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Chapter 6 - Cells
Biol 1002 - Spring 2013
Chapter 6 - Cells
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Chapter 6 - Cells
Due: 9:00am on Wednesday, February 27, 2013
Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy
Chapter 6 Question 2
Part A
The advantage of light microscopy over electron microscopy is that
ANSWER:
specimen preparation for light microcopy does not produce artifacts.
light microscopy provides higher contrast than electron microscopy.
light microscopy provides for higher resolving power than electron microscopy.
light microscopy provides for higher magnification than electron microscopy.
light microscopy allows one to view dynamic processes in living cells.
Correct
Activity: Prokaryotic Cell Structure and Function
Click here to complete this activity.
Then answer the questions.
Part A
_____ are surface appendages that allow a bacterium to stick to a surface.
ANSWER:
Pili
Ribosomes
Cell walls
Mitochondria
Flagella
Correct
Pili enable bacterial cells to stick to a surface.
Part B
What is the function of a bacterium's capsule?
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Chapter 6 - Cells
ANSWER:
protection
DNA storage
protein synthesis
propulsion
adhesion
Correct
A bacterium's capsule has a protective role.
Part C
The DNA-containing region of this bacterial cell is indicated by the letter _____.
ANSWER:
A
B
C
D
E
Correct
The nucleoid region contains DNA.
Part D
Where is a bacterial cell's DNA found?
ANSWER:
ribosomes
nucleus
peroxisome
nucleoid region
capsule
Correct
Bacteria lack a nucleus; their DNA is found in the nucleoid region.
Part E
In a bacterium, where are proteins synthesized?
ANSWER:
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Chapter 6 - Cells
ribosomes
nucleus
peroxisome
nucleoid region
capsule
Correct
Ribosomes are involved in the manufacture of polypeptides (proteins).
Part F
What name is given to the rigid structure, found outside the plasma membrane, that surrounds and supports the bacterial cell?
ANSWER:
capsule
pili
cell wall
flagella
nucleoid region
Correct
The cell wall is a rigid supporting structure.
Part G
The _____ is the bacterial structure that acts as a selective barrier, allowing nutrients to enter the cell and wastes to leave the cell.
ANSWER:
plasma membrane
nucleoid region
ribosome
pili
cell wall
Correct
The plasma membrane is selectively permeable.
Part H
The structure that regulates the passage of material into and out of this bacterial cell is indicated by the letter _____.
ANSWER:
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Chapter 6 - Cells
A
B
C
D
E
Correct
The plasma membrane is selectively permeable.
Activity: Role of the Nucleus and Ribosomes in Protein Synthesis
Click here to complete this activity.
Then answer the questions.
Part A
Beginning within the nucleus, the first step leading to the synthesis of a polypeptide is _____.
ANSWER:
translation of a DNA nucleotide sequence into a sequence of amino acids
transferring of information from DNA to messenger RNA
linking of nucleotides to form a polypeptide
translation of an RNA nucleotide sequence into a sequence of amino acids
removal of introns from RNA and the stitching together of exons
Correct
Transcription is the first of the two main steps of protein synthesis.
Chapter 6 Pre-Test Question 8
Part A
Which of the following are common traits of chloroplasts and mitochondria?
Hint 1.
Mitochondria and chloroplasts each appear to have evolved from free-living bacterial forms.
ANSWER:
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Both reproduce by meiosis.
Both are surrounded by a single membrane.
Both have their own DNA.
Both are found in plant and animal cells.
Proteins for both are synthesized on ribosomes in the rough ER.
Correct
Mitochondria and chloroplasts contain their own DNA and ribosomes.
Tour of a Plant Cell: Structures and Functions (BioFlix tutorial)
Plant cells have many of the same
structures found in animal cells, but plant
cells also have unique structures that suit
their functions as sugar producers.
Before beginning this tutorial, watch the
Tour of a Plant Cell animation.
Part A - Comparing plant cells and animal cells
Plant cells and animal cells share many of the same structures, but each type of cell also has unique structures. In this activity, you will indicate
which cell structures are found only in plant cells, only in animal cells, or in both plant and animal cells.
Drag each cell structure to the appropriate bin. If a structure is found in both plant cells and animal cells, drag it to the "both" bin.
Hint 1. Review of animal cell structures
To review animal cell structures, watch the Tour of an Animal Cell animation.
Hint 2. Which structures are unique to plant cells?
Plant cells have unique structures that function in photosynthesis. In addition, plant cells have other structures not found in animal cells that
function in support and storage.
Which cell structures are unique to plant cells? Select the three that apply.
