Monera (Prokaryotes) Questions in English

(A) Heat-stable enzymes are isolated from organisms that thrive in extreme environmental conditions,such as high temperatures.
These organisms are known as thermophiles.
Archaebacteria,specifically those belonging to the group of thermophilic archaea,possess unique cell wall structures and specialized enzymes that allow them to remain functional at extremely high temperatures $(80^{\circ}C - 90^{\circ}C)$.
Therefore,the correct group is Archaebacteria.

(A) $Nitrosomonas$,$Nitrococcus$,and $Nitrobacter$ are nitrifying bacteria.
These bacteria obtain energy for their metabolic activities by oxidizing inorganic substances like ammonia and nitrites.
Since they synthesize their own food using energy derived from chemical reactions rather than sunlight,they are classified as chemosynthetic autotrophs.

(A) Nitrogen fixation is a biological process carried out by certain prokaryotic organisms. These organisms include bacteria such as $Rhizobium$,$Azotobacter$,and cyanobacteria like $Anabaena$ and $Nostoc$. All these organisms belong to the kingdom $Monera$ because they are unicellular prokaryotes.

(A) $Methylophilus$ $methylotrophus$ is a type of bacterium.
Bacteria are prokaryotic,unicellular organisms that belong to the kingdom $Monera$.
These organisms are often used as a source of Single Cell Protein $(SCP)$ due to their high rate of biomass production and protein content.

(C) In the provided image:
$P$ shows rod-shaped bacteria (bacilli).
$Q$ shows spherical bacteria (cocci).
Therefore,the correct identification is $P$ as rod-shaped bacteria and $Q$ as spherical bacteria.

(A) Methanogens are a group of archaebacteria that produce methane as a metabolic byproduct in hypoxic conditions.
According to the $5$-kingdom classification system,archaebacteria are included under the kingdom $Monera$.
Therefore,methanogens are classified in the kingdom $Monera$.

(B) Methanogens are a group of microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They belong to the domain Archaea and are classified under the group Archaebacteria. These bacteria are commonly found in the gut of ruminant animals like cows and buffaloes,where they help in the breakdown of cellulose.

(D) Methanogens are a group of anaerobic bacteria that produce methane $(CH_4)$ as a metabolic byproduct in anoxic conditions.
$1$. They are commonly found in the rumen (a part of the stomach) of cattle,where they help in the breakdown of cellulose.
$2$. They are also present in marshy areas (waterlogged soils) where they decompose organic matter.
$3$. Since they are present in the rumen,they are also found in the dung of cattle,which is rich in these bacteria.
Therefore,all the given options are correct.

(D) Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments,many of which can fix atmospheric nitrogen.
$Anabaena$ and $Nostoc$ are well-known nitrogen-fixing cyanobacteria that contain specialized cells called heterocysts for this purpose.
$Oscillatoria$ is also a genus of filamentous cyanobacteria that contributes to nitrogen fixation in various ecosystems.
Therefore,all the given options are correct examples of nitrogen-fixing cyanobacteria.

(D) The diversity of prokaryotes is vast and difficult to estimate for several reasons:
$1$. The exact number of prokaryotic species remains unknown because many are yet to be discovered.
$2$. Conventional taxonomic methods (based on morphological characteristics) are often inadequate for identifying microorganisms.
$3$. $A$ large proportion of microbial species cannot be cultured in the laboratory using standard techniques.
$4$. When modern molecular or biochemical criteria (such as $16S$ $rRNA$ sequencing) are applied,the estimated diversity of prokaryotes is found to be in the millions.
Therefore,all the given statements are correct.

(D) $A.$ Incorrect: Mango (Mangifera indica) is placed in the order 'Sapindales',not 'Poales'.
$B.$ Correct: Chemosynthetic autotrophic bacteria use the energy released from the oxidation of inorganic substances like nitrites and ammonia for $ATP$ production.
$C.$ Incorrect: Members of Ascomycetes can be saprophytic,decomposers,parasitic,or coprophilous.
$D.$ Incorrect: In one citric acid cycle,$3 NADH + H^+$,$1 FADH_2$,and $1 GTP$ (or $ATP$) are formed.
$E.$ Incorrect: The equation is technically incorrect because the product should be $NADH + H^+$,and the stoichiometry of the reaction is specific. While the reaction shown is the link reaction,the notation $NADH$ without $H^+$ as a product is incomplete,and the statement is generally considered incorrect in the context of standard biological equations.

