Human diseases are characterized by abnormalities in cellular function. Discuss a human disease caused by defective function of an organelle.
73
The Cell As a City
© Kendall Hunt Publishing Company
3
EssEnTiAls
Theta and Joules are in a clique – Sally is not
accepted
The cell is like a city
Primitive cells absorb mitochondria-like organismsA cell with its organelles
©
ol
iv
er
om
g/
S
hu
tte
rs
to
ck
.c
om
©
K
en
da
ll
H
un
t P
ub
lis
hi
ng
C
om
pa
ny
A
da
pt
ed
fr
om
A
na
to
m
y
I a
nd
P
hy
si
ol
og
y
Le
ct
ur
e
M
an
ua
l b
y
Jo
hn
E
ric
ks
on
ganelles
Microvilli
PeroxisomeCentrioles
Plasma Membrane
Cilia
Lysosome
Nucleus
Nucleolus
Chromatin (Threads)
Nuclear Envelope
Rough Endoplasmic Reticulum
(R.E.R.)
Flagellum
Phospholipid Bilayer
Smooth Endoplasmic Reticulum
(S.E.R.)
Golgi Apparatus
Microtubules
Ribosomes
Mitochondri
Cytosol (Cytoplasmic fluid)
Cytoplasm (Cell contents outside nucleus)
Vesicle
yy
s like a city
al
l H
un
t P
ub
lis
hi
ng
C
om
pa
ny
al
l H
un
t P
ub
lis
hi
ng
C
om
pa
ny
tP
ub
lis
hi
ng
C
om
pa
ny
P
bl
i
hi
C
P
bl
i
hi
C
©
K
d
The cell iss like a city
ll
H
PPP
bl
i
hi
C
bl
i
hi
C
Mitochondria ©
D
es
ig
nu
a,
/S
hu
tte
rs
to
ck
.c
om
C
. M
ic
ha
el
F
re
nc
h.
C
op
yr
ig
ht
©
2
00
7
by
K
en
da
ll
H
un
t P
ub
lis
hi
ng
C
om
pa
ny
. R
ep
rin
te
d
by
p
er
m
is
si
on
ch03.indd 73 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
74 Unit 1: That’s Life
ChECk in
From reading this chapter, you will be able to:
• Explain how differences caused by inherited organelles could have societal implications.
• Describe how the characteristics that are valued change from culture to culture and over time.
• Outline the cell theory, list and describe types of cells, and explain endosymbiosis.
• List and describe the organelles found in a cell, and explain their main functions.
• Explain the processes of diffusion, osmosis, facilitated diffusion, active transport, and bulk transport.
The Case of the Meddling houseguest:
A Friendship Divided
Theta and Joules liked their friend Sally, but when they entered college, they learned
that Sally was different. When they were all young, they played together on the block,
went to each other’s birthday parties, and had some great sleepovers. “We had a lot of
fun with Sally in sixth grade . . . I wish she could join our sorority,” said Theta. Aghast at
the thought, Joules replied, “Don’t even say it – you know what that would mean for us.
We shouldn’t even admit that we know her.”
“Why can I not hang out with people I like? . . . Am I not allowed to be Sally’s
friend because of some test?” thought Theta. “There is no law against me being friends
with Sally!” exclaimed Theta, after a long pause. Joules dismissed Theta smugly, “You
know you can’t do it. It will never happen.” They were expecting Sally to come into the
dorm any minute. Sally was expecting to hang out with them as usual. But on this day,
their friendship had to end. On this day, Joules and Theta were going to pledge their new
sorority . . . and Sally did not have the mark.
It was an advanced society, in 2113 with all of the comforts – space travel beyond
the solar system, teleporting, and no more diseases that the ancients had; instead there
were life spans approaching two centuries for the marked people. Humans had it better
than ever, and teens had the world in their hands. Everyone with parents that had any
sense had a mark on their children to denote their superior genetic lineage. People in
the line of descent from genetically modified mitochondria had an “M” on the inside
of their ears. Their life expectancy was much higher and their health much better than
those without the mark. Finding out about one’s mitochondrial DNA was easy, with tests
dating back over 100 years to trace the origin of one’s genes.
Mitochondria are organelles that make energy for a cell; they are inherited from
mother to children because they have their own genetic material and divide on their
own. Mitochondria are, in fact, separate structures existing within our cells. They were
absorbed some 2.5 billion years ago, with their own set of DNA, making them houseg-
uests in our bodies.
The genes in the mitochondria stay intact from generation to generation. “This is
why the mark was so important – the health benefits,” thought Theta. Mitochondrial
DNA with modified genes of a particular line of mitochondria made people much health-
ier, free of many diseases in the society of this story. Mitochondria are the meddling
houseguests in the title because defects in them cause a range of diseases. For example,
Mitochondria
Is the organelle that
makes energy for a
cell.
Organelle (subcel-
lular structure)
Structures that
function within cells in
a discrete manner
ch03.indd 74 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 75
mitochondrial defects in the 21st century were responsible for many ailments, ranging
from heart disease and diabetes to chronic sweating, optic nerve disorders, and epilepsy.
Joules told Theta, “People without the mark are jealous of us because they die earlier
and have a worse life with more diseases. You know Sally would never understand us.
Sally’s genes are still from the 21st century.” But something still bothered Theta: She
liked Sally. Sally came into the dorm and Joules explained that they were leaving for the
sorority. Sally knew what that meant and said good-bye. Theta looked deeply at Sally,
realizing that their past was gone and that they would not see each other again as friends.
Sally and Theta both had a single tear in their eyes and they knew they were part of each
other’s youth . . . and that meant something.
But Theta looked back one last time and said thoughtfully to herself, “She’s not one
of us.”
Culture, Biology, and social stratification
Culture plays an important role in defining what is desirable and valued in society. Often
decisions on what it means to be “better” are based on cell biology. Our genetic material
makes each of us unique and guides the workings of our cells. We all have the same set
of cell structures or organelles, but, as in our story, genetic variations give each per-
son unique characteristics. While the opening story is science fiction, its possibilities
are real. Gene technology is improving human health and has the potential to “design”
human genes and organelles, possibly leading to social issues like those described in the
conflict faced by Sally, Joules, and Theta.
