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Protoctista Classification Essay

Definition Kingdom Monera 

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The Kingdom Monera includes organisms that are single-celled known as bacteria. The microorganisms in Kingdom Monera are considered as the most ancient living forms on earth. The kingdom is divided into two groups Archaebacteria and Eubacteria. All the organisms of this kingdom are prokaryotes. These cells do not have nuclear membrane, the chromosome is a single and circular, they also lack membrane bound cellular organelles. This kingdom includes bacteria, cyanobacteria, mycoplasma etc. They are unicellular organisms and do not have specific mode of nutrition. They can be either aerobic or organisms have cell wall which is made up of peptidoglycans. The cell organelles are not membrane bound. Cell organelles like endoplasmic reticulum, mitochondria are absent. Reproduction is by spore formation and binary fission.

Kingdom Monera Characteristics

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General characteristics of the kingdom Monera are as follows: 

  • They are primitive organisms.
  • All organisms of the kingdom are prokaryotes.
  • They are present in both living and non-living environment.
  • They can survive in harsh and extreme climatic conditions like in hot springs, acidic soils etc.
  • They are unicellular organisms.
  • Membrane bound nucleus is absent.
  • DNA is in double stranded form, suspended in the cytoplasm of the organism,referred as nucleoid.
  • A rigid cell wall is present.
  • Membrane bound cellular organelles like mitochondria are absent.
  • Habitat - Monerans are found everywhere in hot springs, under ice, in deep ocean floor, in deserts and on or inside the body of plants and animals.
  • Nutrition - autotrophs - can prepare their own food, heterotrophs - depend on others for food, saprophytes - feed on dead and decaying matter, parasitic - live on other host cells for survival and cause, symbiotic - in mutual relation with other organisms, commensalism - it is where one organism is benefited and the other is not affected, mutualism - where both the organisms are benefited.
  • Respiration - respiration in these organisms vary, they may be obligate aerobes - the organisms must have organisms for survival; obligate anaerobes - the organisms cannot survive in the presence of oxygen; facultative anaerobes - these organisms can survive with or without oxygen. 
  • Circulation - is through diffusion. 
  • Movement - is with the help of flagella.
  • Reproduction is mostly asexual, sexual reproduction is also seen. Asexual reproduction is by binary fission, sexual reproduction is by conjugation, transformation and transduction.

Classification of Kingdom Monera

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Kingdom Monera has been classified into two groups - Archaebacteria and Eubacteria. 

Archaebacteria are microbes that live in extreme and harsh conditions, they are known as extremophiles. These bacteria lack cell wall, their cell membrane is made up of different lipids, and their ribosomes are similar to that of eukaryotes.
Archaebacteria are of three major groups of bacteria based on their habitat i.e., thermophiles, halophiles and methanogens.

Some extremophiles live in boiling water like geysers of Yellowstone National Park and and in volcanoes. These are known as 'thermophiles'. 

Some extremophiles live in extremely salty water, the salt loving bacteria are known as 'halophiles'. 

Some bacteria are present in the guts of ruminants and are responsible for production of methane gas from their dung. These bacteria are known as 'methanogens'. 

Eubacteria are true bacteria. The characteristic feature is the presence of rigid cell wall and if present a motile flagelllum that aids in organisms are characterized based on their nutrition and their shapes. 
Classification based on Shape

Bacteria can be classified in four groups based on shape : Spherical or round shaped bacteria are called cocci, Rod-shaped are bacilli, Comma-shaped bacteria are vibrio and spiral shaped bacteria are spirilla. 

Classification Based on Mode of Nutrition

Based on the mode of nutrition bacteria are broadly classified into Autotrophic and Heterotrophic.

Autotrophic bacteria- Bacteria which prepare their own food are autotrophic. (Example Cyanobacteria

Heterotrophic bacteria - Bacteria which are dependent on other organisms for their food are heterotrophic.(Example Escherichia coli)

Autotrophic bacteria can be Chemosynthetic or Photosynthetic.

Chemosynthetic bateria are those which prepare their food with the help of inorganic substrates. Photosynthetic bacteria are autotrophic bacteria which prepare their own food by the process of photosynthesis.

