Biology 1510: Lab Exam I
Name:
_______________________________
Time Limit: 75 minutes
Instructions: During this examination, you may
not consult notes, cell phones, books, or fellow students. Write as legibly as you can. Lab instructor cannot answer any questions
during the test; if the instructions are unclear, just do the best you can. Prior to the test, seating arrangements will
be determined by lab instructor. Answers will be posted within 24 on instructor’s
website. Scores will be graded on a
curve.
Lipids [13 pts]
1. You have been given a liquid containing
fatty acids. You perform TLC (thin layer
chromatography) on it with the results shown on the left.
a. How
many individual fatty acids are present in this sample? [1 pt]
3 fatty acids
b. What
is the Rf value of each of the fatty acids in this sample? [2
pts]
a = 4/10 = 0.4 b= 7/10 = 0.7 c= 9/10 = 0.9
c. All
things being equal, which fatty acid is least soluble in this TLC system? [1
pt]
sample a (OR) the one that traveled
the least (OR) the one with Rf = 0.4
d. Please
identify, with arrows and labels, the origin [1 pt] and the solvent front [1 pt] of this
chromatogram?
X at bottom; thick black line on top
2. My friend Joe gave me 2g of a substance,
which he claims is a lipid. He also
gave me a plain peace of paper, a beaker of water, 2 g of table sugar—and nothing else. Describe in detail 4 simple tests [1
pt each] which
would allow me to decide whether the substance is indeed a lipid. In each of these tests, what would the
control be?
1. Greasy. Check sugar—it’ not
greasy.
2. Translucent when raised against light. Control: sugar isn’t.
3. Water
insoluble. Spread a bit of the fat on
paper, and a bit of sugar some distance away.
Drop of water on both.
4. Lipids float on
water; sugar sinks or dissolves
3. Circle one (a total of 3 circles) in each
underlined group: A reaction
joining a triglyceride to 1 /2 /3
/ 4 / 5 /6 fatty acids / Benedict / monosaccharide / DNA releases / takes up / evaporates / liquefy water
molecules. [1 pt]
3 / fatty acids / releases
4. Fill in the blanks: Saturated lipids contain all the _________
atoms they can possibly have [1 pt]
Hydrogen
5. T/F: Molecule per molecule, carbohydrates
store less energy than lipids True / False [1 pt]
True
Carbohydrates / Nature
of Science [17 pts]
1. The carbohydrates lab involved three tests--Benedict
for reducing sugars, Barfoed for monosaccharides, Iodine for some polysaccharides.
Use the following chart to answer questions a through c.
|
|
Benedict
Test |
Barfoed
Test |
Iodine
Test |
|
Sample
A |
(+) |
(+) |
(-) |
|
Sample
B |
(-) |
(-) |
(-) |
|
Sample
C |
(-) |
(-) |
blue-black |
a. Is
Sample A glucose, maltose, sucrose, glycogen or amylose (from starch)? [1
pt]
reducing, monosaccharide,
non-polysaccharide = glucose
b. Is
Sample B glucose, maltose, sucrose, glycogen or amylose (from starch)? [1 pt]
non-reducing,
non-monosaccharide, non-polysaccharide = sucrose
c. Is
Sample C glucose, maltose, sucrose, glycogen or amylose (from starch)? [1 pt]
non-reducing,
non-monosaccharide, branched polysaccharide = amylose
2. Fill
in 5 blanks: How does the Benedict reaction work? [2
pts] ______ (1/2 pt) in the
Benedict reagent reacts with free _______ or ___________ groups (1/2
pt), turning from blue to _____ (1/2 pt) when ________ (1/2
pt)
copper
/ aldehyde or ketone / red / heated
3. Fill
in 2 blanks: Honey gives a
positive reaction in the ___________ [1 pt] Test because
it is chiefly comprised of ______________
[1 pt]
Barfoed,
Monosaccharides
5. After
we obtained a positive result in the iodine test with glycogen, we boiled the
solution.
a. What happened to
the color? [1 pt]
b. Why? [1
pt]
Color faded somewhat. Iodine assembles with the coils of
poly-s. Boiling the solution breaks the
coils.
6. Fill in 2 blanks: The active positive ingredient of the
Benedict Test which gives the reagent its blue color, and which changes to a
different color in positive reactions is ____________ [1 pt].
When this ingredient
actually changes color, it does so because it gains an ______________. [1
pt]
Copper (or Cu++) / electron
7. Fill in 1 blank: Give one example of a monosaccharide:
___________________ [1
pt]
(glucose, fructose, galactose . . .)
