BIO 101
Characteristics and Classification of Living Organisms
Welcome to the exciting and amazing world of living things.
Go outside and look around you. Look at the sky, the soil, trees, plants, people, animals.
Nature is all around you if you have the eyes to see it. Count how many living things
you can see.
What is it that makes living things different from things that are not alive?
Biology is the study of living things. It deals with what all living things can do, how
they do it and why they do it. In biology, there is always a relationship between the
structure of an organism, its function, and its adaptation to its function or environment.
Biology also tackles the important topics such as population, environmental issues as
well as health issues.
When you have studied this unit, you should be able to:
list and describe the characteristics of organisms
define the terms nutrition, excretion, respiration, sensitivity, reproduction, growth and
movement
outline the use of a hierarchical classification system for living organisms
classify living organisms into kingdoms, orders, classes, families, genera and species
define and describe the binomial system of naming species
construct dichotomous keys
use simple dichotomous keys based on easily identifiable features.
Characteristics of Living Things
There are seven (7) activities which make organisms different from non-living things.
These are the seven characteristics of living organisms.
Nutrition/ Feeding
Living things take in materials from their surroundings that they use for growth or to
provide energy. Nutrition is the process by which organisms obtain energy and raw
materials from nutrients such as proteins, carbohydrates and fats.
Plants, algae, and some bacteria harvest the energy of sunlight through photosynthesis,
converting radiant energy into chemical energy.
These organisms, along with a few others that use chemical energy in a similar way,
are called autotrophs (“self-feeders”).
All other organisms live on the organic compounds autotrophs produce, using them as
food, and are called heterotrophs (“fed by others”).
At least 95% of the kinds of organisms on Earth—all animals and fungi, and most
protists and prokaryotes—are heterotrophs.
Respiration
Respiration is the release of energy from food substances in all living cells.
Living things break down food within their cells to release energy for carrying out the
following processes.
Cellular respiration is the complete oxidation of organic compounds such as
glucose to extract energy from chemical bonds.
1
, Anaerobic respiration:
In animals
Most organisms cannot respire without oxygen. But some organisms and tissues can
continue to respire if the oxygen runs out.
These organisms and tissues use the process of anaerobic respiration.
Animal muscles can respire anaerobically for short periods of time - even though the
process is relatively inefficient, it's better to continue respiring and be able to run away
from danger - or run a race.
The glucose in muscle is converted to lactic acid:
Glucose → Lactic acid (+ energy released)
In general, anaerobic respiration consists of two main basic steps: Glycolysis: the break
down of glucose into two pyruvate, two ATP, and two NADH (an electron carrier)
molecules.
Fermentation: the production of alcohol or lactic acid substrates and NAD+ for energy
production
Movement
All living things move. It is very obvious that a leopard moves but what about the thorn
tree it sits in?
For example, different types of locomotory organs are found in protozoans. They may
bear flagella (flagellates), cilia (ciliates) pseudopodia (sarcodines).
Locomotory organs are absent in the parasitic forms (Sporozoa).
Excretion
All living things excrete. As a result of the many chemical reactions occurring in cells,
they have to get rid of waste products which might poison the cells.
Excretion is an essential process through which body gets rid of metabolic wastes and
maintains osmotic pressure.
Several waste products such as water, carbon dioxide and nitrogenous substances are
generated during cellular activities. These products are harmful to the body if
accumulated and therefore need to be removed. In mammals, specialized organ called
kidney eliminates most of the water and nitrogenous substances from the body.
Excretion is defined as the removal of toxic materials, the waste products of metabolism
and substances in excess from the body of an organism.
In majority of vertebrates, the chief excretory organ is the kidney.
Growth
Growth is seen in all living things. It involves using food to produce new cells.
It is the permanent increase in cell number and size is called growth.
Reproduction
All living organisms have the ability to produce offspring.
Reproduction is the biological process by which new organisms are created from their
parents. There are two main types of reproduction:
Asexual reproduction
A single organism reproduces without the involvement of another organism. The
offspring is genetically identical to the parent.
