Unit 1 Diversity in the Living World Introduction:

Preview

Biology is the science of life forms and living processes.

The fact that present day living organisms are related to each other and also to all organisms that ever lived on this earth, gave rise to cultural movements towards conserving biodiversity.

In the following chapters of this unit, we will get a description of classification of animals and plants from a taxonomist s perspective.

Story box: Ernst Mayr almost single-handedly made the origin of species diversity. He pioneered the currently accepted definition of a biological species. Mayr was awarded the three prizes widely regarded as the triple crown of biology: the Balzan Prize in 1983, the International Prize for Biology in 1994, and the Crafoord Prize in 1999.

Preview:

This chapter will introduce to us, the living and how to go about classifying them for identification and study purposes.

We shall begin by defining living organisms , as those organisms that show distinctive characteristics such as, growth, reproduction, and ability to sense environment and mount a suitable response immediately, metabolism, ability to self-replicate, self-organise and interact.

Then, we will find that there are large number and types of organisms present on earth. Such a rich and diverse distribution of populations of plants and animals is what we call, Biodiversity. Since the local names of these animals would vary from place to place, even within a country, there is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature. A system which lays down the guidelines to naming the organisms systematically is called, The Binomial Nomenclature. It has two components the Generic name followed by the specific epithet. It helps in classification and identification of the organisms. Classification can be defined as the process by which anything is grouped into convenient categories based on some easily observable characters. The study of identification and classification of organisms is termed, Taxonomy. Hence, each of the groups below which the organism is placed is called a taxa . These taxa or taxonomic categories are arranged as: species < genus < family < order < class < phylum (for animals) /division (for plants) < kingdom.

We shall then look at Taxonomical Aids. They act as tools that aid in taxonomic classification of organisms. Some of the taxonomical aids are: Herbarium, Botanical Gardens, Museum, Zoological parks, key; flora and fauna; manuals and monographs.

1.1 What Is Living ?

We define living , as those organisms that show distinctive characteristics such as, growth, reproduction, ability to sense environment and mount a suitable response immediately, metabolism, ability to self-replicate, self-organise and interact.

Questions from section 1.1:

1. What are living organisms?

Key Features of Living Organisms:

1. Growth: All living organisms grow. Increase in mass and increase in number of individuals are twin characteristics of growth. A multicellular organism grows by cell division.

Cell division in organisms:

• In plants, growth by cell division occurs continuously throughout their life span. In animals, this growth is seen only up to a certain age.
• Cell division occurs in certain tissues to replace lost cells.
• Unicellular organisms grow by cell division.  

2. Reproduction: In multicellular organisms, reproduction refers to the production of progeny (offspring) possessing features more or less similar to those of parents.

There are two ways by which organisms reproduce:

a) By sexual reproduction. Examples include: Mammals, birds and most plants.

b) By asexual reproduction. Examples include: Fungi that multiply and spread easily due to the millions of asexual spores they produce. In lower organisms like yeast and hydra, we observe budding. In Planaria (flat worms), we observe true regeneration, that is, a fragmented organism regenerates the lost part of its body and becomes, a new organism. The filamentous algae, the protonema (thread like chain of cells) of mosses, all easily multiply by fragmentation. Unicellular organisms like bacteria, unicellular algae or Amoeba reproduce simply by increasing the number of cells in them. Further, there are many organisms which do not reproduce (mules, sterile worker bees and infertile human couples).

3. Metabolism: All living organisms are made of chemicals. These chemicals, small and big, belonging to various classes, sizes and functions are constantly being made and changed into some other form of biomolecules. These inter-conversions of chemical molecules are called metabolic reactions. The sum total of all the chemical reactions occurring in our body is called, metabolism.

No non-living object exhibits metabolism. However, metabolic reactions can be demonstrated outside the body in cell-free systems. An isolated metabolic reaction(s) outside the body of an organism, performed in a test tube is neither living nor non-living.

Hence, we can say that, while metabolism is a defining feature of all living organisms without exception, isolated metabolic reactions in vitro are not living things but living reactions .

4. Ability to respond: Living organisms have the ability to sense their surroundings or environment and respond to these environmental stimuli (anything that spurs a response). The stimulus could be physical, chemical or biological.

For instance, we sense our environment through our sense organs. Plants respond to external factors like light, water, temperature, other organisms and pollutants. Photoperiod affects reproduction in seasonal breeders, both plants and animals.

1.2 Diversity in the Living World

Biodiversity is the number and types of organisms present on earth.

Nomenclature of organisms: The local names of these animals would vary from place to place, even within a country. Hence, there is a need to standardise the naming of living organisms such that a particular organism is known by the same name all over the world. This process is called nomenclature.

Identification: The nomenclature or naming of organisms can only be done once it is described correctly and the name attached to the organism is known. This is called, identification.

For plants, scientific names are based on agreed principles and criteria, which are provided in International Code for Botanical Nomenclature (ICBN). Likewise, Animal taxonomists have evolved International Code of Zoological Nomenclature (ICZN) for scientific naming of animals.

