We have different form of life on our earth. The variety of life varies
from few micrometre that is the bacteria and goes up to 30 metres like the
Blue whale and in plants it goes upto 200 metres like rose wood tree. This
variety of life around us have evolved on earth over millions of years.
Classifications
Living organisms are classified on the following characteristics:
Classification based on the internal cellular structure. like Eukaryotic
cell has membrane bound organelles including a nucleus which allows
cellular process to be carried out efficiently, organisms which do not have
the well-defined like virus which do not have a clearly demarcated nucleus
and other organelles would need to have their biochemical path organised in
a different way.
Whether the cells are existing singly or they are grouped structure and are
indivisible.
Whether the organism is producing its own food or getting the food from
outside for which a very different body design is necessary.
In animals the different body parts are developed and organized to perform
some special function
Classification and evolution
All living things are identified and categorised on the basis of their body
design in form and function. Most organisms arise by an accumulation of
change in body design that allow the organism to survive better. Charles
Darwin first described this idea of evolution in 1859 in his book the Origin of species.
Hierarchy of classification groups
Scientist tried to classify all living into broad categories called
Kingdoms. Basically, it is classified into five kingdoms: Monera, Protista,
fungi, plantae and animalia.
This groups are formed on the basis of cell structure, mode and source of
nutrition and body organisation.
Monera
Monera do not have a defined nucleus and organelles nor do they show any
multicellular body design. Some of them have cell wall and some of them
don't. These organisms synthesizing their own food or getting it from the
environment.
Bacteria, cyanobacteria, mycoplasma are examples of Monera.
Protista
Protista includes many kinds of unicellular, eukaryotic organisms. Some of
these organisms use appendages such as hair like cilia or whip like
flagella for moving around. Mode of nutrition can be autotrophic or
heterotrophic. Unicellular algae, diatoms and protozoans are example of
Protista.
Fungi
Fungi are heterotrophic, Eukaryotic organism. They use decaying organic
material as food and are therefore called saprophytes. Many of them have
the capacity to become multicellular organism at certain stage of life.
Lichens
Some fungal species live in permanent mutually dependent relationship with
blue green algae. Such relationships are called symbiotic. This symbiotic
life form is called lichens.
Plantae
Plantae are Multicellular, eukaryotes with cell wall. They are autotrophs
and use chlorophyll for photosynthesis. All plants are included in this
group.
Animalia
Animalia includes all organism which are multicellular, Eukaryotic without
cell walls. they are heterotrophic in nature. All animals come in this
group and therefore have many subgroups.
Plantae
Classification among plants depends on whether the plant body has well
differentiated distinct components. Secondly it is based on whether the
differentiated plant body have special tissue for transport of water and
other substance within it. Third classification is on the ability to beer
seeds that are enclosed within fruits.
Thallophyta
Plants that do not have well differentiated body design falls in this
group. The plants in this group are commonly called algae and are
predominantly aquatic. Spirogyra ulothrix, cladophora are some examples of
thallophyta.
Bryophyta
Bryophytes are called the amphibians of the plant Kingdom. The plant body
is commonly differentiated to form stem and leaf like structures. there is
no specialised tissue for the conduction of water and other substance. Moss
and marchantia are examples of bryophyta.
Pteridophyta
In this the plant body is differentiated into roots stem and leaves and has
specialised tissue for the conduction of water and other substance.
Marsilea, ferns and horse-tails are example of pteridophyta.
Cryptogamae
The thallophytes, the bryophytes and the pteridophytes have naked embryos
that are called spores. The reproductive organs of plants in all these
three groups are very inconspicuous, and they are therefore called
"cryptogamae", or "those with hidden reproductive organs".
Gymnosperms
These came from two Greek word gymno means naked and sperma means seed. Plants of this group bear naked seed and
usually perennial evergreen and woody. Pines and Deodar are example of
gymnosperms.
Angiosperms
Came from two Greek words angio means covered and sperma
means seed. Seeds develop inside an organ which is modified to become a
fruit these plants are also called flowering plants. Plant embryos in seeds
have structure called cotyledon and are also called seed leaves because in
many instances the seeds germinate and become green.
Angiosperms are divided into two groups on the basis of number of
cotyledons present in the seed.
Plant seeds having a single cotyledon are called monocotyledonous or monocots. And seeds having two
cotyledons are called dicots.
Animalia
These are organisms which are Eukaryotic, multicellular and heterotrophic.