ANSWER:
lysosome
central vacuole
cellulose cell wall
chloroplast
mitochondrion
endoplasmic reticulum
ANSWER:
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Correct
Plant cells and animal cells have more in common than they have differences. Nevertheless, plant cells’ unique structures play important roles.
Photosynthesis occurs in plant cells’ chloroplasts. The plant cell’s central vacuole takes up most of the space within the cell and serves a variety
of functions, including storage and hydrolysis of organic compounds. Plant cell walls, which are composed primarily of cellulose, protect the cells
from damage and maintain their shape. Cellulose is the most abundant organic compound on the planet.
Part B - Plant organelle functions
Drag the correct description under each cell structure to identify the role it plays in the plant cell.
Hint 1. Structure and function of cell organelles
The structure of each organelle in a eukaryotic cell makes it very well-suited for the task it performs. Some examples are described here.
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Chapter 6 - Cells
Golgi apparatus: The Golgi is composed of a series of flattened membranous discs called cisternae. Each cisterna forms an
enclosed space that houses a distinct set of enzymes used to process proteins in a sequential manner as they are prepared for
transport to different sites.
Mitochondria: The inner membrane of a mitochondrion has extensive infoldings, which greatly increase the surface area available
for key reactions in the energy-producing processes of cellular respiration.
ANSWER:
Correct
Each organelle in a plant cell carries out a specific function. Mitochondria and the Golgi apparatus serve the same functions in both plant cells
and animal cells.
Part C - Structure and function of the chloroplast
The structure of a chloroplast is closely tied to its function as the site of photosynthesis.
Some of the following statements are true for chloroplasts; others are true for mitochondria.
Which statements are true for chloroplasts? Select the three that apply.
Hint 1. The role of chlorophyll
In order for chloroplasts to carry out photosynthesis, they need pigments that can absorb light energy from the sun. One important chloroplast
pigment is chlorophyll, which absorbs light in the red and blue parts of the spectrum. Chlorophyll is the reason plants appear green.
Hint 2. How does chloroplast structure compare to mitochondrion structure?
Mitochondria and chloroplasts are similar in structure, but they also have key differences related to their respective functions in the cell.
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Chapter 6 - Cells
Drag each label to the appropriate bin. If a structure is found in both chloroplasts and mitochondria, drag it to the "both" bin.
ANSWER:
ANSWER:
They have membranous sacs called thylakoids that are surrounded by a fluid called stroma.
They are the sites of reactions that convert solar energy into chemical energy.
They are the sites of reactions that convert chemical energy to ATP.
They contain the green pigment chlorophyll.
Their matrix contains enzymes that function in cellular respiration.
Their inner membrane has infoldings called cristae.
Correct
The chloroplast and the chemical reactions associated with it are extremely important for all living things. The photosynthetic reactions are
responsible for converting solar energy into chemical energy that is used not only by the cells in which photosynthesis occurs but also by other
organisms. For example, all of the foods you eat can be traced back to a plant or other photosynthetic organism. Furthermore, the chloroplast
and its reactions have had a profound influence on the constitution of Earth’s atmosphere due to the fact that oxygen is a byproduct of
photosynthesis.
Connections Between Cells
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Chapter 6 - Cells
Plants and animals are made up of billions of cells. These cells are surrounded by extracellular components that facilitate their interactions and provide a
suitable environment for the construction and protection of tissues.
Part A - Comparing the extracellular environments of plants and animals
The cellular organization and extracellular environments of plants and animals are very different.
Drag the labels to their appropriate locations in the table below. Use only pink labels for the pink targets. Labels may be used more than
once.
Hint 1. How to approach this problem
At the cellular level, the biggest difference between plant tissues and animal tissues is not what is inside the cells, but rather what is outside
the cells. As you read each statement, consider how the presence or absence of a cell wall might influence intercellular interactions. Which
types of junctions do not exist in the presence of a cell wall?
Hint 2. How are animal cells connected to each other?
Animal cells have three main types of intercellular junctions. The occurrence of these junctions depends on the type of cells you are studying.
For example, epithelial cells are rich in all three types of intercellular junctions.
Drag the labels onto the diagram to identify the different intercellular junctions found in animal tissues.
ANSWER:
Correct
The three main types of intercellular junctions in animal tissues are tight junctions, desmosomes, and gap junctions. Tight junctions and
desmosomes hold neighboring cells together, and gap junctions provide channels through which neighboring cells can communicate.
Hint 3. How do substances move between plant cells?
