CHAPTER
2
Diversity:
From Simple to Complex
Specific Expectations
• B1.2 analyze the impact that climate
change might have on the diversity of
living things (2.4)
• B2.1 use appropriate terminology
related to biodiversity (2.2)
• B2.3 use proper sampling techniques to
collect organisms from an ecosystem
and classify the organisms according to
the principles of taxonomy (2.4)
• B3.2 compare and contrast the
structure and function of different types
of prokaryotes, eukaryotes, and viruses
(2.1, 2.2, 2.3)
• B3.3 describe unifying and
distinguishing anatomical and
physiological characteristics of
representative organisms (2.2, 2.4)
• B3.4 explain key structural and
functional changes in organisms as
they have evolved over time (2.1, 2.3)
Why are scientists from the Canadian Space Agency and
universities interested in this strange looking structure at the bottom
of Pavilion Lake in British Columbia? This mound and many others
like it in the lake are covered with different types of bacteria and
other micro-organisms that trap minerals from the water to form the
solid structures beneath them. These structures, called microbialites,
were common on Earth from 2.5 billion to 540 million years ago,
and scientists hope to gain insight into the history of life on Earth
by studying them. Since these structures are usually found in harsh
environments, similar to some of the conditions on Mars and other
solar bodies, understanding more about how they form may also
help scientists in recognizing past or present extraterrestrial life.
50 MHR • Unit 1 Diversity of Living Things
Launch Activity
Classifying the “Invisible”
Micro-organisms, such as bacteria and protists, range in size from
1.0 × 10–3 m to 1.0 × 10–6 m, and smaller. What characteristics would
you use to classify three microscopic entities? Use your observations
of prepared slides or the photograph below to determine some of the
differences among bacteria, protists, and viruses.
Bacterium (E. coli)
Magnification: 3000×
Protist (Amoeba)
Magnification: 85×
Influenza Virus
Magnification: 100 000×
Materials
•
•
•
•
light microscope
prepared slide of a bacterial species
prepared slide of a protist
picture of a virus
Procedure
1. Observe the slide of the bacterium. (Alternatively, you can observe
the photograph above.) Make a sketch, labelling all the structures you
recognize—for example, cell membrane, flagellum, cilia.
2. Repeat step 1 with the protist and the virus.
3. Estimate and record the size of each bacterium, protist, and virus.
Go to Using a Microscope Appendix A to learn more about how to
estimate the size of a specimen.
4. Use a table or graphic organizer to compare and contrast bacteria,
protists, and viruses, based on your observations.
Questions
1. What do viruses, protists, and bacteria have in common?
2. Which characteristic(s) do you think scientists use to help them
distinguish among viruses, protists, and bacteria? Explain your answer.
Chapter 2 Diversity: From Simple to Complex • MHR 51
SECTION
2.1
Key Terms
virus
capsid
replication
lytic cycle
lysogenic cycle
prion
A Microscopic Look at Life’s Organization
Take a moment to think about the differences among the three organisms shown in
Figure 2.1: E. coli bacteria, a blue whale, and western red cedar trees. Each of these
organisms contains cells that are different from the cells contained in the others, such
as the animal cells in the whale and the plant cells in the trees. The organisms also
have different external and internal structures. In other words, these organisms exhibit
structural diversity. In organisms as large as blue whales or western red cedar trees,
there is a range of complexity both within their cells and in the way those cells are
organized in the whole organism. In unicellular organisms, such as bacteria, structural
diversity exists at the cellular level.
A
Figure 2.1 The millions
of species on Earth
demonstrate tremendous
structural diversity. (A) E. coli
bacteria are microscopic,
unicellular, and reproduce
asexually. Blue whales (B)
and western red cedar trees
(C), are huge, multicellular,
and reproduce by sexual
means.
C
Magnification: 5800×
B
Describe one example of
structural diversity among
the organisms shown.
The cells of multicellular organisms undergo division in order to grow and
reproduce. There are two types of cell division: mitosis and meiosis. (Cell division
in unicellular organisms is of a different type, as you will learn later in this chapter.)
During mitosis, cells divide to form two cells that are identical to the parent cell.
Meiosis produces the reproductive cells (egg and sperm), which have half the number
of chromosomes as the parent cell. Meiosis contributes to genetic diversity.
52 MHR • Unit 1 Diversity of Living Things
Prokaryotes and Eukaryotes
The study of cells is an important first step in understanding the diversity of life. Recall
from Chapter 1 that biologists recognize two basic types of cells based on differences
in their size, structure, and other characteristics, as shown in Table 2.1. Bacteria and
archaea are prokaryotes, whose cells lack a true nucleus. Protists, plants, fungi, and
animals are eukaryotes. Recall that eukaryotic cells are larger and more complex than
prokaryotic cells, and they do contain nuclei and other membrane-bound organelles.
Table 2.1 Two Types of Cells
Characteristic
Prokaryotes:
Bacteria, Archaea
Eukaryotes:
Protists, Plants, Fungi, Animals
1–10 μm
100–1000 μm
Size
Genetic material • circular DNA, not bound by a
membrane
• genome made up of a single
chromosome
• DNA in nucleus bounded by
membrane
• genome made up of several
chromosomes
Cell division
• not by mitosis and meiosis
• by mitosis and meiosis
Reproduction
• asexual reproduction common
• sexual reproduction common
Number of cells
• unicellular
• most forms are multicellular
Organelles
• mitochondria and other membranebound organelles absent
• mitochondria and other membranebound organelles present
Metabolism
• many are anaerobic (do not
require oxygen to carry out cellular
respiration)
• most are aerobic (require oxygen to
carry out cellular respiration)
Viruses
Viruses differ from both prokaryotic and eukaryotic cells in several fundamental
ways. The first is that viruses are functionally dependent on the internal workings of
cells—either prokaryotic or eukaryotic. Viruses are not capable of living independently
outside of cells. They must invade cells and use the host cell’s machinery for survival
and reproduction. Outside a cell, viruses are dormant. Viruses also differ structurally
from prokaryotic and eukaryotic cells. Viruses are not cellular, so they have no
cytoplasm, membrane-bound organelles, or cell membranes. For these reasons, some
scientists do not consider viruses to be living organisms.
Although viruses are incapable of living independently and are not considered
living by some scientists, they do affect the lives of other organisms. Viruses cause
disease in plants and animals, which can affect populations, species, and ecosystems.
Certain viruses infect plants, such as wheat, oats, and barley, that are grown as
food sources for humans. Uncontrolled infection can lead to food shortages in some
areas of the world. Other viruses, such as the polio virus, HIV, and H1N1, infect
humans, leading to severe illness. Scientists develop vaccines and new treatments to
fight viral infections. Viruses are also used in biotechnology to clone copies of genes.
virus a structure that
contains strands of
DNA or RNA surrounded
by a protective protein
coat; it cannot live
independently outside
of cells
Chapter 2 Diversity: From Simple to Complex • MHR 53
capsid the outer
protein layer that
surrounds the genetic
material of a virus
replication the
fundamental process
of all cells, in which
the genetic material is
copied before the cell
reproduces
lytic cycle the
replication process in
viruses in which the
virus’s genetic material
uses the copying
machinery of the host
cell to make new viruses
lysogenic cycle the
replication process in
viruses, in which the
viral DNA enters the
host cell’s chromosome;
it may remain dormant
and later activate and
instruct the host cell to
produce more viruses
Classifying Viruses
Because viruses are not cellular they are not formally considered to be organisms. This
means they are not included in the classification of life, covered in Chapter 1. However,
since they have genetic material and reproduce, there are good reasons for considering
them to be alive. Biologists involved in studying viruses do have a system to classify
and name them, but this system is not part of the classification system of life.
One of the methods used by scientists to classify viruses is the size and shape
of the capsid, shown in Figure 2.2. A capsid is the protein coat that surrounds the
genetic material, either DNA or RNA, of a virus. Some viruses, such as the polio virus,
resemble small crystals and may have as many as 20 sides. The HIV that causes AIDS
has a spherical shape. The tobacco mosaic virus, which infects tobacco plants, has a
cylindrical shape. The T4 virus infects bacteria. It has a head attached to a protein tail
and several tail fibres.
Viruses are also grouped by the types of diseases they cause. Viruses that infect
humans are currently classified into 21 groups. These groups differ in their genomes,
or sets of genes, and their method of replication.
A
B
C
D
Figure 2.2 Viruses have a variety of shapes. The viruses shown here include (A) the polio virus,
(B) HIV, (C) the tobacco mosaic virus, and (D) the T4 virus.
Describe the differences among the capsids of the viruses shown here.
Reproduction in Viruses
Since viruses are not cellular, they do not reproduce by cell division. Instead, they are
said to undergo replication within a host cell. The host cell can be either a prokaryote
or a eukaryote, depending on the virus type. Viruses use the host cell to produce
multiple copies of themselves. Then the copies are assembled by the host cell inside it.
The typical replication cycle of viruses, shown in Figure 2.3, is called the lytic cycle.
Sometimes the genetic material of the virus enters the nucleus of the host cell. In the
lysogenic cycle, also shown in Figure 2.3, the viral DNA enters and becomes part
of the host cell’s chromosomes. Once this occurs, the infected cell has viral genes
permanently. The viral DNA that has become part of the host chromosome is then
referred to as a provirus. A provirus can invade a cell, but does not kill it.
54 MHR • Unit 1 Diversity of Living Things
Lysis and Release:
The host cell breaks
open and releases
new viral particles.
DNA or RNA
Assembly:
New viral particles
are assembled.
capsid
Attachment:
Proteins on the surface of
the virus bind to protein
receptors on the surface
of the host cell’s membrane.
bacterial
cell wall
bacterial
chromosome
Lytic
Cycle
Replication:
The host cell makes
more viral DNA or
RNA and proteins.
Entry:
The virus injects
its genetic material
(RNA or DNA) into
the host cell.
Provirus Formation:
Viral DNA becomes
part of the host
cell’s chromosome.
Lysogenic
Cycle
cell division
Provirus leaves the
host’s chromosome.
Provirus replicates
with host’s
chromosome.
Figure 2.3 In the lytic cycle, the entire replication process occurs in the cytoplasm of the host cell.
The virus’s genetic material enters the host cell, and the cell replicates the viral DNA or RNA. The host
cell makes new capsids and assembles new viral particles. The host cell lyses, or breaks open, and
the new viruses leave the cell. In the lysogenic cycle, the virus’s genetic material enters the host cell’s
chromosome. In many cases, the genes are not activated until later. Activation results in a continuation
of the lytic cycle.
Learning Check
1. What does the term structural diversity describe?
4. Describe how scientists classify viruses.
2. Make an argument for or against the following
statement: Viruses are living organisms.
5. Identify the differences between the lytic and
lysogenic cycles involved in viral replication.
3. Make a graphic organizer to explain the differences
among prokaryotes, eukaryotes, and viruses.
6. The soil-borne wheat mosaic virus causes disease
and yield loss in crops such as wheat and barley.
Predict the impact of an uncontrolled infection of
this viral disease.
Chapter 2 Diversity: From Simple to Complex • MHR 55
Viruses and Disease
In the lytic cycle of a virus, newly formed viruses burst from the host cell, usually
killing it. In multicellular hosts, these new viruses then infect neighbouring cells,
causing damage to their host. The amount of damage and its effects on the host vary.
In viruses that undergo the lysogenic cycle, effects on the host may not be
immediate. For instance, the human immunodeficiency virus (HIV) is an example
of a type of virus called a retrovirus. Retroviruses contain an enzyme called reverse
transcriptase. As you can see in Figure 2.4, this enzyme causes the host cell to copy
the viral RNA into DNA. In this form, the viral DNA enters the chromosomes of the
host cell, so it is a provirus. When the host cell divides by mitosis, it replicates the
provirus along with its own DNA. Every descendant of the host cell carries a copy of
the provirus in its chromosomes. This process can continue for years, with no harm to
the host. Because the virus is part of the host chromosomes, it cannot be easily detected
by medical tests. At any time, however, the provirus can separate from the host
chromosomes and complete the more damaging lytic cycle.
