INTRODUCTION
The study of living things and their interactions with nature is called biology. Everything in
the world can be grouped under living and non-living things. Anything that has life is a living
thing.
Living things can also be grouped into two broad categories; animals and plants.
The study
of animals is called zoology and the study of plants is called botany.
The numerous numbers of living and non-living things make classification very important to
scientists.
There are wide range of differences among living things in their reproduction,
responses to stimuli, size, shape, structure, ways of doing things and several others.
These
differences among living things in a defined area is termed as biodiversity. There are also
differences found among non-living things in their physical and chemical properties.
This wide
range of differences found among living and non-living things is known as diversity.
Living and Non-living Things
Aside the difference between living and non-living things, they all relate to each other. All
living things undergo certain biological processes which ensure that they continue to have life.
Such biological processes are known as life processes. All living things become non-living
things when they die.
Difference between Living and Non-living
Things
Living things are distinguished from non-living things by seven basic life processes which
include;
• Nutrition: Nutrition can be defined as the process by which an organism obtains food which
is used to provide energy and materials for its life sustaining activities. Living things such as
green plants manufacture their own food through a process called photosynthesis. Animals
depend directly or indirectly on plants for their food. Non-living things are not able to obtain
nutrition.
• Respiration: It can be defined as the chemical and physical process in which oxygen is
delivered to tissues or cells in an organism to break down complex food substance to release
energy, carbon dioxide and water. It can also be defined as a metabolic process in cells leading to the release of energy from food. The energy is needed by living things to grow,
repair worn out tissues, move, and other things. Non-living things are not able to respire.
• Excretion: It is the process of discharging or removing waste matter from cells, tissues or
organs of living organisms. Non-living things are not able to excrete.
• Movement: It is the change of position and or direction of the body or part of the body of an
organism. Animals can either move their whole body (locomotion) or part of their body
because they contain locomotory structures such as legs, wings and fins but plants can only
move parts of their structures (growth movement). Non-living things are not able to move on
their own.
• Growth: This is the process of increasing in size and complexity of an organism which is
irreversible. Growth occurs as a result of multiplication of body cells. Plants grow by
developing new parts such as branches, new leaves, roots and others. Non-living things are
not able to grow.
• Reproduction: It is the process whereby all living organisms give rise to new young ones of
their own kind. Reproduction is one of the essential functions of living organisms as it is
necessary for the preservation of the species.
Reproduction which involves the fusion of
gametes is referred to as sexual reproduction. Some organisms reproduce using parts of their
body or structures other than gametes. This is termed as asexual reproduction. Non-living
things are not able to reproduce.
• Irritability or sensitivity: this is the process whereby living organisms react or respond to
changes in their environment (stimuli). Non-living things are not able to respond to stimuli.
Even though these life processes are performed or exhibited by living organisms some non-living things may exhibit some of these characteristics.
BIODIVERSITY
Although plants and animals are all living things, they also exhibit a vast difference of
characteristics called biodiversity.
Biodiversity is the vast difference (diversity) in the number
and variety of species of plants, animals, fungi and other microbial organisms within a region
or on the earth as a whole. Here are some differences between plants and animals.
Classification of Living Organisms
Classification, in biology is the identification, grouping and naming of organisms into a formal
system based on similarities such as internal and external anatomy, physiological functions,
genetic makeup, or evolutionary history.
With an estimated 10 to 13 million species on earth,
the diversity of life is vast. Living things must therefore be placed in groups which have certain
features in common which distinguish them from other groups. Initially, classification of
organisms into different categories was based on their physical characteristics and presumed
natural relationships. The leading naturalists of the 18th and 19th centuries spent lives
identifying and naming newly discovered plants and animals.
The study of classification is
known as taxonomy. A person who studies classification is called a taxonomist.
Importance of Classification
• It helps in understanding and easy remembrance
• It helps in the discovery of new or unknown species and grouping them with existing ones.
• It also helps to have a universal language for communication
Historical Background of Classification
Aristotle
One of the earliest classification schemes was established by a Greek philosopher Aristotle,
who lived in the 300s BC. Aristotle believed that the complexity of life could be divided into
a natural order based on dichotomies, or polar opposites. For example, Aristotle divided
animals into those with blood and those without blood.
Aristotle wrote extensively on both plants and animals but his writings on plants were lost.
Fortunately, his pupil Theophrastus applied Aristotle’s taxonomic approach to the study of
plants in his work entitled ‘Inquiry into plants’. Theophrastus subdivided plants based on
shape into such broad categories as trees, shrubs and herbs.
John Ray
John Ray (1627-1705) is an English naturalist who pioneered in the systematic classification
of organisms, which led to the work of the Swedish botanist Carolus Linnaeus. Ray published
a large amount of work and in 1682, he presented his innovative taxonomic methodology,
which established species as the basic unit in botany and stressed the difference between
monocotyledons and dicotyledons. In zoological studies that he took over from others, he used
a wide range of structural characteristics as a basis for classification rather than artificially
selecting some single features as had been done before. His master work which was in three
volumes and entitled ‘Historia Plantarum’ appeared between 1686 and 1704.
Kark von Linne (Carolus Linnaeus)
One of the most important 18th century naturalists was a Swedish botanist and a medical doctor
named Kark von Linne. He wrote extensively describing plants species in detail.
Since most of his writings were mostly in Latin, he is known to the scientific world today as
Carolus Linnaeus which is the Latinized form of his name. In 1735, he published an influential
book entitled ‘Systema Naturae’ in which he outlined his scheme for classifying all known
and yet to be discovered organisms according to the greater or lesser extent of their similarities.
His system of classification known as the Linnaean System of Classification was widely accepted in the early 19th century and it is still the framework for all taxonomy in the biological
sciences today.
