Science In Action

Do Cow Farts Cause Global Warming?

noreply@blogger.com (D. Wheat) — Wed, 02 Jan 2008 20:43:00 +0000

Bovine Flatulence--Threat or Menace?

Cows can digest things we can't, especially including the cellulose in grass and grain. They do this by maintaining cultures of microorganisms in their complicated series of "stomachs" that can break down cellulose. The cows then digest the microbes and the sugars and fatty acids they produce.

(Brief overview of ruminant digestion here. If you are interested in delving into the digestive physiology of ruminants in more detail, start here.)

Some of these microbes produce methane (CH₄). Some of the other microbes can use that methane as food, but a certain amount of it escapes as belches or farts (mostly belches). (Some people have microbes in their guts which produce methane, and thus their farts also contain methane--but nothing compared to the amount cows produce.)

The publication Emissions of Greenhouse Gases in the United States 2006 (pdf) summarizes the total greenhouse gas output of the US:

Of the 605 million metric tonnes CO₂ equivalent of methane shown in the graph, about 115 million tonnes CO₂e is from "livestock enteric fermentation"--mostly cow burps and farts. That is less than 20% of the methane load, and less than 2% of the 7 billion tonne CO₂e total.

Of course raising cattle causes other greenhouse gas emissions.

There are about 56 million tonnes CO₂e of methane and 55 million tonnes CO₂e of nitrogen oxides released from cattle wastes as they decompose. (Some of that methane can be captured and used to generate electricity or heat, while releasing carbon dioxide, a much less potent greenhouse gas.)
About 227 million tonnes CO₂e of nitrous oxide is released from nitrogen fertilization of soils (30% of it from nitrogen fixed by the crops themselves, not from industrially produced fertilizers).
Most of the nitrogen fertilizer used on crops (89%) is used on corn (maize). About half of the corn produced in the US is fed to livestock, a large fraction to cattle, especially dairy cows. So about 50 million tonnes CO₂e emissions associated with fertilizer use should be indirectly blamed on cows.
(Another large fraction of corn is used to make ethanol as a motor fuel, indirectly causing the release of significant amounts of greenhouse gases in the corn production. But that's another story.)

So cattle are responsible for about 3.5% of US greenhouse gas emissions, on a CO₂ equivalent basis. To keep this in perspective:

2% of greenhouse gas production is in the form of methane from garbage decomposing in landfills.
Roughly 2% is chlorofluorocarbons (CFCs) from air conditioners, refrigerators and industrial processes.
Other industrial processes (especially cement manufacture) produce about 2%.
Burning jet fuel accounts for more than 3%.
12% of greenhouse gas emissions are CO₂ emitted generating electricity which is used in residential applications like lighting, TVs, computers, and refrigerators.
17% came from burning gasoline in cars and trucks.

So cow farts and burps do contribute some to greenhouse gases, and thus to global climate change. But they are not a major cause. Nonetheless, improvements in fertilizer use and waste management in agriculture could reduce the cow-related burden on our atmosphere.

Reduced consumption of beef and dairy products would probably have little effect. (If half of US consumers cut their consumption of beef and dairy products in half -- and the resulting drop in prices didn't stimulate the other half to increase their consumption, or drive more exports -- it would reduce national greenhouse gas emissions by about 1%.) Maybe this will become more of an issue in the future.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: global warming, climate change, carbon choices, greenhouse gas emissions, co2, methane, cattle, cows, farts, agriculture

Science on the Small Screen

noreply@blogger.com (D. Wheat) — Mon, 03 Dec 2007 23:53:00 +0000

Check out these science video sites

Several sites have been set up to allow research scientists and educators to post videos of their experiments, lab projects, or results. It's a chance to see real science in action.

Scivee
The Journal of Visualized Experiments
LabAction
DNATube

There's everything from an animation about how the lac operon works to preparing T cell growth factor from rat splenocytes with a French accent to a lecture on centripetal force.

Explore to see some real scientists doing real science, as well as a lot of science stuff lifted from TV, etc.

Why Is The Sky Blue?

noreply@blogger.com (D. Wheat) — Sun, 25 Nov 2007 18:41:00 +0000

Think of the colors you see in the sky. On a clear day, when the Sun is out, the sky may appear blue.

Why is the sky blue? (multiple choice)

a. It isn't colored blue--it only looks blue.
b. Because it isn't red.
c. The sky is colorless--that blue light is from the Sun.
d. all of the above.

The correct answer is "d. All of the above".

The light of the Sun is white (it glows "white hot", emitting lots of radiation over the whole range of wavelengths our eyes can respond to). But when you glance at the Sun it appears yellow. (Don't look too long at the Sun--the UV radiation will hurt your eyes. And never ever look at the Sun with a telescope or binoculars. That could damage your eyes instantly.)

So we really have two questions:

Why does the disc of the Sun appear yellow (rather than white, as it does from space)?
Why does the sky only appear blue when the Sun is out (rather than black as the Moon's sky appears if you are on the Moon, or the Earth's sky when the Sun is down)?

The answer to both questions is the same: The light from the Sun is broken up as it passes through the atmosphere. The blue you see is just part of the sunlight that took a roundabout route.

What breaks the Sun's light into yellow and blue light and sends these colors on different paths?

Most of the atmospheric gases are transparent to visible light. They don't filter the Sun's light and make it yellow, as a yellow filter would. Besides, if colored gases made the Sun appear yellow, where does the blue come from? The part of the atmosphere that changes the Sun's light is the molecules and tiny particles that are floating in it.

There are particles of water--tiny droplets too small to be seen as clouds. There are particles of organic material--smog or haze, condensed from volatile organic chemicals that have gotten into the air. There are particles of sulfuric acid from volcanoes and power plants. There are molecules of gases in the atmosphere.

These tiny particles, much smaller than the wavelengths of sunlight, scatter the sunlight as photons from the Sun interact with the particles. This is called Rayleigh scattering after the British physicist who described how it works. (Larger particles, like the water droplets in clouds, are closer to the wavelengths of sunlight, and they scatter it differently. This is why clouds are not blue.)

You can see the effects of Rayleigh scattering by tiny particles floating in a liquid by trying the following demonstration. Particles in a gas (like the atmosphere) work the same way.

Fill a tall jar or beaker with water. Shine a bright light through it. (An overhead projector works well. You want the bright light to take a long path through the water.) If you look at the light that goes straight through the water (and is projected on the screen if you use an overhead projector) it will appear about the same color that it would appear without the water in the way. If you look at the sides of the jar, at right angles to the beam of bright light, you won't see much of that light. The beam of light goes right through. (Water is transparent and colorless.)

Now add a small amount of milk (about 1/8 teaspoon or less per quart of water). The water will become cloudy as the milk disperses. The tiny particles of fat and protein in homogenized milk will disperse in the water in what is called a colloidal suspension. They float in the water like aerosol particles float in the air.

Now put the suspension in the light beam again. If you look at the light through the suspension (or look at the screen) the light will appear to have a reddish color, different from the color it had when viewed through clear water. If you look at the sides of the jar the cloudy contents may have a bluish tinge. The blue light from the light source is being scattered more than the red light. So some of the blue light emerges from the sides of the jar, leaving a reddish (blue taken away) color in the transmitted light that wasn't scattered.

