Cells make peroxide fizz, a VW-Beetle sized heart, ice (almost) always floats
How does hydrogen peroxide "know" germs when it comes into contact with them?
Peroxide doesn't fizz if you pour it on uncut skin, so it's apparently not
reacting to simple dirt or oils. But, it fizzes up a storm if it contacts germs,
such as in an infected cut. ó Dave, Peralta, New Mexico
One hydrogen peroxide molecule (H2O2), consisting of 2
hydrogen atoms (H2) and 2 oxygen atoms (O2). When peroxide fizzes, a catalyst
splits hydrogen peroxide into two water molecules and an oxygen atom. The
reaction fizzes pure oxygen bubbles. [US Peroxide, Inc]
A: How does hydrogen peroxide "know"? It doesnít. The driving
force is not the chemical but rather living cells. Most cells (like blood in a
cut) cause hydrogen peroxide to change into water and oxygen gas, which, in
turn, bubbles and fizzes. However, cells must produce a catalyst to force
hydrogen peroxide to change. Some cells can manufacture the catalyst and some
Living cells as different as oysters and oak can produce the
catalyst. However, lactic acid bacteria (found now in dairy products like
yogurt) or the bacteria causing botulism or gangrene
cannot. Also, nonliving objects such as dirt or oil cannot manufacture the
catalyst (called catalase).
Most cells learned to make catalase to solve a vicious
problem. When cells metabolize food in the presence of oxygen, most produce
hydrogen peroxide as a side product. Hydrogen peroxide kills cells. The dilemma:
cells must extract energy from food to live. But the process can produce a
poison that kills them. The solution: manufacture a rescue catalyst that changes
hydrogen peroxide to harmless water and oxygen and make that reaction happen:
Therein lies a tale. When Earth was young and lacked oxygen ó
a couple of billion years ago ó simple lactic acid bacteria probably developed first.
These bacteria do not use an oxygen-rich atmosphere to metabolize food (there
wasnít any oxygen) and therefore donít produce hydrogen peroxide. They ducked
the problem. Pour hydrogen peroxide on crushed cheese or yogurt and it wonít
fizz. They never learned to make the rescue catalyst because they didnít produce
Later, but still eons ago, "strict anaerobes", such as the
bacteria that cause botulism and gangrene, developed when Earthís atmosphere
still had no oxygen. Then, they were OK since hydrogen peroxide is an oxygen
compound and canít form without oxygen. Now, these bacteria exist in extreme
danger. You see, the anaerobe bacteria do generate hydrogen peroxide when they
metabolize food but they donít make the rescue catalyst. Now, strict anaerobes
can live only in an airless environment like deep wounds and airtight
Finally, Earthís atmosphere became oxygen rich. Disaster!
Peroxide killed cells as the cells converted food to energy and produced
hydrogen peroxide. Cells solved the problem by contriving catalase. Almost all
advanced organisms since make catalase and convert hydrogen peroxide to fizzy
oxygen and water. Pour peroxide on crushed fruit or leaves, wait a few minutes,
and watch the bubbles.
By the way, white blood cells engulf germs and then kill the
germs by bathing them in poison ó hydrogen peroxide. (Related:
video images showing how white blood
cells kill bacteria with H2O2)
US Peroxide, Inc: Introduction to hydrogen peroxide
US Peroxide, Inc: Why peroxide bubbles
How Stuff Works: Making a rocket engine from hydrogen peroxide and silver.
What animal has the biggest heart? ó Anonymous
A: The animal with the biggest heart is the biggest animal
ever ó the blue whale. This mammalís heart is as big as a small car (like the
Volkswagen Beetle: 2000 pounds, 907 kg). Its main blood vessel (the aorta) is
big enough for a man to crawl through. The heart beats slowly (5 or 6 times a
minute) as it pumps 10 tons of blood through the body.
A Blue Whale swims in the eastern tropical
More surprisingly ó the hummingbirdís heart, pumping in flight
at 1,000 zippy times a minute ó is the biggest heart of all, for the animalís
size. Its heart must pump such an incredible amount each minute to push needed
oxygen and food into cells so the animal can hover like a helicopter and live in
the sky. A whaleís heart is only 0.5% of its body mass; whereas a hummerís heart
is 2%. Thatís 4 times bigger than the whaleís relative to the their respective
Q: Will water always expand if frozen or
are there any exceptions? ó Derrick, Houston, Texas
A: Water is one of the few substances that expands when it
changes to a solid ó silicon is another. Ice (in its ordinary form) always
expands as it freezes and occupies about 1/9th more space than the same amount
of liquid water. Most substances contract as they cool and freeze. Water (H2O)
starts to follow this pattern, contracting until it reaches 39 degrees F (4
six frozen H2O molecules link together to form a hexagonal ring that floats like
a life buoy bobbing on the water. As the temperature drops to freezing, these
rings join to make ice ó a crystal lattice ridden with tiny "ring" holes. The
"holey" configuration is less dense than waterís more "packed together"
structure. Thatís why water expands as it freezes. Itís the holes in the
Six water molecules linked together in an ice ring [Roger
E. Miller, University of North Carolina at Chapel Hill]
By the way, in January 2000, Roger E. Miller, chemist
professor at the University of North Carolina, succeeded in making the worldís
smallest ice "cube"óa single hexagonal ring of six molecules. Quite a feat,
considering thereís 100,000,000,000,000,000,000 molecules in a drop of water.
However, you asked if there are any exceptions. Yes, ice can
be denser than water. But, it doesnít get into that state easily and quickly
leaves such an unnatural state. We can apply high pressure (30 to 50 times the
atmospheric pressure at sea level) to produce ice thatís about 40% denser than
water. It contracts instead of expanding. The strangely dense ice forms either
by bending the hydrogen bonds more than usual or by the hydrogen bonds
penetrating the 6-molecule rings that ice crystals normally make.
Imagine Earth if such dense ice were the normal ice and all
ice sank, suddenly. Ice plunges to the bottom of rivers, lakes, and oceans.
Bottom life perishes. Warm water above insulates the bottom ice. Northern lakes
eventually freeze solid and thaw only a few inches in the summer. Icy sea
bottoms never melt. The moderating effects of large bodies of water cease.
Climate changes drastically. Life all but dies planet-wide...
University of North Carolina at Chapel Hill: Researchers make the smallest ice
Today, Weather Basics: Snow and ice
John L. Finney, University College London: The phase diagram of water/ice and a
new metastable phase of ice
(Answered Aug. 8, 2003)