Sexual reproduction
2
, A male and female organism combine their genetic information to create a new
organism that is genetically unique.
In humans, reproduction involves the following steps:
Gamete production: The male gamete (sperm) and the female gamete (egg) are
produced.
Fertilization: The sperm fertilizes the egg in the female's reproductive system.
Zygote formation: The fertilized egg, now called a zygote, develops into an embryo
and then a fetus.
Sensitivity
All living things are able to sense and respond to stimuli around them such as light,
temperature, water, gravity and chemical substances.
These seven characteristics of living organisms form the basis of the study of Biology.
Whilst many other things carry out one or more of the above processes, only living
organisms possess all of these characteristics.
CLASSIFICATION OF ANIMALS
When the librarian has a new book to add to the library, he or she will group it with
books on a similar to.
Classification can be defined as grouping organisms according to their structural
similarities.
This means that organisms that share similar features are placed in one group. These
groups are arranged from the largest group of organisms to the smallest group of
organisms.
The groups, from largest to smallest, are arranged as follows: kingdom, phylum
(plural phyla), class, order, family, genus (plural genera) and species.
The species is the smallest group of organisms.
As you go through the classification hierarchy, you will see that scientists have used
broader features to put organisms into kingdoms, which are the largest groups of
organisms.
When you move down towards the species, which are the smallest groups of
organisms, features are becoming specific.
In other words, two organisms that belong to the same species share more
features than those in the same kingdom but in different species.
A species can be defined as a group of organisms with similar features, and these
organisms are capable of breeding and produce fertile offspring.
Classification hierarchy has many uses.
First, it helps scientists to sort organisms in order.
Second, it helps them to identify new organisms by finding out which group they
fit.
Third, it is easier to study organisms when they have been properly identified and
correctly named.
Two major classification types are known,
3
, Artificial and Natural classifications.
Artificial classification groups the animals for the purpose of convenience, using few and
easily observed characters.
Most often these characters are imposed on the organisms hence do not reflect phylogenic
and evolutionary relationships. Example of such characters include where the animal lives,
how they move, what they feed on, etc.
Natural classification, on the other hand, groups the animals according to their natural
affinities, using numerous internal and external characters and even characters waiting
to be discovered. They therefore express natural relationships like phylogenic and
evolutionary relationships.
Natural classification is preferable and has been adopted in Biology because it allows
biologists to see the organismal world as having a unique number of groups with
historical and evolutionary relationship.
It introduces a set of classification principles involving
(i) the arrangement of animals in a hierarchical order,
(ii) the arrangement of animals based on structural and natural relationships
(homology) and (iii) an arrangement transcending human interpretation and judgment.
The Linnaean classification is a fine example of this.
Taxonomy is the branch of biology that is involved in identification, naming and
classifying living organisms.
Taxonomy is the science of naming and classifying and organizing organisms in a
universally accepted structure.
Taxonomy is a study of the principle, practice and rules of classification and
nomenclature of living organisms
There are two bases for such classification.
(1). Phenetic taxonomy, which involves grouping on the basis of phenotypic
similarity and engaging complex statistical techniques to obtain a measure of
similarity. Characters used are largely morphological, anatomical, biochemical and
cytological.
(2). Phyletic taxonomy, which involves grouping on the basis of presumed
evolutionary and genetic relationships. The outcomes of the two systems are usually
fairly similar despite the fact that phyletic classification is liable to subjective bias.
A species forms the basic unit of classification of animals. There are different ways of
distinguishing a species.
This form of organization is usually arranged hierarchically from the largest
inclusive grouping to the more specific one.
This is known as the taxonomic rank. This hierarchical taxonomic model (also referred
to as Linnaean system) was invented by Carl Linnaeus, a Swedish zoologist, botanist
and physician.
Systematics is the process of placing organisms into groups or taxa based on certain
relationships between them.
The main categories of classification of living things are- kingdom, division (plants) or
phylum (animals), class, order, family, genus and species.