Here is a description of a similar demonstration. Here is another.

This scattering by suspended particles much smaller than the wavelength of the radiation being scattered makes the sky blue, sunsets red, and the Sun yellow. But how?

When you look at the sky during the day you only see the Sun in one spot, and it appears yellow. But light from the Sun that is not heading directly toward you is being scattered to the sides of the direct path to those other locations, with more blue light being scattered. Any place in the sky where the Sun isn't, as seen from your location, you can see some of this side-scattered blue light. In the sunlight coming directly from the Sun to your eye there has been side-scattering of some of the blue wavelengths, so the Sun is left looking yellow.

If you look toward the Sun at sunset or sunrise, you are seeing the light that has not been scattered, the longer wavelengths. And since at sunset and sunrise the light takes a longer path through the atmosphere to your eye the Sun appears orange or red, not just yellow.

Why is blue light scattered more and red light less?

In 1859 John Tyndall discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red (as in the demonstration above). Later John William Strutt, 3rd Baron Rayleigh, developed equations which approximately describe the behavior of light scattered by small particles and molecules, objects with dimensions much smaller than the wavelength of the radiation in question. Rayleigh's equations predict scattering in terms of the object's size relative to the light's wavelength, and the object's refractive index.

The probability that light will be scattered is proportional to 1/λ⁴. The wavelength of the light ( λ ) has a very pronounced effect when raised to the fourth power like this. The probability that blue light (wavelength 460 nm, 460 nanometers) will be scattered is four times the probability that red light of wavelength 650 nm will be scattered. Stated alternatively, I_α=1/λ⁴ where I_α is the intensity of the scattered radiation.

The shorter the wavelength of the incident light, the more the light is scattered.

for larger particles one would use the equations of Mie theory, of which the Rayleigh equations are a special case. In Mie scattering the wavelength of the incident light has much less effect on the amount and direction of scattering.

Further reading:

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html#c2

demonstration cribbed from Earth Under Siege by Richard P. Turco, 1997 edition, Oxford U. Press, pages 500-501.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, light, atmosphere, education, Science In Action

Is Sex Necessary? Part 1

noreply@blogger.com (D. Wheat) — Mon, 27 Aug 2007 18:45:00 +0000

*Motile Plant Gametes*

"Mommy, Where Do Gametes Come From?"

"I'm glad you asked that, Honey. We usually don't see gametes, but just because they are small doesn't mean they're not important.

"You see, gametes are special haploid cells produced by a kind of cell division called 'meiosis'. Two gametes can unite to form a diploid cell again. That's called 'fertilization' or 'syngamy'. Diploid cells have a set of pairs of chromosomes, but haploid cells have just one copy of each chromosome. In people, most cells have 23 pairs of chromosomes. Chickens have 39 pairs of chromosomes in their diploid cells. Mosquitoes have 4, isn't that cute?

*Day-Old Chick*

"There are two reasons gametes are important, Snookums. First, although human gametes can't survive on their own, they can live long enough for a swimming gamete from a daddy to get to a big round nonmotile gamete in a mommy. When they join they bring genes from the daddy and genes from the mommy together. So a baby has its own set of genes, some from its daddy and some from its mommy. With our 23 pairs of chromosomes there are lots of ways the daddy's genes, half of which he got from his daddy and half from his mommy, can be shuffled and distributed in his gametes. In fact there are about 8 million possible results from shuffling 23 chromosomes, so you can see the possibility of two gametes from the same individual having the same assortment of grandpa and grandma's chromosomes is really, really tiny.

"And there's a second thing even more wonderful about meiosis, Dear. When the pairs of sister chromatids are in the pachytene stage of prophase I, non-sister chromatids can exchange some of their DNA by 'crossing over'. So the DNA from

*A Boy's Chromosomes*

the grandpa and grandma can be even more mixed up! Here, maybe this will be clearer after you watch this little movie.

"All this shuffling and exchanging of DNA means that the baby that grows from the zygote formed by the union of those two gametes probably has a unique set of genes never born on Earth before! Of course if the zygote splits into twins, they will each have the same genetic makeup, but you get the idea.

"This way of making babies is called 'sexual reproduction'. Lots of different life forms do it, but not always in the same way. Bacteria and archaea don't do it at all, since they can't do meiosis. Still, they seem to get along OK. In fact, they are the dominant life forms on our planet!

*A Girl's Chromosomes*

"If such successful and important organisms as bacteria and archaea can get along without it, why do so many other kinds of protists, fungi, plants and animals go to all the trouble to use sexual reproduction? I think the answer, Sweetie, is that by creating so many combinations of genes, and by mixing them up generation after generation, sexually reproducing organisms can try out new combinations of mutations faster. So there is more variation for natural selection to work on, you see. And if the environment is changing novel combinations of genes might be better able to handle the changing selective pressures, so a baby with an adaptive combination of genes might be more likely to grow up to make gametes of its own.

"Lots and lots of eukaryotes have meiosis and fertilization as part their life cycle. Did you know that we are eukaryotes? We (or our ancestor eukaryotes) evolved meiosis and most of us have never given it up. It is strongly selected by natural selection. One result of the more flexible evolution that results from using sexual reproduction is the origin over the ages of so many new species with so many different ways of living -- like us, Pumpkin! That's why people have sex! Isn't that interesting?"

"Yes, I guess so. . . . Mommy, what are 'cells'?"

Two good articles:

Wikipedia on Evolution of Sex

Good review article

Hurricane Numbers Up With Sea Surface Temperatures

noreply@blogger.com (D. Wheat) — Wed, 01 Aug 2007 21:18:00 +0000

Global Warming Means More Atlantic Tropical Storms and Hurricanes

A previous post discussed how global warming seems to be increasing the intensity of Atlantic hurricanes. At that time it wasn't certain that the number of tropical storms in the Atlantic was increasing along with global warming, too.

Now the evidence is in. Recent work shows that there has been a significant increase in the number of tropical storms and hurricanes in the Atlantic over the past century, and especially over the last 20 years. More detailed information is available in a slide presentation in this large pdf file.

The year 2006 was a respite after a series of recent major storms in 2004 and 2005, with only five hurricanes and four other named tropical storms. But it would have been an above average hurricane season in the early 1900s.

"These numbers are a strong indication that climate change is a major factor in the increasing number of Atlantic hurricanes," says study co-author Greg Holland of the National Center for Atmospheric Research. (See NCAR press release.) Although our ability to count tropical storms has improved a lot with the development of aircraft and satellites, "We are of the strong and considered opinion that data errors alone cannot explain the sharp, high-amplitude transitions between the climatic regimes, each with an increase of around 50 percent in cyclone and hurricane numbers, and their close relationship with SSTs," the authors state. (SSTs = sea surface temperatures, which have increased about 0.7 degrees C. in the Atlantic hurricane-forming region over the last century. The area of warm water has expanded also.)

