Taxonomy
• Let’s look at the modern system of taxonomy from
the top down.
Lessons of Classification
• Bacteria and Archaea used to be
grouped together in one kingdom called
Monera.
• Each Kingdom is further divided into
Phylum → Class → Order → Family →
Genus → Species.
• Species is the most specialized level of
classification with the most diversity at
this level.
• When referring to a particular species, a
dichotomous name is used that includes
the genus name and the species name.
• For examples, humans are called Homo
sapiens.
• Homo is the genus name and sapiens is
the species name.
Taxonomy “Tip”
• A good way to remember the levels of taxonomy
is through the use of a mnemonic.
• A mnemonic uses the first letters of what you
need to remember in a memorable phrase.
• In this case, a mnemonic for remembering the
system of taxonomy could be:
• “King Philip Came Over For Good Spaghetti”
representing Kingdom, Phylum, Class, Order,
Family, Genus and Species.
How to Classify
• Taxonomy comes from the Greek word ‘taxis’
which means to order or rank. In this system,
each species is using two parts:
– the name of the genus to which it is assigned
– the "specific name" which identifies the particular
species within the genus.
• Latin names are assigned to both the genus and
species and both words are written in italics.
• Classification is used to identify organisms and
make our meaning as clear as possible.
Kingdom Archeabacteria and
Kingdom Eubacteria
Common characteristics of Eubacteria
and Archeabacteria
1.
2.
3.
4.
Cells are prokaryotic.
All are single celled.
Have single chromosome.
Reproduce asexually through binary fission.
Archeabacteria
• Often live in environments where other
organisms wouldn’t survive
– Usually anaerobic
Three main groups of Archeabacteria
1. Methanogens – produce methane
2. Extreme thermophiles – thrive in
temperatures up to 110⁰C
3. Extreme halophiles – live in very salty water
Three main groups of Eubacteria
• Spherical – coccus/cocci
• Rod-shaped – bacillus/bacilli
• Spiral – spirillum/spirila
• Staphylo – Bunch of grapes
• Diplo – Pairs
• Strepto – Long chains
Typical Structures
Eukaryotic Respiration
A. Obligate aerobes – must have oxygen to
survive.
ex. tuberculosis
B. Obligate anaerobes – only grow in the
absence of oxygen.
ex. Live deep in the soil or marine sediment
C. Facultative anaerobes – can survive with or
without oxygen.
ex. Most bacteria
Eukaryotic Modes of Nutrition
• Heterotrophs – most bacteria; obtain
nutrients from other organisms
– Parasite: obtaining nutrients without contributing
to the health of the of the host (disease causing
bacteria
– Saprophytes: obtain their nutrients from dead and
decomposing matter
• Autotrophs – make food from inorganic
substances by photosynthesis or
chemosynthesis.
Asexual Reproduction in Bacteria
• Binary Fission (similar to mitosis, but simpler)
1. Single DNA strand replicates.
2. The identical pieces of genetic material are
transferred to each new cell.
3. After replication the cell divides and produces a
new cell wall.
Sexual Reproduction in Bacteria
• Conjugation – two bacteria make cell to cell
contact and DNA is transferred from one
(donor) to the other (recipient).
• Not common in bacteria.
Endospores
• During unfavourable environmental conditions
an endospore is formed so that the cell can
remain dormant or “at rest”.
– They are resistant to heat and can not easily be
destroyed.
– When suitable conditions return, an active
bacterial cell emerges.
Protists
• The protist kingdom is the most challenging
group of organisms to classify.
• There are 115 000 species of protists which
display great variation.
• Protists have characteristics that are similar to
organisms found in each of the other
kingdoms. Some are unicellular which is
similar to bacteria.
• However, one distinguishing characteristic
that separates bacteria from protists is the
presence of a nucleus.
• Remember, bacteria are
prokaryotic because their
DNA is free floating within
the cytoplasm.
• All protists are eukaryotic
which means they contain a
distinct nucleus which
surrounds their DNA.
• This evolutionary
development generated the
need for a distinct
classification for these
organisms.
• Classifying protists becomes challenging
because of their vast differences.
• Most protists are unicellular, but there are
some that are multicellular.
• Some are autotrophs while others feed on
organic matter and are heterotrophic.
