Living Things According
to Their Similarities and Differences Group living things
according to their similarities and differences
THE IMPORTANCE OF CLASSIFYING LIVING THINGS
The following are
importances of classification
Classification makes the
study of living things easy
Classification makes
communication easy among biologists from different parts of the world
It provides good
organized system in which a newly identified organism can be easily fitted in future.
It makes it easier to
identify organisms
It can be used to
predict characteristics that are present in the members of the same group.
CLASSIFICATION SYSTEMS
There are two types of
classification
Artificial
classification
Natural classification
ARTIFICIAL CLASSIFICATIONAN
In this type of
classification, unrelated organisms are often placed in the same group
while closely related organisms are often placed in different
groups.
Linnaeus included all
worm-like organisms in a single group, the vermes. This included wide a range of animals as from nematodes, earthworms to snakes.
This was an artificial classification since it did not
consider natural relationships such as the fact that snakes have backbones and earthworms do not have. Thus, snakes
have more features in common with vertebrates than with worms.
Bats and birds would be
placed in the same group because all have the ability to fly
since they posses wings.
But bats share many features with mammals. They have
features like hair, mammary
glands, sweat glands and different types of teeth which are characteristics of mammals. Therefore, bats are more related to
mammals than birds
NATURAL SYSTEM OF CLASSIFICATION
It is based on evolutionary
relationship in which organisms belonging to the same group are believed to have a common ancestor.
Characteristic features
which show homology are distinguished from those which show analogy. Example the fore limbs of mammals, whales, birds and bats
have the same basic pattern and similar bone arrangement, i.e.
homologous.
This suggests that these organisms are coming
from the same ancestor and that can be placed in the same group.
The wings of birds and
grasshoppers are analogous. The wings of birds have internal skeletons while the wings of grasshoppers do not have bones but
they perform similar function. These organisms cannot be placed in
the same group since they are different in many ways.
MERITS AND DEMERITS OF EACH TYPE OF CLASSIFICATION SYSTEM
Advantages of artificial system of classification
It is easy to classify
organisms since it is based on few observable characteristics.
It does not take much
time to classify organisms based on this system (not time
consuming).
It does not need
expertise (even a layman can do).
It is relatively stable
i.e. not easily changing from time to time.
Disadvantages of artificial system of classification
It tends to place
closely related organisms into different groups instead of being
grouped together e.g. a
bat can be placed in a group of birds instead of mammals.
Different or unrelated
organisms may be placed in the same group e.g. bats placed in a group of birds, worms placed with snakes in the same group
The system does not
provide enough information about its members.
It is difficult to
incorporate additional information.
Advantages of natural system of classification
Closely related organisms
are placed in the same group.
It reflects evolutionary
relationships.
Unrelated organisms
cannot be placed in the same group.
It makes it easy to
incorporate additional information.
Disadvantages of natural system of classification
It is difficult since it
considers many features.
It requires expertise
i.e. more knowledge about an organism.
It is time consuming.
It is relatively
unstable i.e. it changes from time to time.
It is more expensive
since more data are required.
Differences between
natural classification and artificial classification
Artificial
classification |
Natural classification |
(i) Considers few
features in common |
Considers many
features in |
(ii) Does not reflect
on evolutionary |
Reflects on
evolutionary |
(iii) It is easy to
classify |
It is difficult to
classify |
(iv) Not time
consuming |
It is time consuming |
(v) Does not require
expertise |
Requires expertise |
(vi) New information
cannot be added |
New information can be
added. |
Currently, there are five major groups (kingdoms) of living things.
Kingdom monera
Kingdom protoctista
Kingdom fungi
Kingdom plantae
Kingdom animalia
There are seven ranks of
classification
Kingdom
Phylum/division
Class
Order
Family
Genus
Species
The highest rank of
classification is the kingdom. The lowest rank of classification is the species. Every known organism has particular place in each
group.
KINGDOM
CLASS
GENUS
It is the basic unit of
scientific classification. Organisms that need to be placed in the same species must have the following characteristics:
Must have many features
in common.
Must be able to breed
one another to produce fertile offspring.
Must be distinct and
different from other organisms.
N.B: The term division
is used by botanists instead of phylum when classifying plants or organisms related to plants.
Classification of some members of animals
Human |
Leopard |
Domestic |
|
Kingdom |
Animalia |
Animalia |
Animalia |
Phylum |
Chordata |
Chordata |
Chordata |
Class |
Mammalia |
Mammalia |
Mammalia |
Order |
Primates |
Carnivore |
Carnivore |
Family |
Hominidae |
Felidae |
Felidae |
Genus |
Homo |
Panthera |
Felis |
Species |
sapiens |
padus |
catus |
SCIENTIFIC NAMING OF LIVING ORGANISMS
The scientific process
of naming organisms is called nomen- clature. Biological
nomenclature is based on
the binomial system (double naming system) pioneered by the work of a Swedish naturalist Carl Linnaeus (1 707-1 778).