Here is the abstract of the recent article by Holland and Webster

We find that long-period variations in tropical cyclone and hurricane frequency over the past century in the North Atlantic Ocean have occurred as three relatively stable regimes separated by sharp transitions. Each regime has seen 50% more cyclones and hurricanes than the previous regime and is associated with a distinct range of sea surface temperatures (SSTs) in the eastern Atlantic Ocean. Overall, there appears to have been a substantial 100-year trend leading to related increases of over 0.7°C in SST and over 100% in tropical cyclone and hurricane numbers. It is concluded that the overall trend in SSTs, and tropical cyclone and hurricane numbers is substantially influenced by greenhouse warming. Superimposed on the evolving tropical cyclone and hurricane climatology is a completely independent oscillation manifested in the proportions of tropical cyclones that become major and minor hurricanes. This characteristic has no distinguishable net trend and appears to be associated with concomitant variations in the proportion of equatorial and higher latitude hurricane developments, perhaps arising from internal oscillations of the climate system. The period of enhanced major hurricane activity during 1945–1964 is consistent with a peak period in major hurricane proportions.

Fire Alarm: Global Warming and Wildfires

noreply@blogger.com (D. Wheat) — Sat, 07 Jul 2007 18:13:00 +0000

Fires Increase Due To Global Temperature Rise

While everybody talks about the threat posed by stronger hurricanes due to global warming (see this earlier post ), the greater danger in the American West is from increased number and severity of forest fires. (Fires are likely to increase in other regions as well: Australia, the Mediterranean basin, and so forth.)

The increase in temperature (0.9 degrees C over recent decades) is primarily responsible for the significant increase in wildfires in the West since the '80s.

Recent research shows that warmer temperatures appear to be increasing the duration and intensity of the wildfire season in the West. Since 1986, longer, warmer summers have resulted in a fourfold increase of major wildfires and a sixfold increase in the area of forest burned, compared to the period from 1970 to 1986. A similar increase in wildfire activity has been reported in Canada from 1920 to 1999.

Research by Westerling et al. (2006) shows that the increase in western U.S. forest wildfires is correlated with warmer spring and summer temperatures, reduced precipitation associated with warmer temperatures, reduced snowpack and earlier spring snowmelts, and longer, drier summer fire seasons. Climate models indicate that these trends are part of plausible climate change scenarios (Running 2006), implying a further increase in the risk of large, damaging forest wildfires in parts of the western U.S.

These simulations unanimously project June to August temperature increases of 2° to 5°C by 2040 to 2069 for western North America. The simulations also project precipitation decreases of up to 15% for that time period. Even assuming the most optimistic result of no change in precipitation, a June to August temperature increase of 3°C would be roughly three times the spring-summer temperature increase that Westerling et al. have linked to the current trends. Wildfire burn areas in Canada are expected to increase by 74 to 118% in the next century, and similar increases seem likely for the western United States. (Running, 2006)

An analysis by Westerling & Bryant predicts significant increases in wildfire damage in Northern California forests as global warming continues. They conclude that this may make "wildfire a particularly important source of potential climate change impacts for the state." So though you might escape hurricanes or sea-level rise by moving to the foothills, you can't run from global warming.

The Really Bad News

According to Running (2006), wildfires add an estimated 3.5 × 10¹⁵ g to atmospheric carbon emissions each year, or roughly 40% as much as fossil fuel carbon emissions. If climate change is increasing wildfire increases in this source of carbon emissions will accelerate the buildup of greenhouse gases and could provide a feed-forward acceleration of global warming.

In other words, the warmer it gets, the more and larger wildfires in western forests, releasing more CO₂ to the atmosphere, resulting in more global warming, which might increase fire numbers, duration, and intensity even more.

In the long run the increase in wildfires in western montane forests will change the composition of plant communities, so that in time the Rockys of Colorado may look like the Sangre de Cristo Mountains of New Mexico look today.

Sources:

Westerling et al., 2006. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. http://www.sciencemag.org/cgi/content/full/313/5789/940

Running, 2006. Is Global Warming Causing More, Larger Wildfires?
http://www.sciencemag.org/cgi/content/full/313/5789/927

Westerling & Bryant, in prep. Climate Change and Wildfire in California. http://ulmo.ucmerced.edu/~westerling/pdffiles/07CC_WesterlingBryant.pdf

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, global warming, climate change, education, Science In Action

What Causes Global Warming?

noreply@blogger.com (D. Wheat) — Tue, 13 Mar 2007 01:34:00 +0000

Did You Know?

For every pound of gasoline your car burns, about three pounds of CO₂ come out the tailpipe. So if your car gets 20 miles per gallon, you are emitting about a pound of CO₂ per mile.

(For every kilo of petrol your car burns, about three kilos of CO₂ come out the tailpipe. So if your car gets 8.5 km per liter, you are emitting about a quarter of a kilogram per kilometer.)

How can the amount of CO₂ that comes out be three times the amount of gas that goes in? It's because of the oxygen. Your car uses a lot of O₂ to burn that pound of gasoline, and some of that oxygen becomes part of the CO₂ emitted. You can review the math here.

So that trip to the store to buy a loaf of bread, bag of dog food, quart of milk or bottle of wine probably put a pound or more of CO₂ into the atmosphere. That is likely as much as all the CO₂ emitted by all the processes involved in growing, manufacturing and packaging that product, and transporting it to your local store.

That is what causes global warming.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, statistics, science education, math, education, Science In Action

Probability and Profiling

noreply@blogger.com (D. Wheat) — Mon, 12 Mar 2007 18:40:00 +0000

The Set-Up:

I am going to test your understanding of "probability" and "randomness". For purposes of this demonstration, assume that the person in this picture has been randomly selected from all Americans. This is a picture of a randomly selected American.

The Question:

Is this person more likely to be a farmer, or a librarian?

The Answer:

Whatever you answered, your answer was almost certainly influenced by your previous knowledge, biases, and thinking about what the woman "probably" was.

You probably ignored the repeated information that this was supposed to be a randomly selected American.

In fact, any "randomly selected" American is much more likely to be a farmer than a librarian, since there are almost seven times as many farmers as librarians in the U.S.A. There are twice as many women farm operators as there are librarians and library technicians put together.

Because I showed you a picture of a woman, and you "know" than most librarians are women and most farmers are men (is that really true?), you probably guessed that the "randomly selected" American in the picture was a librarian. If so, you let your previous knowledge affect your answer. You probably lacked the relevant knowledge about the numbers of farmers and librarians in the U.S. population.

People have a very hard time forgetting their prejudices, biases, and prior information (some of which may be erroneous) when making judgments about things they are told are "random". They impose a structure of belief even on randomness, which by definition has no structure. (Previous post on "randomness".)

This is why "profiling" is so difficult. People go with their "gut feel", their biases, rather than using a true analysis of the situation.

Here are the sources and links to further information:

US Department of Labor, Bureau of Labor Statistics
all occupations
education, training and library occupations

149,680 librarians and 113,520 library technicians -- about 263,000

US Department of Agriculture, National Agricultural Statistics Service, Census of Agriculture 2002

tables
farm operators
pdf version

1,792,000 operators on farms where farming is the principal occupation of the principal operator. 455,500 woman operators same definition.