Cyanobacteria (Blue-green algae) - They have chlorophyll similar to plants and hence they are photosynthetic autotrophs. The marine and terrestrial and they may be unicellular, colonial or filamentous. The colonies are surrounded by gelatinous sheath. They can also fix atmospheric nitrogen.

Example:Nostoc and Anaebena.

Chemosynthetic autotrophs - these organisms oxidise substances like nitrites, nitrates, ammonia etc. The help in recycling substances like nitrogen, sulphur, iron etc. 

Heterotrophic bacteria are those which are dependent on other organism either directly or indirectly for their nutrition. They are most abundant and are important decomposers. Some are helpful in curdling milk, production of antibiotics, in nitrogen fixation and some are pathogens.

 Heterotrophic bacteria can be parasitic and saprophytic. Parasitic bacteria are those which depend on the host for nutrition and cause harm to the host. Saprophytic bacteria feed on dead and decaying matter.

Symbiotic - it is a type where the bacteria are in mutual relation with other organisms. Symbiosis is of two types mutualism and commensalism. Mutualism is where the bacteria and the other organism are benefited due to the relationship. Commensalism is a relationship where the bacteria is benefited while the other organism is not affected by the relationship.

Classification based on Gram's staining 

Gram's staining is a test on cell walls developed by Hans Christian Gram. This method helps classifying bacteria into Gram positive bacteria and Gram negative bacteria. 

Gram Positive Bacteria - The bacteria's cell wall is made up of protein-sugar complex that takes on purple color during gram staining. 

Gram Negative Bacteria - The gram negative bacteria has an extra layer of lipid on the outside of the cell wall and appear pink during the Gram staining procedure. 

Reproduction in Bacteria

Reproduction in bacteria is mainly by unfavourable conditions they reproduce by spores. Sexually bacteria reproduce by a primitive mode of DNA transfer from one bacterium to another i.e., by conjugation, transduction or  transformation. 


Mycoplasma are the known to be the smallest living cells. They completely lack cell wall and can survive without oxygen. Most of the mycoplasma are pathogenic in nature in animals and plants. 

Economic Importance of Bacteria

Lactic acid bacteria like Lactobacillus and Lactococcus have been used in fermentation process for thousands of years.
The ability of the bacteria to degrade variety of organic compounds has been used in waste management processing and biorememdiation.

In pest control, bacteria can be used in the place of pesticides as these pesticides are regarded environmentally friendly. 

Example: Bacillus thuringenesis.

The ability of the bacteria in dividing rapidly and by studies on the bacterial genome, these bacteria can be bio-engineered for the production of  therapeutic proteins like insulin, growth factors and antibodies, etc.

Kingdom Monera Examples

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The Monerans comprises of mostly bacteria. Following are a few well known examples.

Blue-green algae - Cyanobacteria, Cocci shaped bacteria - Streptococcus, Bacilli shaped bacteria -, Vibrio shaped - Vibrio cholerae (cholera), Spiral shaped bacteria - Treponema pallidum (syphilis). 

Gram positive bacteria - Mycobacterium; Gram negative bacteria - (coliforms)

Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Streptococcus pyogens, Clostridium botulinum, Listeria monocytogenes, Salmonella enterica, Vibrio cholerae, Bacillus anthracis, Bacillus cereus.

Kingdom Monera - All the organisms of this kingdom are prokaryotes. Complex structure was the basis of classification of organisms, many centuries ago. According to R.H. Whittaker's five kingdom classification all the bacteria were placed under the Kingdom Monera.

Monera are considered as the most primitive group of organisms. They include various types of bacteria and blue-green algae.

Monerans are most abundant of all organisms, due to their versatility of their is estimated that a single drop of water contains 50 billion bacteria.

All single celled organisms are placed under the Kingdom Protista. The term Protista was first used by Ernst Haeckel in the year This kingdom forms a link between other kingdoms of plants, animals and fungi. Protists represent an important step in early evolution. The first protists evolved probably billion years ago. Members of Protista are primarily aquatic in nature. It is a very large group comprising of at least 16 phyla. Many protists like algae are the primary producers in the aquatic ecosystem, some protists are responsible for serious human diseases like malaria and sleeping sickness.

