Mastering Concepts
3.1
1. What is a cell?
A cell is the smallest unit of life.
2. How have microscopes contributed to the study of cells?
Microscopes have led to the discovery of cells, have allowed us to differentiate structures
in prokaryotic and eukaryotic cells, have allowed us to study the organelles that make up
a eukaryotic cell, and have even let us watch some basic cell functions as they occur.
3. What are the main components of cell theory?
The main components of cell theory are that all life is made of cells, that cells are the
fundamental unit of life, and that all cells come from preexisting cells
4. Describe the differences between light and electron microscopes.
The light microscope can be used to study living organisms, does not distort structures,
can show structures in stained color, and is less expensive than the electron microscope.
However, the light microscope lacks much of the magnification and resolution of the
electron microscope.
5. Which molecules and structures occur in all cells?
All cells have DNA, proteins, RNA, ribosomes, a watery cytoplasm, and a cell
membrane.
6. Describe adaptations that increase the ratio of surface area to volume in cells.
Adaptations that increase the surface area to volume ratio include elongated or flattened
cell shapes. An efficient transportation system, a water-filled vacuole, and improved
efficiency help cells sidestep surface area limitations.
3.2
1. How do prokaryotic cells differ from eukaryotic cells?
Prokaryotic cells lack a nucleus and other membrane-bounded organelles, have cell walls
made of peptidoglycan, and are typically much smaller than eukaryotic cells.
2. How are bacteria and archaea similar to and different from each other?
Bacteria and archaea are small cells that lack nuclei and membrane-bounded organelles.
The two groups differ in the composition of the cell wall and the lipids in the cell
membrane.
3. How do organelles contribute to efficiency in eukaryotic cells?
Organelles contribute to efficiency in eukaryotic cells because they concentrate the
biochemicals needed for chemical reactions so that the reactions proceed more rapidly,
leading to efficiency. Also, because of organelles, a eukaryotic cell can get along with
high concentrations of biochemicals only in certain areas. The biochemicals do not have
to be in high concentrations throughout the cell.
3.3
1. Chemically, how is a phospholipid different from a triglyceride?
A phospholipid has two fatty acids and a phosphate group attached to the glycerol, while
a triglyceride just has three fatty acids that attach to the glycerol.
2. How does the chemical structure of phospholipids enable them to form a bilayer in
water?
The hydrophilic heads naturally make contact with water while the hydrophobic tails
naturally avoid water. When many phospholipids join, the hydrophilic heads and
hydrophobic tails align, forming a bilayer.
3. Where in the cell do phospholipid bilayers occur?
Phospholipid bilayers occur around organelles within the cell and at the cell’s surface as
the plasma membrane.
4. What are some functions of membrane proteins?
Membrane proteins have the following functions:
- transport proteins move substances into and out of cells;
- enzymes facilitate chemical reactions;
- recognition proteins on cell surfaces allow the body to recognize its own cells;
- adhesion proteins allow cells to stick together;
- receptor proteins bind molecules to the outside of the cell and trigger chemical
reactions inside the cell
3.4
1. Which organelles interact to produce and secrete a complex substance such as milk?
The nucleus, ribosomes, smooth ER, Golgi apparatus, and vesicles are organelles
involved in the production of milk.
2. What is the function of the nucleus and its contents?
The nucleus contains DNA (the molecule that contains the instructions for making
proteins) and the nucleolus (where ribosomes are assembled). mRNA molecules also are
present in the nucleus, where they gather information and exit to the cytoplasm through
nuclear pores.
3. Which organelles are the cell’s “recycling centers”?
Lysosomes, vacuoles, and peroxisomes are the cell’s recycling centers.
4. What are some functions of plastids?
Chloroplasts are plastids that carry out photosynthesis. Other plastids store pigments or
food, or they help a plant to detect gravity.
5. Which organelle houses the reactions that extract chemical energy from nutrient
molecules?
Mitochondria house the reactions that extract chemical energy from nutrient molecules.
6. Which three organelles contain DNA?
DNA occurs in the nucleus, chloroplasts, and mitochondria.