Cells do not have cell wall and most of the animals are mobile. They are
further classified on the extent and type of body design.
Porifera
Porifera means organism with holes. these are non-motile animals attached
to some solid support and have propose present all over the body which
leads to the canal system that help in circulating water throughout the
body and also to bring food and oxygen. They have an outer hard covering.
They are commonly called sponges and found in Marine habitats. Euplectelia,
spongilla are examples of Porifera.
Coelenterata
These are animals living in water, shows more body design differentiation.
Their body is made up of 2 or more layer of cells. One layer makes the
outside of the body and other layers make the inner lining of the body.
Some of these species lives in colonies and others have a solitary like
span. Jellyfish and sea anemones are common examples.
Platyhelminthes
The animal body in this group is far more Complex. The body is bilaterally
symmetrical meaning that the left half and the right half of the body have
same design. Three layers of cell differentiated from which tissues are
made and that is why such animals are called triploblastic. the body is
flattened dorsiventrally and are called flatworms. Parasitic animals like
liver flukes is an example.
Nematoda
The body is bilateral, symmetrical and triploblastic. But the body is
cylindrical rather than flattened. They have tissues but no real organs, a
body cavity type or a pseudo coelom is present. These are very familiar as
parasite worm causing disease in the intestine. Ascaris and wuchereria are
some examples of nematode.
Annelida
These animals are bilaterally symmetrical and triploblastic but they have
body cavity which allows true organs to be packed in the body structure.
These animals are found in a variety of habitat like in freshwater, marine
water as well as in land. Earthworm and leeches are examples of Annelida.
Arthropoda
These are the largest group of animals and are bilaterally symmetrical and
segmented. They have an open circulatory system and blood does not flow in
well defined blood vessels. They have joint legs that's why named as
arthropod. Prawns, butterflies, houseflies and spiders are example of
Arthropoda.
Echinodermata
Echino
means Hedgehog and Derma means skin. These are spiny skinned
organisms and are exclusively free-living marine animals, they are
triploblastic and have a coelomic cavity. Starfish and sea urchins are
common examples.
Mollusca
Animals in this group is bilaterally symmetrical and the coelomic cavity is
reduced. They have a little segmentation and an open circulatory system and
a kidney like organ for excretion. Snails and muscles are example of
Mollusca.
Protochordata
Animals in this group are bilaterally symmetrical, triploblastic and have a
coelom. Shows a new feature of body design namely notochord at some stages
during their life. Notochord is a rod like support structure that runs
along the back of animal separating The Nervous tissue from the gut.
balanoglossus, herdemania are some examples of protochordata.
Vertebrata
In this group of animals they have a true vertebral column and internal
skeleton allowing a complete different distribution of muscle attachment
point to be used for movement. Vertebrates are bilaterally symmetrical
coelomic and segmented. They have the following features:
Have a notochord
Have a dorsal nerve cord
Are triploblastic
Have paired Gill pouches
Are coelomate
Pisces
This are the fishes, which are exclusively water living animals. Their skin
is covered with scales or plates. Use dissolved oxygen in water by using
gills. Body is streamlined and muscular tail is used for movement. They are
also cold blooded and their heart have only two chambers. Tuna and rohu are
some example of pisces.
Amphibia
These animals differ from fish and lack sales. instead they have mucous
glands in the skin and a three chambered heart. respiration is through
gills or lungs. they lay eggs in water and I found both in water and land.
frog toad salamanders are some common examples
Reptilia
These are cold blooded animals have scales and breathe through lungs. Most
of them have a three chambered heart but crocodiles have four chambered
heart. These animals lay eggs with tough covering do not need to lay their
eggs in water unlike amphibians. Snakes, turtles and crocodiles are
examples of reptilia.
Aves
These are warm blooded animals and have four chambered heart. Aves lay eggs
and have an outside covering of feathers and 2 fore limbs that are modified
for flight. They breathe through lungs. All birds fall in this category.
Mammalia
Mammals are warm blooded animals with four chambered heart and have mammary
glands for production of milk to nourish their young once. Few of them like
the Platypus and the echidna lay eggs some like Kangaroo give birth to very
poorly developed young ones.
Nomenclature
Scientific naming are nomenclature for the recognition of different
classification of organisms. Certain conventions are followed while writing
the scientific names:
The name of the genus begins with a capital letter.
The name of the species begins with a small letter
When printed, the scientific name is given in italics.
When written by hand the genus name and the species name have to be
underlined separately.