3

chapter

Cell Structure and

Function

A CHICKEN’s egg is large

enough to hold in your
Chapter Concepts hand while most cells take a microscope to
see them. A chicken’s egg is big because much of
3.1 the cellular level of Organization it is stored food for growth of an embryo.
■ What does the cell theory state? 46
Cells are incredibly variable. Bacterial cell
■ What instruments would a scientist use to study and view looks simple compared to those within our
small cells? 46–48
nervous system. However, the bacterial cell is
3.2 Eukaryotic Cells the entire organism; that senses the
■ What boundary is found in all cells? What additional boundary is
environment, obtains food, gets rid of waste,
found in plant cells? 49
and reproduces. In contrast, a human being is
■ What do you call the small structures in eukaryotic cells that carry out
specific functions? 49 composed of approximately 10 trillion cells.
Each type of human cell is specialized to
■ What is the function of the nucleus? 52
perform specific functions, but it still has to do
■ What membranous system within eukaryotic cells is involved in the
production, modification, transportation, storage, secretion, and/or many of the same things a bacterial cell is
digestion of macromolecules? 53–55 required to do.
■ What energy transformation structures are present in plant and animal Cells have still other differences. Some
cells? What does each structure produce? 56–57 bacteria, such as thermophilic (heat-loving)
■ What is the composition of the cytoskeleton, and what is its ones, live in boiling sulfur springs, while others
function? 58–59 exist as parasites within the human body. Most
■ What structures are responsible for movement of the cell? 60–61 bacterial and fungal cells, acquire energy by
3.3 Prokaryotic Cells decomposing the dead remains of organisms,
■ What is the major difference between prokaryotic and but plant cells are able to get their energy from
eukaryotic cells? 62 the sun. Regardless of their differences, there are
3.4 Evolution of the Eukaryotic Cell certain structures that every cell must have and
■ What hypothesis suggests how eukaryotic cells arose? 63 certain functions it must perform. This chapter
discusses the contents of a generalized cell.
46 Part I cell biology

3.1 The Cellular Level of

Organization
The cell marks the boundary between the nonliving and the
living. The molecules that serve as food for a cell and the
macromolecules that make up a cell are not alive, and yet the cell
is alive. Thus, the answer to what life is must lie within the cell,
because the smallest living organisms are unicellular, while larger
—
organisms are multicellular that is, composed of many cells. The
diversity of cells is exemplified by the many types in the human
body, such as muscle cells and nerve cells. But despite variety of
form and function, cells contain the same components. The basic
components that are common to all cells regardless of their
specializations are the subject of this chapter. The Science Focus
on these two pages introduces you to the microscopes most used
today to study cells. Electron microscopy and biochemical
analysis have revealed that a cell actually contains tiny
specialized structures called organelles that perform specific
cellular functions.
Today, we are accustomed to thinking of living things as
being constructed of cells. But the word cell didn’t enter biology
until the seventeenth century. Antonie van Leeuwenhoek of
Holland is now famous for making his own microscopes and
observing all sorts of tiny things that no one had seen before.
Robert Hooke, an Englishman, confirmed Leeuwenhoek’s
observations and was the first to use the term cell. The tiny
chambers he observed in the honeycomb structure of cork
reminded him of the rooms, or cells, in a monastery.
— —
A hundred years later in the 1830s the German
microscopist Matthias Schleiden said that plants are composed of
cells; his counterpart, Theodor Schwann, said that animals are
also made up of living units called cells. This was quite a feat,
because aside from their own exhausting work, both had to take
into consideration the studies of many other microscopists.
Rudolf Virchow, another German microscopist, later came to the
conclusion that cells don’t suddenly appear; rather, they come
from preexisting cells.
Today, the cell theory, which states that all organisms are
made up of basic living units called cells and that cells come only
from preexisting cells, is a basic theory of biology.

The cell theory states the following: ■ All organisms are

composed of one or more cells.
■ Cells are the basic living unit of structure and function

in organisms.
■ All cells come only from other cells.
 Chapter 3 cell structure and function

image is projected is much less for an whereas even living

onto a fluorescent electron microscope objects can be
screen or photographic than for a light observed with a light
film. microscope (10 nm microscope.
The magnification compared to 200 nm1). Ascanning
produced by an The greater resolving electron microscope
electron microscope is power of the electron provides a three-
much higher than that microscope is due to dimensional view of
of a light microscope the fact that electrons the surface of an
(50,000X compared to travel at a much object. Anarrow beam
1,000X). Also, the shorter wavelength of electrons is scanned
ability of the electron than do light rays. over the surface of the
microscope to make However, because specimen, which has
out detail is much electrons travel only in been coated with a thin
greater. The distance a vacuum, the object is layer of metal. The
needed to distinguish always dried out metal gives off
two points as separate before viewing, secondary electrons,

1 nm nanometer. See
Appendix C, Metric
System.
48 Part I cell biology

which are collected to

produce a television-
type picture of the
specimen’s surface on
a screen.
A picture obtained
using a light
microscope is
sometimes called a
photomicrograph, and
a picture resulting
from the use of an
electron microscope is
called a transmission
electron micrograph
(TEM) or a scanning
electron micrograph
(SEM), depending on
the type of microscope
used.
 0.1 nm 1 nm 10 nm 100 nm 1 µm 10 µm 100 µm 1 mm 1 cm 0.1 m 1m 10 m 100 m 1 km

protein chloroplast
mouse
plant and
animal
cells frog
amino acid egg
virus blue whale
atom human
most bacteria egg ant
electron microscope

light microscope human

human eye

FIGURE 3.1 The sizes of living things and their components.

It takes a microscope to see most cells and lower levels of biological organization. Cells are visible with the light microscope, but not in much detail. An
electron microscope is needed to see organelles in detail and to make out viruses and molecules. Notice that in this illustration each measurement is 10 times
—
greater than the lower one. (In the metric system, 1 meter 102 cm 103 mm 106m 109 nm see Appendix C.)