Here is a really interesting article about profiling. (It is about profiling, not pit bulls, so just keep reading.)

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, statistics, science education, math, education, Science In Action

What Are Flowers For?

noreply@blogger.com (D. Wheat) — Mon, 14 Aug 2006 01:31:00 +0000

Flowers, sex and seeds

Flowers are the specialized plant structures which produce pollen and where seeds develop within an enclosing fruit. Each seed (like the faba bean seeds at the right) contains a baby plant.

A baby plant (plant embryo), and its surrounding seed, cannot develop unless pollen is transferred from the pollen-producing parts of the flower to the parts which contain ovules, which can become seeds.

So flowers serve two basic purposes:

they package genetic material (into pollen and ovules) and help move it around so it can combine to produce the seeds for the next generation, and

they enclose those seeds in a fruit to help them successfully grow into a new plant.

If you look closely at this picture of some peanuts, you can see a baby plant where one of the peanut seeds has split in two. Each seed was enclosed in a "seed coat" (the red, papery covering) and several seeds were in each fruit (the peanut shell with the seeds inside -- not shown). (Better yet -- get some peanuts and look at them carefully. This is called "observation" -- a big part of science.)

Not all plants have flowers

Some plants don't make seeds at all (like ferns or mosses). And others (gymnosperms like pines, ginkgos and cycads) make seeds without flowers. (The seeds of gymnosperms aren't enclosed in a fruit that develops from part of a flower. They are just borne externally, although a cone or fleshy outgrowth may surround them as they mature.)

Flowers facilitate plant sex

They typically include structures which produce pollen and other structures where seeds can develop if pollen reaches them. Sexual reproduction means the parent organisms produce “gametes”, which carry a sample of the parent's genetic information (just half of it, but one of every chromosome). These gametes must unite to reconstitute the complete genetic complement that the next generation will need—two of each chromosome. In people the gametes are sperm and the egg. In seed plants they are pollen and ovules.

Usually a seed can develop from union of pollen and an ovule on the same plant. But many flowering plants promote broader mixing of genetic material. They have have forms which encourage the transfer of pollen from one flower to another, and thus often from one plant to another. This transfer of pollen can be done by wind, or by birds, insects or other animals which visit the flowers. Many flowers have evolved specific forms, colors, or other features to attract such “pollinators”.

After pollination (the transfer of pollen to the parts of the flower where the ovule is waiting) and fertilization (the joining of the genetic material from the two gametes), a seed can develop. In flowering plants, seeds are enclosed in a structure called a fruit. A fruit can contain just one seed (like an olive) or many (like a tomato). A fruit can be dry and hard, like a grain of rice, or fleshy like an apple.

Many fruits have specialized structures to help carry the seeds away from their parent plants, like a dandelion (which floats on the wind), burdock (which has prickles to catch on fur of passing animals), Impatiens (“touch-me-not”, where the fruit explodes and scatters the seeds), coconuts (which can float), or the cherry (which has an edible portion surrounding a tough digestion-resistant seed).

So flowers make fruits, and a fruit has three parts:

the embryo (baby plant)

the seed that contains the embryo

the fruit that contains the seed (or seeds). The fruit develops from the structure that contained the ovules before fertilization.

More about plant sex

Flowers are all about sex. Sexual reproduction produces offspring which are not genetically identical to their parents. In fact, each offspring can contain a novel combination of genes never seen before. This helps plants deal with changing environments and other challenges (new competitors, new predators). The plant gets the most novel new combinations if pollen is transferred from one parent to another. Plant sexuality is very diverse, with many complicated sexual mechanisms even just within the flowering plants. These various mechanisms include differences in which flowers produce pollen and which produce ovules, whether the pollen-producing flowers and the ovule-producing flowers are even on the same plant, where within the flowers pollen is released and where it can be received, when the pollen is released and when the ovules are receptive, how the pollen is transferred, and chemical signals which determine which pollen will be allowed to fertilize an ovule. The incredible diversity of the flowering plants (90% of all plants living today, comprising hundreds of thousands of species) is all about trying new ways to have sex.

Although many plants don't use pollinators such as insects (wind pollination is common), the fossil record suggests that flowers and insects evolved together, and that the diversity of each stimulated diversity in the other.

Flowers work

Flowering plants provide the basis of nearly all human nutrition, except for the wild-caught fish we eat. (A few calories also come from algae, pine nuts, fern fiddleheads and the like.) Without flowering plants civilization would certainly be impossible with today's technology. (Could a civilization develop that depended entirely on fish for nutrition?) Flowers, seeds and fruits have, ultimately, made the internet, and every other aspect of civilization, possible.

To review:

Flowers have pollen. If pollen is transferred, flowers grow seeds, and turn into fruits.

Homework

So next time you are looking at a flower, try to see where the pollen is and where it might go to make a seed. How does pollination happen?

Next time you are looking at a fruit, consider how it formed and how it helps its seeds get around. Where are the seeds and how are they dispersed?

Next time you consider a seed, think about the baby plant inside, and how it might grow into a mature plant with flowers of its own.

Here are some links for further information:

Wikipedia: flowers, flowering plants, seeds
Parts of a flower (floral structure)
Good pdf document about floral structure
Good summary page with images of various flowers
Diversity of flowering plants
The Seed Biology Place

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, botany, science education, math, education, Science In Action

Why Is Urine Yellow?

noreply@blogger.com (D. Wheat) — Sat, 01 Jul 2006 18:04:00 +0000

What true scientist has not asked, at some time or other, "Why is pee yellow?"

Some European alchemists in the middle ages apparently thought one possible reason was that there was gold in urine. This led to fruitless, and possibly quite disgusting, efforts to extract that gold.

The yellow color in urine is due to chemicals called urobilins. These are the breakdown products of the bile pigment bilirubin. Bilirubin is itself a breakdown product of the heme part of hemoglobin from worn-out red blood cells. Most bilirubin is partly broken down in the liver, stored in the gall bladder, broken down some more in the intestines, and excreted in the feces (its metabolites are what make feces brown), but some remains in the bloodstream to be extracted by the kidneys where, converted to urobilins, it gives urine that familiar yellow tint. (Here is a great diagram of some of these reactions, from the Boehringer Mannheim Biochemical Pathways at ExPASy.)

These same yellow chemicals also cause the yellow color of jaundice and of bruises, both of which result when more hemoglobin than usual is being broken down and/or the processing of its breakdown products by the liver is not able to keep up.

Why do we pee at all?

