into a gel that fills the spaces between
cellulose fibers. Pectins can be either
dissolved or consolidated by cooking, and
their gel-like consistency is exploited in the
making of fruit jellies and jams (p. 296).
When fruits soften during ripening, their
enzymes weaken the cell walls by modifying
the pectins.
Wilting in vegetables. Plant tissue that is well
supplied with water is filled with fluids and
mechanically rigid (left) . Loss of water
causes cell vacuoles to shrink. The cells
become partly empty, the cell walls sag, and
the tissue weakens (right).
Tough Cellulose and Lignin Cellulose, the
other major cell-wall component, is very
resistant to change, and this is one reason that