Cumberland Times-News

Bob Doyle - Astronomy

May 25, 2013

Life rules reveal just ‘Why Size Matters’

CUMBERLAND — This column will comment on some unusual trends of living organisms revealed in “Why Size Matters,” by biologist John T. Bonner.

Using biological data, graphs and geometry, Bonner demonstrates five rules that apply from one celled organisms through humanity to the largest life forms now alive.

“Why Size Matters” is from Princeton University Press, first published in 2006, and in 2012 as a paperback with ISBN 978-0-691-15233-2.

The first inkling of these rules came from Galileo, the Italian physicist who was put under house arrest for championing the sun centered model of Copernicus (where the Earth both rotates on its axis and orbits the sun).

Galileo wrote a book called “Dialogues Concerning Two New Sciences.” Forbidden to publish his works in Italy, the manuscript was smuggled out of Italy and published in Holland.

Using geometry, Galileo understood that the weight of an organism was roughly proportional to the size cubed.

But at the same time, a life form’s strength was related to the cross sectional area of its muscles. But surface area goes as the square of the size. (For example, the volume of a sphere is proportional to its diameter cubed while its area is proportional to its diameter squared).

Surface area is also important in circulating oxygen and nutrients through a life form, so as the size of an organism grows, there have to be special accommodations for allowing all the cells to be oxygenated, nourished and to allow their wastes and heat to be expelled.

Each human has blood capillaries totaling many thousands of miles, a gastrointestinal tract that is highly convoluted to greatly increase surface area and huge areas in our lungs to allow the capture of oxygen and release of carbon dioxide.

Here are Bonner’s five life rules:

1. Strength is related to weight and directly proportional to area.

2. Surface area of an organism that allow diffusion of oxygen, nutrients and heat will vary with size.

3. The complexity of an organism is proportional to its size. (The bigger the organism, the more different types of cells it has.)

4. Living processes such as metabolism (energy needed to keep basic internal processes operating), generation time, lifespan, speed of motion varies with size. (Smaller organisms have higher metabolic rates than large organisms.)

5. The abundance of a species in nature is related to its size. (The larger the organism, the lower their density in nature.)

Some of the striking diagrams in “Why Size Matters” include Mass versus Molecular Cohesion (showing that gravity is relatively weak in organisms 0.1 cm or smaller), Brain Mass versus Body Mass (only elephants and blue whales are higher than humans and porpoises), Abundance in Nature versus Body Size (the bigger the animal, the less abundant per area), Lifespan versus Body Weight (humans are at the top!).

Planets dance

Very low in the western dusk (start looking about 8:45 p.m.) are three planets clustered together this evening. To see the planets, you need a site with a very flat western horizon.  

Tonight the three planets form a small equilateral triangle (three equal sides) with Mercury on top, bright Jupiter on the left and brilliant Venus on the lower right.

This evening, Mercury is 106 million miles from Earth, Venus at 153 million miles and Jupiter at 564 million miles. So only from the Earth will these planets appear close together.

Tomorrow at dusk, the three planets will form a right triangle with Mercury on top, Venus directly below and Jupiter to the left.

By Thursday, the planets will be in a line with Mercury on top, Venus below and Jupiter at the bottom.

By next Sunday, the spacing between the planets will have grown with Mercury still on top, Venus beneath and Jupiter even lower. Binoculars will be helpful in spotting Mercury, only one third as bright as Jupiter.

Bob Doyle invites any readers comments and questions. E-mail him at rdoyle@frostburg.edu . He is available as a speaker on his column topics.

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Bob Doyle - Astronomy
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