Urine is mostly water, which just has to be replaced. We excrete water not just to get rid of it if we have drunk too much, but primarily to carry away toxins that would otherwise build up in our systems. The important part of urine is urea (also known as carbamide), (NH₂)₂CO. The real waste product our bodies have to get rid of is ammonia (NH₄⁺, when in solution), which is formed by the breakdown of amino acids -- the building blocks of proteins. But ammonia is so toxic that only tiny concentrations can be tolerated. So any ammonia in the bloodstream is rapidly converted to urea in the liver. That urea is then removed from the bloodstream in the kidneys, and left in concentrated form in the urine (about 2% of urine is urea.) (More on the "urea cycle")

Urea was "discovered" by Hilaire Rouelle in 1773 (that is, he was the first chemist to isolate it in pure form and begin to understand its composition). It was the first organic compound to be artificially synthesized from inorganic starting materials when, in 1828, Friedrich Woehler prepared it by the reaction of potassium cyanate with ammonium sulfate. Woehler was really trying to make ammonium cyanate, but by synthesizing urea he disproved the theory that the chemicals of living organisms are fundamentally different from inanimate matter, thus inventing the field of organic chemistry.

Fish and amphibians lack the urea cycle for removing ammonia from the blood, since they can usually excrete ammonia directly via the gills or through the skin. This is one reason that ammonia in the environment is so highly toxic to aquatic animals. So do fish need to pee? Yes: not to excrete nitrogenous compounds, but for osmoregulatory purposes. Freshwater fish are always absorbing water from their environment by osmosis, and have to pump it out. Saltwater fish don't absorb water from the sea (blood and seawater have about the same saltiness and osmotic potential), but they do have some wastes to get rid of. More here.

(More on industrial uses of urea here.)

Where does the ammonia in our systems come from?

Ammonia is generated during the deamination (breakdown) of amino acids in the liver. Other sources of ammonia include bacterial hydrolysis of urea and other nitrogenous compounds in the intestine, the purine-nucleotide cycle and amino acid transamination in skeletal muscle, and other metabolic processes in the kidneys and liver. The normal physiological concentration in blood is less than 35 micromol/l. A five- to ten-fold increase in this concentration causes toxic effects, especially on the central nervous system.

Other urine facts

Unusual-colored urine (black, dark orange, or brown, for example) can be a sign of serious medical problems.
Some other colors can result from pigments in the diet, such as betacyanin found in red beets.
Urea is apparently used as an additive in cigarettes, to enhance flavor.
Urea is widely used as fertilizer, since plants can use it as a source of nitrogen.
Although today urea is manufactured by the millions of tonnes through industrial processes, the urea in urine can be economically valuable if other sources of fixed nitrogen are scarce.
- It can be used as plant fertilizer (when diluted). (It's organic, you know.)
- The urea in urine can be broken down into ammonia again (generating the characteristic smell of stale urine) which be further oxidized by bacteria to nitrate, so useful in the production of gunpowder.

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, physiology, science education, math, education, Science In Action

What Does "Survival of the Fittest" Mean?

noreply@blogger.com (D. Wheat) — Tue, 06 Jun 2006 15:16:00 +0000

Does "survival of the fittest" mean anything?

The phrase "survival of the fittest" is sometimes used as a kind of metaphor to explain what is meant by "evolution by means of natural selection". The phrase was first applied not by a biologist but by an economist, Herbert Spencer. Darwin did incorporate this phrase into later editions of The Origin of Species, using it as a synonym for "natural selection."

The fittest individuals, however, do not survive. Even the fittest is mortal. The fittest die just as inevitably as the less fit. (Remember that "fit", at the time of Darwin and Spencer, usually meant “suited for” or “appropriate to”, not “robust in health”).

What do survive are the traits, genes, alleles, or heritable factors, and those of the more fit (better adapted to the environment or other selection pressures) survive in greater numbers than those of the less fit. That is what “fitness” means to a biologist.

The fittest, the individuals whose traits enable them to leave more progeny than those contemporaries less well suited for the current environment, have more grandchildren. Those grandchildren carry some of the heritable characteristics which made their fitter ancestors capable of begetting more offspring.

Being strong, happy, or living to a ripe old age might be interpreted by the layperson as representing higher fitness, compared to another individual who did not survive as long or who suffered more in life. But this has nothing to do with evolution or natural selection. Natural selection is only concerned with the effect of the environment on the flow of genes to following generations. The age or health of the surviving individuals means nothing if their genes are not represented in offspring.

Let me repeat this important point: Natural selection is not something that happens to individuals, but to populations. It causes changes in those populations (changes in the commonness, or frequency, of genes) across generations.

To the extent that it is a statement about evolution or natural selection, “The survival of the fittest” probably causes more confusion than clarification. If you interpret it to mean “the survival and propagation of the fittest genes”, then it is a restatement of evolution by natural selection, but it is still a tautology, true by its own definition. The “fittest” individuals contribute more of their genes to subsequent generations than do less “fit” contemporaries, but this is just a definition of “fitness”.

The worst influence of this phrase is the sneaky way “fitter” sometimes is taken to mean “better”. This is especially pernicious when the concept is (mis-)applied to social contexts, such as politics or economics. There it is sometimes taken to mean “success of those most worthy of success”. A whole doctrine of “social Darwinism” arose around this concept. Since social dominance, economic success, or political power do not involve the winnowing of heritable traits by natural selection, they have nothing to do with Darwin or biological evolution. Social Darwinism was an effort to borrow the scientific language of biology to justify various social and political programs.

Confusion between the ethical concept of social Darwinism and the scientific concept of evolution hampers communication between scientists and the public to this day. Thanks a lot, Mr. Spencer.

Additional Resources

Social Darwinism:
Wikipedia
social darwinism

Stephen Jay Gould, "Darwin's Untimely Burial," 1976; from Michael Ruse, ed., Philosophy of Biology, New York: Prometheus Books, 1998, pp. 93-98.

Wikipedia "survival of the fittest" article

Here are some other posts on evolutionary topics from this series:
Evolution in a Nutshell
What Species is Best?
Are Humans Still Evolving?

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, evolution, science education, math, education, Science In Action

Evolution In A Nutshell

noreply@blogger.com (D. Wheat) — Sun, 09 Apr 2006 22:30:00 +0000

Evolution -- What is it and how does it work?

Lots of people don't understand evolution or natural selection. Even some writers of essays on evolution don't seem to have a firm grasp of it. Heck, I probably don't completely understand it myself.

But I think I can summarize the key facts. If you absorb these facts you will understand more about evolution than most people do, even more than most high-school science teachers.

The organisms we see on Earth today are different from those of past times. Some that once were common have disappeared. New forms unknown in the past have come into existence. This is what is called “evolution” -- change over time. Everybody agrees that evolution occurs.

The organisms in a population are not all perfectly the same. There are slight differences among individuals. Except for clones (like identical twins) no two individuals are exactly alike. This is common experience. Everybody agrees that this is so.

Offspring tend to resemble their parents, at least in what are termed “heritable” traits. Some traits, such as what language you speak, are not inherited. Other traits, such as degree of skin pigmentation in humans, are clearly influenced by heredity (people tend to resemble their parents and grandparents). In Darwin's time nobody understood how this worked, but today everybody knows about genes, DNA, and stuff. Everybody agrees that many traits are inherited.

In most types of organisms many more offspring are produced than can survive to produce offspring of their own. That is, some individuals die without leaving any progeny, or at least not as many progeny as others -- their traits are not passed on as widely. Everybody who has looked at the natural world at all agrees that this is true for most creatures. (I am trying to think of some kind of plant or animal that isn't capable of producing enough offspring to overtax the resources it needs from its environment in just a few generations. Pandas?)

