Ingredients for Life ■ 57(^10) Lipoproteins are relatively large, combined clumps of both
protein and lipid molecules that circulate in the blood of mammals.
They come in two forms, called HDL and LDL, and they act like
suitcases to move cholesterol, fatty acid remnants, triglycerides,
and phospholipids from one place to another through the
bloodstream. (LDL recirculates lipids throughout the body, while
HDL takes lipids to the liver to excrete them in feces.) Given that
lipids are hydrophobic and proteins can be hydrophilic, which of the
following statements is correct?
(a) The lipid portion of LDL does not dissolve in the bloodstream,
while the lipid portion of HDL does.
(b) The protein portions of both LDL and HDL can dissolve or
interact with the water molecules in the bloodstream.
(c) Neither the protein nor the lipid portions of LDL molecules can
interact with water molecules in the bloodstream.
(d) Both the protein and the lipid portions of HDL molecules can
interact with water molecules in the bloodstream.
(e) none of the above
(^11) You have found an unknown cleaning solution in your
roommate’s under-sink cabinet. You have several spring cleaning
projects to take care of and would like to use this product if it has
the correct pH for the job. You know you need an extremely basic
solution to clean your oven, but an acidic solution like vinegar to
clean your coffee maker. You borrow a few pH indicator strips from
your biology lab TA and test the solution. For each of the following
scenarios, select the best answer.
a. The solution tested at a pH of 11; you will be able to clean your
(oven / coffee maker / both / neither).
b. The solution tested at a pH of 2; you will be able to clean your
(oven / coffee maker / both / neither).
c. The solution tested at pH 7; you will be able to clean your
(oven / coffee maker / both / neither).
d. The solution tested at pH 9; you will be able to clean your
(oven / coffee maker / both / neither).
e. The solution tested at pH 4; you will be able to clean your
(oven / coffee maker / both / neither).
(^12) Laundry detergent molecules have a short polar end and a long
nonpolar end, enabling them to bind to water (on the polar end) and
oils (on the nonpolar end). Suppose you spill some salad dressing
on your shirt. Explain how washing your shirt with detergent will
help remove the dressing.
Leveling Up
(^13) What do you think? Read the articles “Two Miles Under-
ground, Strange Bacteria Are Found Thriving” in News at Princeton
(http://www.princeton.edu/main/news/archive/S16/13/72E53/
index.xml?section=newsreleases) and “Martian Underground
Could Hold Clues to Life’s Origins” (http://www.studentnews
.eu/s/3229/68257-Articles/4014087-Martian-underground
-could-hold-clues-to-lifes-origins.htm). Then answer the following
questions.
a. How are bacteria able to stay alive below Earth’s surface or
(potentially) below the surface of Mars?
b. How does the discovery of bacteria living 2 miles beneath
Earth’s surface relate to the importance of the McLaughlin
Crater on Mars?
c. What research do you think should next occur to answer the
questions brought up by these studies?
d. From what you’ve read, what do you think is the probability of life
on other planets? What would you expect that life to look like?
(^14) Is it science? Life on Earth evolved as carbon-based. Silicon
shares many of the chemical properties of carbon, yet it is not
a building block of life on Earth. Watch the episode of the TV
series The X-Files titled “Firewalker” (http://www.hulu.com/
watch/158588), or read through its story line (https://en.wikipedia
.org/wiki/Firewalker_%28The_X-Files%29). While doing so, make
a list of the scientific concepts presented, and note whether you
think they represent real science or pseudoscience. Then use
your textbook and Internet research to determine whether you
were correct or incorrect in each case. If you evaluated any of
the concepts incorrectly, reflect on how you came to your initial
conclusions.
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