BIOLOGICAL CLASSIFICATION: PART -1 : CBSE CLASS XI

 

BIOLOGICAL  CLASSIFICATION:

Biological Classification Throughout History:

1. Early Attempts at Classification: Since ancient times, humans have instinctively categorized living organisms based on their utility for food, shelter, and clothing. These classifications were not scientific but practical.
2. Aristotle's Contributions: Aristotle made early attempts to establish a more systematic basis for classification. He classified plants into trees, shrubs, and herbs based on their morphological characteristics. He also divided animals into two groups: those with red blood and those without.
3. Linnaeus and the Two Kingdom System: During Linnaeus' time, a two-kingdom system emerged, which included Plantae and Animalia kingdoms, encompassing all plants and animals, respectively. However, this system did not account for critical distinctions like eukaryotes vs. prokaryotes, unicellular vs. multicellular organisms, and photosynthetic (e.g., green algae) vs. non-photosynthetic (e.g., fungi) organisms.
4. Limitations of the Two Kingdom System: The two-kingdom classification proved inadequate as it couldn't accommodate many organisms that didn't fit into either the plant or animal category. This led to the need for a more comprehensive classification system.
5. Evolution of Classification Systems: Classification systems for living organisms have evolved over time, with scientists introducing various criteria such as cell structure, cell wall composition, mode of nutrition, habitat, reproductive methods, and evolutionary relationships.
6. R.H. Whittaker's Five Kingdom Classification (1969): R.H. Whittaker proposed a Five Kingdom Classification, including Monera, Protista, Fungi, Plantae, and Animalia. He based this classification on criteria like cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships.
7. Comparison of the Five Kingdoms:
• Kingdom Monera includes prokaryotes.
• Kingdom Protista encompasses unicellular eukaryotic organisms.
• Kingdom Fungi distinguishes fungi with chitin cell walls from green plants with cellulosic cell walls.
• Kingdom Plantae and Kingdom Animalia are more familiar as the plant and animal kingdoms.
8. Issues with Previous Classifications: Earlier classifications grouped organisms based on single characteristics like the presence of a cell wall, which led to grouping vastly different organisms together. For instance, bacteria and blue-green algae were classified with other eukaryotic groups.
9. Shift Towards Phylogenetic Classification: Modern classification aims to reflect not only morphological, physiological, and reproductive similarities but also phylogenetic relationships, which are based on evolutionary history.
10. Focus of This Chapter: In this chapter, we will delve into the characteristics of Kingdoms Monera, Protista, and Fungi within Whittaker's classification system. Kingdoms Plantae and Animalia will be covered in separate chapters.

The history of biological classification demonstrates the evolving understanding of living organisms and their relationships, with ongoing improvements as our knowledge expands.

KINGDOM  MONERA:

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Kingdom Monera: Bacteria

1. Sole Members of Kingdom Monera:
• Bacteria exclusively belong to the Kingdom Monera.
• They are incredibly abundant microorganisms found ubiquitously in various environments.
2. Ubiquitous Presence:
• Bacteria can be found virtually everywhere.
• Even a handful of soil contains hundreds of different bacterial species.
• They thrive in extreme environments such as hot springs, deserts, snow, and deep oceans where few other life forms can survive.
• Many bacteria are also parasitic, residing inside or on other organisms.
3. Classification by Shape:
• Bacteria are categorized into four main groups based on their shape:
• Coccus (pl.: cocci): Spherical bacteria.
• Bacillus (pl.: bacilli): Rod-shaped bacteria.
• Vibrium (pl.: vibrio): Comma-shaped bacteria.
• Spirillum (pl.: spirilla): Spiral-shaped bacteria.
4. Complex Behavior Despite Simple Structure:
• Despite their simple cellular structure, bacteria exhibit highly complex behaviors.
• They are known for their remarkable metabolic diversity compared to many other organisms.
5. Metabolic Diversity:
• Bacteria display a wide range of metabolic abilities.
• Some bacteria are autotrophic, meaning they can synthesize their own food from inorganic substances.
• Autotrophic bacteria can further be categorized as:
• Photosynthetic Autotrophic: They use photosynthesis to produce their food.
• Chemosynthetic Autotrophic: They utilize chemical reactions to generate their nutrients.
• The majority of bacteria, however, are heterotrophs.
6. Heterotrophic Nature:
• Heterotrophic bacteria rely on other organisms or decomposed organic matter as their food source.

In summary, Kingdom Monera consists exclusively of bacteria, which are incredibly diverse microorganisms found in a wide range of environments. They exhibit a variety of shapes and demonstrate complex behaviors, including an extensive metabolic diversity, with some being autotrophic and others heterotrophic.