All of the above points are true and widely accepted. Here is the new idea Darwin and Wallace had:

Individual organisms' inherited traits can influence their success in leaving progeny. Some traits will help the individual leave more, and more successful, offspring. Such traits might include resistance to disease, attractiveness to mates, efficiency at finding or making food, or ability to avoid being eaten before reproducing. Those traits will be passed on to more progeny than other traits which don't help their possessors survive and reproduce.

In fact some traits may actually hurt their owners' chances of leaving offspring. Individuals with these less-helpful traits (perhaps susceptibility to disease, inefficient food-finding, or less ability to avoid predators) will leave fewer progeny, and thus those traits will not be passed on to as many members of the next generation.

The selection of which traits are favored and which are unhelpful is made by the natural environment, in the determination of how many progeny each individual leaves and how widely its traits are passed on to the next generation. This is “natural selection”.

Thus the differences among individuals, plus pressures from the environment which limit the total numbers of progeny that can survive, will lead to gradual change in the commonness of specific heritable features. That is what is meant by “evolution by means of natural selection”.

If you accept 1 through 4 above, then natural selection seems a very logical and interesting hypothesis to explain how life on Earth changes over time. A century and a half of intense research in all fields of biology (biogeography, paleontology, genetics, molecular biology, ecology, plant and animal breeding, and others) has provided a mountain of evidence that this basic “theory of evolution” about how populations of organisms can change is correct, and accounts for the diversity of life on Earth.

Any questions?

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, evolution, science education, natural selection, education, Science In Action

The Top 10 Science Discoveries . . . Ever!

noreply@blogger.com (D. Wheat) — Fri, 09 Dec 2005 17:13:00 +0000

Great Science Breakthroughs Which Shape Our Modern World

(If you have others you would include, or would drop any of these, use the Comments feature below.)

Invention of Modern Numeration, Arithmetic and Algebra

The Brahmasphutasiddhanta (Brahmagupta, 628) is the earliest known text to treat zero as a number in its own right. It also gives modern rules for the arithmetic of negative numbers and zero.

Abu Abdullah Muhammad bin Musa al-Khwarizmi, through his book On the Calculation with Hindu Numerals written about 825, was principally responsible for the diffusion of the Indian system of numeration in the Islamic world and then Northern Europe. al-Khwarizmi also provided a systematic method for solving linear and quadratic equations, establishing the mathematical field of algebra, a word that is derived from the name of his 830 book on the subject, al-Kitab al-mukhtasar fi hisab al-jabr wa'l-muqabala ("The Compendious Book on Calculation by Completion and Balancing").

Ghiyaseddin Jamsheed Kashani (Al-Kashi) published The Key to Arithmetic in 1427, which gives a description of decimal fractions and their use, including today's place-value system using a decimal point, popularizing these methods. (See Wikipedia article on Hindu-Arabic numeral system)

Copernican Revolution

Nicholas Copernicus presented the heliocentric theory in De revolutionibus orbium coelestium published in 1543. (It had been anticipated in the work of Indian astronomers.) Additional support came from Johannes Kepler's Astronomia nova in 1609, and the foundations of modern dynamics was set out in Galileo's book Dialogo sopra i due massimi sistemi del mondo of 1632. The new theory was not officially accepted by the Roman Catholic Church until two and a half centuries later. The realization that the Earth is not the center of the universe had profound impacts on philosophy.

Calculus

First developed by Indian astronomers and mathematicians, especially those of the Kerala school, between the 13th and 16th centuries, it was re-discovered and elaborated by European mathematicians and unified by Isaac Newton and Gottfried Wilhelm von Leibniz in the latter half of the 1600s. It provides the mathematical foundations for all modern mechanics, dynamics, and most other science and technology. The technologies and research that support modern life would not be possible without calculus.

Classical Mechanics

Building on the work of Tycho Brahe, Johannes Kepler, and Galileo on planetary motion, and Galileo on dynamics, Isaac Newton described the laws that govern the motions of objects, including his universal law of gravitation, in his Philosophiae Naturalis Principia Mathematica in 1687. "Newton's laws" are still used to describe the motions and interactions of macroscopic bodies from projectiles to planets.

Probability and Statistics

Blaise Pascal and Pierre de Fermat developed the modern concept of probability in 1654, and in 1657 Christiaan Huygens gave the earliest known scientific treatment of the subject. Jakob Bernoulli (1713) and Abraham de Moivre (1718) further developed the mathematics. Pierre-Simon Laplace (1774) made the first attempt to deduce a rule for the combination of observations from the principles of the theory of probabilities. Based on these foundations the methods of statistical sampling, statistical inference, and other tools were developed. These tools are essential to all modern science and industry.

Geological Uniformitarianism

Uniformitarianism is one of the most basic principles of modern geology: the theory that fundamentally the same (generally slow but steady) geological processes that operate today also operated in the distant past. This implies that the Earth is very old, since it has taken many hundreds of millions of years for slow processes of erosion, deposition, plate movement and uplift to form the geological structures we see today. The concept was formulated by James Hutton and published in the 1780s and 1790s, and popularized by Charles Lyell in a series of influential textbooks in the 1800s. The implications regarding the age of the Earth were the source of decades of controversy since they contradicted accepted religious doctrines.

Natural Selection

Proposed by Charles Darwin and Alfred Russel Wallace in 1858, and established by Darwin's On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life in 1859. In its modern form (incorporating genetics, statistical analysis and molecular biology), the theory that natural selection is the driving force for biological evolution is the foundation of all modern biology, including ecology, paleontology, taxonomy, biotechnology, etc. Nonetheless, it is still not widely accepted today even by the educated public. Nearly half of Americans believe "life on Earth has existed in its present form since the beginning of time," according to recent polls.

Germ Theory of Disease

The theory that diseases are caused by invisible micro-organisms, rather than by "miasmas", spontaneous generation, or supernatural causes, is the foundation of modern medicine and public health, and a major contributor to the welfare of people all over the world. Ignaz Semmelweis demonstrated in the 1840s that iatrogenic childbed fever could be prevented by making doctors wash their hands. Louis Pasteur proved that spoilage and disease only occurred by contamination or infection (1860s). Joseph Lister (1860s) developed aseptic surgury. In the 1870s Robert Koch proposed his Postulates, which are still used to demonstrate the connection between a specific microbe and a specific disease. Other contributors included Girolamo Fracastoro (1546), Anton van Leeuwenhoek (1670s), Agostino Bassi (1844), and Jakob Henle (1840).

Electromagnetism

James Clerk Maxwell, building on the earlier work of Michael Faraday, André-Marie Ampère, and others, developed a set of differential equations that unified and described electromagnetism, published in 1864. He discovered that light is a form of electromagnetic radiation. These theories were the basis for developments in electricity, electronics, radio, and related technologies, and are one of the great unifying theories of science.

