velamen, present just outside the exodermis. Velamen is said to absorb atmospheric moisture.

What is the Importance of Diversity

Importance of Diversity

India is one of the 12 megabiodiversity countries innumerable life forms of theworld. The harboured by its forests, deserts, mountains, other lands, air and oceans provide food, fodder, fuel, medicine, textiles, etc. The synthetic products and processes, often produce harmful effects and chemical drugs etc., cause undesirable side effects. This is compelling people to use the products and processes based on natural resources. Diverse potentially life forms are important for developments in the fields of food, medicines, textiles, energy, recreation and tourism. Although value and potential of some species are already known. yet potenital of innumerable species is yet to be known. It is, thercfore, cssential to not only conserve the species of known value but also species not yet identified and described from economic point of view. Conservation of all elements of biodiversity is essential because of the interdependence of species in nature. A part from the tremendous economic benefits, biodiversity has aesthetic, ethical, cultural, social and scientific importance. Most of the world’s religious texts teach respect for the diversity of life and concern for its conservation.

For the sake of convenience the importance of biodiversity can be classified into two categories direct values and indirect values.

The direct values simply the use of biodiversity in agriculture, medicine and industry.

A study of human history shows that approximately 80,000 edible plants have been used at one time or another, of which only about 150 have been cultivated on large scale. Today a mere 10 to 20 species provide 80 90% food
requirements of the world. Many rural communities in India, particularly the tribals obtain considerable part of their daily food from wild plants. Similarly variety of faunal species, e.g, insects, molluses, spiders, wild herbivores, etc., are consumed by many tribal and non-tribal communities in India. At one time nearly all medicines were derived from biological resources. Even today they remain vital and as much as 67 70%% of modern medicines are derived from natural products. In developing countries, a large majority of the people rely on traditional medicines, most of which involve the use of plant extracts. Around 20,000 plant species are believed to be used medicinally in the third world. In India almost 95% of the prescriptions are plant-based in the traditional systems of Unani, Ayurveda and Sidha.
Plant material is also used for construction activities. Several house-hold items such as ropes, mats, baskets, brooms, furniture, fishing and agricultural implements are made from plant. Diverse habitats and species also have indirect values. These include tourism, recreation and scientific research. Some other examples of indirect values are the ecosystem processes, such as ecosystem’s ability to absorb pollution, maintain soil fertility and micro-climates. Considering the potential value of biodiversity, it is essential to preserve diverse range of habitats, species and genes.

What is the meaning of CLASSIFICATION?


The organisms inhabiting earth though assessed innumerable life forms still remain undiscovered, unidentified and unnamed. There are variety of animals, plants and microbes of different shapes size and structure. According to the estimates of Global Biodiversity Assessment (1995) there are between 13 to 14 million species of organisms on the earth. Genetic diversity harboured by these species is simply beyond imagination. In India so far 89,000 species of animals and 49,000 species of plants have been described by Zoological Survey of India and Botanical Survey of India, respectively. Many of these organisms have become extinct and others are continuously Changing to accommodate themselves in the changed environment.

To study such and enormous diversity abundance of plants and animals, one would naturally feel the necessity of arranging these innumerable forms in groups according to their similarities and dissimilarities. This is known as

Thus classification is the arrangement of organisms into small or large groups/ on the morphological, anatomical,
basis of their cytological and phylogenetic relationships. These groups are then aranged according to their levels
into categories. Similar individuals are grouped under a ‘species’, similar species under a ‘genus, Similar genera under a family’, and so on.

Need of Classification

In a library books on different subjects are kept in different sections or almirahs. In every section/almirah, books of a particular subject (say Hind,English, History, Physics, Botany, Zoology and so on) are arranged topic wise (e.g.. in English section grammer, literature, language, poems,plays, etc). If there are many books on a topic, they may be arranged author find out a particular book in no time even in a very big library. However, if the books have been kept in a haphazard manner, it would be difficult to find out the required book even in a very small library. Just like a library, there is great diversity of organisms in this world. There are millions of plants and animals varying greatly in their form, structure and complexity. It is impossible to study all of them individually. To make the study of organisms possible and convenient, scientists have divided organisms into two major groups animal kingdom and plant kingdom. Each kingdom is divided into many large and small the basis of similarities and categories on differences of organisms. Thus inspite of great diversity amongst organisms, they have been arranged in a very systematic manner and it has made possible to know in detail about each group of plants and animals. For example, all seed plants have been placed in bearing spermatophyta. They have been classified into Gymnospermae (naked seeds) and Angiospermae (covered seeds). Angiospermae have been further classified into Dicotyledonae and Monocotyledonae and each group again into many smaller categories. Similarly animals have been classified into many large and small categories on the basis of their structural and evolutionary characteristics. Just as in a systematically arranged library we can easily find out the required book, in the same way if the organisms are arranged according to a system, it makes their study easy.

What Are The Significance of Classification?