Biological differences may lead to social changes based on what a society values
at any one time. For example, research shows that certain biological features are used
to decide social value of people: symmetry of one’s face, body fat distribution in both
genders, and musculature in males; smooth skin, good teeth, and a uniform gait. These
are all biologically determined, based on how our cell structures work together. Much
as mitochondrial inheritance, described in the story dictates health and organismal func-
tioning, all cell structures give living systems their characteristics.
Historically, all cultures have used biology to classify people. Humans are suscepti-
ble to group messages, such as the one that influenced Theta’s and Joules’ final decision
to abandon their friendship with Sally. The average American is exposed to about 3,000
marketing messages per day. This sets up a value system that requires us to reflect on
how biology and society can affect our thinking.
ChECk Up sECTion
The exclusion of people in our futuristic science fiction story reflects a theme in human society and
history. As a result of cell differences between Theta and Sally, their friendship ended – each possessed
a different type of mitochondrion.
Choose a particular situation in which a social stratification (layering) system is set up in a society,
in which one group thinks it is better than another. You may choose a present system or one of the
past. Is the stratification system reasonable? Is the system based on cell biology? What are the system’s
benefits? What are its drawbacks?
ch03.indd 75 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
76 Unit 1: That’s Life
BOdy Art And Skin BiOlOgy in SOciety
Body alterations in the quest for physical beauty are as old as history. Egyptians
used cosmetics in their First Dynasty (3100–2907 BC). Hairstyles, corsets, body-
weight goals, and body piercing and tattooing trends have changed through human
history. Scars have been viewed as masculine and a mark of courage, and tattoos
were drawn and carved in ancient European, Egyptian, and Japanese worlds.
Body art was popular in modern western society among the upper classes in
the early 19th century. It lost favor due to stories of disease spreading because
of unsanitary tattoo practices. Only the lower classes adopted body art to show
group affiliation. Tattooing has recently gained popularity; but body art has been
used as a symbol of self-expression and as a social-stratification mechanism in
many cultures: Indian tattoos mark caste; Polynesians used marks for showing mar-
ital status; the Nazis marked groups from their elite SS to concentration camp pris-
oners; and U.S. gangs use it to show group membership. Tattooing has been firmly
established in societies and continues to grow in popularity in the United States.
The canvas for tattoos is skin, which is part of the integumentary system
and has a variety of functions in humans (Figure 3.1). It
• maintains temperature;
• stores blood and fat; and
• provides a protective layer.
We will discuss this important system in a later chapter.
In this chapter, we will look at the structure and function of the eukaryotic cell. We
will see that, while there are marked differences between plant and animal cells, the
basic processes carried out at the cellular level are remarkably the same, as are those of
simple, unicellular organisms. We will compare the organelles (structures) of the cell
to functions of a city to emphasize that all parts are needed. Each organelle has its own
duties, and the parts work together to make an efficient machine. We begin by looking at
the development of the microscope, without which our understanding of cells and how
they function would be incomplete.
Figure 3.1 Tattoos and body art. Dyes penetrate into the skin cells of a tattoo.
©
F
X
Q
u
a
d
ro
/S
h
u
tt
e
rs
to
c
k.
c
o
m
ch03.indd 76 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 77
Exploring the Cell
The Microscope
The human body is composed of over 10 trillion cells, and there are over 200 different
types of cells in a typical animal body, with an amazing variety in sizes (see Figure 3.2).
Despite the variety in size, all of these cells and the structures within them are too small
Figure 3.2 Biological size and cell diversity. When comparing the relatives’ sizes of
cells, we use multiples of 10 to show differences. The largest human cell, the female
egg, is 100 µm, while the smallest bacterial cell is 1000 times smaller at 100 nm. Most
cells are able to be seen with the light microscope. The smallest object a human eye can
see is about 1 mm, the size of a human egg cell (or a grain of sand). From Introductory
Plant Science, by Cynthia McKenney et al.
©
2
01
4
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
0.1 nm
Atoms
Small
molecules
Proteins
Viruses
Nucleus
Mitochondria
Lipids
Ribosomes
Smallest bacteria
Most
bacteria
Most plant and
animal cells
Fish egg
Human height
1 nm
10 nm
100 nm
1 �m
10 �m
1 mm
1 cm
0.1 m
1 m
10 m
100 �m
Li
gh
t m
ic
ro
sc
op
e
U
na
id
ed
h
um
an
e
ye
E
le
ct
ro
n
m
ic
ro
sc
op
e
Bird egg
ch03.indd 77 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
78 Unit 1: That’s Life
to be visible to our naked eyes and can only be identified by using microscopes to
magnify them.
There are several types of microscopes; perhaps the one with which you are already
familiar is the compound light microscope. The compound light microscope uses two
lenses: an ocular and an objective lens. Each of these is a convex lens, meaning that its
center is thicker than its ends. Convex lenses bring light to a central, converging point to
magnify the specimen. A microscope’s parts are seen in Figure 3.3.
The purpose of a microscope is to magnify subcellular parts. What is magnifica-
tion? Magnification is the amount by which an image size is larger than the object’s size.
If a hair cell’s image is 10 times bigger than its original object, the magnification is 10
times. If it is 100 times bigger, then the magnification is 100 times. The microscope uses
two lenses to magnify the specimen: an ocular (eyepiece), which generally magnifies
between 10 and 20 times, and a series of objective lenses (each with higher magnifica-
tions). The total magnification of a specimen is equal to the ocular (in this example let’s
use10 times) times the magnification of one of the objective lenses.
Most animal cells are only 10–30 µm in width. It would take over 20 cells to span the
width of a single millimeter. Recall that a millimeter is only as wide as the wire used to
make a paper clip. See Table 3.1 for measurements used for looking at living structures.
How were cells and their smaller components discovered using the microscope?
Anton van Leeuwenhoek and Marcello Malpighi built microscopes in the late 1600s. At
this time, those instruments were very rudimentary. They consisted of a lens or a com-
bination of lenses to magnify smaller objects, including cells. Both scientists used their
instruments to observe blood, plants, single-celled animals, and even sperm. Van Leeu-
wenhoek’s microscope is shown in Figure 3.4. At about the same time that van Leeuwen-
hoek and Malpighi were making their observations, Robert Hooke (1635–1703) coined
the term cell, as he peered through a primitive microscope of his own construction.
When he viewed tissues of a cork plant, Hooke saw what seemed to be small cavities
separated by walls, similar to rooms or “cells” in a monastery (see Figure 3.4). These
cells are defined as functioning units separated from the nonliving world.
