General Classification: Artificial and Natural system of classification, Practice Problems and FAQs

If we look around us, we can see varieties of organisms, with different sizes, shapes, and structures. All the organisms are not alike. Right? So if somebody asks us to classify the organisms around us, it will not be so easy for us. Firstly we may classify them into plants and animals. Why do we classified them into plants and animals? We will consider the major morphological characteristics which can differentiate plants from animals, like the mode of nutrition, ability to move etc. These characters can be observed easily.

But in the kingdom of plants itself, a variety of plants are present. We can classify them into different other groups, because all the plants are not alike. Can you name all plants in your locality? Not possible. Why?

                                                     Fig: Varieties of plants

A large variety of plants are present in your area which vary in characteristics and you do not know all the names. So think about plants around the world. They vary a lot in different aspects such as body structure, cellular organisation, reproductive structures, life cycles, etc. Thus they need to be classified properly for easy identification and study. Many scientists have proposed their own type of classification in ancient days. Here in this article we are going to discuss some of them in depth.

Table of contents

• Classification
• Systems of classification
• Artificial system of classification
• Natural system of classification
• Differences between artificial and natural system of classification
• Practice Problems
• FAQs

Classification

Classification is the process of creation of a hierarchical system of categories based on the characteristics and natural relationships among organisms. There are different systems of classifications based on the structure, habitats, behaviour and various other characteristics of organisms. 

Need for classification

Organisms need to be classified for many reasons as follows: 

• Since there is a diverse variety of organisms present on the Earth, they should be classified to make identification of organisms easy. 
• It gives an idea about the relationships among different groups of organisms. 
• It can be used for research. 
• Studying a representative from a group gives us an idea about the characteristics of other members. 
• Naming of organisms can be done easily.

Systems of classification

There are three important systems of classification for the living organisms. They are the artificial system of classification, natural system of classification and phylogenetic system of classification. Let’s discuss more about artificial and natural systems of classifications in this article. 

Artificial system of classification

The system of classification which uses few observable characters such as habitat, colour and morphology etc., is called an artificial system of classification. Examples of artificial systems of classification include classification of organisms by Aristotle, classification of plants by Aristotle and Linnaean system of classification.

Classification of organisms by Aristotle

Aristotle classified organisms into three types based on the habitat. He classified animals into air dwellers, land dwellers and water dwellers based on their habitat. Aquatic organisms or water dwellers are the organisms that live in water. Examples include fishes and sea grass. Terrestrial organisms or land dwellers are the organisms that live on land. Examples include lions and rabbits. Air dwellers are the organisms that can fly. Examples include insects and bats. 

Based on the presence or absence of RBCs, he classified animals into enaima (with RBCs) and anaima (without RBCs). 

                                      Fig: Aristotle

Classification of plants by Aristotle

Aristotle classified plants, during the second century, based on the simple morphological characteristics such as height and girth. The classification includes herbs, shrubs and trees.

Herbs are the plants which were short-sized and had no woody tissues. Shrubs are medium-sized plants with woody stems and taller than herbs. Trees include the plants which were tall and had a woody and hard stem.

                             Fig: Classification of plants by Aristotle

Linnaean system of classification

Carl Linnaeus classified 7,300 flowering plants into 24 classes based on superficial morphological characteristics such as the structure of the reproductive organs (number and arrangement of male and female organs). It is commonly called sexual system of classification.

                           Fig: Carl Linnaeus

Disadvantages of artificial system of classification

There are some disadvantages for the artificial system of classification as follows: 

• The organisms with close relationships get separated into different groups. For example bat and whale (homologous organs).
• It gives sexual and morphological characters equal importance while classifying organisms. 
• Morphological characters are prone to changes due to environmental changes.
• Organisms belonging to different groups may be grouped under the same category. For example lotus and fish are included under aquatic organisms.
• It makes studies difficult using a representative of the group. 
• It will not give any idea about the natural relationships between the organisms. 

Natural system of classification

The system of classification which uses all important characteristics of the organisms like cytological, biochemical, developmental, physiological, anatomical, reproductive etc., is called the natural system of classification. The characters which are considered here are relatively constant. These characters bring about the maximum number of similarities in a group. For example, this system classified organisms into mammals, birds and fishes based on the following characters:

Mammals

They possess mammary glands and have hairs on their body. They are viviparous (giving birth to young ones). They possess four chambered hearts.

                                        Fig: Mammal

Birds

They possess wings and their body is covered by feathers. They possess pneumatic bones which help in flight. They are oviparous (laying eggs). They also possess four chambered hearts.

                                                   Fig: Bird

Fishes

They do not possess limbs, instead they have fins. Their bodies are covered by scales. They possess gills for respiration. They are cold blooded and possess two chambered hearts.

                                        Fig: FIsh

Bentham-Hooker’s system of classification 

Bentham and Hooker classified plants, during the 19th century, based on morphology, ultrastructure, anatomy, embryology and phytochemistry (analysis of chemicals obtained from plants). It is considered as a natural system of classification. 

                               Fig: Bentham and Hooker

They classified higher seed bearing plants placed under the subkingdom Phanerogamae into two major groups such as Gymnosperms and Angiosperms.

Gymnosperms are the plants in which the seeds are not enclosed in a fruit. Angiosperms include the plants with seeds enclosed in a fruit. According to Bentham and Hooker, angiosperms can be classified into monocotyledonous plants and dicotyledonous plants. Monocotyledonous plants have seeds with one cotyledon or seed leaf and dicotyledonous plants have seeds with two cotyledons or seed leaves.

                   Fig: Bentham and Hooker’s natural system of classification

Advantages of natural system of classification

The following are some of the advantages of the natural system of classification:

• It places organisms with natural relationships in the same group. 
• It prevents organisms belonging to different groups to be grouped under the same category.
• It processes many characters and gives accuracy to the data. 
• This system indicates evolutionary relationships and the origin of different taxa. 