SuggestedInvestigation
ThoughtLab 2-A, Measles
Immunization
Patterns of Disease
The replication strategies of viruses help explain certain patterns of disease. For example,
the herpes simplex virus causes cold sores in humans. These sores may appear and
disappear on the skin of infected people throughout their lifetime. The sores appear
when the viral cycle destroys cells, and they disappear when the virus is in its provirus
stage. The exact trigger that causes the switch from one phase to another is not known.
Other viruses follow variations of the replication strategies already described. For
example, HIV forms a provirus in the host cell chromosomes, but it also produces
small numbers of new viruses while the cell continues to function normally. This
explains why people may test positive for HIV and still remain healthy for many years.
Only when the infection spreads to more and more cells do the symptoms of AIDS
(acquired immune deficiency syndrome) eventually appear. The symptoms result
from infections by other micro-organisms, because the HIV has destroyed the body’s
T-lymphocytes, which help the immune system fight off other diseases.
RNA
retrovirus
RNA
DNA
reverse
transcriptase
DNA is made from
the viral RNA
entering cell
provirus in
host chromosome
Retrovirus
cycle
mRNA
new virus parts
exiting cell
new virus
forming
Figure 2.4 Retroviruses contain an enzyme that causes the host cell to copy viral RNA into DNA.
This DNA becomes a provirus that continues to produce new viruses without destroying the cell.
56 MHR • Unit 1 Diversity of Living Things
Prions: Non-viral Disease-causing Agents
For many years, scientists worked to determine the cause of several types of brain
diseases in which the disease is usually not detected for decades after a person is
infected. This sounds like the pattern of a viral infection. However, scientists noted that
the infectious agent remained infectious even after it was exposed to radiation, which
would destroy the DNA or RNA. In the 1980s, American researcher Stanley Prusiner
discovered an entirely new type of disease-causing agent called a prion. The discovery
was remarkable for two reasons. First, prions are proteins that are found normally
in the body. Second, they are the only known disease-causing agents that lack RNA
or DNA. Diseases result when prions convert from their normal form into harmful
particles that have the same chemical composition but a different molecular shape.
Prions cause several deadly brain diseases, including Creutzfeldt-Jakob disease (CJD)
in humans, scrapie in sheep, and bovine spongiform encephalopathy (BSE) or “mad
cow disease” in cows.
prion an infectious
particle that causes
damage to nerve cells
in the brain, and that
appears to consist
mostly or entirely of
a single protein
Viruses and Biotechnology
Because viruses enter host cells and direct the activity of the host cell’s DNA, they can
be useful tools for genetic engineers. For example, if researchers want to make a copy
of a gene, they first insert the gene into the genetic material of a virus. The virus then
enters a host cell and directs the cell to make multiple copies of the virus. Each new
virus in each new cell contains the added gene that the researchers want copied.
Activity
2.1
Comparing Prion Diseases
Creutzfeldt-Jakob disease (CJD) and Variant CreutzfeldtJacob disease (vCJD) are two neurological diseases caused
by prions. CJD was first recognized by scientists in the 1920s
and occurs worldwide at a rate of about one case per million
people. vCJD was first described by scientists in 1996. Since
then, about 200 people worldwide have been diagnosed
with vCJD.
In this activity, you will compare the characteristics
of these diseases, including symptoms and test results.
A confirmed diagnosis can only be achieved by examining
the brain tissue of the patient after death.
Characteristics of Two Prion Diseases
Characteristic
CJD
vCJD
Median age at death
68 years
28 years
4–5 months
13–14 months
Symptoms
Memory loss,
difficulty
communicating,
inability to
reason, difficulty
with coordination
and movement
Psychiatric and
behavioural
symptoms,
painful distortion
of sense of touch
Periodic sharp
waves recorded
during test that
measures electrical
activity in brain
Often present
Often absent
Median length of
illness
Procedure
Use the table on the right to answer the questions.
Questions
1. Suppose you are a doctor looking at the magnetic
resonance imaging (MRI) results of your patient. If your
patient has vCJD, what do you expect the MRI to show?
Explain your reasoning.
2. If your patient has vCJD, do you expect to see abnormal
clusters of proteins in his or her brain tissue? Explain your
reasoning.
3. You have a 60-year-old patient who has been
experiencing symptoms such as memory loss and
difficulty with coordination for about three months.
Without further testing, which disease do you suspect
your patient has? What test results do you expect to see
to confirm this diagnosis?
Abnormal signals
Not reported
in certain regions of
the brain on an MRI
Present in over
75 percent of
cases
Presence of prions
in lymph tissue
Readily detected
Not readily
detected
Abnormal clusters
Rare or absent
of protein fragments
in brain tissue*
Present in large
numbers
*Confirmed through tests performed after the death of
the patient
Chapter 2 Diversity: From Simple to Complex • MHR 57
Section 2.1
RE V IE W
Section Summary
• There are two basic cell types—prokaryotic cells and
eukaryotic cells.
• Viruses can be classified by the size and shape of
their capsid.
• Prokaryotic cells are smaller and less complex than
eukaryotic cells. Prokaryotic cells do not have a
membrane-bound nucleus or other membrane-bound
organelles.
• Viruses reproduce through replication within a host
cell. They replicate through the lytic cycle or the
lysogenic cycle.
• Because viruses cannot function independently in any
way, some scientists believe they are not living organisms.
• Prions are infectious particles that appear to consist
mostly or entirely of a single protein.
Review Questions
1.
2.
List three differences between prokaryotic cells
and eukaryotic cells.
8.
Illustrate the differences among a virus, a
prokaryotic cell, and a eukaryotic cell.
Classify each of the organisms shown in
9.
T/I What advantages do you think viruses might
have over cells?
K/U
A
Figure 2.1 as either prokaryotes or eukaryotes.
Explain your reasoning.
3.
Viral replication can be compared to making
a product in a factory. Explain how, and identify the
strengths and weaknesses of this comparison.
4.
C
Draw a diagram to demonstrate how viruses
might be used to copy the genes for producing
human insulin.
5.
10.
K/U These disease-causing agents are not bacterial,
fungal, or a virus. They contain no genetic material, yet
they are responsible for a number of degenerative brain
diseases. Identify these agents and describe how they
cause these diseases.
11.
K/U Why are new retroviruses in humans difficult
to detect?
12.
C
Define the term provirus. Use Figure 2.4 as a
guide to make a flowchart or other graphic organizer
to explain how a retrovirus, such as HIV, develops into
a provirus.
13.
A
Originally, some viruses, such as the
Epstein-Barr virus, were named for the scientists who
discovered them. Others diseases, such as dengue fever
or influenza, were named for the way people imagined
they were contracted. Explain why virologists today are
attempting to develop a standardized scientific naming
system.
14.
In a normal cell, DNA is transcribed into RNA,
and then the RNA is translated into proteins. However,
when a retrovirus is inside of a cell, the first two steps
of that process are switched. Rather than DNA →
RNA → protein, it is RNA → DNA. Reverse
transcription lacks the usual proofreading of DNA
replication. As a result, a retrovirus can mutate often.
Predict the impact of rapidly mutating viruses on the
development of effective treatments, such as anti-viral
medications.
15.
C
Use a Venn diagram or other graphic organizer
to compare and contrast viruses and prions. Include
information about the structure and composition of
these entities, as well as their impact on humans.
C
A
Incubation time is the time for symptoms of a
disease to occur after exposure. Consider the data on
the incubation time of different viral diseases in the
table below. Use the data to predict which diseases are
caused by viruses that undergo the lytic cycle and
which are caused by viruses that undergo the lysogenic
cycle. What is a possible public health consequence of
the incubation time for diseases caused by proviruses?
Incubation Time of Viral Diseases
Disease
Incubation Time
Measles
9–11 days
Shingles
Years
Warts
Months
Cold
2–4 days
HIV
2–5 years
6.
If you were a scientist developing a drug that
would block viral replication, which steps would you
choose to block? (Hint: Refer to Figure 2.3.) Explain
your answer in detail.
7.
C
Viruses replicate; they do not reproduce. Most
viruses replicate through the lytic cycle. Create a
flowchart or point-form outline of the lytic cycle.
T/I
58 MHR • Unit 1 Diversity of Living Things
C
T/I
SECTION
2.2
Comparing Bacteria and Archaea
Prokaryotes are represented by two domains: Bacteria and Archaea. Remember, by
being considered in separate domains, biologists are saying that the two groups are more
different from each other than any two groups within a domain. In other words, bacteria
and archaea are more different from each other than an apple tree is from a blue whale,
two organisms within the same domain, Eukarya. The domain Bacteria contains the
kingdom Bacteria. Similarly, the domain Archaea contains the kingdom Archaea.
Key Terms
Comparing Morphology
extremophile
The most common forms in both bacteria and archaea are spheres and rods. The
spherical forms are known as cocci (singular coccus), and the rod forms are called
bacilli (singular bacillus). A third form present in both is a spiral shape. These three
forms are shown in Figure 2.5. In addition, there are forms that do not fit into these
three types. For example, some bacteria are shaped like cubes, pyramids, and rods with
star-shaped cross sections. Some archaea are shaped like plates and rectangular rods,
and a few species without cell walls have changeable shapes.
A
Magnification: 4000×
B
Magnification: 12 500×
C
Magnification: 6000×
Figure 2.5 There are three common shapes of prokaryotes: (A) cocci (spherical), (B) bacilli
(rod-shaped), and (C) spiral shaped.
Aggregations: Cells Grouped Together
Even though all prokaryotes are unicellular, both domains have members that form
aggregations, in which individual cells group together. Streptococcus bacteria are found
in chains of spheres. Streptobacillus are rod-shaped bacteria that form similar chains.
In the Anabaena, shown in Figure 2.6, the cells in the chains have different functions.
Most of the cells carry out photosynthesis, but a few cells convert nitrogen from the
environment into forms that are usable by other organisms.
bacterium
archaeon
coccus
bacillus
methanogenesis
mesophile
binary fission
conjugation
endospore
Gram stain
bacterium (plural
bacteria) an individual
prokaryotic cell or a
single species that is in
the domain Bacteria
archaeon (plural
archaea) an individual
prokaryotic cell or a
single species that is in
the domain Archaea
coccus (plural cocci) a
micro-organism whose
overall morphology is
spherical or nearly so
bacillus (plural bacilli)
a micro-organism whose
overall morphology is
rod-shaped
Magnification: 275×
Figure 2.6 Anabaena is a bacterium that forms colonies in long chains. Two different cell types
in the chain can have different functions, each of which helps the other cell type.
Chapter 2 Diversity: From Simple to Complex • MHR 59
Comparing Nutrition
methanogenesis a
biological (or chemical)
process that produces
methane as an
by-product
There are many ways in which species in Archaea and Bacteria obtain energy. Some
carry out photosynthesis, some consume other organisms, and still others get energy
from various inorganic compounds such as hydrogen sulfide or iron.
One metabolism that appears to be unique to the Archaea is methanogenesis,
which produces methane gas as a by-product. Methane (CH4) is the simplest organic
compound. It is a useful fuel and a potent greenhouse gas. Methanogenesis is an
anaerobic process that occurs in environments that lack oxygen, and it is often one
of the final stages of decomposition. Methane-producing archaea live in the digestive
tracts of animals such as the cattle shown in Figure 2.7, making these animals a source
of methane gas.
Figure 2.7 The large
mammals used in modern
agriculture, including cattle
and sheep, have digestive
tracts that contain millions
of methane-producing
archaea. Each animal
belches large quantities
of methane every day.
Explain how livestock
farming might play a role
in climate change, given
that methane is a more
potent greenhouse gas
than carbon dioxide.