Although it has progressed in design, materials, and technology, the compound light
microscope is based on the same principle as in the 17th century: light bends as it passes
through the specimen to create a magnified image. Some amount of light always bends
compound light
microscope
Microscope that uses
two sets of lenses
(an ocular and an
objective lens).
Magnification
Is the amount by
which an image size is
larger than the object’s
size.
Figure 3.3 Compound light microscope – its parts and internal lens system.
©
R
Ti
m
a
g
e
s/
Sh
u
tt
e
rs
to
c
k.
c
o
m
ch03.indd 78 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 79
when hitting the edges of the lens, causing scattering in a random way. The random
scattering of light, called diffraction is bad for getting a clear focus on the image. Dif-
fraction also limits the resolution of the image. Resolution is defined as the ability to see
two close objects as separate. (Think about looking at two lines on a chalkboard that is
very far away; chances are they blur together and look like one messy line.) In fact, the
human eye has a resolving power of about 100 µm or 1/10th of a millimeter for close-up
images. In other words, two lines on a paper closer than 1/10th of a millimeter apart look
blurry to us. The light microscope is limited in the same way by diffraction because the
diffracted rays create blurry images.
diffraction
The random scattering
of light.
resolution
Is the ability to see
two close objects as
separate.
Figure 3.4 Hooke’s microscope from the 1600s and van Leeuwenhoek with his
microscope. These simple microscopes led to the first descriptions of cells. Van
Leeuwenhoek’s microscope consisted of a small sphere of glass in a holder.
1 centimeter (cm) =
1/100 meter or 0.4 inch
3 cm
Ch
ick
en
e
gg
(th
e
“y
olk
“)
1 mm
Fr
og
e
gg
, f
ish
e
gg
1 meter = 102 cm = 103 mm = 106 µm =109 nm
Unaided human eye
1 millimeter (mm) =
1/1,000 meter
1 micrometer (µm) =
1/1,000,000 meter
1 nanometer (nm) =
1/1,000,000 meter
100 µm
Hu
m
an
e
gg
Light microscopes
Electron microscopes
10–100
Ty
pic
al
pla
nt
ce
ll
5–30
Ty
pic
al
an
im
al
ce
ll
2–10
Ch
lor
op
las
t
1–5
M
ito
ch
on
dr
ion
5
An
ob
ae
no
(c
ya
no
ba
cte
riu
m
)
1
Es
ch
er
ich
ia
co
li
100 nm
La
rg
e
vir
us
(H
IV
,
inf
lue
nz
a
vir
us
)
25
Ri
bo
so
m
e
7–10
Ce
ll m
em
br
an
e
(th
ick
ne
ss
)
2
DN
A
do
ub
le
he
lix
(d
iam
et
er
)
0.1
Hy
dr
og
en
a
to
m
table 3.1 Measurements Used for Microscopy. The units of measurement used in the study of molecules
and cells correspond with methods by which we are able to detect their presences.
©
K
e
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y
ch03.indd 79 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
80 Unit 1: That’s Life
Higher magnification under the microscope leads to greater diffraction. This is the
reason a compound light microscope can magnify only up to 1000–1500 times (under
oil immersion), after which there is too much diffraction for a clear image to be formed.
To overcome the effect of diffraction and achieve clarity at higher magnifications, oil is
placed on the slide. However, even with oil immersion, only the large nucleus of a cell
can be seen; other organelles appear as small dots or not at all.
So how did the more complex world of even smaller structures within cells get dis-
covered? The 1930s saw the development of the electron microscope that allowed for
magnifications of over 200,000 times greater than that of the human eye. There are two
types of electron microscopes: transmission electron microscope (TEM) and scanning
electron microscope (SEM). Transmission electron microscopy allows a resolving power
of roughly 0.5 nm (see Table 3.1) that visualizes structures as small as five times the
diameter of a hydrogen atom. Electron microscopes use electrons instead of light, which
limits diffraction and increases resolution. Magnets instead of lenses focus electrons to
create the image. The electrons pass through very thin slices of the specimen and form
an image.
A SEM looks at the surfaces of objects in detail, while a TEM magnifies structures
within a cell. The SEM has a resolving power slightly less than the TEM, at 10 nm. (A
depiction of an electron microscope is shown in Figure 3.5.) Electron microscopy has
led to many scientific developments, uncovering subcellular structures to help us under-
stand cell biology. Seeing a mitochondrion enables us to better understand diseases and
perhaps, if our opening story becomes reality, improve societal health through its use.
Cell Theory
Fairly recent advances in microscopy have allowed scientists to learn about the structure
and function of even the tiniest components of cells, but the cell theory, which states key
ideas about cells, developed a long time ago. We have seen that scientists began study-
ing cells in the early 1700s. About a century later, in 1838, a German botanist named
Matthias Schleiden (1804–1881) concluded that all plants he observed were composed
of cells. In the next year, Theodor Schwann (1810–1882) extended Schleiden’s ideas,
transmission elec-
tron microscope
(teM)
A type of electron
microscope that
magnifies structures
within a cell.
Scanning electron
microscope (SeM)
An electron
microscope that
looks at the surfaces
of objects in detail
by focusing a beam
of electrons on the
surface of the object.
Figure 3.5 a. A researcher sits at a modern electron microscope. b. Apple tree pollen grains on cells, an
electron micrograph.
©
L
a
rr
y
Br
u
c
e
/S
h
u
tt
e
rs
to
c
k.
c
o
m
©
D
ra
g
o
n
Im
a
g
e
s
(a) (b)
ch03.indd 80 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 81
observing that all animals are also made of cells. But how did these cells come to survive
generation after generation? The celebrated pathologist Rudolf Virchow (1821–1902)
concluded in 1858 that all cells come from preexisting cells (He wrote this in Latin:
“Cellula e cellula”). These scientists contributed, together, to the postulates of the cell
theory. The cell theory is a unifying theory in biology that places the cell as the center of
life and unifies the many branches of biology under its umbrella. The cell theory states
that:
1) All living organisms are composed of cells.
2) The chemical reactions that occur within cells are separate from their
environment.
3) All cells arise from other cells.
4) Cells contain within them hereditary information that is passed down from par-
ent cell to offspring cell.