Cell Size A small cube, 1 mm tall, has a volume of 1 mm 3 (height width

depth is 1 mm3). The surface area is 6 mm 2. (Each side has a
Figure 3.1 outlines the visual ranges of the eye, light microscope,
surface area of 1 mm2, and 6 1 mm2 is 6 mm2). Therefore, the
and electron microscope. Cells are usually quite small. A frog’s
ratio of surface area to volume is 6:1 because the surface area is
egg, at about one millimeter (mm) in diameter, is large enough to
6 mm2 and the volume is 1 mm3.
be seen by the human eye. But most cells are far smaller than
— Contrast this with a larger cube that is 2 mm tall. The
one millimeter; some are even as small as one micrometer (m) surface area is 24 mm2. (Each side has a surface area of 4 mm 2,
one-thousandth of a millimeter. Cell inclusions and and 6 4 is 24 mm2). The volume of this larger cube is 8 mm 3;
macromolecules are even smaller than a micrometer and are therefore, the ratio of surface area to volume of the larger cube is
measured in terms of nanometers (nm). 3:1. We can conclude then that a small cell has a greater surface
To understand why cells are so small and why we are area to volume ratio than does a larger cell.
multicellular, consider the surface/volume ratio of cells. Therefore, small cells, not large cells, are likely to have an
Nutrients enter a cell and wastes exit a cell at its surface; adequate surface area for exchanging wastes for nutrients. We
therefore, the amount of surface affects the ability to get material would expect, then, a size limitation for an actively metabolizing
in and out of the cell. A large cell requires more nutrients and cell. You can hold a chicken’s egg in your hand, but the egg is
produces more wastes than a small cell. In other words, the not actively metabolizing. Once the egg is incubated and
volume represents the needs of the cell. Yet, as cells get larger in metabolic activity begins, the egg divides repeatedly without
volume, the proportionate amount of surface area actually growth. Cell division restores the amount of surface area needed
decreases, as you can see by comparing these two cells: for adequate exchange of materials. Further, cells that specialize
in absorption have modifications that greatly increase the surface
area per volume of the cell. For example, the columnar cells
along the surface of the intestinal wall have surface foldings
called microvilli (sing., microvillus), which increase their surface
area.

A cell needs a surface area that can adequately exchange

small cell— large cell—
materials with the environment. Surface-areato-volume
more surface area less surface area
per volume per volume considerations require that cells stay small.
46 Part I cell biology

3.2 Eukaryotic Cells TABLE 3.1 EUKARYOTIC STRUCTURES IN ANIMAL

CELLS AND PLANT CELLS

Eukaryotic cells, one of the two major types of cells, have a nucleus.
A nucleus is a large structure that controls the workings of the cell
because it contains the genes. Both animals and plants have Name Composition Function
eukaryotic cells.
Cell wall* Contains cellulose Support and protection
Outer Boundaries of Animal and Plant Cells fibrils

Animal and plant cells are surrounded by a plasma membrane, that Plasma Phospholipid bilayer Defines cell boundary; membrane
with embedded regulation of molecule
consists of a phospholipid bilayer in which protein molecules are
proteins passage into and out of
embedded: cells
Nucleus Nuclear envelope, Storage of genetic
nucleoplasm, information; synthesis of
The chromatin, and DNA and RNA nucleoli
Nucleolus Concentrated area Ribosomal subunit of
chromatin, RNA, formation and proteins
Ribosome Protein and RNA in Protein synthesis two
subunits
Endoplasmic Membranous Synthesis and/or
reticulum flattened channels modification of proteins (ER) and
plasma membrane is a living boundary that separates the living tubular canals and other substances,
contents of the cell from the nonliving surrounding environment. and distribution by vesicle
formation
Inside the cell, the nucleus is surrounded by the cytoplasm, a
semifluid medium that contains organelles. The plasma membrane Rough ER Studded with Protein synthesis
ribosomes
regulates the entrance and exit of molecules into and out of the
cytoplasm. Smooth ER Having no ribosomes Various; lipid synthesis
\\\\\\\\\\\\\\\\\\\\\\\\\\\\Plant cells (but not animal cells) have a in some cells
permeable but protective cell wall, in addition to a plasma Golgi Stack of membranous Processing, packaging, apparatus saccules
membrane. Many plant cells have both a primary and secondary cell and distribution of
wall. A main constituent of a primary cell wall is cellulose proteins and lipids
molecules. Cellulose molecules form fibrils that lie at right angles to Lysosome Membranous vesicle Intracellular digestion
one another for added strength. The secondary cell wall, if present, containing digestive enzymes
forms inside the primary cell wall. Such secondary cell walls contain Vacuole and Membranous sacs Storage of substances vesicle
lignin, a substance that makes them even stronger than primary cell
Peroxisome Membranous vesicle Various metabolic tasks
walls.
containing specific enzymes
Mitochondrion Inner membrane Cellular respiration
Organelles of Animal and Plant Cells (cristae) bounded by an
Originally the term organelle referred to only membranous outer membrane
structures, but we will use it to include any well-defined subcellular Chloroplast* Membranous grana Photosynthesis
structure (Table 3.1). Just as all the assembly lines of a factory are in bounded by two membranes
operation at the same time, so all the organelles of a cell function Cytoskeleton Microtubules, Shape of cell and
simultaneously. Raw materials enter a factory and then are turned intermediate movement of its filaments, actin parts
into various products by different departments. In the same way, filaments
chemicals are taken up by the cell and then processed by the
Cilia and 9 + 2 pattern of Movement of cell flagella
organelles. The cell is a beehive of activity the entire 24 hours of microtubules
every day.
Both animal cells (Fig. 3.2) and plant cells (Fig. 3.3) contain Centriole** 9 + 0 pattern of Formation of basal
microtubules bodies
mitochondria, while only plant cells have chloroplasts.
Only animal cells have centrioles. All the organelles have an *Plant cells
only assigned color that is used to represent them in the illustra- **Animal
cells only tions throughout the text.
 Chapter 3 cell structure and function 47

nuclear pore
chromatin
nucleus
nucleolus
nuclear
envelope

polyribosome

smooth ER
actin filament
(within
cytoskeleton) peroxisome
rough ER vacuole

ribosome cytoplasm
(attached to rough ER) ribosomes
(in cytoplasm)
centriole
Golgi apparatus
mitochondrion
vesicle

lysosome
plasma membrane

microtubule
(within cytoskeleton)

a.

plasma membrane

nuclear envelope

chromatin

nucleolus

endoplasmic reticulum

b.
50 nm
FIGURE 3.2 Animal cell anatomy.
48 Part I cell biology

a. Generalized drawing. b. Transmission electron micrograph. See Table 3.1 for a description of these structures, along with a listing of their functions.

microtubule
(within cytoskeleton)

nuclear
pore
central vacuole
chromatin
nucleus
nucleolus
chloroplast nuclear
envelope

ribosomes
(in cytoplasm)

rough ER
ribosome
(attached to
rough ER)
smooth ER

cell wall

plasma membrane

Golgi apparatus

cytoplasm

mitochondrion
actin filament
(within cytoskeleton)
cell wall of adjacent cell

a.

peroxisome

mitochondrion

nucleus

ribosomes

plasma membrane
central vacuole

chloroplast cell wall

1 µm
b.
 Chapter 3 cell structure and function 49

FIGURE 3.3 Plant cell anatomy.

a. Generalized drawing. b. Transmission electron micrograph of a young leaf cell. See Table 3.1 for a description of these structures, along with a listing
of their functions.