Another key difference between Archaea and Bacteria is photosynthesis. Some
bacteria are photosynthetic—the best known of these are called cyanobacteria. An
example of a cyanobacterium is shown in Figure 2.8. Like green plants, cyanobacteria
use solar energy to convert carbon dioxide and water into sugar. In the process they
produce oxygen. These bacteria are abundant in both fresh and salt water, and they
account for much of the atmospheric oxygen on Earth. Some archaea use the energy
in sunlight as a source of metabolic energy, but researchers are still seeking reliable
evidence of photosynthesis in archaea.
Figure 2.8 Cyanobacteria,
such as Spirulina platensis,
contain chlorophyll and
carry out photosynthesis.
Magnification: 1500×
60 MHR • Unit 1 Diversity of Living Things
Comparing Habitats
Because of the diversity of ways in which bacteria and archaea obtain nutrients, these
organisms are able to occupy a diverse array of habitats. When the term habitat is
used for multicellular organisms, you might think of larger scales, such as freshwater
marshes, coniferous forests, or dry grasslands. For prokaryotes, habitats on smaller
scales must also be considered.
Both archaea and bacteria occupy environments with oxygen (aerobic) and without
oxygen (anaerobic). Methanogenic archaea, for instance, are abundant in the anaerobic
depths of landfill sites, the guts of cattle, and sediments of swamps. Anaerobic bacteria
are found in the human gut and many other environments.
One of the most fascinating things about archaea is their ability to live in extreme
environments. For this reason, they are referred to as extremophiles. Table 2.2 shows
some of the extreme habitats in which different archaea are able to survive.
Most bacteria are mesophiles—organisms that occupy environments with
moderate (less extreme) conditions. There are, however, extremophilic bacteria. And,
as our knowledge of archaea accumulates, there are proving to be many mesophilic
members of that domain too. The extremophilic capacities of prokaryotes have
influenced scientists who are interested in extraterrestrial life. Scientists now know
that life is possible in a much greater range of conditions than the eukaryotic world
had suggested.
extremophile an
organism that lives in
habitats characterized
by extreme conditions
mesophile an organism
that lives in habitats
characterized by
moderate conditions
Table 2.2 Habitats of Extremophiles
Habitat
Example
Type of Extremophile
Deep Sea Vents and Hot Springs
Both of these habitats have extreme
temperatures of over 100°C. The archaea
that live around deep sea vents not only
live with extreme temperatures, but in
the absence of sunlight as well. The hot
springs in Yellowstone National Park in
the United States are home to several
different species of archaea.
Thermophile (“heat-lover”)
The most heat-tolerant
species known is in the genus
Methanopyrus. Individuals
live near deep sea vents in
temperatures as high as 120°C,
which is much higher than the
boiling point of water.
Volcanic Crater Lakes and
Mine Drainage Lakes
These habitats are extremely acidic, with a
pH of less than 3. Sulfur from geothermal
activity creates the acidic conditions of
lakes in the craters of volcanoes. Mine
drainage lakes are human-made; they
result from mining operations.
Acidophile (“acid-lover”)
Picrophilus can live at a pH of 0,
which is the acidity of car
battery acid.
Salt Lakes and Inland Seas
Salt lakes, such as the Great Salt Lake,
and inland seas, such as the Dead Sea,
can have concentrations of salt higher
than 20 percent. The Dead Sea, which
has a high rate of evaporation, has a salt
concentration of about 35 percent. Ocean
water has a salt concentration of about
3.5 percent.
Halophile (“salt-lover”)
When the concentration of salt
in water exceeds 20 percent,
only halophilic archaea, such
as Halococcus, can thrive. Some
live in concentrations as high as
37 percent salt.
Chapter 2 Diversity: From Simple to Complex • MHR 61
Learning Check
7. Identify the three common forms of bacteria
and archaea.
10. What are some possible advantages to being
a mesophile?
8. Which type of bacteria are photosynthetic?
11. Compare and contrast methanogenesis and
photosynthesis.
9. Briefly describe the following types of archaea:
thermophile, halophile, and acidophile.
12. Would you consider an aggregation of Steptobacillus
bacteria to be a multicellular organism? Explain
your reasoning.
Comparing Reproduction
binary fission the
asexual form of
reproduction used
by most prokaryotes
(and some eukaryotic
organelles), in which
a cell divides into two
genetically identical
cells (or organelles)
Since bacteria and archaea lack nuclei, they do not reproduce by mitosis or meiosis.
Recall that the genetic material in prokaryotes is contained in a single chromosome
within the cell. Prokaryotes reproduce through the asexual process of binary fission,
shown in Figure 2.9. In binary fission, as a cell grows, it makes a copy of its original,
single chromosome. When the cell reaches a certain size, it elongates, separating the
original chromosome and its copy. The cell then builds a partition between them,
called a septum, and eventually the original cell splits into two smaller, genetically
identical cells.
chromosome
cell wall
plasma
membrane
A cell elongates
cytoplasm
B septum begins to form
septum
forming
C septum complete,
distinct walls form
septum
complete
Magnification: 5000×
D cells separate
Figure 2.9 Cell division in prokaryotes occurs by binary fission. In favourable conditions, a
prokaryotic cell can grow and divide in as little as 20 minutes. Each new cell can then grow
and produce two more cells 20 minutes later. A sequence of repeated doubling like this allows
bacteria to produce huge populations in a fairly short time.
62 MHR • Unit 1 Diversity of Living Things
Conjugation: New Genetic Content
In less favourable conditions, some bacteria and archaea are able to exchange DNA by
conjugation. This process produces cells with new genetic combinations, and thereby
provides a chance that some may be better adapted to changing conditions. During
conjugation, one cell links to another cell through a bridging structure and transfers
all or part of its chromosomes to the other cell, as shown in Figure 2.10. Unlike asexual
reproduction, conjugation results in cells with new genetic content. The receiving cell
then undergoes binary fission to produce more cells with the same genetic make-up.
conjugation a
process in which there
is a transfer of genetic
material involving
two cells
Figure 2.10 Genetic
material being transferred
through a long, tube-like
pilus.
Predict how conjugation
could be an agent for
increasing biodiversity
among prokaryotic species
that use it.
Magnification: 20 000×
Plasmids: Small Loops of DNA
In most bacteria and archaea, the chromosome is not the only part of the cell that
contains genes. Plasmids are small loops of DNA that are separate from the main
chromosome and that contain genes. These genes are different from those found in the
chromosome. Plasmids can split from the chromosome and rejoin it. Plasmids may
be transferred from one cell to another during conjugation. This makes plasmids an
important means of genetic recombination in prokaryotes.
Endospores: Protecting Genetic Material
When environmental conditions threaten survival, some species of bacteria can form
endospores like the one shown in Figure 2.11. Endospores are hard-walled structures
that protect and store the organism’s genetic material. Endospores are resistant to high
temperatures, drying out, freezing, radiation, and toxic chemicals. When suitable
conditions return, the endospore germinates back into an active bacterium. So far,
endospores have not been found in archaea.
endospore a dormant
bacterial cell able
to survive for long
periods during extreme
conditions
Magnification: 1500×
Figure 2.11 In life-threatening conditions, certain species of bacteria form endospores
that enable them to remain dormant (inactive) for periods of time that range from weeks to
thousands of years.
Chapter 2 Diversity: From Simple to Complex • MHR 63
Classifying and Identifying Bacteria and Archaea
Gram stain a stain that
separates bacteria into
two major divisions
(Gram positive and Gram
negative) based on the
cell wall’s response to
the stain
The biological species concept that uses sexual reproduction in its definition is of no
use for the asexual bacteria and archaea. Instead, biologists have traditionally used a
variety of means to identify and classify these species.
One method developed in the 19th century but still in use is the Gram stain,
shown in Figure 2.12. This technique divides bacteria into two groups. Gram-positive
bacteria have a thick protein layer on their cell wall and stain purple. Gram-negative
bacteria have a thin protein layer on their cell wall and stain pink. Other stains are used
to identify other groups, but none is as widely used as the Gram stain.
Other methods traditionally used to identify and classify prokaryotes include size
and shape, nutrition, movement, and genetic components. However, modern biologists
prefer techniques that rely on DNA comparisons.
A
B
Magnification: 700×
Magnification: 700×
Figure 2.12 The Gram stain divides most bacteria into two groups: Gram-positive (A) and Gramnegative. (B) The Gram-negative group of bacteria are larger in number and have more diverse
species than the Gram-positive group.
Activity
2.2
Classifying Bacteria
Bacteria can be classified into two groups, Gram-negative
and Gram-positive, based on the structure of their cell walls.
In this activity, you will observe and classify several bacteria.
Materials
• oil
• light microscope
• prepared slides of bacteria, numbered 1 to 4
Procedure
1. Observe slide 1 using the oil immersion lens.
2. Identify and record the shape of the bacterial cells.
3. Look at the cell walls of an individual bacterium and
record the colour of the stained cell walls.
4. Repeat steps 1 to 3 for each of the remaining slides.
64 MHR • Unit 1 Diversity of Living Things
Questions
1. Which of the slides contained Gram-negative bacteria?
Which contained Gram-positive bacteria? Explain your
reasoning.
2. Identify other differences among the bacteria you
observed. Choose one difference and explain how it
could be used to classify bacteria.
3. Doctors sometimes take a throat swab to obtain a
sample of bacteria when patients have a sore throat.
Describe two things that the sample can show to help
the doctor diagnose a patient’s illness.
Bacteria and Human Health
Food spoilage and the spread of disease are the result of bacteria carrying out their
normal life functions. For example, botulism is a type of food poisoning caused by
the species of anaerobic bacteria shown in Figure 2.13 (A)—Clostridium botulinum.
Commonly found in the soil, Clostridium botulinum forms endospores that are very
resistant to heat and that germinate in anaerobic conditions. The metabolism of these
bacteria produces toxic products that can cause nausea or even death in humans. The
bacteria are not dangerous, however, unless they are trapped with food for a period of
time under anaerobic conditions. This sometimes occurs when people can, or seal, food
into bottles or jars at home without proper care. To ensure that bacterial endospores are
killed, the food must be heated under high pressure at temperatures above the boiling
point of water. If you have ever had strep throat, an ear infection, or a cavity in your
tooth, then you have experienced a disease caused by bacteria. The bacteria that cause
some of these diseases are shown in Figure 2.13.
A
Magnification: 10 200×
B
Magnification: 4100×
Figure 2.13 (A) Clostridium
botulinum is an anaerobic
bacterium that can cause
illness in humans.
(B) Streptococcus pyogenes
is a Gram-positive
bacterium that causes
strep throat infections.
(C) Streptococcus mutans is
a Gram-positive bacterium
that causes tooth decay.
C
Magnification: 5300×
Bacteria and the Environment
As decomposers, bacteria break down organic materials and release carbon, hydrogen,
and other elements into the environment for use by other organisms. Nutrient cycles
such as the carbon, nitrogen, and sulfur cycles depend on the fact that chemicals excreted
into the environment by one type of organism can be used as nutrients by another type.
These links join together different types of bacteria into microscopic food webs.
Cyanobacteria are major producers of oxygen through the process of photosynthesis.
They were probably among the first organisms on Earth to carry out this process. Two
billion years ago, Earth’s atmosphere had little or no oxygen. By releasing oxygen as
a product of photosynthesis, bacteria altered the composition of the atmosphere and
literally changed the world. Other species of cyanobacteria are the only organisms able
to convert atmospheric nitrogen into a form that is usable by most organisms.
Archaea and Biotechnology
Enzymes that are unique to archaea allow these organisms to live under extreme
conditions of heat, cold, acidity, and salinity. Biotechnology and industry depend
on the use of enzymes for many processes, including DNA analysis and diagnosing
diseases. While most enzymes break down and stop working when they are exposed to
extreme conditions, archaeon enzymes do not. For example, polymerase chain reaction,
or PCR, is a technology that can produce millions of copies of a DNA sequence. PCR
used to be a slow and expensive process because standard enzymes were destroyed
by high temperatures during the process and had to be replaced by hand each time.
But the DNA polymerase from archaea can withstand these high temperatures,
and the PCR process is now fully automated. This revolutionary technology has
become commonplace.