It is well known that cell walls in plants protect the cells from excessive uptake of water, but these walls also serve as a barrier to viruses. It has
been observed, however, that once a plant cell becomes infected, the viruses can easily move throughout the plant despite the fact that a wall
surrounds each cell.
Which structures enable a virus to infect an entire plant quickly?
ANSWER:
tight junctions
desmosomes
gap junctions
plasmodesmata
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Chapter 6 - Cells
ANSWER:
Correct
A primary distinction between plant cells and animal cells is the fact that plant cells are surrounded by cell walls. If it were not for
plasmodesmata, the cell walls would essentially imprison the plant’s cells, making intercellular communication and the distribution of nutrients
nearly impossible.
Animal cells have a variety of intercellular junctions, including tight junctions, desmosomes, and gap junctions. The gap junctions of animal cells
are most similar to the plasmodesmata of plants. Gap junctions tend to be limited to tissues that require rapid and coordinated signal relay
systems, such as heart muscle; they play no role in nutrient distribution.
Activity: Membrane Structure
Click here to complete this activity.
Then answer the questions.
Part A
What is the function of Structure E?
ANSWER:
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Chapter 6 - Cells
detection of environmental change
stabilization of the phospholipids
cell-cell communication
transport across the plasma membrane
structural support of the cell
Correct
Cholesterol helps to stabilize the structure of the plasma membrane.
Part B
Identify Structure D.
ANSWER:
protein
phospholipid bilayer of membrane
extracellular matrix
cholesterol
glycoprotein
Correct
Phospholipids can be recognized by the presence of a head and two tails.
Part C
Identify Structure A.
ANSWER:
protein
cholesterol
glycoprotein
extracellular matrix
phospholipid
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Chapter 6 - Cells
Correct
Structure A is composed of both a carbohydrate and a protein.
Activity: Selective Permeability of Membranes
Click here to complete this activity.
Then answer the questions.
Part A
Structure A in this animation is a(n) _____.
To view the animation, click here. Then click on structure A in the image to start the animation.
ANSWER:
enzyme
receptor molecule
transport protein
structural protein
antibody
Correct
The protein is allowing solute molecules to enter the cell.
Part B
Which of these cannot rapidly pass directly through the phospholipids of the plasma membrane?
ANSWER:
D only
C only
B, C, and D
B only
A only
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Chapter 6 - Cells
Correct
Ions, such as hydrogen ions, and hydrophilic molecules, such as water and glucose, cannot rapidly pass directly through the phospholipids of a
plasma membrane. To move rapidly through the membrane, they must pass through membrane transport proteins.
Osmosis
Osmosis is the
net movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. The water
will continue to move across the semipermeable membrane as the system attempts to reach equilibrium, where both solutions have the same
concentration.
There are three different ways a solution can be described in relation to a cell placed in the solution: isotonic, hypotonic, and hypertonic. Compared to a
cell, an isotonic solution exerts the same osmotic pressure as the cellular fluids. In other words, it behaves as if it had the same solute concentration as
the cell. A hypertonic solution behaves as if it had a higher solute concentration than the cell. A hypotonic solution behaves as if it had a lower solute
concentration than the cell.
If a cell is placed in an isotonic solution, nothing happens to the cell because water moves into the cell at the same rate that it moves out of
the cell.
If a cell is placed in a hypotonic solution, water will flow into the cell, causing it to swell (and possibly burst).
If a cell is placed in a hypertonic solution, water will flow out of the cell, causing it to shrink.
Part A - Determining water movement in osmosis
A semipermeable membrane is placed between the following solutions.
Which solution will decrease in volume?
Hint 1. Movement of molecules in osmosis
During osmosis, only the water molecules can move across the semipermeable membrane. The larger solute molecules cannot pass through
the membrane. The water flows across the membrane in both directions; however, the net movement of water is into the solution with the higher
solute concentration.
Hint 2. In which direction is the net flow of water in osmosis?
Toward which solution will the net flow of water be?
ANSWER:
toward Solution A: 1.4% (m/v) starch
toward Solution B: 7.62% (m/v) starch
ANSWER:
Solution A: 1.4% (m/v) starch
Solution B: 7.62% (m/v) starch
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Chapter 6 - Cells
Correct
The water molecules actually move in both directions, but they move to a greater extent toward Solution B because it has a higher solute
concentration than Solution A. The net movement of water molecules causes Solution A to decrease in volume and Solution B to increase in
volume.
Part B - Further exploration of the movement of water in osmosis
A semipermeable membrane is placed between the following solutions.
Which solution will increase in volume?
