Chapter 2 Review, pages 102–107
Knowledge
1. b
2. d
3. b
4. c
5. c
6. d
7. b
8. c
9. b
10. b
11. b
12. a
13. d
14. c
15. c
16. False. Mitochondria have their own DNA.
17. False. Only plants and some algae have plastids.
18. True
19. True
20. False. The purpose of the cuticle is to protect the outer surface of leaves and prevent water
loss.
21. False. A cell with a double membrane filled with membrane-bound organelles is a eukaryotic
cell.
22. True
23. False. Membranes contain sterols that help to maintain their fluidity.
24. False. Integral membrane proteins are embedded into the phospholipid layer.
25. False. The evolution of more internal membranes allowed for more complex processes to
develop within cells.
26. False. Voltage-gated channels are closed during the rest phase.
27. True
28. True
29. True
30. False. No binding by surface receptors takes place in bulk-phase endocytosis.
31. False. Most materials that are ingested by endocytosis change in form once they enter the
cell.
32. (a) viii
(b) iii
(c) vi
(d) iv
(e) i
(f) vii
(g) ii
(h) v
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33. (a) iii
(b) iv
(c) ii
(d) i
34. A cell that is surrounded by a wall or other secretions is not isolated; it can interact through
cell junctions with other cells and with its surroundings. Cells can send and receive ions,
molecules, and signals through some junctions. Other junctions help cells recognize and stick to
each other and the extracellular matrix.
35. First, the nucleus keeps the DNA isolated from the metabolic reactions of the cell, away
from where it might be damaged. Second, the nucleus has a system of transporters and pumps
that regulate the passage of various molecules across the nuclear membrane, allowing certain
molecules to access DNA and control the production of RNA and proteins.
36. Golgi bodies contain enzymes that modify (attach phosphate groups or sugars, or cleave
polypeptide chains) polypeptide chains and lipids that have been delivered from the endoplasmic
reticulum. They create membrane proteins, enzymes and other proteins for secretion, which are
then packaged and exported in vesicles.
37. The stroma is the semi-fluid interior of a plastid, surrounded by two outer membranes. The
stroma contains enzymes and the plastid’s DNA. A third highly folded membrane inside the
stroma forms a single compartment.
38. The endoplasmic reticulum is a membrane-bound organelle that folds into flattened sacs and
tubes. The rough ER has ribosomes attached to its outer surface, while the smooth ER does not.
The rough ER is involved in the production and folding of proteins. The smooth ER does not
participate in protein production and instead produces most of the cell’s membrane lipids. As
well, smooth ER participates in the breakdown of carbohydrates, fatty acids, and some drugs and
poisons.
39. Chloroplasts produce sugars through photosynthesis that allow the tomato to grow and
mature. As the tomato ripens, green chloroplasts are converted into red chromoplasts: the
chloroplasts lose their chlorophyll and orange and red carotenoids become visible, resulting in a
red tomato.
40. (a) The following organelles have a membrane: nucleus, endoplasmic reticulum, Golgi body,
vesicles, mitochondrion, plastids, lysosome, peroxisome, and vacuole.
(b) The endoplasmic reticulum and Golgi body are the most likely organelles to pinch off
vesicles that contain proteins.
41. Actin microfilaments are part of the cytoskeleton and can strengthen or change the shape of
eukaryotic cells. They can also form at the edge of a cell to drag or extend it in certain
directions. Elongation of microfilaments causes lobes called pseudopods to bulge outward from
the cell, allowing it to move. Finally, microfilaments of myosin and actin in muscle cells
contract the muscle.
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Chapter 2: Cell Structure and Function
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42.
43. (a) The organelle is a chloroplast.
(b) Chloroplasts are found in photosynthetic eukaryotes.
(c) The dark areas in the centre are made of membrane.
44. The pack of microtubules in a sperm make up its tail, which is a type of flagellum. It whips
back and forth to help the sperm cell “swim.”
45.