Biologists assign
scientific names to organisms so as to avoid confusion among themselves since scientists from different countries use different
languages. The
scientific names are
uniform in all languages.
Latin language is used
in assigning the scientific name because it is an official language and that this language is no longer subject to changes; it is
considered to be a dead language hence names once given remain
unchanged.
RULES OF BINOMIAL NOMENCLATURE
Scientific names of
organisms must be in Latin language and if the names are derived from other languages, they must be latinized.
A scientific name of an
organism has two parts, genus name and species name.
A genus name always
starts with a capital letter and a species name follows with a
small letter.
In typed scripts, a
scientific name must be written in italics or underlined if hand
written.
A specific name is
sometimes accompanied with the name of the author who first
described and named the
organism.
When an organism is
known by several names, the valid name is the one which was
established after the
work of Linnaeus.
Example 1
Examples of scientific
names
Human being:Homo
sapiens
Homo is the generic name and sapiens is the specific name.
Other examples of
organisms with their scientific names
Common name |
Scientific name |
|
Earthworm |
Lumbricus |
terrestris |
Cockroach |
Periplaneta |
americana |
Amoeba |
Amoeba |
proteus |
Coffee |
Coffea |
arabica |
Maize |
Zea |
mays |
Bean |
Phaseolus |
vulgaris |
Domestic cat |
Fe |
catus |
Sisal |
Agave |
sisalana |
Ashok tree |
Polyanthia |
longifolia |
Housefly |
Musca |
domestica |
Neem tree |
Azadirachta |
indica |
Flamboyant (Christmas |
De |
regia |
Tropical almond |
Termina |
catapa |
VIRUSES
Viruses were discovered
by a Russian botanist D. I. Ivanovsky and a Dutchman
Beijerink.In 1 852
Ivanovsky prepared an infectious extract from tobacco plants that were suffering from
mosaic disease. When the extract was passed through a filter able to prevent the passage
of bacteria, the filtered fluid was still infectious. 1 898 Beijerink gave the name “virus”
(in latin means, “poison”) to describe the infectious nature of certain filtered plant
fluids.
GENERAL AND DISTINCTIVE
FEATURES OF VIRUSES
Characteristics of Viruses
They are the smallest
living organisms ranging from 20-30nm. On average, they are about 50times smaller
than bacteria.
Viruses do not have
cellular structures, which mean that they lack certain important
organelles like nucleus,
cytoplasm, golgi bodies, etc.
They can only reproduce
inside the living cells hence they are parasitic.
They have a simple
structure consisting of either DNA or RNA but not both, surrounded by a protein or
lipoprotein coat.
They can be described as
living or non-living.
They are highly specific
to their hosts i.e. each virus recognizes only certain types of cells.
Viruses are capable of
replicating themselves only when they are inside the host cell.
VIRUSES AS LIVING THINGS
They possess genetic
material (RNA or DNA).
They reproduce when they
are in the host cell (replication).
They are capable of
identifying their hosts and attack them.
They can undergo
mutation (they mutate) i.e. they undergo different changes in shape.
Like other parasites,
they are specific to host.
VIRUSES AS NON-LIVING
THINGS
They can crystallize
outside the host.
They are metabolically
inert in isolation.
They are non-cellular
i.e. they lack cell organelles.
They do not perform
necessary life processes such as respiration, excretion nutrition
THE STRUCTURE OF VIRUSES
Generally viruses have a
very simple structure consisting of the following:
RNA or DNA which may be
single stranded or double stranded. They form a structure called core.
A protective coat of protein surrounding
the core called capsid.
A nucleocapsid which is a combined structure of core and
capsid.
Envelope – an additional layer of lipoprotein layer
around the capsid.
Capsids are made up of
identical repeating units known as capsomeres.
BACTERIOPHAGE
Bacteriophage is a virus
that attacks and kills bacteria. Some of them have head with a tail sheath.
ADVANTAGES AND
DISADVANTAGES OF VIRUSES
Advantages of viruses
Viruses are used in
developing vaccines, for example, vaccines for measles, polio and rubella are made from
viruses that have been attenuated (weakened).
Viruses are used as
biological weapons to kill organisms.
They are used as vectors
in genetic engineering to transfer genes from one organism to another for improving or
treating the defective genes.
Bacteriophages are
viruses that attack bacteria and hence they help in controlling
infections and diseases.
Viruses are used as
biological weapons in wars and in biological pest control.
DISADVANTAGES OF VIRUSES
Most viruses cause
diseases to both plants and animals. Plant disease such tomato
mosaic, cassava mosaic
and tobacco mosaic; and animal diseases e.g. measles, small pox, poliomyelitis and
yellow fever are caused by viruses.
KINGDOM
MONERA
This kingdom is made up of organisms known as bacteria (singular: bacterium).
