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A tale of two organisms

There are some things in the natural world I tend to take for granted, but that reveal true surprises when I look at them more closely. Such is the case with lichens. I’ve known about lichens since childhood, but it turns out I never really knew anything about them at all. I always assumed they were like mosses, vegetable-like things that grew on the ground, rocks, and trees. In fact, lichens are not even one organism; they are a delicate balance of fungi and algae (and in some cases, cyanobacteria) that coexist in the form of what we see as a lichen growth.

More than this astonishing fact, a study of lichens reveals many other surprises, including examples of their extreme hardiness, the myriad of uses to which they are often put, and the fascination they once inspired in a beloved literary figure. I’ve learned that there is much more to lichens than meets the eye.

One is the Hungriest Number

On the most basic level, lichens exist to fill a need for certain types of fungus. Because fungi are unable to produce food for themselves, they have adapted to take advantage of whatever opportunities they find to gather it, either becoming parasites on other organisms or gaining nutrients from decomposing matter. In the case of lichens, fungi use the photosynthesis abilities of algae and/or cyanobacteria to access nourishment. The fungus makes up most of the bulk of a lichen, with the algae or cyanobacteria cells interspersed amongst so-called “fungal filaments.” Because these cells contain chlorophyll, they are able to convert water and carbon dioxide into fuel for the lichen. In return, the fungus acts as a protective covering for the algae and cyanobacteria. In this way, the two (or more) organisms have a symbiotic relationship.

Various sources estimate that lichens cover 6–8% of the world’s land, and can be found pretty much everywhere there is a stable surface and adequate sunlight. They often grow on surfaces that other organisms would find inhospitable, such as desert sand, bare rock, and arctic tundra. Their four basic forms are: crustose (flat, scaly growths); squamulose (pebble-like growths); foliose (resembling leaves); and fructicose (tube-like branches). Lichens grow extremely slowly, sometimes less than one millimeter per year, and for this reason are helpful to scientists trying to date glacial retreats and other disturbances in the geological record.

Lichens serve as a major food source for many types of animals, including deer, caribou, and reindeer (hence the lichen that’s misleadingly called “reindeer moss”). In addition, some bird and squirrel species use lichens not only as material for building their nests and burrows, but also as food (handy in the winter when nothing else is available). Lichens have sometimes been eaten or brewed as tea in some cultures, but the use of lichens for their decorative and medicinal purposes has been much more common in human history. Their unique usefulness is a result of their adaptive abilities; in response to environmental challenges or to deter predators, lichens of different kinds have created more than 500 biochemical compounds. Dyes made from lichens were once commonly used in coloring textiles and continue to be used for preparing litmus paper. Some lichens have been found to have antibiotic properties, and are used as medicinal remedies in various parts of the world. Since they can be extremely sensitive to environmental conditions, lichens have even been used to detect levels of air pollution in Europe and North America.

A Perfect Licheness

An interesting footnote in the story is the involvement of the famous children’s author and illustrator Beatrix Potter in the early study of lichens. Best known for beloved works such as Peter Rabbit and The Tale of Two Bad Mice, earlier on in her career Potter was commissioned to create scientific drawings of biological specimens, including fungi and lichens. She became so interested in these organisms that she wrote her own scientific treatises on them, and in fact was one of the first to propose that lichens function as a symbiosis between fungi and algae cells. While she enjoyed her study of lichens, the success of her literary works eventually overshadowed this pursuit.

Lichen Strikes Again

Out of all the interesting facts about lichens, I think the most impressive is their extreme hardiness in harsh conditions. For example, lichens can dry out entirely, but then be restored to their original condition once they take on water again. This ability has served them well in regions where water can be scarce, such as deserts and polar regions.

Putting lichens to the ultimate test, the European Space Agency ran an experiment in 2005 that was mind-boggling in its implications. Researchers directly exposed specimens of two different species of lichen to open space for 14.6 days before returning them to Earth (the lichens were shielded during re-entry). Despite their exposure to the vacuum of space, cosmic radiation, full-spectrum UV light, and intense temperatures, the lichens survived and were able to undergo photosynthesis as before. Further experiments on the International Space Station have tested the endurance of lichen, including exposing it to space conditions for a year and a half. A team of scientists in Crete has also explored how lichens would fare in the environment of Mars, leading them to believe that lichens’ ability to survive the harsh climate, coupled with their hydrogen-producing capability, could make them a valuable source of fuel for long-range space exploration.

Lichens truly are amazing; with their incredible adaptive abilities, they have managed to thrive in the most barren of settings on Earth, and can even endure the severe conditions of outer space. The unique partnership of fungus with algae (or cyanobacteria) has benefited both organisms; in the case of lichens, two really is better than one.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on April 30 2007.

Image credit: Alex Proimos from Sydney, Australia [CC BY 2.0], via Wikimedia Commons

There are some of these food- and drink-related daily observations for which I can work up considerable enthusiasm. Wine, dark chocolate, cherry pie—bring it on. Margaritas, well…they’re just OK. They’re not among my top 20 favorite cocktails, and I won’t go out of my way to obtain one today. But if I happened to trip and accidentally knock over a bottle of tequila, some Cointreau (or other orange liqueur), and a bit of lime juice into an iced glass, maybe one that randomly had some salt on the rim for some reason, well, I would feel disinclined to let it go to waste. On account of the vitamin C and antioxidants and whatnot. I’m thrifty that way.

