It contains unicellular organisms with prokaryotic cellular organization. Monera includes unicellular prokaryotic organisms. These are omnipresent. They are found in all types of environment which are not generally inhabited by other living beings. Few are photoautotrophs or chemoautotrophs; but majority are heterotrophic in nature. These organisms do not have well defined nucleus. DNA exists as a simple double stranded circular single chromosome called as nucleoid. Smaller circular molecules of DNA as extrachromosomal genetic elements called plasmids are often present. Cell wall is made up of peptidoglycan (also called murein) which is a polymer of sugars and amino acids. Membrane bound organelles e.g. mitochondria, chloroplast, endoplasmic reticulum are absent. Ribosomes are smaller in size (70S) than in eukaryotic cells. The mode of reproduction in monera is asexual or with the help of binary fission or budding. Very rarely, sexual reproduction is by conjugation method. Morphologicaly, bacteria are categorised into four groups, the sphericalCoccus, the rod-shaped bacillus, the comma or kidney shaped- vibrio and the spiral- spirillum.On the basis of evolution, bacteria can be classified as Archaebacteria and Eubacteria.
These are differentiated from other bacteria on the basis of their different cellular features. These bacteria are mostly found in the extreme environments; hence termed extremophiles. They are found in a variety of places from volcanic craters to salty lakes and hot springs. Their ability to withstand such hostile environment speaks of their capacity to survive in very severe conditions. Bacteria that can withstand high salinities are called halophiles while those that withstand extreme temperature are known as thermophiles. A very common example is of methanogenic bacteria found in gut of ruminants (cows and buffaloes). These bacteria help in production of methane in biogas plants.
These are commonly referred as true bacteria. They have cell wall of peptidoglycan. They are found as autotrophs and heterotrophs. The autotrophs can be photosynthetic like Chlorobium (Green sulphur bacteria) and Chromatium or chemosynthetic like sulphur bacteria.
These are mostly multicellular filamentous forms living in fresh water. The body is covered by mucilagenous sheath. The genetic material is typical prokaryotic. Chl-a, Chl-b, carotenes and xanthothylls are the photosynthetic pigments. Filaments show heterocyst which helps in nitrogen fixation. Heterotrophs are the most abundant. Most of them are decomposers and known for breaking down large molecules in simple molecules or minerals. They can be anaerobes helping in curdling of milk (L actobacilli), fixation of nitrogen (Az otobacter), antibiotic production (Streptomyces), composting and degrading oil. But the story doesn’t end here, some of them are pathogens i.e. causing disease (typhoid, cholera, tuberculosis, tetanus).
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| Cynaobacterium (Nostoc) |
Mycoplasma :
These are smallest of the living forms. They do not have cell wall. Many forms are pathogenic. They are found resistant to common antibiotics due to absence of cell wall.
2. Kingdom Protista :
This group includes all the unicellular but eukaryotic organisms. These organisms show link with all eukaryotic Kingdoms like Plantae, Fungi and Animalia.
a. Plant like protista :
They are also termed Chrysophytes. They are commonly termed phyto-planktons. They are microscopic and mostly photosynthetic and are major producers in oceans. Most of them are referred to as diatoms as the have body wall made up of two soap-box like fitting silica covers. “Diatomaceous earth" is nothing but these shells left behind for so many years. Diatomaceous earth is granular hence finds use in polishing and filtration.
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| Diatoms |
b. Animal like Protista :
They are also termed protozoans. They lack cell wall. They are heterotrophs. They are believed to be primitive animal forms. Amoeboid protozoans have pseudopodia as locomotory organs. Amoeba is free living form but Entamoeba is endoparasite and causes amoebic dysentery. Flagellated protozoans have flagella as locomotory organ. Trypanosoma is a common flagellated pathogen which causes sleeping sickness. Paramoecium is a cilliate protozoan having cilia for locomotion. In Paramoecium,gullet (a cavity) opens on the cell surface. Plasmodium is a sporozoan protozoa. It causes malaria. It forms spores in one of its life stage
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| Paramoecium |
c. Dinoflagellates :
These are aquatic (mostly marine) and photosynthetic. The cell wall is made up of cellulosic stiff plates. They possess a pair of flagella. They have a wide range photosynthetic pigments, which can be yellow, green, brown, blue and red. Gonyaulaxis dinoflagellate that is responsible for famous ‘red tide’. It makes even sea appear red.