8. Fill in the blanks: Carbohydrates are
composed of carbon, ________ and oxygen in a _____ : _____ : ______ ratio [1
pt]
hydrogen;
1:2:1
9. T/F: The glucose molecule is larger
than the amylose molecule True/ False [1
pt]
F
10. I believe that colony collapse disorder
in bees is caused by the widespread use of genetically modified plants. So I take 1000 bees, feed them exclusively
on pollen and nectar taken from genetically-modified crops, and observe that, in
2 days, 950 bees are dead. I then
submit a paper for publication, claiming that I did, at long last, found the
causes for this disorder. To my horror,
the paper is rejected on the grounds that it doesn't prove my hypothesis, along
with a suggestion that I repeat the experiment—with some modifications.
a. In
this case, what was my hypothesis? [1
pt]
c. What might be the
editor's suggestion? What problem does it solve [2 pts]
Hypothesis: genetically modified
plants cause colony collapse disorder.
The experiment needs controls. At the very least, I should take another
1,000 bees and feed them on the exact same plants, but which have not been
genetically modified.
Amino Acids and
Proteins [9 pts]
|
|
1.
Use the TLC sheet to the left to answer questions a and b below. In this sheet, each linear division is equal
to 1 cm.
a. What is the Rf value for the sample with
origin A? [1 pt]
0.4
b. Knowing that the Rf value of alanine is 0.6, please
circle any of the spot(s) containing alanine, if any (don't guess--any
incorrect circle -1 points) [2
pts]
C
and F contain alanine
2. Circle one number: The ninhydrin test must be complemented by
thin layer chromatography because: 1.
The ninhydrin doesn’t color the amino acids
2. The ninhydrin test produces yellow color in a proline sample 3. The
colors of 2 or more different amino acids in the ninhydrin test may be
indistinguishable 4. thin layer
chromatography requires a solvent [1
pt]
3
3. Fill in the blanks:
All amino acids have an identical___________ group and an
identical _____________ group [1
pt]
Amine / carboxyl
4. Fill in the blanks: The C and N atoms
of two amino acids connect to form a (give scientific name, not C-N)
___________ bond. [1 pt]
peptide
5. Circle twice: When a dipeptide breaks
down into its two constituent molecules, it does so by releasing / taking
up / absorbing / breaking / recharging one molecule of polypeptide / nitrogen / water/
peptide bond / biuret [1
pt]
taking up / water
6. T/F: A protein (e.g., insulin) is made
up of one or more chains of glucose molecules. [1 pt]
F; different amino acids
7. T/F: Unlike glycine and proline, the
amino acid alanine has an R group.[1
pt]
F; every amino acid has an R group
Writing a Lab Report [8 pts]
1. The following lab report information should
be included in which of the following 4 parts: Introduction, Materials and
Methods, Results, Discussion:
a. Glucose,
galactose and fructose exhibited positive Benedict tests.
-->Lab
Report Part is ____________ [1
pt].
Results,
indicates test result for three sugars
b. The
color change in the starch sample indicates that it contains amylose.
-->Lab
Report Part is ____________ [1
pt]
Discussion,
explains the results
2. The
following paragraph has been taken from the Introduction section of a
Student's lab report. This paragraph
breaks three rules of proper scientific writing. Circle each rule-breaking sentence, explain why it does not
belong in the introduction section, and suggest a more proper placement for
it. (Remember: Here you
are looking for scientific writing errors, not for errors of fact,
interpretation, grammar, or spelling!) [2
pts each, 1 for error, 1 for explanation and correct placement, for a total of
6 points]
Carbohydrates can be classified
as monosaccharides, disaccharides, or polysaccharides. In the Benedict test, glucose, galactose and
fructose all turned red while sucrose remained blue. Sucrose is, therefore, a non-reducing sugar while glucose,
galactose and fructose are reducing sugars.
Two other tests were performed according to the procedures in the
Carbohydrates exercise found in Experiments in Biology: from Chemistry to
Sex by Linda R. Van Thiel. These
were the Barfoed test to identify monosaccharides and the Iodine test to
identify polysaccharides.
