CLASSIFICATION OF LIVING THINGS Lesson Note
This SS1 Biology lesson note covers CLASSIFICATION OF LIVING THINGS for First Term, Week 3.
Learning Objectives
- At the end of the lesson, students should be able to:
- Define classification of living organisms.
- Explain the importance of classification.
- State the basis for classifying living organisms.
- Mention the major kingdoms of living organisms.
- State the characteristics of the major kingdoms.
- Give examples of organisms in each kingdom.
- Explain the meaning of taxonomy.
- Explain binomial nomenclature.
- State the major levels of classification.
- Differentiate between major groups of living organisms.
Lesson Note
Meaning of Classification
Classification of living things is the arranging of living things(in group) according to their similar characteristics or qualities shared.
The scientific study of classification is called taxonomy.
There are millions of living organisms in the world. Classification makes it easier to identify, name, study and understand them.
B. Importance of Classification
Classification of living organisms is important because it:
It is done for easy references
Helps in the identification of similar organisms
Shows similarities and differences between organisms.
Helps scientists understand relationships between organisms.
Makes it easier to give organisms scientific names.
Prevents confusion caused by different local names.
Helps scientists predict the characteristics of organisms.
Helps for easy research
Shows evolutionary relationships among organisms.
Helps to trace geographical distribution of living things.
C. Basis of Classification
Living organisms can be classified using several characteristics, including:
*Cell type: Whether the organism is prokaryotic or eukaryotic.
*Number of cells: Whether it is unicellular or multicellular.
*Mode of nutrition: Whether it makes its own food or obtains food from other organisms.
*Cell structure: Presence or absence of structures such as cell walls and chloroplasts.
*Method of reproduction.
*Body structure and organisation.
*Evolutionary relationships.
*Genetic characteristics, such as similarities in DNA.
D. Levels of Classification
Living organisms are placed into groups from the broadest group to the most specific group. The major levels are:
Kingdom → Phylum → Class → Order → Family → Genus → Species
For plants, the term Division is often used instead of Phylum.
1. Kingdom
The largest major group in this classification system.
2. Phylum
A group of closely related classes.
3. Class
A group of related orders.
4. Order
A group of related families.
5. Family
A group of related genera.
6. Genus
A group of closely related species.
7. Species
A group of similar organisms that can normally reproduce with one another and produce fertile offspring.
Species is regarded as the basic unit of classification.
Five-Kingdom Classification
A traditional system of classification divides living organisms into five kingdoms:
Monera
Protista
Fungi
Plantae
Animalia
i. Kingdom Monera
Kingdom Monera traditionally includes mainly unicellular prokaryotic organisms, such as bacteria.
Characteristics
They are mostly unicellular.
The cells are prokaryotic
They lack membrane-bound organelles.
Most have a cell wall.
There is no sexual reproduction.
Some make their own food, while others obtain food from other sources.
Examples
Bacteria
Cyanobacteria
ii. Kingdom Protista
Kingdom Protista consists mainly of unicellular eukaryotic organisms, although some are multicellular or colonial.
Characteristics
They are unicellular organisms.
The organisms are all eukaryotic.
Some are plant-like and carry out photosynthesis.
Others obtain food from their surroundings.
They can reproduce sexually or asexually.
Examples: Amoeba, Paramecium and Euglena
iii. Kingdom Fungi
Fungi are organisms that obtain nutrients mainly by absorbing dissolved organic substances from their surroundings.
Characteristics
Most are multicellular, although yeast is unicellular.
Their cells have a true nucleus.
Their cell walls contain chitin.
They do not contain chlorophyll.
They cannot make their own food by photosynthesis.
Many reproduce by spores.
Examples: Mushroom, Yeast and Rhizopus (bread mould)
iv. Kingdom Plantae
Kingdom Plantae consists of plants.
Characteristics
Plants are multicellular.
Their cells have a true nucleus.
Their cell walls are mainly made of cellulose.
Most contain chlorophyll.
Most make their own food through photosynthesis.
They store food mainly as starch.
They may reproduce sexually or asexually.
Examples: Maize, Mango, Fern, Moss and Hibiscus
v. Kingdom Animalia
Kingdom Animalia consists of animals.
Characteristics
Animals are multicellular.
Their cells have a true nucleus.
Their cells do not have cell walls.
They do not contain chlorophyll.
They obtain food from other organisms.
Most animals can move from one place to another during at least one stage of their life.