46. Table 1 Comparison of Lignin Deposits
Type of plant tissue
Property
Lignified
Non-lignified
water proof
more
less
strength
stronger
weaker
susceptibility
lower
higher
to infection
47. The extracellular matrix in fungi is made of chitin. Animal bone is mostly made of collagen,
a fibrous protein, and hardened by mineral deposits.
48. The four functions of membrane proteins are as follows: facilitating the transport of
molecules that cannot freely diffuse across the membrane; enzymatic activity like those
associated with cellular respiration and photosynthesis; triggering signals of specific molecules,
like hormones, by binding of the molecule to the protein and triggering a cascade of events
within the cell; and attachment and recognition of cytoskeleton elements, as well as components
involved in cell-cell recognition and bonding to the extracellular matrix.
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49. A: integral proteins
B: peripheral proteins
C: polar end
D: non-polar end
E: phospholipid molecule
F: cytosol
G: cholesterol
50. The relatively slow movement of proteins within a plasma membrane is mainly due to their
large, ungainly size. The lipid molecules are small and so it is easier for them to spin and flex
and trade places with others of their size.
51. Four examples of biological applications of nano-sized robots include: cancer research, cell
and bone repair, gene therapy, and drug delivery.
52. Metabolic processes require some molecules to enter or exit the cell at a faster rate than they
are able to diffuse across the membrane. For example, large polar or charged molecules do not
readily undergo simple diffusion. These molecules may require facilitated diffusion. Examples
include: water, amino acids, sugar, and ions.
53. When particles diffuse in a space, they move randomly in all directions. In a concentration
gradient, the net movement of particles occurs from a region of higher concentration to a region
of lower concentration, causing the particles to become evenly distributed in space. In the case
of diffusing through the plasma membrane, the particles vibrate and randomly move through the
lipid bilayer down the concentration gradient between the cytosol and extracellular fluid created
and maintained by the plasma membrane.
54. (a) Cells receive ions and small molecules such as sugars and amino acids through passive
transport (simple diffusion and facilitated diffusion) or active transport (primary and secondary).
They can ingest larger molecules such as proteins by endocytosis (pinocytosis, phagocytosis, and
receptor-mediated endocytosis).
(b) Particles can be pumped out of the cell by active transport or secreted from the cell by
exocytosis.
55.
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Chapter 2: Cell Structure and Function
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Understanding
56. Answers may vary. Sample Answer: Vesicles may form by pinching off from the
endoplasmic reticulum. When they pinch off, they carry materials inside them for transport to
another location. By fusing with a lysosome, they might receive digestive enzymes to process
some cell waste. By fusing with the cell membrane, they would transport a protein to the outside
of the cell by exocytosis.
57. Both of these membranes are made of lipid bilayers and both are selective gatekeepers,
letting in certain molecules and keeping out others. However, the nuclear membrane is doubled,
with its outer layer being connected to the endoplasmic reticulum. Some students may say that
the key difference is location, while others might say the doubling over of the lipid bilayer
membrane for the nuclear envelope is the key difference.
58. Rough endoplasmic reticulum is where proteins are synthesized, and pancreatic cells
synthesize a great deal of enzymes for export.
59. (a) Amyloplasts are unpigmented plastids that store starch.
(b) They are abundant in cells of tubers because they store starch energy in those locations.
When packed with starch, they are dense and may function as gravity-sensing organelles.
60. The ribosome makes the protein and injects it into the rough ER, where it will complete its
tertiary folding. The ER will pinch off into a vesicle that will move to fuse with the Golgi
apparatus for the finishing touches to be put on the protein. Then it will travel in a vesicle
pinched off from the Golgi apparatus to the plasma membrane where it fuses for the exocytosis
of the protein.