Chapter 2 Diversity: From Simple to Complex • MHR 65
Section 2.2
RE V IE W
Section Summary
• The two domains into which prokaryotes are classified
are Bacteria and Archaea. Each of these domains has a
kingdom by the same name.
• Extremophiles occupy habitats of extreme conditions,
and most are archaea. Mesophiles occupy habitats that
have moderate conditions. Most bacteria are mesophiles.
• Bacteria and archaea have three basic shapes—cocci,
bacilli, and spiral.
• Prokaryotes reproduce asexually through binary
fission. They can exchange DNA through the process of
conjugation.
• A major group of archaea are methanogens that produce
methane. A major group of bacteria are cyanobacteria
that use photosynthesis.
• Prokaryotes were once classified by shape and responses
to stains, but modern taxonomists use DNA sequences.
Review Questions
1.
Make a table that identifies and describes the
three common shapes for bacteria and archaea. Draw
an example organism for each shape.
7.
Home-preserved fruit is more likely to be a
source of food poisoning caused by Clostridium
botulinum than fresh fruit. Infer why.
2.
K/U Which of the following statements are true of
prokaryotes? Explain your answers.
a. They include both bacteria and archaea.
b. They do not cause disease in humans.
c. They are only found in extremely hot environments.
d. All are parasitic.
8.
K/U The images below show a bacterial cell dividing
into two cells. The sequence of cell division is incorrect.
Redraw the illustrations in the correct sequence, and
explain what is happening at each step.
3.
K/U Why is being able to form endospores
advantageous?
4.
Scientists use several characteristics to classify
prokaryotes.
a. Explain how the Gram stain is used to classify
bacteria.
b. What is the modern approach to classification of
prokaryotes?
9.
A
“Of all types of agriculture, intensive livestock
operations (feedlots) are the most damaging in
terms of greenhouse gas emissions.” Explain this
statement in terms of metabolism of some species of
the kingdom Archaea.
10.
Predict what Earth’s atmosphere might be like
today had cyanobacteria not appeared some two to
three billion years ago.
11.
A
Our intestinal tract is filled with an enormous
number of helpful bacteria called probiotic bacteria.
Probiotic bacteria inhibit the growth of disease-causing
bacteria, particularly those responsible for
gastrointestinal infections. Predict the possible effects
of the overuse of antibiotics on probiotic bacteria living
in our digestive system and the possible consequences
to an individual.
12.
A
An expedition to Iceland’s hot springs has
yielded new strains of bacteria. These bacteria may be
able to produce hydrogen and ethanol fuels from
wastewater that is discharged from factories processing
sugar beets, potatoes, and other plant material. What
would be the advantages of this type of practice?
5.
C
K/U
A
The image shows the cross sections of two cell
walls. Based on what you know about the Gram stain,
which do you think is the cell wall of a Gram-positive
bacterium and which is that of the Gram-negative one?
Why?
cell wall
with thin
layer of
protein
cytoplasm
outer
membrane
cell
membrane
cell wall
with thick
layer of
protein
6.
T/I
cytoplasm
C
Use a flowchart to show the sequence the steps
involved in conjugation.
66 MHR • Unit 1 Diversity of Living Things
T/I
SECTION
Eukaryotic Evolution and Diversity
2.3
For about 1.5 billion years, prokaryotes were the only organisms on Earth. From about
3.5 to 2 billion years ago, prokaryotic organisms thrived in many different ecosystems,
some carrying out photosynthesis while others survived in extreme environments
without light. Today, prokaryotes are still widespread throughout Earth’s ecosystems
and thrive in a diversity of ways. However, they now live in the presence of many other
types of organisms that are larger and more complex than they are. About 2 billion
years ago, eukaryotes evolved, which led to an increase in the diversity of life on Earth.
Eukaryotic organisms are more complex than prokaryotes. Eukaryotes usually have
far more genes than prokaryotes, allowing for greater cellular diversity in terms of size,
shape, mobility, and specialized functions. For example, the single cell that represents
the start of a human being contains instructions for countless cell divisions that
ultimately produce an organism of trillions of cells. Today scientists continue to collect
data and examine evidence to answer an important question: How did eukaryotic
organisms develop?
Key Terms
endosymbiosis
endosymbiont
host cell
Endosymbiosis
One of the main theories about the origin of eukaryotic organisms is that the
eukaryotic cell represents the merger of two or more simpler cells, possibly
prokaryote-like ones. This is known as endosymbiosis, which is shown in Figure 2.14.
In endosymbiosis, one cell engulfs a different type of cell. However, the engulfed cell
survives and becomes an internal part of the engulfing cell.
Recall that prokaryotes lack many internal structures and the only membrane is
the one that surrounds the cell. In contrast, eukaryote structure is internally complex,
with multiple, membrane-bound organelles. It is believed that these organelles are
the ancestors of once free-living prokaryotes. Two eukaryotic organelles present the
strongest evidence of endosymbiosis in early eukaryotes. One is the chloroplast, an
organelle found in photosynthetic eukaryotes that converts solar energy into sugar.
The other is the mitochondrion, an organelle that does the opposite—it extracts energy
stored in sugar so that the cell can do work.
endosymbiosis theory
that explains how
eukaryotic cells evolved
from the symbiotic
relationship between
two or more prokaryotic
cells
aerobic
bacterium
nucleus
endoplasmic
reticulum
cyanobacterium
cell has a
nucleus and other organelles
cell has
mitochondria
cell has
chloroplasts
Figure 2.14 A likely event in the evolution of the eukaryotic cell was the endosymbiotic
engulfing of smaller cells that became part of the larger one.
Chapter 2 Diversity: From Simple to Complex • MHR 67
endosymbiont a
cell that is engulfed
by another cell in
endosymbiosis
host cell a cell that
engulfs another cell in
endosymbiosis
Chloroplasts and Mitochondria
The theory of endosymbiosis suggests that mitochondria and chloroplasts were once
small, free-living prokaryotes. In separate events during evolutionary history, they
were engulfed by other, larger cells. Rather than being digested, they remained intact.
They continued to do inside these cells what they had previously done outside—
convert solar energy into molecular energy in the case of the chloroplast, and convert
molecular energy into work in the case of the mitochondrion. The organelle is called an
endosymbiont and the engulfing cell is a host cell. This arrangement benefited the host
cell by making it more energy efficient.
There is much evidence supporting the endosymbiotic theory. The membranes
of chloroplasts and mitochondria are similar to those of living prokaryotes. The
ribosomes, structures used to assemble proteins, in these organelles are much more
similar to prokaryotic ribosomes than to the ribosomes elsewhere in the eukaryotic
cell. These organelles also reproduce by binary fission within the cell, as shown in
Figure 2.15. Finally, each contains a circular chromosome, and many of the gene
sequences closely match those of living prokaryotes. Not surprisingly, the genes in the
chloroplast most closely match the genes of modern cyanobacteria, the prokaryotes
that are masters of photosynthesis.
nucleoid
mitochondrion
Figure 2.15 Mitochondria have their own genetic material in a bacteria-like chromosome.
Like bacteria, they also divide by binary fission.
Explain how this genetic material and mode of reproduction support the endosymbiotic
theory of eukaryotic evolution.
68 MHR • Unit 1 Diversity of Living Things
Multicellularity
Endosymbiosis may be responsible for the complex eukaryotic cell, but by itself it does
not account for multicellularity, another eukaryotic advance. Recall that prokaryotes
sometimes form aggregations, such as chains. Generally, the cells in prokaryotic
aggregations carry out the same function, without specialization. In addition, these
aggregations are considered to be collections of individuals, not one individual,
although they are often clones of each other.
After eukaryotes appeared on Earth, a great variety of unicellular forms evolved,
but multicellular forms came later. Biologists use a range of evidence to estimate that
the first multicellular organisms existed 1.2 to 1.5 billion years ago, so they have existed
on Earth less than half as long as unicellular organisms. The oldest such fossils are of
red algae found in rocks in arctic Canada, shown in Figure 2.16. These were still simple
organisms by modern standards. Based on fossil evidence, scientists think that large,
complex eukaryotes first developed about 550 million years ago.
Figure 2.16 Ancient
sedimentary rocks of arctic
Canada have provided
fossils that are clues to the
evolution of multicellularity
and sexual reproduction in
eukaryotes.
Scientists hypothesize that the first multicellular organisms arose from colonies
created by dividing individual cells. Genes within these cells contained instructions
for some of the cells to become specialized for different functions. With the passage of
thousands of years, increasing specialization made it possible for different functions
to develop among different groupings of cells in multicellular organisms. For example,
some groups of cells became specialized to absorb nutrients, while others became
specialized to gather information from the environment.
Learning Check
13. List several ways in which eukaryotic organisms can
be considered more complex than prokaryotic ones.
14. What is endosymbiosis? How is it related to the
evolution of eukaryotic cells?
15. In point form, list the evidence that supports the
endosymbiotic theory.
16. Which group of organisms have gene sequences
most similar to the genes found in the circular
chromosome in chloroplasts? Explain why.
17. How do prokaryotic aggregations and multicellular
eukaryotic organisms differ, given that they are both
made of multiple cells?
18. Make a timeline showing the major dates in the
evolution of large, complex eukaryotes.
Chapter 2 Diversity: From Simple to Complex • MHR 69
Life Cycles and Reproduction
Not only are eukaryotes more structurally diverse than prokaryotes, but they have
more reproductive diversity as well. In prokaryotes, cell division and reproduction are
usually the same process: asexual reproduction. In unicellular eukaryotes, this is also the
case sometimes. However, in most eukaryotes, even unicellular ones, things are more
complicated. Some use more complicated methods of asexual reproduction, such as
multiple fission, in which there are multiple copies made of a cell more or less at one time.
More significantly, especially in multicellular individuals, cell division is not the
same as reproduction at the level of the individual. For example, in humans, individual
cells are being reproduced all the time. However, reproduction of individual organisms
is through sexual reproduction. Sexual reproduction is common among eukaryotes. In
sexual reproduction, two individuals make eggs and sperm, known as gametes, which
are haploid. Haploid cells contain only one set of chromosomes, compared to the two
sets of chromosomes in other cells. When an egg and a sperm cell fuse, they form a
zygote, a cell that is diploid. A diploid cell contains two sets of chromosomes, one set
inherited from each parent cell. Sexual reproduction is not possible without meiosis,
which is unique to eukaryotes. You will learn more about meiosis in Chapter 4.
Figure 2.17 compares asexual and sexual life cycles among organisms. Sexual life
cycles vary, but there are features that are common to all. Most importantly, organisms
that reproduce through sexual reproduction alternate between meiosis, which makes
sperm and eggs, and fertilization, which merges sperm and egg. What varies among
organisms is the timing of these two events.
os
is
asexual
reproductive
structures
m
it
Asexual Life Cycle
os
is
haploid or
diploid
organism
t
mi
Sexual Life Cycle
Gametic
Zygotic
Sporic
mitosis haploid
stage
organism
mitosis
mitosis
gametes
diploid
diploid
stage
organism
mi
to s i s
n
tio
iza
til
zygote
n
tio
iza
til
n
tio
iza
til
zygote
diploid
r
fe
r
fe
r
fe
to s i s
mitosis
haploid
haploid
diploid
mi
is
os
haploid
diploid
organism
ei
m
is
os
ei
m
is
os
ei
m
gametes
spores
haploid
organism
spores
zygote
gamete
Figure 2.17 Life cycles can be asexual or sexual.
70 MHR • Unit 1 Diversity of Living Things
Section 2.3
RE V IE W
Section Summary
• Scientists hypothesize that eukaryotic cells developed in
the past through endosymbiosis.
• The two organelles that present the strongest evidence of
endosymbiosis are chloroplasts and mitochondria.
• In eukaryotes, sexual life cycles vary, but they alternate
between meiosis, which produces haploid cells, and
fertilization, which produces diploid cells.
Review Questions
1.
K/U What is the advantage of a eukaryotic cell
having more genes than a prokaryotic cell?
