Practice Test Solutions for Biol 201

 

Instructions:  DO NOT look at these until you’ve tried the test.  The idea here is to see how we’re thinking verus how you’re thinking!

 

1.  Nitrogen (N) is much more electronegative than hydrogen (H).  Which of the following statements is CORRECT about ammonia (NH3)?

Two concepts are being tested here – first, the concept of electronegativity – the tendency of an atom to gather electrons from a neighbor – and second, the usual charge state of an ammonia molecule.  The answer is E, because N gathers the electrons towards itself, leaving the nucleus of the H atoms slightly “underserved” by the shared electrons, and thus partially positive.

 

            a) The nitrogen atom has a strong positive charge

            b) There are covalent bonds between the hydrogen atoms

            c) The nitrogen atom has a partial positive charge

            d) Each hydrogen atom has a slight negative charge

            e) Each hydrogen atom has a partial positive charge

 

2.  What is the maximum number of covalent bonds an element with atomic number 16 can make with hydrogen? (No, you can’t use a periodic table!)

Again, two concepts being tested here – the pattern of distribution of electrons and the octet rule.  Remember 1s2, 2s2, 2p6, 3s2, 3p4 for this atom.  2 bonding orbitals left (in the p shell), so max bonds with H (which is 1s1 by the way) is 2 – answer B.

            a) 4

            b) 2

            c) 3

            d) 1

            e) 5

 

3.  What bond(s) is (are) easily disrupted in the presence of water?

The key word here is disrupted – covalent bonds are not easily broken! Water is highly polar, though, so it can wedge into ionic bonds and break them easily (think of NaCl). The answer is C.

 

            a) covalent

            b) polar covalent

            c) ionic

            d) Both B and C

            e) A, B and C

 

4.  Which of the following best describes chemical equilibrium?

Here the key word is equilibrium.  Most every chemical reaction does not end with equal concentrations of products and reactants, and most all chemical reactions in life do not stop, but are reversible.  Answer C is the proper description of an equilibrium – constant conversion back and forth, yet no net change in concentration of reactants and products.

            a) equal concentrations of reactants and products

            b) reactions have stopped

            c) reactions continuing with no effect on the concentrations of reactants and products

            d) concentrations of products are high

            e) reactions stop only when all of the reactants have been converted to products

 

5.  The shape of a molecule

This was a ‘gimme’ question.  The answer must be E – think about the handedness of amino acids, primary, secondary, tertiary structure of proteins, specificity of enzymes, etc.

            a) determines its biological function

            b) determines how molecules recognize and respond to each other

            c) is determined by orbital positions of its atoms

            d) may aid in the formation of bonds

            e) all of the above

 

6.  Which bonds must be broken for water to vaporize?

If you break covalent bonds, you change the molecule – thus if b or c were correct, you wouldn’t have water anymore, just hydrogen gas and oxygen gas.  Water doesn’t have any ionic bonds to break, so it must be D.

            a) ionic bonds

            b) nonpolar covalent bonds

            c) polar covalent bonds

            d) hydrogen bonds

            e) both C and D are correct

 

7.  Buffers are substances that help resist shifts in pH by

This question is testing whether you truly understand what a basic or acidic solution is.  You’re already told the buffer resists pH shifts, thus it must counterbalance any trend in H+ or OH- concentrations.  Bases have lots of OH-; acids have lots of H+.  The only answer which counters these is C, because H+ combines with OH- to form water.

            a) combining with OH- in acidic solutions

            b) combining with H+ in basic solutions

            c) releasing H+ in basic solutions

            d) releasing H+  in acidic solutions

            e) releasing OH- in basic solutions

 

8.  A given solution is found to contain 0.0001 mole of hydrogen ions (H+) per liter.  Which of the following best describes this solution?

Here you’re challenged to remember the actual definition of pH, which is the negative log of the concentration of H+ ions AND the concept of what a Lewis base or Lewis acid is...since pH 7 is neutral (0.0000001 mole H+ ions per liter), this solution is an acid.  Acids are H+ donors; thus the answer is C.

            a) acidic:  H+ acceptor

            b) basic: H+ acceptor

            c) acidic: H+ donor

            d) neutral

            e) basic: H+ donor

 

9.  A compound contains hydroxyl groups as its predominant functional group.  Which of the following statements is TRUE concerning this compound?