• Scientists have organized protists into three
different groups: animal-like protists, plantlike protists, and fungi-like protists.
• In all, there are 11 phyla in the protist
kingdom.
Animal-like Protists (Protozoa)
• Protozoans are classified by their type of
locomotion, life cycle, reproduction, nutrition and
whether the protist is parasitic or free-living.
• All animal-like protists are heterotrophs. Similar
to organisms in the animal kingdom, these
protists have to be motile to search out food.
• Protozoans can either absorb pre-digested
materials through their cell membrane or they
can engulf their food.
• Sarcodina, Mastigophora, Ciliophora, and
Sporozoa are the four phyla of animal-like
protists. You will now learn about each phylum in
greater detail.
Sarcodina
• The amoeba is probably
the most famous protist in
this phylum. Perhaps you
even had the opportunity
to view an amoeba under a
microscope.
• One of the interesting
characteristics of protists in
this phylum is the way they
• The image above shows an
move.
amoeba moving toward a
• By extending and retracting
its cytoplasm, an amoeba is group of cells. The movement
of the cytoplasm forms the
able to create “false feet”
pseudopods as the amoeba
called pseudopods.
moves towards the food.
• Pseudopods also enable an amoeba to capture and
engulf its food by phagocytosis.
• Below is a sequence of pictures showing an amoeba
engulfing an algal cell.
• In the fourth sequence you will notice the appearance
of the pseudopods surrounding the algal cells.
Mastigophora
• In the phylum Mastigophora, the protists contain
one or more flagellum (pl.flagella) for
locomotion.
• A flagellum resembles a tail and is attached to the
cell body of the protozoan. A protist will generate
motion when the flagellum begins to rotate.
• Most of these protozoans are harmless.
• However, Giardia lamblia, a parasitic
protozoan causes upset stomach and diarrhea
in humans.
• This parasite lives in the digestive tract of
animals, like cows.
• Humans can contract the parasite when they
consume food or water that has come in
contact with the feces of infected animals.
Ciliophora
• Cilates contain cilia, tiny
hair-like structures,
throughout the outer
covering of their cell body.
• In the image on the right,
the cilia appear clear. The
dark spot in the centre of
the paramecium is the
macronucleus which
functions like a nucleus.
• A micronucleus, not shown,
is smaller and is involved in
reproduction.
• Most paramecium
reproduce by binary
fission; however, they can
also undergo conjugation.
Sporozoa
• Sporozoans rely on other
organisms for movement.
They lack cilia, pseudopods,
and flagella. Therefore,
these protists are
all parasitic.
• Malaria is caused by
Plasmodium. Symptoms
include fever, headache,
and vomiting: malaria can • Approximately 40% of the
quickly become lifeworld's population, mostly those
threatening if not treated.
living in the world's poorest
• Malaria can be spread from
countries, are at risk of malaria.
person to person and
• Every year, more than 500 million
through mosquito bites.
people become severely ill with
malaria. (WHO, May 2007)
• Plant-like protists all contain chlorophyll, the
pigment found in plant cells, which is involved
in the process of photosynthesis.
• Most plant-like protists are able to produce
their own food.
• However, some are heterotrophic and ingest
materials from their surrounding.
• There are six phyla within the plant-like protist
group.
Euglenophyta
• In the past, euglenids have
been classified as both plants
and animals because in the
presence of light they are
photosynthetic.
• However, in the absence of
light they become
heterotrophic. The Euglena is
one of the most studied
• One feature of the Euglena
plant-like protists.
which is not shown is its
• The image on the right shows
flagellum. Most species contain
some features of the Euglena.
two flagella which allow for
• The dark spot on the bottom
movement. Similar to animalrepresents the eye spot
like protists, the euglenids
which is used to detect light.
reproduce asexually.
Rhodophyta (Red Algae): Phaeophyta (Brown
Algae) and Chlorophyta (Green Algae)
• The protists in these phyla all contain chloroplast
which means they too photosynthesize.
• In addition to containing chlorophyll, they also
contain other pigments that allow them to
absorb additional wavelengths of light.
• These algae are multicellular and they generally
inhabit moist to wet environments.
• Reproduction varies greatly amongst this group.
The most common form of reproduction is
through binary fission.
• However some algae reproduce sexually.
