30. what are three functions of the cell wall?\n31. what is the composition of the cell wall?

Brief Explanations:

1. Function 1: Provides structural support to the cell, maintaining its shape.
2. Function 2: Protects the cell from mechanical damage and pathogens.
3. Function 3: Regulates the movement of substances in and out of the cell to some extent.

For the composition of the cell - wall, in plant cells, it is mainly composed of cellulose, hemicellulose, and lignin. In bacteria, it is peptidoglycan. Fungal cell - walls are made of chitin.

Answer:

30. 1. Structural support. 2. Protection. 3. Regulation of substance movement.
31. In plant cells: cellulose, hemicellulose, lignin; In bacteria: peptidoglycan; In fungi: chitin.