61. Answers may vary. Students should mention the following:
(a) muscle contraction by cytoskeleton, production of energy by mitochondria
(b) packaging of cell products and waste by the Golgi body for export, and the fusion of
secretory vesicles with the plasma membrane (exocytosis)
(c) production of hair keratin proteins by ribosomes
(d) production of proteins by the rough ER, centrioles organize cytoskeleton elements for
cell division
(e) nucleus stores DNA, cytoskeleton is involved in separation of duplicated chromosomes,
cell division, and gamete motility (flagellum of sperm cells)
(f) the production of digestive enzymes by the rough ER, modification in the Golgi body, and
export by secretory vesicles
62. The lipids that make up the plasma membrane’s bilayers are extremely mobile. They spin,
vibrate, and change places millions of times per second. The membrane is also fluid in the sense
that it can flex, bend, form, and reform. It is even able to open up and then close again. It is
called a mosaic because it has many parts imbedded in the lipid—a variety of proteins and
carbohydrates that have various functions and that act as recognition sites.
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63. Peripheral membrane proteins are perched on the surface of the membrane, and do not insert
into the core of the membrane. Integral membrane proteins contain hydrophobic regions that
allow them to be inserted into, and pass through, the core of the bilayer membrane of a cell.
64.
65. Temperature might affect the efficiency of cell membranes. When temperature is low, the
fatty acids pack more tightly together and the membrane becomes less permeable. The presence
of sterols keeps the membrane more fluid and increases its efficiency. The degree to which the
fatty acids in the membranes are unsaturated also increases fluidity and efficiency.
66. (a) No, even when the concentration is equal on both sides of the membrane, molecules still
flow from one side to the other. In the case of equal concentrations, it is just the case that they
flow in both directions at the same rate.
(b) The solute molecules will flow in a net direction across the membrane toward the side where
there are fewer of them. This situation will last until the concentrations are equal on both sides.
Then molecules will still flow across the membrane in both directions, but at an equal rate.
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67. (a) Answers may vary, but students must provide a description on a concept map or another
graphic organizer and show an understanding of the ability of one or more types of molecules,
for example, hydrophobic molecules; small, uncharged polar molecules; large, uncharged polar
molecules; or ions, to pass through a lipid bilayer, noting size, shape, and speed.
(b) (i) Glucose cannot move across a membrane.
(ii) Glycerol is able to move quite rapidly across a membrane.
(iii) Water is able to move quite rapidly across a membrane.
(iv) Oxygen gas can move very rapidly across a membrane.
68. The plasma membrane is non-polar on the inside, so ionic particles, which are charged, are
not attracted to the nonpolar inner layer of the membrane and don’t pass through. Instead they
remain attracted to the highly polar water molecules on either side.
69. (a) Adenosine triphosphate (ATP) is used to obtain energy for active transport.
(b) About 25 % of the total energy use of a cell is devoted to active transport.
70. The cell has evolved transport proteins that span the plasma membrane. In facilitated
diffusion, molecules that would only slowly diffuse through the membrane can be transported by
these proteins at a faster rate based on the concentration gradient. In active transport, molecules
can be transported against the concentration gradient when energy is supplied to the transport
proteins.
71. In symport transport pumps, the solute moves through the membrane channel in the same
direction as the driving ion. In antiport transport pumps, the driving ion moves through the
membrane channel in one direction, and this provides energy for the active transport of another
molecule in the opposite direction.
72. Voltage-gated ion channels open and close depending on voltage, or a difference in electric
potential across the membrane caused by unequal concentrations of positive and negative ions
on each side. During resting potential voltage-gated channels are closed. As the voltage
increases to a threshold, the electronic environment around the voltage–gated channel causes a
conformational change in the channel. This conformational change causes the channel to open
and allows certain ions to diffuse through it.
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73. (a) endocytosis:
receptor mediated endocytosis:
(b) Both types of endocytosis take nutrients into the cell by pinching off a vesicle from the
membrane. Bulk-phase endocytosis engulfs the extracellular fluid, which is rich in nutrients. In
receptor mediated endocytosis specific nutrient molecules are bound to receptors on the outside
of the cell before the vesicle is formed.