They have specialised cells, tissues and organs.
Examples: Human beings, Goat, Fish, Butterfly and Earthworm
E. Comparison of the Five Kingdoms
Feature Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Organisation Mostly unicell Mostly unicell Mostly multicell Mostly Multicell Mostly multicell
Cell wall Usually present Variable Present Present Absent
Chlorophyll Absent SPI Absent PPT PPT Absent
Nutrition A/HT A/HT H/trophic MAT H/trophic
Examples Bacteria Amoeba Mushroom Maize Human
SPI-some possess it PPT-present in photosynthetic tissue A/HT – auto/heterotrophic
H/trophic – heterotrophic MAT – mainly autotrophic tissue
F. Binomial Nomenclature
Binomial nomenclature is the system of giving each type of organism a genus and species name.
The system was developed and popularised by Carl Linnaeus.
The two parts of a scientific name are:
Genus
Specific epithet
Examples:
Human beings: Homo sapiens
Maize: Zea mays
Mango: Mangifera indica
Rules of Binomial Nomenclature
The genus name begins with a capital letter.
The specific epithet begins with a small letter.
The scientific name is written in italics when typed.
When handwritten, the two parts are usually underlined separately.
Importance of Scientific Names
Scientific names are useful because:
1. They are recognised internationally.
2. They prevent confusion caused by local names.
3. They provide a standard way of identifying organisms.
4. They show relationships between organisms.
5. They make scientific communication easier.
For example, a mango may have different local names in different languages, but Mangifera indica is its scientific name.
Meaning of Species
A species is a group of organisms that are sufficiently similar and can normally interbreed to produce fertile offspring.
For example, human beings belong to the species Homo sapiens.
Species is the basic unit of biological classification.
Modern Classification
Modern scientists do not classify organisms only by their outward appearance.
They also consider:
*DNA and genetic information.
*Cell structure.
*Biochemical characteristics.
*Fossil evidence.
Evolutionary relationships.
This helps scientists determine how closely organisms are related.
Summary
Classification is the systematic arrangement of living organisms into groups based on their similarities, differences and relationships. Taxonomy is the scientific study of classification.
The traditional five kingdoms are Monera, Protista, Fungi, Plantae and Animalia. Organisms are arranged into taxonomic groups: Kingdom, Phylum, Class, Order, Family, Genus and Species.
Scientific names are given using binomial nomenclature, which consists of the genus and specific epithet. Classification makes the study and identification of the large variety of living organisms easier.
Evaluation
OBJECTIVE QUESTIONS
What is classification?
A. The process of feeding organisms
B. The arrangement of organisms into groups based on their characteristics
C. The process of reproduction
D. The study of diseases
The scientific study of classification is called
A. Ecology
B. Anatomy
C. Taxonomy
D. Physiology
Which of the following is the correct order of classification?
A. Species → Genus → Family → Order → Class → Phylum → Kingdom
B. Kingdom → Phylum → Class → Order → Family → Genus → Species
C. Kingdom → Species → Class → Family → Order → Genus
D. Genus → Species → Family → Class → Order → Kingdom
Which of the following is a characteristic of organisms in Kingdom Monera?
A. They all have a true nucleus
B. They are all multicellular
C. Their cells lack a true nucleus
D. They all contain chlorophyll
Which of the following belongs to Kingdom Protista?
A. Mushroom
B. Amoeba
C. Maize
D. Goat
Which of the following is a characteristic of fungi?
A. They contain chlorophyll
B. Their cell walls contain chitin
C. They are all unicellular
D. They produce food by photosynthesis
Which kingdom contains organisms that generally make their own food by photosynthesis?
A. Animalia
B. Fungi
C. Plantae
D. Monera
Which of the following is a characteristic of Kingdom Animalia?
A. Cells have cellulose cell walls
B. Animals contain chlorophyll
C. Animals are generally multicellular and heterotrophic
D. Animals are all unicellular
Binomial nomenclature is used to
A. classify diseases
B. give organisms scientific names
C. measure the size of organisms
D. identify body organs
Which of the following is the scientific name for humans?
A. Mangifera indica
B. Zea mays
C. Homo sapiens
D. Amoeba proteus
Theory Questions
1a. Define classification and taxonomy.
1b. State five importance of classifying living organisms.
2a. State four characteristics of Kingdom Monera.
2b. Differentiate between Plantae and Animalia