Fungi
are living organisms that are distantly related to plants,
and more closely related to animals, but rather different
from either of those groups.
Fungi
can be recognized by the following five characteristics:
(1)
The cells of fungi contain nuclei with chromosomes (like
plants and animals, but unlike bacteria).
(2) Fungi cannot photosynthesize (they are heterotrophic,
like animals)
(3) Fungi absorb their food (they are osmotrophic)
(4) They mostly develop very diffuse bodies made up of a
spreading network of very narrow, tubular, branching filaments
called hyphae. These filaments exude enzymes, and absorb
food, at their growing tips. Although these filaments are
very narrow, they are collectively very long, and can explore
and exploit food substrates very efficiently.
(5) They usually reproduce by means of spores, which develop
on, and are released by, a range of unique structures (such
as mushrooms, cup fungi, and many other kinds of microscopically
small fruiting bodies).
Organisms
which have all five of the features just described can be
found in two of the seven living Kingdoms - they make up
the entire Kingdom Eumycota or true fungi, whose cell walls
(the walls of the hyphae) are made largely of chitin (like
the exoskeletons of insects); and part of the Kingdom Chromista,
whose cell walls are made of cellulose (like plants), and
which also include the brown algae - wracks and kelps (all
these Chromista, though they may look very different, have
similar swimming cells with two flagella at one stage in
their lives). To read a fuller account of the living
kingdoms, click here.
