Biology Explainer: The big 4 building blocks of life–carbohydrates, fats, proteins, and nucleic acids

The short version
  • The four basic categories of molecules for building life are carbohydrates, lipids, proteins, and nucleic acids.
  • Carbohydrates serve many purposes, from energy to structure to chemical communication, as monomers or polymers.
  • Lipids, which are hydrophobic, also have different purposes, including energy storage, structure, and signaling.
  • Proteins, made of amino acids in up to four structural levels, are involved in just about every process of life.                                                                                                      
  • The nucleic acids DNA and RNA consist of four nucleotide building blocks, and each has different purposes.
The longer version
Life is so diverse and unwieldy, it may surprise you to learn that we can break it down into four basic categories of molecules. Possibly even more implausible is the fact that two of these categories of large molecules themselves break down into a surprisingly small number of building blocks. The proteins that make up all of the living things on this planet and ensure their appropriate structure and smooth function consist of only 20 different kinds of building blocks. Nucleic acids, specifically DNA, are even more basic: only four different kinds of molecules provide the materials to build the countless different genetic codes that translate into all the different walking, swimming, crawling, oozing, and/or photosynthesizing organisms that populate the third rock from the Sun.

                                                  

Big Molecules with Small Building Blocks

The functional groups, assembled into building blocks on backbones of carbon atoms, can be bonded together to yield large molecules that we classify into four basic categories. These molecules, in many different permutations, are the basis for the diversity that we see among living things. They can consist of thousands of atoms, but only a handful of different kinds of atoms form them. It’s like building apartment buildings using a small selection of different materials: bricks, mortar, iron, glass, and wood. Arranged in different ways, these few materials can yield a huge variety of structures.

We encountered functional groups and the SPHONC in Chapter 3. These components form the four categories of molecules of life. These Big Four biological molecules are carbohydrates, lipids, proteins, and nucleic acids. They can have many roles, from giving an organism structure to being involved in one of the millions of processes of living. Let’s meet each category individually and discover the basic roles of each in the structure and function of life.
Carbohydrates

You have met carbohydrates before, whether you know it or not. We refer to them casually as “sugars,” molecules made of carbon, hydrogen, and oxygen. A sugar molecule has a carbon backbone, usually five or six carbons in the ones we’ll discuss here, but it can be as few as three. Sugar molecules can link together in pairs or in chains or branching “trees,” either for structure or energy storage.

When you look on a nutrition label, you’ll see reference to “sugars.” That term includes carbohydrates that provide energy, which we get from breaking the chemical bonds in a sugar called glucose. The “sugars” on a nutrition label also include those that give structure to a plant, which we call fiber. Both are important nutrients for people.

Sugars serve many purposes. They give crunch to the cell walls of a plant or the exoskeleton of a beetle and chemical energy to the marathon runner. When attached to other molecules, like proteins or fats, they aid in communication between cells. But before we get any further into their uses, let’s talk structure.

The sugars we encounter most in basic biology have their five or six carbons linked together in a ring. There’s no need to dive deep into organic chemistry, but there are a couple of essential things to know to interpret the standard representations of these molecules.

Check out the sugars depicted in the figure. The top-left molecule, glucose, has six carbons, which have been numbered. The sugar to its right is the same glucose, with all but one “C” removed. The other five carbons are still there but are inferred using the conventions of organic chemistry: Anywhere there is a corner, there’s a carbon unless otherwise indicated. It might be a good exercise for you to add in a “C” over each corner so that you gain a good understanding of this convention. You should end up adding in five carbon symbols; the sixth is already given because that is conventionally included when it occurs outside of the ring.

On the left is a glucose with all of its carbons indicated. They’re also numbered, which is important to understand now for information that comes later. On the right is the same molecule, glucose, without the carbons indicated (except for the sixth one). Wherever there is a corner, there is a carbon, unless otherwise indicated (as with the oxygen). On the bottom left is ribose, the sugar found in RNA. The sugar on the bottom right is deoxyribose. Note that at carbon 2 (*), the ribose and deoxyribose differ by a single oxygen.

The lower left sugar in the figure is a ribose. In this depiction, the carbons, except the one outside of the ring, have not been drawn in, and they are not numbered. This is the standard way sugars are presented in texts. Can you tell how many carbons there are in this sugar? Count the corners and don’t forget the one that’s already indicated!

If you said “five,” you are right. Ribose is a pentose (pent = five) and happens to be the sugar present in ribonucleic acid, or RNA. Think to yourself what the sugar might be in deoxyribonucleic acid, or DNA. If you thought, deoxyribose, you’d be right.

The fourth sugar given in the figure is a deoxyribose. In organic chemistry, it’s not enough to know that corners indicate carbons. Each carbon also has a specific number, which becomes important in discussions of nucleic acids. Luckily, we get to keep our carbon counting pretty simple in basic biology. To count carbons, you start with the carbon to the right of the non-carbon corner of the molecule. The deoxyribose or ribose always looks to me like a little cupcake with a cherry on top. The “cherry” is an oxygen. To the right of that oxygen, we start counting carbons, so that corner to the right of the “cherry” is the first carbon. Now, keep counting. Here’s a little test: What is hanging down from carbon 2 of the deoxyribose?

If you said a hydrogen (H), you are right! Now, compare the deoxyribose to the ribose. Do you see the difference in what hangs off of the carbon 2 of each sugar? You’ll see that the carbon 2 of ribose has an –OH, rather than an H. The reason the deoxyribose is called that is because the O on the second carbon of the ribose has been removed, leaving a “deoxyed” ribose. This tiny distinction between the sugars used in DNA and RNA is significant enough in biology that we use it to distinguish the two nucleic acids.

In fact, these subtle differences in sugars mean big differences for many biological molecules. Below, you’ll find a couple of ways that apparently small changes in a sugar molecule can mean big changes in what it does. These little changes make the difference between a delicious sugar cookie and the crunchy exoskeleton of a dung beetle.