2.
C
Write a short paragraph persuading the reader
to accept the endosymbiosis hypothesis.
3.
C
Draw the hypothesized sequence of events of
endosymbiosis leading to the development of a
plant cell.
4.
T/I Nearly all eukaryotic cells contain
mitochondria, but only some, such as plants and some
protists, contain chloroplasts as well. Which
endosymbiotic event do you think came first, engulfing
a cyanobacterium that became a chloroplast or
engulfing a heterotrophic bacterium that became a
mitochondrion? Explain your reasoning.
5.
K/U What is the main difference between the
gametic and the zygotic life cycles shown in
Figure 2.17?
6.
A
Use the illustration below to explain the possible
evolution of the eukaryotic animal cell.
early bacteria
aerobic bacteria
primitive
prokaryote
ancestral
eukaryote
7.
8.
9.
C
Copy the cell that represents the ancestral
eukaryote in the diagram above into your notebook.
Label the diagram to identify the endosymbiont and the
host cell.
K/U
Explain how mitochondria reproduce.
K/U How do scientists think that multicellular
eukaryotes arose?
10.
A
Relate the idea of groups of specialized cells in
multicellular organisms to three functions in the
human body.
11.
K/U What is the main difference in reproduction
between prokaryotes and eukaryotes?
12.
Use a Venn diagram to compare and contrast a
gamete and a zygote.
13.
A
Refer to Figure 2.17. Identify whether the life
cycle of the organisms described below is asexual or
sexual. For those that you have identified as sexual life
cycles, determine if they are gametic, zygotic, or sporic.
a. Sea lettuce (Ulva) has two life stages. In stage 1,
a zygote undergoes meiosis and releases swimming,
haploid spores. These spores grow into male and
female haploid organisms. In stage 2, the haploid
organisms undergo mitosis to produce mobile male
and female gametes. The gametes fuse together
and swim to the bottom, where they grow into the
zygote once more.
b. Plants have a diploid stage, in which cells
undergoing meiosis produce haploid reproductive
cells called spores. The spores develop into haploid
organisms that produce haploid gametes by mitosis.
The gametes unite to produce a diploid zygote
that grows into a diploid stage organism, thus
completing the cycle.
c. Paramecia are unicellular organisms belonging to
the kingdom Protista. Under normal circumstances,
paramecia reproduce by splitting themselves down
the middle, with each new paramecium receiving
half of the organelles. This process is called binary
fission.
d. A fertilized egg of a fish is called a zygote. The
diploid zygote uses mitosis to develop into an
adult diploid organism. Specialized cells in the
reproductive organs of the adults undergo meiosis
to create haploid gametes. When the adult fish
spawn, the sperm from the male fertilize the eggs
released by the female to form the diploid zygote.
C
Chapter 2 Diversity: From Simple to Complex • MHR 71
SECTION
Protists: The Unicellular Eukaryotes
2.4
A drop of pond water under a light microscope can reveal a great diversity of life that
is invisible to the unaided eye. Single-celled organisms with a variety of shapes and
colours move about using long whips or numerous tiny moving hairs—spinning,
lurching, reversing, and investigating their environment. Compared to the prokaryotic
cells visible only under higher power, these protists are large, diversely shaped, and
captivating to watch.
Key Terms
protist
parasite
pseudopod
cilium
flagellum
red tide
Characteristics of Protists
Most protists are unicellular. They are grouped as protists mainly because they do not
fit into the other kingdoms, rather than because they are similar or closely related to
one another. One group of protists that biologists do not agree on is the multicellular
algae. This group of organisms can be divided into distinct groups (red, green, and
brown algae). However, some taxonomists place them in the plant kingdom, others in
the protist kingdom, and still others consider the red and green algae as plants but the
brown algae as protists. In this textbook, the multicellular algae and their relationship
with plants will be discussed in Chapter 3. Chapter 2 restricts the survey of protists to
the three groups of unicellular eukaryotes shown in Table 2.3. These three groups are
based on the method of obtaining nutrition.
protist a eukaryotic
organism, usually
unicellular, that is not a
fungus, plant, or animal
Table 2.3 Unicellular Protists
Animal-like Protists
(Protozoans)
Group
Amoebas, ciliates (shown below),
and flagellates
Example
Distinguishing
characteristics
Fungus-like Protists
Slime moulds (shown below) and
water moulds
Magnification: 180×
• They are animal-like because
they consume other organisms
for food.
• Some species are parasites.
parasite an organism
that benefits by living in
or on another organism
at the expense of that
organism
Plant-like Protists
Euglenoids, diatoms (shown below),
and dinoflagellates
Magnification: unavailable
• They are fungus-like because
they absorb nutrients from other
organisms, living or dead.
• Some slime moulds consume
other organisms. Some water
moulds are parasites.
• They are plant-like because
they make their own food by
photosynthesis.
• Some consume other organisms
when light is unavailable. Some
live as symbionts within other
organisms.
Animal-like Protists
The animal-like protists, often called protozoans, are heterotrophs. They commonly
consume other organisms for food, especially prokaryotes and other protozoans, or
organic wastes. A number of species are parasites, taking nutrients from the organisms
in which they reside.
72 MHR • Unit 1 Diversity of Living Things
The Cercozoans: Phylum Cercozoa
The most familiar of the cercozoans are the amoebas. Their surface is a cell membrane
without a cell wall. This means they change shape, using their internal cytoskeleton
to move and create different forms. Temporary extensions of the cytoplasm that are
created this way are called pseudopods (“false feet”). Pseudopods are used for both
feeding and locomotion, as shown in Figure 2.18.
pseudopod (plural
pseudopodia) a
temporary cytoplasmic
extension that amoebas
use for feeding and
movement
pseudopodia
cytoplasm
nucleus
food
vacuole
contractile
vacuole
Figure 2.18 When amoebas detect food, they form pseudopods from the cell membrane
and engulf the target.
Amoebas live in salt water, fresh water, and mud, and a few are parasites living
inside an animal host. For example, Entamoeba hystolitica feeds on the lining of the
small intestine in humans and causes a serious illness called amoebic dysentery. Many
other species of intestinal amoeba also live inside humans without causing significant
problems. Intestinal amoebas can be spread by drinking contaminated water or by
eating produce that has been contaminated.
The Ciliates: Phylum Ciliophora
Ciliates, such as the one in Figure 2.19, have many short, hair-like projections that cover
the surface of the cell. These hair-like projections are called cilia (singular cilium).
Cilia have a dual purpose—locomotion and sweeping food particles along the cell
surface to move them into the cell. Some of the best-known ciliates are in the genus
Paramecium, and are known as paramecia.
Many species of ciliates are large and complex, growing to over 100 μm in length.
As with the other groups of protozoans, some members are free-living, like paramecia,
and some are parasites. Only one species of ciliate is known to be a parasite of
humans—Balantidium coli lives in the large intestine and causes diarrhea.
Cilia The cell is covered
by thousands of
tiny hair-like cilia.
cilium (plural cilia)
a short, hair-like
projection that functions
in cell movement and
particle manipulation
when coordinated with
other cilia
Figure 2.19 Paramecia use
cilia to move through the
water and to move food
into the gullet.
Oral groove and gullet
The action of cilia moves
food down the oral groove
into the gullet.
Food vacuole The food
vacuole, where the meal
is digested, forms at the
end of the gullet.
Chapter 2 Diversity: From Simple to Complex • MHR 73
flagellum (plural
flagella) a long, hair-like
projection extending
from the cell membrane
that propels the cell
using a whip-like motion
Magnification: 90×
Figure 2.20 Members of
the genus Trichonympha
have a mutualistic
relationship with termites.
Flagellates: Phylum Zoomastigina
Protists in this phylum are called flagellates because they have one or more flagella
that whip from side to side to move them about. Flagellates have a hard protective
covering over their outer membrane. Some species are free-living, some are parasites,
and some live in mutualistic relationships. Recall that in mutualistic relationships, both
organisms benefit from the relationship.
Some examples of mutualistic flagellates include many species that live in the
digestive tract of animals and help the host animals digest plant material. For example,
termites feed on wood, but they are unable to digest the tough cellulose that makes
up a large part of their diet. Flagellates, like the one shown in Figure 2.20, live in termite
intestines and produce enzymes that convert cellulose to sugars, which the termites
can use. In return, the flagellates receive a steady supply of food and a warm and
protected environment.
The Sporozoans: Phylum Sporozoa
Sporozoans are parasites of animals, taking the nutrients they need from their hosts.
Most members of this group have life cycles that alternate between sexual and asexual
reproduction—and often alternate between two hosts. Protists in the genus Plasmodium
cause malaria in humans. Figure 2.21 shows how these protists are transferred to
humans from mosquitoes. Up to two million people die annually from malaria.
B The reproductive cells fuse inside the mosquito to
A A mosquito feeds on an infected
form a zygote. The zygote divides many times to form
numerous spore-like cell fragments. Eventually, the
zygote breaks open, releasing cells called sporozoites.
person. It ingests reproductive
cells of Plasmodium present in
red blood cells.
zygote
gametes
gut wall
of mosquito
C The sporozoites invade the mosquito’s
salivary gland, from where they will be
injected into a new host when the
mosquito bites again.
sporozoites
human host
E The blood cells rupture, releasing
toxic substances and great numbers
of spores. These spores go on to
infect more red blood cells.
D Inside the human host, the sporozoites reproduce asexually
in the liver to form a second type of spore-like cell. From the
liver, these new spores enter the bloodstream, invade red
blood cells, and multiply rapidly inside them.
Figure 2.21 The life cycle of the malaria-causing protist Plasmodium involves two hosts, a
mosquito and a human. Symptoms of malaria include high fever, chills, nausea, and vomiting.
Explain what happens to sporozoites when they enter a human liver.
74 MHR • Unit 1 Diversity of Living Things
Fungus-like Protists
The members of this group are heterotrophs, but instead of ingesting other organisms,
they absorb nutrients from living organisms, dead organisms, and wastes. Like fungi,
fungus-like protists produce spores. However, they differ from fungi at the cellular
level. For example, the cell wall of fungus-like protists is different from the cell wall of
fungi. Some examples of fungus-like protists include slime moulds and water moulds,
as shown in Table 2.4. Slime moulds are divided into two main groups: plasmodial
slime moulds and cellular slime moulds.
Table 2.4 Fungus-like Protists
Type
Description
Example
Plasmodial slime
moulds: Phylum
Myxomycota
Plasmodial slime moulds are visible to the unaided eye as
tiny slug-like organisms that creep over damp, decaying
plant material in forests and fields. This streaming blob,
called a plasmodium, contains many nuclei. Like amoebas,
these slime moulds feed by engulfing small particles
of food into their cytoplasm. Some of the cytoplasm is
concentrated to form a skeleton-like structure through
which the liquid cytoplasm flows.
Cellular slime
moulds: Phylum
Acrasiomycota
Cellular slime moulds exist as individual amoeboid cells
with one nucleus each. Like protozoans, each cell feeds by
ingesting tiny bacteria or yeast cells. When food becomes
scarce, the cells release a chemical that causes them to
gather together to form a pseudoplasmodium. Despite
their names and similarities, there is no strong evidence
that the two types of slime moulds are closely related.
Water moulds:
Phylum
Oomycota
Water moulds are filamentous organisms that resemble
fungi. Most live on dead organic matter. Some species,
however, are parasites on fish, insects, and plants. They
extend fungus-like threads into their host’s tissues, where
they release digestive enzymes and absorb the resulting
nutrients.
Activity
2.3
Slime Moulds: Science, Technology, Society, and the Environment
Would it surprise you to know that scientists use slime
moulds in cancer research, or to learn more about diseases
such as Alzheimer’s disease? Or that, through the Planetary
Biodiversity Inventory (PBI), scientists are studying the
worldwide distribution of slime moulds and trying to
complete a worldwide inventory of slime mould species?
Although it may not seem like it, slime moulds can have an
interesting and important impact on technology, society,
and the environment.
