Bio 100 Chapter 2


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Bio 100 Chapter 2

  1. 1. Chapter 2Basic Chemistry and Cells
  2. 2. Matter is composed of atoms• Six types of atoms are basic to life = 95% of body weight – C carbon – H hydrogen – N nitrogen – O oxygen – P phosphorus – S sulfur• Element – Substance that cannot be broken down by chemical means into a simpler substance (periodic table of elements shows all known elements)• Atom – Smallest unit of an element that still retains the chemical and physical properties of the element
  3. 3. • Atomic symbol – One or two letters that represent the name of an element (Au, C, O, N)• Subatomic particles – Protons • Positively charged (+) • Within nucleus – Neutrons (0) • Uncharged • Within nucleus – Electrons (-) • Negatively charged • Orbit about nucleus
  4. 4. • Electron shells – Inner shell • Lowest energy level • Holds 2 electrons – All shells beyond inner shell • Holds 8 electrons – Outer shell • Highest energy level • Holds 8 electrons
  5. 5. • Atomic number – Number of protons of an element – Also tells number of electrons when electronically neutral
  6. 6. • Mass number – Number of protons plus neutrons• Isotopes – Atoms of a single element that differ in their number of neutrons• Atomic mass – Average mass of all isotopes
  7. 7. The many medical uses of radioactive isotopes• Low levels of radiation – Tracer to detect tumors• High levels of radiation – Sterilize medical and dental products – Sterilize mail to free it of possible pathogens (anthrax) – Treatment for cancer
  8. 8. Atoms react with one another to form molecules• After atoms react, they have a completed outer shell• Periodic table – Arranges elements based on characteristics • Periods – Horizontal row – How many shells an atom has • Groups – Vertical column – How many electrons an atom has in its outer shell
  9. 9. Periods – how many shellsGroups – how many electrons in outer shell
  10. 10. • Octet rule – Atoms will give up, accept, or share electrons in order to have 8 electrons in the outer shell• Group 8 – Stable – All other groups readily react• Compound – When atoms of two or more elements bond together in fixed proportions• Molecule – Smallest part of a compound that still has the properties of that compound – Molecule is union of two or more atoms of the same or different elements• Naturally occurring molecules – O2, H2, N2, H2O• Naturally occurring compound – H2O
  11. 11. An ionic bond occurs when electrons are transferred• One atom can take electron(s) from another atom• Ions result – Ions that lost electrons are positively charged – Ions that gained electrons are negatively charged• Ionic bonds result – An attraction between negatively and positively charged ions
  12. 12. A covalent bond occurs when electrons are shared• Atoms want to fill their outer shell• Bond notations – H – H share one pair of electrons – O = O share two pairs of electrons – N = N share three pairs of electrons• Molecular – omits the bond line – H2 – O2 – N2• Common bonds required – H – 1 bond – O – 2 bonds – C – 4 bonds
  13. 13. Chemical reactions• Some bonds are broken while others are formed• Reactants – Participate in reaction• Products – Formed by reaction• Photosynthesis – Balanced equation – Same number of each type of atom occurs on both sides of arrow
  14. 14. A covalent bond can be nonpolar or polar• Nonpolar – Sharing of electrons between two atoms is fairly equal
  15. 15. • Electronegativity – Attraction of an atom for the electrons in a covalent bond• H2O –O • Larger atom • more electronegative • Slightly negative –H • Smaller atom • Less electronegative • Slightly positive• Polar – Unequal sharing of electrons in a covalent bondThe polarity of water molecules leads to the formation of hydrogen bonds
  16. 16. Hydrogen bonds can occur between polar molecules• Hydrogen atoms in one molecule are attracted to oxygen atoms in another molecule• Weaker than ionic or covalent bonds• Hydrogen bonds also hold the two strands of DNA together
  17. 17. The properties of water benefit lifeWater molecules stick together and to other materials• Due to hydrogen bonding – Water can be liquid at most temperatures found on earth – Water molecules exhibit cohesion (stick together) – Water molecules exhibit adhesion (stick to other polar material)• Cohesion and adhesion – Create surface tension – Allows water to rise to the top of plants – Allows blood to flow through a body
  18. 18. Water warms up and cools down slowly• This allows organisms to maintain internal temperatures (homeostasis)• Cooling slowly aids organisms in winter• To vaporize water, hydrogen bonds must be broken, this requires a large amount of energy
  19. 19. Water dissolves other polar substances• Solutions are composed of – Solute • What is being dissolved – Solvent • What does the dissolvingCreating sugar water solute – sugar solvent – water
  20. 20. • When ionic salt (NaCl) is put in water, the atoms dissociate and the Na+ and Cl- dissolve into the waterHydrophilic – molecule thatcan attract waterHydrophobic – moleculethat canon attract water (oiland water do not mix)
  21. 21. Frozen water is less dense than liquidWater expands as itfreezesIce floats, allowingbodies of water to freezefrom the surface downand they usually do notfreeze solid, allowingorganisms to survive thewinter
  22. 22. Living things require a narrow pH range• When water dissociates, hydrogen ions (H+) and hydroxide ions (OH-) result in equal concentrations• Acids – Excess hydrogen (H+) ions• Bases – Excess hydroxide (OH-) ions
  23. 23. • The pH scale measures acidity and basicity• pH scale ranges from 0 to 14• Neutral = 7 – This is when H+ concentration equals OH- concentration• Acidic <7• Basic >7
  24. 24. Buffers help keep the pH of the body fluids relatively constant• Buffer – Resists changes in pH• Blood pH needs to stay between 7.35 and 7.45• Carbonic acid (H2CO3) and bicarbonate (HCO3) are present in blood• Carbonic acid can dissociate to release bicarbonate and H+ – This lowers pH• When a base is added (OH-) the carbonic acid dissociates and releases H+, these combine to form water (H2O)• When there is excess H+, carbonic acid reforms
  25. 25. • Breathing releases CO2, which reduces the amount of carbonic acid in the blood• Kidneys also filter acids and bases from the body but act more slowly, although powerfully. A malfunction of the kidneys could cause blood pH to go higher or lower than required levels.
  26. 26. Harmful effects of acid rain• Rainwater pH = 5.6 – Low due to CO2 in the air forming carbonic acid• Acid rain pH < 5 – Contains sulfuric and/or nitric acid – Sulfur dioxide and nitrogen oxides come from burning fossil fuels• Acid rain affects lakes in areas with little to no limestone (a buffer) CaCO3
  27. 27. • Acid rain – Causes mercury to accumulate in fish – Can make bodies of water lifeless – Damages plants – Increases respiratory illness in humans – Breaks down limestone and marble buildings and monuments – Degrades paint on homes and cars