Chapter 2: The Chemical Basis of Life I

I. Summary:

Have you ever wondered how we are made up? Past our outer epidermis we, and all other living organisms are composed of matter. Matter is anything that has mass and occupies space. Within our matter, there are atoms, which are the basic building blocks of matter. I cannot even count how many atoms there are in the human body; lets just say there are a lot!

Atoms consist of protons and neutrons, which are located in the center of the atom called the nucleus. Atoms also have electrons, which are not confined to a single space in the atom; these regions are called orbitals that occupy energy shells. Protons have a positive charge, while electrons have a negative charge and the neutrons are neutral. The protons and electrons create the atom because their opposite charges attract with one another.

Depending on the atom, some can have one or more shells. The first shell of an atom can hold two electrons and every shell after the first can hold up to eight electrons. The electrons in the outermost shell are called valence electrons. Some atoms can easily share electrons, while others have a more difficult time. Electronegativity is the chemical property that describes the tendency of an atom to attract electrons.

There are many types of atoms and each specific type of atom is called an element. You might be asking what elements are we made of? Well the human body is mainly composed of four elements: oxygen, carbon, hydrogen, and nitrogen! There are other elements that humans are composed of but these are the four primary elements in our body. Each element is assigned a certain atomic number (which is the same number as the number of protons in that atom) to recognize it from other elements. Then there is the atomic mass, which is the average mass of atoms in an element.

When a molecule (two or more atoms bonded together) contains two or more different elements it is called a compound. For example, when two hydrogen atoms bond with an oxygen atom it forms...WATER (H2O)!!!

Atoms can form several types of bonds, depending upon the specific types of atoms involved. NOTE: These are not all of the types of bonds that atoms can make, just some of them.

• Covalent Bond: bond in which one or more pairs of electrons are shared by two atoms
• Polar Covalent Bond: bond in which a pair of electrons is shared between two atoms, but the pair is held more closely by one atom
• Non-polar Covalent Bond: bond in which a pair of electrons is shared equally between two atoms
• Double Bond: bond in which atoms share two pairs of electrons
• Hydrogen Bond: bond in which a hydrogen atom of one molecule is attracted to an electronegative atom
• Ionic Bond: bond between two ions (atoms with an electric charge) with opposite charge

Now that I covered mostly everything about atoms and molecules, we can talk about the liquid properties of living organisms, such as WATER! Have you ever wondered what life would be like without water?!?! Let me tell you this, it would not be fun! Since the human body is composed mostly of water (60-70%), even a few days without it would be crucial.

A solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent for chemical reactions in all living organisms is... you guessed it, water!

Depending on the type of bond of molecules, they can be either hydrophobic (water-fearing) or hydrophilic (water-loving). Molecules that have ionic/polar covalent bonds are hydrophilic, while molecules that have non-polar covalent bonds are hydrophobic.

A substance that is dissolved in water can either release or absorb hydrogen ions. When a substance releases hydrogen ions it is called an acid. When a substance absorbs hydrogen ions it is called a base. A substance's concentration of H+ is determined on a pH scale, which measures the acidity or basicity of a solution. The lower the pH the more acidic the concentration is; the higher the pH the more alkaline (basic) the concentration is.

Anyways, this is pretty much everything that we covered in class for chapter two. And remember, for every living organism there is always a CHEMICAL BASIS for life!

II. Useful Materials:

This video is about a science teacher going over the chemical basis of life. He goes over pretty much everything covered in chapter two of our biology textbook. I think this video is very helpful because not only is he talking you through the chapter but there are also pictures and diagrams to help you better understand. He even teaches you some helpful ways to remember important facts. Overall, this video was a useful material to study from, even teaching me new things as well.

When it comes to studying through each chapter, I like to use flash cards as a study technique. Quizlet is a website that has online flash cards that you can use to study. You can even print out the flash cards so you can take them and study where ever you go! Each flash card gives you a definition/question and the answer. I think this is a helpful website if you need help remembering definitions or just want to quiz yourself.

III. Article: Hydrogen and oxygen isotope ratios in human hair are related to geography

As I posted on my blog before, this article talks about how scientists have been researching how isotopes in someone's hair can track where that person may be living.