They are the most ancient and
smallest organisms with a cellular structure. They are mainly single celled. Bacteria
occupy many environments such as soil, dust, water and in the bodies of plants and
animals
Some bacteria are found
in hot springs where temperatures are 78ºC or more. Others can withstand very low
temperatures. Some are found in very deep cracks in the ocean floor, at very high
temperatures, about 360ºC (extreme thermophiles).
GENERAL AND DISTINCTIVE
FEATURES OF THE KINGDOM MONERA
General characteristics of the kingdom monera
They are mainly
unicellular and very small.
They are all prokaryotic
(nucleus not bound by membrane)
They reproduce by binary
fission.
Some members of the
kingdom are autotrophs while others are heterotrophs
They have cell wall made
up of protein material and sometimes lipids.
Some bacteria form
spores during adverse conditions i.e. extreme conditions e.g. high or low temperatures,
drought etc. The spores allow them to survive as they have very thick resistant walls.
Some are aerobes while
others are anaerobes.
The genetic material
(DNA) is scattered in the cytoplasm and they lack internal
membrane bound
organelles such as mitochondria, chloroplasts, golgi bodies etc.
STRUCTURES OF THE
REPRESENTATIVE ORGANISMS OF THE KINGDOM MONERA
General structure of the bacteria
Bacteria have strong and
rigid cell walls due to the presence of murein. The wall
prevents the cell from
bursting when it absorbs much water (as a result of osmosis).
Bacterial cells are
bounded by partially permeable membranes.
Bacteria
possess capsules which are slimy or gummy. They have flagella which aid
motility of the
bacteria. Motile bacteria can move in response to a certain stimulus i.e. tactic movement.
Flagella can easily be seen by electron microscope.
They have small self
replicating circle of extra DNA called a plasmid.
GENERAL STRUCTURE OF
BACTERIUM
Forms of bacteria
Bacterial shape is an
important aid to classification.
There
are four main shapes
COCCUS (PLURAL: COCCI)
They are spherical in
shape and can be of the following types.
Micrococcus – exist singly. They cause sore throat.
Diplococci - this type of bacteria exist in pairs. The
pneumococci (Diplococcus
pneumoniae)
are the only members. They cause pneumonia.
Streptococci – this type of bacteria stick together and form
a chain. Most of them infect upper
respiratory surface and cause diseases e.g. sore throat.
Staphylococci – These bacteria form a grape like bunch. They
cause boils, pneumonia, food
poisoning and other diseases.
BACILLI (SINGULAR: BACILLUS)
These are rod shaped
bacteria. They can be:
Single rods, for example, Escherichia coli commonly living in the gut and Salmonella typhi which cause typhoid
fever.
Rods in chain, for
example, Azotobacter,
a nitrogen-fixing
bacteria, and Bacillus
anthracis which
cause the disease anthrax.
Bacilli
with endospores showing various positions, shapes and sizes of spores. They can be:
Central, not swollen e.g. Bacillus anthracis causes anthrax
Spherical spore, terminal swollen e.g. Clostridium tetani causes tetanus
Sub-terminal, swollen e.g. Clostridium botulism causes botulism.Spores
may also be
central
SPIRILLA (SINGULAR: SPIRILLUM)
These are spiral-shaped
bacteria e.g. Treponema
pallidum which
causes syphilis
VIBRIO
These are comma shaped
bacteria, for example Vibrio cholerae.
KINGDOM PROTOCTISTA
This Kingdom comprises
of unicellular and simple multicellular organisms whose cells have organized nucleus
and membrane bound organelles. It includes the algae and protozoa.
Algae have chlorophyll
hence make their own food through the process of photosynthesis. Protozoa are heterotrophic
taking in ready-made food.
Other organisms, which
are included in this Kingdom are red algae, Brown algae,
Amoeba, Euglena,
plasmodium, trypanosome and paramecium.
GENERAL FEATURES OF
KINGDOM PROTOCTISTA
Some are autotrophs, for
example Euglena while others are multicellular.
They are all eukaryotes
with most of them having locomotery structure.
Most of them live in
moist places or in water.
DISTINCTIVE FEATURES
Most are unicellular
eukaryotes
They reproduce by binary
fission
PHYLA OF THE KINGDOM
PROTOCTISTA
The phyla of kingdom
protoctists include the following:
Euglenophyta e.g.
Euglena
Rhizopodia e.g. Amoeba
Zoomastigma e.g.
Trypanosoma
Apicomplexa e.g.
Plasmodium
Oomycota e.g. White root
Chlorophyta e.g.
Spyrogyra
Cilliaphora e.g.
Paramecium
Rhodophyta e.g. Red
algae
STRUCTURE OF AMOEBA AND
PARAMECIUM
Amoeba belong to phylum
Rhizopoda, organisms with the following extra features:
They are eukaryotes
Unicellular
Parasitic
They move using
pseudopodia
Pseudopodia are projection of the cytoplasm that extend and pull the amoeba forward or engulf food particles.
The Advantages and Disadvantages of Amoeba, Euglena Paramecium and
Plasmodium
Advantages of Paramecium:
Feeding
Reproduction
Movement
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