Monera (Prokaryotes) Questions in English

(C) $Cyanophyceae$,commonly known as blue-green algae,belongs to the kingdom $Monera$.
Members of the kingdom $Monera$ are prokaryotic organisms.
Prokaryotic cells lack a membrane-bound,definite nucleus and membrane-bound cell organelles such as plastids,mitochondria,or endoplasmic reticulum.
Therefore,$Cyanophyceae$ lacks both a definite nucleus and plastids.

(C) The correct answer is $C$. Cyanobacteria (such as $Nostoc$ and $Anabaena$) are unique because they contain chlorophyll $a$ for oxygenic photosynthesis and specialized cells called heterocysts for nitrogen fixation.

(C) Unicellular cyanobacteria reproduce asexually by binary fission.
Filamentous forms of cyanobacteria reproduce by fragmentation or by the formation of specialized structures called hormogones.

(C) Heterocysts are specialized,thick-walled cells found in certain filamentous cyanobacteria such as $Nostoc$ and $Anabaena$.
These cells are specialized for the process of nitrogen fixation ($N_2$ fixation) because they provide an anaerobic environment necessary for the activity of the enzyme nitrogenase,which is sensitive to oxygen.

(C) Cyanobacteria,also known as blue-green algae,are photosynthetic prokaryotes.
They contain chlorophyll-$a$ and phycocyanin (a blue pigment),which gives them their characteristic blue-green color.
Although they are prokaryotic bacteria,they were historically classified as algae due to their photosynthetic nature and presence of pigments.
Therefore,option $C$ is the correct description in the context of their historical classification.

(C) $Nostoc$ is a genus of cyanobacteria (blue-green algae).
Cyanobacteria are prokaryotic organisms that contain chlorophyll $a$,similar to green plants,which allows them to perform oxygenic photosynthesis.
They lack cellulose cell walls (they have peptidoglycan),do not produce flagellated zoospores,and do not undergo sexual reproduction.
Therefore,the presence of chlorophyll $a$ is the characteristic feature among the given options.

(A) $Nostoc$ is a genus of cyanobacteria,which are photosynthetic prokaryotes. They are commonly known as blue-green algae. These organisms are capable of nitrogen fixation and are often found in colonies that look like filaments or beads.

(B) $Nostoc$ is a cyanobacterium that contains photosynthetic lamellae for performing photosynthesis. It also possesses specialized cells called heterocysts,which provide an anaerobic environment suitable for the enzyme nitrogenase to perform nitrogen fixation. Thus,$Nostoc$ can perform both photosynthesis and nitrogen fixation simultaneously.

(D) Blue-green algae,also known as cyanobacteria,are classified as prokaryotes.
Prokaryotic cells are characterized by the absence of a well-defined nucleus and membrane-bound organelles.
Specifically,they possess $DNA$ that is not associated with histone proteins,they lack a nuclear membrane,and they contain $70S$ type ribosomes.
Therefore,all the given options are characteristics of blue-green algae.

(D) $Lyngbya$,$Plectonema$,and $Anabaena$ are all examples of cyanobacteria (blue-green algae),which are photosynthetic prokaryotes.
$Sinorhizobium$ is a genus of nitrogen-fixing soil bacteria that form symbiotic relationships with legumes,but it is not a cyanobacterium.

(D) Prokaryotes are organisms that lack a membrane-bound nucleus and other membrane-bound organelles.
$A$. $Chlorella$ is a genus of single-celled green algae (Eukaryote).
$B$. $Chlamydomonas$ is a genus of green algae (Eukaryote).
$C$. $Protomyces$ is a genus of fungi (Eukaryote).
$D$. $Oscillatoria$ is a genus of filamentous cyanobacteria,which are prokaryotic organisms.
Therefore,the correct answer is $D$.

(C) Cyanobacteria,also known as blue-green algae,were the first organisms to evolve oxygenic photosynthesis.
They appeared on Earth approximately $3.5$ billion years ago.
By releasing oxygen as a byproduct of photosynthesis,they fundamentally changed the Earth's atmosphere,leading to the Great Oxidation Event.

(A) Blue-green algae,also known as $Cyanobacteria$,contain chlorophyll-$a$ which is similar to green plants.
In addition to chlorophyll,they possess accessory pigments called phycobilins.
$Phycocyanin$ is the specific blue pigment that gives these organisms their characteristic blue-green color.
$Phycoerythrin$ is a red pigment,while $Cyanophycin$ is a storage granule.