In the
Benedict test, glucose, galactose and fructose all turned red, while sucrose
remained blue in color - should be in the Results
Sucrose
is, therefore, a non-reducing sugar while glucose, galactose and fructose are
reducing sugars - should be in the Discussion
Two
other tests were performed according to the procedures in the Carbohydrates
exercise found in Experiments in Biology: from Chemistry to Sex by Linda R. Van
Thiel - should be in the Materials and Methods
The Microscope [15 pts]
1. In the paragraph below, a student broke three
rules of handling and/or operating a light microscope. Circle each mistake and
replace it with the proper procedure. (
Note: your answer should be based on the errors written out below--not on
missing information!) [3 pts]
Fatima Aziz wanted to
examine a slide of Paramecium. Using
the microscope, she placed the slide on the stage, turned the highest power
objective, and began to focus. When she
couldn’t see anything, she changed to the 43X high dry objective lens, placed a
drop of oil on the slide, and tried focusing with the fine adjustment. When she was done, she turned off the light,
removed the slide, cleaned the oil off the slide and the lens, and clicked the
highest power objective in place. She
then turned the focus knob so the objective was as close to the stage as it
could get, safely unplugged the scope, loosely wrapped the cord, and returned
the scope to the cabinet.
started
focusing with high power (start at low)
used oil
with high dry lens (use oil only with oil lens)
when
done clicked high power objective in place (should put away with lowest power
in place)
2. Fill in the blanks:
If your field of view, while looking at the dissecting microscope, is 12.56 mm2,
and you are observing an organism that just about extends from the periphery of
your field of view to its center, how long is that organism?___________ [2 pts]
2 (22X3.14=12.56; so the
radium is 2)
3. Your lab manual
describes three principles of the cell theory.
One of these principles claims that “all cells arise from pre-existing
cells.” Describe and explain one
classical experiment (from Raven’s Biology; also mentioned in our lab)
which lends support to this principle. [2
pts]
Here you need to describe Pasteur’s elegant
experiment on spontaneous generation, and explain why it lends support to the
pre-existence principle
4. T/F: Resolution describes the ability
to see two lines as separate lines. true
/ false [1 pts]
answer: true
5. Circle correct answer(s): Chlorophyll is absent from: maple leaves / dog cheek cells / leaves of elodea / leaves of grass / blue-green algae [1 pt]
answer: dog cheek cells
6. T/F:
Among other things, the cell theory claims that all organisms are
composed of cells. True / False
[1 pt]
Answer: True
7. Circle
2 correct answers: Blue-green
algae obtain their energy requirements directly from fungi / sunlight /
DNA / RNA / Leaves of grass / Ocean
waves while animals obtain their energy by eating other animals or by eating
plants / mitochondria / fungi / microscopes / classification schemes [2 pts]
8. Fill
in the blanks: In a microscope, the distance from the objective to
the cover slip is called: ______________ _________________ [1 pt]
working
distance
9. Circle one:
You placed the green letter e in your microscope right-side up, and when you looked at through the
eyepiece, it appeared right-side up / sideways / illegible / red / upside
down / refracted [1 pt]
Upside down
10. Circle
twice: The wider / more focused / more separable / lower the magnification,
the larger / smaller / more circular / narrow is the field of
view [1 pt]
Lower/ larger
Prokaryotes [13 pts]
1. Geeta wanted to gram stain some bacteria she
found growing on her old spaghetti. She
couldn’t find any safranin, but was able to get hold of neutral orange. A call to her Bio 1510 lab instructor
assured her that the two stains served the exact same function in the Gram
staining procedure. So, when she carried
out the gram staining procedure and looked at her slide, she saw two types of
organisms. One was spherical and orange
in color, the other was purple and rod-shaped.
a. What is the shape and color of the gram
positive bacterium? [2 pts]
purple,
rod-shaped
b. What was the gram reaction of the coccus? [1
pt]
gram
negative
c. What color would the G- bacteria have been if
she didn’t add the alcohol? [ pts]Why? [
pts]
purple;
the alcohol decolorizes G- bacteria
2. Circle one: Crystal violet is used in
the Gram staining protocol to make visible the: G+ bacteria / iodine /
G- bacteria / mordant / G neutrality /
safranin / cover slip [1 pt]
Answer: G+
3. Fill in
the 2 blanks: Alcohol in the gram staining protocol is used to
___________________ the gram _________ bacteria [2 pts]
decolorize
/ negative
4. Fill in
the 4 blanks: Eukaryots are comprised of the following 4 major groups:
___________ ___________ _______________ ________________ [2
pts]
animals,
plants, fungi, protists
5. Fill in
the 2 blanks: One useful classification scheme of bacteria involves their
_____________ [1
pt].
Another useful classification scheme involves the ____________
__________ procedure. [1
pt]. Thus,
your class observations showed that E. coli may be classified as a
_________________ _________________ _______________ [1 pt]
Shape / gram-staining /
gram-negative / bacillus