Growth
1) Growth, reproduction, ability to sense environment and mount a suitable
response come 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.
2) Increase in mass and increase in number of individuals are twin
characteristics of growth.
3) A multicellular organism grows by cell division.
4) In majority of higher animals and plants, growth and reproduction are
mutually exclusive events.
5) One must remember that increase in body mass is considered as growth.
6) Non-living objects also grow if we take increase in body mass as a
criterion for growth.
7) Growth, therefore, cannot be taken as a defining property of living
organisms.
Reproduction
1) In multicellular organisms, reproduction refers to the production of
progeny possessing features more or less similar to those of parents.
2) Fungi multiply and spread easily due to the millions of asexual spores
they produce.
3) In lower organisms like yeast and hydra, we observe budding.
4) In Planaria (flat worms), we observe true regeneration, i.e., a
fragmented organism regenerates the lost part of its body and becomes, a new
organism.
5) The fungi, the filamentous algae, the protonema of mosses, all easily
multiply by fragmentation.
6) When it comes to unicellular organisms like bacteria, unicellular algae
or Amoeba, reproduction is synonymous with growth, i.e., increase in number of
cells.
7) Hence, we notice that in single-celled organisms, we are not very clear
about the usage of these two terms – growth and reproduction.
8) Further, there are many organisms which do not reproduce (mules, sterile
worker bees, infertile human couples, etc).
9) Hence, reproduction also cannot be an all-inclusive defining
characteristic of living organisms.
Metabolism
1) All living organisms are made of chemicals.
2) These chemicals, small and big, belonging to various classes, sizes, functions,
etc., are constantly being made and changed into some other biomolecules.
3) These conversions are chemical reactions or metabolic reactions.
4) All plants, animals, fungi and microbes exhibit metabolism.
5) The sum total of all the chemical reactions occurring in our body is
metabolism.
6) No non-living object exhibits metabolism.
7) Hence, while metabolism is a defining feature of all living organisms
without exception, isolated metabolic reactions in vitro are not living things
but surely living reactions.
8) Cellular organisation of the body is the defining feature of life forms.
Consciousness
1) Perhaps, the most obvious and technically complicated feature of all
living organisms is this ability to sense their surroundings or environment and
respond to these environmental stimuli which could be physical, chemical or
biological.
2) All organisms, from the prokaryotes to the most complex eukaryotes can
sense and respond to environmental cues.
3) Photoperiod affects reproduction in seasonal breeders, both plants and
animals.
4) All organisms handle chemicals entering their bodies.
5) All organisms therefore, are ‘aware’ of their surroundings.
6) Human being is the only organism who is aware of himself, i.e., has
self-consciousness.
7) Consciousness therefore, becomes the defining property of living
organisms.
Biodiversity & Nomenclature
1) The number of species that are known and described range between 1.7-1.8
million.
2) This refers to biodiversity or the number and types of organisms present
on earth.
3) For plants, scientific names are based on agreed principles and
criteria, which are provided in International Code for Botanical Nomenclature
(ICBN).
4) Animal taxonomists have evolved International Code of Zoological
Nomenclature (ICZN).
5) The scientific names ensure that each organism has only one name.
6) Each name has two components – the Generic name and the specific
epithet.
7) This system of providing a name with two components is called Binomial
nomenclature.
8) This naming system given by Carolus Linnaeus is being practised by
biologists all over the world.
9) 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 specific
epithet.
3.
Both the words in a biological
name, when handwritten, are separately underlined, or 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. It can be illustrated with the example of
10) Classification is the process by which anything is grouped into convenient
categories based on some easily observable characters.
11) Characterisation, identification, classification and nomenclature are
the processes that are basic to taxonomy.
12) Classification is not a single step process but involves hierarchy of
steps in which each step represents a rank or category.
13) Each category, referred to as a unit of classification, in fact,
represents a rank and is commonly termed as taxon (pl.: taxa).
14) All organisms, including those in the plant and animal kingdoms have
species as the lowest category.
Species
1) Species Taxonomic studies consider a group of individual organisms with
fundamental similarities as a species.
2) Let us consider Mangifera indica, Solanum tuberosum (potato) and
Panthera leo (lion).
3) 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 level of taxon or category.
