Thursday, October 28, 2010

For the love of Chocolate

Continuing with the Halloween theme, today I write about candy. And, not just any candy - chocolate. Almost everyone likes chocolate, and some of us love it. I know I am certainly guilty of raiding my kids’ trick or treat bags in search of the good stuff; which in my book is the solid chocolate without anything else getting in the way. No peanuts, no nuts, no crispies, no crunchies, no wafers, and not even caramel. Just chocolate.

What is it about chocolate that makes so many of us crave it. Turns out there is some solid science behind this apparent madness.

First of all, there is the chemistry. Scientists have discovered several properties of chocolate that literally lead us to crave it. One, it has opioids. Opioids are also found in opium. So, not surprisingly, chocolate, like opium, serves to dull pain and give a general feeling of calm and happiness. Of course, it is present in pretty small doses, so chocolate is a lot safer way to get these feelings! Two, chocolate has caffeine, which is an upper, which tends to make your heart beat just a little faster.

Second – the psychology. Because we tend to give gifts of chocolate to people we love, some theorize that eating chocolate can induce feelings of comfort and/or love for purely psychological reasons. Given the chemistry above, and the biological responses, it is no wonder people have associated chocolate with love. But our resulting cultural association of chocolate with love has trained our emotional responses as well. Even without the underlying chemistry, giving, receiving, or just eating chocolate tends to induce happiness.

Third – the biology. Chocolate really is good for you, at least in moderation. Chocolate contains antioxidants, and flavenoids, both of which are thought to increase your life span through their cardiovascular benefits. In simpler terms, chocolate is good for your heart, biologically-speaking. And, we know that our bodies tend to crave the things that are good for us. It is our bodies’ way of telling us we are short on particular nutrients.

Of course, we also routinely crave what is not so good for us, and too much chocolate definitely falls into that category as well. Chocolate has lots of fats, and sugars. The fact that it contains all those fats, which make it smooth, may also explain some of why we like it so much - the sensation of eating it.

So whatever the reason, enjoy!

Friday, October 15, 2010

Spooky Spiders…

October seems the appropriate month to continue on the theme of spiders and other creepy crawlies who happily decorate our homes right now in larger-than-life form. Last time I wrote about spider silk, and its amazing strength. Spiders are biological wonders from several other perspectives as well. Notably, their long and leggy legs.

First, have you ever noticed that when you find a dead spider, that its legs are all curled up (so long as it is not smashed, that is)? Their legs roll inward towards their bodies and form a sort of ball. This is because spider legs are hydraulic, like pistons. They are held rigid by the fluid inside them, and that fluid must be maintained at pressure in order for them to hold the spider up and allow it to move around. Once the spider dies, the pressure cannot be maintained, and the legs collapse.

To move, the spider has muscles within the legs that allow the seven (yes seven) sections of each leg to bend inward a coordinated manner. But, to straighten the leg, there are no opposing muscles in most spiders, because there is nothing to attach them too. Remember spiders have no bone, just their tough exoskeleton that makes up what we think of as their crunchy skin or shell. The fluid pressure in the leg is changed via changes in the spider’s blood pressure. Increases in pressure straighten the leg, decreases allow it to bend.

Jumping spiders are by far the best at this feat. They can quickly change the blood pressure in the legs which allows them to spring upwards, travelling as far as 25 times their body length. That’d be 25 to 30 feet for the average human. None of us can pull that off.

Running spiders are special again in their own way. They have given up web building entirely for the purposes of capturing food, and obtain their meals hunting them down and then overtaking them with sheer speed. Our common wolf spiders often hunt this way. Luckily, even the largest of wolf spiders is only about an inch long, because spiders running you down is enough to unnerve just about anyone. They play an important role in the control of other insects, however, so be thankful that they are there.

Fishing spiders, however, win the award for amazing legs. Fishing spiders can literally walk on water. They do this by abusing the laws of physics, and taking advantage of simple surface tension. Surface tension is the tendency of particles of water to stick together. This is why you see a drop of water form a round, bead-like drop, and not just scatter into its infinitesimally small molecules. Fishing spiders have tiny leg tips, and light bodies, and when they press these leg tips to the surface of the water, they are able to stay atop the surface, and not break the surface tension. This is due largely to a waxy coating on the legs. You see a small dimple form on the water from the pressure of the leg, but the tension does not break, unless the spider wants it to. These spiders can dash out onto the water to grab prey such as insects, or reach below the surface to grab even small fish. And, when they really need to move, they can rise up on two legs and gallop across the water, reaching speeds of about 30 feet per second, or 2 miles per hour. The average running speed for a person is 6 miles per hour. The world record 100 m dash clocked in at 28 miles per hour. But, when they are just hanging around, or casually need to move from place to place, fishing spiders can also place their legs on the water and sail with the wind.

Not a bad way to get around.

Saturday, October 2, 2010

Stronger than steel...

The strength of nature can be an impressive thing. Biologists, physicists, engineers and chemists alike often spend a lot of time just trying to figure out what makes things as strong as they are. What makes the shell of a clam rigid and tough? What makes the silk of a spider pliable yet strong?

This is an area of research called biomaterials. The study of biological substances and their physical properties in terms of measurements like strength and stiffness.

Recent research by scientists at the University of Puerto Rico has revealed that the toughest material on the planet is spider silk. In particular, the trophy goes to the web-spinning silk of the Darwin's bark spider, which lives on the island of Madagascar. This spider spins enormous webs that extend across rivers. Therefore, they must stretch and contract as the trees (to which they're anchored) move in the wind.

Spider silk, in general, is amazing stuff. It is a protein. It is both strong, meaning it resists breaking, and it is elastic, meaning it can deform and then recover its shape. Many materials have to trade off these properties. A substance can be very strong, like steel. But, steel is not elastic. If you bend steel, it will not return to its original shape. Spider silk, on average, has the same tensile strength as steel. But at the same time, it is very ductile, and can stretch about one and a half times its own length before breaking.

The bark spider of Madagascar spins fibers that are stronger than the strongest known man-made substance, which is Kevlar. Kevlar can resist about twice the force of steel. This is why they make bullet-proof vests from the stuff.

Spiders also can change the properties of their silk, by changing the water content of the silk. Most spiders can also weave more than one kind of silk, generally speaking there is strong silk that creates the support for the web, and sticky silk that catches the prey in the web. When you put these two abilities together, you end up with about a dozen distinctly recognizable kinds silk that can be produced by just one spider depending on the job at hand. The silk used to wrap up prey is even stronger than the silk used to support the web, and the silk used to form egg sacs is stronger still. Therefore, both of these silks are stronger, on average, than steel. At the other end of the spectrum, many spiders, particularly those that have just hatched, can extrude long, very thin strands of gossamer silk used for ballooning to new locations to settle and build their own webs.

The impressive properties of spider silk make it popular for study by engineers hoping to mimic Mother Nature. Unfortunately, it is not possible to create spider ranches so that the spiders can do the work for us. Spiders are not like docile cattle, making them extremely poor candidates for domestication. Spiders are aggressive and will eat one another, making it inadvisable to keep many spiders together in the same space. Reproducing the properties of the silk with man-made mimics is the only viable option, though scientists have created transgenic goats that will produce spider silk (I’ll save the ethical debate about that sort of process for a later article!).

For right now, the score is still Mother Nature 1, Humans 0 in terms of who can make the stronger substance.