(C) Blue-green algae,also known as cyanobacteria,are photosynthetic organisms that lack a membrane-bound nucleus and other membrane-bound organelles.
Because they possess a primitive cellular structure,they are classified under the kingdom $Monera$.
Therefore,blue-green algae are considered $Prokaryotes$.

(D) Water blooms are caused by the excessive growth of photosynthetic organisms in water bodies,a phenomenon known as eutrophication.
Blue-green algae,also known as Cyanobacteria,are prokaryotic organisms that perform oxygenic photosynthesis.
When nutrients like nitrogen and phosphorus are abundant in water,these organisms multiply rapidly,forming dense mats or 'blooms' on the surface of the water.
Therefore,the correct answer is Blue-green algae.

(A) $Nostoc$ is a cyanobacterium that performs nitrogen fixation.
This process occurs specifically in specialized,thick-walled cells called heterocysts.
These cells provide an anaerobic environment,which is essential because the enzyme nitrogenase,responsible for fixing atmospheric nitrogen,is highly sensitive to oxygen.

(C) Cyanobacteria are photosynthetic prokaryotes that contain chlorophyll $a$ and other photosynthetic pigments. They synthesize their own carbohydrate food from $CO_2$ and water. They also possess water-soluble phycobilin pigments,specifically $c$-phycocyanin,which gives them their characteristic blue-green color.

(C) $Nostoc$ is a genus of cyanobacteria that is capable of nitrogen fixation.
It fixes atmospheric nitrogen into ammonia,which enriches the soil with nitrogenous compounds.
This process helps in improving soil fertility and is often used in the reclamation of alkaline or barren soils.

(D) $Nostoc$ is a genus of cyanobacteria that typically reproduces through vegetative methods like fragmentation or by forming specialized cells such as akinetes and heterocysts.
Endospores are primarily characteristic of certain bacteria like $Bacillus$ and $Clostridium$.
$Nostoc$ species do not produce endospores.
Therefore,the correct answer is $None$.

(D) The cell wall of $Nostoc$ (a cyanobacterium) is composed of peptidoglycan (murein),which is characteristic of prokaryotic organisms.
It does not consist of layers of microfibrils like the cellulose cell walls found in plants.
Therefore,none of the given options correctly describe the composition of the $Nostoc$ cell wall.

(C) Hormogonia are short,motile filaments or segments of cells that break off from the main filament (trichome) of certain filamentous cyanobacteria (like $Nostoc$ or $Oscillatoria$).
These fragments serve as a means of vegetative reproduction,as each hormogonium can grow into a new filament.
Therefore,hormogonia are essentially fragmented trichomes.

(D) . Fronds are typically associated with ferns (Pteridophytes),not bryophytes.
$B$. Angiosperms produce non-motile pollen grains; they do not have multiciliate sperms.
$C$. Diatoms are algae that reproduce via auxospores or binary fission; basidiospores are characteristic of Basidiomycetes (fungi).
$D$. $Nostoc$ is a cyanobacterium that contains specialized nitrogen-fixing cells called heterocysts. Therefore,this statement is correct.

(A) Cyanobacteria are prokaryotic organisms belonging to the Kingdom $Monera$.
They lack a well-defined nucleus and membrane-bound organelles,which are characteristic features of primitive organisms.
In contrast,$Bryophytes$,$Gymnosperms$,and $Monocots$ are all eukaryotic organisms belonging to the Kingdom $Plantae$,which are evolutionarily more advanced than prokaryotes.

(D) Cyanobacteria (blue-green algae) contain water-soluble accessory pigments known as phycobilins.
These include $C$-phycocyanin (which gives a blue color) and $C$-phycoerythrin (which gives a red color).
These pigments are located on the thylakoid membranes and assist in photosynthesis.

(A) $Escherichia$ $coli$ ($E.$ $coli$) is a well-studied bacterium.
It is a rod-shaped (bacillus) bacterium.
Its typical length ranges from $1$ to $3$ $\mu$m.
It is classified as a gram-negative bacterium because it has a thin peptidoglycan layer and an outer membrane,which causes it to lose the crystal violet stain during the gram staining procedure.