4
Characteristics and Classification of Living Organisms
Welcome to the exciting and amazing world of living things.
Go outside and look around you. Look at the sky, the soil, trees, plants, people, animals.
Nature is all around you if you have the eyes to see it. Count how many living things
you can see.
What is it that makes living things different from things that are not alive?
Biology is the study of living things. It deals with what all living things can do, how
they do it and why they do it. In biology, there is always a relationship between the
structure of an organism, its function, and its adaptation to its function or environment.
Biology also tackles the important topics such as population, environmental issues as
well as health issues.
When you have studied this unit, you should be able to:
list and describe the characteristics of organisms
define the terms nutrition, excretion, respiration, sensitivity, reproduction, growth and
movement
outline the use of a hierarchical classification system for living organisms
classify living organisms into kingdoms, orders, classes, families, genera and species
define and describe the binomial system of naming species
construct dichotomous keys
use simple dichotomous keys based on easily identifiable features.
Characteristics of Living Things
There are seven (7) activities which make organisms different from non-living things.
These are the seven characteristics of living organisms.
Nutrition/ Feeding
Living things take in materials from their surroundings that they use for growth or to
provide energy. Nutrition is the process by which organisms obtain energy and raw
materials from nutrients such as proteins, carbohydrates and fats.
Plants, algae, and some bacteria harvest the energy of sunlight through photosynthesis,
converting radiant energy into chemical energy.
These organisms, along with a few others that use chemical energy in a similar way,
are called autotrophs (“self-feeders”).
All other organisms live on the organic compounds autotrophs produce, using them as
food, and are called heterotrophs (“fed by others”).
At least 95% of the kinds of organisms on Earth—all animals and fungi, and most
protists and prokaryotes—are heterotrophs.
Respiration
Respiration is the release of energy from food substances in all living cells.
Living things break down food within their cells to release energy for carrying out the
following processes.
Cellular respiration is the complete oxidation of organic compounds such as
glucose to extract energy from chemical bonds.
1
, Anaerobic respiration:
In animals
Most organisms cannot respire without oxygen. But some organisms and tissues can
continue to respire if the oxygen runs out.
These organisms and tissues use the process of anaerobic respiration.
Animal muscles can respire anaerobically for short periods of time - even though the
process is relatively inefficient, it's better to continue respiring and be able to run away
from danger - or run a race.
The glucose in muscle is converted to lactic acid:
Glucose → Lactic acid (+ energy released)
In general, anaerobic respiration consists of two main basic steps: Glycolysis: the break
down of glucose into two pyruvate, two ATP, and two NADH (an electron carrier)
molecules.
Fermentation: the production of alcohol or lactic acid substrates and NAD+ for energy
production
Movement
All living things move. It is very obvious that a leopard moves but what about the thorn
tree it sits in?
For example, different types of locomotory organs are found in protozoans. They may
bear flagella (flagellates), cilia (ciliates) pseudopodia (sarcodines).
Locomotory organs are absent in the parasitic forms (Sporozoa).
Excretion
All living things excrete. As a result of the many chemical reactions occurring in cells,
they have to get rid of waste products which might poison the cells.
Excretion is an essential process through which body gets rid of metabolic wastes and
maintains osmotic pressure.
Several waste products such as water, carbon dioxide and nitrogenous substances are
generated during cellular activities. These products are harmful to the body if
accumulated and therefore need to be removed. In mammals, specialized organ called
kidney eliminates most of the water and nitrogenous substances from the body.
Excretion is defined as the removal of toxic materials, the waste products of metabolism
and substances in excess from the body of an organism.
In majority of vertebrates, the chief excretory organ is the kidney.
Growth
Growth is seen in all living things. It involves using food to produce new cells.
It is the permanent increase in cell number and size is called growth.
Reproduction
All living organisms have the ability to produce offspring.
Reproduction is the biological process by which new organisms are created from their
parents. There are two main types of reproduction:
Asexual reproduction
A single organism reproduces without the involvement of another organism. The
offspring is genetically identical to the parent.