Significance of Classification

  1. Convenience of study. There are millions of animals and plants on the earth and it is impossible to study each one of them. The study of selected organisms of a particular group gives an idea about the remaining organisms of that
    group. For example, study of mango gives the knowledge about all members of dicots.
  2. Knowledge of affinities. The knowledge about relationships or affinities of various groups of organisms comes from classification.
  3. Knowledge of sequence of evolution. Classification gives the sequence of evolution of plants and animals. For example evolution of land plants from aquatic algae could be hypothesized only after plants could be properly classified. For example it is now concluded that angiosperms have evolved from ancestors- like gymnosperms.
  4. Knowledge of connecting links. The transitory stage between two groups of organisms is known as connecting link. It gives the sequence of evolution of organisms. With the help of classification definite position of connecting linksbcan be made clear.
  5. Knowledge of adaptation. By classification we come to know about such characters of organisms which make them
    adaptable to a particular type of environment.
  6. Knowledge of phylogeny. Organisms of one group have evolved from a common ancestor. It is known through classification because this is based on phylogeny.

Basics in Taxonomy

Taxonomy has been described as the theory and practice of classification. Its aim is

(i) to identify the organism,
(ii) to give it a name as per established laws, and
(iii) to assign the organism a definite position in a recognized system of classification. Thus the three main elements of taxonomy are identification, nomenclature and classification.

What are the Identification in Taxonomy?


It is the comparison of an organism with already known organism to determine the similarities and differences in their characteristic features. The comparison is made with a view to establish the identity of the new or unknown organism. For example, if there are three organisms A, B and C, of which A is already identified, it can be used for the identification of B and C by comparing their characters. Suppose B organism shows similarity with ‘A in all major characters, then it can be identified as A’. If C organism shows no or very little similarity with A, then it can be identified as different from A’. Accurate identification of organisms is essential for all types
of scientific studies.


It is the method of assigning correct scientific The names
are given names to organisms. according to international rules set for this purpose. The rules of nomenclature permit only a single valid scientific name for each kind of


It is the arrangement of organisms into groups on the basis of their morphological, anatomical, cytological and phylogenetic relationships. The groups of different kinds are assigned definite categories in a recognized system of classification. The various categories (taxa) used in the systems of classification are species, genus, family, order,
class, division (phylum in zoological classification) and kingdom. The species is the smallest category and kingdom the largest. Each of these categories is also referred to as taxon (pl = taxa).


From time to time different systems of classification of organisms have been adopted.

Two Kingdom System of Classification

Since the time of Aristotle, all living organisms have been classified in two kingdoms–plants and animals, on the basis of differences in form and constitution. These differences exist because of their modes of nutrition. Plants are autotrophs they synthesize the substances needed for their growth and maintenance from inorganic substances. They utilize sunlight as the source of energy and contain light absorbing pigments chlorophylls and carotenoids in the photosynthetically active cells. All plants are characterised by the presence of cell wall outside cell membrane. Most of the plants are fixed to the substratum and move only parts of their body. The body shows branching. In comparison to animals, plants are usually less sensitive to external stimuli and respond slowly.

Animals, on the other hand are heterotrophs. They do not photosynthesize and feed on complex organic subtances obtained from plants and other animals. Compared to plants, animals have a compact body and move about freely whether unicellular (e.g., Amoeba) or multicellular (e.g.fish, elephant, man, etc.). The animal cells are without cell wall. Animals are highly sensitive to external stimuli and show quick repsonse. On the basis of above characteristics, an organism is placed in either of the two
Kingdomsplant kingdom (kingdom Plantae) and the animal kingdom (kingdom Animalia). Plant prokaryotes
(bacteria and kingdom includes cyanobacteria), photosynthetic eukaryotes (all green unicellular and multicellular plants) and some non- photosynthetic eukaryotes (e.g., fungi). The animal Kingdom includes unicellular protozoans and multicellular metazoans.

However, the characteristics assigned to plants are not always present in all cases. For example, cotton-like hyphae of fungi growing on stale bread and mushrooms growing on decaying Wood are colourless. They do not synthesize their food but decompose and absorb organic matter from the substratum. Though fungi lack chlorophyll but are still placed in plant kingdom due to their immobility and spread out appcarance.

Similarly, there aquatic numerous are unicellular and other microscopic organisms present in seas, lakes, ponds and ditches. Some of them are green, yellow, brown or red while others are colourless. A few organisms may also contain ingested remains of other small organisms within them. Likewise, bacteria have a cell wall made of acetyl glucosamine and they absorb their food in solution form. Some bacteria are photosynthetic while others are non-photosynthetic. One would face difficulty in classifying such microorganisms and place them in plant or animal kingdom.

Demerits of Two Kingdom System

The two kingdom system imposes an unnatural division of unicellular organisms into plant and animal kingdoms. Some of the drawbacks of this system are given below.

(1) The two kingdoms are not clearly defined at the lower level of organization.For example, Euglena resembles plants in having chlorophyll and autotrophic mode of nutrition but its motile nature and absence of cell wall makes it animal like. Similarly Chlamydomonas, an alga, has flagella and shows locomotion which animal are characters.
(2) Fungi, which are non-chlorophyllous and heterotrophic, have been included in the plant kingdom.
(3) All prokaryotes have been included in the plant kingdom. Viruses, which lack cell wall, protoplasm and are living only inside the host cell, have been placed in plant kingdom along with bacteria.
(4) The two kingdom system does not take into evolutionary the account relationships between various plant and animal groups.

Thus kingdom two classification is inadequate as it does not provide a suitable place to several organisms of the living world.