The Nucleus
The nucleus, which has a diameter of about 5 m, is a prominent
structure in the eukaryotic cell. The nucleus is of primary
importance because it stores the genetic material DNA which
governs the characteristics of the cell and its metabolic
functioning. Every cell in the same individual contains the same
DNA, but, in each cell type, certain genes are turned on and
certain others are turned off. Activated DNA, with RNA acting
as an intermediary, specifies the sequence of amino acids when a
protein is synthesized. The proteins of a cell determine its
structure and the functions it can perform.
When you look at the nucleus, even in an electron
micrograph, you cannot see a DNA molecule. You can see
chromatin, which consists of DNA and associated proteins (Fig.
3.4). Chromatin looks grainy, but actually it is a threadlike
material that undergoes coiling to form rodlike structures, called
chromosomes, just before the cell divides. Chromatin is
immersed in a semifluid medium called the nucleoplasm.
Adifference in pH between the nucleoplasm and the cytoplasm
suggests that the nucleoplasm has a different composition.
Most likely, too, when you look at an electron
micrograph of a nucleus, you will see one or more regions
that look darker than the rest of the chromatin. These are
nucleoli (sing., nucleolus), where another type of RNA,
called ribosomal RNA (rRNA), is produced and where
rRNA joins with proteins to form the subunits of
ribosomes. (Ribosomes are small bodies in the cytoplasm
that contain rRNAand proteins.)
The nucleus is separated from the cytoplasm by a
double membrane known as the nuclear envelope, which
is continuous with the endoplasmic reticulum discussed on
the next page. The nuclear envelope has nuclear pores of
sufficient size (100 nm) to permit the passage of proteins
into the nucleus and ribosomal subunits out of the nucleus.

The structural features of the nucleus include the

following.
Chromatin: DNA and proteins
Nucleolus: Chromatin and ribosomal
subunits
50 Part I cell biology

Nuclear envelope: Double membrane with pores

nuclear envelope

chromatin nucleolus

nuclear pores

inner membrane

outer membrane
Electron micrographs of
nuclear envelope showing
pores.

FIGURE 3.4 The nucleus and the nuclear envelope.

The nucleoplasm contains chromatin. Chromatin has a special region called the nucleolus, where rRNAis produced and ribosomal subunits are assembled. The
nuclear envelope, consisting of two membranes separated by a narrow space, contains pores. The electron micrographs show that the pores cover the surface of the
envelope.
 Chapter 3 cell structure and function 51

Ribosomes ER is involved in protein synthesis (rough ER) and

Ribosomes are composed of two subunits, one large and various other processes, such as lipid synthesis
one small. Each subunit has its own mix of proteins and (smooth ER). Vesicles transport proteins from the
rRNA. Protein synthesis occurs at the ribosomes. ER to the Golgi apparatus.
Ribosomes can be found within the cytoplasm, either
singly or in groups called polyribosomes. Ribosomes can
also be found attached to the endoplasmic reticulum, a
membranous system of saccules and channels discussed in
the next section. Proteins synthesized at ribosomes
attached to the endoplasmic reticulum have a different
fate. They are eventually secreted from the cell or become
a part of its external surface.

Ribosomes are small organelles where protein ribosome

synthesis occurs. Ribosomes occur in the
cytoplasm, both singly and in groups (i.e.,
polyribosomes). Numerous ribosomes are also smooth
ER
attached to the endoplasmic reticulum.

a.
rough ER
The Endomembrane System
The endomembrane system consists of the nuclear
envelope, the endoplasmic reticulum, the Golgi apparatus,
and several vesicles (tiny membranous sacs). This system
compartmentalizes the cell so that particular enzymatic
reactions are restricted to specific regions. Organelles that
make up the endomembrane system are connected either
directly or by transport vesicles.
b.
400 nm
The Endoplasmic Reticulum ribosome

The endoplasmic reticulum (ER), a complicated system

of membranous channels and saccules (flattened vesicles),
is physically continuous with the outer membrane of the
nuclear envelope. Rough ER is studded with ribosomes on
the side of the membrane that faces the cytoplasm (Fig. polypeptide
carbohydrate
3.5). Here, proteins are synthesized and enter the ER chain
interior, where processing and modification begin. Most glycoprotein
proteins are modified by the addition of a sugar chain,
which makes them a glycoprotein.
Smooth ER, which is continuous with rough ER,
does not have attached ribosomes. Smooth ER synthesizes vesicle
the phospholipids that occur in membranes and has various formation
other functions depending on the particular cell. In the
testes, it produces testosterone, and in the liver, it helps
detoxify drugs. Regardless of any specialized function,
smooth ER also forms vesicles in which proteins are
transported to the Golgi apparatus. transport
vesicle

c.
52 Part I cell biology

FIGURE 3.5 The endoplasmic reticulum (ER).

a. Rough ER has attached ribosomes, but smooth ER does not.
b. Rough ER appears to be flattened saccules, while smooth ER is a network
of interconnected tubules. c. Aprotein made at a ribosome moves into the
lumen of the system, is modified, and is eventually packaged in a
transport vesicle for distribution to the Golgi apparatus.
 Chapter 3 cell structure and function 53

smooth ER
rough ER synthesizes lipids and
synthesizes proteins and performs other functions.
packages them in vesicles.

transport vesicles
from smooth ER.

lysosome
digest molecules or old
cell parts.
Golgi apparatus
modifies lipids and proteins;
sorts and packages them

secretory vesicles incoming vesicle

fuse with the plasma brings substances into the
membrane as secretion cell.

transport vesicles

from rough ER. in

vesicles. occurs.

FIGURE 3.6 Endomembrane system.

The organelles in the endomembrane system work together to carry out the functions noted.
54 Part I cell biology