The cell theory showed not only that cells are the basic unit of life, but that there is
continuity from generation to generation. Genetic material is inherited in what we refer
today as the cell.
Types of Cells
Microscopes allowed researchers to examine differences between organisms that had
previously been impossible to determine. A current classification of organisms defines
five kingdoms, with organisms in those kingdoms having similar types of cells (There
is some debate arguing inclusion of Archaea bacteria as a separate kingdom, and a six-
system classification scheme is thus also accepted). Cells of organisms in the five king-
doms each have many internal differences, as summarized in Table 3.2. Images of some
organisms of each kingdom are given in Figure 3.17 as examples.
Prokaryotes (bacteria) are composed of cells containing no membrane-bound
nucleus and no compartments or membranous organelles. They are much smaller than
eukaryotes, by almost 10 times. Prokaryotic genetic material is “naked,” without the
protection of a membrane and nucleus. They are composed of very few cell parts: a
membrane, cytoplasm, and only protein-producing units called ribosomes. Even without
most structures found in other organisms, prokaryotes contain genetic material to repro-
duce and direct the functions of the chemical reactions occurring within its cytoplasm.
group domain cell type cell number cell Wall component energy Acquisition
Bacteria Bacteria Prokaryotic Unicellular Peptidoglycan Mostly heterotrophic,
some are autotrophic
Protists Eukarya Eukaryotic Mostly unicellular,
some are simple
multicellular
Cellulose, silica; some have
no cell wall
Autotrophic,
heterotrophic
Plants Eukarya Eukaryotic Multicellular Cellulose Autotrophic
Animals Eukarya Eukaryotic Multicellular No cell wall Heterotrophic
Fungi Eukarya Eukaryotic Mostly multicellular Chitin Heterotrophic
From Introductory Plant Science by Cynthia McKenney et al. Copyright © 2014 by Kendall Hunt Publishing Company. Reprinted by
permission.
table 3.2 Differences in Cell Structure within the Five Kingdoms: Plants, Animals and Prokaryotes.
ch03.indd 81 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
82 Unit 1: That’s Life
Prokaryotes have a simple set-up, but all of the needed equipment to carry out life func-
tions. Bacteria have a rapid rate of cell division and a faster metabolism than eukaryotes.
Most organisms on Earth, in terms of sheer number, are prokaryotes.
• As indicated in Chapter 1, prokaryotes include organisms in the Bacteria and
Archae domains. These organisms will be discussed further in Chapter 8.
All other organisms (plants, animals, fungi, and protists) are eukaryotes. Cells of
eukaryotes are complex, containing a membrane-bound nucleus that houses genetic
material. Eukaryotic cells comprise compartments that form a variety of smaller internal
structures, or organelles. Eukaryotic cells are the focus of this chapter, which will give
an overview of the primary organelles and their functions (Figure 3.6).
Eukaryotes may be examined by dividing into its four groups: plants, animals, fungi,
and protists. Plants contain cells that are surrounded by a cell wall, a rigid structure giv-
ing its organisms support. Plant cells contain chloroplasts, which enable plants to carry
out photosynthesis, using energy from sunlight to make food.
• Plant cell walls contain cellulose, which gives structure to plants as discussed
in Chapter 2. The process of photosynthesis, producing food for plants, will be
further discussed in Chapter 4.
Plants also have large vacuoles or storage compartments to hold water and minerals for a
plant’s functions. While both plants and animals have a cell membrane, animal cells are
Photosynthesis
The process by which
green plants use
sunlight to synthesize
nutrients from water
and carbon dioxide.
Figure 3.6 a. Differences between prokaryotes and eukaryotes. Prokaryotes have a
generally simple structure (see top cell in figure above), while eukaryotes (the lower
cell in figure above) have multiple organelles and membranes forming complex com-
partmentalization. From Biological Perspectives, 3rd ed by BSCS. b. Differences between
plants and animals. Plant and animal cells perform different functions, and their subcel-
lular structures are also different. Plant cells have chloroplasts to produce sugar and a
cell wall to give added strength. The animal cell shown has no cell wall or chloroplasts
but possesses centrioles. From Biological Perspectives, 3rd ed by BSCS.
©
2
00
6
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
(a)
ch03.indd 82 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 83
Figure 3.6 (Continued)
(b) ©
20
06
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
ch03.indd 83 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
84 Unit 1: That’s Life
less rigid, surrounded only by a cell membrane and lacking a cell wall for support. Both
plants and animals contain membrane-bound organelles, but animals also contain a set
of small structures called centrioles, which serve in cell division. Animal cells are also
quite complex, as we will see. While lacking certain organelles, such as cell walls and
chloroplasts, they have flexible strategies to perform many functions.
Fungi have cell walls but no chloroplasts. They are not able to make their own food
and, instead live off of dead and decomposing matter as well as other living organisms,
centriole
Minute cylindrical
organelles found in
animal cells, which
serve in cell division
(not given in bold in
text).
(b) C
o
p
yr
ig
h
t
©
20
06
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
Figure 3.6 (Continued)
ch03.indd 84 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 85
to obtain energy. Mushrooms and yeasts are familiar types of fungi, which will be dis-
cussed in Chapter 7.
Some species of protists are a bit animal-like in that they are able to move; other
species are a bit plant-like in that they have chloroplasts. Protists such as Amoeba in
Figure 3.7 have varied environments. Amoeba live in freshwater and, in a rare infectious
disease, grow and destroy human brain cells. We will discuss protists in more detail in
a later chapter.
Figure 3.7 Cells of the five kingdoms. While the cells of organisms in all of the kingdoms perform similar
life functions, their individual structures enable differing functions unique to each kingdom. From Biological
Perspectives, 3rd ed by BSCS.
