Biological Classification Class 11 Biology Chapter 2 Notes

Biological Classification Class 11 Biology Chapter 2 Notes

• Early classification of living organisms was based on practical needs like food and shelter, with Aristotle making early scientific attempts using morphological characteristics.
• Linnaeus introduced a Two Kingdom system (Plantae and Animalia) that didn’t account for important distinctions among organisms.
• Classification systems evolved to consider various characteristics, including cell structure, wall composition, nutrition, habitat, reproduction, and evolutionary relationships.
• R.H. Whittaker’s Five Kingdom Classification (Monera, Protista, Fungi, Plantae, Animalia) considered cell structure, body organization, nutrition, reproduction, and phylogenetics.
• The three-domain system later expanded the classification by splitting Monera, creating six kingdoms.
• The limitations of previous systems led to these changes in classification.
• Characteristics like cell wall composition and organization influenced classification, leading to separate kingdoms for fungi, plants, and animals.
• The criteria for classification have evolved over time, aiming to reflect morphological, physiological, reproductive, and phylogenetic similarities, adapting as our understanding improves.

Kingdom Monera

• Members: Bacteria are the sole members of Kingdom Monera.
• Abundance: Bacteria are the most abundant micro-organisms and can be found in various environments.
• Habitats: Bacteria are ubiquitous, existing in diverse habitats, including soil, hot springs, deserts, snow, and deep oceans, often in extreme conditions where few other life forms can survive.
• Parasitic Behavior: Many bacteria live as parasites, either within or on other organisms.
• Shape-Based Classification: Bacteria are categorized into four groups based on their shape:
  1. Spherical (Coccus, singular; Cocci, plural)
  2. Rod-shaped (Bacillus, singular; Bacilli, plural)
  3. Comma-shaped (Vibrium, singular; Vibrio, plural)
  4. Spiral (Spirillum, singular; Spirilla, plural)
• Simplicity vs. Complexity: While bacteria have a simple cellular structure, they exhibit complex behaviors.
• Metabolic Diversity: Bacteria demonstrate extensive metabolic diversity as a group. Some are autotrophic, synthesizing their own food from inorganic sources. Autotrophic bacteria can be photosynthetic or chemosynthetic. The majority of bacteria are heterotrophic, relying on other organisms or dead organic matter for nutrition.

Kingdom Monera primarily consists of bacteria, showcasing a wide range of forms, behaviors, and metabolic strategies, making them a vital component of Earth’s ecosystems.

1 Archaebacteria

• Habitats: Archaebacteria are remarkable for their ability to thrive in some of the most extreme and harsh environments on Earth.
• Specializations: They have specialized adaptations to survive in these extreme conditions.
• Variety of Extreme Habitats: Some notable groups of Archaebacteria include:
  1. Halophiles: These are adapted to highly salty environments.
  2. Thermoacidophiles: Thriving in hot springs with acidic conditions.
  3. Methanogens: Found in marshy areas and known for their unique metabolic capability.
• Different Cell Wall Structure: Archaebacteria are distinct from other bacteria due to their unique cell wall structure. This difference is a key factor in their survival in extreme conditions.
• Methanogens: Methanogens, a group of Archaebacteria, reside in the digestive systems of ruminant animals like cows and buffaloes. They play a vital role in the production of methane, which is harvested as biogas from the dung of these animals.

Archaebacteria are living examples of extremophiles, thriving in environments that would be inhospitable to most other life forms. Their unique characteristics and metabolic abilities make them of significant interest in various fields of research, including biotechnology and environmental science.