(B) The figure shows a filament of the cyanobacterium Nostoc.
The structure labeled '$A$' is a heterocyst.
Heterocysts are specialized,thick-walled cells found in certain filamentous cyanobacteria like Nostoc and Anabaena.
These cells provide an anaerobic environment suitable for the enzyme nitrogenase,which is essential for atmospheric nitrogen fixation.
Therefore,heterocysts are specialized for nitrogen fixation.

(C) Chemosynthetic autotrophic bacteria are organisms that synthesize their own food using energy derived from chemical reactions rather than sunlight.
These bacteria oxidize various inorganic substances such as nitrates,nitrites,or ammonia.
The energy released during the oxidation of these inorganic compounds is used to produce $\text{ATP}$ and to fix carbon dioxide into organic molecules.
For example,$Nitrosomonas$ oxidizes ammonia $(NH_3)$ to nitrite $(NO_2^-)$ to obtain energy.
Therefore,the correct option is $C$.

(D) In the five-kingdom classification system,kingdom $Monera$ consists of prokaryotic organisms,primarily bacteria.
$1$. Bacteria are classified into four categories based on their shape: coccus (spherical),bacillus (rod-shaped),vibrio (comma-shaped),and spirillum (spiral).
$2$. Bacteria are simple in structure but exhibit complex behaviour,often showing the most extensive metabolic diversity among all organisms.
$3$. While some bacteria are autotrophic (photosynthetic or chemosynthetic),the vast majority of bacteria are heterotrophs,meaning they depend on other organisms or dead organic matter for food.
Therefore,the statement that the vast majority of bacteria are autotrophs is incorrect.

(D) Statement $(A)$ is correct: Archaebacteria have a unique cell wall structure (lacking peptidoglycan) which allows them to survive in extreme conditions.
Statement $(B)$ is correct: Bacteria exhibit the most extensive metabolic diversity among all organisms,utilizing various inorganic and organic sources for energy.
Statement $(C)$ is incorrect: Only photosynthetic autotrophic bacteria (like Cyanobacteria) possess chlorophyll '$a$'. Other Eubacteria do not have this pigment.
Statement $(D)$ is correct: Mycoplasma are facultative anaerobes and can survive without oxygen.
Therefore,statements $(A), (B),$ and $(D)$ are correct.

(A) According to the $5$-kingdom classification system proposed by $R.H. Whittaker$,organisms are classified into $5$ kingdoms: $Monera$,$Protista$,$Fungi$,$Plantae$,and $Animalia$.
Kingdom $Monera$ is the only kingdom that consists exclusively of prokaryotic organisms,such as bacteria and cyanobacteria.
Kingdoms $Protista$,$Fungi$,$Plantae$,and $Animalia$ consist of eukaryotic organisms.
Therefore,prokaryotic organisms are included under Kingdom $Monera$.

(B) The incorrect statement is that bacteria have very simple behavior. In reality,bacteria are very simple in structure but exhibit very complex behavior. They show the most extensive metabolic diversity among all organisms. Heterotrophic bacteria are indeed the most abundant in nature. Bacteria primarily reproduce by fission under favorable conditions. Archaebacteria are distinct from other bacteria because their cell wall structure lacks peptidoglycan,which allows them to survive in extreme environments.

(C) Chemosynthetic autotrophic bacteria are organisms that obtain energy for their metabolic activities by oxidizing various inorganic substances such as nitrates,nitrites,or ammonia.
This energy is then utilized for the production of $\text{ATP}$ and the synthesis of organic compounds from inorganic carbon sources like $\text{CO}_2$.
Unlike photosynthetic autotrophs,they do not rely on light energy.
Therefore,the correct answer is $C$.

(C) Methanogens are a group of archaebacteria that are strictly anaerobic.
They are found in the gut of several ruminant animals such as cows and buffaloes.
These bacteria are responsible for the production of methane (biogas) from the dung of these animals.
Therefore,the correct option is $C$.