©
2
00
6
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
ch03.indd 85 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
86 Unit 1: That’s Life
The Role of inheritance
The stratification system depicted in our opening story is based on the inheritance of
cellular components. We know that organelles are structures that carry out functions
within a cell. In fact, organelles work in concert with one another, coming together to
Figure 3.7 (Continued)
©
2
00
6
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
ch03.indd 86 11/12/15 4:25 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 87
form a complex, dynamic cell. Mitochondria, so important in the society in our story, are
the powerhouses of the cell, providing energy for a cell’s …
73
The Cell As a City
© Kendall Hunt Publishing Company
3
EssEnTiAls
Theta and Joules are in a clique – Sally is not
accepted
The cell is like a city
Primitive cells absorb mitochondria-like organismsA cell with its organelles
©
ol
iv
er
om
g/
S
hu
tte
rs
to
ck
.c
om
©
K
en
da
ll
H
un
t P
ub
lis
hi
ng
C
om
pa
ny
A
da
pt
ed
fr
om
A
na
to
m
y
I a
nd
P
hy
si
ol
og
y
Le
ct
ur
e
M
an
ua
l b
y
Jo
hn
E
ric
ks
on
ganelles
Microvilli
PeroxisomeCentrioles
Plasma Membrane
Cilia
Lysosome
Nucleus
Nucleolus
Chromatin (Threads)
Nuclear Envelope
Rough Endoplasmic Reticulum
(R.E.R.)
Flagellum
Phospholipid Bilayer
Smooth Endoplasmic Reticulum
(S.E.R.)
Golgi Apparatus
Microtubules
Ribosomes
Mitochondri
Cytosol (Cytoplasmic fluid)
Cytoplasm (Cell contents outside nucleus)
Vesicle
yy
s like a city
al
l H
un
t P
ub
lis
hi
ng
C
om
pa
ny
al
l H
un
t P
ub
lis
hi
ng
C
om
pa
ny
tP
ub
lis
hi
ng
C
om
pa
ny
P
bl
i
hi
C
P
bl
i
hi
C
©
K
d
The cell iss like a city
ll
H
PPP
bl
i
hi
C
bl
i
hi
C
Mitochondria ©
D
es
ig
nu
a,
/S
hu
tte
rs
to
ck
.c
om
C
. M
ic
ha
el
F
re
nc
h.
C
op
yr
ig
ht
©
2
00
7
by
K
en
da
ll
H
un
t P
ub
lis
hi
ng
C
om
pa
ny
. R
ep
rin
te
d
by
p
er
m
is
si
on
ch03.indd 73 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
74 Unit 1: That’s Life
ChECk in
From reading this chapter, you will be able to:
• Explain how differences caused by inherited organelles could have societal implications.
• Describe how the characteristics that are valued change from culture to culture and over time.
• Outline the cell theory, list and describe types of cells, and explain endosymbiosis.
• List and describe the organelles found in a cell, and explain their main functions.
• Explain the processes of diffusion, osmosis, facilitated diffusion, active transport, and bulk transport.
The Case of the Meddling houseguest:
A Friendship Divided
Theta and Joules liked their friend Sally, but when they entered college, they learned
that Sally was different. When they were all young, they played together on the block,
went to each other’s birthday parties, and had some great sleepovers. “We had a lot of
fun with Sally in sixth grade . . . I wish she could join our sorority,” said Theta. Aghast at
the thought, Joules replied, “Don’t even say it – you know what that would mean for us.
We shouldn’t even admit that we know her.”
“Why can I not hang out with people I like? . . . Am I not allowed to be Sally’s
friend because of some test?” thought Theta. “There is no law against me being friends
with Sally!” exclaimed Theta, after a long pause. Joules dismissed Theta smugly, “You
know you can’t do it. It will never happen.” They were expecting Sally to come into the
dorm any minute. Sally was expecting to hang out with them as usual. But on this day,
their friendship had to end. On this day, Joules and Theta were going to pledge their new
sorority . . . and Sally did not have the mark.
It was an advanced society, in 2113 with all of the comforts – space travel beyond
the solar system, teleporting, and no more diseases that the ancients had; instead there
were life spans approaching two centuries for the marked people. Humans had it better
than ever, and teens had the world in their hands. Everyone with parents that had any
sense had a mark on their children to denote their superior genetic lineage. People in
the line of descent from genetically modified mitochondria had an “M” on the inside
of their ears. Their life expectancy was much higher and their health much better than
those without the mark. Finding out about one’s mitochondrial DNA was easy, with tests
dating back over 100 years to trace the origin of one’s genes.
Mitochondria are organelles that make energy for a cell; they are inherited from
mother to children because they have their own genetic material and divide on their
own. Mitochondria are, in fact, separate structures existing within our cells. They were
absorbed some 2.5 billion years ago, with their own set of DNA, making them houseg-
uests in our bodies.
The genes in the mitochondria stay intact from generation to generation. “This is
why the mark was so important – the health benefits,” thought Theta. Mitochondrial
DNA with modified genes of a particular line of mitochondria made people much health-
ier, free of many diseases in the society of this story. Mitochondria are the meddling
houseguests in the title because defects in them cause a range of diseases. For example,
Mitochondria
Is the organelle that
makes energy for a
cell.
Organelle (subcel-
lular structure)
Structures that
function within cells in
a discrete manner
ch03.indd 74 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 75
mitochondrial defects in the 21st century were responsible for many ailments, ranging
from heart disease and diabetes to chronic sweating, optic nerve disorders, and epilepsy.
Joules told Theta, “People without the mark are jealous of us because they die earlier
and have a worse life with more diseases. You know Sally would never understand us.
Sally’s genes are still from the 21st century.” But something still bothered Theta: She
liked Sally. Sally came into the dorm and Joules explained that they were leaving for the
sorority. Sally knew what that meant and said good-bye. Theta looked deeply at Sally,
realizing that their past was gone and that they would not see each other again as friends.
Sally and Theta both had a single tear in their eyes and they knew they were part of each
other’s youth . . . and that meant something.
But Theta looked back one last time and said thoughtfully to herself, “She’s not one
of us.”
Culture, Biology, and social stratification
Culture plays an important role in defining what is desirable and valued in society. Often
decisions on what it means to be “better” are based on cell biology. Our genetic material
makes each of us unique and guides the workings of our cells. We all have the same set
of cell structures or organelles, but, as in our story, genetic variations give each per-
son unique characteristics. While the opening story is science fiction, its possibilities
are real. Gene technology is improving human health and has the potential to “design”
human genes and organelles, possibly leading to social issues like those described in the
conflict faced by Sally, Joules, and Theta.
Biological differences may lead to social changes based on what a society values
at any one time. For example, research shows that certain biological features are used
to decide social value of people: symmetry of one’s face, body fat distribution in both
genders, and musculature in males; smooth skin, good teeth, and a uniform gait. These
are all biologically determined, based on how our cell structures work together. Much
as mitochondrial inheritance, described in the story dictates health and organismal func-
tioning, all cell structures give living systems their characteristics.