Image credit: Jon Sullivan [Public domain], via Wikimedia Commons

Taking scuba to new depths

If I end up completing all the tasks on my Life’s To Do List, I’ll live to be a very old man indeed. So many places to visit, books to read, foods to try, experiences to have—and the list is perpetually growing. “Learn scuba diving” is on the list, but like “visit Machu Picchu” or “have sushi at Sukiyabashi Jiro,” it’s something that requires a greater investment of time and money than I am able to make at the moment. Still, it’s something I’d like to do if the opportunity ever presents itself. Yes, there’s a lot of fascinating stuff underwater—the marine life, the shipwrecks, and all—but equally appealing is the geek factor. Scuba diving requires lots of cool, specialized equipment, and just think of the entirely new range of dive-enhancing gadgets I could justify buying!

Then perhaps one day, if I become sufficiently advanced and still have some money to spare, I’ll invest in the ultimate piece of scuba gear: a rebreather. This fabulous piece of kit could set me back as much as US$20,000, not to mention the extensive additional training and certification I’d need to use it. But a rebreather does for scuba diving something like what a hybrid engine does for a car: it provides much greater fuel efficiency while reducing noise and pollution. These things may not seem like a big deal on the road, but underwater, they can make all the difference in the world. (Rebreathers are also used in spacesuits and gear for mountaineering and firefighting, among other applications, but I’ll focus on the underwater use here.)

Heavy Breathing

In ordinary scuba diving, you have one or more tanks of air—or, depending on what sort of dive you’re undertaking, a mixture of oxygen with nitrogen, helium, or other gases in carefully measured proportions. Regulators deliver just the quantity of air you need, at an appropriate pressure, through a mouthpiece; when you exhale, a valve releases the used air into the water. Each time you take a breath, though, your lungs absorb only about a quarter of the oxygen in the air; the rest is exhaled along with the carbon dioxide you produce. So a lot of the oxygen divers take with them is essentially wasted. The deeper you dive, the more rapidly you use up air, so a dive’s maximum duration is determined by its depth and the number of tanks a diver carries. Even though air tanks don’t feel heavy underwater, there are practical limits to how much a diver can carry, and thus limits on the duration of a dive.

Rebreathers change this equation by recirculating the unused oxygen from every exhaled breath. Instead of being expelled into the water, the used air is channeled into a “scrubber,” an assembly that uses a chemical such as a soda-lime mixture (sodium hydroxide and calcium hydroxide) to absorb the carbon dioxide. That leaves a good bit of usable oxygen, which is recirculated into the system and supplemented, as needed, with more oxygen from a tank. In this way, a rebreather can provide dramatically longer dive times with a much smaller and less cumbersome apparatus. In addition, because air isn’t discharged into the water when you exhale, there are no bubbles (or at least very few). As a result, a diver wearing a rebreather can swim almost silently and invisibly—handy if you’re photographing bashful fish or, you know, sneaking up on the enemy spy who’s trying to sabotage your submarine.

In the Loop

Conventional scuba apparatus is “open-loop” (or “open-circuit”), meaning the air goes out of the system when it’s been used. Most rebreathers, by contrast, fall into one of three major categories:

• Oxygen rebreathers are the simplest variety. They use a single tank of pure oxygen, but because of the danger of oxygen toxicity (a situation where pressure forces too much oxygen into the blood), they can be used only at shallow depths of about 6 meters (20 feet) or less.
• Semi-closed circuit rebreathers replace the oxygen tank with a tank of mixed gases, allowing deeper dives. But their design also requires that a portion of the used air be vented into the water to maintain the proper levels of oxygen and other gases.
• Closed-circuit rebreathers are the most complex design. They use two gas tanks: one for air (or at least an oxygen-nitrogen or oxygen-helium mixture) and one for pure oxygen. Oxygen sensors feed data to a microprocessor that regulates the oxygen pressure in such a way that no gas needs to be expelled. Closed-circuit rebreathers also enable the diver to maintain very low levels of nitrogen (or other non-oxygen gases) in the blood, which reduces the need for slow decompression when ascending from deep water.

As great as rebreathers are for certain applications, they have some disadvantages compared to conventional scuba gear. For one thing, because rebreathers are so complex, more things can (and do) go wrong. They must be carefully maintained—and even then, they are far more prone to failure than a simple tank-and-regulator setup. (Failure of one’s breathing apparatus deep underwater, of course, is a rather serious problem.) In addition, it’s surprisingly difficult to regulate oxygen pressure precisely so that it falls into the narrow range between too little (which can result in a potentially deadly condition known as hypoxia) and too much (which can result in the potentially deadly condition of oxygen toxicity). If a rebreather fails to deliver just the right mix of gases, the diver is in trouble.

And of course there’s the price, which is not a big deal for the military, but problematic for many recreational divers. Note to self: Put “become fabulously wealthy” higher on Life’s To Do List than “learn to use a rebreather.”

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on February 17, 2005.

Image credit: Peter Southwood [CC BY-SA 3.0], via Wikimedia Commons

Years ago I ran across a job listing at Apple, and although I don’t recall the specifics, I remember one of the job requirements being the ability to “multitask while multitasking.” And I thought: Ha ha ha ha hard pass. Multitasking is a thing that computers can (sort of) do; it’s not something that humans can do. There are people who think they can multitask, but study after study has shown that when we try to switch rapidly among tasks (which is what multitasking really means, after all), our overall efficiency decreases quite a bit because of the extra cognitive load involved in getting the brain back up to speed where it left off on a previous task. In other words: it’s an illusion, and people who try to do it are not just fooling themselves; they’re actually decreasing their productivity. So just cut it out, already! Today is Single Tasking Day, and you celebrate it like this: Do one thing at a time. That’s it. Finish the thing, or get as much done as circumstances permit, then do the next thing. Repeat indefinitely.

While we’re on the topic…who decided that “single tasking” is the term for the opposite of “multitasking”? It should be “unitasking,” which is what I call it and what I (try to) do!

Image credit: John LeMasney [CC BY-SA 2.0], via Flickr