Sugar and Fuel

A marathon runner keeps fuel on hand in the form of “carbs,” or sugars. These fuels provide the marathoner’s straining body with the energy it needs to keep the muscles pumping. When we take in sugar like this, it often comes in the form of glucose molecules attached together in a polymer called starch. We are especially equipped to start breaking off individual glucose molecules the minute we start chewing on a starch.

Double X Extra: A monomer is a building block (mono = one) and a polymer is a chain of monomers. With a few dozen monomers or building blocks, we get millions of different polymers. That may sound nutty until you think of the infinity of values that can be built using only the numbers 0 through 9 as building blocks or the intricate programming that is done using only a binary code of zeros and ones in different combinations.

Our bodies then can rapidly take the single molecules, or monomers, into cells and crack open the chemical bonds to transform the energy for use. The bonds of a sugar are packed with chemical energy that we capture to build a different kind of energy-containing molecule that our muscles access easily. Most species rely on this process of capturing energy from sugars and transforming it for specific purposes.

Polysaccharides: Fuel and Form

Plants use the Sun’s energy to make their own glucose, and starch is actually a plant’s way of storing up that sugar. Potatoes, for example, are quite good at packing away tons of glucose molecules and are known to dieticians as a “starchy” vegetable. The glucose molecules in starch are packed fairly closely together. A string of sugar molecules bonded together through dehydration synthesis, as they are in starch, is a polymer called a polysaccharide (poly = many; saccharide = sugar). When the monomers of the polysaccharide are released, as when our bodies break them up, the reaction that releases them is called hydrolysis.

Double X Extra: The specific reaction that hooks one monomer to another in a covalent bond is called dehydration synthesis because in making the bond–synthesizing the larger molecule–a molecule of water is removed (dehydration). The reverse is hydrolysis (hydro = water; lysis = breaking), which breaks the covalent bond by the addition of a molecule of water.

Although plants make their own glucose and animals acquire it by eating the plants, animals can also package away the glucose they eat for later use. Animals, including humans, store glucose in a polysaccharide called glycogen, which is more branched than starch. In us, we build this energy reserve primarily in the liver and access it when our glucose levels drop.

Whether starch or glycogen, the glucose molecules that are stored are bonded together so that all of the molecules are oriented the same way. If you view the sixth carbon of the glucose to be a “carbon flag,” you’ll see in the figure that all of the glucose molecules in starch are oriented with their carbon flags on the upper left.

The orientation of monomers of glucose in polysaccharides can make a big difference in the use of the polymer. The glucoses in the molecule on the top are all oriented “up” and form starch. The glucoses in the molecule on the bottom alternate orientation to form cellulose, which is quite different in its function from starch.

Storing up sugars for fuel and using them as fuel isn’t the end of the uses of sugar. In fact, sugars serve as structural molecules in a huge variety of organisms, including fungi, bacteria, plants, and insects.

The primary structural role of a sugar is as a component of the cell wall, giving the organism support against gravity. In plants, the familiar old glucose molecule serves as one building block of the plant cell wall, but with a catch: The molecules are oriented in an alternating up-down fashion. The resulting structural sugar is called cellulose.

That simple difference in orientation means the difference between a polysaccharide as fuel for us and a polysaccharide as structure. Insects take it step further with the polysaccharide that makes up their exoskeleton, or outer shell. Once again, the building block is glucose, arranged as it is in cellulose, in an alternating conformation. But in insects, each glucose has a little extra added on, a chemical group called an N-acetyl group. This addition of a single functional group alters the use of cellulose and turns it into a structural molecule that gives bugs that special crunchy sound when you accidentally…ahem…step on them.

These variations on the simple theme of a basic carbon-ring-as-building-block occur again and again in biological systems. In addition to serving roles in structure and as fuel, sugars also play a role in function. The attachment of subtly different sugar molecules to a protein or a lipid is one way cells communicate chemically with one another in refined, regulated interactions. It’s as though the cells talk with each other using a specialized, sugar-based vocabulary. Typically, cells display these sugary messages to the outside world, making them available to other cells that can recognize the molecular language.

Lipids: The Fatty Trifecta

Starch makes for good, accessible fuel, something that we immediately attack chemically and break up for quick energy. But fats are energy that we are supposed to bank away for a good long time and break out in times of deprivation. Like sugars, fats serve several purposes, including as a dense source of energy and as a universal structural component of cell membranes everywhere.

Fats: the Good, the Bad, the Neutral

Turn again to a nutrition label, and you’ll see a few references to fats, also known as lipids. (Fats are slightly less confusing that sugars in that they have only two names.) The label may break down fats into categories, including trans fats, saturated fats, unsaturated fats, and cholesterol. You may have learned that trans fats are “bad” and that there is good cholesterol and bad cholesterol, but what does it all mean?

Let’s start with what we mean when we say saturated fat. The question is, saturated with what? There is a specific kind of dietary fat call the triglyceride. As its name implies, it has a structural motif in which something is repeated three times. That something is a chain of carbons and hydrogens, hanging off in triplicate from a head made of glycerol, as the figure shows.  Those three carbon-hydrogen chains, or fatty acids, are the “tri” in a triglyceride. Chains like this can be many carbons long.

Double X Extra: We call a fatty acid a fatty acid because it’s got a carboxylic acid attached to a fatty tail. A triglyceride consists of three of these fatty acids attached to a molecule called glycerol. Our dietary fat primarily consists of these triglycerides.

Triglycerides come in several forms. You may recall that carbon can form several different kinds of bonds, including single bonds, as with hydrogen, and double bonds, as with itself. A chain of carbon and hydrogens can have every single available carbon bond taken by a hydrogen in single covalent bond. This scenario of hydrogen saturation yields a saturated fat. The fat is saturated to its fullest with every covalent bond taken by hydrogens single bonded to the carbons.