3.5
1. What are some functions of the cytoskeleton?
The cytoskeleton provides a structural framework for the cell, is a transportation system
within the cell, allows the cell to move, and connects cells together.
2. What are the main components of the cytoskeleton?
The major components of the cytoskeleton are microtubules, microfilaments, and
intermediate filaments.
3. How are cilia and flagella similar, and how are they different?
In eukaryotes, cilia and flagella are similar in their internal structure (the 9+2
arrangement of microtubules). Both structures move, but they differ in their length and in
how they move. Cilia are short and move in wave-like motions. Flagella are much longer
and move with a whiplike motion.
3.6
1. What functions do cell walls provide?
Cell walls provide rigidity, prevent a cell from bursting if it takes on too much water, and
allow interactions with other cells to determine how a cell of a complex plant becomes
specialized.
2. What is the chemical composition of a plant cell wall?
Plant cell walls are made mostly of cellulose but also contain hemicellulose and pectin.
3. What are plasmodesmata?
Plasmodesmata are tunnels that connect adjacent cell walls.
4. What are the three types of junctions that link cells in animals?
Tight junctions, gap junctions, and anchoring junctions link cells in animals.
3.7
1. How did the researchers use multiple lines of evidence to answer their question?
The researchers used microscopy with fluorescent tags, altered genes, and studies of
molecules in multiple species as independent corroborating lines of evidence in support
of their conclusion that the actin in eukaryotic cytoskeletons has a functional counterpart
in bacteria.
2. How would the bacterial cells in figure 3.27 look different if Mbl occurred throughout
the cytoplasm?
If Mbl occurred throughout the cell then the radioactive parts of the cell would appear
throughout and not just at the cell surface.
Write It Out
1. How has improved technology enabled the expansion of the cell theory from Schleiden
and Schwann’s original formulation?
New microscopes have allowed scientists to view cells in much greater detail. Scientists
now understand much more about what cells are made of, how they use energy, and how
they divide.
2. Until recently, biologists thought that there were only two types of cells. How has that
view changed?
Investigation has revealed that not all prokaryotes are alike. Biologists now recognize
three types of cells: eukaryotes, bacteria, and archaea.
3. List the features that all cells share, then name three structures or activities found in
eukaryotic cells but not in bacteria or archaea.
All cells have: DNA, RNA, protein, ribosomes, cytoplasm, and a cell membrane.
Structures or activities found only in eukaryotic cells include any of the organelles, a
nucleus, or the activities of the endomembrane system.
4. The simplest viruses consist only of a protein coat surrounding DNA or RNA. What
does a simple virus have in common with cells? What does it lack that all cells have?
Viruses share 3 things with cells: DNA, RNA (but not both together), protein. Viruses
lack: ribosomes, cytoplasm, and a cell membrane.
5. In what ways is a prokaryotic cell like a baseball stadium, but a eukaryotic cell is more
like an office building?
A prokaryotic cell is more like a baseball stadium because it has a simple structure with
few internal compartments. A eukaryotic cell is more like an office building because it is
more complex and has many different internal compartments and specialized areas.
6. Biologist J. Craig Venter has designed and built an artificial chromosome, based on the
DNA in a bacterial cell. If he wants to use that DNA in an artificial cell, what other
ingredients will he need? Can you foresee any benefits from, or ethical problems with,
the ability to create artificial life? What do you need to know to be able to answer these
questions?
He will need a membrane in which to enclose the cell, RNA to act as enzymes and help
make proteins, ribosomes to help make proteins, and cytoplasm containing proteins.
Some benefits could include a better understanding of how life might have begun on
earth or the ability to manufacture cells with all the desired characteristics. Ethical
questions w include whether or notwe have the right to create life, and to consider the
costs of introducing completely novel life to current ecosystems. To answer these
questions you would need knowledge of future impacts, which we do not have access to..
7. Your friend claims that an ostrich egg is the largest single cell, but you are skeptical
that one cell can be that large. If you had access to an ostrich egg and a high-quality light
microscope, what features would you look for to resolve the argument?
One visible clue that the egg is made of just one cell would include the presence of just
one nucleus and just one cell membrane. If the ostrich egg were made of multiple cells, it
would contain multiple nuclei.