Hint 1. Movement of molecules in osmosis
During osmosis, only the water molecules can move across the semipermeable membrane. The larger solute molecules cannot pass through
the membrane. The water flows across the membrane in both directions; however, the net movement of water is into the solution with the higher
solute concentration.
Hint 2. In which direction is the net flow of water in osmosis?
Toward which solution will the net flow of water be?
ANSWER:
toward solution C: 9% (m/v) NaCl
toward solution D: 12.4% (m/v) NaCl
ANSWER:
Solution C: 9% (m/v) NaCl
Solution D: 12.4% (m/v) NaCl
Correct
The water molecules actually move in both directions, but they move to a greater extent toward Solution D because it has a higher solute
concentration than Solution C. This net movement of water molecules causes Solution D to increase in volume and Solution C to decrease in
volume.
Part C - Three types of solutions
A red blood cell has been placed into three different solutions. One solution is isotonic to the cell, one solution is hypotonic to the cell, and one
solution is hypertonic to the cell. Determine which type of solution is in each beaker based on the cell's reaction.
Drag each item to the appropriate bin.
Hint 1. What are the definitions of hyper-, hypo-, and isotonic?
Define the following types of solution in relation to a red blood cell.
Drag each word to the appropriate blank.
ANSWER:
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Chapter 6 - Cells
ANSWER:
Correct
For a cell in an isotonic solution, water flows into the cell to the same extent that it flows out of the cell. If a cell is in a hypotonic solution, water
flows into the cell, which causes it to swell and potentially burst. For a cell in a hypertonic solution, water flows out of the cell, which causes it to
shrink.
Part D - Animal cells: crenation and hemolysis
An animal cell placed in a hypertonic solution will shrink in a process called crenation. An animal cell placed in a hypotonic solution will swell and
potentially burst in a process called hemolysis.
To prevent crenation or hemolysis, an animal cell must be placed in an isotonic solution such as 0.9% (m/v) NaCl or 5.0% (m/v) glucose. This does not
mean that a cell has a 5.0% (m/v) glucose concentration; it just means that 5.0% (m/v) glucose will exert the same osmotic pressure as the solution
inside the cell, which contains several different solutes.
A red blood cell is placed into each of the following solutions. Indicate whether crenation, hemolysis, or neither will occur.
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Chapter 6 - Cells
Solution A:
Solution B:
Solution C:
Solution D:
Solution E:
3.21% (m/v) NaCl
1.65% (m/v) glucose
distilled H2O
6.97% (m/v) glucose
5.0% (m/v) glucose and 0.9%(m/v) NaCl
Drag each solution to the appropriate bin.
Hint 1. How to approach the problem
You know that a 5.0% (m/v) glucose solution will exert the same osmotic pressure as a red blood cell. You also know that a 0.9% (m/v) NaCl
solution will also exert the same osmotic pressure as a red blood cell.
This means that any solution with a higher total solute concentration than either of these isotonic solutions will be hypertonic to the cell.
Conversely, any solution with a lower total solute concentration than an isotonic solution will be hypotonic to the cell.
Hint 2. How does crenation differ from hemolysis?
If a red blood cell is placed in a hypertonic solution, _____ will occur. If a red blood cell is placed in a hypotonic solution, _____ will occur.
ANSWER:
crenation / hemolysis
hemolysis / crenation
Hint 3. Which solutions are hypertonic, isotonic, or hypotonic?
Classify each solution as hypertonic, isotonic, or hypotonic to a red blood cell.
Solution A:
Solution B:
Solution C:
Solution D:
Solution E:
3.21% (m/v) NaCl
1.65% (m/v) glucose
distilled H2O
6.97% (m/v) glucose
5.0% (m/v) glucose and 0.9%(m/v) NaCl
Drag each solution to the appropriate bin.
ANSWER:
ANSWER:
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Chapter 6 - Cells
Correct
This activity shows why it is very important to use solutions that are isotonic to body fluids in intravenous solutions (IVs). If an IV solution were
hypertonic to the body fluids, cells in the body would shrink. If an IV solution were hypotonic to the body fluids, cells in the body would swell.
Chapter 6 Question 9
Part A
The volume enclosed by the plasma membrane of plant cells is often much larger than the corresponding volume in animal cells. The most reasonable
explanation for this observation is that
ANSWER:
plant cells can have lower surface-to-volume ratios than animal cells because plant cells synthesize their own nutrients.
plant cells have a much more highly convoluted (folded) plasma membrane than animal cells.
plant cells are capable of having a much higher surface-to-volume ratio than animal cells.
animal cells are more spherical, whereas plant cells are elongated.
plant cells contain a large vacuole that reduces the volume of the cytoplasm.
