A cell wall material present only in blue-green algae and bacteria is
a. Muramic acid
b. Cellulose
c. Chitin
d. Pectin

Hint: The cell wall of blue-green algae comprises 2-3 layers which are located below the mucilaginous layer. The bacterial cell wall is located outside the plasma membrane. It provides the cell structure, rigidity and protection from the external environment.

Complete answer:
> Option A: Both blue-green algae or cyanobacteria and bacteria possess muramic acid and diaminopimelic acid in their cell wall. Muramic acid is an amino acid sugar. Muramic acid is the key component of peptidoglycan that forms the cell wall of both blue-green algae and bacteria. It is responsible for providing the structure to the cell wall of bacteria and algae.

> Option B: Cellulose is a polysaccharide that is found in the cell walk of the plant cell, some algae, and oomycetes. It is also found in the biofilm of some bacteria. Cellulose cannot be digested by humans but it is a necessary fibre source of human diet. Commercially cellulose is used in paper production.

> Option C: Chitin is a polysaccharide which is generated from the modified glucose chain. Chitin is responsible for the formation of the exoskeleton of arthropods and the cell wall of fungi.

> Option D: Pectin is a heteropolysaccharide, found in the cell wall, primary and middle lamella of terrestrial plants. It is mainly composed of galacturonic acid. Galacturonic acid is a derivative of galactose sugar.

Hence, the correct answer is option (A).

Note: There are many similarities found between blue-green algae and bacteria. These both lack true chromosomes, they both are capable of fixing nitrogen, they both possess mucilage sheath, both possess a saprophytic mode of life.