Wednesday, November 30, 2011

THE LIVING WORLD


-ADDITIONAL MATERIAL FOR EAMCET STUDENTS TO COVER NEET-2012
UNIT-1 DIVERSITY IN THE LIVING WORLD
Chapter 1 The Living World

Biology is the science of life forms and living processes.
Ernst Mayr(1904 – 2004)has been called‘The Darwin of the 20th century’,
Mayr assuming the title Alexander Agassiz Professor of Zoology Emeritus.
He almost single-handedly made the origin of species diversity the central question of
evolutionary biology that it is today.
He also 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, the International Prize forBiology, and the Crafoord Prize
1.1 WHAT IS ‘LIVING’?
Distinctive characteristics exhibited by living organisms. Growth, reproduction, ability
to sense environment,mount a suitable metabolism, ability to self-replicate,
self-organise,interact and emergence
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. In plants, this growth by cell division occurs continuously throughout their life span. In animals, this growth is seen
only up to a certain age.
Non-living objects also grow if we take increase in body mass as a criterion for growth.
Mountains, boulders and sand mounds do grow. However, this kind of growth exhibited by non-living objects is by accumulation of material on the surface.
Growth, therefore,cannot be taken as a defining property of living organisms.
Reproduction, likewise, is a characteristic of living organisms.
Fungi 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, i.e., a fragmented organism regenerates the lost part of its body and becomes, a new organism.
The fungi, the filamentous algae, the protonema of mosses, all easily multiply by fragmentation.
unicellular organisms like bacteria, unicellular algae or Amoeba,reproduction is synonymous with growth, i.e., increase in number of cells.
many organisms which do not reproduce (mules, sterile worker bees, infertile human couples, etc). Hence, reproduction 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.
metabolism is a defining feature of all living organisms without exception.
The sum total of all the chemical reactions occurring in our body is metabolism.
No non-living object exhibits metabolism.
            cellular organisation of the body is the defining feature of life forms.
            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
All organisms, from the prokaryotes to the most complex eukaryotes can sense
 and respond to environmental cues.
Photoperiod affects reproduction in seasonal breeders, both plants and animals.
Human being is the only organism who is aware of himself, i.e., has self-consciousness.
Consciousness therefore, becomes the defining property of living organisms.
1.2 DIVERSITY IN THE LIVING WORLD
the number and types of organisms present on earth refers to biodiversity
The number of species that are known and described range between 1.7-1.8 million.
a particular organism is known by the same name all over the world. This process is called nomenclature.
nomenclature 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.
scientific names are based on agreed principles and criteria, which are provided
in International Code for Botanical Nomenclature (ICBN), International Code
of Zoological Nomenclature (ICZN).
characterisation, identification, classification and nomenclatureare the processes that are basic to taxonomy.
knowing more about different kinds of organisms 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’. Linnaeus used Systema Naturae    as the title of his publication.
Systematics takes into account evolutionary relationships between organisms.
1.3 TAXONOMIC CATEGORIES
the category is a part of overall taxonomic arrangement, it is called the
taxonomic category
all categories together constitute the taxonomic hierarchy.
Taxonomical studies of all known organisms have led to the development of common categories such as kingdom, phylum or division(for plants), class, order, family, genus and species.
1.3.1 Species
Taxonomic studies consider a group of individual organisms with
fundamental similarities as a species.
Mangifera indica, Solanum tuberosum (potato) and 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
1.3.2 Genus
genera are aggregates of closely related species.
potato,tomato and brinjal are three different species but all 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. This genus
differs from another genus Felis which includes cats.
1.3.3 Family
Family, has a group of related genera with still less number of similarities as compared to genus and species.
Solanum,Petunia and Datura are placed in the family Solanaceae.
genus Panthera, comprising lion, tiger, leopard is put along with genus, Felis (cats) in the family Felidae.
cat and a dog are separated into two different families – Felidae and Cancidae, respectively.
1.3.4 Order
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 Cancidae.
1.3.5 Class
order Primata comprising monkey, gorilla and gibbon is placed in class
Mammalia along with order Carnivora that includes animals like
tiger, cat and dog.
1.3.6 Phylum
fishes, amphibians, reptiles, birds along with mammals are included inphylum Chordata
due to the 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.
1.3.7 Kingdom
All animals belonging Kingdom Animalia
The Kingdom Plantae, on the other hand, is distinct, and comprises all plants
Common        Biological      Genus      Family       Order        Class     Phylum/ Division
Name                  Name
Man          Homo sapiens     Homo      Hominidae     Primata     Mammalia      Chordata
Housefly        Musca          Musca      Muscidae       Diptera      Insecta            Arthropoda
                     domestica
Mango       Mangifera    Mangifera   Anacardiaceae   Sapindales   Dicotyledonae    Angiospermae
                     indica
Wheat    Triticum     Triticum         Poaceae        Poales       Monocotyledonae      Angiospermae
              aestivum
1.4 TAXONOMICAL AIDS
1.4.1 Herbarium
Herbariaalso serve as quick referral systems in taxonomical studies.
1.4.2 Botanical Gardens
The famous botanical gardens are at Kew (England), Indian Botanical
Garden, Howrah (India) and at National Botanical Research Institute,
Lucknow (India).
1.4.3 Museum
Museums have collections of preserved plant and animal specimens for study and reference
1.4.4 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.
1.4.5 Key
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.

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