BY DR. JOSE PALU-AY DACUDAO
(Part 1)
AS PREVIOUSLY noted, for centuries the traditional way of classifying things in nature was to divide them into three ‘kingdoms’ – namely animal, plant, mineral. Though this is seemingly instinctive, it is certainly not scientific. ‘Mineral’ is now under the physical sciences, such as physics, chemistry, geology, and so on.
In modern biology, we limit ourselves to the classification of living organisms. That is animals and plants. Traditionally, animals moved and ate other creatures. Animals were often referred to as fauna, especially if referring to a collection of them. Plants were immobile and often photosynthesized, effectively feeding on water, carbon dioxide, and other inorganics. They were also called flora, especially for a collection of them. However, non-photosynthesizing immobile creatures were also classified as plants. Thus, bacteria and immobile fungi were also referred to as flora.
Flora is still a useful term in biology. For example, bacteria in the gastrointestinal tract is still often referred to as gut flora. Similar aggregations on our skin are often called skin flora. And so on. After all they don’t move around by themselves for the most part.
In brief. our instinctive definition of an animal is a living organism that moves about and does not photosynthesize.
Are there relatively common large organisms that do not photosynthesize and don’t move around? First thing that comes to your mind is probably a mushroom, if only we have all eaten it. A mushroom is that structure of many fungi that bear spores, a unit of reproduction often designed for survival and dispersal (similar to seeds). Being immobile, we think of fungi as plants or flora. The study of fungi (Mycology) traditionally has been regarded as part of Botany, the general study of plants. Traditionally they have been classified as plants, just the non-photosynthesizing ones. Right?
Wrong, and that’s the surprise.
As mentioned, fungi do not photosynthesize, like animals. They are mostly saprotrophs, organisms that obtain needed nutrients by extracellular digestion, like animals. They are immobile, but then so are some animals.
A clue is to the mystery of fungi is chitin. Chitin (C8H13O5)n is the second most abundant polysaccharide in the biosphere after cellulose to which it is similar chemically. (As mentioned in a previous article, cetaceans have gut florae similar to their even-toed hoofed cousins, such as carabaos, and these gut florae are able to degrade chitin.) Chitin is famously known as the major component of the exoskeletons of arthropods (such as crustaceans, which is now a clade that includes insects, another surprise). It is also well known that chitin is quite common in mollusks, being found in their radulae, and in the pen and beaks of squids and other cephalopods. Less well-known is that the integuments of nematodes (probably the most numerous multicellular animals on Earth) contain chitin. In other words, many animals synthesize extracellular chitin. (To be continued)/PN