• Green algae play an
important role in
providing oxygen through
photosynthesis; algae are
also part of the aquatic
food chain.
• You may have noticed
green algae forming in
ponds or in shallow rivers
and lakes.
• Fertilizer run-off may lead
to excessive growth of
green algae causing an
imbalance in the natural
environment.
Chrysophyta
• Diatoms provide much
of the nourishment for
aquatic organisms.
• These protists are
unicellular and each
species has a very
unique shape.
• Structurally, they are
composed of two halves
that fit perfectly
together.
This is an image of various diatoms
showing circular and triangular shapes.
• When they reproduce asexually, they split and
separate into two.
• Then each original part grows into a new half.
• After several generations of reproducing
asexually, the size of the diatom reduces
significantly.
• When this occurs, the diatoms reproduce
sexually by producing a zygote.
• While diatoms do not contain flagella, many
other protists in this phylum are flagellated.
Pyrrophyta
• Have you ever had the opportunity to watch the
ocean light up from within its depths?
• This phenomenon is the result of dinoflagellates, a
protist from this phylum. When water containing
large amounts of dinoflagellates becomes agitated,
bright flashes of light are visible.
• In response to excessive nutrients or elevated
water temperatures, dinoflagellates experience
rapid growth called a bloom.
• In addition to tinting the water red,
dinoflagellates produce toxins.
• These toxins accumulate in the bodies of fish
which can then affect humans who consume the
toxic fish.
• Dinoflagellates are photosynthetic, but they can
also ingest materials from their environment.
• They are generally unicellular, contain two flagella
and reproduce asexually.
Fungus-like Protists
• These protists are
generally referred to as
slime moulds and are
classified in the phylum
Gymnomycota.
• These protists are
heterotrophic and
generally feed on dead
organic materials.
• By extending its cytoplasm,
• The characteristics of slime similar to an amoeba, slime
moulds vary greatly during moulds are able to move and
their lifecycle.
unite to form multicellular
• They begin their life as a
masses. These masses shrink
single cell.
in size and eventually produce
spores.
Quiz – True or False?
1.
Protists can be prokaryotic or eukaryotic.
2.
Animal-like protists contain chlorophyll.
3.
An amoeba moves by extending its cytoplasm and producing pseudopods.
4.
Flagella provide locomotion for protists in the phylum Ciliophora.
5.
Parasitic protists are responsible for disease in humans.
6.
Plant-like protists have no need to move, therefore do not contain flagella.
7.
Euglena is a plant-like protist that is both autotrophic and heterotrophic.
8.
Global warming will have an effect on green algae growing in lakes and rivers.
9.
Slime moulds show the potential for complex speciation.
10. The Protist kingdom is very diverse.
Answers
1. False – The classification of protists is based on
the fact that they all contain a nucleus and
therefore are eukaryotic. They cannot be
classified in the animal or plant kingdom
because they lack specialized tissues.
2. False – Only plant-like protists contain
chlorophyll. Remember this is the pigment that
allows these protists to photosynthesize.
3. True – The false feet produced by the extension
of cytoplasm provide mobility to an amoeba. In
addition, the pseudopods also allow amoeba to
engulf their food by phagocytosis.
4. False – Protists in the phylum Ciliophora contain
tiny hair-like structures called cilia that surround
their cell body. The motion of these structures
provides movement for these protists.
5. True – Parasitic organisms rely on a host for
survival. Some protists cause serious illnesses such
as malaria and have been responsible for outbreaks
like the Irish potato famine in the mid 1800's.
6. False – Many plant-like protists contain flagella
including Euglena and dinoflagellates.
7. True – Euglena contain chlorophyll and will
photosynthesize when light is available. In dark
conditions, Euglena will feed off of organic material.
8. True – Elevated water temperatures increase the
growth rate of green algae. This causes an imbalance in
the ecosystem. The overgrowth of the algae inhibits the
growth and survival of other organisms.
9. True – Unicellular slime moulds uniting to form a
multicellular mass illustrates the potential for
specialization. Soon, cells may become specialized to
carry out a specific task.
10. True – There is great variation in reproduction; from
asexual fragmentation to sexual conjugation. Protists
can be autotrophic or heterotrophic or a combination of
both. Locomotion may involve a flagellum or cilia.
Finally, protists may be free living or parasitic.