(B) The cell wall of $Gram$ positive bacteria contains teichoic acid,which binds with $Mg^{2+}$ ions to form $Magnesium$ ribonucleate. This complex provides structural stability to the cell wall against changes in $pH$ and temperature. $Gram$ negative bacteria lack this specific teichoic acid-magnesium complex.

(B) The cell wall of Gram-negative bacteria is relatively thin compared to Gram-positive bacteria. Its thickness typically ranges from $10$ to $15 \, nm$ (nanometers). Therefore,option $(b)$ is correct.

(C) The correct answer is $C$. Porins are specialized proteins found in the outer membrane of Gram-negative bacteria. These proteins form channels that allow the passage of hydrophilic,low-molecular-weight substances,such as nutrients and signaling molecules,from the environment into the periplasmic space,thereby enabling the bacteria to detect and respond to chemical changes in their surroundings.

(B) The correct answer is $B$. Marine archaebacteria (specifically hyperthermophiles) possess unique cell membrane structures,such as branched-chain lipids and ether-linked lipids,which provide high stability at extreme temperatures. This allows them to survive and multiply in environments like hydrothermal vents where temperatures reach $100-105^{\circ}C$.

(B) $Mycoplasma$ are prokaryotic organisms that lack a cell wall.
Because they have a cell membrane and metabolic machinery similar to bacteria,they are sensitive to antibiotics like $Tetracycline$ that inhibit protein synthesis.
In contrast,viruses are obligate intracellular parasites that lack their own metabolic machinery and are not affected by antibiotics like $Tetracycline$.

(D) Mycoplasmas are the smallest known prokaryotic organisms that lack a cell wall. They are known to cause various diseases in plants.
$1$. Clover phyllody is a plant disease caused by phytoplasmas (a type of mycoplasma).
$2$. Stripe disease of sugarcane is also associated with mycoplasma-like organisms (MLOs).
$3$. Yellows dwarf of tobacco is another well-documented disease caused by mycoplasmas.
Since all the listed diseases are caused by mycoplasmas,the correct option is $D$.

(C) $Mycoplasma$ are the smallest known prokaryotic organisms that lack a cell wall.
Due to the absence of a cell wall, they are pleomorphic and resistant to antibiotics that target cell wall synthesis, such as penicillin.
They require specialized, complex media for growth in laboratory conditions.
Hayflick's medium, which is a cell-free medium containing sterols (essential for $Mycoplasma$ membrane stability), is the standard medium used for their cultivation.

(A) Heterocysts are specialized,thick-walled cells found in certain filamentous cyanobacteria like $Nostoc$ and $Anabaena$.
These cells are specialized for nitrogen fixation.
Because heterocysts have a different cell wall structure and are often slightly larger than vegetative cells,they create a point of mechanical weakness in the filament or trichome.
Consequently,the trichome often breaks at the site of the heterocyst,making it the weakest link in the trichome.

(A) $Nostoc$ is a genus of cyanobacteria that exists in the form of filaments.
These filaments are known as trichomes,which are unbranched.
The individual cells within these trichomes are spherical or barrel-shaped and are arranged in a chain,giving the filament a bead-like appearance,which is described as moniliform.

(B) $Myxoxanthophyll$ is a photosynthetic pigment found in $Cyanobacteria$. It is a type of carotenoid pigment that helps in light harvesting during photosynthesis.

(C) The process of transformation in cyanobacteria was experimentally established by $W. F. Doolittle$ in $1972$. Transformation is a form of horizontal gene transfer where a bacterium takes up naked $DNA$ from its environment and incorporates it into its own genome.

(D) The 'Red Sea' gets its characteristic reddish color due to the massive bloom of a cyanobacterium (blue-green alga) known as $Trichodesmium \, erythraeum$. This organism contains a red pigment called phycoerythrin,which,when present in high concentrations,gives the water a reddish appearance.

(C) The term $Ray \ fungi$ is a common name used for $Actinomycetes$.
These are Gram-positive bacteria that form branching filaments or hyphae,which resemble the mycelium of fungi,hence the name $Ray \ fungi$.
They are prokaryotic organisms,unlike true fungi which are eukaryotic.

(C) The correct answer is $C$. Bacteria are the smallest living cells that possess a rigid cell wall.
$A$. Viroids are infectious $RNA$ particles without a protein coat or cell wall.
$B$. Algae are eukaryotic organisms with cell walls,but they are generally much larger than bacteria.
$D$. Mycoplasma are the smallest known living cells,but they are characterized by the complete absence of a cell wall.