The Golgi Apparatus Occasionally, a child inherits the inability to make a

The Golgi apparatus is named for Camillo Golgi, who lysosomal enzyme, and therefore has a lysosomal storage
discovered its presence in cells in 1898. The Golgi apparatus disease. Instead of being degraded, the molecule
consists of a stack of three to twenty slightly curved saccules accumulates inside lysosomes, and illness develops when
whose appearance can be compared to a stack of pancakes (Fig. they swell and crowd the other organelles. In Tay Sachs
3.6). In animal cells, one side of the stack (the inner face) is disease, the cells that surround nerve cells cannot break
directed toward the ER, and the other side of the stack (the outer down a particular lipid, and the nervous system is affected.
face) is directed toward the plasma membrane. Vesicles can At about six months, the infant can no longer see and,
frequently be seen at the edges of the saccules. then, gradually loses hearing and even the ability to move.
The Golgi apparatus receives protein and also lipidfilled Death follows at about three years of age.
vesicles that bud from the smooth ER. These molecules then
move through the Golgi from the inner face to the outer face.
The endomembrane system consists of the
How this occurs is still being debated. According to the
maturation saccule model, the vesicles fuse to form an inner face
endoplasmic reticulum, Golgi apparatus,
saccule, which matures as it gradually becomes a saccule at the lysosomes, and transport vesicles.
outer face. According to the stationary saccule model, the
molecules move through stable saccules from the inner face to
the outer face by shuttle vesicles. It is likely that both models
apply, depending on the organism and the type of cell. Vacuoles
During their passage through the Golgi apparatus, A vacuole is a large membranous sac. A vesicle is smaller
glycoproteins have their sugar chains modified before they than a vacuole. Animal cells have vacuoles, but they are
are repackaged in secretory vesicles. Secretory vesicles much more prominent in plant cells. Typically, plant cells
proceed to the plasma membrane, where they discharge have a large central vacuole so filled with a watery fluid
their contents. Because this is secretion, the Golgi that it gives added support to the cell (see Fig. 3.3).
apparatus is said to be involved in processing, packaging, Vacuoles store substances. Plant vacuoles contain
and secretion. not only water, sugars, and salts but also pigments and
The Golgi apparatus is also involved in the formation toxic molecules. The pigments are responsible for many of
of lysosomes, vesicles that contain proteins and remain the red, blue, or purple colors of flowers and some leaves.
within the cell. How does the Golgi apparatus direct traffic The toxic substances help protect a plant from herbivorous
— animals. The vacuoles present in unicellular protozoans
in other words, what makes it direct the flow of proteins
are quite specialized, and they include contractile vacuoles
to different destinations? It now seems that proteins made for ridding the cell of excess water and digestive vacuoles
at the rough ER have specific molecular tags that serve as for breaking down nutrients.
“zip codes” to tell the Golgi apparatus whether they belong
in a lysosome or in a secretary vesicle. The final sugar
chain serves as a tag that directs proteins to their final Vacuoles are larger than vesicles. Plants are well
destination. known for having a large central vacuole area for
Lysosomes storage of various molecules.
Lysosomes are membrane-bounded vesicles produced by
the Golgi apparatus. Lysosomes contain hydrolytic
digestive enzymes.
Sometimes macromolecules are brought into a cell
by vesicle formation at the plasma membrane (Fig. 3.6).
When a lysosome fuses with such a vesicle, its contents
are digested by lysosomal enzymes into simpler subunits
that then enter the cytoplasm. Some white blood cells
defend the body by engulfing pathogens by vesicle
formation. When lysosomes fuse with these vesicles, the
bacteria are digested. Even parts of a cell are digested by
its own lysosomes (called autodigestion). Normal cell
rejuvenation takes place in this manner.
Lysosomes contain many enzymes for digesting all
sorts of molecules. The absence or malfunction of one of
these results in a so-called lysosomal storage disease.
 Chapter 3 cell structure and function 55

Energy-Related Organelles
Life is possible only because of a constant input of energy used
for maintenance and growth. Chloroplasts and mitochondria are
the two eukaryotic membranous organelles that specialize in
converting energy to a form that can be used by the cell.
Chloroplasts use solar energy to synthesize carbohydrates, and
carbohydrate-derived products are broken down in mitochondria
(sing., mitochondrion) to produce ATP molecules, as shown in
the following diagram:

carbohydrate
(high chemical energy)

0.5 µm
solar
energy
FIGURE 3.7 Peroxisomes.
Peroxisomes are vesicles that oxidize organic substances with a resulting
buildup of hydrogen peroxide. Peroxisomes contain the enzyme catalase,
which breaks down hydrogen peroxide (H2O2) to water and oxygen.

Peroxisomes chloroplast mitochondrion

Peroxisomes, similar to lysosomes, are membrane-bounded
vesicles that enclose enzymes (Fig. 3.7). However, the enzymes
in peroxisomes are synthesized by cytoplasmic ribosomes and ATP usable
transported into a peroxisome by carrier proteins. Typically, energy
CO2 + H2O for cells
peroxisomes contain enzymes whose action results in hydrogen
(low chemical energy)
peroxide (H2O2):
Only plants, algae, and cyanobacteria are capable of
RH2 O2→R H2O2 carrying on photosynthesis in this manner:

R remainder of molecule solar energy + carbon dioxide + water carbohydrate + oxygen

Hydrogen peroxide, a toxic molecule, is immediately broken
down to water and oxygen by another peroxisomal enzyme Plants and algae have chloroplasts while cyanobacteria
called catalase. carry on photosynthesis within independent thylakoids.
The enzymes in a peroxisome depend on the function of Solar energy is the ultimate source of energy for cells
the cell. Peroxisomes are especially prevalent in cells that are because nearly all organisms, either directly or indirectly,
synthesizing and breaking down fats. In the liver, some use the carbohydrates produced by photosynthesizers as an
peroxisomes break down fats and others produce bile salts from energy source.
cholesterol. In the movie Lorenzo’s Oil, the cells lacked a carrier All organisms carry on cellular respiration, the
protein to transport an enzyme into peroxisomes. As a result, process by which the chemical energy of carbohydrates is
long chain fatty acids accumulate in his brain and Lorenzo converted to that of ATP (adenosine triphosphate). ATP is
suffers from neurological damage. the common carrier of chemical energy in cells. All
Plant cells also have peroxisomes. In germinating seeds, organisms, except bacteria, complete the process of
they oxidize fatty acids into molecules that can be converted to cellular respiration in mitochondria. Cellular respiration
sugars needed by the growing plant. In leaves, peroxisomes can can be represented by this equation:
—
carry out a reaction that is opposite to photosynthesis the carbohydrate + oxygen carbon dioxide + water + energy
reaction uses up oxygen and releases carbon dioxide.

Typically, the enzymes in peroxisomes break down

molecules and as a result produce hydrogen peroxide
molecules.
 56 Part I cell biology

Here energy is in the form of ATP molecules. When a cell

needs energy, ATP supplies it. The energy of ATP is used
for synthetic reactions, active transport, and all energy-
requiring processes in cells.
Chloroplasts
Plant and algal cells contain chloroplasts, the organelles
that allow them to produce their own organic food.
– –
Chloroplasts are about 4 6 m in diameter and 1 5 m in
length; they belong to a group of organelles known as
plastids. Among the plastids are also the amyloplasts,
common in roots, which store starch, and the
chromoplasts, common in leaves, which contain red and
orange pigments. A chloroplast is green, of course,
because it contains the green pigment chlorophyll.
A chloroplast is bounded by two membranes that
enclose a fluid-filled space called the stroma (Fig. 3.8). A
membrane system within the stroma is organized into
interconnected flattened sacs called thylakoids. In certain
regions, the thylakoids are stacked up in structures called
grana (sing., granum). There can be hundreds of grana
within a single chloroplast (Fig. 3.8). Chlorophyll, which
is located within the thylakoid membranes of grana,
captures
the solar energy needed to enable chloroplasts to produce
carbohydrates. The stroma also contains DNA, ribosomes,
and enzymes that synthesize carbohydrates from carbon
dioxide and water.
Mitochondria
outer membrane
double
inner membrane
membrane

granum

independent
thylakoids
stroma overlapping
thylakoids
500 nm
a. b.

