The Chemistry of Life

Question 1

What is an element?

Answer 1

The simplest form of matter to have unique chemical properties.

Question 2

What is the atomic number?

Answer 2

Each element has an atomic number which identifies the number of protons in its nucleus.

Question 3

How many naturally occurring elements are there on earth?

Answer 3

91 naturally occurring elements are on Earth. 24 play a pivotal, normal physiological role in the human body

Question 4

What are the six elements that account for 98.5% of the body’s weight ?

Answer 4

Oxygen, nitrogen, hydrogen, carbon, calcium and phosphorus

Question 5

What are the six elements that account for 0.8% of the body weight ?

Answer 5

Sulfur, potassium, sodium, chlorine, magnesium, iron

Question 6

What are the trace elements that together account for 0.7% of the body weight, each no more than 0.02%?

Answer 6

Chromium, Cobalt, Copper, Flourine, Iodine, Manganese, Molybdenum, selenium, silicon, Tin, Vanadium, Zinc

Question 7

What can other elements without natural physiological roles do to the body?

Answer 7

They can contaminate the body and severely disrupt its function, as in heavy metal poisoning with lead or mercury.

Question 8

Are some elements minerals?

Answer 8

Yes- some elements are classified as minerals - these are inorganic elements that are extracted from the soil by plants and passed up the food chain to humans and other organisms. Minerals function in body structure, enabling the function of enzymes and other organic molecules, Almost 75% of this is Calcium and Phosphorus- other minerals are Cl, Mg, K, Na, and S

Question 9

What is the atomic mass of an element?

Answer 9

It is approximately equal to its total number of protons and neutrons. Electrons have very low mass - it takes 1836 electrons to equal the mass of one proton, so for most purposes we can disregard their mass.

Question 10

Discuss the significance of electrons in the atomic structure.

Answer 10

Electrons are equal to the number of protons in a neutrally charged atom and swarm about the nucleus in regions called electron shells (energy levels) The more energy an electron has, the farther away from the nucleus its orbit lies. Electrons, specifically the valence electrons, determine the chemical properties of an atom, thereby governing what molecules can exist and what chemical reactions can occur.

Question 11

What are isotopes ?

Answer 11

Not every atom of an element is identical; what is different may be the number of neutrons.

Isotopes are variations of an element in which there are a different number of neutrons and hence a different mass number. Hydrogen has three isotopes for example - respectively containing 0, 1, and 2 neutrons. Over 99% of carbon atoms have an atomic mass of 12 (6 protons and 6 neutrons) but a small percentage of carbon atoms have seven neutrons or 8 neutrons. A sample of carbon can contain different isotopes of that element- different atoms may have the same of different number of neutrons.

Question 12

Do all isotopes of a given element behave the same chemically? What about physically ?

Answer 12

Yes. An isotope of hydrogen for example called Deuterium (containing one neutron) reacts with oxygen the same way hydrogen (containing 0 neutrons does) Physically, not all behave the same.

Question 13

What is a radioisotope?

Answer 13

An unstable isotope that decay(break down) into more stable isotopes by giving off radiation. The process of decay is called radioactivity. There are stable isotopes and there are unstable isotopes. Every element has at least one radioisotope- oxygen has three stable isotopes and five radioisotopes.

Question 14

What are some harmless forms of radiation? What is ionizing radiation?

Answer 14

Light and radio waves have low energy and are harmless. Ionizing radiation causes electrons to be ejected from the atom and converts atoms into ions. Ionizing radiation can be very dangerous to the body as it can destroy molecules and produce dangerous free radicals and ions in human tissues. Examples of ionizing radiation include UV rays, X-rays and three kinds of radiation produced by nuclear decay” alpha particles, beta particles and gamma rays.

Question 15

What is the physical half life of a radioisotope?

Answer 15

The time required for 50% of the radioisotope’s atoms to decay ti a more stable state.

Question 16

What is the biological half life of a radioisotope?

Answer 16

The time it takes 50& of a radioisotope’s atoms to disappear from the body. Some of it is lost by radioactive decay and even more of it by excretion from the body.

Question 17

What is an ion?

Answer 17

Charged particles with an unequal number of protons and electrons. Electronshave either been added tor lost. An ion can consist of a single atom with + or - charge or be as large as a protein with many charges on it.

Question 18

The charge of an ion is also called its_______

Answer 18

Valence. Some elements have two or more ionized forms or different charges such as Fe²⁺ and Fe³⁺.

Question 19

In the body, what do ions with opposite charges tend to do?

Answer 19

Ions with opposite charges are attracted to each other and tend to follow each other through the body. Thus when Na⁺ is excreted in the urine, Cl^- tends to follow it.

The attraction of cations and anions to each other is important in maintaining the excitability of muscle and nerve cells.

Question 20

What are electrolytes ?

Answer 20

Electrolytes are substances that ionize (AKA become ions) in water and form solutions capable of conducting electricity.