74. Answers may vary. Students should use concept maps and/or diagrams in their answers.
Sample answers:
(a) Proteins are synthesized in the rough endoplasmic reticulum, and completed in the Golgi
body. They look similar, except the endoplasmic reticulum may have ribosomes on it and is
joined to the nuclear envelope.
(b) Both control what goes in and out (of the nucleus, or of the cell). The nuclear membrane
does not perform endocytosis and exocytosis, but does have transport “pores.” The nuclear
envelope is a double layer, consisting of two lipid bilayers that are folded together, while the
plasma membrane consists of a single lipid bilayer.
(c) Exocytosis gets rid of waste and exports cell products such as enzymes, while endocytosis
ingests nutrients. Endocytosis can be receptor-mediated, which is more specific. Endocytosis
makes the membrane smaller as it pinches off a vesicle, while exocytosis makes it bigger as a
vesicle joins the membrane.
(d) Lysosomes contain digestive enzymes and help to chop up the building blocks the cell needs,
while vacuoles generally only store particles. Lysosomes are usually smaller than vacuoles.
Vacuoles in plant cells can expand to help cells hold their shape.
75. (a) Active muscle cells will be actively producing energy and will have active mitochondria
providing the cells with ATP. Also, microfilaments of the cytoskeleton will be active in bringing
about muscle cell contraction.
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(b) Cells in a growing seedling will have an active endomembrane system busy producing
proteins and lipids to be used in the new cell. During cell division, microtubules of the
cytoskeleton will be involved in separation of duplicated chromosomes.
(c) Cells in a spider’s spinnerette contain active rough endoplasmic reticulum that produces silk
proteins. Golgi bodies may play a role in directing the proteins to be transported out of the cells
via secretory vesicles.
76. (a) During receptor-mediated endocytosis the molecules to be ingested are captured by
recognition proteins, known as receptors, on the outside of the cell. After enough of the particles
are attached, the cell folds inward into a clathrin-coated pit, pinches off into a vesicle, and joins
with a lysosome to deliver its cargo of nutrients or building blocks to the cell. This molecular
recognition does not occur in regular bulk-phase endocytosis.
(b) Answers may vary. Sample answer: Cells would have the most desire for specific proteins.
This is because some amino acids cannot be manufactured by the cell, so it would need to import
them. Also, proteins are much too large to diffuse through the plasma membrane
Analysis and Application
77. The many mitochondria in muscle cells give them plenty of energy to move. Fungus cells
only need enough energy for stationary life activities. So, muscle cells are expected to have more
mitochondria.
78. (a) The ribosomes do not have a membrane and do not need one for their function of
assembling polypeptide chains (for proteins). However, they do need to be bathed in a soup that
contains the building blocks for their protein. Having no membrane ensures that the ribosome
has unimpeded access to these building blocks. Once the polypeptide chain is assembled,
however, the ribosome injects it into the endoplasmic reticulum where it can complete its tertiary
folding. Then, membrane-bound organelles like the endoplasmic reticulum and pinched-off
vesicles help to transport the protein where it needs to go.
(b) Answers may vary. Sample answer: It is beneficial for ribosomes to interact with organelles
that do have a membrane because it allows the ribosomes to specialize and focus on their most
important function — building protein chains, which they can do more efficiently without a
membrane.
79. Answers may vary. Sample Answer: The cell is a “Cell City” where the nucleus is City Hall,
the mitochondria are power plants, Golgi bodies are packing plants, ribosomes are factories,
endoplasmic reticulum, vacuoles and cytoplasm are internal transportation such as roads within
the city, while the plasma membrane is the city limits and controls what can enter and exit.
Limitations to the analogy include: a city only functions because people in its various parts do
the work, and this does not apply in a cell. In addition some features of the analogy are overly
simplistic, for example, endoplasmic reticula play a broader role in a cell than simple
transportation.
