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In Biology, taxonomy plays a vital role. It is the scientific study of naming, defining and classifying organisms based on shared characteristics. In 1758, Carolus Linnaeus proposed a two-kingdom system of classification namely the plant kingdom and the animal kingdom. This was the easiest classification to understand. However, it did not include all the organisms since some of them didn’t fit into any.
Read Also: Heterotrophic Bacteria
| Table of Content |
Key Terms: Linnaeus’ two-kingdom system of classification, Kingdom Plantae, Kingdom Animalia, Binomial nomenclature, Taxa, Difference between Plant and Animal Kingdom, Limitations of Plant and Animal Kingdom, Prokaryotes and Eukaryotes.
Two Kingdom System of Classification
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The two-kingdom system of classification is the classification coined by Swedish botanist Carolus Linnaeus in which the division of living organisms was done in two categories. These two - kingdoms of classification consisted of Regnum Animale, meaning animal kingdom, and regnum vegetable, meaning plant kingdom.
Several features of the Linnean two-kingdom system of classification are as follows:
- This classification was based on nutrition and locomotion. Those organisms which could move and had a defined shape and structure and were able to ingest food in either liquid or solid-state were classified under kingdom Animalia while others under kingdom Plantae.
- Linnaeus’ two systems of classification are the oldest system of categorizing animals and plants and the easiest to decipher. All modern classification has its roots in Linnean taxonomy. Linnaeus is known as the “father of taxonomy”.
- Since Linnaeus’ two systems of classification is the oldest system of classification, therefore, it didn’t include a large number of organisms that couldn’t fit into either of the categories.
- It follows binomial nomenclature which means every species will have two names, its genus name and species name. For example, Homo is the genus name and sapiens is the species name. This system is helpful in the scientific naming of organisms thereby simplifying the nomenclature for the scientists.
- Linnaeus also created a hierarchy of taxa which is a grouping of one or more types of organisms to form a unit. It ranged from the kingdom to the species.
Read More:
| Chapter Related Topics | ||
|---|---|---|
| Biological Classification | Five Kingdom Classification | economic importance of fungi |
| Mycology | Components of Ecosystem | where do microorganisms live |
Kingdom Plantae
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The Plant Kingdom includes all the plants that have some shared characteristics. These are bacteria(prokaryotes), photosynthetic plants and several non-photosynthetic plants and fungi. Several features of Kingdom Plantae are as follows:
- They do not possess the ability to move. They are immobile and usually remain in one place only.
- They have branches that spread out and green leaves due to the presence of chlorophyll.
- They are autotrophic mode of nutrition which means they prepare their food with the help of water, sunlight and carbon dioxide. It is also known as self-nutrition.
- They indulge in photosynthesis during the day and hence more carbon dioxide is required during the day and at night it is released.
- They reserve their food in the form of starch. For example, Algae.
- They have a rigid wall around their cell known as a cell wall made up of cellulose.
- There is no presence of the nervous system and excretory system.
- Reproduction is dependent on air, insects and water. Asexual and vegetative method of reproduction is observed.
- The non-photosynthetic plants obtain their food through parasitism, i.e through their host. For example, Indian pipe.
Read Also : Solutions to Class 11 Biology Chapter 2 Biological Classification
Kingdom Animalia
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Animal Kingdom includes all the unicellular protozoans and multi-cellular animals. Several features of Kingdom Animalia are as follows:
- They can move, i.e., locomotion is one of the prominent features of animals.
- They do not have any wall covering the cell which means cell wall is absent in them.
- They get the nutrition from other living beings since they cannot prepare their food. This mode of nutrition is also known as the heterotrophic or holozoic mode of nutrition.
- They do not possess the ability to photosynthesize, unlike plants. They take in oxygen and release carbon dioxide.
- They have a compact body and a well-defined nervous and excretory system.
- They cannot only respond to stimulus but respond to selective stimulus and filter out the rest.
- The mode of reproduction is sexual which leads to the fusion of male and female gametes known as a zygote.
Read Also: Salient Features of Kingdom
Difference between Animal and Plant Kingdom
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The difference between Animal and Plant Kingdom are as follows:
| Animal Kingdom | Plant Kingdom |
|---|---|
| Absence of cell wall | Presence of cell wall |
| Presence of locomotion | Absence of locomotion |
| Cannot photosynthesize | Can photosynthesize |
| Heterotrophic mode of nutrition | Mostly autotrophic mode of nutrition |
| Presence of well defined nervous and excretory system | Absence of well-defined nervous and excretory system |
| Food is stored in form of glycogen | Stored food is starch |
| Lives for a certain number of years | Can live for years |
| Sexual reproduction is found | Asexual reproduction is found |
| Gives carbon dioxide, takes in oxygen | Releases oxygen, takes in carbon dioxide |
| The cells are smaller in length (10-30mm) | The cells are larger in length (10-100mm) |
Limitations of Two Kingdom System of Classification
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The two-kingdom system of classification is the earliest classification and hence it takes into account only two kingdoms. However later, many new kingdoms have been added. The limitations of Linnaeus’ two-kingdom system of classification are as follows:
- Certain species have both plants as well as animal-like characteristics. For example, some species of Euglena are autotrophic while others are heterotrophic. The positioning of such an organism is not specified in the two kingdoms system of classification.
- Fungi lack chlorophyll and perform heterotrophic mode of nutrition. Yet, they are placed in the plant kingdom.
- This system of classification did not distinguish between eukaryotic cells (organisms with a true nucleus) and prokaryotic cells (organisms that do not have true nuclei)
- Lichens that show both plant-like and animal-like characteristics are placed in the plant kingdom.