Correct
Chapter 6 Question 11
Part A
Which of the following statements concerning cells of bacteria and archaea is correct?
ANSWER:
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Archaea contain small membrane-enclosed organelles; bacteria do not.
Archaea contain a membrane-bound nucleus; bacteria do not.
DNA is present in the mitochondria of both bacteria and archaea.
DNA is present in both archaea and bacteria.
Correct
Chapter 6 Question 14
Part A
If radioactive deoxythymidine triphosphate (dTTP) is added to a culture of rapidly growing bacterial cells, where in the cell would you expect to find the
greatest concentration of radioactivity?
ANSWER:
nucleoid
endoplasmic reticulum
ribosomes
cytoplasm
nucleus
Correct
Chapter 6 Question 36
Part A
One of the key innovations in the evolution of eukaryotes from a prokaryotic ancestor is the endomembrane system. What eukaryotic organelles or
features might have evolved as a part of, or as an elaboration of, the endomembrane system?
ANSWER:
chloroplasts
nuclear envelope
mitochondria
plasma membrane
none of these
Correct
Tour of an Animal Cell: The Endomembrane System (BioFlix tutorial)
Eukaryotic cells have an integrated network of organelles, including the endoplasmic reticulum (ER), the Golgi apparatus, and lysosomes, which is
collectively referred to as the endomembrane system. The endomembrane system serves a variety of functions within the cell, including protein synthesis
and transport, metabolism of lipids, and detoxification.
Before beginning this tutorial, watch the Endomembrane System animation.
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Chapter 6 - Cells
Part A - Organelles of the endomembrane system
The various parts of the endomembrane system serve different functions in the cell. In this activity, you will identify the roles of each part of the
endomembrane system.
Drag each function to the appropriate bin.
Hint 1. Cisternal maturation
Cisternal maturation is the process by which the cisternae of the Golgi apparatus progress from the cis face to the trans face.
Hint 2. Which organelle of the endomembrane system functions in protein synthesis?
The part of the endomembrane system that is studded with ribosomes for protein synthesis is the _____.
ANSWER:
smooth ER
Golgi apparatus
rough ER
Hint 3. In what ways is the endomembrane system similar to a factory?
The endomembrane system performs so many different functions in the cell that it is often compared to a factory with elaborate assembly lines
and shipping capabilities.
Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used.
ANSWER:
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Chapter 6 - Cells
ANSWER:
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Chapter 6 - Cells
All attempts used; correct answer displayed
The endomembrane system is critical for the synthesis, processing, and movement of proteins and lipids in the cell. The smooth ER functions
mainly in lipid synthesis and processing. The rough ER is the site of secretory protein synthesis. These proteins are processed further in the
Golgi apparatus, from where they are dispatched in vesicles to the plasma membrane. Lysosomes, whose enzymes and membranes are made
and processed by the rough ER and Golgi apparatus, function in the hydrolysis of macromolecules, such as in phagocytosis and autophagy.
Part B - Sites of protein synthesis
All proteins are synthesized by ribosomes in the cell. Some ribosomes float freely in the cytosol, while others are bound to the surface of the
endoplasmic reticulum. Most proteins made by free ribosomes function in the cytosol. Proteins made by bound ribosomes either function within the
endomembrane system or pass through it and are secreted from the cell.
Which of the following proteins are synthesized by bound ribosomes?
Select all that apply.
Hint 1. How to approach this problem
To determine whether a protein is synthesized by free ribosomes or bound ribosomes, be sure to consider where the protein ultimately ends up.
In general, there are two classes of proteins:
those that function in the cytoplasm or in environments that are in direct contact with the cytoplasm (Note that although the
nucleus is enveloped by two membranes, the interior is still considered to be in direct contact with the cytoplasm via the
numerous pores that allow transport between these two environments.)
those that function in locations separated from the cytoplasm by a cellular membrane
The proteins in the first class are synthesized by free ribosomes; they will ultimately function in the cytoplasm or within the nucleus. The
proteins in the second class are synthesized by bound ribosomes; they will ultimately reside in or pass through the endomembrane system.
Hint 2. Where in the cell are nuclear proteins made?
Some proteins must pass into and out of the nucleus to regulate a variety of activities, including the synthesis of DNA, RNA, and ribosomes.
Which of the following pathways would a protein destined for the interior of the nucleus follow?
ANSWER:
The protein is translated at the surface of the rough ER, is packaged into a vesicle, and the vesicle fuses with the nuclear envelope,
depositing the protein inside.
