Detailed Notes Chapter2-Biological Classification

Introduction

1. Early Classification Attempts:

   • Classification of living organisms began instinctively for practical purposes such as food, shelter, and clothing.
   • Aristotle made early attempts at classification, using simple morphological characters to classify plants and animals.

2. Linnaeus’ Two Kingdom System:

   • Developed a two-kingdom system with Plantae and Animalia kingdoms.
   • Did not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms, or photosynthetic and non-photosynthetic organisms.
   • Found inadequate due to a large number of organisms not fitting into either category.

3. Need for More Comprehensive Classification:

   • Besides gross morphology, other characteristics like cell structure, nature of the cell wall, mode of nutrition, habitat, reproduction, and evolutionary relationships were needed for classification.

4. R.H. Whittaker’s Five Kingdom Classification:

   • Proposed in 1969, included Monera, Protista, Fungi, Plantae, and Animalia kingdoms.
   • Criteria for classification included cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships.

5. Issues with Earlier Classifications:

   • Earlier systems grouped diverse organisms together based solely on shared characteristics like having a cell wall.
   • Didn’t differentiate between prokaryotic and eukaryotic organisms, unicellular and multicellular, or autotrophic and heterotrophic organisms.

6. Changes in Classification Criteria:

   • With the inclusion of additional characteristics like cell wall composition, fungi were separated into their own kingdom.
   • Kingdom Protista brought together unicellular eukaryotic organisms, previously classified differently, based on updated criteria.

7. Importance of Evolutionary Relationships:

   • Modern classification systems aim to reflect not just morphological, physiological, and reproductive similarities but also evolutionary relationships.

8. Focus of Study in the Chapter:

   • The chapter will focus on characteristics of Kingdoms Monera, Protista, and Fungi from Whittaker’s system, with separate chapters for Plantae and Animalia.

2.1 KINGDOM MONERA

1. Definition and Abundance:

   • Bacteria are the sole members of the Kingdom Monera.
   • They are the most abundant microorganisms, found almost everywhere, including soil, extreme habitats like hot springs and deep oceans, and as parasites in other organisms.

2. Diversity of Bacteria:

   • Bacteria are grouped into four categories based on their shape: cocci (spherical), bacilli (rod-shaped), vibrio (comma-shaped), and spirilla (spiral).
   • Despite their simple structure, bacteria exhibit complex behavior.

3. Metabolic Diversity:

   • Bacteria show extensive metabolic diversity compared to many other organisms.
   • Some bacteria are autotrophic, synthesizing their own food from inorganic substrates.
   • Autotrophic bacteria may be either photosynthetic or chemosynthetic.
   • The vast majority of bacteria are heterotrophs, relying on other organisms or dead organic matter for food.

2.1.1 Archaebacteria

1. Adaptation to Extreme Habitats:

   • Some bacteria, known as halophiles, thrive in extreme salty areas.
   • Others, called thermoacidophiles, inhabit hot springs, enduring both high temperatures and acidic conditions.
   • Methanogens are found in marshy areas and are capable of producing methane gas.

2. Archaebacteria and Unique Cell Wall Structure:

   • Archaebacteria, a distinct group within bacteria, possess a different cell wall structure compared to other bacteria.
   • This unique feature contributes to their ability to survive in extreme conditions.

3. Role of Methanogens:

   • Methanogens are present in the gastrointestinal tract of several ruminant animals like cows and buffaloes.
   • They play a crucial role in the digestion process of these animals, particularly in the breakdown of cellulose.
   • Methanogens are responsible for the production of methane gas (biogas) from the dung of these animals

2.1.2 Eubacteria

1. Diversity:

   • There are thousands of different eubacteria, also known as ‘true bacteria’.
   • They exhibit a wide range of shapes, sizes, and characteristics.

2. Characteristics:

   • Eubacteria are characterized by the presence of a rigid cell wall and, if motile, a flagellum.

3. Cyanobacteria (Blue-Green Algae):

   • Cyanobacteria are a type of eubacteria that possess chlorophyll a, similar to green plants.
   • They are photosynthetic autotrophs and can be unicellular, colonial, or filamentous.
   • Often found in freshwater, marine, or terrestrial environments, cyanobacteria colonies are typically surrounded by a gelatinous sheath.
   • Some cyanobacteria, like Nostoc and Anabaena, can fix atmospheric nitrogen in specialized cells called heterocysts.

