Could you survive a desert island?

You've seen it on TV-16 contestants battling it out in the remote Pearl Islands of Panama for a $1 million grand prize and the title of "Sole Survivor." But what does it take to survive on a remote desert island without a production crew or cast to back you up? Take our quiz, below, then flip the page to learn the science behind three basics of survival: water, fire, and shelter. Do you have the scientific know-how to survive?

LIQUID GOLD

In the desert, water is known as liquid gold--and for good reason: You can't survive without it. Up to 65 percent of the human body is made of water, including 70 percent of your brain. You can't think without water, let alone ship out your body's waste and cool off with sweat. "Water lets the chemistry of our body proceed," says Wayne Askew, food and nutrition professor at the University of Utah.

On a desert island, finding water is your top priority--you can only survive an average of 10 days without it. "If you aren't drinking water and you're working in a hot environment, you can lose a quart of water (about four pounds) per hour due to sweat," says Askew. Lose only 4 percent of your body weight in water and you become dangerously dehydrated (medical condition in which the body uses more fluids than it takes in). Result: dizziness, headaches, and fatigue followed by hallucinations. That's why the body has a triggering mechanism called thirst. When your body is dehydrated by a mere 2 percent, it signals you to drink water.

Obey Your Thirst

An island is, by definition, surrounded by water. So why worry about finding enough to drink? The ocean's salt water won't slake your thirst. In fact, it makes it worse. Salt water is packed with sodium, a salt ion (charged particle) that causes your stomach to draw water from your blood. If you don't replenish that water, your cardiovascular system (heart and blood vessels) shuts down.

No clean freshwater source? Be creative. As the temperature drops at night, moisture in the air condenses (changes from a gas to a liquid) and falls to the ground as dew. To collect this water: Tie a T-shirt around your ankles and walk through the grass. Then suck the water from the wet shirt. Or use whatever containers nature provides, such as empty coconut shells, to catch rainwater.

Island vegetation can be another source of fresh water. That's because--like people--trees sweat, too. Plants only use about 10 percent of the water they suck from the ground. The rest is lost through stomata, tiny holes on the surface of their leaves. You can trap that water by lying a plastic bag around the leaves. Sunlight causes the water to evaporate (change from a liquid to a gas) into the air inside the bag. At night, as the air cools, the water condenses like dew, forming a pool inside the bag. "It's called a solar still," says Askew.

S'MORE SCIENCE

If you've ever watched contestants on Survivor compete for a box of matches, you know a fire means the difference between choking down raw, slimy seafood or dining on warm, tender crabmeat. But on a deserted island, starting a fire is a lot harder than winning a contest. "It's almost impossible to start a fire without matches or something burning already," says Sherri Dingley, fire chemist at the U.S. Forest Service. The right tools and a little science know-how, however, can help you roast roaches, if not marshmallows. Fire is simply a chemical reaction that sheds heat and light you can feel and see: "It's the visible result of the combustion (chemical breakdown) of fuel," says Dingley. In chemistry, a fuel is any compound that releases energy when heated. Wood sparks when it reaches 315[degrees]C (600[degrees]F). In fact, almost all organic (living) materials are good fire-starters, because they're made mostly of carbon and hydrogen--the same elements found in coal and oil, fossil fuels burned to make electricity. That's why driftwood, branches, or dry leaves are best for sparking a flame.

Light My Fire How to heat wood without a lighter? "The easiest way is with a flint (quartz or metal that sparks when hit with steel) or a lens," Dingley advises. Strike the flint and touch it to a pile of kindling (easy-to-light materials such as dry leaves, twigs, and paper). Or aim a magnifying glass, or even a pair of eyeglasses, toward the pile. Says Dingley: "Lenses focus the sunlight's energy into one spot, which often creates enough heat to start a fire."

In a pinch, do like Castaway star, Toro Hanks: Rub sticks together. Grind the point of a stick into a flat piece of wood to create friction (resisting force). Friction heats the wood, and the stick's tip concentrates the heat in one spot. When the wood reaches about 150[degrees]C (300[degrees]F), its molecules start to break apart and form smoke, a toxic gas made of hydrogen, carbon, and oxygen. But don't stop yet! At about 315[degrees]C the gas breaks up even more and reacts with oxygen in the air. The stick's tip glows red. Now the combustion reaction is hot enough to start a tire in kindling. To keep the tire going, add larger pieces of wood over the pile in a teepee shape--this allows oxygen in while protecting the tire from wind. Unfortunately, this "hand drill" method could rub the skin off your fingers before you ever see a wisp of smoke.

