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BIOLOGY 1A03 (168)
Chapter 2

Biology Chapter 2.docx

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Lovaye Kajiura

Biology Chapter 2: Water and Carbon: The Chemical Basis of Life Chemical Evolution  Proposition that in early Earth, simple compounds in the atmosphere and ocean combined to form larger, more complex substances  Process responsible for this pattern was the conversion of kinetic energy in sunlight and heat to chemical energy in the form of bonds between atoms that formed large, complex compounds  Hypothesis was that one complex compound was able to self-replicate and as it multiplied, chemical evolution became biological evolution  Eventually a self-replicating molecule became surrounded by a membrane  FUNCTION FOLLOWS STRUCTURE  Chemical evolution got under way because o Abundant sources of outside energy were available to trigger endergonic reactions o Some of these molecules produced by chemical evolution are found in organisms living today Building Blocks of Chemical Evolution  An atom is most stable when its valence shell is filled  One way that shells can be filled is through the formation of chemical bonds  Covalent bonding (sharing of electrons) o As two hydrogen atoms move closer together, their positively charged nuclei repel each other and negatively charged electrons repel each other o But each protons attract both electrons and vice versa o Covalent bonds form when the attractive forces overcome the repulsive forces o Nonpolar covalent bond  Asymmetric sharing of electrons results in polar covalent bonds (dependent on electronegativity)  Ionic bonding (transferring of electrons)  The degree to which electrons are shared in chemical bonds forms a continuum  Mass of one mole of any molecule is the same as its molecular weight (sum of mass numbers of all atoms in a molecule) expressed in grams ( )  Molarity is the number of moles of the substance present per litre of solution Properties of Water  Water is vital as a universal solvent  When two liquid water molecules approach each other, partial positive charge on hydrogen attracts partial negative charge on oxygen to form hydrogen bonds  Hydrogen bonding allows almost any charged or polar molecule to dissolve in water  Cohesion o Binding between like molecules o Adhesion (binding between unlike molecules) o Water is cohesive due to its hydrogen bonds o Because hydrogen bonding exerts a pulling force at the surface of any body of water, water molecules are not stable at the surface o Water is most stable when its total SA is minimized so it will resist any force that increases its SA o Resistance makes water surface act as if it had an elastic membrane (surface tension)  Water is denser as a liquid than solid o Water expands from liquid to solid o Hydrogen bonds in ice cause the water molecules to form a regular and repeating structure, giving fairly large amounts of space between molecules  Water has a high capacity for absorbing energy o Specific heat is the amount of energy required to raise the temperature of 1 gram of substance by 1 C o Large amounts of energy needed to break hydrogen bonds Acid-Base Reactions and pH  Water molecules continuously undergo a chemical reaction (dissociation) into hydrogen ions and hydroxide ions  Substances that give up protons and raise the hydrogen ion concentration are acids  Substances that acquire protons and lower the hydr
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