Classification of Living Things | Biology Form One Topic 4 New Syllabus
Jipatie Kitabu Chenye Notes Zote za Biology Form One Silabasi Mpya, Wasiliana na Mwalimu kwa Kugusa Hapa
There are different kinds of organisms in the world. Some are too small, they can not be seen with naked eyes. Such organisms are called micro-organisms. Others can be seen with naked eyes and are called macro-organisms.Concept of Classification
Classification is the process of grouping organisms according to their similarities and differences.
Organisms are grouped on the basis of similarities in terms of their evolutionary relationship or the way they carry out life processes, such as feeding and reproduction.
The field of biology that deals with classifying organisms is called taxonomy.
Organisms such as snails, orange trees, crocodiles, birds, lions, and baobab trees belong to different groups.
Activity: Grouping living things according to their similarities and differences
Materials:
A variety of small plants, insects, and other animals, notebook, and a pen or pencil.
Procedure:
Walk around the school compound and collect a variety of plants, insects, and other small animals.
Observe and group the collected organisms according to their similarities and differences.
Write the similarities and differences among the grouped organisms.
Caution
(a) Avoid collecting dangerous organisms, such as wasps, scorpions and snakes, and poisonous plants, such as milkweed and oleander.
(b) Avoid collecting weak or injured specimens as they will lead to incorrect observations.
Questions
What did you learn from the activity?
Why do you think it is important to classify organisms?
The importance of classification
Classification is important in the study of living things because of the following reasons:
(a) It makes easier to study and identify living things, because the members of the group have many characteristics in common.
(b) It makes communication among biologists in the world easier.
(c) It enables scientists to predict characteristics of an organism based on the characteristics of a group it belongs to.
When we know the characteristics of a group then we can predict the characteristics of an organism in that group.
For example, both an eagle and a chicken are birds. If we know the structure of the heart of a chicken, we can predict the structure of the heart of an eagle even if we have not seen it.
(d) It helps to understand how organisms are related in terms of their evolutionary history.
Classification systems
There are two main types of biological classification systems:
- Artificial classification systems
- Natural classification systems
Artificial system of classification
Artificial classification system groups organisms according to a few observable features, for example, the presence of legs or wings.
Based on this, bees, birds, and bats would be grouped together because they have wings.
Snakes, earthworms, and snails would also be grouped together because they do not have legs.
Artificial classification system also involves the use of some other characteristics, such as size, how organisms move, where they live, or what they eat.
In the third century BC, Aristotle (a Greek philosopher) used artificial classification system to classify plants.
He grouped them according to their shape, size, and their usefulness or usefulness to humans.
Activity: Classifying living things using artificial system of classification
Materials:
A variety of living things or charts that show pictures of a bird, bat, bee, snake, snail, earthworm, notebook and pen or pencil.
Procedure:
Observe the organisms in Figure 4.2 and note as many observable features as you can.
Advantages of artificial system of classification
(a) It is based on simple and easily observable features. Artificial classification is therefore straightforward and easy to use.
(b) It is simple to identify and classify organisms since newly discovered organisms with just a few known features can be easily fitted in.
(c) It is stable because it does not change with time or new discoveries.
(d) It is less expensive because it uses few observable features to group the organisms.
(e) It does not require special classification techniques or highly skilled personnel.
Disadvantages of artificial system of classification
(a) Some organisms that are unrelated in their internal structure such as bats and birds can be grouped together because of the resemblance of their external features.
(b) Similar organisms may be placed in different groups because of the use of only few observable features, for example, bats and rats can be grouped in different groups.
(c) It provides only limited information about each member. For example, some organisms such as bacteria and some fungi are grouped as micro-organisms because they are microscopic.
(d) This classification ignores other features, such as modes of feeding, reproduction, and cell structure.
(e) It is less accurate because it uses only few observable characteristics, such as mode of feeding, habitat, locomotion, or presence of wings.
Natural system of classification
In the natural system of classification, organisms are grouped based on many features in common, particularly those related to evolutionary relationships.
In this system, characters that show homology or similarity of origin must be distinguished from those showing analogy or similarity of use.
For example, the arms of man, forelimbs of whales, and wings of birds and bats are homologous structures.
In contrast, the wings of birds and wings of insects perform similar functions but they are different in origin, hence, they are analogous.
Natural classification system uses homologous characters.
Advantages of natural system of classification
(a) It allows organisms which are genetically and evolutionarily related to be grouped together.
(b) It is more accurate, since it involves scientific research to gather enough information before the actual placement of an organism into a particular group is decided.
(c) It enables placing of newly discovered organisms into correct groups they belong.
(d) It allows addition of new features when they are discovered.
Disadvantages of natural system of classification
(a) It is very expensive since it involves experiments, researches, and high level of classification skills.
(b) It is tedious and time consuming since it uses many features in grouping organisms.
(c) It is not stable because it can change any time due to discovery of new features or information.
Differences between artificial and natural system of classification
Artificial system of classification | Natural system of classification |
- Considers external features only. - Requires simple skills. - Based on an individual’s interest. - It is usually fast and less expensive. - Less accurate. - Has limited predictive value. | - Considers both internal and external features. - Requires advanced scientific skills. - Based on international standards. - Takes more time and is expensive. - More accurate. - Has high predictive value. |
Activity: Classifying organisms based on artificial and natural system
Materials: A variety of living things or charts showing pictures of organisms
Procedures
Observe the external features of organisms and note as many features as you can.
