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Chapter 4 Reading Guide- Cells and Their Environment
Section 1 (pages 74-80)
Name__KEY_____________
Date___________ Period ___
1. All organisms and their cells must respond to external conditions to _maintain _ _stability_.
This is called maintaining _homeostasis__.
2. Movement across the membrane that does not require energy from the cell is called _passive_ __transport__.
A difference in the concentration of a substance across a space is called a _concentration _ _gradient____.
Eventually the concentration will be equal in the two spaces and this is called _equilibrium____________.
3. If there is a concentration gradient in the solution, the substance will move
from an area of _high_ concentration to an area of __low__ concentration.
4. The movement from an area of _high_ concentration to an area of
__low___ concentration is called _diffusion___________.
5. If this is allowed to continue, eventually the substance reaches equilibrium.
6. Only substances that can pass through a cell membrane will _diffuse___
down through the cell membrane.
7. The cell membrane is _selectively__ __permeable__________________
to substances. This means that it allows some things to pass through, but not others.
The _interior__ is nonpolar and it repels ions and other polar molecules.
Molecules that are very _small__ or nonpolar can diffuse across the membrane,
_down__ its concentration gradient.
Page 76
8. Water molecules are small and can diffuse through the cell membrane. This is called __osmosis__.
9. What causes _osmosis_? Water molecules can move freely, but the dissolved substances cannot. So water moves
across the membrane to _even_ out the concentration of the substance on both sides of the cell membrane.
Page 77
10. There are _3_ possibilities for water movement. 1. Water moves out. 2. Water moves in. 3. No net water movement.
11. When water diffuses out of the cell, it _shrinks_. The solution that causes the cell
to shrink is called a ___hypertonic____solution_______. This happens when the fluid
outside of the cell has a __higher___ concentration of particles and it means that it has a
lower concentration of water. This means the concentration of water inside is _higher___
and therefore it will flow _out_ _of_ _the_ _cell_. (opposite of substances-see picture in text)
12. When water diffuses into the cell, it _swells___. The solution that causes the cell
to swell is called a __hypotonic_ __solution_____. This happens when the fluid
outside of the cell has a _lower___ concentration of particles and it means that it has a
higher concentration of water. This means the concentration of water inside is __lower____
and therefore it will flow _into_ _the_ _cell_. (opposite of substances see picture in text)
13. If inside and outside of the cell have the _same___ concentration of free water molecules, water
diffuses inside and outside at ___equal__ __rates_. This means there is _no_ net movement
of water in or out of the cell. The cell stays the _same_ size and we say it is in a state of _equilibrium_.
If this happens, we say that this cell is in an _isotonic_ _solution__. (see picture in text)
14. If left unchecked, cells in a _hypo_tonic solution could _burst_. Different cells deal with this problem in
different ways. The cells of plants and fungi have rigid _cell_ _walls_ that keep the cell from getting too big. Some
single-celled organisms have a __contractile_ _vacuoles__, that collects excess water from inside the cell and forces
it out. Animal cells don’t have either of these, but they reduce swelling by removing _dissolved_ _particles_ from the
cytoplasm.
Page 78
15. Most ionic and polar molecules cannot pass across the cell membrane because the interior of the cell membrane is
nonpolar.
16. However, they can go across the membrane with the help of
Transport proteins or channels.
17. Selectivity is one of the most important properties of the cell
membrane because it lets the cell control what enters and leaves the cell.
18. Even though ions cannot diffuse through the nonpolar (uncharged) interior of the
lipid bilayer, they can go through ion channels
19. An ion channel is a transport protein with a polar (charged) pore
through which ions (charged molecules) can pass. Some pores are always
open_. Others have gates that can be closed. None of these require any energy
because the ions always move down their concentration gradient.
Page 80
20. Some cells have different proteins that bind to the substance on one
side, carry it across the membrane and then release it on the other side.
These are called carrier proteins. If these things move
substances down their concentration gradient it is called facilitated
diffusion. This is a type of passive transport.
In your own words, write the three steps of facilitated diffusion from page 80.
1. (answers will vary see page 80)
2.
3.
Molecule to
be carried
Section 2 (pages 81-86)
1. The transport of molecules across the cell membrane against its concentration gradient is
called active trasnport. This requires energy in the form of ATP.
Since it is going against the concentration gradient molecules move from low to high.
Page 83
2. Some substances are too large to moved by transport proteins. Instead, they are moved
across the membrane by vesicles. The movement into a cell by a vesicle is
called endocytosis. In your own words, write the 3 steps of endocytosis (page 83)
1. (answers will vary see page 83)
endocytosis
Energy
Molecule
being carried
2.
3.
