BACKGROUND:
Cell walls are made primarily of
cellulose but there are also other substances like hemicelluloses,
minerals, tannins, resins, pigments, proteins, mucilages, and gums that
can be found in plant cell walls. Cell walls are porous, allowing an
exchange with substances outside the cell wall. Cellulose has a straight
chain structure, forming strong fibers that are ideal cell-wall
structural materials and useful in making products.
Cellulose is used commercially in
making paper, rayon, explosives, cellophane, buttons, and many other
materials. Cellulose comprises approximately 80 per cent of the dry
weight of wood, and forests are the source of many valuable articles in
addition to lumber. Plant fibers are twisted together to manufacture
thread or yarn from which fabrics are woven. The fibers are obtained
primarily from the cotton, flax, or hemp plants.
Lumber is mainly cellulose. There are
two zones of wood on a tree, the sapwood, a light-colored outer zone and
the heartwood, surrounding a generally darker-colored zone. The sapwood
functions in sap conduction and food storage, the heartwood is used for
mechanical support. Sapwood will eventually turn into heartwood.
Heartwood is the more durable portion of lumber.
PROCEDURE:
- In this lab, students will look at
six different products made from cellulose and will determine if there
are any characteristics that can help identify the items that came from
plants. Students will need to look at the material with a microscope or
good hand lens. You can either use the module or get six different
specimens of materials made from plants.
- Many specimens show evidence that
they have been derived from plants. Cotton fibers or threads will show a
twisting in the fiber which can be seen with a microscope. Lumber shows
portions of growth rings which are often visible to the naked eye. Dried
moss, which is used as a decoration for artificial plants, still has a
green color and has its structure except for the roots. Different types
of hemp or rope-like decorations show elongated fibers. Paper, however,
doesn't show much evidence that it can from plants, but that is mainly
because the wood pulp from which it was derived has been pulverized and
squashed to hide any connection to plants.
