Kingdom Monera - NEET Important Topic

Before we start with the classification and characteristics of Monera, let us first discuss what is Monera? Monera is a biological kingdom in which all the prokaryotes are grouped together. Prokaryotes are organisms that do not have a nucleus and other organelles.

R.H. Whittaker proposed a Five Kingdom Classification in 1969. The kingdoms he defined were the names Monera, Protista, Fungi, Plantae and Animalia. The main criterion for the classification used by him includes the cell structure, body organisation, mode of nutrition, reproduction and phylogenetic relationships. Bacteria are the sole members of the Kingdom Monera that are the most abundant microorganisms. Members of Monera may not always be a bacterium, but a bacterium would be considered a moneran.

Monerans are directly beneficial to humans as they are utilized in the fermentation process, which helps make foods such as yogurt and cheese. Monera is also found naturally in our intestines and helps with the digestion of food.

Characteristics of Kingdom Monera

• Monerans belong to the prokaryotic family and are unicellular organisms.

• They have 70S ribosomes, which are composed of small 30S and large 50S subunits.

• They lack a nucleus, hence their DNA is naked and is not bound by a nuclear membrane.

• They also lack organelles such as mitochondria, lysosomes, plastids, Golgi bodies, endoplasmic reticulum, centrosome, and so on.

• Their cell wall is made up of peptidoglycan and is rigid in nature.

Bacteria

Bacteria are present almost everywhere as they are the oldest organisms on earth. They live in extreme habitats where very few other life forms can survive such as hot springs, snow, deserts and deep oceans. Many of them also live as parasites which are present either on or in the body of other organisms (host).

They exhibit various shapes such as spherical Coccus, rod-shaped bacillus, comma-shaped Vibrum and spiral spirillum, and so on.

Shapes of Bacteria

Nutrition in Bacteria

They show the most extensive metabolic diversity. The following are the four nutritional categories found in bacteria:

1. Autotrophs: Synthesise their own organic food.

2. Saprotrophs: Feed on dead organic matter.

3. Symbionts: Use food from other living organisms with which they have a mutual relationship

4. Parasites: Absorb food from living organisms and cause harm to them 

Respiration in Bacteria

Respiration in bacteria may be either of the two types:

1. Aerobic: Using oxygen for respiration

2. Anaerobic: Respiration in the absence of oxygen

Monera Kingdom Classification

Monera are classified into two categories: Archaebacteria and Eubacteria.

1. Archaebacteria

Archaebacteria are special, as they live in some of the harshest habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). They are prokaryotic microorganisms that are believed to be the first form of life on the planet. They have a different cell wall structure that makes them different from other bacteria. Their cell wall is responsible for their survival in extreme conditions. 

Methanogens are archaebacteria which are present in the gut of several ruminant animals such as cows and buffaloes. These methanogens are responsible for the production of methane (biogas) from the dung of these animals.

2. Eubacteria 

Eubacteria are prokaryotic microorganisms consisting of a single cell that lacks a nucleus and contains DNA which is a single circular chromosome. They are also called True bacteria. They have rigid cell walls and a thread-like structure called a flagellum that helps in mobility.

Classification of Eubacteria

Based upon the mode of nutrition, they are classified into 3 categories:

1. Photosynthetic autotrophs: Bacteria that make their own food through the process of photosynthesis are called phototrophic autotrophs such as cyanobacteria, which are also called blue-green algae. They have chlorophyll similar to green plants. They are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. The colonies of cyanobacteria are generally surrounded by a gelatinous sheath that makes a homogenous surface around the cells.

2. Chemosynthetic autotrophs: The bacteria that oxidise various inorganic substances such as nitrates, nitrites and ammonia, and also use the released energy for their ATP production are called chemosynthetic autotrophs. These bacteria play a great role in recycling nutrients such as nitrogen, phosphorus, iron and sulphur.
   
   

3. Heterotrophic bacteria: The bacteria that use organic carbon as food are called heterotrophic bacteria. These bacteria are abundant in nature and the majority of them are decomposers. They also have a significant impact on human affairs as they help in making curd from milk, production of antibiotics, fixing nitrogen in legume roots, and so on. Some act as pathogens that cause damage to human beings, crops, farm animals and pets. Cholera, typhoid and tetanus are well-known diseases caused by different bacteria.

Monera Kingdom Organisms

The Monera kingdom contains all the single-celled organisms also called eukaryotes that do not possess a true nucleus. Monera kingdoms are commonly referred to as bacteria which involve organisms such as eubacteria, cyanobacteria, proteobacteria, spirochaetes, and so on.

Unique Features of Kingdom Monera

Monerans are unicellular prokaryotes that do not have a well-defined nucleus and other membrane-bound organelles except ribosomes. Their genetic material is not surrounded by a nuclear membrane; instead, they have a single piece of DNA present either in a linear form or circular form. They also don’t have membrane-bound organelles such as the Golgi body, mitochondria, endoplasmic reticulum, etc. They contain ribosomes as membrane-bound organelles.

Monera Examples

All bacteria including E. coli, Helicobacter pylori, salmonella etc, blue-green algae, Methanogens, and so on.

Mycoplasma 

One of the members of Monera lacking a cell wall is Mycoplasma. These bacteria are the smallest living cells known and can survive without oxygen. Many mycoplasmas are pathogenic in nature and cause harm to living organisms.

A Mycoplasma

Reproduction in Monera

Monera reproduces asexually through the process of binary fission during favourable conditions and sometimes even reproduces through endosperm formation during unfavourable conditions. They also reproduce sexually by the process of conjugation.

Structure of Monera

Structure of a Bacterial Cell

All prokaryotes have a cell wall surrounding the cell membrane that protects the cell except mycoplasma, which lacks a cell wall. Each bacterial cell contains a membrane situated just internal to the cell wall called the plasma membrane. The fluid matrix filling the cell is called cytoplasm. There is no well-defined nucleus in prokaryotes. The genetic material is basically naked and is not enveloped by a nuclear membrane. 

In addition to the genomic DNA (the single chromosome/circular DNA), many bacteria have small circular DNA outside the genomic DNA. These smaller DNAs are called plasmids. No organelles, like the ones found in eukaryotes, are present in the prokaryotes except ribosomes. Prokaryotes have something unique in the form of inclusions.

A specialised differentiated form of the cell membrane called mesosomes is the characteristic of prokaryotes; these are essentially infoldings of the cell membrane. They also have a thread-like structure called flagella that helps them to swim. Apart from flagella, they also have some tiny or small hairlike outgrowths called pili.

Conclusion

This article has given all the necessary detail about the Kingdom Monera with respect to the NEET syllabus. The questions added at the end of the article are frequently asked questions and are important from the exam point of view thus the student can have a clearer understanding of the type of questions that might appear in the exam.