Need for scientific names:

  Uniqueness: The scientific names ensure that each organism has only one name.

  Universality: Description of any organism should enable the people in any part of the world to arrive at the same name.

  Unambiguousness: They also ensure that such a name has not been used for any other known organism.

The Binomial Nomenclature Components and Rules:

Each name has two components the Generic name and the specific epithet (an attribute or quality). This system of providing a name with two components is called Binomial nomenclature.

This universal naming system was given by Carolus Linnaeus.

It was used all over the world as the naming system of using a two word format was found convenient.

For example, the scientific name of mango is written as Mangifera indica. In binomial nomenclature, this name, Mangifera represents the genus while indica , is a particular species assigned by a specific epithet.

Important rules of this system of nomenclature are as follows:

1. Biological names are generally in Latinised (or derived from Latin) and written in italics.

2. The first word in a biological name represents the genus while the second component denotes the specific epithet.

3. Both the words in a biological name, when handwritten, are separately underlined; if printed, both words are printed in italics to indicate their Latin origin.

4. The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter as illustrated in the example, Mangifera indica.

5. Name of the author appears after the specific epithet, that is, at the end of the biological name and is written in an abbreviated form, like, Mangifera indica Linn. Linn indicates that this species was first described by Linnaeus.

Classification:

Definition box: Classification is the process by which anything is grouped into convenient categories based on some easily observable characters.

For example, we easily recognise groups such as plants or animals or dogs, cats or insects. The moment we use any of these terms, we associate certain characters with the organism in that group.

Based on differing characteristics, living organisms can be classified into different taxa. This process of classification is called, taxonomy.

Basis for placing organisms into different taxa:

a) External and internal structure including the structure of their cells,

b) their development process and

c) ecological information of the organism

Note box: Systematics: The study of different kinds of organisms, their diversities and the relationships among them was called, systematics. The word systematics is derived from the Latin word systema which means systematic arrangement of organisms. Hence, Linnaeus also used Systema Naturae as the title of his publication.

1.3 Taxonomic Categories

Each category, or unit of classification, represents a rank and is commonly termed as taxon (pl.: taxa).

For example, Insects represent a taxonomic group of organisms sharing common features like three pairs of jointed legs.

Taxonomic classification helps in identifying similarities and dissimilarities among the individuals of the same kind of organisms as well as of other kinds of organisms.

Taxonomic categories include: kingdom, phylum or division (for plants), class, order, family, genus and species.

1.3.1 Species

Species: A group of individual organisms with fundamental similarities constitute a species.

Hence, we distinguish one species from the other closely related species based on the distinct morphological differences.

For example, Mangifera indica, Solanum tuberosum (potato) and Panthera leo (lion). The three names, indica , tuberosum and leo , represent specific epithets or species, while the first words Mangifera, Solanum and Panthera are genera which represent the next higher level of taxon or category.

Each genus may have one or more than one specific epithets representing different organisms, but having morphological similarities.

For example,

• The Panthera genus has another specific epithet called tigris;

• The Solanum genus includes species like nigrum and melongena.

• Human beings belong to the species sapiens which is grouped in the genus, Homo. The scientific name thus, for human being, is written as Homo sapiens.

1.3.2 Genus

Genus: A group of closely related species which have characters in common are said to belong to one genus.

For example,

– potato and brinjal are two different species but both belong to the genus Solanum.

– Lion (Panthera leo), leopard (P. pardus) and tiger (P. tigris) with several common features, are all species of the genus, Panthera (P).

– Similarly, cats belong to another genus, Felis.

1.3.3 Family

Family: A group of related genera with similarities in vegetative and reproductive features are grouped under one family.

For example,

– Among plants, three different genera, Solanum, Petunia and Datura are placed in the family, Solanaceae.

– Among animals, the genus Panthera (comprising of lion, tiger, leopard) is placed along with the genus, Felis (cats) in the family Felidae.

– Dogs belong to the family Canidae.

1.3.4 Order

Taxonomic categories like order and other higher taxonomic categories are identified and grouped based on the aggregates of characters.

Order: Order is the assemblage of families which exhibit a few similar characters.

For example,

• Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales mainly based on the floral characters.

• The animal order, Carnivora, includes families like Felidae and Canidae.

1.3.5 Class

Class: A class is a taxonomic category which includes related orders.

For example, order Primata comprising monkey, gorilla and gibbon is placed in class Mammalia along with order Carnivora that includes animals like tiger, cat and dog. Class Mammalia has other orders along with Primata and Carnivora.

1.3.6 Phylum

Phylum: A group of classes related to each other less closely than those forming a family or a class.

For example,

• Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute a Phylum, chordata based on the common features like presence of notochord and dorsal hollow neural system.

• In case of plants, classes with a few similar characters are assigned to a higher category called Division.

Note box: Division is the counterpart of phylum in plant taxonomy.

