Daniel LeVan, age 10, of Allentown, Pennsylvania, for his question:
How does the paramecium divide?
The paramecium, of course, is a protozoan one of those miraculous midgets made from only one living cell. Most single celled animals resemble soft little blobs of jelly. The paramecium is somewhat more complicated. For one thing, it has a stiffer outer covering which gives it a permanent shape. It looks like a microscopic slipper and unlike most protozoans, it has a front and rear end. It also has unusual methods of simple cell division.
Most living cells have only one nucleus, the small unit that governs all the miraculous processes of life. The paramecium's one and only cell has two nuclei. Nobody knows exactly why this is so. But these nuclei are somewhat different and seem to divide the duties of an average nucleus between them.
When other protozoans divide, they form duplicate copies of the single nucleus, one copy for each new cell. When the paramecium divides, both nuclei form duplicate copies. They grow longer and pull apart as the cell stretches and separates. Each half becomes a new cell with copies of the original nuclei. If a colony of paramecia gets plenty of food, their cells divide two or three times a day and the population explodes at a fantastic rate.
The paramecium, the amoeba and other protozoans multiply by dividing their single cells into pairs of identical twin cells. The key to success is in the nuclei that govern the complex activities of life. They contain the instructions that the cells need to carry on their duties and survive. These blueprints are DNA chemicals, wound in tight strands inside the nucleus of every cell. When cell division begins, each of these strands makes a copy of itself and separates lengthwise down the middle.
In the paramecium, the strands in both nuclei create duplicates. The copies move to opposite ends of the cell and the cell begins to pinch a waist in the middle. The waist gets thinner and finally breaks. The paramecium is now two paramecia, each with a duplicate of two slightly different nuclei. The process of cell division may take an hour or so and if food is plentiful, the twins soon grow to normal size.
Sometimes paramecia multiply by a sort of mating process. Two cells come together and their larger nuclei break apart. Their smaller nuclei divide twice, but only one copy survives in each cell. It divides, and the two cells exchange copies. The two cells then separate and each divides into a set of quadruplets. This method of reproduction is not simple cell division because the two original cells exchange their basic DNA material.