The protein is translated on free ribosomes and then passes through the pore complex to enter the nucleus.
The protein is translated at the surface of the rough ER and then moves from the interior of the ER to the interior of the nucleus.
The protein is translated on free ribosomes and then passes between the lipids of the nuclear envelope to enter the nucleus.
ANSWER:
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Chapter 6 - Cells
lysosomal enzyme
actin
ER protein
insulin
ribosomal protein
DNA polymerase
Correct
Most proteins that function in the cytosol (such as actin) or in the nucleus (such as DNA polymerase) are synthesized by free ribosomes.
Proteins that function within the endomembrane system (such as lysosomal enzymes) or those that are destined for secretion from the cell (such
as insulin) are synthesized by bound ribosomes.
As a protein destined for the endomembrane system is being synthesized by a ribosome, the first amino acids in the growing polypeptide chain
act as a signal sequence. That signal sequence ensures that the ribosome binds to the outer membrane of the ER and that the protein enters the
ER lumen.
Part C - The pathway of secretory proteins
Proteins that are secreted from a eukaryotic cell must first travel through the endomembrane system.
Drag the labels onto the diagram to identify the path a secretory protein follows from synthesis to secretion. Not all labels will be used.
Hint 1. How to approach this problem
Not all of the labels will be used in the flowchart. Review the functions of each organelle listed and eliminate the organelles not involved in the
synthesis, modification, or transport of secretory proteins. Then place the remaining organelles in the correct order.
Hint 2. Where are the organelles of the endomembrane system located?
Knowing the structure and locations of the compartments that make up the endomembrane system can help you understand how substances
move within and between the organelles.
Drag the labels to their appropriate locations on the diagram.
ANSWER:
Hint 3. How does cargo move through the Golgi?
As cargo passes through the Golgi apparatus, it is modified in a step-wise manner prior to being transported to the plasma membrane or to
other locations in the endomembrane system. These distinct modifications are based on the presence of different Golgi enzymes in each
cisterna.
Complete this sentence.
Cargo leaves the endoplasmic reticulum and is sent to the _____ Golgi cisterna, which then matures through the redistribution of enzymes to
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Chapter 6 - Cells
become a _____ Golgi cisterna and eventually the _____ Golgi cisterna.
ANSWER:
cis; trans; medial
cis; medial; trans
medial; cis; trans
trans; medial; cis
ANSWER:
Correct
As they are being synthesized, secretory proteins enter the lumen of the endoplasmic reticulum. From the ER, vesicles transport these proteins
to the Golgi, where they are sequentially modified and concentrated in a cis-to-trans direction. Secretory vesicles bud from the Golgi and move
along cytoskeletal filaments to eventually fuse with the plasma membrane, secreting their protein cargo. Each of these transport steps requires
specialized proteins to ensure that the cargo is sent to the proper location and is able to fuse with the target membrane.
Part D - Pulse-chase experiments and protein location
Scientists can track the movement of proteins through the endomembrane system using an approach known as a pulse-chase experiment. This
experiment involves
the “pulse” phase: Cells are exposed to a high concentration of a radioactively labeled amino acid for a short period to tag proteins that
are being synthesized.
the “chase” phase: Any unincorporated radioactively labeled amino acids are washed away and large amounts of the same, but
unlabeled, amino acid are added.
Only those proteins synthesized during the brief pulse phase are radioactively tagged. These tagged proteins can be tracked through the chase period
to determine their location in the cell.
The data below were obtained from a pulse-chase experiment in which cells were examined at different times during the chase period. The numbers
represent the radioactivity (measured in counts per minute) recorded at each of the indicated sites. The higher the number, the greater the radioactivity.
Based on these data, what is the most likely function of the cells in this experiment?
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Chapter 6 - Cells
Hint 1. Understanding the pulse-chase experiment
The pulse-chase experiment is similar to fitting newly synthesized proteins with identification collars, much as one would do in the field to track
animals. By using a chase, this cohort of newly synthesized proteins can be tracked as they move to different regions of the cell, without any
subsequently synthesized proteins complicating the results. By tracking these proteins over time, the target region where the proteins function
can be identified based on the concentration of radioactivity.
Hint 2. How can the results of this experiment be represented graphically?
The data from this experiment can be represented in line graphs. The change in radioactivity in each part of the cell has been plotted over time.
Drag a label to the target beneath each graph to indicate which part of the cell the graph represents. Labels can be used once or
not at all.
ANSWER:
Hint 3. What is phagocytosis?
Some cells ingest smaller particles through the process of phagocytosis.
