Biology

Biology is the science of life forms and living processes. The living world comprises an amaz
ing diversity of living organisms. Early man could easily perceive the difference between ina
nimate matter and living organisms. Early man deified some of the inanimate matter (wind, s
ea, fire etc.) and some among the animals and plants. A common feature of all such forms of i
nanimate and animate objects was the sense of awe or fear that they evoked. The description
of living organisms including human beings began much later in human history. Societies wh
ich indulged in anthropocentric view of biology could register limited progress in biological k
nowledge. Systematic and monumental description of life forms brought in, out of necessity,
detailed systems of identification, nomenclature and classification. The biggest spin off of suc
h studies was the recognition of the sharing of similarities among living organisms both horiz
ontally and vertically. That all present day living organisms are related to each other and also
to all organisms that ever lived on this earth, was a revelation which humbled man and led to
cultural movements for conservation of biodiversity. In the following chapters of this unit, yo
u will get a description, including classification, of animals and plants from a taxonomist’s pe
rspective.

Ernst Mayr
(1904 – 2004)
Born on 5 July 1904, in Kempten, Germany, Ernst Mayr, the Harvard University evolutionary biolog
ist who has been called ‘The Darwin of the 20th century’, was one of the 100 greatest scientists of all
time. Mayr joined Harvard’s Faculty of Arts and Sciences in 1953 and retired in 1975, assuming the t
itle Alexander Agassiz Professor of Zoology Emeritus. Throughout his nearly 80-year career, his res
earch spanned ornithology, taxonomy, zoogeography, evolution, systematics, and the history and phi
losophy of biology. He almost single-handedly made the origin of species diversity the central questi
on of evolutionary biology that it is today. He also pioneered the currently accepted definition of a bi
ological species. Mayr was awarded the three prizes widely regarded as the triple crown of biology: t
he Balzan Prize in 1983, the International Prize for Biology in 1994, and the Crafoord Prize in 1999.
Mayr died at the age of 100 in the year 2004.

Chapter 1

The Living World

Mark Done
1.1 What is ‘Living’?
1.2 Diversity in the Living World
1.3 Taxonomic Categories
1.4 Taxonomical Aids

How wonderful is the living world! The wide range of living types is amazing. The extraordinary ha
bitats in which we find living organisms, be it cold mountains, deciduous forests, oceans, fresh water
lakes, deserts or hot springs, leave us speechless. The beauty of a galloping horse, of the migrating bi
rds, the valley of flowers or the attacking shark evokes awe and a deep sense of wonder. The ecologi
cal conflict and cooperation among members of a population and among populations of a community
or even the molecular traffic inside a cell make us deeply reflect on – what indeed is life? This questi
on has two implicit questions within it. The first is a technical one and seeks answer to what living is
as opposed to the non-living, and the second is a philosophical one, and seeks answer to what the pur
pose of life is. As scientists, we shall not attempt answering the second question. We will try to refle
ct on – what is living?