4. Chemosynthetic Autotrophic Bacteria:

   • Chemosynthetic autotrophic bacteria oxidize various inorganic substances such as nitrates, nitrites, and ammonia to produce ATP.
   • They play a crucial role in recycling nutrients like nitrogen, phosphorous, iron, and sulfur.

5. Heterotrophic Bacteria:

   • Heterotrophic bacteria are the most abundant in nature and primarily function as decomposers.
   • They play essential roles in various ecological processes and have significant impacts on human affairs.
   • Some heterotrophic bacteria are utilized in beneficial processes such as curd formation, antibiotic production, and nitrogen fixation in legumes.

6. Cell Wall Absence:

   • Mycoplasma are organisms that completely lack a cell wall.
   • This sets them apart from other bacteria, which typically have cell walls made of peptidoglycan.

7. Size and Oxygen Requirements:

   • Mycoplasma are noted as the smallest living cells known.
   • They have the ability to survive without oxygen, making them adaptable to various environments.

8. Pathogenicity:

   • Many mycoplasma species are pathogenic, meaning they can cause diseases, in both animals and plants.
   • Their pathogenicity makes them significant in veterinary and agricultural contexts, where they can impact animal and crop health.

2.2 KINGDOM PROTISTA

1. Definition and Boundaries:

   • Kingdom Protista encompasses all single-celled eukaryotic organisms.
   • The boundaries of this kingdom are not well-defined, leading to variations in classification among biologists.
   • What one biologist may classify as a photosynthetic protist, another may categorize as a plant.

2. Included Organisms:

   • In this book, Chrysophytes, Dinoflagellates, Euglenoids, Slime molds, and Protozoans are classified under Protista.
   • These organisms exhibit a wide range of characteristics and lifestyles.

3. Habitats:

   • Members of Protista are primarily aquatic, although some may inhabit terrestrial environments as well.

4. Cellular Structure:

   • Protists are eukaryotes, meaning their cells contain a well-defined nucleus and other membrane-bound organelles.
   • Some protists possess flagella or cilia, which aid in movement.

5. Reproduction:

   • Protists reproduce both asexually and sexually.
   • Reproduction involves processes such as cell fusion and zygote formation.

2.2.4 Slime Moulds

1. Nature and Habitat:

   • Slime moulds are saprophytic protists, meaning they obtain nutrients by decomposing organic material.
   • They typically inhabit environments rich in decaying organic matter such as decaying twigs and leaves.

2. Life Cycle:

   • Slime moulds exhibit a unique life cycle characterized by two main stages: plasmodium and fruiting bodies.
   • Under suitable conditions, slime moulds form an aggregation called a plasmodium.
   • The plasmodium can grow and spread over several feet, actively engulfing organic material.
   • During unfavorable conditions, the plasmodium undergoes differentiation and forms fruiting bodies.
   • Fruiting bodies bear spores at their tips, which are produced for reproduction.

3. Spore Characteristics:

   • The spores produced by slime moulds possess true walls.
   • These spores are highly resistant and can survive for many years, even under adverse conditions.

4. Dispersal:

   • Slime mould spores are dispersed by air currents, allowing them to colonize new areas and continue their life cycle.

2.2.5 Protozoans

1. General Characteristics:

   • All protozoans are heterotrophs, meaning they obtain nutrients by consuming other organisms.
   • They predominantly live as predators or parasites.
   • Protozoans are considered primitive relatives of animals, exhibiting similar characteristics in their cellular structure and behavior.

2. Major Groups:

   • There are four major groups of protozoans: a. Amoeboid protozoans b. Flagellated protozoans c. Ciliated protozoans d. Sporozoans

3. Amoeboid Protozoans:

   • These organisms live in various aquatic environments such as freshwater, seawater, or moist soil.
   • They move and capture prey by extending pseudopodia (false feet), as seen in Amoeba.
   • Some amoeboid protozoans, like Entamoeba, are parasitic.

4. Flagellated Protozoans:

   • Members of this group may be free-living or parasitic.
   • They possess flagella, which aid in movement.
   • Parasitic forms, such as Trypanosoma, can cause diseases like sleeping sickness.

5. Ciliated Protozoans:

   • These organisms are aquatic and exhibit active movement due to thousands of cilia.
   • They possess a cavity (gullet) that opens to the cell surface, facilitating ingestion of food particles.
   • Example: Paramecium.

6. Sporozoans:

   • This group includes diverse organisms with an infectious spore-like stage in their life cycle.
   • Notably, Plasmodium is a sporozoan responsible for causing malaria, a disease with significant effects on human populations.