Which of the following are true statements about phagocytosis, the vesicles formed during phagocytosis (called phagosomes, or food vacuoles),
and the fate of the ingested particles?
Select all that apply.
ANSWER:
Phagocytosis only occurs in protists.
Phagocytosis occurs when part of the cell’s plasma membrane engulfs a particle, forming a phagosome.
Lysosomes fuse with phagosomes formed during phagocytosis.
Phagosomes by themselves can digest the ingested particles into molecules the cell can use.
The contents of phagosomes are digested with the help of hydrolytic enzymes in lysosomes.
ANSWER:
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Chapter 6 - Cells
detoxification
muscle contraction
phagocytosis
secretion
Correct
The cells in this experiment were macrophages. These immune system cells have many lysosomes for the destruction of bacteria and other
invaders brought into the cell via phagocytosis. The enzymes (hydrolases) that carry out this catabolic activity are synthesized in the endoplasmic
reticulum, modified in the Golgi, and transported to the lysosomes.
Chapter 6 Question 16
Part A
Large numbers of ribosomes are present in cells that specialize in producing which of the following molecules?
ANSWER:
proteins
cellulose
glycogen
lipids
nucleic acids
Correct
Activity: Cilia and Flagella
Click here to complete this activity.
Then answer the questions.
Part A
The cilia and flagella of eukaryotic cells are composed of _____.
ANSWER:
intermediate filaments
tonofilaments
microfilaments
pili
microtubules
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Chapter 6 - Cells
Correct
Eukaryotic cilia and flagella are composed of microtubules.
Chapter 6 Question 43
Part A
Movement of vesicles within the cell depends on what cellular structures?
ANSWER:
actin filaments and motor proteins
actin filaments and ribosomes
actin filaments and microtubules
centrioles and motor proteins
microtubules and motor proteins
Correct
Chapter 6 Pre-Test Question 9
Part A
Which of the following functions is NOT associated with the cytoskeleton in eukaryotic cells?
Hint 1.
The cytoskeleton is a network of fibers that is involved in structural organization and motion.
ANSWER:
maintaining the position of the nucleus in the cell
determining the shape of animal cells
the contraction of muscle cells in animals
the beating of cilia or flagella
Movement of RNA molecules from the nucleus to the cytoplasm
Correct
RNA molecules exit the nucleus via nuclear pores.
Chapter 7 Pre-Test Question 1
Part A
Which of the following statements about a typical plasma membrane is correct?
Hint 1.
Consider the composition, structure, and function of biological membranes.
ANSWER:
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Chapter 6 - Cells
The hydrophilic interior of the membrane is composed primarily of the fatty acid tails of the phospholipids.
The two sides of the plasma membrane have different lipid and protein composition.
The plasma membrane is a covalently linked network of phospholipids and proteins that controls the movement of solutes into and out of a
cell.
Carbohydrates on the membrane surface are important in determining the overall bilayer structure.
Phospholipids are the primary component that determines which solutes can cross the plasma membrane.
Correct
Because the membrane serves different functions on the cytoplasmic and exterior surfaces, the structure and composition of the surfaces must
be different.
Chapter 7 Pre-Test Question 2
Part A
Which of the following best describes the structure of a biological membrane?
Hint 1.
Consider how the molecular components of a biological membrane are organized.
ANSWER:
a fluid structure in which phospholipids and proteins move freely between sides of the membrane
two layers of phospholipids with proteins embedded between the two layers
a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot
two layers of phospholipids (with opposite orientations of the phospholipids in each layer) with each layer covered on the outside with
proteins
two layers of phospholipids with proteins either crossing the layers or on the surface of the layers
Correct
The membrane proteins can be found either embedded in or attached to the surface of the phospholipid bilayer.
Activity: Diffusion and Osmosis
Click here to view this animation.
Then answer the questions.
Part A
Which of the following factors does not affect membrane permeability?
Hint 1.
What factors allow some molecules to pass through a membrane more readily than others?
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Chapter 6 - Cells
ANSWER:
The amount of cholesterol in the membrane
The polarity of membrane phospholipids
Temperature
The saturation of hydrocarbon tails in membrane phospholipids
Correct
Phospholipids contain both a polar head and a nonpolar hydrocarbon tail, both of which are necessary for their ability to form membrane bilayers.
Part B
How can a lipid be distinguished from a sugar?
Hint 1.
What is the definition of a lipid?
ANSWER:
A lipid dissolves in water.
Lipids are mostly nonpolar.
A lipid is made up of only hydrocarbons.
