Mucopeptides and muramic acid are the components of cell wall of members to which of the following class ?

Question

Accepted Answer

The correct option is 1:
Cyanophyceae is the correct class because the key components mentioned, **mucopeptides** (or peptidoglycan) and **muramic acid**, are the defining structural elements of the cell walls in **prokaryotic organisms**. Cyanophyceae, commonly known as blue-green algae, are actually a group of photosynthetic bacteria known as **cyanobacteria**. As prokaryotes, they fall under the Kingdom Monera. Their cell wall is structurally rigid and composed of a macromolecule called peptidoglycan. Peptidoglycan is a polymer made of two alternating amino sugars, specifically N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM, or muramic acid), cross-linked by short peptides. The presence of N-acetylmuramic acid is a universally characteristic feature of the peptidoglycan layer of bacterial (prokaryotic) cell walls, making the class Cyanophyceae the only biologically correct choice among the options provided, as all others are eukaryotic classes.

The incorrect option is 2:
Bacillariophyceae, also known as diatoms, are eukaryotic organisms belonging to the major group of algae known as Heterokontophyta. Their cell wall, which is often referred to as a **frustule**, is unique in the biological world because it is primarily composed of **silica** (hydrated silicon dioxide), which forms an intricate glass-like structure. This silica wall is composed of two overlapping halves, resembling a petri dish. The presence of silica is their distinguishing feature and provides significant structural support. Crucially, the cell wall of Bacillariophyceae does not contain mucopeptides or muramic acid, as these are components specific to prokaryotic cells.

The incorrect option is 3:
Phaeophyceae represents the brown algae, which are large, multicellular **eukaryotic** organisms, including the giant kelps. Like most plant-like eukaryotes, the cell wall of Phaeophyceae is fundamentally different from the prokaryotic structure. Instead of mucopeptides, their cell wall consists of an inner layer of **cellulose** and an outer layer composed of gelatinous substances called **algin** (or alginic acid) and fucans. Alginic acid is a hydrocolloid that gives the characteristic slippery or slimy texture to brown algae. These complex polymers are unrelated to peptidoglycan, thus eliminating Phaeophyceae as the correct choice.

The incorrect option is 4:
Charophyceae is a class of green algae that is highly significant because its members are considered the closest living relatives to land plants (Embryophytes). They are, without question, **eukaryotic** organisms belonging to the Kingdom Plantae or a related Protist group. The cell wall of Charophyceae is structurally similar to that of true plants, being predominantly composed of the polysaccharide **cellulose**. Cellulose is a polymer of glucose units and forms microfibrils that provide rigidity and strength. While they share this plant-like feature, their cell wall lacks the N-acetylmuramic acid and mucopeptide structure characteristic of cyanobacteria.