The Linnaean system of classification uses two Latin name categories, genus and species to
designate each type of organism. Such a dual level designation is referred to as a binomial
nomenclature or binomen (literally meaning “two names” in Latin).
BINOMIAL NOMENCLATURE
Binomial nomenclature is defined as the Linnaean system of classification whereby two Latin
names are assigned to each organism of which the first one is a genus and the later, a species.
Example, Linnaeus described humans in his system with the binomen Homo sapiens. Homo is
our genus name and sapiens is our species name.
Living things have been classified into seven main taxonomic ranks of hierarchical order which
are Kingdom, Phylum or Division, Class, Order, Family, Genus and Species.
Kingdom: this is the highest rank or taxon. Taxonomists grouped all living things into five
made up of a large number of organisms which share many general characteristics.
Phylum: a phylum (plural; phyla) is a taxonomic rank below kingdom and above class. Phylum
is equivalent to the botanical term division. A phylum is made up of related classes.
Class: members of phylum are divided into classes. Thus, class is a smaller group under
phylum. Organisms in a class have more common characteristics than those in a phylum.
Order: living things that belong to a class are also divided into smaller groups called order.
Members of an order resemble each other than those in a class. An order contains groups of
related families.
Family: organisms in an order are divided into a family. A family consist of organisms that
are more closely related than those in an order.
Genus: organisms in a genus are members who are subdivided from a family. Thus, members
of a genus share similar characteristics and are more closely related but do not produce fertile
offspring.
A genus may have one or more species under it.
Species: species is a group of closely related organisms that are able to interbreed and produce
fertile offspring. Members of organisms that do not belong to the same species cannot
interbreed.
Example:
It is from the binomial system that scientific names are obtained. In that sense the scientific
name of maize is written as Zea mays. When writing scientific or botanical names, the genus
name should begin with a capital letter even when it is found in the middle or at the end of a
sentence while the species name begins with a small letter. In manual writing because it cannot
be italic, both the genus and species name should be underlined.
Kingdom Prokaryotae (Monera)
Examples are bacterial, blue-green algae.
Characteristics of organisms in
Kingdom Prokaryotae
1. They are unicellular (single celled)
2. They are microscopic (Very tiny)
3. Have no definite nucleus
4. Cytoplasm is surrounded by membrane
5. Have no membrane around the nucleus
Kingdom Protoctista (Protista)
Examples are Amoeba, Paramecium,
plasmodium, Spirogyra, Euglena, green
algae, slime mould, Trypanosoma.
Characteristics of organisms in
Kingdom Protoctista
1. Mostly unicellular (few are
multicellular)
2. Have membrane around nucleus
(Eukaryotic)
3. Have normal cells, but no tissue or
organs.
Kingdom Fungi
Examples are fungus, moulds, mushrooms,
rhizopus, penicillium, mucor, yeast.
Characteristics of organisms in
Kingdom Fungi
1. They are multicellular
2. They have no roots, stem or leaves
3. Have no chlorophyll
4. Are not photosynthetic (cannot produce
their own food).
5. Reproduce by mean of spore formation
6. Vegetative part, called mycelium
consist of hyphae.
Kingdom Plantae
Examples of organisms in Kingdom
Plantae are: flowering plants, ferns, shrubs,
mosses etc.
Characteristics of organisms in
Kingdom Plantae
1. They are multicellular (have many
cells)
2. Have chlorophyl
3. Have definite nucleus
4. Cell wall made of cellulose
5. They are photosynthetic (prepare their
own food through photosynthesis)
Kingdom Animalia
Examples of organisms in Kingdom
Animalia are: man, birds, fish, snakes
Characteristics of organisms in
Kingdom Animalia
1. They are multicellular
2. Are not photosynthetic
3. Have no cell wall
4. Have nucleus bound by a membrane
5. Do not have chlorophyll
Classification of Non-living Things
The basis of classifying non-living things is on their common properties they share as found in
living things. Non-living things are grouped into metals and non-metals. Metals and non- metals in their simplest form are called elements.
The system for classifying the elements is
the periodic system. Metals and non-metals in their simplest form (elements) are substances
made up of only atoms that have the same atomic number.
Elements are arranged in order of increasing atomic number or the number of electrons in an
atom of each element.
In the periodic table, elements are arranged in order of increasing atomic
number so that elements with similar properties are placed in vertical columns known as
groups or horizontal rows known as periods.
The regular occurrence of similar chemical and
physical properties when elements are arranged in order of increasing atomic number is called
periodicity.
Ninety-four natural elements have been detected in the universe. More than 110 elements have
been identified, with some created in laboratories as artificial elements. Under certain
conditions, one element may be changed into another element through processes that add or
remove protons from a nucleus.
The arrangement of all known elements in the periodic table
is based on the law of a Russian chemist, Dmitry Mendeleyev.
The law states that elements
show a periodicity (regular pattern) when they are arranged according to increasing atomic
weight.
Virus
A virus is an infectious agent which is non-cellular and virtually infects all forms of life
including humans, plants, fungi, and bacteria.
Viruses consist of two parts – either
deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) and a protein coat called capsid.
Viruses are obligate intracellular parasites (can only function when they are inside a living
host).
Due to their unusual characteristics, viruses are not members of any of the five kingdoms. They
are much smaller than bacteria and occur in various shapes and sizes. Some are hexagonal,
spiral, spherical and rod shaped. Because viruses are very small, they can only be seen under
the electronic microscope.
Biologists regard viruses as border line creatures between living and non-living things because
they are not able to exhibit characteristics of living things when outside a living host or cell.
Viruses cause a lot of diseases including measles, hepatitis, polio, mumps, sore throat, yellow
fever, AIDS, foot and mouth rot and mosaic disease in cassava and tobacco
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