Kingdom Protista Definition

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Kingdom Protista is a diverse group of eukaryotic organisms. Protists are unicellular, some are colonial or multicellular, they do not have specialized tissue organization. The simple cellular organization distinguishes the protists from other eukaryotes. The cell body of the protists contain have a nucleus which is well defined and membrane bound organelles. Some have flagella or cilia for locomotion. Reproduction in protists is both asexual and sexual. They live in any environment that contains water.

Characteristics of Kingdom Protista

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General characteristics of Kingdom Protista are as follows: 

  • They are simple eukaryotic organisms.
  • Most of the organisms are unicellular, some are colonial and some are multicellular like algae.
  • Most of the protists live in water, some in moist soil or even the body of human and plants.
  • These organisms are eukaryotic,  since they have a membrane bound nucleus and endomembrane systems.
  • They have mitochondria for cellular respiration and some have chloroplasts for photosynthesis. 
  • Nuclei of protists contain multiple DNA strands, the number of nucleotides are significantly less than complex eukaryotes.
  • Movement is often by flagella or cilia.
  • Protists are multicellular organisms, they are not a plant, animal or fungus.
  • Respiration - cellular respiration is primarily aerobic process, but some living in mud below ponds or in digestive tracts of animals ares strict facultative anaerobes.
  • Nutrition - they can be both hetreotrophic or autotrophic. 
  • Flagellates are filter feeding, some protists feed by the process of endocytosis (formation of food vacuole by engulfing a bacteria and extending their cell membrane).
  • Reproduction - some species have complex life cycle involving multiple organisms. Example: Plasmodium. Some reproduce sexually and others asexually. 
  • They can reproduce by mitosis and some are capable of meiosis for sexual reproduction.
  • They form cysts in adverse conditions.
  • Some protists are pathogens of both animals and plants. Example: Plasmodium falciparum causes malaria in humans.
  • Protists are major component of plankton.

Kingdom Protista Classification

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Kingdom Protista are categorized into two taxons: 

Protozoans - animal-like single-celled organisms. 

Algae - plant-like single or multi-celled organisms.

Animal-like Protists - PROTOZOANS

Protists that have resemblance to animals are known as protozoans. They in moist and watery enviroments. The characteristics similar to animals are - their ability to move and their inability to produce their own food (heterotrophs). They differ from animals being unicellular while animals are multicellular.

Protozoans are classified on the way they move into four categories: 

  • Sacordinians - move using pseudopod.
  • Zooflagellates - move using flagella.
  • Ciliaphorans - move using cilia.
  • Sporozoans - forms spores.
Phylum Sarcodina - The movement in sarcodinians is by extending lobes of cytoplasm known as pseudopodia. The pseudopoda is used for movement and feeding. During the formation of the pseudopodia the cytoplasm streams into the lobe causing the lobe to 'ooze' and grow. Because of this the peudopodians have a 'blob like appearance. Example: Amoeba,Foraminiferans.

Phylum Mastigophora (Zooflagellata) - These protozoans move with the help of flagella. Most of them are parasitic. Many flagellates are seen in the intestine of humans, in termites and other animals, some flagellates are harmful. Example: Trypanosoma gambiense causes sleeping sickness in cattle and human. 

Phylum Ciliophora (Ciliates) - Protozoans of this phylum move with hair like structures called cilia. The cilia stick out of their cells. The movement of cilia is paddle like, it sways back and forth for movement and fast beating of the cilia causes movement of the organism. The cilia is also used to sweep food particles into the organism. Example: Paramecium - It is a ciliate protozoan found in fresh water and ponds. It commonly known as the slipper animal-cule. 

Phylum Sporozoa - All members of this phylum are non-motile and parasitic. They forms spores and hence the name sporozoa. They lack locomotory structures and they are carried  in their hosts by their body fluids. Many sporozoans causes serious diseases in humans. Example: Plasmodium - this parasite causes malaria in humans. 

