Biological Classification
Biological classification is a fundamental concept in biology that involves organizing organisms into groups based on shared characteristics. This systematic arrangement helps scientists understand the evolutionary relationships between different species and study their diversity. Over centuries, scientists have developed various classification systems, each building upon the previous one.
Aristotle's Scientific Classification
One of the earliest attempts at classification was made by Aristotle, who classified organisms into two groups: plants and animals. This division was based on simple morphological features. However, this system proved to be inadequate as it did not account for the vast diversity of life forms.
Five Kingdom Classification System
In the 20th century, R.H. Whittaker proposed the Five Kingdom Classification System, which is widely accepted today. This system divides organisms into five kingdoms:
1. Monera: Unicellular prokaryotic organisms like bacteria and cyanobacteria.
2. Protista: Unicellular eukaryotic organisms like amoeba and paramecium.
3. Fungi: Multicellular eukaryotic organisms that are heterotrophic and have a cell wall made of chitin.
4. Plantae: Multicellular eukaryotic organisms that are autotrophic and have a cell wall made of cellulose.
5. Animalia: Multicellular eukaryotic organisms that are heterotrophic and lack cell walls.
Classification of Organisms: Features and Controversies
The classification of organisms is a complex process that involves considering various features, including morphological, anatomical, physiological, biochemical, and genetic characteristics. However, there are still controversies and debates surrounding the classification of certain organisms, particularly those that exhibit characteristics of multiple kingdoms.
Domain and Kingdom Hierarchy
In recent years, the three-domain system has gained prominence. This system divides life into three domains: Bacteria, Archaea, and Eukarya. The domain is the highest taxonomic rank, followed by kingdom, phylum, class, order, family, genus, and species.
Prokaryotic Structure and Cell Envelope
Prokaryotes are unicellular organisms that lack a nucleus and other membrane-bound organelles. They have a simple cell structure, consisting of a cell wall, cell membrane, cytoplasm, and genetic material (DNA). The cell wall provides structural support and protection, while the cell membrane regulates the transport of substances into and out of the cell.
Bacteria Classification and Structure
Bacteria are diverse and ubiquitous organisms. They can be classified based on their shape (coccus, bacillus, spirillum), mode of nutrition (autotrophic or heterotrophic), and other characteristics. Bacteria play crucial roles in various ecological processes, including nutrient cycling and decomposition.
Autotrophic and Heterotrophic Nutrition
Autotrophic organisms, such as plants and some bacteria, can synthesize their own food using energy from sunlight or chemical reactions. Heterotrophic organisms, such as animals and fungi, obtain energy by consuming other organisms or organic matter.
Kingdom Monera and Its Characteristics
Kingdom Monera includes prokaryotic organisms like bacteria and cyanobacteria. They are characterized by their simple cell structure, lack of a nucleus, and diverse metabolic capabilities. Some bacteria can survive in extreme environments, such as hot springs and deep-sea hydrothermal vents.
Extreme Habitat Bacteria: RK and U Bacteria
RK and U bacteria are examples of extremophiles that can thrive in harsh conditions. RK bacteria can survive in extremely acidic environments, while U bacteria can tolerate high levels of radiation.
Mycoplasma: Unicellular, Non-Motile Organisms
Mycoplasma are the smallest known self-replicating organisms. They lack a cell wall and are often parasitic. Mycoplasma infections can cause various diseases in humans and animals.
The Living World | Handwritten Notes | Class 11th | NEET | NCERT
Kingdom Protista: Unicellular Eukaryotes
Kingdom Protista includes a diverse group of unicellular eukaryotic organisms. They exhibit a wide range of characteristics, including different modes of nutrition, reproduction, and locomotion. Protists play important roles in aquatic ecosystems and can be both beneficial and harmful to humans.
Protista Reproduction and Nutrition
Protists reproduce through both asexual and sexual methods. Asexual reproduction involves cell division, while sexual reproduction involves the fusion of gametes. Protists exhibit diverse modes of nutrition, including photosynthesis, ingestion of food particles, and absorption of nutrients from the environment.
Biological Classification | Handwritten Notes | Class 11th | NEET | NCERT