FIGURE 3.8 Chloroplast structure.

Electron micrograph. b. Generalized drawing in which the outer and inner membranes have been cut away to reveal the grana.
All eukaryotic cells, including those of plants and algae, contain
mitochondria. This means that plant cells contain both
 Chapter 3 cell structure and function 57

chloroplasts and mitochondria. Most mitochondria are usually

– –
0.5 1.0 m in diameter and 2 5 m in length.
Mitochondria, like chloroplasts, are bounded by a double
membrane (Fig. 3.9). In mitochondria, the inner fluidfilled space
is called the matrix. The matrix contains DNA, ribosomes, and
enzymes that break down carbohydrate products, releasing
energy to be used for ATP production.
The inner membrane of a mitochondrion invaginates to
form cristae. Cristae provide a much greater surface area to
accommodate the protein complexes and other participants that
produce ATP.
Mitochondria and chloroplasts are able to make some
proteins, but others are imported from the cytoplasm.

Chloroplasts and mitochondria are membranous organelles

whose structures lend themselves to the energy transfers
that occur within them.

a. 200 nm

outer membrane
double cristae matrix
membrane inner membrane

b.

FIGURE 3.9 Mitochondrion structure.

a. Electron micrograph. b. Generalized drawing in which the outer membrane and portions of the inner membrane have been cut away to reveal the cristae.
58 Part I cell biology

The Cytoskeleton
The cytoskeleton is a network of interconnected filaments and
tubules that extends from the nucleus to the plasma membrane in
eukaryotic cells. Prior to the 1970s, it was believed that the
cytoplasm was an unorganized mixture of organic molecules.
Then, high-voltage electron microscopes, which can penetrate
thicker specimens, showed that the cytoplasm is instead highly
organized. It contains actin filaments, microtubules, and
intermediate filaments. The technique of immunofluorescence
microscopy identified the makeup of these protein fibers within
the cytoskeletal network (Fig. 3.10).
The name cytoskeleton is convenient in that it compares
the cytoskeleton to the bones and muscles of an animal. Bones
and muscles give an animal structure and produce movement.
Similarly, the fibers of the cytoskeleton maintain cell shape and
cause the cell and its organelles to move. The cytoskeleton is
dynamic; assembly occurs when monomers join a fiber and
disassembly occurs when monomers leave a fiber. Assembly and
disassembly occur at rates that are measured in seconds and
minutes. The entire cytoskeletal network can even disappear and
reappear at various times in the life of a cell.

FIGURE 3.11 Microtubules.

a. Microtubules are visible in this cell due to a technique called
immunofluorescence. b. Microtubules act as tracks along which
organelles move. The motor molecule kinesin, bound to a vesicle,
breaks down ATP and uses the energy to move along the microtubule.

plasma
microtubule membrane

centrosome Microtubules
Microtubules are small, hollow cylinders about 25 nm in
diameter and from 0.2 to 25 m in length.
Microtubules are made of a globular protein called
tubulin. When microtubules assemble, tubulin molecules
come together as dimers, and the dimers arrange
themselves in rows. Microtubules have 13 rows of tubulin
dimers surrounding what appears in electron micrographs
to be an empty central core. In many cells, microtubule
assembly is under the control of a microtubule organizing
center, MTCO, called the centrosome. The centrosome
lies near the nucleus. Before a cell divides, the
intermediate actin microtubules assemble into a structure called a spindle that
filament filament distributes chromosomes in an orderly manner. At the end
of cell division, the spindle disassembles, and the
FIGURE 3.10 The cytoskeleton. microtubules reassemble once again into their former
Diagram comparing the size relationship of microtubules, intermediate
array.
filaments, and intermediate filaments. Microtubule construction is
When the cell is not dividing, microtubules help
controlled by the centrosome.
maintain the shape of the cell and act as tracks along which
organelles can move. Motor molecules are proteins that
 Chapter 3 cell structure and function 59

derive energy from ATP to propell themselves along a

protein filament or microtubule. Whereas, the motor
molecule myosin is associated with actin filaments, the
motor
FIGURE 3.12 Actin filaments.
a. Actin filaments are visible in this cell due to a technique called
immunofluorescence. b. In the presence of ATP, myosin, a motor
molecule, attaches to an actin filament, pulls it, and then reattaches at
a different location. This is the mechanism that allows muscle to
contract.
FIGURE 3.13 Intermediate filaments.
a. Intermediates are visible in this cell due to a technique called
immunofluorescence. b. Fibrous subunits account for the ropelike structure
of intermediate filaments.
60 Part I cell biology

molecules kinesin and dynein move along microtubules. to assemble and disassemble in the same manner as actin
One type of kinesin is responsible for moving vesicles filaments and microtubules.
along microtubules, including microtubules, including the
transport vesicles of the endomembrane system. The
vesicle is bonded to the kinesin, and then kinensin “walks”
The cytoskeleton contains microtubules, actin filaments,
along the microtubule by attaching and reattaching itself
and intermediate filaments. These maintain cell shape and
further along the microtubule. There are different types of
allow organelles to move within the cytoplasm.
kinesin proteins, each specialized to move one kind of
Sometimes they are also involved in movement of the cell
vesicle or cellular organelle. One type of dynein molecule, itself.
called cytoplasmic dynein, is closely related to the dynein
found in flagella (Fig. 3.11).

Actin Filaments
Actin filaments (formerly called microfilaments) are long,
extremely thin fibers (about 7 nm in diameter) that occur
in bundles or meshlike networks. The actin filament
contains two chains of globular actin monomers twisted
about one another in a helical manner.
Actin filaments play a structural role by forming a
dense complex web just under the plasma membrane, to
which they are anchored by special proteins. Also, the
assembly and disassembly of a network of actin filaments
lying beneath the plasma membrane accounts for the
formation of pseudopods, extensions that allow certain
cells to move in an amoeboid fashion.
Actin filaments are seen in the microvilli that project
from intestinal cells, and their presence most likely
accounts for the ability of microvilli to alternately shorten
and extend into the intestine. In plant cells, actin filaments
apparently form the tracks along which chloroplasts
circulate or stream in a particular direction.
How are actin filaments involved in the movement of the
cell and its organelles? They interact with motor molecule called
myosin. Myosin has both a head and a tail. In the presence of
ATP, the myosin head attaches, and then reattaches to an actin
filament at a more distant location (Fig. 3.12). In muscle cells,
the tails of several muscle myosin molecules are joined to form a
thick filament. In nonmuscle cells, cytoplasmic myosin tails are
bound to membranes, but the heads still interact with actin.
During animal cell division, the two new cells form when actin,
in conjunction with myosin, pinches off the cells from one
another.

