Download Science Focus 10 Chapter 8 Review KEY

Chapter 8 Dynamic Cells• MHR
CHAPTER AT A GLANCE
Student Book Page 315
Answers
(a) The cell membrane is composed of a phospholipid
bilayer in which proteins (and molecules such as
cholesterol) are embedded. Carbohydrate chains are
attached to the outer surface. The bilayer itself has a
fluid structure.
(b) A semi-permeable membrane allows the passage of
some types of materials, but not others, often
because the materials are too large, or because they
are too strongly hydrophilic or charged.
(c) If the cell membrane was permeable to all materials,
harmful substances could enter the cell and the cell
would lose required materials, such as food
molecules. If the cell membrane was impermeable
to all materials, the cell would be a closed system
and therefore would not be functional.
(d) Some membrane proteins function in facilitated diffusion. These proteins, called transport proteins,
include channel proteins, which allow the passage of
ions down a concentration gradient and across the
membrane; and carrier proteins, which change conformation upon binding a molecule, thereby allowing the molecule to pass through the membrane,
again, moving with a concentration gradient. Active
transport can move materials against a concentration
gradient by use of carrier proteins; active transport
requires cellular energy. Receptors on the cell surface are involved in receptor-mediated endocytosis.
(e) Particles that are in equilibrium are distributed randomly in a space. While the particles are in constant
motion, there is no net flow of particles from one
area to another (such as from the external environment to the cytoplasm).
(f) Carrier proteins fuelled by cellular energy (active
transport) can pump materials against a concentration gradient.
(g) The net movement of water molecules will always
be from a region of lower solute concentration to a
region of higher solute concentration.
(h) Endocytosis includes phagocytosis (cell eating) and
pinocytosis (cell drinking). With phagocytosis the
cell membrane surrounds and engulfs particulate
matter. The cell membrane then closes in on itself,
and the particle is enclosed in a vesicle, which
pinches off inside cell. Some single-celled organisms, such as amoeba, feed using phagocytosis.
White blood cells defend the body by phagocytising
bacteria. With pinocytosis, fluid droplets are
engulfed by the cell membrane. A pocket pinches
off as a vesicle in the cytoplasm. The vesicle shrinks
as the fluid particles diffuse into the cytoplasm.
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With endocytosis, vesicles containing materials fuse
with the cell membrane. The vesicle’s contents are
then released outside the cell. Exocytosis is used to
rid the cell of wastes or secrete cell products.
(i) Some shapes (flat and/or long, for instance) have a
high surface-area-to-volume ratio compared to others (completely spherical, for instance).
(j) Diffusion rates within a hypothetical really large cell
would be quite slow. It would therefore be too inefficient for cells to grow extremely large (such cells
would have low surface-area-to volume ratios).
Multicellular organisms can only grow large because
they are composed of many cells.
Prepare Your Own Summary
• Answers will vary. A sample map is provided here.
multicellularity
limits cell size
surface area-to-volume ratio
determine surface area
membrane
structure
membranes
transport
in/out of cell
semi-permeable
phospholipid
bilayer
endocytosis/
exocytosis
fluid nature
proteins
receptors
osmosis
channel proteins
carrier
proteins
diffusion
transport
down
concentration
gradient
transport
against
concentration
gradient
does not use
cellular
energy
requires
cellular
energy
passive
transport
active
transport
facilitated
diffusion
• Answers will vary, but should address the semi-permeable nature of cell membranes and the ability of
active transport to move materials across the membrane against concentration gradients.
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MHR • Unit 3 Cycling of Matter in Living Systems
Type of transport
How transport-type works
Factors influencing
direction of transport
osmosis
water molecules pass
through cell membrane
concentration of
solutes in or around
the cell
diffusion
diffusion of molecules
through the cell membrane
direction of
transport is down a
concentration
gradient
facilitated
diffusion
transport proteins enable
ions or molecules to pass
through the cell membrane
by way of channel proteins
or carrier proteins, without
using cellular energy
direction of
transport is down a
concentration
gradient
active
transport
transport of molecules or
ions through the cell
membrane by use of carrier
proteins; process requires
cellular energy
direction of
transport may be
against
concentration
gradient (or with it)
endocytosis/
exocytosis
pinocytosis and phagocytosis independent of
include ways in which cells
concentration
gradients
engulf and take in large
particles such as fluid
droplets (pinocytosis) or dead
cells or bacteria
(phagocytosis); exocytosis
allows transport of proteins
and other macro-molecules
and wastes out of the cell
• Answers will vary. Consider having students present
some of their poems or songs to the class.
CHAPTER 8 REVIEW ANSWERS
Student Book Pages 316–317
Key Terms
See glossary in student book.
Understanding Key Concepts
1. The cell membrane consists of two layers of phospholipid molecules.
2. a, c, and d are open systems because they allow the
inward and outward flow of matter.
3. (a) This figure illustrates facilitated diffusion using
a carrier protein.
(b)
carrier
protein
cholesterol
membrane
phospholipid
4. (a) A bacterial cell would be transported by endocytosis. It could be stored in a vacuole or transported in a vesicle.
(b) Carbon dioxide is transported by diffusion.
(c) Water is transported by osmosis.
(d) Sodium ions are transported by active transport
or facilitated diffusion.
5. The particle model of matter states that all matter
is made up of particles that are in constant, random
motion. This model describes the water and dissolved molecules that fill and surround cells. It is
the molecules’ random movement that causes those
with sufficient kinetic energy to spread out from a
concentrated area and distribute themselves evenly.
Diffusion is the term used to describe the
molecules’ net movement down the gradient.
6. Channel proteins - transport ions down a concentration gradient; carrier proteins enable active
transport or facilitated diffusion; receptors (proteins
with marker molecules) - cell-cell recognition, communication, protection from infection, receptormediated endocytosis.
7. Phospholipid molecules have a head end that readily dissolves in water and an oily tail end that does
not dissolve in water. In water, each phospholipid
molecule automatically orients itself so that its head
end points toward the water molecules and the tail
end points toward other phospholipid tails. A bilayer arrangement, with the tails sandwiched in the
middle of the layer and the head ends pointing outward, is the most stable arrangement of the phospholipids.
8. A dialysis membrane contains very small pores that
are large enough to allow the diffusion of dissolved
ions and other small molecules, but too small to
allow the movement of red or white blood cells. As
the patient’s blood passes through tubing made
from a dialysis membrane, small dissolved wastes
can diffuse out and needed materials diffuse in,
while blood cells are retained.
9. Surface area-to-volume ratio limits cell size. As cell
size increases, this ratio gets lower, and as a result,
nutrients and other important materials cannot diffuse fast enough to areas in the cell where they are
required. As well, as cell size increases it is difficult
for wastes to be expelled fast enough.
10. Both receptor-mediated endocytosis and active
transport move substances into the cell that cannot
be transported across the membrane by passive diffusion. Both processes use membrane proteins to
recognize specific substances for transport, and both
consume cellular energy in the process. However,
active transport is used to move very small dissolved
atoms or molecules via carrier proteins embedded in
the cell membrane. In contrast, receptor-mediated
endocytosis is used to transport bulky items, such as
small cells or droplets of fluid. Rather than moving
Chapter 8 Dynamic Cells• MHR
these items through a pore, they are taken in
through the formation of a vesicle or vacuole.
Developing Skills
11. (a)
Hypertonic
Hypotonic
Isotonic
potato is soft
potato is firm
potato is firm
(b) The potato cube in the relatively hypertonic
solution will become soft, while the other potato
cubes will be firm.
12. Models should include phospholipids, different
types of proteins, and carbohydrate chains.
13. (a) Manipulated variables – type of alcohol and concentration
Responding variable – leakage of pigment from
beet root cells as measured by absorbance
Amount of Beet Pigment Extracted by
Alcohols as Measured by Absorbance
Absorbancy (nm)
700
600
500
Methanol
Ethanol
Propanol
400
300
200
100
0
02
04
06
08
Concentration (%)
0
100
(b) Methanol was most damaging to beet cell membranes.
(c) Methanol seems to damage the membranes the
most, as determined by the amount of pigment
leaking from the beet root cells. In all but one
trial, methanol was equal to or more damaging
than ethanol. Methanol was equal to or more
damaging than propanol in all trials.
Problem Solving/Applying
14. Some possible household items that contain or have
features of a semi-permeable membrane include:
– cheesecloth, which allows fluid to pass through
the fabric mesh, while retaining large cheese
curds during cheese making
– kitchen strainers or colanders, which allow fluid
to pass through wire mesh or holes in a metal
bowl during draining of foods cooked or rinsed in
water
– vacuum cleaners that have air vents lined with
foam padding that allow air to pass through while
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retaining dust particles
– dust masks, which prevent inhalation of dust particles and other airborne substances and that are
made of paper, which is permeable to air but not
to small particles
15. Use one solution to fill the dialysis tubing, then tie
the ends and immerse it in the other solution. Take
and record the mass of the “cell” over time and
record the cell’s change in mass. Changes in the
amount of fluid filling the cell will indicate in which
direction osmosis has occurred. If the cell increases
in mass, this indicates that water has flowed into the
cell by osmosis. Therefore, the solution inside the
cell must have the stronger solute concentration.
Conversely, if the cell decreases in volume, this
indicates that water has flowed out of the cell by
osmosis. Therefore, the solution outside the cell
must have the stronger solute concentration.
16. Answers will vary. Students should be able to clearly
distinguish between their hypotheses and predictions. One experiment could be to place unshelled
eggs in solutions of different solute concentrations.
17. The organisms living in the dried up ponds will
likely lose water to the environment if they do not
have adaptations to counteract this pressure. The
organisms could dehydrate and die.
Critical Thinking
18. The cell membrane acts as a physical barrier that
excludes many materials from entering or exiting
the cell. Substances that are large or electrically
charged cannot easily diffuse through the membrane. Despite this barrier, the cell is still an open
system. Very small dissolved molecules can diffuse
passively through the membrane. Some other items
are recognized by membrane proteins and are
transported into or out of the cell by facilitated diffusion, active transport, or endocytosis/exocytosis.
19. Such a cell would have no protection from substances in the environment. Also, this cell would
not be able to “hold on” to important nutrients and
other molecules. The cell would not be able to
form proper compartments in which biological
reactions could take place.
20. The flat cell shape provides a thin surface through
which oxygen must diffuse to reach the blood. The
thinner the shape, the more easily the oxygen diffuses. Therefore, this cell shape improves the ability
of our lungs to provide oxygen to the bloodstream.
21. Experiments in which human and mouse cells were
fused illustrated the fluidity of cell membranes.
This experiment, as described in the Think&Link
Investigation 8–A: Fusing Fluid Cell Membranes,
demonstrated that membrane proteins move laterally through the membrane. Micrographs of cells
phagocytosing particles also suggest that the cell
membrane has a fluid structure, since the membrane stretches and folds in this process.