 

ARCHAEBACTERIA

Archaebacteria: Survivors of Extreme Environments

1. Unique Habitat Specialists:
• Archaebacteria are remarkable microorganisms known for their ability to thrive in some of the most extreme and inhospitable environments.
• They inhabit environments such as:
• Extreme Salty Areas (Halophiles): Archaebacteria known as halophiles can endure highly saline conditions.
• Hot Springs (Thermoacidophiles): Thermoacidophiles are archaebacteria that can withstand the extreme heat and acidic conditions of hot springs.
• Marshy Areas (Methanogens): Methanogens, another group of archaebacteria, thrive in marshy environments.
2. Distinct Cell Wall Structure:
• Archaebacteria set themselves apart from other bacteria due to their unique cell wall structure.
• This distinct cell wall plays a critical role in their ability to survive in extreme conditions.
3. Methanogens in the Gut:
• Methanogens are a specific type of archaebacteria found in the digestive tracts of several ruminant animals, including cows and buffaloes.
• These methanogens are responsible for a fascinating ecological role: they facilitate the production of methane gas (biogas) during the digestion of these animals' dung.

Archaebacteria's extraordinary adaptability to extreme habitats, distinct cell wall structure, and the important role of methanogens in biogas production highlight their uniqueness and significance in microbiology and ecology.

EUBACTERIA

Eubacteria: The True Bacteria

1. Abundant Diversity:
• Eubacteria, often referred to as 'true bacteria,' encompass a vast and diverse group consisting of thousands of different species.
2. Key Characteristics:
• Eubacteria are distinguished by specific characteristics:
• Rigid Cell Wall: They possess a rigid cell wall.
• Flagellum (if Motile): Motile eubacteria have a flagellum, which enables movement.
3. Cyanobacteria (Blue-Green Algae):

   

   
   
• Cyanobacteria, also known as blue-green algae, are a subset of eubacteria.
• They contain chlorophyll a, similar to green plants, making them photosynthetic autotrophs.
• Cyanobacteria exhibit various forms, including unicellular, colonial, or filamentous.
• They can be found in freshwater, marine, or terrestrial environments.
• Many cyanobacteria form colonies surrounded by a gelatinous sheath and can create blooms in polluted water bodies.
• Some cyanobacteria, like Nostoc and Anabaena, have specialized cells called heterocysts for nitrogen fixation.
4. Chemosynthetic Autotrophic Bacteria:
• Chemosynthetic autotrophic bacteria are another subgroup of eubacteria.
• They oxidize inorganic substances such as nitrates, nitrites, and ammonia to generate energy for ATP production.
• These bacteria play a crucial role in nutrient recycling, including nitrogen, phosphorous, iron, and sulfur.
5. Abundance of Heterotrophic Bacteria:
• Heterotrophic bacteria are the most abundant in nature.
• They are significant decomposers, breaking down organic matter.
• Many have practical applications, including curd production, antibiotic manufacturing, and nitrogen fixation in legume roots.
• However, some heterotrophic bacteria can be pathogens, causing diseases in humans, crops, farm animals, and pets.
• Examples of diseases caused by different bacteria include cholera, typhoid, tetanus, and citrus canker.
6. Reproduction and Genetic Exchange: 
   
   
   
• Bacteria primarily reproduce through fission, a form of asexual reproduction.
• Under unfavorable conditions, they may produce spores.
• Bacteria can also engage in a primitive type of sexual reproduction involving DNA transfer between individual bacteria.
7. Mycoplasma:
• Mycoplasma are unique organisms within the eubacteria.
• They lack a cell wall, making them distinct from other bacteria.
• Mycoplasma are exceptionally small living cells and can survive in anaerobic conditions without oxygen.
• Many mycoplasma species are pathogenic, affecting both animals and plants.

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Eubacteria, or true bacteria, exhibit remarkable diversity and adaptability, with representatives like cyanobacteria contributing to photosynthesis and chemosynthetic autotrophic bacteria playing essential roles in nutrient cycling. Heterotrophic bacteria, while often beneficial, can also be responsible for various diseases. Mycoplasma, unique due to their lack of a cell wall, can thrive in unusual conditions and have pathogenic potential.

KINGDOM: PROTISTA

Kingdom Protista: The Realm of Single-Celled Eukaryotes

1. Heterogeneous Boundaries:
• Kingdom Protista encompasses all single-celled eukaryotic organisms.
• However, the precise boundaries of this kingdom remain somewhat ambiguous, and definitions can vary among biologists.
2. Diverse Inclusions:
• In this context, we include various groups such as Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds, and Protozoans under the Kingdom Protista.
• Notably, what one biologist might consider 'a photosynthetic protistan' might be classified as 'a plant' by another.
3. Primarily Aquatic Environment:
• Members of the Protista kingdom are primarily found in aquatic environments, including freshwater and marine habitats.
4. Connecting Link:
• Kingdom Protista serves as a crucial link between other kingdoms, bridging the gap between plants, animals, and fungi.
• These organisms are classified as eukaryotes due to the presence of a well-defined nucleus and other membrane-bound organelles within their cell bodies.
5. Motility via Flagella or Cilia:
• Some protists possess structures like flagella or cilia that enable them to move through their aquatic habitats.
6. Modes of Reproduction:
• Protists reproduce both asexually and sexually, involving processes such as cell fusion and zygote formation.

