The earth has a huge plant kingdom which includes algae,
fungi, mosses, grasses, vegetables, trees, etc. Plants are
stationary and have no nervous system, and the cell wall
contains large amounts of cellulose. They are the primary
source of food for all other living organisms. All plants,
except fungi, contain chlorophyll. In addition to sunlight,
water and carbon dioxide, plants need nutrients for their
normal growth. Their metabolic processes are vital to the
maintenance of life on earth and are the result of
following products: (a) oxygen (from respiration),
(b) carbohydrates (from photosynthesis), (c) amino acids
and proteins (from nitrates and nitrogen-fixing bacteria),
(d) fats and oils, (e) vitamins, (f) natural fibers, (g) coal,
and (h) various other substances like alkaloid drugs,
rubber, etc.
Green plants are unique in being able to synthesize
their own organic molecules from carbon dioxide and
water using light energy by a process known as
photosynthesis.
Although the more primitive plants vary
considerably in their overall structure, the higher plants
(gymnosperms and angiosperms) are much the same in their anatomy and morphology. In a typical angiosperm,
four main regions or parts can be recognized: the root,
the stem, the leaf and the flower. Each part has one or
more basic functions.
Any plant portion contains thousands of tiny cells
packed tightly together. The cells are not all alike and
each has to perform a certain function. The basic plant
cell tends to be rectangular and has a tough wall of
cellulose which gives it its shape. The cell membrane,
just inside the wall, contains protoplasm which contains
the nucleus, the chloroplasts and many other microscopic
structures. In the center of protoplasm, there is a large
sap-filled vacuole, which maintains the cell's shape and
plays an important part in the working of the whole plant.
Both sexual and asexual reproductions are possible
in the plant kingdom.
