Essential Chemistry for Biology Campbell Chapter 2

Some definitions Matter: anything that occupies space and has mass Three phases: solids, liquids, gases Chemical element: a substance that cannot be broken down into other substances by chemical reactions 92 naturally occurring elements on Earth; Listed on the periodic table 25 are essential for life CHOPKINS CaFe

Atoms Atoms: the smallest unit of matter that still retains the properties of an element. Protons: Positively charged, in the nucleus Neutrons: Electically neutral, in the nucleus Electrons: negative charge, orbiting the nucleus Multiple layers Outer shell electrons Atomic Number: the number of protons in an atom Defines an element; all atoms of any element have the same number of protons 1 = hydrogen; 2= helium, 6= carbon, etc Atomic Mass/Mass Number: the number of protons + neutrons Ions: unequal numbers of protons and electons Cations: lose an electon Anions: gain an electron Chemical bonds

Molecules Molecules: combinations of two or more atoms Compounds: substances that contain two or more elements in a fixed ratio Water: H20 Salt NaCl Trace elements: required in only very small amounts and essential for life Iodine: goiter Isotopes: different forms of atoms of a single element Defines the isotope: C12, C13, C14 Radioactive isotopes are unstable and decay, emitting energy

Chemical Bonds Hold atoms close together in a molecule Three types: Based on sharing electons in the outer shell Three types: Covalent: equal sharing Ionic: absolute transfer from one atom to another Polar bonds: unequal sharing of electrons between atoms in a molecule Molecules can be held together in a substance Hydrogen bonds: weak attractions resulting from uneven distribution of electrons in a molecule Chemical reactions involve making or breaking bonds Molecules can be formed or destroyed They can be moved together (condensation) or apart (evaporation)

Chemical Reactions Rearrangement of atoms among molecules Breaking apart: catabolism Joining together: anabolism Exchanging Chemical Equations reactants, the starting materials, and products, the end materials Usually include information abut the state (solid, liquid, gas, solution) Balanced: # of atoms of each element is the same on each side of the equation 2 H2 (g) + O2 (g)  2 H2O (l)

Water: More Precious than Gold Life began and evolved in water Cells = 70-95% water Water is the universal solvent of living things Most biomolecules dissolve in water Polarity of water molecules means that water dissolves a wide range of biological compounds Heat capacity regulates internal temperature Evaporative cooling occurs when a substance evaporates and the surface of the liquid remaining behind cools down.

Properties of Water Polarity leads to surface tension, the difficulty of breaking or stretching the surface of a water droplet essential for transport within plant tissues high heat capacity: water resists changes in temperature Heat: the amount of energy associated with the movement of the atoms and molecules in a body of matter Resists evaporation and freezing extends the liquid phase through a wide temperature range

Acids and Bases Solution: a liquid consisting of a homogeneous mixture of two or more substances Solvent: The dissolving agent Solute: The dissolved substance Syrup: sugar dissolved in water Acid: molecule with a hydrogen atom that it can shed HCl(aq)  H+(aq) + Cl-(aq) HCOOH(aq)  H+(aq) + COOH-(aq) Base: molecule which can accept a hydrogen atom NH3(aq) + H2O  NH4+(aq) + OH-(aq)

Buffers Aqueous solutions allow solutes to gain or lose their hydrogen ions more easily by stabilizing the products Vinegar is acetic acid: CH2COOH In pure form it is a neutral molecule: CH2COOH(l) In aqueous solution it can dissociate into a hydrogen ion and an acetate ion H+(aq) and CH2COO-(aq) Buffers: substances that resist pH change Biological liquids contain dissolved salts that act as buffers Living things exist within a narrow range of acidity

Biology and Society Drought severe crop damage, shortages of drinking water, dust storms, famine, habitat loss, and mass migration

Biology and Society: Ocean Acidification Increases in atmospheric CO2 concentrations may lead to the acidification of the oceans Gas phase carbon dioxide will dissolve in ocean water CO2(aq) + H2O  H+(aq) + HCO3-(aq) ecological disasters Coral reef death

Life cannot exist without water If life similar to ours has evolved elsewhere in the universe, then it too would depend upon water Researchers at NASA missions have found evidence that water was once abundant on Mars Microbial life may exist below the Martian surface