Saturated fats have predictable characteristics. They lie flat easily and stick to each other, meaning that at room temperature, they form a dense solid. You will realize this if you find a little bit of fat on you to pinch. Does it feel pretty solid? That’s because animal fat is saturated fat. The fat on a steak is also solid at room temperature, and in fact, it takes a pretty high heat to loosen it up enough to become liquid. Animals are not the only organisms that produce saturated fat–avocados and coconuts also are known for their saturated fat content.

The top graphic above depicts a triglyceride with the glycerol, acid, and three hydrocarbon tails. The tails of this saturated fat, with every possible hydrogen space occupied, lie comparatively flat on one another, and this kind of fat is solid at room temperature. The fat on the bottom, however, is unsaturated, with bends or kinks wherever two carbons have double bonded, booting a couple of hydrogens and making this fat unsaturated, or lacking some hydrogens. Because of the space between the bumps, this fat is probably not solid at room temperature, but liquid.

You can probably now guess what an unsaturated fat is–one that has one or more hydrogens missing. Instead of single bonding with hydrogens at every available space, two or more carbons in an unsaturated fat chain will form a double bond with carbon, leaving no space for a hydrogen. Because some carbons in the chain share two pairs of electrons, they physically draw closer to one another than they do in a single bond. This tighter bonding result in a “kink” in the fatty acid chain.

In a fat with these kinks, the three fatty acids don’t lie as densely packed with each other as they do in a saturated fat. The kinks leave spaces between them. Thus, unsaturated fats are less dense than saturated fats and often will be liquid at room temperature. A good example of a liquid unsaturated fat at room temperature is canola oil.

A few decades ago, food scientists discovered that unsaturated fats could be resaturated or hydrogenated to behave more like saturated fats and have a longer shelf life. The process of hydrogenation–adding in hydrogens–yields trans fat. This kind of processed fat is now frowned upon and is being removed from many foods because of its associations with adverse health effects. If you check a food label and it lists among the ingredients “partially hydrogenated” oils, that can mean that the food contains trans fat.

Double X Extra: A triglyceride can have up to three different fatty acids attached to it. Canola oil, for example, consists primarily of oleic acid, linoleic acid, and linolenic acid, all of which are unsaturated fatty acids with 18 carbons in their chains.

Why do we take in fat anyway? Fat is a necessary nutrient for everything from our nervous systems to our circulatory health. It also, under appropriate conditions, is an excellent way to store up densely packaged energy for the times when stores are running low. We really can’t live very well without it.

Phospholipids: An Abundant Fat

You may have heard that oil and water don’t mix, and indeed, it is something you can observe for yourself. Drop a pat of butter–pure saturated fat–into a bowl of water and watch it just sit there. Even if you try mixing it with a spoon, it will just sit there. Now, drop a spoon of salt into the water and stir it a bit. The salt seems to vanish. You’ve just illustrated the difference between a water-fearing (hydrophobic) and a water-loving (hydrophilic) substance.

Generally speaking, compounds that have an unequal sharing of electrons (like ions or anything with a covalent bond between oxygen and hydrogen or nitrogen and hydrogen) will be hydrophilic. The reason is that a charge or an unequal electron sharing gives the molecule polarity that allows it to interact with water through hydrogen bonds. A fat, however, consists largely of hydrogen and carbon in those long chains. Carbon and hydrogen have roughly equivalent electronegativities, and their electron-sharing relationship is relatively nonpolar. Fat, lacking in polarity, doesn’t interact with water. As the butter demonstrated, it just sits there.

There is one exception to that little maxim about fat and water, and that exception is the phospholipid. This lipid has a special structure that makes it just right for the job it does: forming the membranes of cells. A phospholipid consists of a polar phosphate head–P and O don’t share equally–and a couple of nonpolar hydrocarbon tails, as the figure shows. If you look at the figure, you’ll see that one of the two tails has a little kick in it, thanks to a double bond between the two carbons there.

Phospholipids form a double layer and are the major structural components of cell membranes. Their bend, or kick, in one of the hydrocarbon tails helps ensure fluidity of the cell membrane. The molecules are bipolar, with hydrophilic heads for interacting with the internal and external watery environments of the cell and hydrophobic tails that help cell membranes behave as general security guards.

The kick and the bipolar (hydrophobic and hydrophilic) nature of the phospholipid make it the perfect molecule for building a cell membrane. A cell needs a watery outside to survive. It also needs a watery inside to survive. Thus, it must face the inside and outside worlds with something that interacts well with water. But it also must protect itself against unwanted intruders, providing a barrier that keeps unwanted things out and keeps necessary molecules in.

Phospholipids achieve it all. They assemble into a double layer around a cell but orient to allow interaction with the watery external and internal environments. On the layer facing the inside of the cell, the phospholipids orient their polar, hydrophilic heads to the watery inner environment and their tails away from it. On the layer to the outside of the cell, they do the same.
As the figure shows, the result is a double layer of phospholipids with each layer facing a polar, hydrophilic head to the watery environments. The tails of each layer face one another. They form a hydrophobic, fatty moat around a cell that serves as a general gatekeeper, much in the way that your skin does for you. Charged particles cannot simply slip across this fatty moat because they can’t interact with it. And to keep the fat fluid, one tail of each phospholipid has that little kick, giving the cell membrane a fluid, liquidy flow and keeping it from being solid and unforgiving at temperatures in which cells thrive.

Steroids: Here to Pump You Up?

Our final molecule in the lipid fatty trifecta is cholesterol. As you may have heard, there are a few different kinds of cholesterol, some of which we consider to be “good” and some of which is “bad.” The good cholesterol, high-density lipoprotein, or HDL, in part helps us out because it removes the bad cholesterol, low-density lipoprotein or LDL, from our blood. The presence of LDL is associated with inflammation of the lining of the blood vessels, which can lead to a variety of health problems.

But cholesterol has some other reasons for existing. One of its roles is in the maintenance of cell membrane fluidity. Cholesterol is inserted throughout the lipid bilayer and serves as a block to the fatty tails that might otherwise stick together and become a bit too solid.