To overcome this problem Ernst H. Haeckel of (1886), a German biologist, created a third Copeland kingdom-the Protista. He included all ‘simple forms of life, such as bacteria, many algac,protozoa multicellular fungi and sponges in

Use of electron microscope and biochemical techniques to study the ultrastructure of cells led to the recognition of two general patterns of cellular organization Prokaryotic (Gr. pro primitive; karyon = nucleus) and eukaryotic (Gr.
eu true, karyon= nucleus). In late 1950s H.F Copeland, R. Y. Stanieir, C.B. van Niel andR. H. Whittaker placed bacteria in a separate kingdom of anucleate (lacking cell nucleus) organisms. In 1956, Lynn Margulies and H. F
Copeland proposed a four kingdom system for the classification of prokaryotes and eukaryotes.

  1. Kingdom Monera. All prokaryotes, including true bacteria and blue-green algae.
  2. Kingdom Protoctista. All eukaryotic algae, protozoa and fungi.
  3. Kingdom Plantae: All green plants.
  4. Kingdom Animalia: All animals derived from a zygote (a cell formed by the fusion of an egg and a sperm).

Five Kingdom System of Classification

Robert H. Whittaker proposed a five kingdom system of biological classification in 1969. It is one of the most widely
accepted systems. Whittaker’s system is based on the following three criteria:
(1) Complexity of cell structure, i.e., whether the cell structure is prokaryotic or eukaryotic.
(2) Complexity of the body organization, i.e.,whether the organism is unicellular and simple or multicellular and complex.
(3) Mode of nutrition, i.e., the methods used by organisms to obtain nourishment. It may be autotrophic (photosynthetic) or heterotrophic (ingestion or absorption). Whittaker considered fungi, which acquire
nutrition solely by absorption, sufficiently different
from plants. Therefore, he placed fungi in a separate kingdom. He, in fact, retained the three of the four kingdoms proposed by Margulies and Copeland (Monera, Plantae and Animalia) annimalia) and separated the Protoctista into two kingdom.Protista and Fungi.

A major advantage of Whittaker’s system is the clarity with which it deals with microorganisms. lt places all prokaryotes in the Kingdom Monera and most unicelular simple eukaryotes in the Kingdom Protista.

Explain Kingdom Monera?

Kingdom Monera Definition

(Kingdom of Prokaryotes)

General characters

(1) The Kingdom Monera (also called Kingdom Prokaryotae) consists of all prokaryotic organisms, viz., eubacteria (true bacteria), eyanobacteria and the archaebacteria.
(2) All monerans are unicellular; they lack true nuclei. Other membrane enclosed organellees such mitochondria,
as chloroplasts, lysosomes, etc.,also are absent. Thylakoids are, however, present in photoautotrophs.
(3) Most monerans have a rigid cell wall made of murein, also called peptidoglycan.
(4) The DNA has little or no protein associated with it. Coiled DNA strands lie in the cytoplasmn (without enclosing nuclear membrane). This structure is known as nucleoid.
(5) Flagella, if present, consist of a single thread, made of several identical protein sub-units called flagellin.
(6) Reproduction in the Kingdom Monera occurs mainly by binary fission but may undergo genetic recombination.
(7)Show extreme variation in their mode of nutrition. Most of them are heterotrophs; they absorb their nutrition in the form or solution. The autotrophic forms prepare
their food by reducing carbon dioxide, using either light energy (photoautotrophs) or energy derived from chemical reactions Chemoautotrophs). Besides these,
some cyanobacteria (c.g., Nostoc, Anabaena thrive symbiotically with higher forms of life. A few are parasites.

(8) Some cyanobacteria fix atmospheric nitrogen into nitrogenous compounds that are utilized by other plants. Organisms other than monerans, do not have the ability of fixing atmospheric nitrogen.
(9) Many monerans cause serious diseases in animals, plants and human beings.
(10) Monerans are the important decomposers and mineralisers in the biosphere.

Explain Kingdom Protista

Kingdom Protista Definition

(Kingdom of Unicellular Eukaryotes)

General characters

(1) All protists are unicellular eukaryotes. There are some colonial forms but the cells are not organised into tissues.
(2) The kingdom includes a variety of life forms. For example, among the protists are algae which resemble plants (e.g., diatoms), the protozoa which resemble animals (e.g. Amoeba, Paramecium) and the euglenoids (e.g., Euglena) which have both plant and animal characteristics.
(3) Most of the protists are aquatic organisms and form planktons.
(4) Cell wall, if present, is made of cellulose. Slime molds do not possess cell wall during vegetative phase, but is developed only during the reproductive phase.
(5) The cells are typically eukaryotic havingbmembrane bound organelles like mitochondria,chloroplasts
photosynthetic protists), golgi bodies, endoplasmic reticulum, nucleus, etc.
(6) DNA is associated with histones and shows typical double stranded helical structure. definite organised into
DNA is chromosomes.
(7) Locomotion may be with pseudopodia, cilia or flagella. Flagella show 9+ 2 microtubular which is structure, characteristic of all eukaryotes.
(8) Nutrition in protists is variable. Many of them are floating photosynthetic organismsbwhich form phytoplanktons. Some protists are holozoic, i.e., engulf solid food and eliminate the wastes in various ways. A
few are saprobic or parasitic. Non- photosynthetie free-floating protists, which feed on other protists from zooplanktons.
9) They reproduce both by asexual and sexual methods.
(10) They exhibit two types of life cycles–

(i) life cycles showing zygotic meiosis, and
(ii) those showing genetie meiosis. The forms showing zygotic .meiosis normally live in haploid state and whenever sexual reproduction occurs the haploid cells fuse
to form diploid zygote. The zygote then undergoes meiosis to produce haploid cells. The protists showing genetic meiosis normally live in diploid state and reproduce asexually. Whenever sexual reproduction occurs the diploid vegetative cells divide meiotically to form haploid gametes. Gametes fuse in pairs to form diploid cells.