Historically, all cultures have used biology to classify people. Humans are suscepti-
ble to group messages, such as the one that influenced Theta’s and Joules’ final decision
to abandon their friendship with Sally. The average American is exposed to about 3,000
marketing messages per day. This sets up a value system that requires us to reflect on
how biology and society can affect our thinking.
ChECk Up sECTion
The exclusion of people in our futuristic science fiction story reflects a theme in human society and
history. As a result of cell differences between Theta and Sally, their friendship ended – each possessed
a different type of mitochondrion.
Choose a particular situation in which a social stratification (layering) system is set up in a society,
in which one group thinks it is better than another. You may choose a present system or one of the
past. Is the stratification system reasonable? Is the system based on cell biology? What are the system’s
benefits? What are its drawbacks?
ch03.indd 75 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
76 Unit 1: That’s Life
BOdy Art And Skin BiOlOgy in SOciety
Body alterations in the quest for physical beauty are as old as history. Egyptians
used cosmetics in their First Dynasty (3100–2907 BC). Hairstyles, corsets, body-
weight goals, and body piercing and tattooing trends have changed through human
history. Scars have been viewed as masculine and a mark of courage, and tattoos
were drawn and carved in ancient European, Egyptian, and Japanese worlds.
Body art was popular in modern western society among the upper classes in
the early 19th century. It lost favor due to stories of disease spreading because
of unsanitary tattoo practices. Only the lower classes adopted body art to show
group affiliation. Tattooing has recently gained popularity; but body art has been
used as a symbol of self-expression and as a social-stratification mechanism in
many cultures: Indian tattoos mark caste; Polynesians used marks for showing mar-
ital status; the Nazis marked groups from their elite SS to concentration camp pris-
oners; and U.S. gangs use it to show group membership. Tattooing has been firmly
established in societies and continues to grow in popularity in the United States.
The canvas for tattoos is skin, which is part of the integumentary system
and has a variety of functions in humans (Figure 3.1). It
• maintains temperature;
• stores blood and fat; and
• provides a protective layer.
We will discuss this important system in a later chapter.
In this chapter, we will look at the structure and function of the eukaryotic cell. We
will see that, while there are marked differences between plant and animal cells, the
basic processes carried out at the cellular level are remarkably the same, as are those of
simple, unicellular organisms. We will compare the organelles (structures) of the cell
to functions of a city to emphasize that all parts are needed. Each organelle has its own
duties, and the parts work together to make an efficient machine. We begin by looking at
the development of the microscope, without which our understanding of cells and how
they function would be incomplete.
Figure 3.1 Tattoos and body art. Dyes penetrate into the skin cells of a tattoo.
©
F
X
Q
u
a
d
ro
/S
h
u
tt
e
rs
to
c
k.
c
o
m
ch03.indd 76 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 77
Exploring the Cell
The Microscope
The human body is composed of over 10 trillion cells, and there are over 200 different
types of cells in a typical animal body, with an amazing variety in sizes (see Figure 3.2).
Despite the variety in size, all of these cells and the structures within them are too small
Figure 3.2 Biological size and cell diversity. When comparing the relatives’ sizes of
cells, we use multiples of 10 to show differences. The largest human cell, the female
egg, is 100 µm, while the smallest bacterial cell is 1000 times smaller at 100 nm. Most
cells are able to be seen with the light microscope. The smallest object a human eye can
see is about 1 mm, the size of a human egg cell (or a grain of sand). From Introductory
Plant Science, by Cynthia McKenney et al.
©
2
01
4
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
0.1 nm
Atoms
Small
molecules
Proteins
Viruses
Nucleus
Mitochondria
Lipids
Ribosomes
Smallest bacteria
Most
bacteria
Most plant and
animal cells
Fish egg
Human height
1 nm
10 nm
100 nm
1 �m
10 �m
1 mm
1 cm
0.1 m
1 m
10 m
100 �m
Li
gh
t m
ic
ro
sc
op
e
U
na
id
ed
h
um
an
e
ye
E
le
ct
ro
n
m
ic
ro
sc
op
e
Bird egg
ch03.indd 77 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
78 Unit 1: That’s Life
to be visible to our naked eyes and can only be identified by using microscopes to
magnify them.
There are several types of microscopes; perhaps the one with which you are already
familiar is the compound light microscope. The compound light microscope uses two
lenses: an ocular and an objective lens. Each of these is a convex lens, meaning that its
center is thicker than its ends. Convex lenses bring light to a central, converging point to
magnify the specimen. A microscope’s parts are seen in Figure 3.3.
The purpose of a microscope is to magnify subcellular parts. What is magnifica-
tion? Magnification is the amount by which an image size is larger than the object’s size.
If a hair cell’s image is 10 times bigger than its original object, the magnification is 10
times. If it is 100 times bigger, then the magnification is 100 times. The microscope uses
two lenses to magnify the specimen: an ocular (eyepiece), which generally magnifies
between 10 and 20 times, and a series of objective lenses (each with higher magnifica-
tions). The total magnification of a specimen is equal to the ocular (in this example let’s
use10 times) times the magnification of one of the objective lenses.
Most animal cells are only 10–30 µm in width. It would take over 20 cells to span the
width of a single millimeter. Recall that a millimeter is only as wide as the wire used to
make a paper clip. See Table 3.1 for measurements used for looking at living structures.
How were cells and their smaller components discovered using the microscope?
Anton van Leeuwenhoek and Marcello Malpighi built microscopes in the late 1600s. At
this time, those instruments were very rudimentary. They consisted of a lens or a com-
bination of lenses to magnify smaller objects, including cells. Both scientists used their
instruments to observe blood, plants, single-celled animals, and even sperm. Van Leeu-
wenhoek’s microscope is shown in Figure 3.4. At about the same time that van Leeuwen-
hoek and Malpighi were making their observations, Robert Hooke (1635–1703) coined
the term cell, as he peered through a primitive microscope of his own construction.
When he viewed tissues of a cork plant, Hooke saw what seemed to be small cavities
separated by walls, similar to rooms or “cells” in a monastery (see Figure 3.4). These
cells are defined as functioning units separated from the nonliving world.
Although it has progressed in design, materials, and technology, the compound light
microscope is based on the same principle as in the 17th century: light bends as it passes
through the specimen to create a magnified image. Some amount of light always bends
compound light
microscope
Microscope that uses
two sets of lenses
(an ocular and an
objective lens).