Intermediate Filaments
–
Intermediate filaments (8 11 nm in diameter) are intermediate in
size between actin filaments and microtubules. They are ropelike
assemblies of fibrous polypeptides (Fig. 3.13) that support the
nuclear envelope and the plasma membrane. In the skin,
intermediate filaments made of the protein keratin give great
mechanical strength to skin cells. Recent work has shown
intermediate filaments to be highly dynamic. They also are able
 Chapter 3 cell structure and function 61

one microtubule one pair of centrioles

triplet

two pairs of centrioles 200 nm

FIGURE 3.14 Centrioles.

Left and top right. Anondividing cell contains a pair of centrioles in a centrosome outside the nucleus. Bottom, right. Just before a cell divides, the centrosome
divides so that there are two pairs of centrioles. During cell division, the centrosomes separate so that each new cell has one pair of
centrioles. Centrioles, which are short cylinders with a 9 0 pattern
of microtubule triplets, may be involved in microtubule
formation and in the organization of cilia and flagella.
Centrioles
Centrioles are short cylinders with a 9 0 pattern of microtubule Cilia and Flagella
— Cilia and flagella are hairlike projections that can move
triplets that is, a ring having nine sets of triplets with none in
the middle (Fig. 3.14). In animal cells, a centrosome contains either in an undulating fashion, like a whip, or stiffly, like
two centrioles lying at right angles to each other. The an oar. Cells that have these organelles are capable of
centrosome is the major microtubule organizing center for the movement. For example, unicellular paramecia move by
cell, and centrioles may be involved in the process of means of cilia, whereas sperm cells move by means of
microtubule assembly and disassembly. flagella. The cells that line our upper respiratory tract have
Before an animal cell divides, the centrioles replicate, and cilia that sweep debris trapped within mucus back up into
the members of each pair are again at right angles to one another the throat, where it can be swallowed. This action helps
(Fig. 3.14). Then, each pair becomes part of a separate keep the lungs clean.
centrosome. During cell division, the centrosomes move apart In eukaryotic cells, cilia are much shorter than
and may function to organize the mitotic spindle. Plant cells flagella, but they have a similar construction. Both are
have the equivalent of a centrosome, but it does not contain membranebounded cylinders enclosing a matrix area. In
centrioles, suggesting that centrioles are not necessary to the the matrix are nine microtubule doublets arranged in a
assembly of cytoplasmic microtubules. circle around two central microtubules. Therefore, they
Centrioles are believed to give rise to basal bodies that have a 9 2 pattern of microtubules. Cilia and flagella move
direct the organization of microtubules within cilia and flagella. when the microtubule doublets slide past one another (Fig.
In other words, a basal body does for a cilium (or flagellum) 3.15).
what the centrosome does for the cell. As mentioned, each cilium and flagellum has a basal
body lying in the cytoplasm at its base. Basal bodies have
the same circular arrangement of microtubule triplets as
centrioles and are believed to be derived from them. The
62 Part I cell biology

basal body initiates polymerization of the nine outer

doublets of a
cilium or flagellum

Cilia and flagella, which have a 9 2 pattern of

microtubules, enable some cells to move.
-visual focus
64 Part I cell biology

outer
The shaft of microtubule
flagellum has a ring doublet
of nine microtubule
doublets anchored
to a central pair of dynein
microtubules. side arms
central
microtubules
radial
spokes

Flagellum
flagellum 25 nm
cross section dynein side arm
The side arms of each
doublet are composed
of dynein, a motor
molecule.
plasma
membrane

Sperm Flagellum

shaft

ATP

triplets In the presence of ATP,

the dynein side arms
reach out to their
neighbors, and bending
occurs.

Basal body
The basal body of a flagellum
has a ring of nine
microtubule triplets with no
central microtubules.

Basal body
cross section 100nm

FIGURE 3.15Structure of a flagellum or cilium.

A basal body, derived from a centriole, is at the base of a flagellum or cilium. The shaft of a flagellum (or cilium) contains microtubule
doublets whose side arms are motor molecules that cause the flagellum (such as those of sperm) to move. Without the ability of sperm to
move to the egg, human reproduction would not be possible.

6
1
 3.3 Prokaryotic Cells many different kinds of enzymes. Prokaryotes are
adapted to living in almost any kind of environment
Prokaryotic cells, the other major type of cell, does not and are diversified to the extent that almost any kind
have a nucleus as eukaryotic cells do. Archaea and bacteria of organic matter can be used as a nutrient for some
are both prokaryotes, cells so small they are just visible particular type. The cytoplasm is the site of thousands
with the light microscope. of chemical reactions, and prokaryotes are more
Figure 3.16 illustrates the main features of bacterial metabolically competent than are human beings.
anatomy. The cell wall contains peptidoglycan, a complex Given adequate nutrients, most prokaryotes are able
molecule with chains of a unique amino disaccharide joined to synthesize any kind of molecule they may need.
by peptide chains. In some bacteria, the cell wall is further Indeed, the metabolic capability of bacteria is
surrounded by a capsule and/or gelatinous sheath called a exploited by humans, who use them to produce a
slime layer. Motile bacteria usually have long, very thin wide variety of chemicals and products for human
appendages called flagella (sing., flagellum) that are use.
composed of subunits of the protein called flagellin. The
flagella, which rotate like propellers, rapidly move the
Bacteria are prokaryotic cells with these constant
bacterium in a fluid medium. Some bacteria also have
features.
fimbriae, which are short appendages that help them attach
to an appropriate surface. Outer boundaries: Cell wall
The cytoplasm of prokaryotic cells like that of Plasma membrane
eukaryotic cells is bounded by a plasma membrane. Cytoplasm: Ribosomes
Prokaryotes have a single chromosome (loop of DNA) Thylakoids (cyanobacteria)
located within a region called the nucleoid but it is not
Innumerable enzymes
bounded by membrane. Many prokaryotes also have small
accessory rings of DNA called plasmids. The cytoplasm Nucleoid: Chromosome (DNA only)
has thousands of ribosomes for the synthesis of proteins. In
addition, the photosynthetic cyanobacteria have light-
sensitive pigments, usually within the membranes of
flattened disks called thylakoids.
Although prokaryotes are structurally simple,
they are actually metabolically complex and contain

flagellum ribosome plasma membrane

cytoplasm
cell wall nucleoid
ribosome
slime layer
nucleoid
capsule thylakoid

cell wall cytoplasm

plasma membrane

250 nm 25 µm
a. b.

