Grade 11 Botany Note



Biodiversity:It is the total verity of the life on the earth. Scientist can only guess how many millions of species that exist on the planet. Biodiversity is the variability among living organism in all sources.  In other word, it encompasses the total number, variety and variability of life form, level and combinations existing within the living world. It is not the sum of all ecosystem, species and genetic material. Rather it includes diversity within species, between species and of ecosystem. The biodiversity mainly consist of three categories, they are

1. Ecosystem diversity: An ecosystem comprises a dynamic complex of plant, animal and micro-organism communities and their non-living environment which interact as a functional unit. Thus, ecosystem commonly exists within ecosystems. Ecosystem diversity refers to the variety and frequency of distinct ecosystems including the variety of habitats, biotic communities and their change in composition and structure over time and ecological processes in the biosphere.

2.Species diversity: Species is defined as a population of organism whose members able to interbreed freely under natural conditions. A species represents groups of organisms which has evolved distinct inheritable features and occupies a unique geographical area. Species diversity is used to describe the frequency and variety of species within a geographical area. The total number of species in a globe has been estimated to range from 5 to 30 million.

3. Genetic Diversity: Genes are the principle units of heredity which are passed from an organism to its offspring. These are composed of nucleic acid and are located along an organism’s chromosomes, in the plasmids of bacteria and other extra chromosomal forms as well. Genes, either individually or in groups contribute many different attributes to an organism such as its physical appearance, its ability to resist certain insects, or genes within living organisms, that is, the genetic differences among population of a single species and among individuals within a population.


Scope of Biodiversity:

1. Biological diversity is the main resource on which human beings depend. The existence of human is intimately related with the wide variety of plant and animal species found around us.

2. Biodiversity provides the vast majority of foodstuffs. Many kinds of animals and plants are lived and grow in different climate and geographical conditions. These plants and animals supply lots of food products such as fruits, cereals, nuts, mushroom, honey, meat, mike etc.

3. It is estimated that 80% of people in the developing world depend directly on traditional medicines derived from plants and animals.

4. More than 1500 plants of Nepal have medicinal value.

5. Biological diversity exerts direct influences on regional and local weather patterns.

6. Plant purifies the air and regulates the composition of the atmosphere, recycling oxygen and filtering harmful particles release due to industrial activities.

7. Biodiversity provides various raw materials for textile, leather, tannis, dyes, furniture industries.

8. Biological diversity is the main sources on which human beings depend. The existence of human is intimately related with the wide variety of plant and animal species found around us.


Floral diversity of Nepal:

Nepal comprises only 0.1% of land area on a global scale, but is highly rich on biological diversity. In Nepal , there has been relatively much work done in higher groups of plants, while research on lower groups of plants, in general has not done seriously and systematically. The number of species reported are 465 species of lichens, 1822 species of fungi, 687 species if Algae, 853 species of bryophytes, 380 species of pteridophytes, 28 species of gymnosperm and 5856 species of angiosperms. Nepal has been ranked as the 10th highest in flowering plant diversity in Asia and 27th in the world in biodiversity richness (Shrestha 2001).



Taxonomy (Greek, taxis-arrangement or classification; nomas-law or rules) is the branch of biology that deals with identification, nomenclature and classification of organism. Literally taxonomy is known as the law of classification of the organisms in different groups or kingdom according to their resemblances and differences in outer structure. When limited to plants it is referred as systematic botany.

Identification is determination of unknown organism by comparing with other known organism or by use of taxonomic keys.

Nomenclature is the process of naming identified organism according to nomenclature system.

Classificationis the process of placing identified organism in proper group such as division, class, order, family, genus, and species.

History: The term taxonomy was first given by A.P. de Candle in 1813, which is applied to the process of classification. As the number of organism in surrounding is large, it is necessary to divide them into small groups which can make easier to study about it. The classification is the system of arrangement of organism into groups showing relationship. Biologist from early time made simple attempt to work out a scientist method of classification of organism. Some scientist who contribute in the field of taxonomy are Aristotle (384-322 B.C.), Charaka (1st century A.D.), John Ray(1627-1705 A.D.), Carolus Linnaeus(1707-1778).                                                                                                                                                                                                                            System of classification

Classificationis the process of placing identified organism in proper group such as division, class, order, family, genus, and species. Classification may base on habit of plants, i.e. herbs, shrubs, or tree. The various types of classification put forward from the time of Aristotle to the present day are based on one of the three fundamental types.

1. Artificial system of classification: The classification was mainly based on few characters such as habit, habitat, number of organ etc. e.g. Aristotle system, Theophrastes system.

2. Natural system of classification: the classification was based on natural relationship/structure resemblance among species, e.g. Bentham and hooker system.

3. Phylogenetic System of classification: The classification is based on evolution history and genetic relationship, e.g. Hutchinson System.

Modern trends in taxonomy: This classification is mainly based on disciplines like cytology, genetics, physiology, biochemistry, palenthology. The impact of these disciplines on the modern taxonomy has changed the face of it from classic to modern kind. New classification claims to solve many problems created by classic kind of classification.