Magnification
Is the amount by
which an image size is
larger than the object’s
size.
Figure 3.3 Compound light microscope – its parts and internal lens system.
©
R
Ti
m
a
g
e
s/
Sh
u
tt
e
rs
to
c
k.
c
o
m
ch03.indd 78 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 79
when hitting the edges of the lens, causing scattering in a random way. The random
scattering of light, called diffraction is bad for getting a clear focus on the image. Dif-
fraction also limits the resolution of the image. Resolution is defined as the ability to see
two close objects as separate. (Think about looking at two lines on a chalkboard that is
very far away; chances are they blur together and look like one messy line.) In fact, the
human eye has a resolving power of about 100 µm or 1/10th of a millimeter for close-up
images. In other words, two lines on a paper closer than 1/10th of a millimeter apart look
blurry to us. The light microscope is limited in the same way by diffraction because the
diffracted rays create blurry images.
diffraction
The random scattering
of light.
resolution
Is the ability to see
two close objects as
separate.
Figure 3.4 Hooke’s microscope from the 1600s and van Leeuwenhoek with his
microscope. These simple microscopes led to the first descriptions of cells. Van
Leeuwenhoek’s microscope consisted of a small sphere of glass in a holder.
1 centimeter (cm) =
1/100 meter or 0.4 inch
3 cm
Ch
ick
en
e
gg
(th
e
“y
olk
“)
1 mm
Fr
og
e
gg
, f
ish
e
gg
1 meter = 102 cm = 103 mm = 106 µm =109 nm
Unaided human eye
1 millimeter (mm) =
1/1,000 meter
1 micrometer (µm) =
1/1,000,000 meter
1 nanometer (nm) =
1/1,000,000 meter
100 µm
Hu
m
an
e
gg
Light microscopes
Electron microscopes
10–100
Ty
pic
al
pla
nt
ce
ll
5–30
Ty
pic
al
an
im
al
ce
ll
2–10
Ch
lor
op
las
t
1–5
M
ito
ch
on
dr
ion
5
An
ob
ae
no
(c
ya
no
ba
cte
riu
m
)
1
Es
ch
er
ich
ia
co
li
100 nm
La
rg
e
vir
us
(H
IV
,
inf
lue
nz
a
vir
us
)
25
Ri
bo
so
m
e
7–10
Ce
ll m
em
br
an
e
(th
ick
ne
ss
)
2
DN
A
do
ub
le
he
lix
(d
iam
et
er
)
0.1
Hy
dr
og
en
a
to
m
table 3.1 Measurements Used for Microscopy. The units of measurement used in the study of molecules
and cells correspond with methods by which we are able to detect their presences.
©
K
e
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y
ch03.indd 79 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
80 Unit 1: That’s Life
Higher magnification under the microscope leads to greater diffraction. This is the
reason a compound light microscope can magnify only up to 1000–1500 times (under
oil immersion), after which there is too much diffraction for a clear image to be formed.
To overcome the effect of diffraction and achieve clarity at higher magnifications, oil is
placed on the slide. However, even with oil immersion, only the large nucleus of a cell
can be seen; other organelles appear as small dots or not at all.
So how did the more complex world of even smaller structures within cells get dis-
covered? The 1930s saw the development of the electron microscope that allowed for
magnifications of over 200,000 times greater than that of the human eye. There are two
types of electron microscopes: transmission electron microscope (TEM) and scanning
electron microscope (SEM). Transmission electron microscopy allows a resolving power
of roughly 0.5 nm (see Table 3.1) that visualizes structures as small as five times the
diameter of a hydrogen atom. Electron microscopes use electrons instead of light, which
limits diffraction and increases resolution. Magnets instead of lenses focus electrons to
create the image. The electrons pass through very thin slices of the specimen and form
an image.
A SEM looks at the surfaces of objects in detail, while a TEM magnifies structures
within a cell. The SEM has a resolving power slightly less than the TEM, at 10 nm. (A
depiction of an electron microscope is shown in Figure 3.5.) Electron microscopy has
led to many scientific developments, uncovering subcellular structures to help us under-
stand cell biology. Seeing a mitochondrion enables us to better understand diseases and
perhaps, if our opening story becomes reality, improve societal health through its use.
Cell Theory
Fairly recent advances in microscopy have allowed scientists to learn about the structure
and function of even the tiniest components of cells, but the cell theory, which states key
ideas about cells, developed a long time ago. We have seen that scientists began study-
ing cells in the early 1700s. About a century later, in 1838, a German botanist named
Matthias Schleiden (1804–1881) concluded that all plants he observed were composed
of cells. In the next year, Theodor Schwann (1810–1882) extended Schleiden’s ideas,
transmission elec-
tron microscope
(teM)
A type of electron
microscope that
magnifies structures
within a cell.
Scanning electron
microscope (SeM)
An electron
microscope that
looks at the surfaces
of objects in detail
by focusing a beam
of electrons on the
surface of the object.
Figure 3.5 a. A researcher sits at a modern electron microscope. b. Apple tree pollen grains on cells, an
electron micrograph.
©
L
a
rr
y
Br
u
c
e
/S
h
u
tt
e
rs
to
c
k.
c
o
m
©
D
ra
g
o
n
Im
a
g
e
s
(a) (b)
ch03.indd 80 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 81
observing that all animals are also made of cells. But how did these cells come to survive
generation after generation? The celebrated pathologist Rudolf Virchow (1821–1902)
concluded in 1858 that all cells come from preexisting cells (He wrote this in Latin:
“Cellula e cellula”). These scientists contributed, together, to the postulates of the cell
theory. The cell theory is a unifying theory in biology that places the cell as the center of
life and unifies the many branches of biology under its umbrella. The cell theory states
that:
1) All living organisms are composed of cells.
2) The chemical reactions that occur within cells are separate from their
environment.
3) All cells arise from other cells.
4) Cells contain within them hereditary information that is passed down from par-
ent cell to offspring cell.
The cell theory showed not only that cells are the basic unit of life, but that there is
continuity from generation to generation. Genetic material is inherited in what we refer
today as the cell.