8. Suppose you discover a new organism and that you have access to light and electron
microscopes to examine its cells. List a specific question you could answer by using each
type of microscope.
With the light microscope you can look for a nucleus and determine if the cell is
prokaryotic or eukaryotic. With the electron microscope you can look for different
organelles and determine whether the cell is a plant or animal.
9. Why are large organisms made of numerous small cells instead of a few large ones?
Nutrients and wastes must enter and leave each cell through its surfaces. All cells
therefore require a large surface area through which they can interact with the
environment. The larger a cell, the lower the ratio of surface area to volume.
10. A liver cell has a volume of 5000 μm3. Its total membrane area, including the inner
membranes lining organelles as well as the cell membrane, is 110,000 μm2. A cell in the
pancreas that manufactures digestive enzymes has a volume of 1000 μm3 and a total
membrane area of 13,000 μm2. Which cell is probably more efficient in carrying out
activities that require extensive membrane surfaces? Why?
The liver cell is probably more efficient because it has more membrane surface area
relative to its volume.
11. Which has a greater ratio of surface area to volume, a hippopotamus or a mouse?
Which animal would lose heat faster in a cold environment and why?
A mouse has a higher surface area to volume ratio and would lose more heat since the
heat of its body comes in contact with the cold environment in more places relative to its
volume.
12. What advantages does compartmentalization confer on a large cell?
Compartmentalization means that a cell must maintain high concentrations of each
biochemical only in certain organelles and not throughout the entire cell. Internal
compartments also increase the membrane surface area available for chemical reactions.
13. List the chemicals that make up cell membranes.
The chemicals in cell membranes are phospholipids, sterols, proteins, and sugars.
14. Emulsifiers are common food additives. A typical emulsifier molecule has a
hydrophilic end and a hydrophobic end. Draw a diagram explaining how an emulsifier
can enable oil to mix with water.
Answer will be visual but should have the hydrophilic end facing the water and the
hydrophobic end facing the oil.
15. Compare and contrast the phospholipid bilayer with two pieces of Velcro sticking to
each other.
The two pieces of Velcro have the fabric backing sandwiching the hooks and loops
inside, similar to the phospholipid tails sandwiched between the two layers of heads. The
nature of the backing (not able to attach) and the hook and loops (able to attach) are
different, similar to how tails are hydrophobic and heads are hydrophilic. However, what
holds the two pieces of Velcro together are actual attachments between the hooks and
loops; the phospholipids tails do not attach to each other, they just orient themselves
based on their mutual dislike of water.
16. Choose one of the functions of membrane proteins mentioned in this chapter. If a
person were born with a faulty version of a protein with that function, what symptoms
might you predict?
If a person were born with a faulty version of recognition proteins, then they might have
immune system problems and would easily get sick.
17. One way to understand cell function is to compare the parts of a cell to the parts of a
factory. For example, the Golgi apparatus would be analogous to the factory’s shipping
department. How would the other cell parts fit into this analogy?
The nucleus would be the management office where decisions are made, and the
endoplasmic reticulum would be the assembly line for production. The forklifts would be
transport vesicles shipping things throughout the factory, and the generators would be the
mitochondria. The girders and steel beams that make up the structure of the building
would be the cytoskeleton.
18. Which three organelles in a eukaryotic cell are surrounded by a double membrane?
The nucleus, mitochondria, and chloroplasts have a double membrane.
19. This chapter used the endomembrane system to illustrate the organelles involved in
milk production. Once a baby drinks the milk, which organelles in the infant’s cells
extract the raw materials and potential energy in the milk to fuel growth?
Peroxisomes would break down the lipids in the milk, and the rest of the breakdown
would be done by enzymes inside and outside of the mitochondria.
20. Why does a muscle cell contain many mitochondria and a white blood cell (an
immune cell that engulfs bacteria) contain many lysosomes?
White blood cells have many lysosomes because they engulf and dispose of debris and
bacteria. Muscle cells require a lot of energy to move parts of the body; mitochondria use
aerobic cellular respiration to extract energy from food.