2 Eubacteria

• Abundance: Eubacteria, also known as ‘true bacteria,’ encompass thousands of diverse bacterial species.
• Characteristics:
  • Eubacteria are characterized by the presence of a rigid cell wall.
  • If motile, they possess a flagellum for movement.
• Cyanobacteria (Blue-Green Algae):
  • Cyanobacteria are a subset of Eubacteria that exhibit unique characteristics.
  • They contain chlorophyll a, similar to green plants, and are photosynthetic autotrophs.
  • Cyanobacteria can be unicellular, colonial, or filamentous, with various habitat preferences.
  • Often, they form colonies surrounded by a gelatinous sheath.
  • Some cyanobacteria, like Nostoc and Anabaena, can fix atmospheric nitrogen in specialized cells called heterocysts.
• Chemosynthetic Autotrophic Bacteria:
  • Some Eubacteria oxidize inorganic substances such as nitrates, nitrites, and ammonia to produce energy for ATP production.
  • They play a crucial role in recycling essential nutrients like nitrogen, phosphorus, iron, and sulfur.
• Heterotrophic Bacteria:
  • Heterotrophic bacteria are the most abundant in nature and serve as important decomposers.
  • They have diverse roles, including curd production, antibiotic production, and nitrogen fixation in legume roots.
  • However, some heterotrophic bacteria are pathogens that cause diseases in humans, crops, farm animals, and pets. Examples include cholera, typhoid, tetanus, and citrus canker.
• Reproduction: Bacteria primarily reproduce through fission. In unfavorable conditions, they can produce spores. Some bacteria also undergo a primitive form of DNA transfer for reproduction.
• Mycoplasma: These are unique organisms within Eubacteria as they lack a cell wall. They are the smallest known living cells and can survive without oxygen. Many mycoplasmas are pathogenic in both animals and plants.

Eubacteria encompass a wide range of bacterial species with various ecological roles, from beneficial decomposers to harmful pathogens, and even those capable of unique metabolic processes like photosynthesis and nitrogen fixation.

Kingdom Protista

• Characterization:
  • Kingdom Protista includes all single-celled eukaryotic organisms.
  • The boundaries of this kingdom are not well-defined and can vary among biologists.
• Inclusion in Protista:
  • In this context, Chrysophytes, Dinoflagellates, Euglenoids, Slime molds, and Protozoans are included in the Kingdom Protista.
  • Protists are primarily aquatic organisms.
• Link to Other Kingdoms:
  • Kingdom Protista serves as a connecting link between the kingdoms of plants, animals, and fungi.
• Eukaryotic Characteristics:
  • Being eukaryotes, protists have well-defined nuclei and other membrane-bound organelles.
  • Some protists possess flagella or cilia for movement.
• Reproduction:
  • Protists reproduce both asexually and sexually.
  • Reproduction often involves processes like cell fusion and zygote formation, contributing to genetic diversity within the kingdom.

Kingdom Protista is a diverse group of eukaryotic microorganisms, showcasing a wide range of characteristics and lifestyles. Its boundaries are somewhat fluid, as organisms may be classified differently by different biologists, and the kingdom serves as a bridge between other major kingdoms in the classification system.

1. Chrysophytes

• Inclusion: The Chrysophytes group encompasses diatoms and golden algae, including desmids.
• Habitats: Chrysophytes are found in both freshwater and marine environments.
• Size: They are microscopic in size and often float passively in water currents, where they are considered plankton.
• Photosynthetic: Most Chrysophytes are photosynthetic, utilizing light for energy.
• Unique Cell Wall of Diatoms:
  • Diatoms, a subgroup of Chrysophytes, have a distinctive feature in their cell walls.
  • Diatom cell walls consist of two thin, overlapping silica-embedded shells, which fit together like a soapbox.
  • Silica content makes diatom cell walls exceptionally durable and indestructible.
• Diatomaceous Earth: Over billions of years, diatoms have accumulated large amounts of their indestructible cell wall deposits in their habitat, creating what is known as “diatomaceous earth.”
  • Diatomaceous earth is gritty and is utilized in various applications such as polishing and the filtration of oils and syrups.
• Ecological Role: Diatoms, in particular, play a vital role in marine ecosystems as primary producers, contributing significantly to ocean food chains and the production of oxygen.

Chrysophytes, with their microscopic yet robust and unique cell wall structures, have a significant impact on both their ecosystems and human industries, where diatomaceous earth is a valuable resource.

