|
Since fungi are achlorophyllous (Fig. 1-17) and
cannot manufacture their own food (heterotrophic), they must derive
nutrients from other sources.
Fig. 1-17. Two common fungi, a poisonous species
of Amanita (L) and a coral fungus (R).
Fungal cells or filaments (hyphae)
have walls that prevent them from engulfing food (Fig. 1-18),
therefore they must absorb
their nutrients.
Fig. 1-18. Fungal hyphae as viewed with a
compound microscope.
The process of photosynthesis in the
plant cell involves the absorption of CO2 and H2O and the production of
O2 and simple sugars (Fig. 1-19).
Fig. 1-19. A diagrammatic representation of what
takes place in the process of photosynthesis.
CLICK
HERE TO GO TO TOP OF RIGHT SIDE COLUMN
|
Since fungi have no chlorophyll,
they rely on other organisms and must absorb their nutrient. This is
possible by the secretion of
enzymes into the substrate on which they grow. Enzymes break down
solids into a liquid form that the fungus can absorb. Fungi over
thousands of years have evolved some of the most extensive and complex
enzyme systems which have enabled them to grow on or in almost any
organic material available. Green plants and cyanophilous bacteria with
chlorophyll are the only organisms on our planet that can manufacture
their own food through photosynthesis.
Four basic types of relationships exist between fungi and the material
they utilize as food. Most
fungi are saprobes, i.e. they
derive nutrient from decaying organic material. Others are parasitic,
i.e. they derive their nutrient from living organisms, and they are not
particular and will parasitize all kinds of plants, animals, and fungi! Those that
require a living host on which to complete their life
cycle in nature are referred to as
obligate parasites. Some
have adapted a lifestyle in which they live predominantly as saprobes
but have the faculty or ability to live also as a parasite. These are called facultative
parasites. Whereas, there are others that live predominantly as
parasites but once the host is killed are able to live as a saprobe.
These are called facultative saprobes. There are a number of parasites that cause no apparent damage to their host while they are
providing benefit to the host. These are called symbiotic fungi and include such fungi as lichens (an algal host), mycorrhizae
(a higher plant host), endophytes
(growing in leaves and stems of various plants and providing
protection from insects etc.), and symbiotic species inside of insects
and other animals. Saprobic fungi that grow in association with and
deriving nutrient without damage to the host are called commensals.
Ecologically, on earth we have three basic roles that organisms play:
producers
(those organisms with chlorophyll); consumers (largely animals,
but also fungi and bacteria); and decomposers (largely the fungi)
(Fig. 1-20).
Fig. 1-20. An outline of the major roles of fungi on our planet.
Simply, plants absorb minerals and water from the earth
and through photosynthesis form new matter. Animal, with a little help
from fungi, protozoa, and bacteria, consume most of the matter, and
largely the fungi decompose what is left over from dead plants.
|
