Biology 123 Dr. Raut’s Class
Session two 1/14/15
1) What are isotopes? Are all isotopes unstable or radioactive?
Isotopes are different atomic forms of an element which have the same number of protons, but different numbers of neutrons. Example: Carbon 12 (126C), Carbon 13 (136C), and Carbon 14 (146C). Not all isotopes are unstable or radioactive. In a radioactive isotope, the nucleus decays spontaneously giving of particles of energy.
2) What are the three kinds of bonds? Which ones are strongest? Which ones are weakest?
The three types of bonds are covalent bonds, ionic bonds, and intermolecular bonds. Covalent bonds are the strongest. Intermolecular bonds are the weakest, and they actually are not bonds but forces of attraction.
3) What are the two types of covalent bonds? How do they differ?
The two types of covalent bonds are nonpolar and polar. Nonpolar covalent bonds are the result of equal sharing of electrons. Polar covalent bonds are the result of unequal sharing of electrons, due to a difference in electronegativity among the atoms.
4) What are the two types of intermolecular bonds? How do they work?
The two types of intermolecular bonds are hydrogen bonds and Van der Waals interactions. Hydrogen bonds are the result of a hydrogen bond that is already covalently bonded to an electronegative atom being attracted to another electronegative atom due to the partial positive in the hydrogen and the partial negative in the electronegative atom. Van der Waals interactions are very brief attractions of two molecules due to the ever changing location of partial positive and partial negatives in a molecule (even if it is nonpolar). Molecules must be very close together for Van der Waals.
5) What is the difference in an anion and a cation? How do ions stay together?
An anion is a negative ion that has accepted an electron. A cation is a positive ion that has donated an electron. Ions are held together through the attraction of positive and negative ions. They form a three-dimensional lattice type of bonding and usually result in salts.
6) Why is molecular shape so important in biology?
Molecular shape is absolutely vital in biology mostly due to proteins. Proteins are absolutely everywhere in the body and do just about everything. Proteins, especially enzymes, will often have an active spot in which a specific molecule fits due to its size and shape. If the molecule were a different shape, it would be completely unreactive.
7) What about water’s molecular makeup helps make it such a vital molecule? You should be able to draw this out and demonstrate how it works.
Water is a polar molecule with tons of hydrogen bonding. While hydrogen bonds are relatively weak, that strength multiplied by thousands adds up and is the cause for many of the emergent properties
8) List the four emergent properties of water.
Cohesion of water molecules, moderation of temperatures by water, floating of ice on liquid water, and water’s versatility as a solvent
9) Define both cohesion and adhesion. What is the difference? What does this have to do with surface tension?
Cohesion-hydrogen bonds in a body of water holding the substance together
Adhesion- water clinging to another substance (through hydrogen bonds)
Cohesion is water binding to water, while adhesion is water binding to another substance. Cohesion is the reason for surface tension. All of the tiny little hydrogen bonds across water’s surface make it more difficult to break the surface.
10) What is an example of cohesion and adhesion working together in biology?
Water traveling up the xylem in plants. As the water travels against the force of gravity, it is held up by both its attraction to other water molecules (cohesion) and its attraction to the sides of the xylem (adhesion).
11) How does water moderate temperatures?
Water is able to moderate temperatures, because it will absorb heat from warm air and release heat out into cooler air. Neither of these processes will drastically change the temperature of the water.
12) What is specific heat, and what does it have to do with water moderating temperatures?
Specific heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1o C. This is important in water’s ability to moderate temperatures, because water has a relatively high specific heat. This enables water to absorb or release a lot of heat without changing its temperature greatly.
13) How does evaporative cooling work? Is this important to us?
Evaporative cooling is related back to the heat of vaporization which is the quantity of liquid that a liquid must absorb for 1 g of it to be converted to a gas. Water has a high heat of vaporization which means it will absorb heat when it evaporates. This is very important to animals! It means that when you sweat the water will absorb heat as it evaporates, cooling you down.
14) Why does ice float? You should be able to draw this!
Ice floats because of hydrogen bonds. As a liquid cools down the molecules begin moving slower and slower. As water is cooling, it eventually reaches a point that allows optimal hydrogen bonding. At this point (freezing temperatures), the water becomes locked in hydrogen bonds in a crystalline lattice. This causes the molecules to spread out, which leads to ice being less dense than liquid water.
15) Will an entire pond ever freeze? Why or why not? Why is this important?
While small puddles may freeze solid, no relatively large body of water will ever freeze solid. Floating ice acts as an insulator to the water below it. This keeps the water below from freezing and allows for animals below the water’s surface to live through the winter. If entire bodies of water could freeze up during the winter, it would make life in them impossible.
16) Define solution, solvent, and solute.
Solution- a liquid that is a complete homogeneous mixture of two or more substances
Solvent- the dissolving agent in a solution (usually water in biology)
Solute- the substance being dissolved in the solvent
17) What makes water a good solvent? You should be able to draw this!
Water is a good solvent because of its ability to form a hydration shell. Water works to surround itself around whatever hydrophilic molecule is dissolved into it.
18) Define hydrophilic, hydrophobic, and a colloid. Give examples of hydrophilic and hydrophobic molecules.
Hydrophilic- a substance with an affinity for water (polar molecules and ionic molecules)
Hydrophobic- a substance that seems to repel water (nonpolar and nonionic molecules)
Colloid- a stable suspension of fine particles in a liquid
19) What is the basic definition of an acid and a base?
Acid- a substance that increases the hydrogen ion concentration in a solution
Base- a substance that reduces the hydrogen ion concentration in a solution
20) What is the difference between a strong acid and a weak acid?
A strong acid completely dissociates, releasing all of its protons into the solution. A weak acid does not completely dissociate in water and therefore only releases a portion of its protons into the solution. Eventually, a weak acid will reach an equilibrium, and they are very useful as buffers.
21) Draw the Carbonic acid-biocarbonate buffer. Which way does the equilibrium shift if the solution becomes basic? How about acidic?
H2CO3 ↔ HCO3- + H+
If the solution becomes basic, the equilibrium will shift towards the products (or the right), releasing more protons into the solution to lower the pH. If the solution becomes acidic, the equilibrium will shift towards the reactants (or the left), reducing the proton concentration in the solution and therefore raising the pH.
22) Which of the following molecules would be capable of forming hydrogen bonds?
a) CH4
b) CH4O
c) NaCl
d) H2
e) a, b, and d can form hydrogen bonds
23) Some archaea are able to live in lakes with pH values of 11. How does pH 11 compare with the pH 7 typical in your body cells?
a) It is four times more acidic than pH 7.
b) It is four times more basic than pH 7.
c) It is a thousand times more acidic than pH 7.
d) It is a thousand times more basic than pH 7.
e) It is ten thousand times more basic than pH 7.