The short answer is to protect the inside of a cell by keeping certain substances out and allowing certain substances in. Another function is to help the cell maintain its shape. A cell membrane is not made of one solid piece but made mostly from compounds of proteins and phospholipids. The phospholipids make up the bulk of the membrane and the proteins are found around tiny holes in the membrane that helps it move compounds in and out of the cell.
The short answer: no. Is it possible that of the seven billion people in the world, all sleeping at some point during a 24 hour period, some might accidentally eat a spider during their sleep? Sure, it’s possible but very unlikely.
The source of this urban legend is generally unknown but a plausible explanation (from snopes.com) is this. In the early days of the Internet, a columnist named Lisa Holst wanted to prove a point that many people would believe all sorts of crazy things if they saw it in a list of “facts,” that had been emailed to them. She completely made up a list of false facts to prove how easily they would be accepted by a certain number of gullible recipients in the (then relatively new) world of email. One of her facts was that the average person swallows X number of spiders in their sleep every year. Read more…
To understand this, we should first answer what causes hair color to begin with. All hair, whether on your head, your arms, or your cat’s tail has pigment cells called melanocytes. These melanocytes produce a pigment called melanin- more specifically, the chemicals eumelanin and pheomelanin. Hair with more eumelanin will be darker (brownish to black) and hair with more pheomelanin will have a red/orange/yellow tint. Hair with less of either will be lighter.
These melanocytes also pass this pigment to cells called keratinocytes (which produce hair’s main component, the protein keratin). When the keratinocyte cells die, they keep the melanin which is what is visible and gives hair its color.
As we get older, the melanocytes get less active, thus producing less pigment and making your hair lighter. Eventually all the melanocyte cells die and there are none left to produce any color.
So what are the factors that control this production of pigment? Many are genetic. Alleles of the recently-discovered MC1R gene have been shown to produce red hair in mammals. Other genes, many as yet unidentified, are likely responsible for other hair colors. According to Laurence Meyer, a dermatologist at the University of Utah, “Generally speaking, among Caucasians 50 percent are 50 percent gray by age 50. There is, however, wide variation.” Of course, these percentages are different for different ethnic groups, which further emphasize the role genetics play in the color of your hair.
Scientific American: http://www.scientificamerican.com/article.cfm?id=why-does-hair-turn-gray
In the late sixteenth century, two Dutch eyeglass makers discovered that objects appear magnified when viewed through multiple convex lenses in a tube. For this simple discovery, Hans Janssen and his son Zaccharias are considered by some to have invented the microscope around 1590. About this same time, another eyeglass maker from Holland, Hans Lippershey came up with the same idea and is also considered by some to be one of the inventors.
“The coining of the name “microscope” has been credited to Giovanni Faber, who gave that name to Galileo Galilei’s compound microscope in 1625. [wikipedia]
Anton van Leeuwenhoek (1632-1723) is really considered to be the “father of microscopy” when he worked as an apprentice in a dry goods store where magnifying glasses were used to count the threads in cloth. He taught himself new methods for grinding and polishing lenses of great curvature which gave magnifications up to 270 times, the greatest known in that day. These led to the building of his microscopes and the biological discoveries for which he is famous. He was the first to see and describe bacteria, yeast plants, the teeming life in a drop of water, and the circulation of blood corpuscles in capillaries. During a long life he used his lenses to make pioneer studies on an extraordinary variety of things, both living and non living, and reported his findings in over a hundred letters to the Royal Society of England and the French Academy. [source about.com]
You might think the animal with the longest gestation period would be one of the larger mammals, but in fact it is the Alpine black salamander. It is a viviparous amphibian which lives in the high altitude Swiss Alps. At altitudes above 4,600 feet, it’s gestation period can be up to 38 months. It bears two fully metamorphosed young.
As of March 2011, there are two age-verified Americans over 114 years old. Besse Berry Cooper of Georgia and Walter Breuning of Montana. Besse was born on August 26, 1896 and Walter was born on September 21, 1896 (26 days her junior).
Image source: http://supercentenarianstudy.blogspot.com/
According to Wikipedia, there are less than 100 verified centenarians (persons living past the age of 100). And of centenarians, about 1 in 1,000 will live to be a super-centenarian (one who is living into their 12th decade.) Even rarer, is one who lives past the age of 115, which current estimates predict only 1 in 50,000 centenarians will reach.
An interesting study is observing the trend life expectancies have been changing over the past century. The following graph is the average life expectancy in the United States for each decade since 1900.
Note, statistics weren’t as accurately kept for the first part of the century but the overall trend is probably fairly accurate. Source of these data: U.S. Dept. of Commerce, Bureau of the Census. The report can be downloaded here.
Many of the processes that happen in the human body are chemical in nature and involve chemical reactions. While a student can be very knowledgeable in any single one of the three major scientific fields (biology, chemistry and physics), to truly master biology he or she will need at least a fundamental understanding of chemistry and physics. Granted, a physicist or chemist can get by with knowing little biology, the same can’t Read more…