Sexual reproduction
2
, A male and female organism combine their genetic information to create a new
organism that is genetically unique.
In humans, reproduction involves the following steps:
Gamete production: The male gamete (sperm) and the female gamete (egg) are
produced.
Fertilization: The sperm fertilizes the egg in the female's reproductive system.
Zygote formation: The fertilized egg, now called a zygote, develops into an embryo
and then a fetus.
Sensitivity
All living things are able to sense and respond to stimuli around them such as light,
temperature, water, gravity and chemical substances.
These seven characteristics of living organisms form the basis of the study of Biology.
Whilst many other things carry out one or more of the above processes, only living
organisms possess all of these characteristics.
CLASSIFICATION OF ANIMALS
When the librarian has a new book to add to the library, he or she will group it with
books on a similar to.
Classification can be defined as grouping organisms according to their structural
similarities.
This means that organisms that share similar features are placed in one group. These
groups are arranged from the largest group of organisms to the smallest group of
organisms.
The groups, from largest to smallest, are arranged as follows: kingdom, phylum
(plural phyla), class, order, family, genus (plural genera) and species.
The species is the smallest group of organisms.
As you go through the classification hierarchy, you will see that scientists have used
broader features to put organisms into kingdoms, which are the largest groups of
organisms.
When you move down towards the species, which are the smallest groups of
organisms, features are becoming specific.
In other words, two organisms that belong to the same species share more
features than those in the same kingdom but in different species.
A species can be defined as a group of organisms with similar features, and these
organisms are capable of breeding and produce fertile offspring.
Classification hierarchy has many uses.
First, it helps scientists to sort organisms in order.
Second, it helps them to identify new organisms by finding out which group they
fit.
Third, it is easier to study organisms when they have been properly identified and
correctly named.
Two major classification types are known,
3
, Artificial and Natural classifications.
Artificial classification groups the animals for the purpose of convenience, using few and
easily observed characters.
Most often these characters are imposed on the organisms hence do not reflect phylogenic
and evolutionary relationships. Example of such characters include where the animal lives,
how they move, what they feed on, etc.
Natural classification, on the other hand, groups the animals according to their natural
affinities, using numerous internal and external characters and even characters waiting
to be discovered. They therefore express natural relationships like phylogenic and
evolutionary relationships.
Natural classification is preferable and has been adopted in Biology because it allows
biologists to see the organismal world as having a unique number of groups with
historical and evolutionary relationship.
It introduces a set of classification principles involving
(i) the arrangement of animals in a hierarchical order,
(ii) the arrangement of animals based on structural and natural relationships
(homology) and (iii) an arrangement transcending human interpretation and judgment.
The Linnaean classification is a fine example of this.
Taxonomy is the branch of biology that is involved in identification, naming and
classifying living organisms.
Taxonomy is the science of naming and classifying and organizing organisms in a
universally accepted structure.
Taxonomy is a study of the principle, practice and rules of classification and
nomenclature of living organisms
There are two bases for such classification.
(1). Phenetic taxonomy, which involves grouping on the basis of phenotypic
similarity and engaging complex statistical techniques to obtain a measure of
similarity. Characters used are largely morphological, anatomical, biochemical and
cytological.
(2). Phyletic taxonomy, which involves grouping on the basis of presumed
evolutionary and genetic relationships. The outcomes of the two systems are usually
fairly similar despite the fact that phyletic classification is liable to subjective bias.
A species forms the basic unit of classification of animals. There are different ways of
distinguishing a species.
This form of organization is usually arranged hierarchically from the largest
inclusive grouping to the more specific one.
This is known as the taxonomic rank. This hierarchical taxonomic model (also referred
to as Linnaean system) was invented by Carl Linnaeus, a Swedish zoologist, botanist
and physician.
Systematics is the process of placing organisms into groups or taxa based on certain
relationships between them.
The main categories of classification of living things are- kingdom, division (plants) or
phylum (animals), class, order, family, genus and species.
4