(B) Prokaryotes are organisms whose cells lack a membrane-bound nucleus and other membrane-bound organelles.
$A$. $Agaricus$ is a fungus,which is a eukaryote.
$B$. $Salmonella$ is a type of bacteria,which is a prokaryote.
$C$. Green algae are photosynthetic eukaryotes.
$D$. $Bacteriophage$ is a virus,which is neither a prokaryote nor a eukaryote as it is acellular.

(C) Chromatophores are membranous infoldings of the plasma membrane found in some prokaryotes,such as cyanobacteria. They contain pigments like chlorophyll and other accessory pigments. In many cases,the presence of these accessory pigments masks the green colour of chlorophyll,allowing the organism to perform photosynthesis effectively.

(C) $Nostoc$ is a genus of cyanobacteria,which are prokaryotic organisms.
Prokaryotic cells contain $70$ $S$ type ribosomes.
These ribosomes consist of two subunits: a larger $50$ $S$ subunit and a smaller $30$ $S$ subunit.
Therefore,the correct answer is $70$ $S$.

(C) Organisms that lack a defined nucleus and nuclear membrane are classified as prokaryotes.
In prokaryotic cells,the genetic material $(DNA)$ is not enclosed by a nuclear envelope and is found in a region called the nucleoid.
Bacteria and cyanobacteria (blue-green algae) are both examples of prokaryotic organisms.
In contrast,green algae and red algae are eukaryotic organisms,which possess a well-defined nucleus with a nuclear membrane.

(D) The correct answer is $D$.
Bacteria are classified as prokaryotic organisms.
Prokaryotes are characterized by the absence of a membrane-bound nucleus and other membrane-bound organelles.
In contrast,green algae,fungi,and lichens are eukaryotes,which possess a well-defined nucleus enclosed by a nuclear envelope.

(A) Cells that lack a well-defined nucleus and a nuclear membrane are known as prokaryotic cells.
Bacteria are prokaryotic organisms,meaning their genetic material is not enclosed within a nuclear membrane.
In contrast,Algae,Fungi,and Lichens are eukaryotic organisms,which possess a distinct nucleus surrounded by a nuclear membrane.

(D) Blue-green algae,also known as cyanobacteria,are prokaryotic organisms.
Prokaryotes lack a membrane-bound nucleus and complex organelles.
Cell division in prokaryotes occurs primarily through binary fission,where the cell replicates its genetic material and divides into two equal halves.
Bacteria are also prokaryotic organisms that undergo cell division via binary fission.
Therefore,the process of cell division in blue-green algae is similar to that in bacteria.

(A) Blue-green algae,also known as Cyanobacteria,are photosynthetic prokaryotes.
They perform oxygenic photosynthesis.
The primary photosynthetic pigment present in blue-green algae is Chlorophyll $a$,which is similar to that found in higher plants.
They do not contain Chlorophyll $b$.

(B) In prokaryotic organisms like cyanobacteria,the photosynthetic machinery is located in specialized membrane structures called photosynthetic lamellae or thylakoids. Unlike eukaryotes,these are not organized into complex chloroplasts. Instead,they remain as isolated vesicles or lamellae scattered within the cytoplasm,as prokaryotes lack membrane-bound organelles like the nucleus or chloroplasts.

(B) . Chemosynthetic bacteria are able to manufacture all their organic food from inorganic raw materials in the absence of light.
These organisms obtain energy by oxidizing inorganic substances such as ammonia,nitrites,or sulfur compounds.
The general reaction for chemosynthesis is:
$6CO_2 + 24[H] \xrightarrow{\text{Enzymes/Energy}} C_6H_{12}O_6 + 6H_2O$

(B, C, D) Chromatophores are specialized membrane-bound vesicles found in some photosynthetic prokaryotes (like cyanobacteria) that contain pigments for photosynthesis.
They are absent in eukaryotic organisms such as $Pteridophyta$,$Gymnosperms$,and $Angiosperms$ because these organisms possess specialized membrane-bound organelles called chloroplasts for photosynthesis.
Since the question asks where they are absent,and options $B$,$C$,and $D$ are all eukaryotes,this question is technically flawed as it has multiple correct answers. However,in the context of typical biology curriculum,chromatophores are specifically associated with prokaryotic cells. If the question implies which of these groups lacks them entirely,all three $(B, C, D)$ are correct.