2. Dinoflagellates

• Habitats: Dinoflagellates are primarily marine organisms, and most of them are photosynthetic.
• Pigment Diversity: They exhibit a range of colors, including yellow, green, brown, blue, or red, depending on the dominant pigments in their cells.
• Cell Wall Structure: The cell wall of dinoflagellates features rigid cellulose plates on the outer surface, providing structural support.
• Flagella: Many dinoflagellates are equipped with two flagella:
  • One flagellum runs longitudinally, parallel to the cell’s long axis.
  • The other flagellum lies transversely in a furrow between the cellulose wall plates.
• Red Tides: Some species of dinoflagellates, notably red dinoflagellates like Gonyaulax, undergo rapid and prolific multiplication at times, causing the sea to appear red, a phenomenon known as “red tides.”
• Toxins: Large populations of red dinoflagellates can release toxins, which can have harmful effects on marine ecosystems. These toxins can even be lethal to other marine animals, including fish.

Dinoflagellates are diverse, colorful, and sometimes notorious for their role in red tides and the associated release of toxins, which can impact marine life and ecosystems.

3. Euglenoids

• Habitats: Euglenoids are primarily found in freshwater environments, particularly in stagnant water bodies.
• Cell Wall Substitute: Instead of a traditional cell wall, euglenoids possess a protein-rich layer called a pellicle, which imparts flexibility to their bodies.
• Flagella: Euglenoids have two flagella:
  • A short flagellum.
  • A long flagellum.
• Photosynthesis and Heterotrophy: Euglenoids are unique in that they are photosynthetic in the presence of sunlight. They contain pigments similar to those found in higher plants, allowing them to capture and utilize light energy.
  • However, when deprived of sunlight, they can switch to a heterotrophic mode, preying on smaller organisms for nutrition.
• Example: Euglena is a well-known example of a euglenoid.

Euglenoids are notable for their adaptability, being capable of both photosynthesis and heterotrophy. Their pigments are akin to those of higher plants, allowing them to harness sunlight for energy when available, and they can resort to predation in the absence of light.

4. Slime Moulds

• Nutrition and Lifestyle: Slime moulds are saprophytic protists, meaning they obtain their nutrition by feeding on decaying organic material.
• Locomotion: These organisms exhibit a unique mode of movement as their body moves along decaying twigs and leaves, engulfing organic matter in their path.
• Plasmodium Formation: Under suitable environmental conditions, slime moulds can come together to form an aggregate called a “plasmodium.”
  • The plasmodium can grow and spread over several feet, forming a gel-like mass.
• Fruiting Body Formation: When conditions become unfavorable, the plasmodium differentiates and transforms into fruiting bodies. These fruiting bodies bear spores at their tips.
  • The spores possess true walls, making them resistant to adverse conditions.
• Survival and Dispersal: These hardy spores can survive for many years, even under unfavorable environmental conditions.
  • They can be dispersed by air currents, ensuring their potential to colonize new habitats.

Slime moulds represent a unique group of protists with a saprophytic lifestyle, intriguing movement patterns, and the ability to form resistant spores for survival and dispersal in the environment.

5. Protozoans

• Heterotrophic Nature: Protozoans are all heterotrophic organisms, primarily living as predators or parasites. They depend on other organisms for their nutrition.
• Primitive Relatives of Animals: Protozoans are believed to be primitive relatives of animals, sharing common ancestry with the animal kingdom.