Cholesterol’s other starring role as a lipid is as the starting molecule for a class of hormones we called steroids or steroid hormones. With a few snips here and additions there, cholesterol can be changed into the steroid hormones progesterone, testosterone, or estrogen. These molecules look quite similar, but they play very different roles in organisms. Testosterone, for example, generally masculinizes vertebrates (animals with backbones), while progesterone and estrogen play a role in regulating the ovulatory cycle.

Double X Extra: A hormone is a blood-borne signaling molecule. It can be lipid based, like testosterone, or short protein, like insulin.

Proteins

As you progress through learning biology, one thing will become more and more clear: Most cells function primarily as protein factories. It may surprise you to learn that proteins, which we often talk about in terms of food intake, are the fundamental molecule of many of life’s processes. Enzymes, for example, form a single broad category of proteins, but there are millions of them, each one governing a small step in the molecular pathways that are required for living.

Levels of Structure

Amino acids are the building blocks of proteins. A few amino acids strung together is called a peptide, while many many peptides linked together form a polypeptide. When many amino acids strung together interact with each other to form a properly folded molecule, we call that molecule a protein.

For a string of amino acids to ultimately fold up into an active protein, they must first be assembled in the correct order. The code for their assembly lies in the DNA, but once that code has been read and the amino acid chain built, we call that simple, unfolded chain the primary structure of the protein.

This chain can consist of hundreds of amino acids that interact all along the sequence. Some amino acids are hydrophobic and some are hydrophilic. In this context, like interacts best with like, so the hydrophobic amino acids will interact with one another, and the hydrophilic amino acids will interact together. As these contacts occur along the string of molecules, different conformations will arise in different parts of the chain. We call these different conformations along the amino acid chain the protein’s secondary structure.

Once those interactions have occurred, the protein can fold into its final, or tertiary structure and be ready to serve as an active participant in cellular processes. To achieve the tertiary structure, the amino acid chain’s secondary interactions must usually be ongoing, and the pH, temperature, and salt balance must be just right to facilitate the folding. This tertiary folding takes place through interactions of the secondary structures along the different parts of the amino acid chain.

The final product is a properly folded protein. If we could see it with the naked eye, it might look a lot like a wadded up string of pearls, but that “wadded up” look is misleading. Protein folding is a carefully regulated process that is determined at its core by the amino acids in the chain: their hydrophobicity and hydrophilicity and how they interact together.

In many instances, however, a complete protein consists of more than one amino acid chain, and the complete protein has two or more interacting strings of amino acids. A good example is hemoglobin in red blood cells. Its job is to grab oxygen and deliver it to the body’s tissues. A complete hemoglobin protein consists of four separate amino acid chains all properly folded into their tertiary structures and interacting as a single unit. In cases like this involving two or more interacting amino acid chains, we say that the final protein has a quaternary structure. Some proteins can consist of as many as a dozen interacting chains, behaving as a single protein unit.

A Plethora of Purposes

What does a protein do? Let us count the ways. Really, that’s almost impossible because proteins do just about everything. Some of them tag things. Some of them destroy things. Some of them protect. Some mark cells as “self.” Some serve as structural materials, while others are highways or motors. They aid in communication, they operate as signaling molecules, they transfer molecules and cut them up, they interact with each other in complex, interrelated pathways to build things up and break things down. They regulate genes and package DNA, and they regulate and package each other.

As described above, proteins are the final folded arrangement of a string of amino acids. One way we obtain these building blocks for the millions of proteins our bodies make is through our diet. You may hear about foods that are high in protein or people eating high-protein diets to build muscle. When we take in those proteins, we can break them apart and use the amino acids that make them up to build proteins of our own.

Nucleic Acids

How does a cell know which proteins to make? It has a code for building them, one that is especially guarded in a cellular vault in our cells called the nucleus. This code is deoxyribonucleic acid, or DNA. The cell makes a copy of this code and send it out to specialized structures that read it and build proteins based on what they read. As with any code, a typo–a mutation–can result in a message that doesn’t make as much sense. When the code gets changed, sometimes, the protein that the cell builds using that code will be changed, too.

Biohazard!The names associated with nucleic acids can be confusing because they all start with nucle-. It may seem obvious or easy now, but a brain freeze on a test could mix you up. You need to fix in your mind that the shorter term (10 letters, four syllables), nucleotide, refers to the smaller molecule, the three-part building block. The longer term (12 characters, including the space, and five syllables), nucleic acid, which is inherent in the names DNA and RNA, designates the big, long molecule.

DNA vs. RNA: A Matter of Structure

DNA and its nucleic acid cousin, ribonucleic acid, or RNA, are both made of the same kinds of building blocks. These building blocks are called nucleotides. Each nucleotide consists of three parts: a sugar (ribose for RNA and deoxyribose for DNA), a phosphate, and a nitrogenous base. In DNA, every nucleotide has identical sugars and phosphates, and in RNA, the sugar and phosphate are also the same for every nucleotide.

So what’s different? The nitrogenous bases. DNA has a set of four to use as its coding alphabet. These are the purines, adenine and guanine, and the pyrimidines, thymine and cytosine. The nucleotides are abbreviated by their initial letters as A, G, T, and C. From variations in the arrangement and number of these four molecules, all of the diversity of life arises. Just four different types of the nucleotide building blocks, and we have you, bacteria, wombats, and blue whales.

RNA is also basic at its core, consisting of only four different nucleotides. In fact, it uses three of the same nitrogenous bases as DNA–A, G, and C–but it substitutes a base called uracil (U) where DNA uses thymine. Uracil is a pyrimidine.

DNA vs. RNA: Function Wars

An interesting thing about the nitrogenous bases of the nucleotides is that they pair with each other, using hydrogen bonds, in a predictable way. An adenine will almost always bond with a thymine in DNA or a uracil in RNA, and cytosine and guanine will almost always bond with each other. This pairing capacity allows the cell to use a sequence of DNA and build either a new DNA sequence, using the old one as a template, or build an RNA sequence to make a copy of the DNA.