Kingdom Protista encompasses a diverse array of single-celled eukaryotic organisms. While the boundaries of this kingdom may lack precision, it serves as a vital bridge between other biological kingdoms. Protists exhibit various means of locomotion and possess the characteristic eukaryotic cellular structure, with a defined nucleus and organelles. Their reproductive strategies include both asexual and sexual methods, involving cell fusion and zygote formation.

CHRYSOPHYTES:

Chrysophytes: Microscopic Water Dwellers

1. Inclusion of Diatoms and Golden Algae:
• Chrysophytes constitute a group that includes diatoms and golden algae, also known as desmids.
2. Habitat Range:
• Chrysophytes can be found in both freshwater and marine environments.
3. Microscopic Nature:
• These organisms are typically microscopic in size, and they tend to passively float in water currents, often being part of the plankton community.
4. Primarily Photosynthetic:
• The majority of chrysophytes are photosynthetic, utilizing light to produce energy.
5. Diatoms and Their Unique Cell Walls:
• Diatoms, a subgroup of chrysophytes, are especially distinctive.
• Their cell walls consist of two thin, overlapping shells, resembling a soapbox.
• These walls are impregnated with silica, making them exceptionally durable and resistant to decomposition.
6. Formation of Diatomaceous Earth:
• Over billions of years, diatoms have contributed to the accumulation of substantial deposits of their indestructible cell walls in their habitats.
• This accumulation is known as 'diatomaceous earth.'
• Diatomaceous earth is gritty in texture and finds application in tasks such as polishing and the filtration of oils and syrups.
7. Key Role in Marine Ecosystems:
• Diatoms are vital organisms in ocean ecosystems, often serving as the primary producers, playing a crucial role in the marine food chain.

Chrysophytes, including diatoms and golden algae, are microscopic aquatic organisms inhabiting both freshwater and marine environments. While most are photosynthetic, diatoms stand out with their unique, silica-reinforced cell walls. These diatomaceous cell walls have practical uses in various industries. Additionally, diatoms are essential contributors to oceanic ecosystems as primary producers.

DINOFLAGELLATES:

Dinoflagellates: Vibrantly Colored Marine Microorganisms

1. Marine Habitat Dominance:
• Dinoflagellates are predominantly marine organisms, thriving in saltwater environments.
2. Photosynthetic Nature:
• These microorganisms are primarily photosynthetic, harnessing light energy for their metabolic processes.
3. Diverse Pigment Colors:
• Dinoflagellates exhibit a spectrum of colors, including yellow, green, brown, blue, or red, depending on the predominant pigments within their cells.
4. Distinctive Cell Wall:
• Dinoflagellates possess a unique cell wall composed of rigid cellulose plates on the outer surface, providing structural support.
5. Flagella Arrangement:
• Most dinoflagellates feature two flagella, hair-like appendages responsible for locomotion.
• One flagellum extends longitudinally, while the other runs transversely within a furrow between the cellulose wall plates.
6. Formation of Red Tides:
• Some dinoflagellates, particularly the red ones like Gonyaulax, are notorious for their rapid population growth.
• This explosive multiplication can lead to the phenomenon known as "red tides," where the sea appears red due to the abundance of these organisms.
7. Toxin Release and Environmental Impact:
• Large numbers of red dinoflagellates in red tides can release toxins into the water.
• These toxins can be harmful to other marine animals, including fish, potentially leading to mass deaths among the affected populations.

Dinoflagellates are captivating marine microorganisms characterized by their vibrant colors, with pigments determining their hues. They possess a unique cellulose-based cell wall and utilize two flagella for movement. Red dinoflagellates are notorious for causing red tides, which can have detrimental effects on marine ecosystems due to toxin release.

EUGLENOIDS:

Euglenoids: Flexible Freshwater Microorganisms

1. Preferred Freshwater Habitat:
• Euglenoids are primarily inhabitants of freshwater environments, often found in stagnant water bodies.
2. Distinctive Pellicle Layer:
• Unlike many other microorganisms, euglenoids lack a cell wall.
• Instead, they possess a protein-rich layer called a pellicle, which imparts flexibility to their body structure.
3. Flagella Configuration:
• Euglenoids are equipped with two flagella: one short and one long.
4. Photosynthetic Capability:
• In the presence of sunlight, euglenoids are photosynthetic organisms, utilizing light energy for metabolic processes.
5. Heterotrophic Behavior in Darkness:
• When deprived of sunlight, euglenoids exhibit a shift in behavior and act as heterotrophs.
• They predate on smaller organisms to obtain nutrients and energy.
6. Shared Pigments with Higher Plants:
• Remarkably, the pigments found in euglenoids are identical to those present in higher plants.
7. Example: Euglena:
• A well-known example of euglenoids is Euglena, which showcases these unique characteristics.

Euglenoids are distinctive freshwater microorganisms with a flexible body structure due to their pellicle layer. They possess both short and long flagella and can switch between photosynthetic and heterotrophic modes depending on sunlight availability. Euglenoids share pigments with higher plants and are exemplified by the well-studied organism Euglena.