(A) Statement-$I$ is correct because bacteria are prokaryotic organisms,and a defining characteristic of prokaryotes is the absence of a well-defined membrane-bound nucleus.
Statement-$II$ is correct because methanogens are a group of Archaebacteria found in anaerobic environments (like the gut of ruminant animals or marshy areas) that produce methane $(CH_4)$ as a metabolic byproduct.
Since both statements are factually accurate,the correct option is $A$.

(B) The kingdom $Monera$ consists of prokaryotic organisms,primarily bacteria.
These organisms exhibit the most extensive metabolic diversity among all living organisms.
They can be autotrophic (photosynthetic or chemosynthetic) or heterotrophic (saprophytic or parasitic).
Some bacteria can survive in extreme environments like hot springs,deserts,snow,and deep oceans,utilizing various chemical substances for their energy requirements,which is not observed to the same extent in other kingdoms.

(B) The incorrect statement is that bacterial structure is very complex and they have very simple behaviour. In reality,bacteria have a very simple structure but exhibit complex behaviour. Heterotrophic bacteria are indeed the most abundant in nature. Bacteria primarily reproduce by fission. Archaebacteria are distinct from other bacteria due to their unique cell wall structure,which allows them to survive in extreme environments.

(B) Rhizobia are soil bacteria that fix nitrogen after becoming established inside root nodules of legumes. Morphologically,they are classified as $Rod$-shaped bacteria (bacilli).

(A) Statement $I$ is correct because $Anabaena$ is a well-known heterocystous cyanobacterium capable of nitrogen fixation.
Statement $II$ is incorrect because $Anabaena$ typically forms symbiotic associations with plants like $Azolla$ (a water fern) and $Cycas$ (a gymnosperm),whereas cyanobacteria like $Nostoc$ or $Tolypothrix$ are more commonly associated with lichens.

(D) In cyanobacteria like $Aulosira$,$Tolypothrix$,and $Nostoc$,specialized cells called $heterocysts$ are responsible for nitrogen fixation.
These cells have thick walls and an anaerobic environment,which protects the enzyme $nitrogenase$ from oxygen,allowing it to function efficiently in the conversion of atmospheric nitrogen into ammonia.

(D) The shapes of bacteria are classified based on their morphology:
$1$. $A$. Coccus: These are spherical or oval-shaped bacteria.
$2$. $B$. Bacillus: These are rod-shaped bacteria.
$3$. $C$. Vibrio: These are comma-shaped bacteria.
$4$. $D$. Spirillum: These are spiral-shaped bacteria.
Therefore,the correct matching is $A-iii, B-i, C-iv, D-ii$.

(B) $Mycoplasma$ is the correct answer.
$Mycoplasma$ are the smallest living cells known and are unique because they completely lack a cell wall,which makes them naturally resistant to antibiotics like penicillin that target cell wall synthesis.

(C) $Mycoplasma$ are the smallest known living cells.
They completely lack a cell wall,which makes them naturally resistant to antibiotics that target cell wall synthesis (like penicillin).
They are facultative anaerobes,meaning they can survive without oxygen.
Therefore,option $C$ is the correct description.

(A) $Mycoplasmas$ are the smallest living cells known and they completely lack a cell wall.
They are pleomorphic,meaning they can change their shape.
Many $Mycoplasmas$ are pathogenic in animals and plants.
They are facultative anaerobes,meaning they can survive and grow in the absence of oxygen.

(D) is the correct answer.
$Nostoc$ is a genus of cyanobacteria that is prokaryotic,autotrophic,and filamentous.
However,it is not macroscopic.
Although it forms colonies that appear as gelatinous masses visible to the naked eye,these masses are composed of microscopic filaments of cells.
Therefore,the individual organism $Nostoc$ remains microscopic.

(D) endospores.
Endospores are highly resistant,dormant structures formed by certain bacteria under unfavorable environmental conditions.
These structures are capable of withstanding extreme heat,radiation,desiccation (dryness),and toxic chemicals.
They protect the bacterial $DNA$ and essential cellular components until favorable conditions return,allowing the bacterium to germinate and resume normal activity.

(A) The correct answer is $A$.
Blue-green algae (Cyanobacteria) are prokaryotic organisms.
They lack a well-defined nucleus and membrane-bound cell organelles,which are characteristic features of eukaryotic cells.
In contrast,Green algae,Golden brown algae,and Red algae are all eukaryotic organisms.