And spiralling around as well
A look at the diminutive, fantastically diverse life forms and their activity in a single drop of water can be a truly amazing experience – provided of course you have not chosen tap or rainwater. A drop of water from the edge of a weedy pond (or a puddle near a penguin rookery, which was my source for a study) examined under a simple light microscope does, however, reveal a microcosm of hidden life. In amongst the jittering soup of miniature plants and animals, it is the group of ciliated protozoans that are the greatest attention getters. The smallest may not even reach 50 microns, while Paramaecium and Euplotes maximally attain 1 mm and the biggest like Spirostomum may reach a length of 3-4 mm.
Single-celled and usually only just visible with the naked eye, most of these ciliated (hairy appearing) microscopic vacuum cleaners spiral their way around, ingesting phytoplankton, algal spores, bacteria and detritus through a clearly visible “cell mouth” (the cytostome) and venting wastes through a cytoproct (the “cell anus”. In fact spiraling would describe movement in one plane, but these little critters (apart from Euplotes that prefers to crawl along) move around in a three-dimensional space and a medium, which to them is anything else but frictionless and drag-free. They literally screw their way forward and up and down in what to them is a viscous medium hard to move around in water. A helical advance seems therefore energetically the most appropriate modus operandi. Every now and then, as if to catch their breath or to evaluate their path, they halt, reverse, or change direction.
For reproductive purposes they can split lengthwise in half, cloning themselves and doubling the population, but for the purpose of re-juvenation, nuclei between unrelated individuals may be exchanged. These one-cell-bundles of life and energy can detect different ions in the water, react to concentration gradients of oxygen and carbon dioxide, respond to increasing and decreasing temperatures and sense variations in the level of salinity and ambient light. They react to bumping into each other or some inanimate object and they have means to defend themselves against microscopic attackers. And they do all this as a single cell with no brain. But even if all parameters are optimal and there is no shortage of suspended food particles, life has its difficulties for them -and I am not referring to just predators.
The smaller an animal, the tougher it becomes to move around in be it air or, even worse, water. An ocean liner, for instance, forced to stop abruptly at full speed, coasts for several hundred metres before it comes to a halt; a small fish may coast for a few centimetres when it suddenly stops swimming, but our ciliated protozoans in a drop of water, it has been calculated, would not coast for more than a fraction of 1/1000 of a millimetre. Water to them is a kind of syrup and for their helical advance they use cilia like Roman galley slaves used oars. Their frequently pear- or slipper-shaped minute bodies must also be seen as solutions to the environmental challenge that the viscosity medium they inhabit provides.
Despite their diminutive size, most of the ciliates are speedsters reaching velocities of close to 0.5 mm per second at full speed. This corresponds to roughly one body length and in human terms (1.8 m tall person) would mean a swim of 100 m in 55 seconds (and no Olympic medal), but still faster than most of us I suppose.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
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