21 May 2004

The kingdoms of life

Forrest M. Mims III

Biologists divide living things into several broad categories.

Kingdom Monera is for the bacteria. Also included are the cyanobacteria, special bacteria that can make food from sunlight.

Bacteria are too small to see, but you see evidence of cyanobacteria when you look at the lichens that encrust a fence post or tree trunk. That's because a lichen is formed when a certain fungus traps stray cyanobacteria and steals some of the food they produce.

Kingdom Protista includes the algae and the protozoa. Algae are commonly seen, because chains of some of them become large enough to form strands or mats in water.

The algae serve us well, for they produce huge volumes of oxygen. You can see evidence of this in the form of green bubbles sprinkled across mats of algae.

Some people, certainly not readers of this column, frown on the lowly algae, even calling it slimy and icky. They need to know that some of the air they breathe contains pure, life-giving oxygen that bubbled up through a slimy green film floating on a pond.

Protozoa are microscopic creatures that travel through water looking for tiny specks of food. In March, I found protozoa in snow high in the mountains of New Mexico. When the snow melted, three different kinds of protozoa could be seen through Sarah's microscope as they swam or oozed their way through a droplet of water.

The third kingdom is the fungi, which were once classified as plants. But, unlike plants, fungi cannot produce their own food. Their root-like hyphae search for plant or animal matter to consume.

The fungi reproduce by periodically producing numerous spores, each of which can become a complete fungus. Mushrooms and toadstools are the most obvious fruiting bodies of some fungi. Their only job is to produce and scatter millions of spores.

Plants are the fourth kingdom. There are some 250,000 species of them. The novelty of plants is that they can produce their own food. They do this by using sunlight to combine carbon dioxide with water to form sugars and starches.

Animals form the fifth kingdom. Animals and fungi share at least one trait, for neither can produce food. There are some 1,000,000 species of animals.

Spring is a good time to observe the amazing variety of life's five kingdoms. Having just spent a day whacking, cutting and sawing a nature trail through some pointy, sharp, poisonous, sticky and beautiful forms of the plant kingdom, today seemed like a good time to describe them.

Forrest M. Mims III and his science are featured online at http://www.forrestmims.org/.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.