Chitin is a polysaccharide. The chitin monomer is a β-glucose molecule with one OH group replaced by an NHCOCH3 group. NHCOCH3 can be represented by N(Ac).

Figure 1 shows the monomer that forms chitin and the chitin polymer.

Chitin has a similar structure to cellulose.

Use Figure 1 to describe three ways the structure of chitin is similar to the structure of cellulose.

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Chitin keeps the tracheae open in the tracheal system of gas exchange in an insect. Gas exchange does not occur in the tracheae.

Explain the importance of one adaptation of the gas exchange surface in the tracheal system of an insect.

Lignin is a polymer found in the walls of xylem vessels in plants. Lignin keeps the xylem vessel open as a continuous tube.

Explain the importance of the xylem being kept open as a continuous tube.