• “Alien” Invasion: Fuligo septica (Common Name: Dog
Vomit Slime Mould)
• Slime Moulds Form Hirano Bodies: Used in Alzheimer’s
Research
2. Use the Internet to research information about your topic.
Questions
1. Answer the following questions as you complete your
research:
Procedure
a. What is the story behind the topic?
1. Choose one of the following topics about slime moulds
to research. Or, you could choose your own topic.
b. What, if any, research is being conducted on this topic?
• Slime Mould Physarum polycephalum: Used to Solve
Traffic Jams?
• Phytophthora infestans and the Irish Potato Famine
c. How does this topic impact technology, society, or
the environment?
2. Prepare a short presentation of your topic to share with
the class. Consider questions your audience may ask
about the topic as you prepare your presentation.
Chapter 2 Diversity: From Simple to Complex • MHR 75
Learning Check
19. Most organisms are grouped together because
they are similar or closely related to each other.
How does the grouping of protists by taxonomists
differ from this?
22. Compare and contrast plasmodial slime moulds and
cellular slime moulds.
20. What is the function of a pseudopod?
24. Interpret the following statement for a Grade 6
student. “Many scientists use the word protozoan
to refer to a eukaryotic, unicellular, heterotrophic
protist, such as an amoeba or a ciliate.”
21. Use a Venn diagram to compare and contrast cilia
and flagella.
23. Give two examples of protists that are parasites and
the problems they cause their host.
Plant-like Protists
Plant-like protists contain pigments in their chloroplasts to carry out photosynthesis.
The most common of these pigments is chlorophyll, which gives many of them
a green colour. Unicellular plant-like protists include diatoms, dinoflagellates, and
euglenoids.
Magnification: 125×
Figure 2.22 The many
species of diatoms have
different shapes and sizes
based on differences in
their silica walls.
Diatoms: Phylum Chrysophyta
Phytoplankton are single-celled, free-floating aquatic organisms. Diatoms, shown
in Figure 2.22, are among the most diverse and abundant phytoplankton and are an
important source of food for larger marine organisms. Diatoms have rigid cell walls
with an outer layer of silica, a common ingredient in sand and glass. The walls are made
of two unequal parts, the smaller of which fits neatly inside the other, like a box with
a lid. Most of the time, diatoms reproduce asexually by mitosis. Sexual reproduction
is less common and occurs under unfavourable environmental conditions. The
reproductive cycle of diatoms is shown in Figure 2.23.
mitosis
SuggestedInvestigation
mitosis
Inquiry Investigation 2-B,
Sampling Pond Organisms
wall formation
around cell
Asexual reproduction
meiosis
Sexual reproduction
zygote
gametes
fusion of
gametes
sperm
released
Figure 2.23 Diatoms usually reproduce asexually, but under certain conditions they
also reproduce sexually.
Describe the steps involved in sexual reproduction of diatoms.
76 MHR • Unit 1 Diversity of Living Things
Dinoflagellates: Phylum Pyrrophyta
Like diatoms, most dinoflagellates are phytoplankton. A distinguishing feature of
dinoflagellates is that they have two flagella at right angles to each other. As the flagella
beat, a twirling motion is produced, so these organisms move by spinning through
the water.
Under conditions such as plentiful nutrients, dinoflagellates reproduce very quickly.
The resulting population explosion is called a bloom or algal bloom. In species that
have red photosynthetic pigments, the bloom is referred to as a red tide, an example
of which is shown in Figure 2.24. The species that form red tides produce a toxin that
becomes concentrated in the tissues of plankton-eating shellfish. If humans eat those
shellfish, they can become seriously ill or die.
red tide a coastal
phenomenon in which
dinoflagellates that
contain red pigments
are so concentrated
that the seawater has a
distinct red colour
Magnification: 12 000×
Figure 2.24 Dinoflagellates, such as Gonyaulax catenella, can cause red tides, in which many
marine organisms can die and shellfish can become toxic.
Some species of dinoflagellates live inside other organisms. The best known of these
are the reef-building corals. Living inside many species of coral are dinoflagellates of
the genus Symbiodinium. The protists benefit by using nitrogen wastes and carbon
dioxide obtained by the coral, and the coral gains the benefits of photosynthesis,
which is carried on by the protists. If ocean temperatures rise to abnormal levels, the
coral-protist partnership breaks down and the protists are expelled in a process referred
to as coral bleaching. Bleaching often results in the death of the corals. As Earth’s
climate has warmed in recent decades, more frequent incidences of dinoflagellates
being expelled from corals have occurred. Permanent damage has resulted, including to
Australia’s Great Barrier Reef. When coral reefs are permanently damaged as a result of
bleaching, other organisms that consume coral or live on the reef are also affected.
Euglenoids
There are over one thousand species of euglenoids, most of which are found in shallow
fresh water. Although they have chloroplasts and conduct photosynthesis, they also have
flagella and can absorb nutrients. With both plant-like and animal-like characteristics,
euglenoids tend to be autotrophs in sunlight and heterotrophs in the dark.
Euglenoids in the genus Euglena, such as the one shown in Figure 2.25, have a
light-detecting structure called an eyespot. This light receptor does not create an image
like the animal eye, but it does allow these protists to use their flagella to orient toward
the light.
Magnification: 300×
Figure 2.25 Euglena
gracilis are commonly
found in slow-moving
or standing water, such
as ponds on or near
agricultural fields.
Chapter 2 Diversity: From Simple to Complex • MHR 77
Section 2.4
RE V IE W
Section Summary
• Protists are generally divided into three groups based
on how they obtain nutrition: animal-like protists,
fungus-like protists, and plant-like protists.
• Animal-like protists are called protozoans and include
amoebas and paramecia.
• Fungus-like protists include slime moulds and water
moulds.
• Plant-like protists include diatoms, dinoflagellates, and
euglenoids. Dinoflagellates can cause red tides when
nutrients are plentiful.
• Some protozoans, such as Entamoeba hystolitica and
Balantidium coli, can cause intestinal infections in
humans. Several types of sporozoans cause malaria
in humans.
Review Questions
1.
K/U Explain how the kingdom Protista is different
from other kingdoms.
2.
K/U List the three main groups in the kingdom
Protista. What are their modes of nutrition?
3.
C
Use a graphic organizer to summarize the
following information about protozoans: representative
organisms, methods of locomotion, their relationships
with other organisms, and how they affect an
ecosystem.
4.
K/U In what way do slime moulds resemble the
following?
a. fungi
b. plants
c. protists
5.
A
In coastal areas of Canada where shellfish are
harvested for human consumption, local authorities
monitor the populations of dinoflagellates in the water
during harvest season. Why do they do this?
6.
T/I During an ecology field trip, a group of students
collected data about diatoms in a pond. They measured
the number of cells in the water at various depths. They
produced the graph below based on their data. Use the
graph to answer the following questions.
a. At what time were the highest concentrations of
diatoms at the surface?
b. At what time were the highest concentrations of
diatoms below the surface?
c. Why might the diatoms show the pattern shown in
the graph?
Location of Highest
Concentration
of Diatoms
Locations of Diatoms
7.
A
In the 1800s, malaria was a fairly common
disease in parts of North America. One method for
fighting the incidence of malaria was to eliminate
swampy and marshy areas by filling them in with soil.
a. What reasoning do you think was used to come up
with this method?
b. What are some possible negative consequences of
using this method to reduce the incidence of malaria?
8.
K/U Study the drawings below. Identify the phylum
to which each organism belongs. Explain how you
decided where each organism belongs.
a.
9.
100 cm
12 A.M.
12 P.M.
12 A.M.
Time
78 MHR • Unit 1 Diversity of Living Things
12 P.M.
c.
d.
C
Make a concept map that relates the following
terms: plant-like, protozoans, Entamoeba hystolitica,
protists, fungus-like, water moulds, cercozoans,
Euglena gracilis.
10.
Explain why it would be difficult to categorize a
euglenoid protist as a producer or a consumer.
11.
C
Use Figure 2.23 to construct a graphic organizer
summarizing the reproductive life cycle of a diatom.
12.
K/U Identify two examples of protists that have
mutualistic relationships with other organisms. Explain
how each organism benefits from the relationship.
13.
Use a flow chart to sequence the events that can
occur on a coral reef if water temperatures rise too
high. In the last box, predict what could happen to
organisms that consume coral or live on the reef.
Surface
50 cm
b.
A
C
ThoughtLab
2-A
INVESTIGATION
Skill Check
Measles Immunization
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Measles is a viral infection that causes high fever and a cough. A vaccine for
measles has been available since the early 1960s. The World Health Organization
(WHO) tracks data on the incidence of measles as well as the percentage of
people around the world who receive the measles vaccine each year. In this
investigation, you will study the relationship between the percentage of people
immunized and the incidence of measles.
Materials
• graph paper
• coloured pencils
Pre-Lab Questions
• ruler
1. Why is measles considered to be a public health issue?
Measles Incidence and Immunizations
2. What are the independent and dependent variables in this investigation?
3. How will you show the relationship between the variables?
Year
1980
Incidence of
Measles
(* indicates
estimation)
4 211 431
Percent
Immunized
13
1981
4 450 892*
18
1982
4 100 301*
19
1983
3 843 120*
36
1984
3 390 233*
38
1985
3 029 892*
42
1986
2 375 248*
60
1987
1 904 678*
62
1988
1 807 233*
66
1989
1 984 329*
73
1990
1 374 083
80
1991
1 450 609*
80
1992
1 499 898*
80
1993
1 293 102*
80
1994
900 304*
80
1995
760 634*
80
1996
851 904*
81
1997
753 819*
82
1998
694 466
80
1999
752 407
80
2000
852 937
81
2001
846 765
72
2002
574 171
77
2003
680 454
81
2004
509 734
85
2005
601 232
84
2006
373 941
90
2007
280 771
90
Question
What is the relationship between immunization and the incidence of measles?
Organize the Data
1. Construct a graph to plot the data. Place Year on the x-axis. Place Incidence
on the left y-axis and Percent Immunized on the right y-axis.
2. Determine how you will represent each portion of the data on your graph.
For example, you may choose to represent the Incidence data using bars and
the Percent Immunized data using a line.
3. Use the coloured pencils to plot the points on your graph.
Analyze and Interpret
1. Identify the relationship between the incidence of measles and the
percentage of people receiving a vaccine each year.
2. Explain why you think this relationship exists.
Conclude and Communicate
3. In Ontario, it is mandatory for students to receive a measles vaccine.
Exemptions from the vaccine are available. For example, some people
may be allergic to the vaccine. People with immune disorders often are
advised not to receive a vaccine. Others might have a religious objection to
receiving vaccines. Write a short paragraph expressing your opinion about
exemptions. Consider how exemptions might affect public health.
4. Suppose the virus that causes measles was completely eliminated as a result
of vaccine use. Do you think this would constitute a risk to the diversity of
living things? Explain your answer.
Extend Further
5. INQUIRY How do vaccines affect the immune system? What variables
might you monitor in an investigation that asks this question?
6. RESEARCH Would a vaccination program be an effective way to reduce the
incidence of bacterial infections such as E. coli? Why or why not?
Chapter 2 Diversity: From Simple to Complex • MHR 79
Inquiry
INVESTIGATION
2-B
Skill Check
Initiating and Planning
✓
Performing and Recording
✓
Analyzing and Interpreting
✓
Communicating
Materials
• sample of pond water
• thread
• methyl cellulose solution
• iodine
• paper towel
Sampling Pond Organisms
The microscopic organisms that float at or near the surface of bodies of water
are collectively known as plankton. Phytoplankton are plankton that carry
out photosynthesis. They may be members of the kingdom Bacteria, Protista,
or Plantae. Zooplankton move and consume other organisms. They may be
members of the kingdom Protista or Animalia. In this investigation, you will use
techniques of sampling and classification to measure the diversity of organisms
in pond plankton.
Pre-Lab Questions
1. What distinguishing features will you look for to help you identify different
types of plankton?