These two different uses of A-T/U and C-G base pairing serve two different purposes. DNA is copied into DNA usually when a cell is preparing to divide and needs two complete sets of DNA for the new cells. DNA is copied into RNA when the cell needs to send the code out of the vault so proteins can be built. The DNA stays safely where it belongs.

RNA is really a nucleic acid jack-of-all-trades. It not only serves as the copy of the DNA but also is the main component of the two types of cellular workers that read that copy and build proteins from it. At one point in this process, the three types of RNA come together in protein assembly to make sure the job is done right.


 By Emily Willingham, DXS managing editor 
This material originally appeared in similar form in Emily Willingham’s Complete Idiot’s Guide to College Biology

Survival is Gendered, According to Scholastic

[Editor's note: We were going to write this as a she said/he said sort of thing with Emily Willingham and Matthew Francis, but then Francis got all serious and did an analysis and stuff. So his smart analysis appears first, and Willingham's (not quite) equally sober chapter-by-chapter evaluation of the "girls" book follows.]

Last week Ryan North, purveyor of the excellent webcomic Dinosaur Comics, stumbled across a pair of books published by Scholastic. The books are titled For Boys Only: How to Survive Anything and For Girls Only: How to Survive Anything, which already should be a tip-off, but the tables of contents really hammer home a message. As North says, “Maybe – MAYBE – How To Pick Perfect Sunglasses is actually in the same class as Surviving When Your Parachute Fails.” However, it’s obvious that boys and girls are not expected to want to survive the same things, and that the very idea of survival is gendered in these books.

Thanks to the outcry, Scholastic has already announced they will discontinue the titles, which is great. However, I wonder why they approved them in the first place, and their announcement shows that they don’t really understand what the big deal is. My friend JeNel, who is a children’s librarian, points out that Scholastic’s displays are always gendered, with a lovely regressive social agenda. So, shall we break it down for Scholastic?

First, anytime you name two books “For Boys Only” and “For Girls Only”, put an alligator on the cover of one and a pink cell phone on the cover of the other, you’re telling your audience of impressionable children that these books aren’t going to be equivalent. It’s almost inevitable that the “boy” book is going to be full of adventure and the “girl” book is going to be full of social stuff, and that’s the case here. “Survival” for boys includes broken legs, tornadoes, and earthquakes (since boys are obviously the only ones who will ever experience those), while “survival” for girls includes frenemies, brothers, and teaching your cat how to sit. (I suppose treating cat scratches and bites is kind of a survival skill.) In other words, “survival” for girls is a set of potentially useful social skills – which I guess boys don’t need to know. I split the contents into five categories, and assigned each chapter to one of the categories. 

Here’s the breakdown:

  1. True survival skills, where the knowledge could save your life or at least help you cope with injuries (forest fires, flash floods, snakebites, etc.). Not all of these are likely to be experienced (such as polar bear attack), but at least they could happen. The score: “boys” 22, “girls” 0.
  2. Survival skills for science fiction or fantasy scenarios, which are fun, but will never happen in real life (ghost attack, vampire attack, dinosaur attack, etc.). The score: “boys”  4, “girls” 3.
  3. Useful skills and advice for daily life or unusual situations (dealing with annoying people, getting over rejection, etc.). Not all of these are of equal um…significance, unless you think picking the right sunglasses is equivalent to coping with bullies, but I didn’t want to break the categories up too much. The score: “boys” 0, “girls” 23.
  4. Skills and advice for sudden stardom or suddenly becoming rich, which are fun to dream about, I suppose. The score: “boys” 0, “girls” 3.
  5. Teaching your cat how to sit. The score: “boys” 0, “girls” 1.

Let’s ignore the hyperbolic titles, since obviously neither book is intended to actually teach you to survive everything. However, the implications are clear: Boys need to know how to survive broken legs and earthquakes, but girls evidently will never experience that sort of thing. (Or perhaps Scholastic is assuming the girls will always have a knowledgeable boy around to help out. That sentence caused me psychological pain to even type.) Similarly, boys won’t ever need help dealing with bullies, frenemies, or learning how to camp. Either that, or (as Greg Gbur suggests) girls already know how to deal with the hard survival stuff, so they don’t need the book.


———————————————————————–

So, like, talking on a cell phone held in
one hand while engaged in this activity is so
totally NOT a survival technique. 