FIGURE 3.16 Bacterial cells.

a. Nonphotosynthetic bacterium. b. Cyanobacterium, a photosynthetic bacterium, formerly called a blue-green alga.
66 Part I cell biology

3.4 Evolution of the Eukaryotic Cell Chapter 3 cell structure and function

How did the eukaryotic cell arise? Invagination of the

plasma membrane might explain the origin of the vesicle, and the inner one may be derived from the
nuclear envelope and organelles, such as the plasma membrane of the original prokaryote.
endoplasmic reticulum and the Golgi apparatus. 3. Mitochondria and chloroplasts contain a limited
Some believe that the other organelles could also amount of genetic material and divide by splitting.
have arisen in this manner. Their DNA (deoxyribonucleic acid) is a circular loop
Another, more interesting, hypothesis has been like that of prokaryotes.
put forth. It has been observed that, in the laboratory, 4. Although most of the proteins within mitochondria
an amoeba infected with bacteria can become and chloroplasts are now produced by the eukaryotic
dependent upon them. Some investigators believe host, they do have their own ribosomes and they do
that mitochondria and chloroplasts are derived from produce some proteins. Their ribosomes resemble
prokaryotes that were taken up by a much larger cell those of prokaryotes.
(Fig. 3.17). Perhaps mitochondria were originally 5. The RNA (ribonucleic acid) base sequence of the
aerobic heterotrophic bacteria, and chloroplasts were ribosomes in chloroplasts and mitochondria also
originally cyanobacteria. The host eukaryotic cell suggests a prokaryotic origin of these organelles.
would have benefited from an ability to utilize
It is also just possible that the flagella of eukaryotes
oxygen or synthesize organic food when, by chance,
are derived from an elongated bacterium that became
the prokaryote was taken up and not destroyed. In
attached to a host cell (Fig. 3.17). However, it is important
other words, after these prokaryotes entered by
to remember that the flagella of eukaryotes are constructed
endocytosis, a symbiotic relationship would have
differently. In any case, the acquisition of basal bodies,
been established. Some of the evidence for this
which could have become centrioles, may have led to the
endosymbiotic hypothesis is as follows:
ability to form a spindle during cell division.
1. Mitochondria and chloroplasts are similar to bacteria
in size and in structure.
According to the endosymbiotic hypothesis,
2. Both organelles are bounded by a double membrane heterotrophic bacteria became mitochondria, and
— cyanobacteria became chloroplasts after being taken
the outer membrane may be derived from the
up by precursors to modern-day eukaryotic cells.
engulfing

FIGURE 3.17 Evolution of the eukaryotic cell.

Invagination of the plasma membrane could account for the formation of the nucleus and certain other organelles. The endosymbiotic hypothesis
suggests that mitochondria, chloroplasts, and flagella are derived from prokaryotes that were taken up by a much larger eukaryotic cell.
ubioethical focus
Use of Stem by Nazis when they umbilical blood for
experimented on future use. Once
Cells death camp inmates researchers have the
— know-how, it may

S
“after all, they are
tem cells are eventually be
going to be killed possible to use any
immature cells anyway.”
that develop type of stem cell to
Parkinson disease cure many of the
into mature, and Alzheimer
differentiated cells disorders afflicting
disease are human beings.
that make up the debilitating
adult body. For neurological
example, the red bone disorders that people
marrow contains stem Decide Your
fear. It is possible that
cells for all the many Opinion
one day these
different types of disorders could be 1. Should
blood cells in the cured by supplying researchers have
bloodstream. the patient with new access to
Embryonic cells are nerve cells in a embryonic stem
an even more suitable critical area of the cells? Any
source of stem cells. brain. Suppose you source or just
The early embryo is had one of these certain sources?
simply a ball of cells, disorders. Would you Which sources
and each of these want to be denied a and why?
cells has the potential cure because the 2. Should an
to become any type government doesn’t individual have
— support
of cell in the body a access to stem
muscle cell, a nerve experimentation on cells from just
cell, or a pancreatic human embryonic his own body?
cell, for example. stem cells? Also from a
The use of stem There are other relative’s body?
cells from aborted possible sources of Also from a
embryos or frozen stem cells. It turns out child’s umbilical
embryos left over that the adult body cord? From
from fertility not only has blood embryonic cells?
procedures is stem cells, it also has
3. Should
controversial. Even neural stem cells in
differentiated
though quadriplegics, the brain. It has even
cells
like Christopher been possible to coax
fromwhatever
Reeve, and others blood stem cells and
source eventually
with serious illnesses neural stem cells to
become some other be available for
may benefit from this sale to patients
research, so far the types of mature cells
found in the body. A who need them?
government will not
possible source of After all, you are
fund such research.
blood stem cells is a now able to buy
One senator said it
baby’s umbilical artificial parts,
reminds him of the
cord, and it is now why not living
rationalization used
possible to store parts?
Summarizing the micrometers. Cells must
remain small in order to have
Concepts an adequate amount of surface
area per cell volume for
exchange of molecules with
3.1 The Cellular Level of the environment.
Organization
All organisms are composed of
3.2 Eukaryotic Cells
cells, the smallest units of
The nucleus of eukaryotic
living matter. Cells are capable
cells, which include animal and
of self-reproduction, and new
plant cells, is bounded by a
cells come only from
nuclear envelope containing
preexisting cells. Cells are so
pores. These pores serve as
small they are measured in
passageways between the molecules by producing
cytoplasm and the hydrogen peroxide that
nucleoplasm. Within the is subsequently broken
nucleus, the chromatin is a down.
complex of DNA and protein. Cells require a
In dividing cells, the DNAis constant input of energy
found in discrete structures to maintain their
called chromosomes. The structure. Chloroplasts
nucleolus is a special region of capture the energy of the
the chromatin where rRNA is sun and carry on
produced and where proteins photosynthesis, which
from the cytoplasm gather to produces carbohydrates.
form ribosomal subunits. Carbohydratederived
These subunits are joined in products are broken
the cytoplasm. Ribosomes are down in mitochondria at
organelles that function in the same time as ATP is
protein synthesis. They can be produced. This is an
bound to ER or can exist oxygen-requiring
within the cytoplasm singly or process called cellular
in groups called respiration.
polyribosomes. The cytoskeleton
The endomembrane contains actin filaments,
system includes the ER (both intermediate filaments,
rough and smooth), the Golgi and microtubules. These
apparatus, the lysosomes, and maintain cell shape and
other types of vesicles and allow the cell and its
vacuoles. The endomembrane organelles to move.
system serves to Microtubules radiate out
compartmentalize the cell and from the centrosome and
keep the various biochemical are present in centrioles,
reactions separate from one cilia, and flagella. They
another. Newly produced serve as tracks along
proteins enter the ER lumen, which vesicles and other
where they may be modified organelles move due to
before proceeding to the the action of specific
interior of the smooth ER. The motor molecules. Actin
smooth ER has various filaments, the thinnest
metabolic functions depending filaments, interact with
on the cell type, but it also the motor molecule
forms vesicles that carry myosin in muscle cells
proteins and lipids to the Golgi to bring about
apparatus. The Golgi apparatus contraction; in other
processes proteins and cells, they pinch off
repackages them into daughter cells and have
lysosomes, which carry out other dynamic functions.
intracellular digestion, or into Intermediate filaments
vesicles that fuse with the support the nuclear
plasma membrane. Following envelope and the plasma
fusion, secretion occurs. membrane and probably
Vacuoles are large storage participate in cell-to-cell
sacs, and junctions.