21. List the components and functions of the cytoskeleton.
Three components of the cytoskeleton are microtubules, microfilaments, and intermediate
filaments. The cytoskeleton forms a transportation system, provides structural support
necessary to maintain the cell’s characteristic three-dimensional shape, enables cells or
parts of the cells to move, aids in cell division, and helps connect cells to one another.
22. How do plant cells interact with their neighbors through the rigid cell wall?
Plant cells interact with their neighbors via plasmodesmata, which are channels that
connect adjacent cells. Plasmodesmata are essentially tunnels in the cell wall, through
which the cytoplasm and some of the organelles of one plant can interact with those of
another.
23. Describe how animal cells use junctions in different ways.
Tight junctions create a seal between adjacent cells. Anchoring junctions are “spot
welds” that secure cells in place. Gap junctions allow adjacent cells to exchange
cytoplasmic material.
24. List examples of highly folded organelles with huge surface area.
Examples would include the endoplasmic reticulum, Golgi apparatus, mitochondria, and
chloroplast.
Pull ItTogether
1. What are the functions of each structure in a eukaryotic cell?
[Table 3.2 contains the complete answer]
Plasma Membrane – to contain and protect the cell
Nucleus – to contain the DNA, to synthesize RNA from DNA
Rough Endoplasmic Reticulum – to synthesize proteins from RNA
Smooth Endoplasmic Reticulum – to synthesize lipids
Golgi Apparatus – to fold proteins into their mature form, augment them with sugars, and
shuttle them towards the correct part of the cell
Cytoskeleton – the internal framework of the cell, which provides support for the cell,
aids cellular division, transports materials, and connects cells to one another.
Transport vesicles – vesicle used to move proteins and other molecules around the cell,
along the cytoskeleton
Mitochondria – the organelles that break down sugar to provide usable sources of
molecular bond energy for enzymes throughout the cell
Chloroplasts – the organelles that use light energy, carbon dioxide and water to
synthesize sugar, which can then be converted to usable molecular bond energy
Lysosomes – organelles used to break down and recycle molecular waste
Peroxisomes – containers for enzymes that can break down toxic molecules
Central Vacuole – membrane bound structure for storage of water and various molecules
Cell Wall – stiff structure that provides a cell shape
2. How do a cell’s organelles interact with one another?
Vesicles, or small bubbles of membrane, carry proteins or other structures from one
organelle to another. Since each organelle has specific functions, vesicles allow
organelles to divide tasks among each other. The production of milk, as described in the
chapter, is a good illustration of how organelles use vesicles to interact.
3. Add the eukaryotic kingdoms of life to this concept map.
“Domain Eukarya” could connect with the phrase “consists of” to four boxes titled
“Protists”, “Fungi”, “Plants”, and “Animals”.
4. How do plant cells differ from animal cells?
Plant cells have two key organelles that animal cells generally do not have: chloroplasts
and vacuoles. Outside of the plasma membrane, plant cells have a cell wall that animal
cells lack. Plant cells are connected by plasmodesmata, but lack the other forms of
connections found in animal cells.
5. How do plant and animal cells stick together and communicate with their neighbors?
Animal cells stick together and communicate in several ways. Many animal cells are
connected by complex protein structures called junctions. Anchoring junctions tightly
link the intermediate filaments of neighboring cells. Large pores, called gap junctions,
connect other cells. Tight junctions hold cells completely flat against each other, with
proteins extending from one plasma membrane into the other. Communication is possible
between some of these connections. Cells sharing a tight junction can readily share
chemical signals with each other by exporting them through their membranes.
Neighboring cells held in place by anchoring junctions can likewise send chemical
signals to each other, but not as efficiently. Gap junctions allow cells to act in unison by
providing free flow for nutrients and chemical signals.
Plant share gaps in their adjoining cells walls called plasmodesmata. These connections
work like gap junctions to allow free flow of nutrients and chemical signals between the
cells.
6. Which cell types have a cell wall?
Plants, algae, fungi, bacteria and archaea all have cell walls, but the walls are made of
different materials. Plants have a cell wall composed of cellulose. Fungi cells have a cell
wall containing chitin. Bacteria and archaea have cell walls made of peptidoglycan.
Algal cell walls can be made of a variety of materials, including peptidoglycans.