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Cells make peroxide fizz, a VW-Beetle sized heart, ice (almost) always floats

Q: 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. — 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 doesn’t. 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 can’t.

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: fast!

Therein lies a tale. When Earth was young and lacked oxygen — a couple of billion years ago — simple lactic acid bacteria probably developed first. These bacteria do not use an oxygen-rich atmosphere to metabolize food (there wasn’t any oxygen) and therefore don’t produce hydrogen peroxide. They ducked the problem. Pour hydrogen peroxide on crushed cheese or yogurt and it won’t fizz. They never learned to make the rescue catalyst because they didn’t produce the poison.

Later, but still eons ago, "strict anaerobes", such as the bacteria that cause botulism and gangrene, developed when Earth’s atmosphere still had no oxygen. Then, they were OK since hydrogen peroxide is an oxygen compound and can’t 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 don’t make the rescue catalyst. Now, strict anaerobes can live only in an airless environment like deep wounds and airtight containers.

Finally, Earth’s 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 — hydrogen peroxide. (Related: video images showing how white blood cells kill bacteria with H2O2)

Further Surfing:

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.

Q: What animal has the biggest heart? — Anonymous

A: The animal with the biggest heart is the biggest animal ever — the blue whale. This mammal’s 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 Pacific [NOAA]

More surprisingly — the hummingbird’s heart, pumping in flight at 1,000 zippy times a minute — is the biggest heart of all, for the animal’s 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 whale’s heart is only 0.5% of its body mass; whereas a hummer’s heart is 2%. That’s 4 times bigger than the whale’s relative to the their respective body sizes.

Further Surfing:

NOAA: Blue whales

Q: Will water always expand if frozen or are there any exceptions? — Derrick, Houston, Texas

A: Water is one of the few substances that expands when it changes to a solid — 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 degrees C).

Then 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 — a crystal lattice ridden with tiny "ring" holes. The "holey" configuration is less dense than water’s more "packed together" structure. That’s why water expands as it freezes. It’s the holes in the lattice.

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 world’s smallest ice "cube"—a single hexagonal ring of six molecules. Quite a feat, considering there’s 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 doesn’t 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 that’s 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...

Further Surfing:

University of North Carolina at Chapel Hill: Researchers make the smallest ice "cube"

USA 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)