Explain Kingdom Fungi

Kingdom Fungi Definition

(Kingdom of Multicellular Decomposers)

General characters

(1) Fungi (sing. = fungus) are achlorophyllous spore-bearing, eukaryotic thallophytes. It includes all the fungi of the two kingdom classification except slime molds (they have been included in kingdom Protista).
(2) Fungi occur almost everywhere in nature. They grow in water, soil, air, on food,leather, clothes, optical instruments, etc.They can also be seen on our hair, mouth, eyes and even intestine. The economic losses they cause are out of all proportionbto their size and importance as plants.
(3) They are thalloid (i.e., not differentiated into stem, root and leaves). There is great variation in shape and structure of thallus. They may be minute, microscopic and unicellular (e.g… Saccharomyces, yeast).filamentous (c.g Mucor, Aspergillus,Penicillium) or macroscopic (e.g., mushrooms: Agaricus, morels: Morchella).

  1. Fungal filaments are known as hyphae (sing. hypha) which usually form a network called mycelium. The hyphae are septate or aseptate, if septate the cells are either uninucleate (monokaryotic) or may have two nuclei (dikaryotic). Aseptate;usually coenocytic hyphae are (multinucleate).
  2. The cell wall of most of the fungi is made of chitin, a polysaccharide (also found in the exoskeleton of arthropods such as ticks and spiders).
  3. Fungi are a diverse group of heterotrophs; they include saprophytes (e.g Mucor, Rhizopus), parasites (e.g., Puccinia or rust fungi, Ustilago or smut fungi) or symbionts
  4. All fungi have lysosomal enzymes that (e.g., lichens, mycorrhiza). digest damaged cells and help parasitic
    fungi to invade hosts.
  5. They store excess food material in the form of glycogen (polysaccharide) or oil.
  6. They reproduce by vegetative, asexual and sexual methods. Vegetative reproduction takes place by fragmentation, fission and budding.
  7. Asexual reproduction takes place during unfavourable conditions by various types of motile (zoospores) or non-motile sporesb(e.g, conidia, oidia, chlamydospores, or aplanospores).
  8. Sexual reproduction involves three steps plasmogamy (fusion of protoplasm of two sexually compatible spores, gametes or vegetative cells), karyogamy (fusion of two nuclei brought together by plasmogamy) and meiosis.
  9. Fungi are either homothallic (e.g Puccinia Neurospora tetrasperma,malvacearum) or heterothallic (Aspergillus
    heterothallicus, Erysiphe). The homothallic Species are sexually self-fertile and self- compatible. Thus sexual reproduction can Occur in a colony derived from a single spore. The heterolhallic species has more than one strain of thalli. A single thallus is sexually self-sterile and requires the help of another compatible thallus of different mating type for sexual reproduction. In such fungi sexual reproduction is possible only when mycelia of two different mating types are growing close to each other.
  10. The gametic copulation (fusion of gametes) is either isogamous (when fusing gametes are morphologically similar and motile), anisogamous (fusing gametes are motile but the male gamete is smaller than female gamete) or gamouus (the female gamete is larger and non-motile and the male gamete is smaller and motile).
  11. Some fungi, such as yeasts, are known to have plasmids (extra-chromosomal genetic material).
  12. In ecosystem, fungi are important decomp0sers. They secrete enzymes which are essential for decomposition of lignins and other woody substances.The decomposing quality of fungi is due to
    (i) their ability to penetrate the host,
    (ii) digest and absorb nutrients from host cells.
  13. Fungi excrete metabulic wastes that are toxic to other organisms, especially soil microorganisms. Production of such toxic substances, which are antibiotic, is called antibiosis.
  14. Fungi also cause huge economic losses by infecting and producing diseases in plants and aninmals.

