these Use questions to determine if you know your stuff.
1) In considering the origin of cells, why do biologists focus on the origin of the plasma
membrane?
2) Think about the cubes that were drawn on the board. Many cells, however, are spherical.
The surface area of a sphere is 4r2 and the volume is (4/3)(r3). What is the surface
area-to-volume ration of a spherical cell with a diameter of 2 m and one with a diameter
of 3 m? What are the implications of this difference between the two cells for cell
function?
3) What evolutionary advantages does a eukaryotic cell have compared with a prokaryotic
cell?
4) Describe the structures that are present in all prokaryotic cells.
5) Flagella are made up of proteins that have other functions, and are present in all
prokaryotes. What is the evolutionary advantage of a bacterium that has flagella over
bacteria that do not?
6) Make a table that summarizes eukaryotic cell organelles with regard to size, numbers per
cell, and functions.
7) What are some functions of the cell nucleus? What are the advantages of confining these
functions within the nucleus, separated from the cytoplasm?
8) Compare the structural and functional differences between rough and smooth
endoplasmic reticulum.
9) In I-cell disease, an enzyme in the endomembrane system that normally adds
phosphorylated sugar groups to proteins is lacking, and the proteins are not targeted to
the lysosomes as they would be in normal cells. The I stands for inclusion bodies that
appear in the cells. What do you think these inclusions are, and why do they accumulate?
10) Make a table that compares the three major components of the cytoskeleton with regard
to composition, structure, and function.
11) The neuron (nerve cell) has a long extension called an axon. Molecules made in the
cells main body must travel a long distance to reach the end of the axon. The axon is
lined with microtubules. Explain how motor proteins, vescicles, and microtubules move
these molecules along the axon.
12) Compare the extracellular matrix of plant cells and animal cells.
13) What kinds of cell junctions would you expect to find, and why, in the following
situations:
a. In the digestive system, where material must pass through cells and not go
through the extracellular material, to get from the intestine to the blood vessels.
b. In a small animal, where a chemical signal passes rapidly through cells to go from
the head to the tail.
c. In the lining of the intestine, where cells in the lining are constantly jostled by the
churning of the underlying muscle.
14) When cancer spreads from its primary location to other parts of the body (a process
called metastasis), tumor cells detach from their original location and then reattach at a
different location. How would the integrin-collagen system involved be in this process?
15) What are the differences between peripheral and integral membrane proteins?
16) Why do phospholipids shaken in a water environment assemble into vescicles surrounded
by a lipid bilayer?
17) What is the evidence for membrane fluidity?
18) If cells that recognize and attach to one another are separated, they reaggregate because
of binding between their membrane glycoproteins. What would happen if the same
experiment were conducted with cells treated to remove cell surface carbohydrates?
19) What properties of a substance determine whether, and how fast, it will diffuse across a
membrane?
20) Compare the process of facilitated diffusion through a channel and by a carrier protein.
Which might be faster, and why?
21) After celery is stored in an open refrigerator for two days, it is wilted. However,
immersing the cut stalk in water for a few hours restores the integrity of the celery.
How?
22) What distinguishes water potential, solute potential, and pressure potential?
23) Here are measurements of water potential () in a 100-m-tall tree and its surroundings:
Region
(MPa)
Soil water
-0.3
Xylem of root
-0.6
Xylem of trunk
-1.2
Inside of leaf
-2.0
Outside air
-58.5
Gravity exerts a force of -0.01 MPa per meter of height above ground.
a) Is the water potential in the leaf sufficiently low to draw water to the top of
the tree?
b) Would transpiration continue if soil water potential decreased to -1.0?
c) What would you expect to happen to the xylem water potential if all of the
stomata closed?
24) Why is energy required for active transport?
25) The drug ouabain inhibits the activity of the NA+-K+ pump. A nerve cell is incubated in
ouabain. Make a table in which you predict what would happen to the concentrations of Na+
and K+ inside the cell, as a result of the action of ouabain.
26) How would you use experiments to distinguish between the following two ways for
glucose to enter a cell: facilitated diffusion via a carrier protein and secondary active
transport?
27) What is the difference between phagocytosis and pinocytosis?
28) Would a small molecule such as an amino acid enter a cell by receptor-mediated
endocytosis?
29) Exocytosis involves the fusion of the membranes of a vesicle and the plasma membrane.
Explain how this might occur.
30) Explain what a countercurrent multiplier in the kidney means and how it enables the
production of hypertonic urine.
31) Many diseases, including high blood pressure and heart failure, result in water
accumulation in the body. Drugs called diuretics are frequently used to increase the loss of
water in these patients. One drug, bumetanide, decreases the activity of the Na+ transporters
in the thick ascending limb of the loop of Henle. How would this drug cause increased water
loss?