Double-Helical Structure of DNA

James Watson and Francis Crick, using X-ray diffraction data from Maurice Wilkins and Rosalind Franklin, figured out how the hereditary material DNA is arranged and how it self-replicates. This discovery forms the foundation for modern molecular biology, biochemistry, biology, genetics and medicine.

Other breakthroughs I had to leave out of the "Top Ten"

Can you make an argument that any of these, or any other discoveries, should replace one or more of my top ten?

Atomic theory and the periodic table

Einstein's Special Theory of Relativity

Einstein's General Theory of Relativity

Alan Mathison Turing 1930s and 1940s: computer science

Quantum mechanics

Size and Age of the Universe (Edwin Powell Hubble's discovery of galaxies beyond our Milky Way.and discovery of the rate of expansion of the universe, 1929.)

Discovery of microscopic organisms, cells (Anton van Leeuwenhoek, Robert Hooke)

Thermodynamics

Classical Greek science (especially logic and geometry?)

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, history of science, science education, math, education, Science In Action

World AIDS Day, 2005

noreply@blogger.com (D. Wheat) — Fri, 25 Nov 2005 18:25:00 +0000

AIDS Can Be Stopped, But It's Not Stopping Yet, And It Won't Stop By Itself

1 December is World AIDS Day 2005.

The 2005 report of the Joint United Nations Programme on HIV/AIDS (UNAIDS) says that the number of people living with HIV/AIDS rose this year to a record 40 million. There were a record number of new infections, about 4.9 million. And about three million people died of AIDS in 2005, including more than 500,000 children.

In addition to the individual human tragedies of suffering, loss and destitution reflected in these grim figures, there is other bad news:

Only one in ten of those infected with HIV has been tested and knows his or her status.

The epidemic is gaining strength in Asia, where the toll of death and economic disruption is potentially much higher than in the current centers in sub-saharan Africa. (South Africa has the largest number of people living with HIV/AIDS. Second is India, where the epidemic is just getting started.)

The outgoing chief of India's official National Aids Control Organization, S.Y. Quraishi, said 70 percent of Indian sex workers either did not know what a condom was or how to use one.

High mortality among working-age adults erodes productivity and imposes additional costs on businesses. In regions where infection rates are high this may be a significant deterrent to investment, both by private firms, by governments (for instance in education), and by individuals themselves.

This underinvestment in future generations, together with costs of prevention and treatment, and reduced productivity in industry and agriculture, will reduce the economic growth of many nations, and could even cause the economic collapse of some.

Refugees from such economic collapse will threaten the stability of affected countries and regions, and their neighbors.

In many countries, marriage, and women’s own fidelity are not enough to protect them against HIV infection.
Among women surveyed in Harare (Zimbabwe), Durban and Soweto (South Africa), 66% reported having one lifetime partner, 79% had abstained from sex at least until the age of 17 (roughly the average age of ﬁrst sexual encounter in most countries in the world). Yet, 40% of the young women were HIV-positive. Many had been infected despite staying faithful to one partner. In Colombia, 72% of the women who tested HIV-positive at an antenatal site reported being in stable relationships. In India, a significant proportion of new infections is occurring in women who are married and who have been infected by husbands who (either currently or in the past) frequented sex workers. (From the 2005 report -- see last year's discussion of AIDS and women's issues.)

On the other hand, there is some good news:

In several countries HIV infection rates have fallen recently. There have also been reversals of worrying trends in such countries as Brazil and Thailand. These reversals indicate that it is possible to control epidemics using effective prevention programs.

So although epidemics continue to worsen in many regions, there are demonstrated strategies for stopping HIV/AIDS, if those strategies can be applied.

Access to HIV treatment has improved over the past two years. There are now more than one million people in developing countries living longer and better lives because they are on antiretroviral therapy.

In short, "AIDS is a problem with a solution," says Dr. Peter Piot, UNAIDS Executive Director

The key to containing, and someday reversing, the number of new AIDS infections will be the willingness of the developed world to spend tens of billions of dollars to help affected nations implement effective long-term prevention and treatment programs. Given the "disaster fatigue" already affecting donor nations, and their own economic problems associated with the costs of war and welfare reform, what will it take to mount an effective effort?

Even in the United States, with all its resources, the number of new HIV infections has held steady at 40,000 per year for the past five years, and may even be increasing slightly.

The world seems to be willing to accept rampant HIV/AIDS and associated social, economic, and personal suffering in Southern Africa. Will similar crises in Eastern Europe, India or China be as easily ignored?

Additional Resources

Test your awareness with this HIV/AIDS quiz

UNAIDS site

World AIDS Day is coordinated by Avert.org

Another useful AIDS information site

Excellent report on The Macroeconomics of HIV/AIDS from the International Monetary Fund

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, AIDS, HIV, science education, math, education, Science In Action

Epidemic? Pandemic? Why Should I Care?

noreply@blogger.com (D. Wheat) — Sat, 19 Nov 2005 19:00:00 +0000

Should You Be Scared About "Bird Flu"?

We read a lot in the news recently about the threat of a bird-flu pandemic. Is this just media scare, or is it something we should really be worried about? A severe pandemic of a novel, virulent avian influenza would kill millions, stunt economic growth, and maybe even topple governments. However, some of the current scare is overblown. Here are some facts:

A "pandemic" is an epidemic that covers a large geographical area. A "global epidemic".

An "epidemic" is a significant outbreak of an infectious disease, more cases than expected. So malaria in most tropical poor countries is not "epidemic", even though it kills millions of people every year, because this is the "expected" rate. If malaria broke out in Washington, D.C., and killed even ten people, it might be considered a malaria "epidemic". Similarly, about 36,000 people die every year from influenza in the U.S. So an "epidemic" would have to infect a much larger number.

Influenza

The "flu" is caused by a virus. It affects the upper respiratory tract (nose, throat and lungs), and is spread by transfer of virus particles in saliva or mucus droplets, usually expelled in coughs or sneezes. The infection causes fever, body aches, headache, sore throat, fatigue, and coughing and sneezing. Most people will recover in one to two weeks. The disease is life-threatening particularly for the elderly and the young, and for people with underlying medical conditions such as heart or lung disease.

Bird Flu

"Bird flu" or "avian influenza" is a disease of aquatic birds. Sometimes people catch it (if they have been in very close contact with infected birds, usually involved in raising domestic fowl) and if they catch a virulent strain like H5N1 it is very serious. More than half the infected individuals die. Around 100 people have died of bird flu world wide in recent months.

The reason for global concern about bird flu is that influenza viruses can mutate to become more infectious (more easily transmitted). If one of the dangerous (pathogenic = disease-causing) strains of the virus were to mutate to become "human-adapted", so that it could be easily transmitted from one person to another, the stage would be set for a very serious epidemic, or even a pandemic.

The Great Influenza Pandemic of 1918-1919

This global disaster was caused by a novel and deadly strain of avian influenza virus. More than 25 million people died, most of them in poorer countries. In the United States about 28% of the population became ill and more than half a million people died. For comparison, HIV/AIDS has killed about 25 million people over 25 years, while the 1918 pandemic killed the same number in a few months. This is why public health officials are so concerned.