Explain Kingdom Plantae

Kingdom Plantae Definition

(Kindgom of Multicellular Producers)

General characters

(1) It is a kingdom of macroscopic autotrophic plants (called metaphytes). All of them are multicellular and eukaryotic.
(2) Except for some filamentous algae (e.g., show they Spirogyra), Ulothrix, differentiation of tissues.
(3) They have a rigid cell wall made of cellulose. It is present outside the cell membrane. The cells possess plastids and a large central vacuole but centrosome is generally absent from plant cells..
(4) The kingdom includes sea weeds like green, red and brown algae, all thalloid and foliose bryophytes, ferns, conifers and flowering plants (angiosperms).
(5) They are primary producers on land and along sea shores. They also occur in all other types of aquatic habitats (lakes, ponds, streams, etc).
(6) Plants synthesize complex organic molecules from carbon dioxide and water by trapped light utilize energy
and chlorophyll molecules. In this process is liberated (Oxygenic Oxygen photosynthesis).
(7) A few flowering plants show heterotrophic mode of nutrition; they are either partial Loranthus) or complete
(e.g., Viscum, parasites (e.g., Cuscuta, Orobanche).
(8) Some plants are insectivorous; they fulfil their nitrogen requirements by digesting insects.
(9) Reproduction takes place by asexual and sexual methods.
(10) In higher plants multicellular embryo is formed as a result of fertilization.
(11) In lower plants (algae and bryophytes) the gametophyte forms the dominant phase of the life cycle whereas in higher plants (pteridophytes, gymnosperms and angiosperms) thesporophytic phase is and the gametophytes dominant are inconspicuous. The sporophytic and gametophytic phases alternate.
(12) Growth is usually indefinite. It is localized to the meristematic regions only i.e., apical (shoot and root apices), lateral (vascular cambiumn and cork cambium) or intercalary (at the base of leaves and at nodes).
(13) Plants usually show very slow and poor response to stimulus.
(14) Most of the plants remain anchored to the soil by their roots. Therefore they show only movements of curvature or variation.
(15) Food is stored mainly in the form of starch and/or fats.

Explain Kingdom Animalia

Kingdom Animalia Definition

(Kingdom of Multicellular Consumers)

General characters

(1)The Kingdom Animalia includes multicellular heterotrophic organisms (also called metazoa).
(2) Most of the animals show organ-system organization, i.e., the cells form tissues (e.g., epithelial tissue, glandular tissue) various types of tissues form organs (e.g. stomach, intestine, liver), and different organs coordinate to form systems (e.g., digestive system, reproductive system). only cellular animals
(3) A few show organization (e.g., sponges) or tissueorganization (e.g., Hydra).
(4) Animal cells are without cell wall, central vacuole and plastids but possess centrosome.
(5) It includes all the animals of the two kingdom classification, except protozoa. The various groups of organisms includedin the kingdom Animalia are invertebrates (sponges, corals, worms, insects, molluscs, etc.) and vertebrates (fishes, amphibians, reptiles, birds and mammals).
(6) Their principal mode of nutrition is holozoic, i.e., ingestion of food. They are herbivorous (e.g., goat, cow, rabbit).
carnivorous (e.g.. tiger) lion, or omnivorous (e.g., human beings, fish, dog).
(7) Some animals (e.g., worms) are parasites in humans and other animals and absorb readymade food from the cells of their hosts. Some parasites live inside the body their (endoparasites, e.g., host of tapeworms,roundworms) while others live on the surface of the hosts (ectoparasites,e.g., leeches, ticks, mites, etc.).
(8) They generally reproduce by sexual method. Gametes are formed in gonads. Haploid phase is represented only by gametes.
(9) Embryo development takes place after fertilization.
(10) Animals show a quick response to stimulus. They possess nerve cells which conduct the impulses.
(11) Animals can move physically from one place to another and thus are capable of locomotion.
(12) Growth in animals is diffused, i.e., it takes place all over the body. unlike plants there are no well defined growing points in animals.
(13) Some lower animals have power of regeneration.

(14) Ecologically animals are consumers. They form links in different food chains and complex food webs.

Merits and Demerits of Five Kingdom System


(1) The system is more natural because it indicates gradual evolution of early organisms into plants and animals.
(2) Prokaryotes, which differ from all other organisms in cell structure and reproduction, have been placed in a separate kingdom- Monera.
(3) Organisms like Chlamydomonas, Euglena,intermediate or slime molds, etc., are transitional unicellular eukaryotes. Earlier they had been included in both plants and animals. Whittaker included all such intermediate unicellular eukaryotes in a single kingdom-Protista, thus removing the anomaly.
(4) Fungi differ from all other plants in their Hence, biochemistry. physiology and Whittaker wisely placed them in a separate kingdom-Fungi.
(5) The system is based on the complexity of cell structure and body organization, and mode of nutrition. These features evolved very early and became established in life forms existing even today.


(1) The system does not reflect true phylogenetic relationships, particularly in lower forms. For example, some green algae are known to obtain hydrogen from sources other than water like photosynthetic bacteria. But these two groups (i.c., algae and bacteria) have been placed in separate kingdoms.
(2) One anomaly of this system is that the algae have been separated into 3 kingdoms Blue green algae in kingdom Monera, unicellular algae in kingdom Protista and multicellular algae in kingdom Plantae.
(3) Though Whittaker classified organisms on the basis of complexity of cell structure and body organization, and mode of nutrition,kingdom Monera and Protista are, however, still heterogeneous. Both these kingdoms
include walled and wall-less organisms, photosynthetic and non-photosynthetic organisms, and unicellular and filamentous or mycelial forms.
(4) Viruses have not been assigned to any kingdom.