(a) Group the organisms based on artificial system of classification.
(b) Group the organisms based on natural system of classification.
Questions
What are the main features used to place organisms into procedures number 2 (a) and (b)?
The following are the five major groups of living things that constitute the five kingdoms.
(a) Kingdom Monera, example, bacteria.
(b) Kingdom Protoctista, examples, amoeba, Plasmodium sp., and Euglena sp.
(c) Kingdom Fungi, examples, mushroom and yeast.
(d) Kingdom Plantae, examples, maize, bean, and banana plants.
(e) Kingdom Animalia, examples, human beings, dogs, and rats.
However, viruses have not been included in these five kingdoms because they possess features of both living and non-living things. Examples of viruses include Corona virus, Ebola virus, and HIV.
Ranks of classification
In classification of living things, there are seven main ranks or taxonomic units which are arranged hierarchically in a descending order from the highest to the lowest rank.
Each unit is called a taxon (plural is taxa).
The main taxa are Kingdom, Phylum or Division, Class, Order, Family, Genus, and Species.
The highest rank is Kingdom and the lowest is Species.
Hierarchical arrangement of the taxonomic units or ranks is referred to as taxonomic hierarchy.
Kingdom Animalia is subdivided into phyla (singular is phylum) while kingdom Plantae is subdivided into divisions.
The phyla or divisions are further subdivided into classes.
Each class is subdivided into orders.
An order is subdivided into families and families are subdivided into genera (singular is genus).
A genus is subdivided into species.
A species is a group of closely related organisms that can interbreed freely under natural conditions and produce fertile offspring.
Kingdom Animalia → Phylum → Class → Order → Family → Genus → Species
Kingdom Plantae → Division → Class → Order → Family → Genus → Species
Kingdoms contain different varieties of organisms.
At kingdom level, organisms share few features in common. As you move down the ranks, each subsequent unit has fewer organisms and the members of each unit have many features in common.
At the species level, organisms share many features.
Members of the same species can interbreed to produce fertile offspring, but organisms from different species do not interbreed.
If they interbreed, they do not produce fertile offspring. This is because of differences in genetic make-up, behaviour, and morphological features, such as structure of sexual organs.
However, there are a few exceptions to this rule.
For example, a horse and a donkey can interbreed to produce a mule.
Mules are usually but not always infertile.
Dogs and wolves can interbreed to produce fertile offspring.
Binomial nomenclature
Binomial nomenclature is a scientific system of naming organisms using a two-part name.
The first part of the name represents the genus. It is also called the generic name.
The second part of the name represents the specific epithet. The two parts form the name of a species or scientific name.
This system was first introduced by Carl Linnaeus, who is also referred to as the father of classification.
Rules of binomial nomenclature
The following rules are observed when writing scientific names:
(a) All scientific names must be written in Latin language or in a Latinised form.
(b) The name should have two parts; the first part represents the genus and the second part represents the specific epithet.
(c) The generic name is written before the specific epithet.
(d) The generic name must start with a capital letter and the specific epithet begins with a small letter.
(e) In published documents, such as books, scientific names should be written in italics, for example Zea mays and Homo sapiens. When handwritten, the names must be underlined separately, for example, Zea mays and Homo sapiens.
Scientific names of common organisms
Common name Scientific name
Common frog Rana temporaria
Domestic cat Felis catus
Coconut palm Cocos nucifera
Mango tree Mangifera indica
Garlic Allium sativum
Onion Allium cepa
Pea plant Pisum sativum
Housefly Musca domestica
Lion Panthera leo
Mimosa plant Mimosa pudica
Classification is the grouping of organisms based on their similarities and differences.
Importance of classification
(a) It makes it easier to identify and study the millions of organisms in the world.
(b) Each organism (species) is referred to by the same name all over the world.
(c) It is easier to study organisms when they are in groups.
(d) It enables scientists to make predictions of information.
Revision exercise
1. Match each item from Column A with its corresponding item in Column B.
List A
(i) Kingdoms
(ii) Classification
(iii) Types of classification systems
(iv) Scientific naming
(v) Human being
(vi) Maize plant
(vii) The father of classification
List B
(a) Natural and artificial systems
(b) Division, genus, species
(c) Zea mays
(d) Monera, Animalia
(e) Binomial nomenclature
(f) Pisum sativum
(g) Felis catus
(h) Homo sapiens
(i) Aristotle
(j) Carl Linnaeus
2. Write TRUE for a correct statement and FALSE for an incorrect statement in the space provided.
(a) Artificial system of classification is based on few observable features. ______
(b) The process of sorting living things into groups is called classification. ______
(c) Organisms of the same species exhibit a low degree of similarity. ______
(d) The lowest rank in classification is the genus. ______
(e) Classification is based on similarities and differences among organisms. ______
3. Differentiate:
(a) Classification from taxonomy.
(b) Natural from artificial systems of classification.
4. Explain the concept of the biological species.
5. How would you apply the concept of classification in a real-world context?
6. Starting from the highest rank, outline the hierarchical ranks of classification in biology.
7. Explain why a chicken and a duck cannot interbreed even if they are kept in the same coop.
8. In a biology class, your fellow students classified pigeon and butterfly in the same group based on the presence of wings. Explain the shortcomings of their classification.
9. Diana wrote the scientific name of human beings as homosapiens. Explain why she was wrong.
Jipatie Kitabu Chenye Notes Zote za Biology Form One Silabasi Mpya, Wasiliana na Mwalimu kwa Kugusa Hapa
