CBSE Class 9 Answered

Cutin is a waxy substance on plant surfaces that tends to make the surface waterproof and can protect leaves from dehydration and disease. It is an insoluble polymer that, embedded in waxes, forms the cuticle covering the epidermal cell walls in the aerial parts of higher plants. In desert plants, it forms the thick waxy coating outside the epidermis.

Suberin is a wax like fatty substance, occurring in cork cell walls and in or between other cells. On alkaline hydrolysis it yields chiefly suberic acid. Suberin is highly hydrophobic and its main function is to prevent water from penetrating the tissue. In roots suberin is deposited in the radial and transverse cell walls of the endodermal cells. This structure is known as the Casparian strip or Casparian band. Suberin is found in the phellem layer of the periderm (or cork). This is outermost layer of the bark. The cells in this layer are dead and abundant in suberin, preventing water loss from the tissues below.

Lignin is a chemically complex substance found in many plants, which bonds the cellulose fibers. It forms the woody cell walls of plants and the "cement" between them. Lignin is found together with cellulose and is resistant to biological decomposition. Lignin is the chief constituent of wood other than carbohydrates. The cell walls of sclerenchymatous tissue are thickened due to lignin deposition.