Plant-like Protists - ALGAE

Plant-like protists have chlorophyll like that in plants. The green substance in their cells enable them to make food bu photosynthesis. They produce and release oxygen like the plants. It is believed to be the most supply of oxygen on Earth is from the plant-like protists. The plant-like protists are the major food source and primary producers for water organisms. 


Phylum Chlorophyta (Green Algae) - The green algae include unicellular and multicellular algae. They are mostly fresh water. Body is sheet-like thallus. They have cell walls made of cellulose and pectin. Food is reserve starch which is stored in pyrenoids. Example: Spirogyra - it is a unicellular green alga, it grows as a green thread or filament. 

Phylum Rhodophyta (Red Algae) - Red algae are mostly large and multicellular. They grow in oceans. The algae 'Nori' and Gelidium are used as food, in parts of Asia. Carragean and agar are glue-like substances in red-a;gae. Agar is used as a medium used for growing bacteria and other organisms under laboratory conditions. Agar is also used to make gelatin capsules. and a base for cosmetics. Carragean is used as a stabilizer and thickener in dairy products. It is also used to give toothpaste its creamy texture. 

Phylum Phaeophyta (Brown Algae) - Brown algae are multicellular. They grow on rocks in shallow water of the sea. Large brown algae are called kelps. Kelps may grow densely in the sea and form kelp forests. They form important food sources for fish and invertebrates. The brown algae growing on rocks are known as rockweed. Example of rockweed is Sargassum. Algin is a substance derived from some algae which is used in making ice cream, lotion and plastics. 

Phylum Chrysophyta (Golden algae)- 'Chryso' means 'color of gold'. There are three types of golden-algae: yellow-green algae, golden brown algae, diatoms. Diatoms are the most abundant  and are found in seawater and freshwater habitats. The shell of diatoms are made of silica. They are major source of food to may aquatic organisms. The shells of fossil diatoms form thick deposits on the sea floor known as 'diatomaceous earth'. It is used as water filters, abrasive and to add sparkling to products such as paint and fingernail polish. 

Phylum Pyrrophyta (Fire Algae) - It contains of species of one-celled algae called dinoflagellate which means 'spinning swimmers'. They store food in the form of starch and oils. The red color is due to chlorophyll a and c and xanthophylls. These organisms have ability of bioluminescence. Almost all species like in marine water. Some species causes the 'red tide phenomenon'. The dinoflagellates causing red tides are known as Gonyaulax, which contain a neurotoxin and are poisonous to marine fauna. 

Fungus-like Protists

Slime Molds - Slime molds are saprophytic protists. They are very bright in appearance. They live in moist soil, decaying plants and trees. They are single-celled organisms. During favorable condition they form multicellular aggregations called plasmodium. During unfavorable conditions, plasmodia differentiate to form fruiting bodies bearing spores at the tip. These spores posses resistant true walls, which help in survival for a long time during adverse conditions. These spores disperse by air currents. 

Kingdom Protista Examples

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Few well known examples are follows: 

Green algae - Spirogyra, Ulva, Chlamydomonas, Volvox.

Red algae - Porphyra, Rotalgen.

Brown algae - Laminaria, Nereocystis.

Water molds - Saprolegnia.

Phylum Ciliata - Paramecium, Vorticella.

Phylum Dinoflagellata - Ceratium, Gonyaulax.

Phylum Mastigophora - Trypanosoma, Trichonympha.

Phylum Sarcodina - Amoeba.

Economic Importance of Protists

Protists are useful in the following manners:

Source of food - Some protists like kelps are edible.

Source of commercial products - Marine protists are source of useful substances like algin, agar, carragean and antiseptics.

Primary producer of aquatic ecosystem - Many protists are primary producers, they play a basic role in food cahins, providing food and oxygen.

Source of medicines - Sodium laminaria sulphate, Fucoidin, Heparin are algal products used as blood coagulants. Lyngbya produces an anti-cancer compound. 

Source of mineral - Kelps are rich in sodium, potassium, iodine etc, they are good source of minerals. 

Biological research - They are used in biological research, e.g., Chlorella is unicellular, non-motile alga.

Pathogens - Thhese ar pathogenic organisms and may cause many disease in man and also in fruits and vegetables it causes late blight potatoes and causes disease in some fishes.