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| Gonyaulax |
d. Fungi like protista :
They are commonly from the group Myxomycetes. These are saprophytic organisms found on decaying leaves. Their cells aggregate to form a large cell mass called plasmodium (not a malaria parasite). The spores produced by plasmodium are very tough and survive even very harsh conditions.
e. Euglenoids :
They lack cell wall but have a tough covering of proteinaceous pellicle. They possess two flagella, one short and other long. They behave as heterotrophs in absence of light but possess pigments, similar to that of higher plants, for photosynthesis.
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| Euglena |
3. Kingdom Plantae :
The kingdom is dominated by autotrophs. It also includes some semiautotrophic members, the insectivorous plants like Venus fly trap, pitcher plant, bladderwort, as well as heterotrophic parasitic members like Cuscuta. Members of this kingdom are multicellular, having eukaryotic cells containing chlorophyll. Cells have cell wall mostly made up of cellulose. Plants exhibit alternation of generation i.e., life cycle has two distinct phases. Kingdom Plantae is divided into two major groups Cryptogamae / Cryptogamsand Phanerogamae / Phanerogams. We will study this kingdom in detail in next chapter.
4. Kingdom Fungi :
These are eukaryotic heterotrophs showing extracellular digestion. They are found in warm and humid places. They have simple body which may be unicellular or made up of long thread like structures called hyphae. Large fungi such as mushrooms have a compact mass of cells. Unicellular organisms have a protoplast with many nuclei.
Ex. Rhiz opus, Saccharomyces (Yeast-unicellular fungus).
Filamentous fungi consist of a body called mycellium in which hyphae are present. The hyphae may be with septa or without septa. They may be uni or multinucleate. The non-septate multinucleate hyphae are called coenocytic hyphae. The cell wall in fungi is composed of chitin, a polysaccharide or fungal cellulose. The fungi exhibit hetrotrophic mode of nutrition. Mostly they are saprophytic, some
are parasitic or predators. They reproduce sexually as well as asexually. Asexual reproduction takes place by fragmentation, fission and budding. Some fungi are symbiotic;
either live with algae as lichens or as mycorrhiza in association with roots of higher plants. They are useful as well as harmful. Mushrooms are consumed as food, yeast is used in bakery and breweries. Penicillium, a fungus, is well known for antibiotic production. Harmful fungi cause diseases in plants and animals. e.g. Puccinia.The fungi are further classified on the basis of their structure, mode of spore formation and fruiting bodies as follows -
a. Phycomycetes :
These are commonly called algal fungi. Mycelium is made up of aseptate coenocytic hyphae. They commonly grow in moist and damp habitats, on decaying organic matter as well as in aquatic habitats or as parasites on plants.
Ex. Mucor, Rhiz opus (bread mould), Albugo (parasitic fungus on mustard).
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| Mucor |
b. Ascomycetes :
These are called as sac-fungi. These fungi are mostly multicellular. Rarely unicellular varieties include yeast. The hyphae are branched and septate. Sac fungi can be decomposers, parasites or coprophilous (grow on dung). Morels and truffles are varieties of sac fungi that are consumed as delicacies. N eurospora is useful in genetic and biochemical assays.
Ex. Aspergillus, Penicillium, Claviceps, Neurospora, Saccharomyces.
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| Aspergillus |
c. Basidiomycetes :
These are commonly called club fungi. They have branched, septate hyphae.
Ex. Agaricus (mushrooms), Ganoderma (bracket fungi), U stilago (smuts), Puccinia (rusts), etc.
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| Mushroom |
d. Deuteromycetes :
These are called imperfect fungi, which are known to reproduce only asexually.
Ex. Alternaria, Colletotrichum.
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| Alternaria |
5. Kingdom Animalia :
Members of this kingdom are heterotrophs; adapted to holozoic nutrition. Most of them have capacity of locomotion. They are multicellular eukaryotes where cells lack chlorophyll as well as cell wall. Growth is determinate.