64
vesicles are smaller ones. 3.3 Prokaryotic Cells
The large single plant Prokaryotic cells do not
cell vacuole not only have a nucleus. They do
stores substances but have a plasma
also lends support to the membrane and
plant cell. cytoplasm. Prokaryotic
Peroxisomes cells have a nucleoid that
contain enzymes that is not bounded by a
were produced by nuclear envelope. They
cytoplasmic ribosomes. also lack most of the
These enzymes oxidize other organelles that
compartmentalize b. chloroplasts,
eukaryotic cells. chloroplasts
c. thylakoids,
chloroplasts
3.4 Evolution of the d. chloroplasts,
Eukaryotic Cell thylakoids
The nuclear envelope, –
most likely, evolved For questions 6 9,
through invagination of match the statements to
the plasma membrane, the terms in the key.
but mitochondria and Key:
chloroplasts may have a. chloroplasts
arisen through b. amyloplasts
endosymbiotic events. c. vacuoles
Testing Yourself d. nucleus
6. All eukaryotic cells
7. Photosynthetic site
Choose the best 8. Stores starch
answer for each 9. May contain toxins
question. 10. The Golgi apparatus can
1. Proteins produced at be found in
cytoplasmic ribosomes ____________ cells.
are a. animal
a. used in the cell. b. plant
b. used by other c. bacteria
cells. d. Both a and b are
c. never used at correct.
all. 11. ___________ are (is)
d. None of the produced by the Golgi
above is correct. and contains
2. Which is associated with ____________.
DNA? a. Lysosomes,
a. chromatin DNA
b. chromosome b. Mitochondria,
c. nucleus DNA
d. All of the above c. Lysosomes,
are correct. enzymes
3. Secondary cell walls are d. Nucleus, DNA
Chapter 3
found in ____________
and contain 65
________________. a.
animals, ligand
b. animals, 12. Mitochondria and
cellulose chloroplasts contain
c. plants, ligand ____________ and are
d. plants, cellulose able to synthesize
___________. a. RNA ,
4. Which is characteristic of
fatty acids
prokaryotic cells?
b. DNA, proteins
a. nucleus
c. DNA, fatty acids
b. mitochondria
d. cholesterol, fatty acids
c. nucleoid
d. All of the above 13. Which of these are
are correct. involved in the movement
of structures inside a cell?
5. Eukaryotic cells are
a. actin
associated with
b. microtubules
____________, and
c. centrioles
prokaryotic cells are
d. All of the above are
associated with
correct.
____________. a.
chloroplasts, nucleus
14. Peroxisomes import 22. Vacuoles are more
enzymes from the common in
____________ and are a. animal cells.
numerous in cells b. plant cells.
breaking down c. Both a and b are
______________. a. correct.
Golgi, glucose d. Neither a nor b
b. Golgi, fats is correct.
c. cytoplasm, glucose 23. A “9 2” formation refers
d. cytoplasm, fats to
15. Which of these could you a. cilia.
see with a light b. flagella.
microscope? c. centrioles.
a. atom d. Both a and b are
b. amino acid correct.
c. proteins 66 Part I cell biology
d. None of the
above is correct.
24. The “waste” products of
–
For questions 16 20, match the photosynthesis are
structure to the function in the a. carbohydrates and
key. oxygen.
Key: b. carbon dioxide and
a. movement of cell water.
b. processing of proteins c. oxygen and water.
c. photosynthesis d. carbohydrates and
d. ribosome formation water.
e. synthesizes 25. Label the structures in
phospholipids this prokaryotic cell.
16. Chloroplasts 31. Which of the
17. Flagella following
structures
18. Golgi
would be
19. Smooth ER found in both
20. Nucleolus plant and
21. Which of these depicts a animal cells? a.
hypothesized evolutionary centrioles
scenario? b. chloroplasts
c. cell wall
a. cyanobacteria→
d. mitochondria
mitochondria
e. All of these are found
b. Golgi→mitocho
in both types of cells.
ndria
c. mitochondria→
cyanobacteria
d. cyanobacteria→ Understanding the
chloroplast Terms

c. a. Cells
d. form
e. as
organelles and
b. molecules become
groupedtogether in an
a.
organized manner.
b. The normal
functioning of an
organism does not
dependon its
individual cells.
c. The cell is the basic
unit of life.
26. The cell theory states:
 d. Only eukaryotic chromatin 52
organisms are made of (pl., nucleoli) 52
cells.
chromosome 52
27. The small size of cells is
nucleoplasm 52
best correlated with
a. the fact that they are cilium (pl., cilia) 60
self-reproducing. nucleus 52
b. their prokaryotic
versus eukaryotic cristae 57
nature.
c. an adequate surface
cytoplasm 49
area for exchange of
peroxisome 55
materials.
d. their vast versatility. cytoskeleton 58
e. All of the above are membrane 49, 62
correct.
28. Mitochondria endoplasmic reticulum
a. are involved in plasmid 62
cellular respiration. (ER) 53
b. break down ATP to polyribosome 53
release energy for
cells. endosymbiotic
c. contain grana and prokaryotic cell 62
cristae.
d. have a convoluted hypothesis 63
outer membrane. ribosome 53, 62
e. All of the above are eukaryotic cell 49
correct. secretion 54
29. Which of these is broken
down during cellular flagellum (pl., flagella)
respiration? slime layer 62
a. carbon dioxide
60, 62
b. water
c. carbohydrate glycoprotein 53
d. oxygen thylakoid 57, 62
e. Both c and d are
correct. Golgi apparatus 54
30. Which of the following is vacuole 55
not one of the three granum (pl., grana) 57
components of the vesicle 53
cytoskeleton? a. flagella
b. actin filaments lysosome 55
c. microtubules
d. intermediate filaments Match the terms to these
capsule 62 matrix 57 definitions:
a.__________________
cell 46
__ Unstructured
microtubule 58 semifluid
cell theory 46 substance that
mitochondrion 56 fills the space
between cells in
cell wall 49, 62 connective
motor molecule 58 tissues or inside
organelles.
centriole 60 nuclear b._________________
envelope 52 ___ Dark-
staining,
centrosome 58 spherical body in
nuclear pore 52 the nucleus that
chloroplast 56 produces
nucleoid 62
 ribosomal
subunits.
c.__________________
__ Internal
framework of the
cell, consisting
of microtubules,
actin filaments,
and intermediate
filaments.
d.__________________
__ Organelle
consisting of
saccules and
vesicles that
processes,
packages, and
distributes
molecules about
or from the cell.
e.__________________
__ System of
membranous
saccules and
channels in the
cytoplasm, often
with attached
ribosomes.