What are the Three Domain Classification System

Robert Whittaker and other earlier workers placed all bacteria in Kingdom Monera or Prokaryotae. This was mainly based on the microscopic observations of the cells. But later studies using modern techniques of biology and
biochemistry revealed that many prokaryotes differ from other taxa of Monera in the characteristics of cell wall, sequence of nucleotides in ribosomal RNA (TRNA), sensitivity to antibiotics and many other features. Therefore, in 1978 Carl Woese, G.E. Fox and others suggested that instead of two cell types (prokaryotic and eukaryotic), there are three cell types eukaryotes and two different types of prokaryotes, viz., eubacteria or eukarya and Archaea. Woese proposed a new taxonomic category, the domain above the level of Kingdom. The domain Eukarya contains all the kingdoms of eukaryotic organisms (i.e., animals, plants, fungi and protists). The traditional kingdom Monera has been divided into two

domains-the domain Eubacteria (eu = true) and the domain Archaea The Archaea exhibit many differences from the Eubacteria (see Table 4). Archaea includes three kingdoms the methanogens, extreme halophiles and extreme thermoacidophiles. The methanogens are strictly anaerobic organisms, having been isolated from such divergent anaerobic environments as waterlogged soils like sediments, marshes, marine sediments and gastrointestinal tract of animals including humans. They produce

methane from carbon dioxide and hydrogen. Extreme halophiles grow in highly saline environments, such as salt lakes, salt evaporation ponds and the surfaces of salt preserved food. They are obligate anaerobes. Extreme thermoacidophiles Occur in unique habitats where bacteria are very rarely found, such as hot springs, geothermally
heated marine sediments and submarine hydrothermal vents. The optimum temperature for the growth of these bacteria usually exceeds 20°C. They are obligate aerobes, facultative aerobes or obligate anaerobes. The characteristics of eubacteria and eukarya are described in appropriate chapters of this book.

Status of Bacteria

Traditionally living organisms are grouped into plant and animal kingdoms. Later, when several micro-organisms with characteristics not strictly resembling with plants and or animals were discovered, the need of a revised classification to accommodate such forms was felt. E. H. Haeekel (1886), therefore, suggested that the living living organisms, instead of two should be divided into three kingdoms-Animalia, Plantae and Protists. He placed bacteria in the Protists along with fungi, algae and protozoa. Copeland (1956) opined that bacteria and blue-green algae are different from other protists, hence he suggested four kingdoms,

instead of three. He placed bacteria and blue-green algae in the fourth kingdom Monera and fungi in the third kingdom Protista. Whittaker (1969) in his five kingdom system also retáined bacteria in Monera on the basis of their prokaryotic organization and fungi in a separate

What is kingdom fungi.

Bacteria show resemblance with plants in many characteristics. They possess a rigid cell wall made of peptidoglycan (also called murein). Some bacteria (e.g., Spirillum, Spirochaete) form filaments similar to algae. Several photosynthetic bacteria (e.g.) use carbon dioxide for the synthesis of their organic food material. They also have the ability to synthesize certain enzymes and vitamins that animals cannot.

Considering structural organization and nutrition of bacteria, it is very reasonable to place them in a separate kingdom of prokaryotes.

Status of Viruses

DmitriIwanowski (1892),Russian a bacteriologist, while studying tobacco mosaic disease believed the infectious agent to be a bacterium small enough to pass through the filter. Later, Martinus Beijerinck, a Dutch botanist observed that the behaviour of this infectious agent was different from that of bacteria. It was American Chemist W. M. Stanley (1935) who carried out the chemical and structural studies of these agents and concluded that these are exceptionally complex aggregation of proteins and nucleic acid. A bit of nucleic acid can generate a like nucleic acid. Thus these organisms may be some properties of life. considered to have Structurally, a virus has a small amount of nucleic acid (RNA or DNA) surrounded by a protective coat of proteins. Since these are inert outside the living host cells, they are not considered to be living. They have no enzymes of their own for metabolism. However, they can regenerate by taking over the command of the mctabolic machinery of an appropriate archaeal, bacterial or eukaryotic host. Thus viruses are obligatory intracellular parasites which essentially require living host cells in order to multiply.


Man has been dependent on plants and animals for food, clothing, shelter and a host of other useful products. Long before the beginning of Christian era, he possessed considerable knowledge useful particularly of plants
organisms, agricultural and medicinal value. Figures of plants carved or painted on tombs by Assyrians and
Egyptians as long ago as 4000 BC are the earliest evidences of man’s knowledge of plants.