Samples of the 1918 pathogen have been recovered and analyzed. Recently its complete genetic makeup has been published.

What would a flu pandemic be like today?

In contrast to 1918, today we know what causes influenza (a virus) and how it is transmitted. We have some anti-viral drugs (but not many, and they would not be widely available, especially to the poor). We know how to produce flu vaccines, though it takes time to manufacture and administer them. Would these advances enable us to prevent or control a flu pandemic?

Current models of the possible impact of a flu epidemic in the U.S. suggest that between 15% and 35% of the population would be affected, and 100,000 to 200,000 would die ("medium-level" case). Rates of infection and mortality would probably be similar in other developed economies. In poorer countries the impact would be greater. The World Health Organization base case predicts 2 million to 7.5 million deaths world wide.

Political and economic effects could be severe. Restrictions on travel and trade, and reduced business activity due to closed businesses and reduced productivity, would be like a recession. Political instability could develop in places where governments do not appear to be responding effectively or fairly to the crisis. Reduced agricultural productivity and restrictions on food trade could create localized food crises.

Recent disasters have hurt the government in power if their responses are perceived as ineffective (Hurricane Katrina). On the other hand, crises can be used to consolidate political power (September 11th).

Managing A Pandemic Today

Flu epidemics in 1957-1958 and in 1968 killed about 70,000 and 34,000 Americans, respectively. The primary public health tools used to minimize the impact of these outbreaks were vaccination, information, regulation, and more effective treatment.

Vaccination -- After a new strain of influenza virus emerges and is determined to present a threat of widespread human disease, it takes several months for vaccine targeted at that strain to be developed and manufactured. As the vaccine first becomes available it will be used to protect health care workers and others who are both at high risk of being exposed to the disease and in a position to spread it to others. As larger quantities of vaccine are available they will be allocated by public health services to stop the spread of the disease in particular areas, such as specific cities, military bases, or the like. The standard "flu vaccine" available now is not designed to prevent avian influenza, but is targeted at the normal influenza strains identified earlier this year as most likely to be dominant during the current "flu season".

Information -- Public health agencies will try to teach people behaviors that will protect them from catching and spreading the disease.
- "Hygiene" and "sneeze etiquette" will be strongly recommended. Covering your nose and mouth when you sneeze can reduce the dispersal of airborne droplets of mucus which can potentially carry the virus to others.
- Washing your hands frequently can prevent infecting yourself with virus you have picked up, and can help prevent you from spreading the virus to others. Regular soap and water or alcohol hand cleaning solutions work fine. Antibacterial soaps provide zero additional effect.
- Masks may be suggested, or even required in some places. One key benefit of a mask is to remind you not to touch your face, thus reducing transmission of virus on the hands. Masks will not filter out viruses, but may prevent dispersal of mucus droplets when you sneeze. Proper disposal of contaminated masks is important. Wearing of masks by the non-infected public may not actually do much to slow the spread of the disease, but it may make people feel more secure.
- People with flu symptoms will be encouraged, or indeed in some cases required, to stay at home.
Regulation -- To reduce the rate of spread of any new, contagious, virulent flu virus several public health measures are likely to be put in place:
- Travel from regions where the new strain has broken out will be discouraged or forbidden.
- More aggressive monitoring of flu cases will be required, and cases or clusters of cases may have to be isolated (quarantined).
- Schools will be closed when the disease breaks out, and some other activities where people gather may be curtailed (e.g. entertainment and sporting events). Some businesses will close or be required to close.
Treatment -- There are some antiviral drugs which may be used to reduce the severity of the disease, and even some which appear to prevent getting it. Unfortunately, existing flu strains are already evolving resistance to some of these drugs. The drugs would effectively be rationed to be used to protect health-care workers and other essential workers, and to treat the elderly, the young, and others at high risk of complications or death.

Antibiotics do not affect viruses, but many flu deaths are due to secondary bacterial infections such as pneumonia. Antibiotics would be used to treat these cases.

Summary

Flu epidemics will happen in the future, but nobody knows when. Preparations are under way to minimize the social, economic, and public-health impact of the next big one. The best protections against any influenza virus are washing your hands and avoiding getting sneezed on by an infected person. Those most at risk of death in a flu epidemic are those without access to an effective health care system, which includes people in poor countries, people in regions of conflict, and elderly people living alone in developed countries.

Additional Information

CDC site

WHO bird flu site

U.S. Government site

WHO "10 Things You Need To Know" site

WHO Influenza site

WHO January 2005 threat assessment report

David Wheat's Science In Action site has articles about science and math in the real world, weird science, science news, unexpected connections, and other cool science stuff. There is an index of the articles by topic here.

tags: science, influenza, bird flu, science education, math, education, Science In Action

Cool Science Sites II

noreply@blogger.com (D. Wheat) — Tue, 15 Nov 2005 05:04:00 +0000

Science In Action

Do Cow Farts Cause Global Warming?

Bovine Flatulence--Threat or Menace?

Science on the Small Screen

Check out these science video sites

Why Is The Sky Blue?

Why is the sky blue? (multiple choice)

What breaks the Sun's light into yellow and blue light and sends these colors on different paths?

Why is blue light scattered more and red light less?

Is Sex Necessary? Part 1

"Mommy, Where Do Gametes Come From?"

Hurricane Numbers Up With Sea Surface Temperatures

Global Warming Means More Atlantic Tropical Storms and Hurricanes

Fire Alarm: Global Warming and Wildfires

Fires Increase Due To Global Temperature Rise

The Really Bad News

What Causes Global Warming?

Did You Know?

Probability and Profiling

The Set-Up:

The Question:

The Answer:

What Are Flowers For?

Flowers, sex and seeds

Not all plants have flowers

Flowers facilitate plant sex

So flowers make fruits, and a fruit has three parts:

More about plant sex

Flowers work

To review:

Homework

Why Is Urine Yellow?

What true scientist has not asked, at some time or other, "Why is pee yellow?"

Why do we pee at all?

Where does the ammonia in our systems come from?

Other urine facts

What Does "Survival of the Fittest" Mean?

Does "survival of the fittest" mean anything?

Additional Resources

Evolution In A Nutshell

Evolution -- What is it and how does it work?

The Top 10 Science Discoveries . . . Ever!

Great Science Breakthroughs Which Shape Our Modern World

Invention of Modern Numeration, Arithmetic and Algebra

Copernican Revolution

Calculus

Classical Mechanics

Probability and Statistics

Geological Uniformitarianism

Natural Selection

Germ Theory of Disease

Electromagnetism

Double-Helical Structure of DNA

Other breakthroughs I had to leave out of the "Top Ten"

World AIDS Day, 2005

AIDS Can Be Stopped, But It's Not Stopping Yet, And It Won't Stop By Itself

Additional Resources

Epidemic? Pandemic? Why Should I Care?

Should You Be Scared About "Bird Flu"?

Influenza

Bird Flu

The Great Influenza Pandemic of 1918-1919

What would a flu pandemic be like today?

Managing A Pandemic Today

Summary

Additional Information

Cool Science Sites II

More links to cool science sites I have come across: