Download 5 Chapter Review

CHAPTER
5
Chapter Review
SUGGESTED ANSWERS
WHAT DO YOU REMEMBER?
1.
“Selectively permeable” means only certain things can pass through. In a cell membrane, proteins act as
gatekeepers, allowing some particles to pass through, but not others. The layers of fat particles making up
the membrane allow some small particles to diffuse through directly, but prevent larger particles from
doing so.
2.
Particles diffuse from an area where they are more concentrated to an area where they are less
concentrated.
3.
Without a concentration gradient, diffusion would not occur. The concentration gradient allows particles
to move from an area where they are more concentrated to an area where they are less concentrated.
4.
Oxygen and carbon dioxide are exchanged across the cell membranes of red blood cells and muscle cells.
5.
Particles of water, oxygen, and carbon dioxide are all small enough to diffuse freely across the cell
membrane.
6.
Osmosis is a type of diffusion in which water moves across a membrane. The more solute particles you
have on one side of the membrane, the greater the concentration gradient. Water particles will move from
the side of the membrane where they are more concentrated (and the solute particles are less concentrated)
to the side where they are less concentrated (and the solute particles are more concentrated).
7.
A turgid plant cell is one that is swollen with water.
8.
A cell might use exocytosis to remove wastes from the cell or to send chemicals out of the cell that are
needed elsewhere in the body.
9.
When a living thing takes in nutrients from its environment, we say it is eating. Phagocytosis, which
means “cell eating,” is a good name for the type of exocytosis in which the cell takes in large particles
from its environment because many cells use the process to take in nutrients.
10.
Sample answer: An air freshener is a good model of diffusion because the scent particles are initially
concentrated around the freshener and gradually move by diffusion through the rest of the room where
the scent particles are less concentrated. An open perfume bottle or a drop of food coloring in a glass of
water would be other good models for diffusion.
11.
In the picture some dye has been placed in a beaker of water. The dye moves from areas of high dye
concentration to lower dye concentration. Over time, the dye will spread evenly throughout the beaker.
12.
Water moves by osmosis into a cell because the concentration of water is greater outside the cell than
inside the cell. As water enters the cell, the central vacuole fills and the cell swells. As the cell swells, the
cell membrane pushes outward (against the cell wall in plants), resulting in turgor pressure.
13.
Osmosis is a form of diffusion that takes place across a membrane. In both processes, particles move
down a concentration gradient from an area where they are more concentrated to an area where they are
less concentrated.
14.
An animal cell has a greater concentration of solutes (and a lower concentration of water particles) than
distilled water. If you placed an animal cell into a beaker of distilled water, water particles would move by
osmosis from where they are more concentrated in the beaker to where they are less concentrated in the
cell. The cell would swell up and might die.
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Unit B: Cells
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15.
Water that moves into a plant cell causes the cell to swell, pushing the cell membrane up against the cell
wall. The rigid cell wall keeps the cell from bursting.
WHAT DO YOU UNDERSTAND?
16.
Applying too much fertilizer to the grass will create a concentration gradient between the solution in the
soil and the solution inside the plant cells. The concentration of solute outside the plant cells will be
greater than that inside and water will leave the plant cells by osmosis. The plant cells will shrink and
cause the plants to wilt or even die.
17.
Patients receive a salt solution by intravenous injection to match the concentration of the fluids inside
cells. If doctors injected plain water, there would be a higher concentration of solutes inside the blood
cells, water would enter by osmosis, and the blood cells would burst.
18.
The cells of plants from the ocean have a concentration of solutes inside that is equal to the concentration
of solutes in sea water. If these plants are placed in fresh water, water will enter the plant cells by osmosis
and will likely damage the plant cells. This may be the reason why the saltwater plants do not thrive in
freshwater environments.
19.
The celery wilted because some of the water inside the cells left the cells by osmosis and evaporated. Mary
placed the wilted celery into a glass of water so that water would enter the cells of the celery by osmosis.
SOLVE A PROBLEM!
20.
Sample answer:
Dear Principal Johnson,
Many schools have a “no scents policy.” When I first heard of this idea I thought it was silly. I thought
that if a person is allergic to perfume, then it would only be a problem if she wore the perfume. But I
know now that particles will move from an area where they are more concentrated to an area where they
are less concentrated, which is called diffusion. So if one person wears a scent, the scent particles can still
move from that person throughout the room where they can affect a person with allergies. I think our
school should implement this policy in order to be sensitive to the needs of those who are sensitive to
perfumes and colognes.
Sincerely,
Student
21.
Sample answer:
To Whom It May Concern:
I know that the town puts salt on the road in winter to help melt the ice. But I wanted the town leader to
know how bad this can be for plant life along the roads. Salt can end up in the soil, which can kill the
plants. The salt disrupts the process of osmosis that helps bring water into a plant’s roots. If salts are more
concentrated in the water in the soil than in the plant’s cells, water will move out of the cell where the
water is more concentrated into the soil where the water is less concentrated (and salts are more
concentrated). I hope the town can find a way to put less salt on the road or to prevent the salt from
reaching the plants nearby.
Sincerely,
Student
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Chapter 5 Cells in Their Environment
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22.
The flowers have wilted because there is not enough water entering the cells to swell the cells and push
the cell membranes against the cell walls. You could try to revive the plant by watering it. Water would
enter the cells by osmosis, filling the central vacuole and causing the cell to swell. Thus turgor pressure
would be restored.
CREATE AND EVALUATE!
23.
Student stories and comic strips will vary widely, but should demonstrate an understanding that diffusion
works only if a concentration gradient exists, and that particles diffuse from an area where they are more
concentrated to an area where they are less concentrated.
24.
Sample answer: My strategy would be to ask questions about diffusion and answer them with drawings.
For example, I could ask what causes the particles to move, or do the particles ever stop moving? My
drawing could show the fewer particles calling the greater particles to join them. Some limitations are that
I would have to be able to answer the questions to draw the answers, and also that the drawing would
only approximate reality.
25.
To “rejuicify” the fruit you would have to place the fruit in a solution that had a higher water
concentration than the inside of the fruit. Pure water has the highest water concentration, so this would
be the best. The main advantage is that the company can ship more fruit and reduce their transportation
cost. I’m not sure if this would work, however, because I think the fruit is badly damaged by the drying
process. I think you might just end up with a soggy piece of dried apricot.
REFLECT ON YOUR LEARNING
26.
Sample answer: I never understood before why it was dangerous for people to drink salt water. But now I
understand that water would move out of a person’s cells because the concentration of water inside the
cells would be lower than the concentration of water outside the cells. Drinking ocean water could be
deadly!
27. (a)
(b)
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Sample answer: Substances enter and leave the cell through the cell membrane though a variety of
processes. Smaller particles simply diffuse into or out of the membrane, going from areas of high
concentration to areas of low concentration. Cells can also use endocytosis to move larger particles
into the cell. Phagocytosis is a form of endocytosis where the fingerlike projections of the cell
membrane are used to engulf a particle.
How do the protein channels shown in Figure 1 of Section 5.1 keep some particles out and let other
particles into the cell?
Unit B: Cells
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