Major Groups of Protozoans:

1. Amoeboid Protozoans:
   • Habitats: These organisms can be found in fresh water, sea water, or moist soil.
   • Locomotion: They move and capture their prey by extending pseudopodia (false feet), similar to Amoeba.
   • Silica Shells: Marine forms often have silica shells on their surface.
   • Example: Some amoeboid protozoans like Entamoeba are parasitic, causing diseases.
2. Flagellated Protozoans:
   • Free-Living and Parasitic: Members of this group can be either free-living or parasitic.
   • Flagella: They possess flagella, which are whip-like structures used for movement.
   • Disease: Some parasitic forms, like Trypanosoma, are responsible for diseases, such as sleeping sickness.
3. Ciliated Protozoans:
   • Aquatic Habitats: These organisms are typically found in aquatic environments.
   • Cilia: They have thousands of cilia, tiny hair-like structures, which allow them to actively move.
   • Feeding: These ciliated protozoans have a cavity (gullet) that opens to the outside of the cell surface. The coordinated movement of rows of cilia helps steer water laden with food into the gullet.
   • Example: Paramoecium is a well-known example.
4. Sporozoans:
   • Infectious Spore-Like Stage: This group includes diverse organisms that have an infectious spore-like stage in their life cycle.
   • Malarial Parasite: One of the most notorious sporozoans is Plasmodium, which is responsible for causing malaria, a disease with a significant impact on the human population.

Protozoans represent a diverse group of microscopic organisms with various modes of locomotion and lifestyles. They play important roles in various ecosystems and can also be pathogenic, causing diseases that affect humans and other animals.

Kingdom Fungi

• Unique Heterotrophic Organisms: Fungi form a distinctive kingdom of heterotrophic organisms, displaying a wide diversity in morphology and habitat.
• Common Occurrence: Fungi can be commonly observed on moist bread, rotten fruits, mushrooms, and toadstools, making them easily recognizable.
• Parasitic Fungi: Some fungi cause diseases in plants and animals; for example, wheat rust, caused by Puccinia, is a significant plant disease.
• Useful Fungi: Fungi also have beneficial roles, such as being the source of antibiotics like Penicillium, and yeast, which is used in baking and brewing.
• Ubiquitous Distribution: Fungi are cosmopolitan and are found in various environments, including air, water, soil, and on animals and plants.
• Preferred Habitat: They tend to grow in warm and humid conditions.
• Role of Refrigeration: Food is stored in refrigerators to prevent spoilage due to bacterial and fungal infections.
• Morphology: Except for unicellular yeasts, fungi are filamentous, consisting of long, slender, thread-like structures known as hyphae. The network of hyphae is called mycelium.
• Types of Hyphae: Some hyphae are continuous tubes filled with multinucleated cytoplasm (coenocytic hyphae), while others have septae (cross walls) in their hyphae.
• Cell Wall Composition: Fungal cell walls are composed of chitin and polysaccharides.
• Nutritional Modes:
  • Most fungi are saprophytes, obtaining nutrition by absorbing soluble organic matter from dead substrates.
  • Fungi that depend on living plants and animals are called parasites.
  • Fungi can also live as symbionts, forming associations with algae as lichens or with the roots of higher plants as mycorrhiza.
• Reproduction:
  • Fungi can reproduce by vegetative means, including fragmentation, fission, and budding.
  • Asexual reproduction is achieved through spores like conidia, sporangiospores, or zoospores.
  • Sexual reproduction occurs through spores like oospores, ascospores, and basidiospores.
• Fruiting Bodies: The various spores are produced in specialized structures known as fruiting bodies.
• Sexual Reproduction Process: Sexual reproduction in fungi involves the fusion of protoplasms in plasmogamy, followed by the fusion of two nuclei in karyogamy, and ultimately meiosis in the zygote, leading to the formation of haploid spores.
• Dikaryophase: In some fungi, a dikaryotic stage (n + n, i.e., two nuclei per cell) occurs before the formation of diploid cells (2n). This intermediate phase is called the dikaryophase.
• Fruiting Body Formation: Fungi form fruiting bodies where reduction division takes place, resulting in the production of haploid spores.
• Classification Basis: The morphology of the mycelium, mode of spore formation, and the structure of fruiting bodies form the basis for the classification of fungi into various classes.

Fungi represent a unique and diverse group of organisms with various ecological roles, from decomposing organic matter to causing diseases, and from forming mutualistic associations to providing valuable resources like antibiotics.