DIfferences between artificial and natural systems of classification

Practice Problems

Q 1. Select the incorrect statement about the natural classification system from the options given below:

a. Cryptogams and phanerogams are two divisions of plants
b. Gymnosperms, dicotyledons, and monocotyledons are the three types of phanerogams
c. The earliest leaves to emerge from a growing seed are called cotyledons
d. Flowering plants are cryptogams, and non-flowering plants are phanerogams

Answer: The categorisation of Bentham and Hooker is an example of a natural system of classification. It takes into account the various characteristics of plants such as ultrastructure, anatomy, embryology, and phytochemistry. All plants in the Plant kingdom are divided into two divisions called cryptogams and phanerogams according to this categorisation. Plants that do not produce flowers are known as cryptogams. Algae or thread-like green stuff in rivers, mosses on rocks, or a clump of ferns near rivers are examples. Phanerogams are flowering plants that are divided into gymnosperms and angiosperms. Gymnosperms are plants with seeds that are not protected by the fruit. Angiosperms are plants that have seeds inside their fruits. Angiosperms are again classified as dicotyledonous (dicot) or monocotyledonous (monocot). The earliest leaves to emerge from a growing seed are called cotyledons or seed leaves. Dicots have two seed leaves, whereas monocots have only one seed leaf. Hence the correct option is d.

Q 2. Match the classification system in column I to the characteristics that go with it in column II:

a. A - 3, B - 4, C - 1, D - 2 
b. A - 4, B - 2, C - 3, D - 1 
c. A - 3, B - 1, C - 4, D - 2
d. A - 1, B - 2, C - 3, D - 4

Answer:  Utility was used to classify organisms as early as 2 million years ago. At that time, all known plants were divided into three categories: edible plants, medicinal plants, and poisonous plants. The height and girth of the plants were used by Aristotle to classify them. This approach was no longer in use since the characters were not solid enough to classify the entire range of plants. The physical properties of the reproductive parts (male and female) of the plant, such as stamens, were used by Carl Linneaus to classify them. It is called the sexual system of classification. Stamens are delicate plant structures, they are easily influenced by climate or environment. This can change their shape, thus it is not a reliable attribute for classification. The categorisation of Bentham and Hooker is an example of a natural system of classification. It takes into account the various characteristics of the plant such as ultrastructure, anatomy, embryology, and phytochemistry. Hence the correct option is c.

Q 3. Choose the option that contains correct comments concerning the reason for the kingdom Plantae's further classification:

a. It is easy to add new organisms.
b. Categorisation facilitates the classification of newly discovered organisms.
c. Sort the enormous variety of organisms.
d. A jumble of organisms is unattractive, but classification is presentable.

1. Only I 
2. Only II and III 
3. Only I and IV 
4. Only I, II and III 

Answer: Algae, Bryophyta, Pteridophyta and Spermatophyta are the four divisions of the Kingdom Plantae. Gymnospermae, and Angiospermae are the two subdivisions of the division Spermatophyta. This classification is used to divide around 3,74,000 plant species into divisions so that species with similar characteristics can be grouped together. This separation makes it easier to examine the various species. In addition, newly discovered species can be classified depending on divisional characteristics. This might enable scientists to foresee other characteristics of freshly discovered organisms. Hence the correct option is d.

Q 4. What are the advantages of the natural system of classification?

Answer: The system of classification which uses all important characteristics of the organisms like cytological, biochemical, developmental, physiological, anatomical, reproductive etc., is called the natural system of classification. 

Natural system of classification places organisms with natural relationships in the same group. It prevents organisms belonging to different groups to be grouped under the same category. It processes many characters and gives accuracy to the data. This system indicates evolutionary relationships and the origin of different taxa. 

FAQs

Q 1. What type of evidence is most commonly used to classify newly discovered organisms today?
Answer: DNA evidence is nowadays commonly used to classify newly discovered creatures. The genetic coding of an organism reveals a great deal about its similarity and relationship with other creatures, and this classification frequently contradicts standard morphological classification. Scientists are discussing which species are connected the most and why. There are current studies in New Zealand to sequence kiwi and tuatara (reptile) DNA, which could change the way we think about these species and their closest living relatives. However, because DNA technology is still expensive and time-consuming, the first phase in any categorisation process still relies on morphological traits, much like Linnaeus did in the 1700s.

Q 2. Who was the first to suggest an artificial system of classification?
Answer: On the basis of their habit, Theophrastus, a Greek botanist and father of botany, categorised the plants into four groups: herbs, undershrubs, shrubs, and trees. He was the first to suggest a classification system that was artificial. ‘Enquiry into plants’ (also known as Historia Plantarum) and ‘Causes of plants’ (also known as De causis plantarum) are his two writings on plants. He wrote about about 500 different plant species, calling them after popular names at the period. The plants were divided into three categories: annuals, biennials, and perennials. He also established the groundwork for the study of floral morphology by pointing out key differences between dicots and monocots.

Q 3. What was the total number of species discovered by Linnaeus?
Answer: The most famous work of Carl Linnaues, Systema Naturae, was twelve pages long. It listed around 4,400 animal species and 7,700 plant species by the time it reached its tenth edition in 1758.

Q 4. Why are herbarium specimens classified using Bentham and Hooker's classification systems?
Answer: Bentham and Hooker’s system of classification is the most natural way of classification, as it is based on actual specimen examinations. Taxa description at all levels is one of the study's most valuable inputs. The description given is accurate here and simple to classify plant species to the family level.

YOUTUBE LINK: https://www.youtube.com/watch?v=MmOx8pv8784

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