GIRLS ONLY: How to Survive Anything!  
Table of Contents

  • How to survive a BFF Fight (Boys don’t have friends and fight with them? What is that thing they’re doing when they’re rolling around all over the floor trying to kill each other?)
  • How to Survive Soccer Tryouts (assuming very male David Beckham once had to do this)
  • How to Survive a Breakout (like this?)
  • How to Show You’re Sorry (because being a boy means never having to show you’re sorry)
  • How to Have the Best Sleepover Ever (My sons have sleepovers; just discreetly double-checked their gonads)
  • How to Take the Perfect School Photo (like this guy did?)
  • How to Survive Brothers (My sons have brothers, two each; they could really use some tips on this)
  • Scary Survival Dos and Don’ts (if it’s scary, don’t do it)
  • How to Handle Becoming Rich (Nooo! Not RICH!)
  • How to Keep Stuff Secret (It’s like, so hard, to like, keep your mouth shut, you know?)
  • How to Survive Tests (At first I thought this said “testes,” and I was confused. That said, apparently females do have more test anxiety than males. It’s because we’re too stressed about that perfect school photo).
  • How to Survive Shyness (Have you met my husband? No? That’s because he’s shy)
  • How to Handle Sudden Stardom (Boys and men never suddenly become stars. Ever)
  • More Stardom Survival Tips (because one chapter on stardom just isn’t enough)
  • How to Survive a Camping Trip (Boys never go camping. Or they automatically know how because they have testes. Or something like that)
  • How to Survive a Fashion Disaster (You see, fashion is an equal-opportunity threat, people)
  • How to Teach Your Cat to Sit (a critical skill, no doubt, but one boys need to know, too)
  • How to Turn a No Into a Yes (I just …  no)
  • Top Tips for Speechmaking (because we’ve never, ever seen a boy give a bad speech)
  • How to Survive Embarrassment (gentlemen, clearly no concern of yours, sudden erections during algebra notwithstanding)
  • How to Be a Mind Reader (I see what you’re thinking here. No. Just no)
  • How to Survive a Crush (So for boys, is the corollary “How to Survive a Lust?”, or what?)
  • Seaside Survival (More than half of the US population lives in a coastal county. I guess all the males in that portion are expendable)
  • How to Soothe Sunburn (like this fellow did)
  • How to Pick Perfect Sunglasses (living proof that boys could use some help with this, too)
  • Surviving a Zombie Attack (two of these people are male)
  • How to Spot a Frenemy (Paul, meet John. Mick, meet Keith. Simon, meet Garfunkel. Freud, meet Jung. See? Boys have frenemies, too!)
  • Brilliant Boredom Busters (Am copying these now for my three sons, for whom a houseful of toys, books, art supplies, games, videos, and movies simply isn’t enough)
  • How to Survive Truth or Dare (see “No., Just no” above)
  • How to Beat Bullies (Is this a recommended approach? ‘Cause I need to do some time traveling, if so)
  • How to be an Amazing Babysitter (You can start by not taking a gendered approach to every single facet of existence of the child you’re babysitting)

There will never be another Curie…and that’s a good thing

For your serious Sunday consideration, from Double X Science physics editor, Matthew Francis.


The above courtesy of xkcd, a webcomic of romance,
sarcasm, math, and language.

If you had to name the top scientists of the 20th century, any reasonable list must include Polish-French scientist Marie Sklodowska Curie. She won the Nobel Prize twice, a feat only matched by three others: once in physics (in 1903) for her work in radioactivity, a term she coined; and once in chemistry (in 1911) for her discovery of the two chemical elements radium and polonium. Her first prize was shared with her husband Pierre, himself an excellent physicist. She went on hiking trips with Einstein, who complained that she was too energetic in her walking style, as he preferred to dawdle. She was also the only female participant in the great Solvay Conference of 1927, which included many of the great innovators in modern physics. The element curium (96 on the periodic table) and several research institutes are named for her.

How can you not admire Curie? Let’s face it: she kicks all of our butts.

Lise Meitner. Photo in US public domain,
via Wikimedia Commons.

It’s easy to think of her as one of the Great Woman Scientists, but without a doubt she was a greater scientist than most of us can ever hope to be, male or female. At the same time, anyone thinking they aren’t great because they aren’t a Madame Curie should stop worrying. One side effect of tokenism — letting one or two representatives from non-majority groups stand in for their entire group — is that it truly sets standards far higher than are reasonable. Curie was an outstanding scientist by any Continue reading

Science is For Everyone, Including (Gasp!) Moms

Looking through magazines aimed specifically at women (including most parenting magazines), you might be forgiven for thinking that women have no interest in science or technology. I’m not the demographic these publications are aimed at, of course: I’m not even a parent, much less a woman. Of course there are plenty of magazines consumed by women and men alike, though I can also think of some that are far too guy-focused.

That’s not what this is about: for a busy woman who doesn’t have time to read much, women’s magazines and woman-oriented blogs (like Double X Science) may be a primary outlet. Women working outside the home still spend a lot more time doing housework than men in similar situations, so obviously there are societal pressures that limit leisure time for reading for many women. However, in my view, that’s an even stronger argument for expanding the content of women’s and parenting magazines. 

Moms aren’t one-dimensional creatures, focused entirely on domestic matters: They are full human beings with wide-ranging interests. (That I’m even saying this is absurd. Come on, society.)

My friend and colleague Elana (with whom I’m collaborating on a research project) is an applied mathematician currently working in mathematical biology. (Here’s an explanation of one aspect of our project.) She is also mother to a young boy, and she writes: “I may actually read the parenting magazines if they had something about advice for science activities and teaching science to kids.”

I imagine she’s not along in that sentiment; even people who read the parenting magazines primarily for advice on potty training may also wish for sciency goodness as well. I care deeply about public science education: Science is for everyone. When I was planetarium director, obviously a lot of parents brought their kids in for shows, and I made a point of trying to reach both the kids and grown-ups in the crowd. After all, kids are going to ask questions of their mom or dad, and Mom deserves the dignity of knowing and providing those answers herself.

 You might ask whether woman-oriented magazines and blog networks are the right venue, but I say “why not?” Most of us don’t subscribe to or buy that many magazines; I bet that magazines could increase their subscriptions (and possibly even advertising revenue) if they expanded content, and they probably wouldn’t lose anybody. In fact, Elana reminds me that women’s magazines used to have science sections and puzzles, which have mostly vanished over the years.

I can’t imagine anyone saying “I’m not interested in science, so I’ll stop subscribing to a magazine because they run one article per issue about astronomy.” Really the only argument against expanding to include stuff like this is a belief that women are dumb one-dimensional creatures, who care for nothing but home-making. (Emily Willingham on Twitter used the phrase “monolith of maternity”, which is a truly excellent description of that stereotype.) Try that one, editors. See how far insulting the intelligence of your readers gets you.

The fracturing of media into niche markets has its good and bad points, but if you think “Mommy” with no interests outside the home is a legitimate market, you relegate a huge section of the world to irrelevance. Not every mom is a scientist, and not every kid with curiosity about the natural world (which is every kid!) will become a scientist. However, to have an educated population, you need to reach everyone, and talk about things that aren’t just how to remove stains, important as that knowledge is to parents and pet owners.

Mothers are role models to their children. Mothers are also human beings with their own needs and thirst for knowledge. The sooner we as a society acknowledge all of that, the better off all of us will be. 