Utility of Systematics: It is the scientific study which deals with kinds and diversity of all organisms and the existing relationship amongst them. The knowledge of systematics plays various roles in biology which can be summarized as follows:

1. It can provide the information about plant and animal on the earth.

2. It is helpful to identify the organism whether it is harmful or beneficial for human health.

3. It is helpful in the conservation of beneficial plants and animals.

4. It helps in understanding the chain of evolution.

5. It enables us to identify the newly discovered organism.

Use of keys for identification:

A taxonomy key is a easy way to identify an organism using distinguishing characters. It helps to identify unknown organism by using such keys. It is done in following three ways.

i) by placing specimens of the species classified in museum.

ii) by publishing descriptions and illustration of the species.

iii) By construction taxonomic keys.


Binomial Nomenclature

Binomial nomenclature (called binominal nomenclature or binary nomenclature) is a formal system of naming species of living things by giving each a name composed of two parts. Such a name is called abinomial name (which may be shortened to just "binomial"), a binomen or a scientific name; more informally it is also called a Latin name. The first part of the name identifies the genus to which the species belongs; the second part identifies the species within the genus.

Rules of Binomial Nomenclature:

Because scientific names are unique species identifiers, they ensure that there is never any confusion as to which organism a scientist may be referring. Additionally, there are some important rules that must be followed to keep all binomial names standardized:

1. Each organism consists of generic name and specific name.

2. The entire two-part name must be written in italics (or underlined when handwritten).

2. The genus name is always written first and followed by specific name.

3. The genus name must be capitalized.

4. The specific epithet is never capitalized.

5. The mane of the author who first indentifie the specific must be written after specific name in short or full name.

6. The scitific name can be taken from place, personality, utility, or any other characterstics, e.g. Mangifera indica, Citrus sinensis etc.



Advantage of scientific name:

a) Scientific name are universal.

b) Each organism consists of only one scientific name but many local names.

c) Scientific name help to provide information about genus, species, family etc.

Taxonomic categories and Hierarchy

The obligate taxonomy categories as kingdom, division, class, order, family, genus, and species.

The sequence of taxonomic categories in classification is taxonomical hierarchy.

Kingdom: Plantae

Division: Angiosperm

Class: Dicotyledons

Order: rosales

Family: rosaceae

Genus: Rosa

Species: indica


Species: It is the group of individual which are similar in all aspects and interbreed freely with each other to produce fertile offsprings, e.g Brassica compestris

Genus: The group of closely related species.e.g. Brassica compestris

Family: The group of closely related genus.

Order: The group of closely related family, e.g. Rosales and Malaes.

Class: The proup of closely related order, e.g. Dicotyledonae.

Division: The group of closely related class, e.g. Angiosperm.

Kingdom: The group of closely related Division, e.g. Plantae.


Arrangement of taxonomic categories in their proper order on the basis of their taxonomic ranks is called Hierarchy.Biological classification, or scientific classification in biology, is a method of scientific taxonomy used to group and categorize organisms hierarchically. Rank-based systems use a fixed number of levels in the hierarchy, such as kingdom, family, genus or species. Rank less systems use an arbitrary number of levels. The groups in the classification are known as taxa (singular: taxon).




































Two kingdoms System: the two kingdom system was proposed by Carolos Linnaeus. The two kingdoms are plantae and animalia. He classified two kingdome on the basis of following characters.


Presence of cell wall.


Absence of locomotion.

 Absence of nervous system.



Absence of cell wall.


Presence of locomotion

Presence of nervous system, .e.g. higher animal, protozoa, bacteria.


Limitation of two kingdom systems.

It kept prokaryotes with eukaryotes in same kingdom.

Unicellular and multicellular were kept in same kingdom.

It kept non-photosynthetic fungi with plant.

It is unable to classify virus.

Bacteria couldn’t be classified in both kingdoms.

Lichen is duel organism which show different character kept in Plantae.

Euglena Which show both autotrophic and heterotrophic mode of nutrition, kept in both kingdoms.

Slime mould, a unicellular organism lack cell wall in vegetative stage but present in reproductive stage but kept in both kingdom.



Five kingdoms System: The five kingdom system was purposed by Robert Whitakar in 1969. He classified five kingdoms on the basis of following criteria.

a. complexity of cell: Prokaryotic or eukaryotic.

b. Complexity of organism’s Body: Unicellular or multicellular.

c. Mode of nutrition: autotrophic or heterotrophic.


The five kingdoms are

A) Monera: Unicellular, prokaryotic, e.g. Bacteria, Blue green algae.

B) Protista: Unicellular, eukaryotic, e.g. Protozoan.

C) Mycota: Multicellular, decomposer, e.g. Mushroom, Mucor.

D) Plantae: Multicellular, procedure, e.g. plant, some algae.

E) Animalia:  multicellular, consumer, e.g. animal.



Merit of FIVE kingdoms System.

It separate prokaryotics from eukaryotics and kept in monera.

It separate unicellular organism from multicellular organism and kept in monera and Protista.

It separate non-photosynthetic fungi from green plant and kept in Mycota.

Multicellular procedure were kept in plantae.

Multicellular consumer were kept in animalia.

The classification was based on phylogeny and nutrition.


Demerit of FIVE kingdoms System.

It still unable to classify the virus.

Unicellular eukaryotic organism Chlamydomnasstill kept in plantae.

Unicellular eukaryotic yeast still in Mycota.

Archaebacteria, mycoplasma which shows difference character from bacteria, kept in monera.

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