- In this system, unicellular organisms are put together with multicellular organisms.
- The two-kingdom system does not acknowledge diversified life forms. Many organisms have not found space in any of the categories.
Read Also: difference between fungi and lichens
Things to Remember
- The two-kingdom system of classification was proposed by Carolus Linnaeus which divided all living organisms into two kingdoms namely the plant kingdom and the animal kingdom.
- This system of classification is based primarily on the locomotion and nutrition of living organisms. The plant kingdom included bacteria(prokaryotes), photosynthetic plants, and several non-photosynthetic plants and fungi while the animal kingdom included all the unicellular protozoans and multi-cellular animals.
- The primary difference between the plant and the animal kingdom is that plants do not show the property of locomotion while the animals show the property of locomotion. Besides locomotion, plants can also prepare their food while animals depend on others for their food.
- There are certain drawbacks of the two-kingdom system of classification. Unicellular and multicellular organisms are placed together and there is no differentiation between eukaryotes and prokaryotes. Certain organisms like Euglena and slime mold have properties of both plant and animal. They are not put in any of the categories.
- The two-kingdom system of classification is heterogenous which means it has dissimilar organisms clubbed together in one kingdom.
Read More:
| Important Topics | ||
|---|---|---|
| Incomplete dominance | Chromosomes and genes | Linkage and crossing over |
| Cyanobacteria | Heterotrophic Bacteria | Saprophytes |
| What are Lichens? | Mycorrhiza | Prions |
Previous Years Questions
- Meiosis takes place in...[NEET 2013]
- The sexual reproduction is absent in….[NEET 1995]
- For union between stock and scion in grafting which one is the first to occur….[NEET 1990]
- A clone is ......… [KCET 2011]
- Animals which possess cleidoic eggs exhibit….[KCET 2011]
- Which among these is not a post fertilization event ?...[KCET 2016]
- Type of asexual reproduction found in Hydra is..[KEAM]
- Which of the following is having longitudinal binary fission ?….[KEAM]
- In grafting, the stock and scion should be joined….
- The mode of asexual reproduction in Euglena is….[CUCET 2010]
- Isogamy is found in...[CUCET 2010]
- In these plants artificial vegetative reproduction is possible through….[GUJCET 2006]
- Apomixis in plant means development of a plant… [BHU UET 2008]
- Which one of the following plants reproduces vegetatively by epiphyllous buds?
Sample Questions
Ques. What is a two-kingdom system of classification? (3 Marks)
Ans: The two-kingdom system of classification is proposed by Carolus Linnaeus in 1758. According to this system of classification, all living organisms are divided into two kingdoms namely Plants and Animals. Those who can make their food and couldn’t move were kept in the Plant kingdom while those that could not prepare their food and could show the ability of locomotion or movement were kept in the Animal kingdom.
Ques. What is the major drawback of the two kingdom systems of classification? (3 Marks)
Ans: The major drawback of the two kingdom system of classification is that certain species of Euglena couldn’t fit into either Plant kingdom or Animal kingdom. Hence such organisms were not placed into any. Another organism like Fungi was placed in the Plant kingdom despite it following a heterotrophic mode of nutrition. Lichens were also placed in the plant kingdom even though they possessed the characteristics of both plant and animal.
Ques. How is the Plant Kingdom different from Animal Kingdom? (3 Marks)
Ans: The plant kingdom consists of all the living organisms that do not have the ability to locomotion. Animal kingdom on the other hand consists of organisms that can show locomotion. The plant kingdom comprises organisms that have a cell wall around their cell and can photosynthesize. Organisms in the animal kingdom do not have cell walls nor do they photosynthesize. While plants release oxygen, animals take in oxygen and release carbon dioxide which can be used by the plants.
Ques. What is a taxon? According to Linnaean classification, how many taxons are there? (2 Marks)
Ans: A taxon is a grouping of one or more types of organisms to form a unit. It ranged from the kingdom to the species. There are seven taxa in the Linnaean classification. They are species, genus, family, order, class, phylum, and kingdom.
Ques. How is a Linnaean classification different from a modern classification? (3 Marks)
Ans: Linnaean classification took into account only two kingdoms which were the Plant kingdom and the Animal kingdom. This two-kingdom system of classification was heterogeneous. Many organisms which even though had dissimilar features were clubbed together in either of the groups. For example, Euglena and Mosses which showed the characteristics of both animals and plants were placed in the Plant kingdom.
On the contrary, the modern system of classification consists of six major kingdoms namely Plantae, Animalia, Protista, Fungi, Monera, Archaea proposed by Woese in 1977. This new system of classification overcame all the limitations of the Linnaean system of classification.
Ques. What is Binomial system of nomenclature? (2 Marks)
Ans: The binomial system of nomenclature refers to the nomenclature of organisms in which every species will have two names, its genus name and species name. For example, Homo is the genus name and sapiens is the species name. This system is helpful in the scientific naming of organisms thereby simplifying the process of naming the organisms.
Ques. What is the difference between Prokaryotes and Eukaryotes? (2 Marks)
Ans: Prokaryotes are those unicellular organisms that do not have a nucleus while Eukaryotes can be both unicellular and multicellular organisms that have a true nucleus. The size of Prokaryotes ranges in size from 0.2 μm–2.0 μm in diameter while the size range of Eukaryotes is between 10 μm–100 μm in diameter.
Ques. Which organisms were wrongly placed in Linnean classification and why? (2 Marks)
Ans: Organisms like Lichens, Fungi, and Algae were all placed in the plant kingdom despite them showing abilities of Animal kingdom too or lacking basic characteristics of Plant kingdom
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