 |
Introduction |
| |
The present system of classification, recognises the living organisms under five kingdoms. |
|
Kingdom Monera |
| |
The kingdom Monera includes the most ancient, the smallest, the simplest and the most widely distributed group of living organisms that are generally described by the term prokaryotes. |
|
Bacteria |
| |
Bacteria are minute microscopic prokaryotes. They are unicellular organisms, which are usually identified by their specific activities, more than their general organisation. |
|
Bacterial Cell Structure |
| |
A lose gelatinous sheath called slime layer is usually deposited around the bacterial cell wall. It is usually composed of polysaccharides. In some bacteria, the slime layer becomes thick due to the presence of some nitrogen compounds and forms a capsule. A capsule is particularly common in the parasitic forms. |
|
Nutrition in Bacteria |
| |
Bacteria exhibit different modes of nutrition. On this basis, broadly two types of bacteria can be recognised autotrophic bacteria and heterotrophic bacteria. |
|
Reproduction in Bacteria |
| |
It is the most common mode of asexual reproduction. The cytoplasm and nucleoid of a bacterial cell divide equally into two, following replication of DNA. The cell wall and cytoplasm also split resulting in the formation of two daughter cells. |
|
Cyanobacteria |
| |
The group cyanobacteria includes another successful group of prokaryotes namely blue green algae. They are photoautotrophic prokaryotes occupying a wide range of habitats. They are predominantly aquatic, found mostly in fresh water bodies. Some species occur in marine water. |
|
Kingdom Protista |
| |
The Kingdom Protista includes with a few exceptions, all the unicellular eukaryotic micro-organisms. They are predominantly aquatic where they occur as solitary cells. Some of them may form colonies consisting of similar cells. The protists are regarded as ancestors of all multicellular eukaryotic organisms. |
|
Photosynthetic Protists |
| |
They are also known as protistan algae or plantlike protists. They are represented by mainly the unicellular algae. These organisms are mostly planktonic and represent the phytoplanktons which account for nearly 80% of the total photosynthetic activity in the biosphere. Following are major groups of photosynthetic protists. |
|
Slime Moulds |
| |
These are a group of peculiar organisms which share characteristics of fungi and animals. Hence, they are also called as Mycetozoa. In the modern classification they are described as protistan fungi. |
|
Protozoan Protists |
| |
The protozoan protists are also known as animal-like protists. They are represented by unicellular animals which were earlier placed in the phylum Protozoa under Animal kingdom. They are now identified in four groups zooflagellates, sarcodines, ciliates and sporozoans. |
|
Kingdom Mycota or Fungi |
| |
The kingdom Mycota includes exclusively the fungi. The fungi are a group of organisms which has a plant body called thallus that may be unicellular or multicellular. They are achlorophyllous and non-vascular. |
|
Fungal Reproduction |
| |
Fungi exhibit three major modes of reproduction - vegetative, asexual and sexual. It is the type of reproduction which involves the somatic portion of the fungal thallus. |
|
Classification of Fungi |
| |
The classification of fungi is generally based on the following criteria: Morphology of reproductive structures, Types of spores formed, Characteristics of the life cycle, Morphology of the thallus. |
|
Lichens |
| |
Lichens are a group of aberrant organisms formed by a symbiotic association of algae and fungi. The fungi component is called mycobiont and the alga component is called phycobiont. The two components are involved in an inseparable symbiotic association. The fungal component provides a structural cover and moisture while the algal component is involved in manufacturing food. |
|
Kingdom Metaphyta |
| |
The kingdom Metaphyta (or the plant kingdom in its true sense) includes all the eukaryotic, multicellular, photosynthetic plants found in this biosphere. It consists of three major groups of plants algae, bryophytes and tracheophytes. |
|
Algae |
| |
Three groups of Algae - Rhodophyta (red algae), Phaeophyta (brown algae) and Chlorophyta (green algae) have been included in the Kingdom Metaphyta. As you have already learnt, the group cyanophyta (blue-green algae) has been placed in the Kingdom Monera while the group Bacillariophyta (golden-brown algae) has been placed in Kingdom Protista. |
|
Bryophytes |
| |
Bryophytes are a group of simple and primitive plants. They grow in moist and shady places forming a dense mass or mat on damp soil, rock, logs and other substrata. They are basically terrestrial forms, but require the presence of water for completing the life cycle. Hence, they are commonly described as 'amphibians of the plant kingdom'. |
|
Tracheophytes (Vascular plants) |
| |
Tracheophytes include the true land plants or vascular plants. The adult plant body is a sporophyte and shows definite root, stem and leaves. Vascular tissues xylem and phloem are present for the translocation of water and food respectively. Gametophytic phase is short lived. It may be parasitic on the sporophyte or independent. |
|
Pteridophytes |
| |
The division Pteridophyta includes a group of primitive vascular plants, commonly called pteridophytes. The adult plant body in these plants is a sporophyte. It shows differentiation into true roots, stem and leaves. The stem is mostly herbaceous. Leaves may be smaller or larger. Vascular tissues are present in all the vegetative parts of the plant body. |
|
Gymnosperms |
| |
The gymnosperms are seed producing land plants. However, the seeds are not enclosed in fruits. Most of them have now become extinct and only about 900 species are known to be surviving. The living gymnosperms are widely distributed in the cold climates where snow, rather than rain, is the source of water. Only one group called cycads thrive in warmer regions. |
|
Angiosperms |
| |
Angiosperms represent the most advanced group of vascular plants. They are commonly called 'Flowering plants'. They exceed all other major groups of living plants in number and diversity. |
|
Kingdom Metazoa |
| |
The Kingdom Metazoa includes all multicellular animals. The unicellular animals have been placed in the phylum protozoa which is now a part of the kingdom protista. Thus, all the remaining animals from sponges to mammals are now placed in the Kingdom Metazoa. |
|
Summary |
| |
In the modern system of classification, living organisms are grouped under five kingdoms, as proposed by Whittaker (1966). The Kingdom Monera includes bacteria and blue green algae, both of which possess prokaryotic cells. |
