The practice of classifying organisms based on shared characteristics is known as biological classification. The two kingdoms of classification were proposed by Linnaeus. He divided organisms into two kingdoms: the animal world (Animalia) and the plant kingdom (Plantae). The two kingdom classification had some drawbacks, such as the inability to distinguish between eukaryotes and prokaryotes, unicellular and multicellular species, and photosynthetic and non-photosynthetic organisms. As a result, this field underwent further development, with R.H. Whittaker’s Five Kingdom classification serving as the primary example.
In 1969, R.H. Whittaker proposed a classification of five kingdoms. He designated five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. He primarily uses cell structure, body organization, mode of nourishment, reproduction, and phylogenetic linkages as classification criteria.
All eukaryotic organisms that contain chlorophyll and are usually known as plants are classified as Plantae. A few species, like parasites and plants that feed on insects, are partially heterotrophic. Insectivorous plants include bladderwort and Venus fly traps, and parasites like Cuscuta feed on them. The eukaryotic structure of plant cells has large chloroplasts and a cell wall comprised primarily of cellulose. Algae, bryophytes, pteridophytes, gymnosperms, and angiosperms are all part of the plant kingdom.
The haploid gametophytic and the diploid sporophytic phases of a plant’s life cycle alternate with one another. Various plant families have different haploid and diploid phase lengths and whether they are independent or reliant on others. Alternation of generation is the name given to this phenomenon.
This kingdom is distinguished by heterotrophic multicellular eukaryotic creatures without cell walls. They rely on plants for food either directly or indirectly. They consume food, digest it inside, and store the energy they need as glycogen or fat. Holozoic nutrition refers to food consumption as their mode of nutrition. They develop according to a specific growth pattern, becoming adults with a specific shape and size. More advanced types have sophisticated sensory and neuromotor systems. Most of them have some form of mobility. Male and female copulation is the primary method of sexual reproduction through embryonic development.
The only other inhabitants of the Kingdom Monera are bacteria. They are the microorganisms that are most prevalent. There are bacteria practically everywhere. One grain of soil contains hundreds of bacteria. Additionally, they can be found in harsh environments like hot springs, deserts, deep oceans, and snow, where very few other living things can endure. Many of them are parasites that live in or on other organisms.
The four shapes of bacteria-the spherical Coccus, the rod-shaped Bacillus, the comma-shaped Vibrium, and the spiral Spirillum are used to classify them.
Archaebacteria: The oldest known living things on earth are archaebacteria. They are categorized as bacteria because, when viewed under a microscope, they resemble bacteria and are members of the Monera kingdom. They are fully unique from prokaryotes other than this.
Eubacteria: Eubacteria are prokaryotic microorganisms made up of a single cell without a nucleus that houses a single circular chromosome that contains DNA. Eubacteria are significant in the fields of commerce, agriculture, and medicine and can be either gram-negative or gram-positive. E. coli, Lactobacilli, and Azospirillum are some of them.
Simple eukaryotic organisms known as protozoa are not classified as either plants, animals, or fungi. Although they are often unicellular, protozoa can also be found as a colony of cells. The majority of protists are parasites or live in wet terrestrial habitats. The cells of these organisms, which are typically unicellular, have a nucleus that is connected to the organelles. Some of them even have locomotion-supporting features like flagella or cilia.
In light of the fact that plants, animals, and fungi all evolved from a common protist-like ancestor billions of years ago, scientists suggest that protists serve as a connecting link between these three kingdoms. Despite being a hypothetical organism, this “protists-like” ancestor may have shared certain genes with current animals and plants.
Eukaryotic creatures known as fungi include yeasts, molds, mushrooms as well as other microbes. These organisms fall under the category of fungus. The creatures that make up the Kingdom Fungi are pervasive and have a cell wall. They come under heterotrophs among living things. Additionally, they are present in the majority of fungal illnesses including skin infections. All of the examples we gave feature damp environments if we look closely. We can therefore conclude that fungi typically grow in environments that are both moist and warm enough to support them.
Basis of Biological Classification
The first man to propose a scientific basis for classification was Aristotle. To categorize plants as trees, shrubs, and herbs, he employed straightforward morphological characteristics. He divided living beings into two categories:
- Enaima (with red blood)
- Anaima (without red blood)
But a proper system of biological classification was always thought to be necessary.
Types of Classification Systems
The taxonomy system’s founder, Linnaeus, separated all living things into two kingdoms in the year 1758. Animalia and Plantae are these.
Two Kingdom Classification System (given by Linnaeus in 1758)
Classified organisms into two kingdoms.
Three-kingdom Classification System (given by Ernst and Haeckel in 1866)
Added Protista: lacks the capability of tissue differentiation.
Four Kingdom Classification System (given by Copeland in 1956)
Added monera EM studies showed prokaryotes possess different nuclear structures.
Five Kingdom Classification System (given by RH Whittaker in 1969)
Separated group of fungi (classified on the basis of five criteria).
Six Kingdom Classification System (given by carl woese in 1990)
Three domains are divided into 6 kingdoms.
- Archea- Archeabacteria
- Bacteria- Eubacteria
- Eukarya- Protista, Fungi, Plantae, Animalia
Need for Classification of Living Organisms
- To understand the key characteristics of the group, more research is needed than just a study of one or two organisms.
- Not all types of organisms can be found in one place.
- Knowing the relationships between the many groupings of organisms is aided by classification.
- Understanding how species evolved in connection to one another is helpful.
FAQs on Introduction of Biological Classification
Question 1: What are the commercially significant uses of heterotrophic bacteria and archaebacteria?
- Heterotrophic bacteria: Through nitrogen fixation, ammonification, and nitrification, they keep the soil fertile such as Rhizobium. Bacteria make milk products like cheese and curd.
- Archaebacteria: Methanogens from animal manure generate biogas.
Question 2: In Whittaker’s proposed five-kingdom division, list the eukaryotic kingdoms.
The five kingdoms of eukaryotes are as follows: Protista, Fungi, Animalia, Plantae, and Monera.
Question 3: What function do fungi play in our day-to-day lives?
Fungi have the following roles in our daily lives:
- When the dead and decaying matter is acted with by saprophytic fungus, the complex compounds are broken down into simpler ones, which are then absorbed by the plants as nutrients.
- Some fungi have the ability to bond with soil, improving the soil’s suitability for cultivation. Mucor, Absidia, etc., as examples.
- They offer protection from pests.
- Due to their ability to cause fermentation, fungi are utilised in the manufacturing of alcohol and yeast.
Question 4: Name some different shapes of bacteria.
There are four shapes of bacteria- the spherical Coccus, the rod-shaped Bacillus, the comma-shaped Vibrium, and the spiral-shaped Spirillum.
Question 5: What is biological classification?
The practice of classifying living things is known as biological classification. R.H. Whittaker suggested the five-kingdom division. According to factors like cell structure, thallus organisation, reproduction, mechanism of nourishment, etc.