What is the Two Kingdom System of Classification? Explain.

Introduction

In this topic, you will learn about the history, classification, merits, demerits, and limitations of the Two Kingdom System of Classification. Classification is defined as the distribution of organisms into groups and subgroups based on similarities and dissimilarities.

Classification tells us how organisms are related and how they are different from each other.

A similar organism is placed in the same group. For example, sparrows and pigeons make their nest and lay eggs converted into new offspring. Both have the same characteristics in feeding and their lifestyle lives. Their nest reproduction method is the same, so they are placed in the same group. Dissimilar character shows that they can live in the same group, so they are placed in a different group.

History

Aristotle started Classification in 600 A.E. when Aristotle started Classification, there was no proper apparatus or microscope for studying organisms. He makes classify based on their food-making process. After that, further work was done by Linnaeus.

Carolus Linnaeus proposed the two-kingdom classification scheme in 1758. This classification system divides all living organisms into the two kingdoms of Plants and Animals. Those who could manufacture their food but could not move were kept in the Plant kingdom, while those who could not make their food but could move were held in the Animal kingdom.

Plants are called Autorophes ( Auto means self, and trophs means taking food). Autotrophs are those organisms that make their food by the process of Photosynthesisesis or nitrogen fixation.

They can make food by combining inorganic compounds (Co2 + H2o + light ) to create the organic compound Glucose (C6H12O6) .these organisms are almost all plants, fungi, algae, cyanobacteria, etc. these organisms put in the kingdom Plantae.

While the organism which cannot prepare their food is known as Hetrtrophes ( Hetro means other Trophs taking food ), they get their food from autotrophs in the form of leaves, grass, and meat, so they are placed in the kingdom Animalia. These organisms include almost all types of animals, including humans. Major types of bacteria, some types of fungi, etc.

Two Kingdom System of Classification

1. Kingdom Plantae
2. Kingdom Animalia

1. Kingdom Plantae:

This kingdom includes bacteria(Prokaryotes), photosynthetic plants, and non – photosynthetic fungi. The characteristic features of this kingdom are as below:

• Plants have branches and asymmetrical bodies with green leaves.
• Plants are non-motile and fixed in a place.
• During the daytime, plants are more actively involved in Photosynthesisesis than in respiration and hence take more CO2 and liberate O2. During the night, O2 is taken in, and CO2 is released.
• They are autotrophic in their mode of nutrition since they synthesize their food.
• Plants have growing points that have unlimited growth.
• The excretory system and nervous system are absent.
• The Reserve food material is starch.
• Cells have a cell wall. Cells have a lager vacuole.
• Plant cells lack centrosomes, and they may have inorganic crystals.
• Reproduction takes place with the help of agents such as air, water, and insects. Asexual and vegetative method of reproduction is also not uncommon.

2. Kingdom Animalia

This kingdom includes unicellular protozoans and multi-cellular animals or metazoans. They are characterized by:

• The definite shape of the body and the absence of branches.
• Ability to move from place to place.
• During day and night, take in O2 and release CO2, i.e., only respiration takes place, and there is no photosynthesis.
• Holozoic mode of nutrition since no chlorophylls are present and hence they are heterotrophs.
• Growth is limited in animals. Growth stops after attaining a particular size and age.
• The excretory system and nervous system are well developed.
• The Reserve food material is glycogen.
• They Lack cell walls and have small vacuoles.
• Centrosomes are present. Cells do not have inorganic crystals.
• Animals do not depend on any external agents for sexual reproduction.
• Regeneration of body parts and asexual reproduction is found only in lower organisms.

Difference between Animal and Plant Kingdom

Animal Kingdom	Plant Kingdom
they have no cell wall	They have a cell wall
The show locomotion	locomotion is Absencet
photosynthesize os absent	Can photosynthesize
Heterotrophic mode of nutrition	Mostly have an autotrophic mode of nutrition
They have well-defined nervous and excretory system	They do not have
Food stored is  glycogen	Stored food is a starch
they live for a certain number of years	they Can live for years
Sexual reproduction is Present	Asexual reproduction is Present
Gives out carbon dioxide and takes in oxygen	Releases out oxygen takes in carbon dioxide
Their cells are smaller in length (10-30mm)	Their cells are more prominent in length (10-100mm)

Limitations and Drawbacks of two-kingdom Classification

The two-kingdom Classification proposed by Carolus Linnaeus has been used for a long time. But later, it proved inadequate and unsatisfactory in view of new information and discoveries about the lower forms of organisms. The following are the shortcomings of the two kingdom systems of Classification.

• Certain organisms share the characteristics of both plants and animals. eg. Euglena and Sponges. In Euglena, some species have chlorophyll and are autotrophic like plants. However, like animals, they depend on an external supply of vitamins B and B12, which they cannot synthesize.
• A few species of Euglena lack chloroplasts and are therefore colorless and non-photosynthetic (heterotrophic). They have a saprotrophic mode of nutrition, carrying out extra-cellular digestion.
• Other colorless forms ingest small food particles and carry out intracellular digestion (holozoic nutrition). If green species of Euglena are kept in the darkness, they lose their chloroplasts, become colorless, and survive saprotrophically.
• Chloroplasts return when the organisms are returned to the light. Euglena is also characterized by the presence of an animal pigment astaxanthin in the eyespot.
• Fungi are a group of organisms that have features of their own. They lack chlorophyll; They are heterotrophic like animals. They are placed along with green plants.
• Many primitive organisms such as bacteria did not fit into either category, and organisms like slime molds are amoeboid but form fruiting bodies similar to fungi.
• The status of viruses, whether living or non-living, is debatable.

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