Why Is Milk White? (32 page)

Some spreads are a mixture of margarine and butter, to achieve the flavor people like.

Energy is measured in calories. The three components of food that are responsible for most of the calories we consume are fats, carbohydrates, and proteins.

Fats have the most calories. Each gram of fat contains nine food calories. A food calorie is the energy needed to raise a liter of water by one degree Celsius. Non-food calories, the kind chemists and physicists use, are 1/1,000 of a food calorie. A pound of fat contains over 4,000 food calories, enough to support a man for two days.

Carbohydrates are sugars and things made from sugars, such as starches. Carbohydrates contain 4 calories per gram, or just over 1,800 calories per pound—about a day's worth of calories.

Proteins also contain 4 calories per gram if they are burned in the body instead of used to make new proteins. If there is not enough energy in the other foods we eat, the protein will be burned
for fuel. But much of the protein in a normal diet goes into building enzymes, skin, hair, muscle, and fingernails, some of which is lost every day and must be replaced.

Getting enough energy in your food is not the same as feeling energetic. You might feel most energetic in the morning before breakfast, when you haven't eaten for eight hours or more. Or some people may be addicted to the caffeine in their morning coffee and not feel energetic at all until after a cup or more of the stimulant.

So-called energy drinks take advantage of this confusion and contain both stimulants and lots of sugar. The stimulants wake you up and make your muscles overactive (jittery), which is often confused with being energetic.

Some medicines taste awful by themselves. Medicines are compounds chemists have found to have an effect on our bodies. In many cases, they are small doses of poisons that plants, bacteria, or fungi have evolved to produce in order to kill whatever is eating them, by disrupting the attacker's internal chemistry.

Humans takes advantage of those millions of years of evolution by using small amounts of those poisons to change their body chemistry. But we humans have also evolved for millions of years alongside these other organisms, and we have evolved sensors in our tongues and noses to detect when something is poisonous. So many of our medicines taste awful, usually quite bitter.

We mask those bitter tastes by adding sugar and acids to overwhelm the tongue and by adding aromas and flavorings to overwhelm the nose. Even so, some flavored medicines still taste awful. And that is a good thing, because many are poisonous if too much is taken. You still want to be reminded that these things are dangerous if not used properly.

Bubble gum is stretchy because it is made of rubber. Natural rubber is made from the sap of the rubber tree. It is called latex, and it is a white sap similar to that of milkweed plants and dandelions. The word
gum
refers to the sap of plants, and gums are used for sealing envelopes and gluing things together.

Bubble gum and chewing gums these days are made from the sap of the
manilkara chicle
tree. The sap itself is just called chicle. It was once used as a substitute for natural rubber but is now mainly used for chewing gums. The name for one brand of chewing gum, Chiclets, comes from the word for the raw sap. A cheaper form of synthetic rubber is now used in many chewing gums.

Rubber and chewing gum are both examples of polymers, long chains of atoms strung together. The strings are tangled together and occasionally
cross-linked
so that one strand is connected to another, often in several places. This is what makes the rubber bounce back or pull together after being stretched. It is what gives something a rubbery, stretchy feel.

Because humans have evolved to crave salt.

Plants don't need sodium, but animals do. Since plants don't need it, they don't absorb it from the soil and they don't store it. As a result, animals that get most of their calories from plants need to find other things to eat that do contain sodium.

Some soils contain salt, and of course the ocean does. Animals have evolved taste sensors to tell them what things contain salt, and the brain has evolved to make eating salty things pleasurable so that animals will eat salty things, even if there is no other food value associated with them. Animals will walk miles to get to salt licks.

Humans are no different. We need salt, and our brains send pleasure signals when we get salt, just as we get pleasure from sweet things. And, just like sweets, people who make foods
know that if there is more salt (up to a point) people will like the food more.

As the makers of food compete with one another for consumers' money, they find that consumers buy things that are saltier. Some food makers add salt so they can make more money.

Even at home, most people salt their food with more salt than they require in their diet, just because they have evolved to like the taste.

It doesn't. The myth of sugar-induced hyperactivity has been disproven many times. But people continue to believe it, because situations that cause children to get excited, such as parties and holidays, are also situations where a lot of sugar is present. But in fact, the sugar may cause the most excitement before it is eaten, rather than afterward.