A review of Vedic literatures (2500 to 650 BC) that Indians had good reveals no client knowledge of plants and animals. In these literary works there is mention of 740 plants and animals. In Chandyogya Upanishad animals have been classified (viviparous), Andaja into Divaja (oviparous) and Udbhija (minute animals). Vrikshayurveda, compiled by Parasara even before the christian era, is perhaps the first Indian work dealing with plants in a scientific manner. This system of classification seems to be more advanced than those developed in Europe before the 18th century. Parasara’s description of cells (rasakosa), transporting system (syandani) and chlorophyll (ranjakena pacyamanat) shows that he had some kind of lens or mangnifying glass. He classified flowering plants (angiosperms) into Dvimatruka (dicotyledons), and Ekamatruka (monocotyledons). The dicotyledons Were characterised by jalikaparna (leaves with reticulate venation) and monocotytedons with maunlaparna (leaves with parallel venation). Vrikshayurveda also has description of many families(mentioned as ganas) such as Samiganyam (Leguminosae), Svastika-ganiyam (Cruciferae), and Tripusaganyam (Cucurbitaceae). In Susruta Samhita (600 BC), an ancient ayurvedic text, living beings have been classified into Sthavar (immobile, refers to plants), and Jangama (mobile, refers to animals). Plants have been further grouped into Vanaspati., Vrksa. Virudha and Osadhi. Similarly animals have been differentiated into Kulacara, Matsya, Janghala and Guhasaya. In Charak Samhita, which is a later treatise, plants have been classified on the basis of their food value into shook dhanya (cereals), sami dhanya (leguminous plants), shak, phal, harit etc. Greek scholars Hippocrates (460-377 BC) and Aristotle (384-322 BC), known as father of zoology, classified animals into four major groups and Whales.Fishes Birds, Insects, Theophrastus (370-287 BC), an outstanding Greek naturalist, is known as Father of Botany’. In his book Historia Plantarum, the oldest Theophrastus existence, in botanical work described some 500 species of cultivated plants. He classified them into four groups herbs,undershrubs, shrubs and trees. He considered trees to be the most highly developed of all. Pliny (23-79 AD), a Roman naturalist and scholar, mentioned nearly a thousand plants in his Historia Naturalis, a series of thity seven volumes. His studies were largely of encyclopedic nature and each volume dealt with topics such as medicinal properties, timber trees, plant anatomy,
practice of horticulture, etc. John Ray (1628-1705 AD), the son of a British blacksmith, was another great contributor of the Seventeenth century. In his work Historia Generalis Plantarum, produced in three volumes, he described 18,000 plants and animals. He divided the plant kingdom into wo groups,viz., Herbae and Arbores. He was also the first to recognise two major taxa of flowering plants Dicotyledons and Monocotyledons. He also tried to divide plants into several families which he called ‘classes”. He placed 25 classes under dicotyledons and 4 classes under monocotyledons. John Ray was the first to introduce the term species. He used this word for a group of morphologically similar organisms and also tried to differentiate bctween genus and species. It would not be an exagerration to say that eighteenth century belonged to Carolus Linnaeus (1707-1778), a great Swedish naturalist. He studied natural sciences al the Uppsala University. In 1732 the Aecademy of Sciences of Uppsala sponsored Linnaeusbotanical exploration of Lapland. During this exploration he covered about 4800 miles and collected more than 500 specimens. He published the results of this exploration in the form of Flora Lapponica. Later in 1735 he travelled to Netherlands study medicine. It was in to Netherlands where a Dutch botanist J.F. Gronovius financed the publication of his Systema Naturae. In this work he proposed a sexual system for the classification of plants and divided plant kingdom into 24 classes depending on the number and nature of stamens. Later in 1753 he published his Species Plantarum which contained description of some 7300 species and also arrange them according to the sexual characters of the plants. He is rightly called the father of modern botany’. Linnaeus introduced a binomial system of
nomenclature according to which the scientific names of all organisms consist of -two parts the first part called generic name, represents the genus while the second part refers to the name of the species (specific name). For example, the scientific name of human beings is Homo sapiens (Homo = generic name, sapiens = specific name) and that of potato is Solanum tuberosumn (Solanum generic name, uberosum = specific name). Bionomial system of nomenclature is still valid and used throughout the world.

All the of classification systems from Aristotle to Linnaeus were based on limited morphological characters, observable by unaided eye, such as habit of plants (herbs, shrubs, trees) and sexual characters (number of stamens and carpels and their nature). Such systems of classification are called artificial as they are based on few superficial characters. These systems being convenient, became very popular and were in use for several decades. But as artificial systems were based on limited number

many unrelated and diverse of characters, organisms were placed in the same or closely related groups. It led scientists to realize that several natural characters, instead of limited numbers, should be considered while classifying the organisms. Such a procedure would make evident their relationship to each other. It is a fundamental fact of biological science that relationships are present in varying degrees in all living organisms. A system that attempts to show the natural relationship amongst organisms is known as natural system.

Amongst natural systems of classification, Bentham and Hooker’s system is the most popular and is widely used in the herbarias and practical laboratories.

The publication of Darwin’s Origin of Species’ in 1859, completely changed the outlook of taxonomy. Biologists besides using morphological characters, also tried to establish affinity amongst organisms on the basis of evolutionary and genetic relationships. The information is derived from comparative anatomical studies of various organs (e.g., flowers, embryos) and from cytological studies. Although such studies have contributed to a better understanding of relationships amongst various plant groups but many unsolved riddles still exist. It is probably because of many missing links about which information is lacking. This system of classification is known as phylogenetic classification. It is also called cladistics (Latin Clados= branch) because this classification shows evolution from a parent stock along different lines or branches (of phylogenetic tree). Such diagrams are useful but should be received with some reservation as there may be some gaps because of the missing fossil records. This new phase is described as new systematics or biosystematics. Sir Julian Huxley (1940) is the father of new systematics.

Systems of Plant Classification

The plant kingdom thus comprises individuals which are structurally and functionally unlike one another. This diversity is seen amongsts 3,45,000 valid plant species recorded so far. It makes their study difficult. Hence, there arises a need to find out some basic characters to help us to place the plants into related groups. Attempts have been made over the years to arrange these plants according to some orderly system. These systems are called classifications.