LABEL THESE PICTURES FROM PAGE 83
3. The movement of a substance by a vesicle to the outside of the cell
is called exocytosis. During this process, vesicles in the cell fuse
with the cell membrane, releasing their contents.
exocytosis
Chapter 4 Extra Practice Answers
Name__answer key_______
Date_______ Period _____
1. The random motion of particles of a substance that causes the substance to move from an area of high concentration to an area
of lower concentration is called __diffusion____.
2. The diffusion of _water___ through cell membranes is called osmosis.
3. Substances always flow from an area of high concentration to an area of ___low___ concentration.
4. When the concentration of free water molecules is higher outside a cell than inside the cell, water will diffuse __into_ the cell.
5. If a cell is placed in a(n) _hypertonic___________________ solution, water will flow out of the cell.
6. If a cell is placed in a(n) _hypotonic___________________ solution, water will flow into the cell.
7. If a cell is placed in a(n) _isotonic__ solution, water flows into the cell at a rate that is equal to the rate at which water flows
out of the cell.
8. Diffusion of ions through ion channels is a form of __passive__________________ transport.
9. If the interior of a typical cell is negatively charged, __positively_ charged ions will not require energy to diffuse into the cell
using an ion channel.
10. In facilitated diffusion, _carrier__ proteins are used to transport substances down their concentration gradient.
11. In _facilitated diffusion___, carrier proteins do not require energy to transport amino acids into a cell.
12. Carrier proteins _change _____ shape to transport sugars to the interior of cells.
13. A cell does not expend _energy____ when diffusion takes place.
14. Active transport requires the use of __ATP/energy_____ by a cell.
15. The movement of a substance into a cell by a vesicle is called __endocytosis____.
16. Refer to the illustration to the right.
The process shown in figure B is called __exocytosis__________________.
17. Refer to the illustration to the right. Cells often engulf extracellular
particles and fluid, as shown in figure A. This is called _endocytosis____________.
18.
A
What substance passes through the cell membrane by the process of osmosis? water
B
19.
The diagram to the right shows the same type of molecules in area A and area B.
With the passage of time, some molecules move from area A to area B.
This movement is the result of the process of _diffusion________
20.
The movement of molecules through protein channels in a membrane
(when no energy is required) is called _facilitated diffusion___.
21.
A biologist observed a plant cell in a drop of water as shown in diagram A.
The biologist added a 10% salt solution to the slide and observed the cell
as shown in diagram B. The change in appearance of the cell resulted from
more water moving _out__ of the cell than _into__ the cell
22.
The series of diagrams to the right represents a process carried
out by a unicellular organism known as __phacocytosis_____
23.
When a potato is placed in a sucrose solution that has a lower solute concentration outside of the cell, the water will
__enter______ the cell and the solution outside the cell is called a __hypotonic______________ solution.
= food
particle
24.
The diagram to the right shows the process of osmosis. Only the
water molecules could enter the cell because water molecules
a. are more numerous that the protein molecules.
b. have more energy than the protein molecules.
c. are smaller than the protein molecules.
d. contain more hydrogen than the protein molecules.
25.
A microorganism which releases water into its environment to regulate its
salinity (salt content) during osmosis is undergoing a process that is similar
to a human being who releases moisture on a hot day. The process that helps keep both the microorganism and the
human body fluids in balance is known as ___homeostasis____.
26.
The arrows in the diagrams to the right represent the direction of
movement of a certain type of molecule through the cell membrane
of two different cells. The dots represent the relative concentrations
of this molecule. Which processes area illustrated in the diagrams?
a. phagocytosis and diffusion
c. active transport and diffusion
b. pinocytosis and osmosis
d dehydration synthesis and circulation
Answer questions 27-28 using the experiment below.
In an experiment, animal cells were placed in sucrose solutions of varying
concentrations. The rate at which the animal cells absorbed sucrose, a very
large molecule, from the solution was then measured for the different
concentrations. The results are summarized in the graph to below/right.
27.
In this experiment, there was a positive sucrose uptake.
Sucrose probably entered the cells by means of
a. active transport
b. osmosis
c. exocytosis
d. facilitated diffusion
28.
Which statement is best supported by information in the graph?
a. The rate of sucrose uptake increases at a constant rate from 0 to 30 mmol/L.
b. The rate of sucrose uptake decreases at a varying rate from 0 to 30 mmol/L.
c. The rate of sucrose uptake declines between 30 and 40 mmol/L.
d. The rate of sucrose uptake is constant between 30 and 4.0 mmol/L
29.
A student was studying the responses of cells to solutions of
varying salt concentrations. Which solution to the right would
cause no change in cell size?
30.
a.
c.
b.
d.
A student observed a wet mount of some stained plant cells in the high power
field of a compound microscope. Diagram A represents the general appearance
of these cells. The student then added several drops of a liquid to the wet mount
and continued the observations. Diagram B represents the general appearance of
the cells a few minutes after adding the liquid. The liquid that the student added
to the water was most likely (Choose one: hypotonic/hypertonic/isotonic)