80. The vesicles function in a cyclical manner. There are vesicles that go from the ER to the
Golgi bodies and there are also vesicles that go from the Golgi bodies to the ER.
81. Smooth ER is responsible for detoxification of toxic substances such as drugs and alcohol.
The liver is responsible for most of your body’s detoxification processes. Liver cells respond to
the constant influx of alcohol and other drugs by synthesizing more smooth ER to try and cope
with the increased presence of these toxic substances.
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82. Answers may vary. Sample answer: Traditional medicine applies a wide variety of beneficial
techniques that have been shown to help improve health. Many of these involve obtaining and
adapting products from nature. Nanotechnology utilizes nano-scale machines to target and repair
specific cells and has the potential to become common practice medicine. Currently,
nanotechnology is not advanced enough to be safely implemented in medical practice.
83. When a freshwater fish is accidentally placed in a saltwater tank, the concentrated salt
solution will be hypertonic to the cytosol of the fish gill cells. Therefore, water will flow out of
the cells into the surrounding solution by osmosis, and the cells will shrink.
84. Since pure water contains no solutes, giving it intravenously would make the blood
hypotonic. As a result, the red blood cells would swell and burst releasing their hemoglobin into
the watery plasma.
85. Answers may vary. Student answers should indicate what materials they are using, which
materials represents the barrier and type, and which materials are the solutes.
86. Salt water is a hypertonic solution—having a higher concentration of dissolved particles than
the plant cells. Water would flow out of the plant cells into the environment by osmosis causing
the plant to shrivel and die.
Evaluation
87. Answers may vary. The generally accepted hypothesis is that the prokaryotic cell appeared
first in terms of evolution. One hypothesis, the endosymbiotic hypothesis, suggests that aerobic
eukaryotic cells came from the mutualistic interaction between aerobic prokaryotes and early
anaerobic eukaryotes.
88. Answers may vary. Sample answer: We would not be able to function easily. Many solutes
would be passed back and forth into cells but only when there is enough energy to do so.
89. All three diseases are caused by mutations in specific genes. Genes are recipes for making
proteins, which provide structure to our cells and drive the chemical reactions inside them.
Mutations in genes may result in missing or defective proteins, disrupting their function and
leading to different diseases.
• The inherited mutation in the cystic fibrosis (CF) gene directs the body’s epithelial cells to
produce a defective form of a protein called the cystic fibrosis transmembrane conductance
regulator (CFTR), found in cells that line the lungs, digestive tract, sweat glands, and
genitourinary system. When the CFTR protein is defective, epithelial cells can't move chloride
ions across plasma membranes and out of the cell. This prevents an electrical gradient—which
would normally lead to the movement of sodium ions out of the cell and cause water to follow
by osmosis—from being created. Lack of hydration disrupts the essential balance of salt and
water needed to maintain a normal thin coating of fluid and mucus inside the lungs, pancreas,
and passageways in other organs. The mucus becomes thick, sticky, and hard to move. The
buildup of mucus can block pancreatic ducts, blocking digestive enzymes from entering the
small intestine and leading to poor nutrient uptake. The inability to gain weight, the mucus in the
lungs causing a wheezing breath, and the salty skin suggest that the young girl has CF.
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Chapter 2: Cell Structure and Function
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• Friedreich’s ataxia (FA) is an inheritable disease that results in nervous system damage. Some
characteristics are muscle weakness and impaired speech. FA is caused by defects, or mutations,
in the frataxin gene that reduce expression of the frataxin protein. Scientists believe the frataxin
protein regulates the levels of iron inside mitochondria. It is not yet fully understood how the
frataxin gene mutation causes FA, but reduced frataxin protein levels may result in excess
accumulation of iron in mitochondria leading to oxidative tissue damage. The girl’s symptoms
do not seem related to common symptoms of Friedreich’s ataxia.