Matthew Francis
(Many thanks to Elana Fertig, Dawn Everard, and Emily Willingham for helping me shape this post, whether they knew they were helping or not.) 
Twitter @DrMRFrancisThis post originally apppeared at Galileo’s Pendulum

Mirror Mirror On the Wall, Mirrors Don’t Switch Hands at All

Nearly every kid has asked some variation on the question, “Why do mirrors switch left and right, but not up and down?” Maybe you still ask yourself that question too – it doesn’t seem to make sense. After all, there’s nothing special about “left and right” vs. “up and down” as far as a mirror goes. If you lean sideways, it still looks like your left and right are being switched, leaving your up and down the same.

That’s the clue to solve the mystery: mirrors actually don’t reverse left and right, however it may look. It’s a common misconception – I’ve even seen science museum displays say it. If you really want to see what mirrors do, hold your hand up between your face and the mirror with your palm toward the mirror, so that you can see both your hand and its reflection at the same time. You see the back of your hand, but the reflection shows the palm of your hand, a view you aren’t able to see without the mirror. The mirror is actually reversing front and back! The front of your hand (the side you see without the mirror) is the back of your hand in the reflection.

We can see why mirrors fool us into thinking left and right are swapped, though: it looks like a second person is standing in the mirror, looking back at us. When you raise your right hand, the mirror person appears to raise her left hand. However, what’s really happening is that the mirror person is still raising her right hand, just that the front of your hand is the back of hers, the front of your head is the back of hers, and so forth. If the mirror really flipped left and right, the mirror person would be facing the same way you are: you’d be seeing the back of her head instead of her face!

Concave Mirrors for Makeup and Telescopes

Ordinary bathroom mirrors are flat, but there a kind of mirror that flips left and right as well as front-to-back – but it also reverses up and down, too. This type of mirror is a concave mirror: one like the inside of a polished metal bowl or the cupped part of a soup spoon. Again, you’ve probably played with making faces into a shiny metal spoon: one side gives you an upside-down reflection. (I’ll talk about the other side of the spoon in a little bit – that’s a third kind of mirror.) A spoon is kind of an odd shape, since reflecting your image isn’t their main purpose, but many makeup and shaving mirrors are closer to being ideal concave mirrors.

The upside-down and backward image you see will always appear smaller than you are, but it will also seem to be closer to the mirror than you are. Unless the mirror is nearly flat, your face will appear to be distorted: a big protruding nose and smaller ears fading in the distance. If you sway left, your image will sway right; if you duck down, your image will bob up. That’s how we know the image is truly reversed, unlike the flat mirror! A big concave mirror can be a bit headache-inducing (at least if you’re like me): the image looks very strange compared to the image in your bathroom mirror. That’s because it’s what is known as a real image: it’s on the same side of the mirror as your face, so your eyes have a lot of trouble focusing on it. In fact, if you put a piece of paper at the right location, you can actually project the image from a concave mirror onto it.
There’s a special distance from the mirror known as the focal length, where the light focuses. A very curved mirror has a small focal length, while one that is nearly flat has a large focal length.(Also, the flatter the mirror, the less distortion you see in the image.) If you stand close to the mirror than its focal length, your image will be right-side up and magnified. That’s the real reason many makeup and shaving mirrors are concave: they have large focal lengths, so that your image in the mirror is slightly larger than your actual face – and appears closer to the mirror than your face really is. You can guess the advantage of that: you can see your eyelashes or the contours of your face more clearly.

Let’s go beyond the everyday for a bit: if you want to build a really big telescope, a concave mirror is the way to go. Unlike lenses, you don’t have to make a telescope out of a single flawless piece of glass: you can make a huge metal dish, or make one big mirror out of a bunch of smaller mirrors in a tile pattern. The Keck telescopes in Hawaii are about 30 feet in diameter (actually 10 meters, to be precise): the width of a large classroom or a substantial house! These mirrors focus light onto a detector, creating the wonderful and often beautiful images astronomers use in their work. The huge size of the mirrors allow observatories to see both farther and with higher resolution than smaller telescopes. (If you’re shopping for telescopes, look for words like Newtonian or Cassegrain: those tell you you’re looking at a ‘scope with a mirror rather than lenses.)

You might have a satellite dish; that’s another type of concave mirror, but for radio waves or
microwaves instead of visible light, which is why they don’t look like mirrors at first glance. Again, the purpose is to focus the signal from the satellite. Big radio telescopes are also mirrors: the biggest mirror in the world is the Arecibo radio telescope in Puerto Rico: that one is 1000 feet (305 meters) across!



Objects In Mirror Are
Closer Than They Appear

If you still have your spoon from the previous section (and I hope you do – the author is not responsible for lost utensils), turn it around so that your image appears right-side up. This type of mirror is convex: like the flat mirror, it flips back and front, but not left and right. Like the concave mirror, it distorts your image, but makes your face appear farther away than it really is.

As a quick aside: if you have trouble remembering the difference between “convex” and “concave”, here’s a mnemonic. Concave includes the word “cave”: that’s a
mirror that bows inward. Convex rhymes with “flex”: that’s a mirror that bows outward. At least that’s how I remember which is which!

The passenger-side mirror of a car bears the message “Objects in mirror are closer than they appear”. (Hopefully the object is not a tyrannosaurus.) That mirror is convex, and it’s designed to give a wider view of the side and rear of the car than can be done with a flat mirror. The price of the wider field of vision is that objects do end up looking farther away than they really are. You also see convex mirrors in shops, so that the staff can look down aisles out of their direct vision, and in a famous self-portrait by M.C. Escher.


Reflections

We’ve come a long way in a short time from a basic flat bathroom mirror: we’ve seen why normal mirrors don’t flip left and right, but why concave mirrors do. We connected
makeup mirrors to the biggest telescopes in the world, and shop mirrors to cars. Even better, you probably have all these types of mirror easily accessible, especially if you’re willing to goof around with spoons. Try them out, see how they work, and the next time someone tells you that mirrors reverse left-to-right, you can help get them facing back the correct way.