Acids, bases or salts are electrolytes.

Electrolytes are important for their chemical reactivity (as when calcium phosphate becomes incorporated into bone), osmotic effects (influence on water content and distribution in the body) and electrical effects (which are essential to nerve and muscle function)

Electrolyte balance is one ofthe most important considerations in patient care.

Question 21

What are free radicals? Why are they harmful to the body

Answer 21

Chemical particles with an odd number of electrons. These can be produced by normal metabolic reactions of the body, by radiation and by chemicals.

An example is a molecule of oxygen, O₂.

If an additional electron is added it becomes a free radical called the superoxide anion,

They combine quickly with molecules such as fats, proteins and DNA converting them into free radicals and triggering chain reactions that destroy more molecules. Free radicals can cause some forms of cancer and myocardial infection, the death of heart tissue.

Question 22

What are antioxidants?

Answer 22

Antioxidants are chemicals that neutralize free radicals.

Question 23

What are molecules?

Answer 23

Molecules are chemical particles composed of two or more atoms united by a chemical bond. Atoms may be identical (belonging to the same element) or different. (other elements atoms are also present)

Question 24

What are compounds?

Answer 24

Compounds are molecules composed or two or more elements.

CO₂

Question 25

What holds a molecule together?

Answer 25

Molecules are held together and attracted to one another by forces called chemical bonds.

Question 26

What is an ionic bond?

Answer 26

The attraction of a cation to an anion. Sodium (Na+) and Chloride (Cl-) are attracted to each other and form the compound sodium chloride, NaCl.

Ionic bonds are weak and easily dissociate (break up) in the presence of something more attractive, such as water.

Question 27

Covalent bonds- what are they ?

Answer 27

These form by the sharing of electrons between atoms. Two hydrogen atoms share valence electrons to form a hydrogen molecule, H₂.

Question 28

What is the strongest of all chemical bonds?

Answer 28

Nonpolar covalent bonds- when shared electrons spend approximately equal time around each nucleus.

Question 29

What is a polar covalent bond ?

Answer 29

If shared electrons spend significantly more time orbiting one nucleus than they do the other, they lend their negative charge to the region where they spend the most time. When hydrogen bonds with oxygen for example, the electrons of the hydrogen atoms are more attracted to the oxygen nucleus and orbit it more than they do the hydrogen. This makes the oxygen region of the molecule slightly negative and the hydrogen regions slightly positve.

Question 30

DIscuss hydrogen bonds?

Answer 30

Hydrogen bonds are enormously important to physiology- these are weak attractions between slighly positive hydrogen atoms in one molecule and a slightly negative oxygen or nitrogen atom in another. Water molecules are weakly attracted to each other by hydrogen bonds.

Hydrogen bonds also form between different regions of the same molecule, espcially in very large molecules such as proteins and DNA. They cause such molecules to fld or coil into precise three dimensional shapes.

Hydrogren bonds are relatively weak.

Question 31

What are Van der Waals forces?

Answer 31

These are weak, brief attractions between neutral atoms as the electrons fluctuate around the orbit, causing sides of the atom to become slightly negative or positive depending on where the electrons congregate. This affects nearby atoms to which respond with disurbances in its own electron cloud. oppositely charged regions of the two atoms then attract each other for a very brief moment.

These forces are magnified when large molecules meet; in human structure they are especially important in protein building, the binding of proteins to each other and to other molecules such as hormones.

Question 32

What is a mixture?

Answer 32

Two substances that have physically combined but not chemically- each substance retains its own chemical properties.

A compound has properties much different than the properties of its elements.

Question 33

Discuss the significance of the solvency of water?

Answer 33

Solvency - the ability to dissolve other chemicals. Hydrophobic substances do not dissolve in water while hydrophillic substances do dissolve in water.

Virturally all metabolic reactions depend on the solvency of water. Biological molecules must be dissolved in water to move freely and be able to come together and react. The solvency of water also makes it the body’s primary means of transporting substances from place to place.

Question 34

What are the three types of mixtures ?

Answer 34

Solutions, colloids and suspensions

Emulsions arre a suspension of liquid in another , such as oil and vinegar salad dressing.

Question 35

What is one advantage of percentage over molarity as a measure of solute concentration? What is one advantage of molarity over percentage ?

Answer 35

Molarity is the number of moles per solute per solution.

Percentage solute concentration is is simple to compute but that unit of measurement is inadequate for many purposes.

The physiological effect of a chemical depends on how many molecules of it are present in a given volume, not the weight of the chemical.

Solutions with the same percentage concentrations can differ greatly in the number of molecules per volume because of differences in molecular weights of the solutes.

Question 36

What is the difference between a physical change and a chemical change?

Answer 36

A physical change is a change in the form of the matter (solid, liquid, gas, solution) but not its chemical composition. This change is easily reversible

A chemical change involves a change in the chemical composition of matter.