4) Each genus may have one or more than one specific epithets representing
different organisms, but having morphological similarities. For example,
Panthera has another specific epithet called tigris
and Solanum includes species like nigrum and melongena.
5) Human beings belong to the species sapiens which is grouped in the genus
Homo.
6) The scientific name thus, for human being, is written as Homo sapiens.
Genus
1) Genus comprises a group of related species which has more characters in
common in comparison to species of other genera.
2) We can say that genera are aggregates of closely related species.
3) 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.
4) This genus differs from another genus Felis which includes cats.
Family
1) Family, has a group of related genera with still less number of similarities
as compared to genus and species.
2) Families are characterised on the basis of both vegetative and
reproductive features of plant species.
3) Among plants for example, three different genera Solanum, Petunia and
Datura are placed in the family Solanaceae.
4) Among animals for example, genus Panthera, comprising lion, tiger,
leopard is put along with genus, Felis (cats) in the family Felidae.
5) Similarly, if you observe the features of a cat and a dog, you will find
some similarities and some differences as well.
6) They are separated into two different families – Felidae and Canidae,
respectively
Order
1) Generally, order and other higher taxonomic categories are identified
based on the aggregates of characters.
2) Order being a higher category, is the assemblage of families which
exhibit a few similar characters.
3) The similar characters are less in number as compared to different
genera included in a family.
4) Plant families like Convolvulaceae, Solanaceae are included in the order
Polymoniales mainly based on the floral characters.
5) The animal order, Carnivora, includes families like Felidae and Canidae.
Class
1) This category includes related orders.
2) 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.
Phylum
1) Classes comprising animals like fishes, amphibians, reptiles, birds
along with mammals constitute the next higher category called Phylum.
2) All these, based on the common features like presence of notochord and
dorsal hollow neural system, are included in phylum Chordata.
3) In case of plants, classes with a few similar characters are assigned to
a higher category called Division.
Kingdom
1) Kingdom All animals belonging to various phyla are assigned to the
highest category called Kingdom Animalia in the classification system of
animals.
2) The Kingdom Plantae, on the other hand, is distinct, and comprises all
plants from various divisions.
3) Henceforth, we will refer to these two groups as animal and plant
kingdoms.
TAXONOMICAL AIDS
Herbarium
1) Herbarium is a store house of collected plant specimens that are dried, pressed
and preserved on sheets.
2) Further, these sheets are arranged decreasing.
3) Lower the taxa, more are the characteristics that the members within the
taxon share.
4) Higher the category, greater is the difficulty of determining the relationship
to other taxa at the same level.
5) These specimens, along with their descriptions on herbarium sheets,
become a store house or repository for future use.
6) 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.
7) Herbaria also serve as quick referral systems in taxonomical studies.
Botanical Gardens
1) Botanical Gardens These specialised gardens have collections of living plants
for reference.
2) Plant species in these gardens are grown for identification purposes and
each plant is labelled indicating its botanical/scientific name and its family.
3) The famous botanical gardens are at Kew (England), Indian Botanical
Garden, Howrah (India) and at National Botanical Research Institute, Lucknow
(India).
Museum
1) Museum Biological museums are generally set up in educational institutes
such as schools and colleges.
2) Museums have collections of preserved plant and animal specimens for
study and reference.
3) Specimens are preserved in the containers or jars in preservative
solutions.
4) Plant and animal specimens may also be preserved as dry specimens.
5) Insects are preserved in insect boxes after collecting, killing and
pinning.
6) Larger animals like birds and mammals are usually stuffed and preserved.
7) Museums often have collections of skeletons of animals too.
Zoological Parks
1) Zoological Parks These 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.
2) All animals in a zoo are provided, as far as possible, the conditions
similar to their natural habitats.
3) Children love visiting these parks, commonly called Zoos.
Key
1) Key is another taxonomical aid used for identification of plants and
animals based on the similarities and dissimilarities.
2) The keys are based on the contrasting characters generally in a pair
called couplet.
3) It represents the choice made between two opposite options.
4) This results in acceptance of only one and rejection of the other.
5) Each statement in the key is called a lead.
6) Separate taxonomic keys are required for each taxonomic category such as
family, genus and species for identification purposes.
7) Keys are generally analytical in nature.
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