The purpose of this chapter is to acquaint the students with a basic arrangement of the plants. Hence, only a few fundamental systems-one orthodox and other comparatively recent have been described.

[I] Classification proposed by A. W. Eichler August Wilhelm Eichler (1839-1887), a Viennese botanist, divided plant kingdom into two sub- groups:

(1)Cryptogamae and (2) Phanerogamae.

This system is one of the earliest to be proposed but still retains its value.

Sub-group I. Cryptogamae
(Kryptos = concealed, gamos = marriage)

All plants without flowers and seeds are included in this sub-group. They reproduce by means of spores. This sub-group includes three divisions
(1) Thallophyta,
(2) Bryophyta and
(3) Pteridophyta.

Division 1. Thallophyta. In general, thallophytes have a plant body that is not clearly differentiated into root, stem and leaves. They do not have well developed conducting tissue and sex organs are simple. Most of them are microscopic. Thallophyta consists of two classes

(1) Algae and (2) Fungi.

Class 1. Algae. Green, autotrophic thallophytes (e.g., Ulothrix, Spirogyra).

Class 2. Fungi. Non-green thallophytes, having heterotrophic (saprophytic or parasitic) mode of nutrition (e. g. Albugo, Mucor, Yeast, Aspergillus).

Division 2. Bryophyta.

The plant body is gametophytic, macroscopic, either thalloid (e.g.Riccia) or foliose (e.g., Funaria). Instead of roots, rhizoids are present. Conducting tissue is either
absent (e.g.. Riccia )or represented by a few thick walled cells (e.g., Funaria). Sex organs are multicellular and jacketed. These plants show regular alternation of two morphologically distinct phases. Embryo is formed.
Bryophyta is divided into two classes

(1) Hepaticae and (2) Musci.

Class 1. Hepaticae (Liverworts). Gametophyte thalloid (e. g., Riccia, Marchantia ).
Class 2. Musci (Mosses). Gametophyte foliose (e.g.Funaria).

Division 3. Pteridophyta.

Plant body is sporophytic, well differentiated into root, stem/rhizome and leaves. Conducting tissue is made of xylem and phloem (herce called vascular Sex cryptogams). They reproduce by spores.
organs are complex like those of bryophytes Embryo is always present. Sporophytic and gametophytic phases are morphologically distinct and show regular alternation. three

Pteridophyta includes following classes

Class 1. Equisetineae
e. g, Equisetum (Horse tail).

Class 2. Lycopodineae
e. g., Lycopodium (Club moss).

Class 3. Filicineae
e. g., Dryopteris (Fern).

Sub group II. Phanerogamae
(Phaneros= visible, gamos = marriage)

All plants included in this sub-group bear flowers
Hence, they are also known as and seeds. Spermatophytes, (sperma = seeds, phyton = plant). Phanerogams have been divided into two divisions
(1) Gymnospermae and
(2) Angiospermae

Division 1. Gymnospermae (Gymnos naked, sperma = seed). This division includes simpler or primitive phanerogams. Flowers are represented by unisexual cones. These are naked- seeded plants. They bear naked ovules (which later develop into seeds) on the surface of megasporophylls. Their seeds are thus not enclosed within the ovary. Gymnosperms are sometimes also called Phanerogams without ovary. The division includes cycads and conifers.

Division 2. Angiospermae (Angeion enclosed, sperma seed). It includes advanced phanerogams. Angiosperms have distinct unisexual or bisexual flowers. Ovules (seeds) are enclosed within the ovary wall (fruit wall). The fruits are
formed as a result of fertilization. Angiospermae includes two classes

Class 1. Monocotyledonae. Seeds possess only one cotyledon; e. g.. wheat, rice.
Class 2. Dicotyledonae. Seeds possess two cotyledons; e.g.. pea, mango.

Classification proposed by H. J. Fuller and Oswald Tippo

The system of classification outlined above is basically artificial and natural only in part. Most phycologists believe that sub-division Algae is an artificial group made of a number of groups which are not closely related. They are of the opinion that the term algae refers to a level of development, or to a mode of life rather than to natural group. Similarly, mycologists believe that the sub-division Fungi is actually made of atleast three unrelated groups-the bacteria, the slime molds and the higher or true fungi. Therefore, the Division Thallophyta is now regarded as a highly unnatural assemblage of unrelated forms.

According to H. J. Fuller and Oswald Tippo particularly comparative morphological, palaeobotanical investigations have tended to break down the distinction between the Pteridophyta and Spermatophyta. The discovery of the fossils of seed ferns (Cycadofilicales) has suggested that the ferns are more nearly allied to the gymnosperms and angiosperms than they are to so-called fern allies -the horsetails and club- mosses.

Based on above findings Fuller and Tippo proposed a natural system of classification. They divided plant kingdom into two sub-kingdoms Thallophyta and Embryophyta. Sub-kingdom Thallophyta included algae and fungi of the older systems and in the sub-kingdom Embryophyta bryophytes, pteridophytes, gymnosperms and angiosperms were included. An outline of Fuller and Tipo’s classification is given below.

“Live like a plant Don’t let your growth be soiled by what’s around you Rise above it and you will sprout into the person of your dreams Turn the bad energy of of others into somehing of substance And never forgel your roots”


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