Biological classification: NEET Biology:Class 12th Biology

R.H. Whittaker (1969) proposed a Five Kingdom Classification. The
kingdoms defined by him were named Monera, Protista, Fungi, Plantae
and Animalia. The main criteria for classification used by him include cell
structure, body organisation, mode of nutrition, reproduction and
phylogenetic relationships. Table 2.1 gives a comparative account of different
characteristics of the five kingdoms.
The three-domain system has also been proposed that divides the Kingdom
Monera into two domains, leaving the remaining eukaryotic kingdoms in the
third domain and thereby a six kingdom classification. You will learn about
this system in detail at higher classes.
Let us look at this five kingdom classification.KINGDOM MONERA
Bacteria are the sole members of the Kingdom Monera. They are the most
abundant micro-organisms. Bacteria occur almost everywhere. Hundreds
of bacteria are present in a handful of soil. They also live in extreme habitats
such as hot springs, deserts, snow and deep oceans where very few other
life forms can survive. Many of them live in or on other organisms as
parasites.
Bacteria are grouped under four categories based on their shape: the
spherical Coccus (pl.: cocci), the rod-shaped Bacillus (pl.: bacilli), the
comma-shaped Vibrium (pl.: vibrio) and the spiral Spirillum (pl.: spirilla).KINGDOM PROTISTA
All single-celled eukaryotes are placed under Protista, but the boundaries
of this kingdom are not well defined. What may be ‘a photosynthetic
protistan’ to one biologist may be ‘a plant’ to another. In this book we
include Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds and
Protozoans under Protista. Members of Protista are primarily aquatic.
This kingdom forms a link with the others dealing with plants, animals
and fungi. Being eukaryotes, the protistan cell body contains a well defined
nucleus and other membrane-bound organelles. Some have flagella or
cilia. Protists reproduce asexually and sexually by a process involving
cell fusion and zygote formation.
Amoeboid protozoans: These organisms live in fresh
water, sea water or moist soil. They move and capture their prey by putting out pseudopodia (false feet) as in Amoeba. Marine
forms have silica shells on their surface. Some of them such as Entamoeba
are parasites.
Flagellated protozoans: The members of this group are either free-living
or parasitic. They have flagella. The parasitic forms cause diaseases such
as sleeping sickness. Example: Trypanosoma.
Ciliated protozoans: These are aquatic, actively moving organisms because
of the presence of thousands of cilia. They have a cavity (gullet) that opens
to the outside of the cell surface. The coordinated movement of rows of
cilia causes the water laden with food to be steered into the gullet. Example:
Paramoecium (Figure 2.4d).
Sporozoans: This includes diverse organisms that have an infectious
spore-like stage in their life cycle. The most notorious is Plasmodium
(malarial parasite) which causes malaria, a disease which has a staggering
effect on human population.
KINGDOM FUNGI
The fungi constitute a unique kingdom of heterotrophic organisms. They
show a great diversity in morphology and habitat. You must have seen
fungi on a moist bread and rotten fruits. The common mushroom you eat
and toadstools are also fungi. White spots seen on mustard leaves are due
to a parasitic fungus. Some unicellular fungi, e.g., yeast are used to make
bread and beer. Other fungi cause diseases in plants and animals; wheat
rust-causing Puccinia is an important example. Some are the source of
antibiotics, e.g., Penicillium. Fungi are cosmopolitan and occur in air, water,
soil and on animals and plants. They prefer to grow in warm and humid
places. Have you ever wondered why we keep food in the refrigerator ? Yes,
it is to prevent food from going bad due to bacterial or fungal infections.
With the exception of yeasts which are unicellular, fungi are
filamentous.Virus.