1.3.7 Kingdom

Kingdom: Animals and Plants belonging to various phyla are categorized under the highest category called, Kingdom.

There are two major kingdoms: Animalia and Plantae.

• Animals are classified under the system, animalia. The Kingdom Plantae, on the other hand, is comprised of all plants from various divisions.

• Henceforth, we will refer to these two groups as animal and plant kingdoms.

• The taxonomic categories from species to kingdom have been shown in ascending order starting with species in Figure 1.1.

Note box: Taxonomists have also developed sub-categories in this hierarchy to facilitate more sound and scientific placement of various taxa. The number of common characteristics goes on decreasing as we go up the list. Lower the taxa, more are the characteristics that the members within the taxon share. Hence, higher the category, greater is the difficulty of determining the relationship to other taxa at the same level.

Table 1.1 indicates the taxonomic categories to which some common organisms like housefly, man, mango and wheat belong:

Organisms with their Taxonomic Categories

Questions from sections 1.2 and 1.3:

1. What is biodiversity?

2. List the reasons as to why we need to have scientific names for plants and animals.

3. Explain in detail, the composition of binomial nomenclature and the rules.

4. Define the term, classification . What are the bases for placing organisms into different taxa?

5. What do we mean by taxonomy?

6. Write a brief note on the following taxa, giving examples for each:

a) species

b) genus

c) family

d) order

e) class

f) phylum and division

g) kingdom

1.4 Taxonomical Aids

Taxonomic studies of various species of plants, animals and other organisms are useful in agriculture, forestry, industry and in general, in knowing our bio-resources and their diversity.

Definition box: Taxonomical aids are collections of samples or preserved organisms which help in extensive research of identification of each taxonomical hierarchy.

Taxonomical Aids (or) Ingredients necessary for taxonomic classification:

These studies would require correct classification and identification of organisms.

Identification of organisms requires intensive laboratory and field studies.

The collection of actual specimens of plant and animal species is essential and is the prime source of taxonomic studies. These specimens form the fundamental basis for study of systematics. In addition, it is used for classification of individual organism, and the information gathered is also stored along with the specimens. In some cases the specimen is preserved for future studies.

Biologists have established certain procedures and techniques to store and preserve the information as well as the specimens as we will see in the following sub-sections.

1.4.1 Herbarium

Herbarium is a store house of collected plant specimens that are dried, pressed and preserved on sheets.

These sheets are arranged according to a universally accepted system of classification.

These specimens, along with their descriptions on herbarium sheets, become a store house or repository for future use (Figure 1.2).

The herbarium sheets also carry a label providing information about date and place of collection, English, local and botanical names, family and collector s name.

Herbaria also serve as quick referral systems in taxonomical studies.

1.4.2 Botanical Gardens

• These specialised gardens have collections of living plants for reference.
• Plant species in these gardens are grown for identification purposes.
• Each plant in the garden is labelled with its botanical or scientific name and its family.
• The famous botanical gardens are: Kew (England), Indian Botanical Garden, Howrah (India) and at National Botanical Research Institute, Lucknow (India).

1.4.3 Museum

• Biological museums are generally set up in educational institutes such as, schools and colleges.
• Museums have collections of preserved plant and animal specimens for study and reference.
• Specimens are preserved in the containers or jars in preservative solutions or are preserved as dry specimens.
• Insects are preserved in insect boxes after collecting, killing and pinning. Larger animals like birds and mammals are usually stuffed and preserved. Museums often have collections of skeletons of animals too.

1.4.4 Zoological Parks

Zoological Parks (Zoos) are the places where wild animals are kept in protected environments under human care and which enable us to learn about their food habits and behaviour.

All animals in a zoo are provided, as far as possible with the conditions similar to their natural habitats.

1.4.5 Key

Key is another taxonomical aid (used for taxonomical classification) used for identification of plants and animals based on the similarities and dissimilarities.

• A key represents the choice made between two opposite options or traits. These contrasting characters which generally occur in a pair constitute for a couplet.

• This results in acceptance of only one and rejection of the other.

• Each statement in the key is called a lead.

• Separate taxonomic keys are assigned for each taxonomic category such as family, genus and species for identification purposes.

• Keys are generally analytical in nature.

Other Taxonomical Aids:

• Flora, manuals, monographs and catalogues are some other means of recording descriptions. They also help in correct identification.

• Flora contains the actual account of habitat and distribution of plants of a given area. These provide the index to the plant species found in a particular area.  Its counterpart, for animals is called, Fauna. The fauna comprises or accounts for the animals of a particular region, habitat, or geological period.

• Manuals provide information for identification of names of species found in an area.

• Monographs contain information on any one taxon.

Questions from section 1.4:

1. Define Taxonomicalaids. What are the essentials required for taxonomic classification?

2. Write a note on the following taxonomical aids:

a) Herbarium

b) Botanical gardens

c) Museum

d) Zoological parks

e) Key

f) Flora and Fauna

g) Manuals

h) Monographs