1.1 What is ‘Living’?

When we try to define ‘living’, we conventionally look for distinctive characteristics exhibited by liv
ing organisms. Growth, reproduction, ability to sense environment and mount a suitable response co
me to our mind immediately as unique features of living organisms. One can add a few more features
like metabolism, ability to self-replicate, self-organise, interact and emergence to this list. Let us try t
o understand each of these.
All living organisms grow. Increase in mass and increase in number of individuals are twin characte
ristics of growth. A multicellular organism grows by cell division. In plants, this growth by cell divis
ion occurs continuously throughout their life span. In animals, this growth is seen only up to a certain
age. However, cell division occurs in certain tissues to replace lost cells. Unicellular organisms grow
by cell division. One can easily observe this in in vitro cultures by simply counting the number of cel
ls under the microscope. In majority of higher animals and plants, growth and reproduction are mutu
ally exclusive events. One must remember that increase in body mass is considered as growth. Non-
living objects also grow if we take increase in body mass as a criterion for growth. Mountains, bould
ers and sand mounds do grow. However, this kind of growth exhibited by non-living objects is by ac
cumulation of material on the surface. In living organisms, growth is from inside. Growth, therefore,
cannot be taken as a defining property of living organisms. Conditions under which it can be observe
d in all living organisms have to be explained and then we understand that it is a characteristic of livi
ng systems. A dead organism does not grow.
Reproduction, likewise, is a characteristic of living organisms. In multicellular organisms, reprod
uction refers to the production of progeny possessing features more or less similar to those of parents
. Invariably and implicitly we refer to sexual reproduction. Organisms reproduce by asexual means al
so. Fungi multiply and spread easily due to the millions of asexual spores they produce. In lower org
anisms like yeast and hydra, we observe budding. In Planaria (flat worms), we observe true regenerat
ion, i.e., a fragmented organism regenerates the lost part of its body and becomes, a new organism. T
he fungi, the filamentous algae, the protonema of mosses, all easily multiply by fragmentation. When
it comes to unicellular organisms like bacteria, unicellular algae or Amoeba, reproduction is synony
mous with growth, i.e., increase in number of cells. We have already defined growth as equivalent to
increase in cell number or mass. Hence, we notice that in single-celled organisms, we are not very cl
ear about the usage of these two terms – growth and reproduction. Further, there are many organisms
which do not reproduce (mules, sterile worker bees, infertile human couples, etc). Hence, reproductio
n also cannot be an all-inclusive defining characteristic of living organisms. Of course, no non-living
object is capable of reproducing or replicating by itself.
Another characteristic of life is metabolism. All living organisms are made of chemicals. These chem
icals, small and big, belonging to various classes, sizes, functions, etc., are constantly being made an
d changed into some other biomolecules. These conversions are chemical reactions or metabolic reac
tions. There are thousands of metabolic reactions occurring simultaneously inside all living organism
s, be they unicellular or multicellular. All plants, animals, fungi and microbes exhibit metabolism. Th
e sum total of all the chemical reactions occurring in our body is metabolism. No non-living object e
xhibits metabolism. 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, while metabolism is a defining feature of all living organisms without e
xception, isolated metabolic reactions in vitro are not living things but surely living reactions. Hence
, cellular organisation of the body is the defining feature of life forms.
Perhaps, the most obvious and technically complicated feature of all living organisms is this ability t
o sense their surroundings or environment and respond to these environmental stimuli which could b
e physical, chemical or biological. We sense our environment through our sense organs. Plants respo
nd to external factors like light, water, temperature, other organisms, pollutants, etc. All organisms, f
rom the prokaryotes to the most complex eukaryotes can sense and respond to environmental cues. P
hotoperiod affects reproduction in seasonal breeders, both plants and animals. All organisms handle
chemicals entering their bodies. All organisms therefore, are ‘aware’ of their surroundings. Human b
eing is the only organism who is aware of himself, i.e., has self-consciousness. Consciousness there
fore, becomes the defining property of living organisms.
When it comes to human beings, it is all the more difficult to define the living state. We observe pati
ents lying in coma in hospitals virtually supported by machines which replace heart and lungs. The p
atient is otherwise brain-dead. The patient has no self-consciousness. Are such patients who never co
me back to normal life, living or non-living?
In higher classes, you will come to know that all living phenomena are due to underlying interactions
. Properties of tissues are not present in the constituent cells but arise as a result of interactions amon
g the constituent cells. Similarly, properties of cellular organelles are not present in the molecular co
nstituents of the organelle but arise as a result of interactions among the molecular components comp
rising the organelle. These interactions result in emergent properties at a higher level of organisation.
This phenomenon is true in the hierarchy of organisational complexity at all levels. Therefore, we ca
n say that living organisms are self-replicating, evolving and self-regulating interactive systems capa
ble of responding to external stimuli. Biology is the story of life on earth. Biology is the story of evol
ution of living organisms on earth. All living organisms – present, past and future, are linked to one a
nother by the sharing of the common genetic material, but to varying degrees.