First you must know what the hydroxyl group is ( -OH); then you must know if it is a polar group, nonpolar group, etc.  OR you could just eliminate the answers which all agree with each other (a,b,c and d) to yield answer E.

            a) It should dissolve in a nonpolar solvent

            b) It is hydrophobic

            c) It is probably a lipid

            d) It won’t form hydrogen bonds with water

            e) It should dissolve in water

 

10.  Glucose and fructose are

This question relies on vocabulary knowledge; otherwise you’re basically cooked.  You should know these are both sugars (they end in –ose), and you should know they’re both 6 carbon sugars with the same chemical formula.  IF you know they’re structurally different (glucose is a six-sided ring; fructose is a five-sided ring) then you can find the correct answer, D.

            a) structural isomers

            b) enantiomers

            c) functional groups

            d) geometric isomers

            e) hydrocarbons

 

11. Which two functional groups are always found in amino acids?

The key word here is ALWAYS.  This means we must look at the backbone, not the R groups.  Thus we have an amino group, an alpha carbon, and a carboxyl group...and the answer B.

            a) carbonyl and carboxyl

            b) carboxyl and amine

            c) amine and sulfhydryl

            d) ketone and amine

            e) alcohol and aldehyde

 

12.  Which type of molecule would be most abundant in a typical cell?

This is a tricky question.  You could argue protein, because it defines life...or perhaps lipids, because the membranes envelop all cells and organelles...but you’re forgetting the basis of all life is that it’s an aqueous environment – answer C.

            a) carbohydrate

            b) protein

            c) water

            d) hydrocarbon

            e) lipid

 

13.  At which level of protein structure are interactions between R groups MOST important?  This is a difficult question, because you have to choose the most important level.  We can eliminate b and e automatically, because the primary structure (aa chain) has no R group interactions.  Secondary structure is from H bonding of the –N-C alpha-CO- backbone to form the alpha helix or beta sheet, so it’s out.  That leaves tertiary and quaternary.  R group interactions are important for both, but especially for tertiary – think about disulfide bridges from cysteine, which are only ‘in play’ for tertiary structure.  Thus the best answer is C.

            a) quaternary

            b) primary

            c) tertiary

            d) secondary

            e) they are all equally important at all levels

 

14.  What is a triacylglycerol?

Definition time again.  Three organic acids and a glycerol make...a lipid!  Answer A.

            a) a lipid made of three fatty acids and glycerol

            b) a carbohydrate with three sugars

            c) a kind of lipid that makes up much of the plasma membrane

            d) a molecule formed from three alcohols

            e) a protein with tertiary structure

 

15.  Which of the following descriptions best fits the class of molecules known as nucleosides?

Careful!   The reflex response is answer B, because that’s what you learned in high school.  But the question asked about nucleosides, NOT nucleotides.  The answer is C; it lacks the phosphate group found in a nucleotide.

            a) a five-carbon sugar and adenine or uracil

            b) a nitrogen base, a phosphate group, and a five-carbon sugar

            c) a nitrogen base and a five-carbon sugar

            d) a nitrogen base and a phosphate group

            e) a five-carbon sugar and a phosphate group

 

Short-answer questions:

 

1.  Consider confocal fluorescence microscopy.  Give TWO significant advantages of this technique over conventional light microscopy and state WHY they’re significant.  Use appropriate terms. (6 pts)

 

Must discuss fluorescence – the concept that the structure of interest in the cell is itself emitting visible light, thus giving a more precise image (2 pts).  Concept of targeted fluorescent molecule bound to structure of interest (2 pts) through linkage to an antibody molecule specific to the structure being studied (1 pt).  Concept of UV light bombarding subject, visible light emitted (1 pt).  Other details of mechanism (dichroic mirrors, etc.) 1 pt.  Max total this part – 3 pts.

 

Must discuss confocal concept – optical slices by focusing in steps up and down (through; z-axis) specimen (2 pts).  Storage of images as digital information (1 pt).  Computer reconstruction of images in 3 dimensions (2 pts).  Ability to see structures from an angle different than the original optical path (2 pts).  Max total this part – 3 pts.

 

 

 

2.  A seed may have a protective covering consisting of cross-linked carbohydrate polymers.  This covering is highly resistant to digestion by grazing animals.  Suggest a specific biochemical mechanism that would support this phenomenon.  Be specific!  (4 pts)

 

Remember here that animals can digest glucose alpha (1,4) links and alpha (1,6) links – and grazing animals can digest cellulose (beta 1,4) links.  Scoring rubric follows:

 

 

If answer consists of discussion of beta-linked glucoses or beta (1,4) linked glucoses, total score is only 1 point.  These are grazing animals, and thus have the ability to digest cellulose (with the help of bacteria in their stomachs) – thus beta (1,4) linkages will be cleaved and the seeds digested.

 

An answer that focuses on chemically modified carbohydrates (additional functional groups) without specifying an example or class of modifications is worth 2 pts.

 

An answer that suggests the covering may be chitin (N-acetylglucosamine) is worth 3 pts, although it’s not true.

 

An answer that suggests a glucosamine base for the carbohydrate covering scores 4 pts.

 

An answer that suggests the inclusion of beta (1,6) branching links scores 4 pts.  (Careful – NOT alpha (1,6) branching)

 

An answer that suggests modifications or ‘decorations’ at the 2,3,or 6 positions of the sugar scores 4 pts.

 

An answer that suggests cross-linkages of the sugars at any point other than (1,4) or (1,6) scores 4 pts.

 

An answer that suggests some chemical change to the sugar to prevent it from engaging the digestive enzymes properly is worth 2 or 3 pts, depending on quality of answer.