• methylene blue stain
2. Where should you look on your slide to find heterotrophic plankton?
• prepared slides of protists
(e.g., amoeba, paramecium,
spirogyra, vorticella)
3. Why should you turn off the light on your microscope when you are not
looking through the lens?
• light microscope
• dropper
• depression slide
• cover slip
Safety Precautions
• Some protists cause disease. Do
not eat or drink while performing
this lab.
• Iodine stains clothing and skin.
Question
How can you collect and classify pond plankton to accurately reflect the
diversity of the pond ecosystem?
Procedure
1. Obtain samples of pond water from your teacher or by collecting them
yourself during a class field trip.
2. Prepare a table in your notebook to record the name of each organism, the
kingdom and subgroup in which it is classified, its relative abundance, and a
labelled sketch of the organism.
3. To become familiar with the appearance and identity of some common
pond micro-organisms, study the illustrated field guide to protists
below and on the next page. Examine several prepared slides under the
microscope.
• Methylene blue may stain clothing
and skin.
Guide to Common Protists
The illustrations on these two pages are not drawn to scale.
• Wash your hands with soap and
water upon completion of this
investigation.
paramecium
carchesuim
chlorella
amoeba
colpoda
lacrymaria
pandorina
chlamydomonas
80 MHR • Unit 1 Diversity of Living Things
vorticella
mayorella
arcella
coleps
4. Place a drop of the sample on a slide and prepare a wet
mount by placing a piece of thread across the sample
and a drop of methyl cellulose (to slow down any
protozoans) before placing the cover slip on.
5. Observe the slide under low power of your microscope
and orient the slide so that the thread is in the centre
of the field of view. Scan up and down the thread until
you find an area that contains particulates or algae.
Zooplankton will likely be found in this area as well.
6. Select one species from your slide sample and study it
under medium and then high power. Using the Guide
to Common Protists (below), decide which group it
belongs to. Record the identity and relative abundance
of the organism in your table. If you cannot identify
it, make a sketch. Note whether your organism is very
common in your sample, or whether it is relatively rare.
Analyze and Interpret
1. Which kingdom was the most common in your sample
of pond water?
2. How did you distinguish between protists and the
members of other kingdoms?
3. Which subgroup showed the most diversity in your
sample?
Conclude and Communicate
4. Name three factors that might increase the diversity of
plankton species living in a pond. Name three factors
that might decrease the diversity of plankton species in
the pond.
5. Did your sampling have any biases that might have
affected your results? Explain your answer.
6. Did you record more species of phytoplankton or
zooplankton? Suggest why.
7. Make sure you turn the microscope light off when
you are not looking at any specimens. The increased
temperature will kill your specimens.
7. Compare your results of pond organism diversity
with the results of other students in your class.
Note any differences. Using this information, explain
why knowledge of sampling methods and taxonomy
might be important for studying diversity in different
environments.
8. Return to low power and repeat the procedure with
another species. Observe as many different species as
you have time for. If you observe all of the species on
your slide sample, prepare another wet mount using
a different sample of pond water taken from a
different location.
8. Create a dichotomous key to be used to classify the
organisms you identified.
9. To see more detail in samples of phytoplankton,
introduce some iodine stain by placing a drop of stain
on the side of your cover slip and placing a piece of
paper towel on the other side. This will draw the stain
across the slide.
Extend Further
9. INQUIRY You have been chosen to assess and manage
the quality of a watershed that supplies drinking water.
Based on your experiences during this investigation,
develop a procedure to show how you would proceed
with this task. List at least two questions you would
need to answer before you could make your plan.
10. To see more detail in samples of protozoans, repeat
step 9 using methylene blue stain. Note: This will kill
your plankton.
chilomonas
10. RESEARCH How would the diversity in a local pond
ecosystem be affected if run-off from lawns in a local
subdivision was allowed to flow directly into the
pond? Research the impact of phosphates and other
pollutants on a pond ecosystem.
bodo
peranema
difflugia
cymbella
euplotes
diatoma
spirostomum
actinosphaerium
asterionella
navicula
tokophyra
stentor
didinium
Chapter 2 Diversity: From Simple to Complex • MHR 81
Chapter 2
Section 2.1
SUMMARY
A Microscopic Look at Life’s Organization
Prokaryotic cells are smaller than eukaryotic cells, have
less complex cell structure, and have no capacity for
multicellularity. Viruses are smaller than cells and are
dependent on cells for copying themselves.
KEY TERMS
capsid
lysogenic cycle
lytic cycle
prion
replication
virus
KEY CONCEPTS
• There are two basic cell types—prokaryotic cells and
eukaryotic cells.
Section 2.2
coccus
conjugation
endospore
extremophile
Gram stain
mesophile
methanogenesis
KEY CONCEPTS
• The two domains into which prokaryotes are classified
are Bacteria and Archaea. Each of these domains has a
kingdom by the same name.
Section 2.3
• Viruses reproduce through replication within a host cell. They
replicate through the lytic cycle or the lysogenic cycle.
• Prions are infectious particles that appear to consist mostly
or entirely of a single protein.
• Bacteria and archaea have three basic shapes—cocci,
bacilli, and spiral.
• A major group of archaea are methanogens that produce
methane. A major group of bacteria are cyanobacteria that
use photosynthesis.
• Extremophiles occupy habitats of extreme conditions, and
most are archaea. Mesophiles occupy habitats that have
moderate conditions. Most bacteria are mesophiles.
• Prokaryotes reproduce asexually through binary fission.
They can exchange DNA through the process of conjugation.
• Prokaryotes were once classified by shape and responses
to stains, but modern taxonomists use DNA sequences.
KEY CONCEPTS
• Scientists hypothesize that eukaryotic cells developed in
the past through endosymbiosis.
• The two organelles that present the strongest evidence
of endosymbiosis are chloroplasts and mitochondria.
KEY TERMS
endosymbiont
endosymbiosis
host cell
• In eukaryotes, sexual life cycles vary, but they alternate
between meiosis, which produces haploid cells, and
fertilization, which produces diploid cells.
Protists: The Unicellular Eukaryotes
Protists are eukaryotes that are classified into three
groups: plant-like, fungus-like, or animal-like.
KEY TERMS
cilium
flagellum
• Viruses can be classified by the size and shape of their capsid.
Eukaryotic Evolution and Diversity
Eukaryotic cells likely evolved through endosymbiosis.
This process resulted in larger, more complex cells that
eventually led to multicellularity.
Section 2.4
• Because viruses cannot function independently in any way,
some scientists believe they are not living organisms.
Comparing Bacteria and Archaea
Bacteria and archaea are small prokaryotic single-celled
organisms that are in separate domains.
KEY TERMS
archaeon
bacillus
bacterium
binary fission
• Prokaryotic cells are smaller and less complex than
eukaryotic cells. Prokaryotic cells do not have a membranebound nucleus or other membrane-bound organelles.
parasite
protist
pseudopod
red tide
• Animal-like protists are called protozoans and include
amoebas and paramecia.
• Some protozoans, such as Entamoeba hystolitica and
Balantidium coli, can cause intestinal infections in humans.
Several types of sporozoans cause malaria in humans.
• Fungus-like protists include slime moulds and water moulds.
KEY CONCEPTS
• Protists are generally divided into three groups based on
how they obtain nutrition: animal-like protists, fungus-like
protists, and plant-like protists.
82 MHR • Unit 1 Diversity of Living Things
• Plant-like protists include diatoms, dinoflagellates, and
euglenoids. Dinoflagellates can cause red tides when
nutrients are plentiful.
Chapter 2
REVIEW
Knowledge and Understanding
Select the letter of the best answer below.
1. Which is a method scientists use to classify viruses?
a. size and shape of the capsid
b. presence or absence of a cell wall
c. composition of cell membranes
d. way they obtain nutrition
e. composition of cell walls
2. During the lytic cycle, what happens to a virus after it
enters a host cell?
a. It forms a provirus.
b. It replicates.
c. It dies.
d. It becomes inactive.
e. It undergoes cell division.
3. Which statement about bacteria is true?
a. They cannot exchange DNA.
b. They occur in three main shapes—round, cubic,
and spiral.
c. They are all heterotrophs.
d. They are eukaryotes.
e. They are commonly known as extremophiles.
4. Which best describes plasmids?
a. They are small components of plasma.
b. They are an important means of genetic
recombination in prokaryotes.
c. They help amoebas to move and capture food.
d. They contain genes that are the same as those found
in the chromosome.
e. Once they split from the bacterial chromosome,
they cannot rejoin it.
5. Which structures do some bacteria form when they are
faced with unfavourable environmental conditions?
a. capsids
b. toxins
c. chloroplasts
d. endospores
e. zygotes
6. Which statement about diatoms is true?
a. They are heterotrophs.
b. They are prokaryotes.
c. They have two flagella.
d. They have rigid cell walls with an outer layer of
silica.
e. They lack diversity and only occur in small
numbers.
7. The structure and biochemistry of which two
organelles support the hypothesis of endosymbiosis?
a. cell wall and mitochondria
b. chloroplasts and Golgi body
c. endoplasmic reticulum and cell membrane
d. mitochondria and chloroplasts
e. nucleus and cytoplasm
8. Which is an example of a plant-like protist?
a. Balantidium
d. Paramecium
b. Entamoeba
e. Plasmodium
c. Euglena
Answer the questions below.
9. State whether you agree or disagree with the following
statement, and explain your reasoning: Protozoans are
heterotrophic protists.
10. Which are thought to be more closely related, a
bacterium and an archaeon, or an apple tree and a
great white shark? Why?
11. Why are disease-causing prokaryotes that form
endospores more of a concern for human health than
those that do not?
12. Identify the shapes of the three types of bacteria shown
in the photographs.
A
Magnification:
unavailable
B
Magnification: 300×
C
Magnification: 1200×
13. How are mitochondria and chloroplasts distinct from
other organelles?
14. What are the three main groups of protists, based on
their mode of obtaining nutrition?
15. Compare sexual and asexual reproduction in diatoms.
How do the end products differ genetically from one
another?
16. What is it about the way that euglenoids obtain
nutrition that makes them unique as protists?
Chapter 2 Diversity: From Simple to Complex • MHR 83
Chapter 2
REVIEW
Thinking and Investigation
17. Anabaena is a prokaryote that is found in chains with
two different cell types. What information would
you want to know in order to decide whether it is a
multicellular organism?
18. White blood cells in humans are part of the immune
system and engulf bacteria and act like independent,
living, single-celled organisms. What protist does this
remind you of, and what would you expect to be a
major difference between them?
19. What argument would you make in support of the idea
that the first organisms on Earth were archaea?
20. People have various bacteria that are normally present in
most of their body systems, including the skin, mouth,
and digestive tract. These are essential for maintaining
good health. Comment on the use of antibacterial
soaps, the use of mouthwash that kills all bacteria, and
antibiotics that kill a variety of digestive tract bacteria.
Discuss the pros and cons of using these products.
21. Design and write the procedure for an experiment that
would help you decide if a particular type of bacteria
could grow in anaerobic conditions. Be sure to include
a control and to list the different variables you would
use. (Do not carry out the experiment.)
22. In an experiment, a species of freshwater protozoans
was observed to study its behaviour in different
circumstances. Salt water, vinegar, and sugar water
were added to the protozoans’ environment while
variables such as water temperature, light exposure,
and food availability stayed the same. Answer the
following questions concerning the experiment.
a. What conditions should the control group have?
b. What was the independent variable? What was the
dependent variable?
c. Write a hypothesis that might go with this
experiment.
23. Bacteria, such as the Rhizobium species, play an
important role in the nitrogen cycle, including
converting nitrogen into a form that plants can use.
Rhizobium inoculum is a commercially prepared
solution of living bacteria that is usually applied to the
seed coat of plants at the time of planting. Design an
investigation to test the following hypothesis: If bean
plants are inoculated with Rhizobium species, then
they will have a higher yield of green biomass than
bean plants that are not inoculated with these bacteria.