1.2 Diversity in the Living World

If you look around you will see a large variety of living organisms, be it potted plants, insects, birds,
your pets or other animals and plants. There are also several organisms that you cannot see with your
naked eye but they are all around you. If you were to increase the area that you make observations in,
the range and variety of organisms that you see would increase. Obviously, if you were to visit a den
se forest, you would probably see a much greater number and kinds of living organisms in it. Each di
fferent kind of plant, animal or organism that you see, represents a species. The number of species th
at are known and described range between 1.7-1.8 million. This refers to biodiversity or the number
and types of organisms present on earth. We should remember here that as we explore new areas, an
d even old ones, new organisms are continuously being identified.
As stated earlier, there are millions of plants and animals in the world; we know the plants and anima
ls in our own area by their local names. These local names would vary from place to place, even with
in a country. Probably you would recognise the confusion that would be created if we did not find wa
ys and means to talk to each other, to refer to organisms we are talking about.
Hence, there is a need to standardise the naming of living organisms such that a particular organism i
s known by the same name all over the world. This process is called nomenclature. Obviously, nom
enclature or naming is only possible when the organism is described correctly and we know to what
organism the name is attached to. This is identification.
In order to facilitate the study, number of scientists have established procedures to assign a scientific
name to each known organism. This is acceptable to biologists all over the world. For plants, scientif
ic names are based on agreed principles and criteria, which are provided in International Code for Bo
tanical Nomenclature (ICBN). You may ask, how are animals named? Animal taxonomists have evol
ved International Code of Zoological Nomenclature (ICZN). The scientific names ensure that each or
ganism has only one name. Description of any organism should enable the people (in any part of the
world) to arrive at the same name. They also ensure that such a name has not been used for any other
known organism.
Biologists follow universally accepted principles to provide scientific names to known organisms. Ea
ch name has two components – the Generic name and the specific epithet. This system of providing a
name with two components is called Binomial nomenclature. This naming system given by Carolus
Linnaeus is being practised by biologists all over the world. This naming system using a two word fo
rmat was found convenient. Let us take the example of mango to understand the way of providing sci
entific names better. The scientific name of mango is written as Mangifera indica. Let us see how it i
s a binomial name. In this name Mangifera represents the genus while indica, is a particular species,
or a specific epithet. Other universal rules of nomenclature are as follows:
1. Biological names are generally in Latin and written in italics. They are Latinised or derived from
Latin irrespective of their origin.
2. The first word in a biological name represents the genus while the second component denotes the s
pecific epithet.
3. Both the words in a biological name, when handwritten, are separately underlined, or printed in ita
lics 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. It can be illustrated with the example of Mangifera indica.
Name of the author appears after the specific epithet, i.e., at the end of the biological name and is wri
tten in an abbreviated form, e.g., Mangifera indica Linn. It indicates that this species was first describ
ed by Linnaeus.
Since it is nearly impossible to study all the living organisms, it is necessary to devise some means to
make this possible. This process is classification. Classification is the process by which anything is g
rouped into convenient categories based on some easily observable characters. For example, we easil
y recognise groups such as plants or animals or dogs, cats or insects. The moment we use any of thes
e terms, we associate certain characters with the organism in that group. What image do you see whe
n you think of a dog ? Obviously, each one of us will see ‘dogs’ and not ‘cats’. Now, if we were to th
ink of ‘Alsatians’ we know what we are talking about. Similarly, suppose we were to say ‘mammals’
, you would, of course, think of animals with external ears and body hair. Likewise, in plants, if we tr
y to talk of ‘Wheat’, the picture in each of our minds will be of wheat plants, not of rice or any other
plant. Hence, all these - ‘Dogs’, ‘Cats’, ‘Mammals’, ‘Wheat’, ‘Rice’, ‘Plants’, ‘Animals’, etc., are co
nvenient categories we use to study organisms. The scientific term for these categories is taxa. Here
you must recognise that taxa can indicate categories at very different levels. ‘Plants’ – also form a ta
xa. ‘Wheat’ is also a taxa. Similarly, ‘animals’, ‘mammals’, ‘dogs’ are all taxa – but you know that a
dog is a mammal and mammals are animals. Therefore, ‘animals’, ‘mammals’ and ‘dogs’ represent t
axa at different levels.
Hence, based on characteristics, all living organisms can be classified into different taxa. This proces
s of classification is taxonomy. External and internal structure, along with the structure of cell, devel
opment process and ecological information of organisms are essential and form the basis of modern t
axonomic studies.
Hence, characterisation, identification, classification and nomenclature are the processes that are basi
c to taxonomy.
Taxonomy is not something new. Human beings have always been interested in knowing more and
more about the various kinds of organisms, particularly with reference to their own use. In early days
, human beings needed to find sources for their basic needs of food, clothing and shelter. Hence, the
earliest classifications were based on the ‘uses’ of various organisms.
Human beings were, since long, not only interested in knowing more about different kinds of organis
ms and their diversities, but also the relationships among them. This branch of study was referred to
as systematics. The word systematics is derived from the Latin word ‘systema’ which means systema
tic arrangement of organisms. Linnaeus used Systema Naturae as the title of his publication. The sco
pe of systematics was later enlarged to include identification, nomenclature and classification. Syste
matics takes into account evolutionary relationships between organisms.