Lipids are mostly saturated.
Correct
Lipids are nonpolar molecules, whereas sugars are polar.
Part C
True or false? Osmosis is a type of diffusion.
Hint 1.
What process occurs during osmosis?
ANSWER:
True
False
Correct
Osmosis is the diffusion of water across a selectively permeable membrane.
Part D
What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?
Hint 1.
Think about how oils can be isolated from water.
ANSWER:
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Chapter 6 - Cells
Permeability
Amphipathic nature
Hydrophobic nature
Solubility in water
Correct
Detergents form micelles around the grease, which are then washed away because the polar head groups facing outward on the micelle are watersoluble.
Part E
Which of the following particles could diffuse easily through a cell membrane?
Hint 1.
Remember that small nonpolar molecules pass most easily through cell membranes.
ANSWER:
Hydrogen ion (H+)
Sodium ion (Na+)
Oxygen (O2)
Glucose
Correct
Small nonpolar molecules such as oxygen can diffuse across cell membranes.
Part F
True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate
group.
Hint 1.
Think about the orientation of the phospholipids that make up a cell membrane.
ANSWER:
True
False
Correct
The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.
Part G
If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?
Hint 1.
Consider the movement of water when the solute concentration inside the cell is different from that of the surrounding environment.
ANSWER:
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Chapter 6 - Cells
Hypertonic
Hypotonic
Isotonic
Osmotic
Correct
The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.
Activity: Membrane Transport Proteins
Click here to view this animation.
Then answer the questions.
Part A
What distinguishes facilitated diffusion from simple diffusion?
Hint 1.
What is facilitated diffusion?
ANSWER:
Membrane proteins help move molecules across the membrane.
No energy is used to move molecules across the membrane.
Molecules move from a region of higher concentration to a region of lower concentration.
Molecules move from a region of lower concentration to a region of higher concentration.
Correct
Membrane proteins facilitate the movement of molecules across the membrane.
Part B
Which of the following transporters does not use passive transport to move molecules across a membrane?
Hint 1.
Which of following transporters uses energy?
ANSWER:
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Chapter 6 - Cells
Valinomycin
GLUT-1 glucose transporter
Gramicidin ion channel
Sodium–potassium pump
Correct
This pump uses the energy provided by ATP hydrolysis to transport sodium and potassium ions across the membrane.
Part C
True or false? Active transport differs from passive transport in that active transport does not require an input of energy.
Hint 1.
What is the definition of active transport?
ANSWER:
True
False
Correct
Active transport requires the input of energy, whereas passive transport is primarily driven by the gradient.Active transport requires energy,
whereas passive transport does not.
Part D
Which membrane protein would be used to move glucose across a membrane from a region of higher concentration to a region of lower concentration?
Hint 1.
Consider what type of molecule is being transported under these conditions.
ANSWER:
Ion channel
Pump
Transporter
No protein is necessary.
Correct
The GLUT-1 transporter assists the diffusion of glucose through the membrane.
Part E
Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel?
Hint 1.
Consider the requirements that must be met for passive diffusion to occur.
ANSWER:
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Chapter 6 - Cells
For every ion that diffuses through the membrane, a different ion diffuses in the opposite direction.
The cell expends energy as the ion passes through the membrane.
There is a higher concentration of ions on the side of the membrane toward which the ion diffuses.
The charge on the other side of the membrane is generally the opposite of the ion's charge.
Correct
Ions tend to move toward regions of unlike charge.
Part F
True or false? During active transport through the sodium-potassium pump, ATP hydrolysis provides the energy to pump three sodium ions into the cell
for every two potassium ions pumped out of the cell.
Hint 1.
The concentration gradients of the ions are a form of potential energy that can be used to perform work.
ANSWER:
True
False
Correct
The sodium-potassium pump maintains a state in which the concentration of sodium is low inside the cell relative to the outside and the
concentration of potassium is high inside the cell relative to the outside; thus, three sodium ions are pumped out of the cell and two potassium
ions are pumped into the cell against the electrochemical gradient.
Part G
Lactose transport by membrane proteins occurs under conditions in which the concentration of lactose inside the cell is higher than the concentration
outside the cell. What type of transport is used to move lactose into the cell?
Hint 1.
Consider how lactose moves in relation to its concentration gradient.
ANSWER:
Simple diffusion
Facilitated diffusion
Osmosis
Active transport
Correct
Under these conditions, lactose moves against its concentration gradient, so its transport will require energy.
Score Summary:
Your score on this assignment is 89.2%.
You received 15.16 out of a possible total of 17 points.
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