Types of Cells
Microscopes allowed researchers to examine differences between organisms that had
previously been impossible to determine. A current classification of organisms defines
five kingdoms, with organisms in those kingdoms having similar types of cells (There
is some debate arguing inclusion of Archaea bacteria as a separate kingdom, and a six-
system classification scheme is thus also accepted). Cells of organisms in the five king-
doms each have many internal differences, as summarized in Table 3.2. Images of some
organisms of each kingdom are given in Figure 3.17 as examples.
Prokaryotes (bacteria) are composed of cells containing no membrane-bound
nucleus and no compartments or membranous organelles. They are much smaller than
eukaryotes, by almost 10 times. Prokaryotic genetic material is “naked,” without the
protection of a membrane and nucleus. They are composed of very few cell parts: a
membrane, cytoplasm, and only protein-producing units called ribosomes. Even without
most structures found in other organisms, prokaryotes contain genetic material to repro-
duce and direct the functions of the chemical reactions occurring within its cytoplasm.
group domain cell type cell number cell Wall component energy Acquisition
Bacteria Bacteria Prokaryotic Unicellular Peptidoglycan Mostly heterotrophic,
some are autotrophic
Protists Eukarya Eukaryotic Mostly unicellular,
some are simple
multicellular
Cellulose, silica; some have
no cell wall
Autotrophic,
heterotrophic
Plants Eukarya Eukaryotic Multicellular Cellulose Autotrophic
Animals Eukarya Eukaryotic Multicellular No cell wall Heterotrophic
Fungi Eukarya Eukaryotic Mostly multicellular Chitin Heterotrophic
From Introductory Plant Science by Cynthia McKenney et al. Copyright © 2014 by Kendall Hunt Publishing Company. Reprinted by
permission.
table 3.2 Differences in Cell Structure within the Five Kingdoms: Plants, Animals and Prokaryotes.
ch03.indd 81 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
82 Unit 1: That’s Life
Prokaryotes have a simple set-up, but all of the needed equipment to carry out life func-
tions. Bacteria have a rapid rate of cell division and a faster metabolism than eukaryotes.
Most organisms on Earth, in terms of sheer number, are prokaryotes.
• As indicated in Chapter 1, prokaryotes include organisms in the Bacteria and
Archae domains. These organisms will be discussed further in Chapter 8.
All other organisms (plants, animals, fungi, and protists) are eukaryotes. Cells of
eukaryotes are complex, containing a membrane-bound nucleus that houses genetic
material. Eukaryotic cells comprise compartments that form a variety of smaller internal
structures, or organelles. Eukaryotic cells are the focus of this chapter, which will give
an overview of the primary organelles and their functions (Figure 3.6).
Eukaryotes may be examined by dividing into its four groups: plants, animals, fungi,
and protists. Plants contain cells that are surrounded by a cell wall, a rigid structure giv-
ing its organisms support. Plant cells contain chloroplasts, which enable plants to carry
out photosynthesis, using energy from sunlight to make food.
• Plant cell walls contain cellulose, which gives structure to plants as discussed
in Chapter 2. The process of photosynthesis, producing food for plants, will be
further discussed in Chapter 4.
Plants also have large vacuoles or storage compartments to hold water and minerals for a
plant’s functions. While both plants and animals have a cell membrane, animal cells are
Photosynthesis
The process by which
green plants use
sunlight to synthesize
nutrients from water
and carbon dioxide.
Figure 3.6 a. Differences between prokaryotes and eukaryotes. Prokaryotes have a
generally simple structure (see top cell in figure above), while eukaryotes (the lower
cell in figure above) have multiple organelles and membranes forming complex com-
partmentalization. From Biological Perspectives, 3rd ed by BSCS. b. Differences between
plants and animals. Plant and animal cells perform different functions, and their subcel-
lular structures are also different. Plant cells have chloroplasts to produce sugar and a
cell wall to give added strength. The animal cell shown has no cell wall or chloroplasts
but possesses centrioles. From Biological Perspectives, 3rd ed by BSCS.
©
2
00
6
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
(a)
ch03.indd 82 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 83
Figure 3.6 (Continued)
(b) ©
20
06
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
ch03.indd 83 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
84 Unit 1: That’s Life
less rigid, surrounded only by a cell membrane and lacking a cell wall for support. Both
plants and animals contain membrane-bound organelles, but animals also contain a set
of small structures called centrioles, which serve in cell division. Animal cells are also
quite complex, as we will see. While lacking certain organelles, such as cell walls and
chloroplasts, they have flexible strategies to perform many functions.
Fungi have cell walls but no chloroplasts. They are not able to make their own food
and, instead live off of dead and decomposing matter as well as other living organisms,
centriole
Minute cylindrical
organelles found in
animal cells, which
serve in cell division
(not given in bold in
text).
(b) C
o
p
yr
ig
h
t
©
20
06
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
Figure 3.6 (Continued)
ch03.indd 84 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 85
to obtain energy. Mushrooms and yeasts are familiar types of fungi, which will be dis-
cussed in Chapter 7.
Some species of protists are a bit animal-like in that they are able to move; other
species are a bit plant-like in that they have chloroplasts. Protists such as Amoeba in
Figure 3.7 have varied environments. Amoeba live in freshwater and, in a rare infectious
disease, grow and destroy human brain cells. We will discuss protists in more detail in
a later chapter.
Figure 3.7 Cells of the five kingdoms. While the cells of organisms in all of the kingdoms perform similar
life functions, their individual structures enable differing functions unique to each kingdom. From Biological
Perspectives, 3rd ed by BSCS.
©
2
00
6
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
ch03.indd 85 11/12/15 4:24 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
86 Unit 1: That’s Life
The Role of inheritance
The stratification system depicted in our opening story is based on the inheritance of
cellular components. We know that organelles are structures that carry out functions
within a cell. In fact, organelles work in concert with one another, coming together to
Figure 3.7 (Continued)
©
2
00
6
b
y
Ke
n
d
a
ll
H
u
n
t
Pu
b
lis
h
in
g
C
o
m
p
a
n
y.
R
e
p
rin
te
d
b
y
p
e
rm
iss
io
n
ch03.indd 86 11/12/15 4:25 pm
C
R
O
O
M
,
D
O
N
A
V
A
N
4
6
4
5
T
S
Chapter 3: The Cell As a City 87
form a complex, dynamic cell. Mitochondria, so important in the society in our story, are
the powerhouses of the cell, providing energy for a cell’s …