1.3 Taxonomic Categories

Classification is not a single step process but involves hierarchy of steps in which each step represent
s a rank or category. Since the category is a part of overall taxonomic arrangement, it is called the ta
xonomic category and all categories together constitute the taxonomic hierarchy. Each category, re
ferred to as a unit of classification, in fact, represents a rank and is commonly termed as taxon (pl.: t
axa).
Taxonomic categories and hierarchy can be illustrated by an example. Insects represent a group of or
ganisms sharing common features like three pairs of jointed legs. It means insects are recognisable c
oncrete objects which can be classified, and thus were given a rank or category. Can you name other
such groups of organisms? Remember, groups represent category. Category further denotes rank. Ea
ch rank or taxon, in fact, represents a unit of classification. These taxonomic groups/categories are di
stinct biological entities and not merely morphological aggregates.
Taxonomical studies of all known organisms have led to the development of common categories suc
h as kingdom, phylum or division (for plants), class, order, family, genus and species. All organisms,
including those in the plant and animal kingdoms have species as the lowest category. Now the quest
ion you may ask is, how to place an organism in various categories? The basic requirement is the kno
wledge of characters of an individual or group of organisms. This helps in identifying similarities an
d dissimilarities among the individuals of the same kind of organisms as well as of other kinds of org
anisms.

1.3.1 Species
Taxonomic studies consider a group of individual organisms with fundamental similarities as a speci
es. One should be able to distinguish one species from the other closely related species based on the
distinct morphological differences. Let us consider Mangifera indica, Solanum tuberosum (potato) an
d Panthera leo (lion). All the three names, indica, tuberosum and leo, represent the specific epithets,
while the first words Mangifera, Solanum and Panthera are genera and represents another higher leve
l of taxon or category. Each genus may have one or more than one specific epithets representing diffe
rent organisms, but having morphological similarities. For example, Panthera has another specific ep
ithet called tigris and Solanum 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.

Mark Done
1.3.2 Genus
Genus comprises a group of related species which has more characters in common in comparison to
species of other genera. We can say that genera are aggregates of closely related species. For exampl
e, potato and brinjal are two different species but both belong to the genus Solanum. Lion (Panthera l
eo), leopard (P. pardus) and tiger (P. tigris) with several common features, are all species of the genu
s Panthera. This genus differs from another genus Felis which includes cats.

Mark Done
1.3.3 Family
The next category, Family, has a group of related genera with still less number of similarities as com
pared to genus and species. Families are characterised on the basis of both vegetative and reproductiv
e features of plant species. Among plants for example, three different genera Solanum, Petunia and D
atura are placed in the family Solanaceae. Among animals for example, genus Panthera, comprising l
ion, tiger, leopard is put along with genus, Felis (cats) in the family Felidae. Similarly, if you observe
the features of a cat and a dog, you will find some similarities and some differences as well. They are
separated into two different families – Felidae and Canidae, respectively.

1.3.4 Order
You have seen earlier that categories like species, genus and families are based on a number of simil
ar characters. Generally, order and other higher taxonomic categories are identified based on the aggr
egates of characters. Order being a higher category, is the assemblage of families which exhibit a few
similar characters. The similar characters are less in number as compared to different genera include
d in a family. 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.
Figure 1.1 Taxonomic categories showing hierarchial arrangement in ascending order

1.3.5 Class
This category includes related orders. For example, order Primata comprising monkey, gorilla and gi
bbon is placed in class Mammalia along with order Carnivora that includes animals like tiger, cat and
dog. Class Mammalia has other orders also.

1.3.6 Phylum
Classes comprising animals like fishes, amphibians, reptiles, birds along with mammals constitute th
e next higher category called Phylum. All these, based on the common features like presence of noto
chord and dorsal hollow neural system, are included in phylum Chordata. In case of plants, classes w
ith a few similar characters are assigned to a higher category called Division.