• Tay-Sachs is another disease that leads to nervous system damage, resulting in eventual
paralysis and death. Patients with classic Tay-Sachs and Sandhoff diseases lack alysosomal
digestive enzyme (protein) called hexosaminidase. There are two versions of this enzyme, hex A
and hex B. Patients with Tay-Sachs disease do not make hex A, and patients with Sandhoff
disease do not make either hex A or hex B. A small number of babies with Tay-Sachs disease
(AB variant) make both versions of the enzyme but lack another protein that is needed for these
enzymes to work properly. Hexosaminidase is necessary for breaking down certain fatty
substances in cells of the brain. Without this enzyme, these fatty substances build up and
gradually destroy brain cells, until the entire central nervous system stops working. The girl’s
symptoms do not seem related to common symptoms of Tay-Sachs.
Given the mechanisms of the three diseases, I would suggest the diagnosis of cystic fibrosis is
probably the correct one.
Reflect on Your Learning
90. Answers may vary. Yes, I was surprised by the action of cells to cause large-scale actions.
However, I have to remember that the actions of many small cells can have a cumulative effect.
91. Answers may vary. Students’ answers should include evidence of thought about their own
study methods and several diagrams of various membrane components and processes. If students
answer this question properly it should take them at least a half an hour and they should
summarize all of the learning from Section 2.4.
92. Answers may vary. Students are generally very good at this and it helps elucidate gaps in
their knowledge, and it allows students to get help with from their peers.
93. Student answers will vary. In evaluating these answers, let students know that they must be
able to defend each choice they make of modelling material and design. Many students do really
well with this type of activity to integrate their knowledge. Consider giving a week or so to do
the assignment, and having class presentations.
94. Answers may vary. Students might give any answer but should back up their choice with
facts. Sample answer: I would pick the nucleic acids as the MVP, because without them, none of
the other particles would know what to do. I would thank the carbohydrates, because without
them, the cell would not have the energy to survive, and the proteins, because without them, the
cell would have no structure or enzymes to make things happen. The lipid molecules are
absolutely vital to our defense. Without our membranes, we wouldn’t be together at all.
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Chapter 2: Cell Structure and Function 2-12
Research
95. Hemolysis in red blood cells and turgor pressure in plant cells are both affected by osmosis.
Hemolysis refers to the bursting of a red blood cell. It results from excessive dilution of the
blood plasma, resulting in water entering red blood cells by osmosis and causing the destruction
of red blood cells and the release of hemoglobin. Turgor pressure is the pressure exerted by a
plant cell against its cell wall. Changes in turgor pressure are caused by water moving into or out
of the cell by osmosis, resulting in flaccid (when the cell goes limp under isotonic conditions),
turgid (when the cell swells and pushes against its wall under hypotonic conditions), or
plasmolyzed (when the cell shrinks and pulls away from its wall under hypertonic conditions)
states of plant cells.
96. People who live with cystic fibrosis have learned how to eat foods that prevent the buildup of
mucus to some extent, and have learned ways to use physical activity to help them clear out the
mucus instead of letting it build up.
97. (a) Wallace had a mitochondrial myopathy.
(b) Answers may vary. Sample answer: The cause of mitochondrial myopathy is typically found
in the mitochondrial DNA (which is different from the DNA found in the cell’s nucleus).
Mutations in mitochondrial DNA impair the normal functioning of these organelles, disrupting
energy production. When mitochondria malfunction, as in mitochondrial myopathy, the nerve
and muscle cells in particular become worn out since these cells have a high energy requirement.
This may cause symptoms such as fatigue, muscle weakness, and exercise intolerance.
98. Answers may vary. Sample answer: When the plasma membrane does not function properly,
the cells ability to function is limited. Red blood cell membrane disorders include 1) hereditary
spherocytosis, in which the membrane breaks down easily. Symptoms include anemia, jaundice,
and gallstones. 2) hereditary elliptocytosis: symptoms include severe anemia, 3) hereditary
stomatocytosis: symptoms vary but can include anemia, stomatin deficiency, and hemolysis,
and 4) hereditary pyropoikilocytosis: symptoms also include anemia.