Matthew Francis, Double X Science Physics Editor
@DrMRFrancis

How fluorescent lights work: quantum mechanics in the home


We have a tendency to think that “quantum mechanics” is synonymous with “out of the ordinary.” I do that, too, since there’s so much strange to talk about: the blurring of particles and waves, the apparent randomness that drove Einstein crazy, and so forth. It’s easy to forget that quantum mechanics also is an everyday matter. The odds are pretty good you’re reading this post on a computer screen (as opposed to a printout), and possibly the light you’re using is fluorescent.


The three major types of lights you can buy are incandescent bulbs, fluorescent lights (including compact fluorescent lights), and light-emitting diodes. Incandescent bulbs are the “normal” type (though they are becoming less so): They light up when an electric current runs through a thin wire made of tungsten, which heats up. The wattage of an incandescent is a measure of how much power it consumes, and most of that power goes to heat, not light, which is why you can burn your hand if you touch a bulb that’s been on any length of time. Because of the wasteful nature of that kind of bulb, a lot of people have made the switch to compact fluorescent lights (CFLs), which don’t run hot and use a lot less power for the same amount of light. And they work by using quantum mechanics!


Of course even incandescent bulbs are quantum-mechanical underneath: after all, everything Continue reading

Why is the sky pink?


On Mars, the sky is pink during the day, shading to blue at sunset. What planet did you think I was talking about?

On Earth, the sky is blue during daytime, turning red at as the sun sinks toward night.

Scattering light

Well, it’s not quite as simple as that: if you ignore your dear sainted mother’s warning and look at the Sun, you’ll see that the sky immediately around the Sun is white, and the sky right at the horizon (if you live in a place where you can get an unobstructed view) is much paler. In between the Sun and the horizon, the sky gradually changes hue, as well as varying through the day. That’s a good clue to help us answer the question every child has asked: why is the sky blue? Or as a Martian child might ask: why is the sky pink?

First of all, light isn’t being absorbed. If you wear a blue shirt, that means the dye in the cotton (or whatever it’s made of) absorbs other colors in light, so only blue is reflected back to your eye. That’s not what’s happening in the air! Instead, light is being bounced off air molecules, a process known as scattering. Air on Earth is about 80% nitrogen, with almost all of the rest being oxygen, so those are the main molecules for us to think about.

As I discussed in my earlier article on fluorescent lights, atoms and molecules can only absorb light of certain colors, based on the laws of quantum mechanics. While oxygen and nitrogen do absorb some of the colors in sunlight, they turn right around and re-emit that light. (I’m oversimplifying slightly, but the main thing is that photons aren’t lost to the world!) However, other colors don’t just pass through atoms as though they aren’t there: they can still interact, and the way we determine how that happens is again the color.

The color of light is determined by its wavelength: how far a wave travels before it repeats itself. Wavelength is also connected to energy: short wavelengths (blue and violet light) have high energy, while long wavelengths (red light) have lower energy. When a photon (a particle of light) hits a nitrogen or oxygen molecule, it might hit one of the electrons inside the molecule. Unless the wavelength is exactly right, the photon doesn’t get absorbed and the electron doesn’t move, so all the photon can do is bounce off, like a pool ball off the rail on a billiards table. Low-energy red photons don’t change direction much after bouncing–they hit the electron too gently for that. Higher-energy blue and violet photons, on the other hand, scatter by quite a bit: they end up moving in a very different direction after hitting an electron than they moving before. This whole process is known technically as Rayleigh scattering, for the physicist John Strutt, Lord Rayleigh.

The blue color of the sky

Not every photon will hit a molecule as it passes through the atmosphere, and light from the Sun contains all the colors mixed together into white light. That means if you look directly at the Sun or the sky right around the Sun during broad daylight, what you see is mostly unscattered light, the photons that pass through the air unmolested, making both Sun and sky look white. (By the way, your body is pretty good at making sure you won’t damage your vision: your reflexes will usually twitch your eyes away before any injury happens. I still don’t recommend looking at the Sun directly for any length of time, especially with sunglasses, which can fool your reflexes into thinking everything is safer than it really is.) In other parts of the sky away from the Sun, scattering is going to be more significant.

The Sun is a long way away, so unlike a light bulb in a house, the light we get from it comes in parallel beams. If you look at a part of the sky away from the Sun, in other words, you’re seeing scattered light! Red light doesn’t get scattered much, so not much of that comes to you, but blue light does, meaning the sky appears blue to our eyes. Bingo! Since there is some green and other colors mixed in as well, the apparent color of the sky is more a blue-white than a pure blue.

(The Sun’s light doesn’t contain as much violet light as it does blue or red, so we won’t see a purple sky. It also helps that our eyes don’t respond strongly to violet light. The cone cells in our retinas are tuned to respond to blue, green, and red, so the other colors are perceived by triggering combinations of the primary cone cells.)

At sunset, light is traveling through a lot more air than it does at noon. That means every ray of light has more of a chance to scatter, removing the blue light before it reaches our eyes. What’s left is red light, making the sky at the horizon near the Sun appear red. In fact, you see more gradations of color too: moving your vision higher in the sky, you’ll note red shades into orange into yellow and so forth, but each color is less intense.

So finally: why is the Martian sky pink? The answer is dust: the surface of Mars is covered in a fine powder, more like talcum than sand. During the frequent windstorms that sweep across the planet, this dust is blown high into the air, where light (yes) scatters off of it. Since the grains are larger than air molecules, the kind of scattering is different, and tends to make the light appear red. (Actually, the sky’s “true” color is very hard to determine, since there is a lot more variation than on Earth.) When there is less dust in the atmosphere, the Martian sky is a deep blue, when the Sun’s light scatters off the carbon dioxide molecules in the air.

By DXS Physics Editor Matthew Francis