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From Carbon to Coffee Bean, A Visual Scale
Jul 30 2011 7:07:39 pm EST
Topics:From the Genetics Science Learning Center at the University of Utah, I found this excellent Flash animation that displays a scaled representation of various organisms, bacteria, viruses, and molecules down to a carbon atom.
The animation helps put in perspective the size of the systems responsible for life. In particular, I am surprised by the size of viruses, and can appreciate the difficulty in detecting them.
Bodily Surface and Volume in an Organism
Jul 25 2011 5:00:00 pm EST
Topics:D’Arcy Wentworth Thompson notes that there is a tendency in all organisms for bodily surface to keep pace with volume.
Multicellular organisms, like unicellular organisms, require a constant supply of nutrients and various gasses. A unicellular organism may absorb the various nutrients and respiratory gases directly from their surrounding environment. However, as the sheer quantity of cells increases in an organism, the distance between the environment and the cells increases, and various organ systems are required to transport nutrients and gasses.
The circulatory system utilizes fractal branching structures to maximize surface area for distribution of these gases and nutrients. Air sacs and alveoli greatly increase the respiratory surface of the lung. The long tract of the intestine is itself lined with small villi to maximize nutrient absorption. These systems each utilize some method to increase surface area to keep pace with volume. Consider the following passage from “On G
Bird Coloration: Pigments and Structural Colors
Jul 22 2011 5:00:00 pm EST
Topics:The remarkable diversity in color and iridescence of birds is achieved by pigments and structural colors.
Pigments are colored substances that reflect certain wavelengths of light, while absorbing others. It is the reflected light that is identified as the pigment’s color. Pigments are located on the skin or feathers of the bird and are independent of the structure of the feather. Bird pigments come in three different groups: melanins, carotenoids, and porphyrines.
Melanins are the primary determinate in human skin color. They also serve to color the skin and feathers of birds, as well as providing strength and durability to feathers. Melanins produce blacks, reddish browns, and pale yellows.
Interestingly, a feather without any pigmentation is the weakest of all. White birds will often have melanin fortified black feathers on their wings where they are subject to the greatest stress.
Carotenoids are naturally occurring organic pigments in the chloroplasts and chromoplas
Color Range Perception, Evolution of the Eye:
Jul 21 2011 10:15:55 am EST
Topics:From the entire range of the electromagnetic spectrum, most life that can perceive light evolved to perceive a narrow band—the visible light spectrum (400 nm-700 nm). This range of perception is based on hundreds of millions of years of adaptation.
An interesting phenomenon of the visible spectrum is that it penetrates water by about 6 orders of magnitude better than adjacent frequencies. In other words, the visible spectrum penetrates water much better than other frequencies. This phenomena is demonstrated in the graph below (Fernald, 1997).
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Size of Organism and the Eye, Scaling
Jul 18 2011 5:00:00 pm EST
Topics:Many biological systems vary in proportion to the size of the animal. For example, as an animal increases in size, the skeletal system must increase in proportion to handle the added weight. However, the eye has ranges and limitations of magnitude of its own, resulting in less straightforward scaling.
From the simple eyespots of a unicellular organism, to the diverse range of simple and compound eyes of multicellular organisms, the eye has evolved to detect a narrow band of electromagnetic radiation: visible light. In the case of the unicellular organism, it might only be able to detect the presence of light and perhaps its direction. Whereas vertebrates have evolved to differentiate wavelengths of light as color, and determine shape and movement. In all cases, the shape and size of the eye is determined more by what the animal needs to see and less by the animal’s size. As D’Arcy Wentworth Thompson points out, “A big do
Fairyflies are tiny parasitic wasps whose eggs are laid and larvae reared within the tiny eggs of larger insects. Their size varies to less than half a millimeter, to 4 mm. One genus (Alaptus), parasitic on Psocoptera eggs, approaches the record of 0.18 mm.
The required thrust and lift is so tiny proportional to the body that the wings of some fairyflies are made of tiny hairs or bristles instead of a continuous membrane.
Practical Limits on the Size of an Exoskeleton
Jun 7 2011 9:28:48 am EST
Topics:The perils of molting, the force of gravity, and the percentage of oxygen in the atmosphere play a role in the practical limit on the size of an exoskeleton.
Unlike an endoskeleton, which allows an organism to grow in small increments, an exoskeleton needs to be discarded to allow the organism to grow—the process of molting. In between the shedding of the old exoskeleton, and the hardening of the new, the organism is vulnerable to predation and the forces of gravity. Too large an organism would take too long molting, and risks collapsing under its own weight.
Similarly, a fully hardened exoskeleton needs to be scaled appropriately to the dimensions of the organism to prevent it from collapsing. Since strength is proportional to the square of the linear dimensions, whereas mass is proportional to the cube of the linear dimensions, the skeleton needs to become ever thicker as size increases. At a certain point, the design becomes impractical.
Since an exoskeleton serves as a r
The Effect of Gravity on an Organism
Jun 6 2011 7:52:56 am EST
Topics:Through his studies on swimming, walking, and flight, D’Arcy Wentworth Thompson determined that in every case, speed tends to vary as the square root of the linear dimensions on an animal (Froude’s Law). He also notes that as the length of a limb decreases, its rhythm tends to increase rapidly, due to the simple fact that decreasing the length of a pendulum proportionately increases the rate of swinging.
He extends his observations to all the rhythmic motions of the body, such as heart rate and rate of breathing, noting that as size decreases, the tempo increases. In other words, a mouse’s heart rate and breathing is much faster than ours, while an elephant’s is much slower than ours.
Furthermore, he notes the profound effect gravity has on the form and action of most all organisms, and changing the force of gravity would have a dramatic effect on the growth and form of an organism. Consider the following passage from
On Evolution Of Flight, D'Arcy Wentworth Thompson
Jun 5 2011 9:26:02 am EST
Topics:Nature has developed many dynamic and efficient solutions to break its ties to the ground. The soaring Bald Eagle circles upwards in thermal updrafts, catching the wind in its long broad wings, gliding from updraft to updraft during migration. The Wandering Albatross repeatedly dives into the valleys of ocean waves, wheeling back up into the air, utilizing dynamic soaring to travel many thousands of miles using very little energy from flapping. Canadian Geese maintain continuous flapping flight in formation to reduce drag. The voracious hummingbird beats its wings anywhere from 8-100 times a second, depending on size, and generates thrust in both the upstroke and downstroke to maintain hovering flight. Not to mention the wonders of insect flight…
However, nature, as man, began with rudimentary evolutionary experiments. As we have refined human technology over hundreds of years, so has nature over hundreds of millions of years.
D’Arcy Wentworth Thompson summari
On Flight Dynamics: Influence on Living Systems
May 31 2011 1:33:00 pm EST
Topics:Regarding flight, D’Arcy Wentworth Thompson expresses the unique requirements to remain aloft, and the effect these requirements have on the structure of an organism. From On Growth and Form:
The bird’s case is of peculiar interest. In running, walking or swimming, we consider the speed which an animal can attain, and the increase of speed which increasing size permits of. But in flight there is a certain necessary speed—a speed (relative to the air) which the bird must attain in order to maintain itself aloft, and which must increase as its size increases. It is highly probable, as Lanchester remarks, that Lilienthal met his untimely death (in August 1896) not so much from any intrinsic fault in the design or construction of his machine, but simply because his engine fell somewhat short of the power required to give the speed necessary for its stability (41).
…a bird,
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