The parents of the children have been taught to expect hyperactivity due to sugar, and so when they see hyperactivity and sugar together, they infer a cause and effect. But when there is hyperactivity and no sugar present, they don't wonder that excitement can happen in the absence of sugar. This is similar to an effect called the full moon effect, named because nurses were once convinced that hospitals are busier during a full moon, despite records proving otherwise. The nurses would see a busy hospital and a full moon and associate the two. But when the hospital was busy when there was no full moon, they did not think to associate the lack of a full moon with the busy hospital.

Actually, plain sugar doesn't stay in your mouth long enough to feed the bacteria that inhabit the film on your teeth. But foods such as dried fruits and many candies, which have sticky particles that slowly dissolve, will cause the bacteria to grow.

Your teeth are coated with a thin layer of material called plaque. This material is formed by bacteria in the mouth, which glue themselves to your teeth to avoid being swallowed. The bacteria eat sugar. When they eat the sugar, they produce acids. The bacteria do not eat your teeth, but the acids do dissolve tooth material if they accumulate enough to raise the acidity levels to a damaging level. It takes the bacteria about 20 seconds to convert sugar into acid, and the acid stays trapped in the plaque next to the teeth for about a half hour.

Soft drinks with sugar are more of a problem than plain sugar alone. First, they contain sugar. Second, they contain a lot of sugar. Third, they are consumed over a long period, so the sugar will feed the bacteria constantly. And lastly, they are more acidic than the acid the bacteria make from the sugar. Sour candies are similar— they contain high levels of acid that are more harmful to the teeth than the sugar they contain.

It is not the amount of sugar that is important, but how often you eat sugar. If you only eat it at mealtimes, the acids will be gone half an hour later. But if you sip a soda or a sugared coffee all day long, you will have a bigger problem, since the acid will be next to your teeth for many hours at a time.

As Alexa read my answers to her questions, there were occasionally words that were unfamiliar to her. Some of the words I simply define here, but others are best explained by a more detailed examination of the concepts that they describe. So instead of a short a glossary item I will sometimes expand it into a longer explanation.

Albino
An animal that lacks pigment (color) in the skin, hair, and eyes, making the skin and eyes pink and the hair white.

Alkali
The opposite of an acid. In water, acids donate protons (a hydrogen atom that is missing its electron). Alkalis accept protons. Thus alkalis and acids neutralize one another in water, forming salts.

Bicarbonate
The bicarbonate ion is a carbon atom with three oxygen atoms attached and a hydrogen attached to one of the oxygen atoms.

When carbon dioxide reacts with water, it forms carbonic acid.

You can see the carbon dioxide in the molecule (the carbon and the two oxygens) and you can see the water (the two hydrogens and the third oxygen). Acids are things that easily lose a proton (a hydrogen atom without its electron). When carbonic acid loses a proton, it becomes a bicarbonate ion. You can see that the bicarbonate ion is missing the hydrogen nucleus (the proton), but it still has the electron. This gives it a negative charge. An alkali is usually what makes the acid give up the proton. Alkalis are proton-hungry molecules. One strong alkali is called sodium hydroxide.

When sodium hydroxide reacts with carbonic acid, the proton from the carbonic acid swaps places with the sodium atom in the sodium hydroxide. The result is water and sodium bicarbonate, which is the stuff called baking soda. It looks like this:

Bipolar disorder
A condition in which a person goes between being in a very good mood and a very bad mood, sometimes very quickly.

Chromatography
A way of separating the molecules in a solution according to how well they travel in something like paper.

Capillaries
Capillaries are the tiny blood vessels that bring oxygen and food to the cells in your body. Arteries are the larger blood vessels that pump the blood from the heart and lungs to the capillaries. Veins are the large blood vessels that take the blood from the capillaries back to the heart and lungs to get more oxygen.

Corrode
To destroy or damage something by chemical reactions. When iron rusts, that is corrosion. When silver tarnishes, that is corrosion. A shiny copper penny becomes dull brown when it corrodes, and sometimes it can turn blue or green, depending on the type of chemical reaction causing the corrosion.