GRE Subject Test: Biology › Understanding the Cell Wall
What polymer is commonly found in the cell walls of fungi?
Chitin
Cellulose
Peptidoglycan
Glycogen
Although cell walls often serve very similar functions for different species, the composition of the cell walls can vary significantly. Plant cell walls employ cellulose, while bacteria use peptidoglycan. Fungal cell walls use the polymer chitin.
In bacteria, what is the polymer that makes up the cell wall?
Peptidoglycan
Cellulose
Glycogen
Starch
Chitin
The correct answer is peptidoglycan. Cellulose composes the cell walls of plants, whereas chitin composes the cell walls of fungi. Starch and glycogen are stored polymers of glucose in plants and animals, respectively.
Which statement correctly describes a Gram-positive bacterial cell?
Contains no outer membrane outside of the peptidoglycan layer
Contains a periplasmic space
Has a very thin peptidoglycan layer
Stains red in the Gram stain
Stains red in the acid-fast stain
A Gram-positive cell has the following basic structural characteristics: stains dark purple in the Gram stain, has a thick peptidoglycan layer, and possesses no outer membrane beyond this layer. Thus, there is also no periplasmic space. Acid-fast stains are only used for specific bacteria that have waxy cell walls.