CAMP OUT

The island sun could leave you as fried as a bucket of bucket of extra-crispy chicken: "If you're working hard in the middle of the day and not drinking water you can suffer heat stroke," says Sherrie Collins, head of emergency services at Grand Canyon National Park. Heat stroke is a deadly condition that hits when the body's com temperature climbs above 40[degrees]C (104[degrees]F).

Normally the brain's thermostat keeps the body at 37[degrees]C (98.6[degrees]F) even in blazing sun. "Humans are very adaptable to the heat," says Collins. As the body warms, blood vessels balloon to pump more blood across the skin, increasing heat loss. And sweat pours out of more than 3 million sweat glands--the tiny holes in your skin that would stretch 9.5 km (6 mi) if placed end-to end! Sweat absorbs your body heat and then evaporates, cooling the skin. In a heat-stroke victim, the brain gets so hot it shuts down, cutting off these cooling systems. Victims suffer disorientation and eventually Collapse. Avoid heat stroke by drinking water and staying in the shade.

Take Cover Shelter from the sun is as simple as sitting under a palm tree. Why? Sunlight travels at about 300,000 km (186,000 mi) per second via waves of energy. The waves hit exposed skin, warming it. Leaves can block the energy. It can be up to 20 degrees cooler in the shade. You also need shelter from wind and rain. To build a tent, tie a tope of vine between two trees of branches stuck in the ground and sling a waterproof tarp or life rail on top. Pile on stones to prevent the sides from flapping in the wind. Your new home may not make it onto MTV Cribs, but it can keep you safe until help arrives.

Locate 10 items in the picture (left) that will help this teen weather a remote desert island until help arrives. List the items below along with their potential uses. Be creative!

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4--

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6--

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HOW LONG CAN YOU LIVE WITHOUT ...

                FOOD?          WATER?          AIR?           SLEEP?

 AVERAGE      One Month       10 Days      Three Minutes     10 Days
  LENGTH
 OF TIME
THE RECORD     60 Days      A teen spent     A toddler      A teenager
                              18 days      spent an hour    stayed up
                              without      and 6 minutes   for 11 days
                            water in an     under water    for a scince
                              Austrian                       project.
                               jail.
BELIEVE IT   Locusts have    Camels can     Lack of air     After five
  OR NOT       almost 3       lose 40        can cause      days, you
              times more     percent of     foaming at       start to
             protein than   their weight    the mouth.     hallucinate.
                steak.       in water.

Did You Know?

* In extreme situations, a dehydrated person can survive by drinking blood. "It's not terribly bad because blood is a high source of protein, so you get energy and fluid from the blood," says Wayne Askew. But it's not optimal because even though blood is 82 percent water, your body still has to use water to digest the proteins in the animal's blood. And animals can carry deadly diseases. So drinking blood should only be a last resort.

* Shade in a humid environment is much warmer than the shade in a dry environment. "The water droplets in the air will hold the heat," says Sherrie Collins. Humidity also makes it harder for sweat on your skin to evaporate because the air is already saturated with moisture. To avoid heat stroke in this environment, con off in deep water of bury yourself in sand, which reflects the heat.

* "Heat stroke basically roasts your brain inside your skull," says Collins. Your brain gets too hot to carry out the chemical reactions that mare it tick. The record temperature for heatstroke survivor at Grand Canyon National Park was set by a hiker who survived 43.33[degrees]C (110[degrees]F) core body temperatures for several hours without suffering any brain damage.

Cross-Curricular Connection

Geography/Social Studies: The Hawaiian Islands haven't always been inhabited. Research and report on how one island's history, culture, and habitat evolved.

Take It Further: Watch the PG-13 movie Cast Away starring Tom Hanks. Find tire ways he uses science theory or principle to survive.

Resources

For ah entertaining guide to Surviving a desert island, read Castaway Survivor's Guide by Rory Storm, Scholastic, 2000.

For more on tire chemistry visit:

science.howstuffworks.com/fire.htm

Here's a kid-friendly explanation of why your body needs water:

kidshealth.org/kid/stay_healthy/food/water.html

For an in-depth description of heat stroke and its symptoms see:

abcnews.go.com/sections/living/Healthology/ heatwave_dangers.html