1.3.7 Kingdom
All animals belonging to various phyla are assigned to the highest category called Kingdom Animali
a in the classification system of animals. The Kingdom Plantae, on the other hand, is distinct, and co
mprises all plants from various divisions. Henceforth, we will refer to these two groups as animal an
d plant kingdoms.
The taxonomic categories from species to kingdom have been shown in ascending order starting with
species in Figure 1.1. These are broad categories. However, taxonomists have also developed sub-
categories in this hierarchy to facilitate more sound and scientific placement of various taxa.
Look at the hierarchy in Figure 1.1. Can you recall the basis of arrangement? Say, for example, as we
go higher from species to kingdom, the number of common characteristics goes on decreasing. Lowe
r the taxa, more are the characteristics that the members within the taxon share. Higher the category,
greater is the difficulty of determining the relationship to other taxa at the same level. Hence, the pro
blem of classification becomes more complex.

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

TABLE 1.1 Organisms with their Taxonomic Categories

 ```

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. These studies wo
uld 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 are also fundamental to studies and e
ssential for training in systematics. It is used for classification of an organism, and the information ga
thered is also stored along with the specimens. In some cases the specimen is preserved for future stu
dies.
Biologists have established certain procedures and techniques to store and preserve the information a
s well as the specimens. Some of these are explained to help you understand the usage of these aids.

1.4.1 Herbarium
Herbarium is a store house of collected plant specimens that are dried, pressed and preserved on shee
ts. Further, these sheets are arranged according to a universally accepted system of classification. Th
ese 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, collector’s name, etc. Herbaria al
so serve as quick referral systems in taxonomical studies.

Figure 1.2 Herbarium showing stored specimens

1.4.2 Botanical Gardens

These specialised gardens have collections of living plants for reference. Plant species in these garde
ns are grown for identification purposes and each plant is labelled indicating its botanical/scientific n
ame and its family. The famous botanical gardens are at Kew (England), Indian Botanical Garden, H
owrah (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. Muse
ums have collections of preserved plant and animal specimens for study and reference. Specimens ar
e preserved in the containers or jars in preservative solutions. Plant and animal specimens may also b
e preserved as dry specimens. Insects are preserved in insect boxes after collecting, killing and pinni
ng. Larger animals like birds and mammals are usually stuffed and preserved. Museums often have c
ollections of skeletons of animals too.

1.4.4 Zoological Parks

These are the places where wild animals are kept in protected environments under human care and w
hich enable us to learn about their food habits and behaviour. All animals in a zoo are provided, as fa
r as possible, the conditions similar to their natural habitats. Children love visiting these parks, comm
only called Zoos (Figure 1.3).
Figure 1.3 Pictures showing animals in different zoological parks of India

1.4.5 Key
Key is another taxonomical aid used for identification of plants and animals based on the similarities
and dissimilarities. The keys are based on the contrasting characters generally in a pair called couplet
. It represents the choice made between two opposite options. 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 req
uired for each taxonomic category such as family, genus and species for identification purposes. Key
s are generally analytical in nature.
Flora, manuals, monographs and catalogues are some other means of recording descriptions. They al
so 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. Manuals are u
seful in providing information for identification of names of species found in an area. Monographs c
ontain information on any one taxon.

Summary
The living world is rich in variety. Millions of plants and animals have been identified and described
but a large number still remains unknown. The very range of organisms in terms of size, colour, habit
at, physiological and morphological features make us seek the defining characteristics of living organ
isms. In order to facilitate the study of kinds and diversity of organisms, biologists have evolved cert
ain rules and principles for identification, nomenclature and classification of organisms. The branch
of knowledge dealing with these aspects is referred to as taxonomy. The taxonomic studies of variou
s species of plants and animals are useful in agriculture, forestry, industry and in general for knowing
our bio-resources and their diversity. The basics of taxonomy like identification, naming and classifi
cation of organisms are universally evolved under international codes. Based on the resemblances an
d distinct differences, each organism is identified and assigned a correct scientific/biological name co
mprising two words as per the binomial system of nomenclature. An organism represents/occupies a
place or position in the system of classification. There are many categories/ranks and are generally re
ferred to as taxonomic categories or taxa. All the categories constitute a taxonomic hierarchy.
Taxonomists have developed a variety of taxonomic aids to facilitate identification, naming and class
ification of organisms. These studies are carried out from the actual specimens which are collected fr
om the field and preserved as referrals in the form of herbaria, museums and in botanical gardens an
d zoological parks. It requires special techniques for collection and preservation of specimens in herb
aria and museums. Live specimens, on the other hand, of plants and animals, are found in botanical g
ardens or in zoological parks. Taxonomists also prepare and disseminate information through manual
s and monographs for further taxonomic studies. Taxonomic keys are tools that help in identification
based on characteristics.

Prepared by
Kapil Gupta