99. Recent research suggests that the Golgi body plays a larger role than previously expected in
cell division, differentiation, and development. The Golgi body also plays a role in the
progression of neurodegenerative disorders, such as Alzheimer’s disease, among others.
Changes in the size and function of the Golgi bodies in patients with those diseases have been
noted. Antibodies, which help our bodies fight off invading pathogens, and are an important
component of the immune system, are converted to final form and packaged in the Golgi body.
100. Answers may vary. Students’ answers should mention the following: bone contains marrow
stem cells, osteoblasts, and osteoclasts; the structure of the bone is built up by many collagen
fibres and mineral deposits; blood cells are made in the marrow; blood vessels flow through
bone marrow tissue; Vitamin D and calcium are known essential nutrients for bone formation
and health. Osteoporosis is one common disease in which the bones begin to degenerate.
101. Answers may vary. Sample answer: Both the ER membrane and the plasma membrane are
lipid bilayers and contain proteins such as receptors and ion pumps. Unlike the plasma
membrane, the ER membrane is folded into flattened sacs and tubes. Output by the ER happens
by vesicles pinching off from the main organelle or fusing with it, while at the plasma membrane
the output and intake of bulk molecules occurs by exocytosis and endocytosis, respectively.
102. Nanopipettes are tiny, nanometer-scale hollow tubes or cones. They are expected to be able
to inject fluids into individual cells and even directly into specific organelles, or remove tiny
molecules such as DNA from a cell without needing to remove the cell from the organism or
culture it in a Petri dish.
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Chapter 2: Cell Structure and Function 2-13
103. Answers may vary. Sample answer: Carbon nanotubes, tiny tube-shaped particles, are being
explored as therapeutic agents for drug delivery to cells. For example, the nanotubes could be
loaded with anti-cancer drugs, tagged with molecules that bind specifically to receptors on
cancer cells, and taken into the cancer cells by receptor-mediated endocytosis. Targetting the
nanotubes to bind only cancer cells would ensure that normal cells are not damaged, unlike in
traditional chemotherapy. However, some possible drawbacks of using carbon nanotubes as drug
carriers are the potential toxic effects of the nanotubes themselves.
104. Generally, all antidepressants increase the availability of certain signalling molecules in the
brain, known as neurotransmitters. For example, some antidepressants block the reuptake of one
or more neurotransmitters, increasing the neurotransmitter’s signal in the brain. TCAs lead to
increased levels of the neurotransmitters norepinephrine and serotonin. SSRIs lead to increased
levels of serotonin. TCAs are considered “dirty drugs” because they react with a number of
receptors in the brain, other than the one responsible for the therapeutic effect, causing many
side effects. Side effects of TCAs include blurred vision, urinary retention, constipation, postural
hypotension, dizziness, reflex tachycardia, and sedation. Side effects of SSRIs include nausea,
loss of appetite, diarrhea, anxiety or irritability, problems sleeping or drowsiness, loss of sexual
desire or ability, headaches or dizziness, and weight gain. Since SSRIs are more selective and
have fewer side effects, they are preferable to TCAs. Antidepressants in general have been
associated with suicidal thoughts, particularly in youth and young adults. Some antidepressants
are more likely to cause particular side effects so working with a doctor to get the correct
medication and dosage is critical. Answers may vary on benefits and risks.
105. Answers may vary. Students’ answers should follow along the guides of the questions
given. Generally, studies have found that exercise affects the course of aging and increases life
expectancy. Precisely how exercise alters the aging process remains unknown, but one
possibility may be that it rejuvenates mitochondrial function. Aging is associated with decreased
mitochondrial function, and mitochondrial damage may contribute to accelerated aging. Studies
have shown that endurance training results in healthier, more active mitochondria. Much of the
research is based on aerobic exercise but other forms seem to be effective as well.
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