84 MHR • Unit 1 Diversity of Living Things
24. If someone proposed that viruses were the ancestors
of life on Earth, would you accept this idea? Why or
why not?
Communication
25. Make a six-panel cartoon of the lytic cycle. Add text in
a caption or text bubbles to explain what is happening
in each stage of the cycle.
26. Create a poster of a coral, in which you demonstrate at
least three endosymbiotic relationships.
27. Imagine you are a taxonomist and you wish to
persuade your colleagues to abandon the idea of a
protist kingdom. Write an argument of approximately
five sentences in which you explain why the kingdom
Protista is an artificial one and what kingdom(s) you
propose to replace it.
28. Use a Venn diagram to compare and contrast bacteria
and archaea.
29. The bacterium Mycobacterium tuberculosis causes the
often fatal disease tuberculosis (TB) in humans. TB,
which attacks the lungs, was thought to be almost
eradicated from North America, but in recent times
this disease is making a comeback. The bacteria
are easily passed from person to person. As social
problems such as homelessness increase, people are
crowding in shelters in larger and larger numbers.
As well, many strains of the bacterium are becoming
resistant to antibiotics. Some people believe that new
technology is the answer to this disease—science
and technology should produce new medicines, and
discovering these drugs should be a priority to the
medical community. Others believe that prevention
is the solution—society must eliminate conditions
that support spreading the bacteria, and ensure that
infected people finish prescribed medications.
a. Write an essay about your ideas concerning this
problem. What do you think the priorities
should be?
b. Outline a strategy to deal with the rise in cases of
TB in Canada.
30. Copy the beginning of the concept map shown below
into your notebook. Complete the concept map
comparing the four phyla of animal-like protists.
Protozoa
Cercozoa
Ciliophora
Zoomastigina
Sporozoa
T4 Viral Particles in Culture
Time
Number of T4 Viral Particles
13:00
3
14:00
3
15:00
126
16:00
585
17:00
602
a. Draw a line graph representing these results.
b. Describe the growth of T4 bacteriophages.
c. Predict what will happen to the T4 population after
five hours.
d. How would the graph have looked if she had started
with a culture of dead E. coli cells? Explain your
answer.
32. Summarize your learning in this chapter using
a graphic organizer. To help you, the Chapter 2
Summary lists the Key Terms and Key Concepts. Go to
Using Graphic Organizers in Appendix A to help you
decide which graphic organizer to use.
Application
33.
All living things can be classified according
to their anatomical and physiological
characteristics. You discover an unusual organism
growing in the damp leaf litter of an autumn forest.
In the lab, you look at its cells under a microscope,
and you see it is single-celled, is eukaryotic, and has
chloroplasts. Can you place it in a kingdom? Explain
your reasoning in detail.
34. Many humans with diabetes need regular injections
of insulin. Imagine you could engineer a virus that is
specialized. It can infect the cells of a lab animal so that
the animal carries the human gene for making insulin
in addition to its own genes. Why would this be an
advantage?
35.
Human activities affect the diversity of
living things in ecosystems. By creating
extreme environments, such as water or soil that
contains high amounts of toxins or acid, are we
encouraging the evolution of new archaea? What would
be the positive and the negative consequences of this?
36. During the construction of the Panama Canal,
malaria was a serious threat to the workforce. The
graph below shows the percentage of the workforce
that was hospitalized due to malaria during the years
of construction. While construction proceeded, a
mosquito control program was initiated. Several
measures were taken to try to control the mosquito
population and reduce people’s exposure to
mosquitoes, including
• draining pools near residential areas
• using insecticides to kill mosquito larvae
• placing screens on windows
• killing adult mosquitoes
Incidence of Malaria
Percentage of
Employees
Hospitalized
Due to Malaria
31. Bacteriophages are viruses that attack bacterial cells
such as E. coli. A virologist added T4 bacteriophages
to a live culture of E. coli. Every hour from 13:00 h
to 17:00 h, she determined the relative number of
T4 viral particles present in a sample of the culture.
Her data are shown in the table below.
10
8
6
4
2
0
1905
1906
1907
1908
1909
Year
Based on the information in the graph, do you think
the program was successful? Explain how each method
was intended to stop the spread of malaria.
37. Diatoms have rigid cell walls with an outer layer of
silica. Diatomaceous earth is a fine, white, crystalline
powder made up of the fossilized shells of diatoms.
Lightweight, gritty, and porous, diatomaceous earth
has a surprising number of uses. Identify, through
research, three products or industrial uses of
diatomaceous earth.
38. In 1991, Iraqi military forces in Kuwait opened
valves at the Sea Island oil terminal near Kuwait
City, releasing more than 900 million litres of crude
oil into the Persian Gulf. Much of the marine life,
including fish, sea turtles, and sea birds, was not
able to survive. Two years later, however, large
mats of cyanobacteria were growing on top of the
oil-soaked soil on the beach. Embedded in the mats
of cyanobacteria were millions of other bacteria,
such as Cycloclasticus spirillensus, consuming the
oil and breaking it down into carbon and energy.
Bioremediation is the breakdown of contaminating
compounds using micro-organisms, such as bacteria
and cyanobacteria. These naturally occurring microbes
use contaminants as a food source. Explain why you
think bioremediation might be useful in the clean-up
of an oil spill in the Great Lakes.
Chapter 2 Diversity: From Simple to Complex • MHR 85
Chapter 2
SELF-ASSESSMENT
Select the letter of the best answer below.
1.
K/U Which organism is a prokaryote?
a. amoeba
b. Euglena
c. green algae
d. cyanobacteria
e. paramecium
2.
What do Balantidium coli, a parasitic protist,
and the most common cause of bacterial pneumonia,
Streptococcus pneumoniae, have in common?
a. both are prokaryotic cells
b. both contain DNA
c. both have membrane-bound organelles
d. both have a membrane-bound nucleus
e. both use mitosis and meiosis for cell division
6.
K/U Staphylococcus, Streptococcus, and Enterococcus
are bacteria that are stained dark blue or violet by
Gram stain. Which statement about these organisms
is false?
a. All are Gram-positive bacteria.
b. All are Gram-negative bacteria.
c. All are spherical bacteria.
d. All are prokaryotic cells.
e. All can cause diseases.
7.
K/U Which theory does the evidence listed below
support?
• Membranes of the chloroplasts and mitochondria are
similar to living prokaryotes.
• Ribosomes in chloroplasts and mitochondria are
similar to ribosomes in prokaryotes.
• Mitochondria and chloroplasts reproduce by binary
fission.
• Chloroplasts and mitochondria have a circular
chromosome.
a. endospore theory
b. endosymbiotic theory
c. theory that Archaea carry out photosynthesis
d. theory of how eukaryotes became multicellular
e. theory that viruses are cells
K/U
3.
Diseases such as bovine spongiform
encephalopathy (BSE) and scrapie in sheep are caused
by this group of disease-causing agents.
a. prions
b. viruses
c. parasites
d. bacteria
e. fungi
4.
Identify the most common shapes of bacteria
and archaea.
a. polyhedral, spherical, and cylindrical
b. gametic, zygotic, and sporic
c. spherical, rod, and spiral
d. animal-like, fungus-like, and plant-like
e. ciliated, flagellated, and amoebic
8.
K/U Which group includes organisms that are
parasites of fish, insects, and plants?
a. sporozoans
b. amoebas
c. paramecia
d. water moulds
e. flagellates
5.
K/U Which is a key difference between archaea and
bacteria?
a. Archaea are prokaryotic while bacteria are
eukaryotic.
b. Archaea can live in anaerobic conditions while
bacteria can only live in aerobic conditions.
c. Archaea can only live in less extreme conditions,
while bacteria can live in more extreme conditions.
d. Archaea do not use photosynthesis as a source
of metabolic energy, while some bacteria can use
photosynthesis as a source of metabolic energy.
e. Archaea have membrane-bound organelles while
bacteria do not have membrane-bound organelles.
9.
K/U Which group of protists has rigid cell walls
made of silica?
a. diatoms
b. dinoflagellates
c. euglenoids
d. amoebas
e. paramecia
K/U
K/U
86 MHR • Unit 1 Diversity of Living Things
10.
K/U Which group of protists has chloroplasts and
conducts photosynthesis but is also heterotrophic?
a. diatoms
b. dinoflagellates
c. euglenoids
d. amoebas
e. paramecia
Use sentences and diagrams as appropriate to answer the
questions below.
12.
13.
14.
15.
16.
17.
A
In humans, lytic infections of plasma cells by the
Epstein-Barr virus (EBV) result in mononucleosis.
Lysogenic infections of B cells by EBV predispose a
person to lymphoma. Lymphoma is a type of cancer
that can appear when an error occurs in the way a
lymphocyte is produced. Use this information to
compare and contrast lytic and lysogenic viruses.
A
Bacteria such as Salmonella enterica and Listeria
monocytogenes are known to cause food-borne
illnesses. Food-borne illness is often referred to as food
poisoning, and it can feel like the flu. Symptoms may
include stomach cramps, nausea, vomiting, and fever.
What steps can be taken to prevent harmful bacteria
from growing in food and potentially causing
food-borne illness?
19.
T/I The graph below shows how quickly bacteria
can multiply when conditions are favourable.
A
Like other organisms that usually reproduce
asexually, diatoms sometimes reproduce sexually
when conditions are poor. Why do you think
organisms switch to sexual reproduction when
conditions are poor?
Growth Rate of Bacteria
Number of Bacteria
(millions)
11.
18.
K/U Compare the function of a chloroplast to the
function of a mitochondrion.
K/U Which group is currently classified in the
kingdom Protista by some taxonomists and into the
kingdom Plantae by others? Explain why there is so
much confusion.
35
30
25
20
15
10
5
0
20
40
60
80
100
120
Time (minutes)
a. What happens to the size of the bacteria population
every 20 minutes?
b. Predict the size of the population after 160 minutes.
c. Explain how bacteria reproduce so quickly.
C
Use captioned diagrams to compare a gametic
life cycle used by sexually reproducing organisms to
binary fission, which is the asexual technique used
by prokaryotes.
Bacteriophages are viruses that prey on bacteria.
They typically attack only a single bacterial strain. This
specificity, together with the killing capacity of
bacteriophages, makes them the natural enemies of
bacteria. Bacteriophages are similar to antibiotics in
that they have remarkable antibacterial properties.
Predict the advantages and disadvantages of using
bacteriophages rather than antibiotics to treat bacterial
infections.
20.
T/I In 1958, a science fiction/horror movie called
The Blob was released. In the movie, a mysterious
extraterrestrial organism that looks like a giant blob of
jelly creeps over the ground engulfing food, including
people, as it slides along! The blob gets larger as it
continues to engulf food. Based on this information,
infer which protist may have served as a model for
this fictional organism, and explain your answer.
21.
Compare the feeding strategies and locomotion
of an amoeba and a paramecium.
22.
T/I Summarize the theory of endosymbiosis as it
relates to the evolution of eukaryotic cells.
23.
T/I Individual bacterial cells may have plasmids
with the genes that protect the bacterial cells from
antibiotics. Explain how this trait may be passed on to
other bacterial cells in the colony.
24.
K/U Describe why many individuals infected by HIV
can test positive for this virus but still remain healthy
for many years.
25.
K/U Compare and contrast the structure of viruses to
the structures of bacteria and protists.
12
13
A
In most respects, the environment on Mars
is very harsh. In winter, temperatures are as low as
-100°C. The atmosphere contains little oxygen, and
without the benefit of a thick ozone layer the Martian
surface is bombarded with ultraviolet (UV) solar
radiation. Explain why scientists looking for life on
Mars would also be interested in some species in the
kingdom Archaea.
A
K/U
Self-Check
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2.4 2.1 2.1 2.2 2.2 2.2 2.3 2.4 2.4 2.4 2.1 2.4 2.3 2.4 2.3 2.1 2.2 2.2 2.2 2.4 2.4 2.3 2.2 2.1 2.1
Chapter 2 Diversity: From Simple to Complex • MHR 87