1. Phycomycetes

• Habitats: Members of Phycomycetes are commonly found in aquatic habitats, on decaying wood in moist and damp locations, or as obligate parasites on plants.
• Mycelium: The mycelium of Phycomycetes is aseptate (lacking cross-walls) and coenocytic (having a multinucleate cytoplasm).
• Asexual Reproduction: Asexual reproduction in Phycomycetes occurs through the production of zoospores (motile spores) or aplanospores (non-motile spores). These spores are generated endogenously in sporangia.
• Zygospore Formation: Phycomycetes reproduce sexually by the formation of zygospores. These zygospores result from the fusion of two gametes. The gametes can be similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).
• Examples: Common examples of Phycomycetes include Mucor, Rhizopus (the bread mold), and Albugo (a parasitic fungus found on mustard).

Phycomycetes are a group of fungi with a variety of ecological roles and modes of reproduction. They are often found in aquatic environments and play important roles in the decay of organic matter and as parasites on plants.

2. Ascomycetes

• Common Name: Ascomycetes are commonly known as sac-fungi.
• Multicellular and Unicellular: They can be either multicellular (e.g., Penicillium) or rarely unicellular (e.g., yeast, Saccharomyces).
• Ecological Roles: Ascomycetes can be saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
• Mycelium: The mycelium of ascomycetes is branched and septate, meaning it has cross-walls.
• Asexual Reproduction: Asexual spores are called conidia, produced exogenously on specialized mycelium structures known as conidiophores. Conidia, upon germination, give rise to mycelium.
• Sexual Reproduction: Sexual spores in ascomycetes are called ascospores, and they are produced endogenously within sac-like structures called asci (singular ascus). These asci are arranged in various types of fruiting bodies known as ascocarps.
• Examples: Common examples of ascomycetes include Aspergillus, Claviceps, and Neurospora. Neurospora is widely used in biochemical and genetic research. Some members, like morels and truffles, are edible and are considered delicacies.

Ascomycetes, as the name suggests, are characterized by the presence of asci and ascospores in their sexual reproduction. They have diverse ecological roles and are of significant importance in various fields, including research and culinary uses.

3. Basidiomycetes

• Common Forms: Basidiomycetes are commonly known as mushrooms, bracket fungi, or puffballs. They can be found growing in various habitats, including soil, logs, tree stumps, and living plant bodies as parasites (e.g., rusts and smuts).
• Mycelium: The mycelium of basidiomycetes is branched and septate, similar to that of ascomycetes.
• Asexual Reproduction: Generally, asexual spores are not found in basidiomycetes. Instead, they often reproduce vegetatively by fragmentation.
• Sex Organs: Basidiomycetes lack traditional sex organs but achieve plasmogamy (fusion of cytoplasm) by the fusion of two vegetative or somatic cells from different strains or genotypes.
• Dikaryotic Structure: This fusion results in a dikaryotic structure, where two different nuclei coexist within the same cell.
• Basidium Formation: The dikaryotic structure eventually gives rise to the formation of a structure called a basidium.
• Karyogamy and Meiosis: Karyogamy (fusion of nuclei) and meiosis (reduction division) occur within the basidium, resulting in the production of four basidiospores.
• Basidiospores: Basidiospores are produced exogenously on specialized structures known as basidia (singular basidium).
• Fruiting Bodies: Basidia are arranged in fruiting bodies called basidiocarps.
• Examples: Common examples of basidiomycetes include Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).

Basidiomycetes are characterized by the presence of basidia, which are responsible for the production of basidiospores. They are well-known for producing mushrooms and other distinctive fruiting bodies, and they have various ecological roles, including some as plant parasites.

4. Deuteromycetes

• Common Name: Deuteromycetes are commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are known.
• Reclassification: In many cases, when the sexual forms of these fungi were discovered, they were reclassified into their respective classes.
• Linkages and Correct Identification: It’s possible that the asexual and vegetative stages were given one name (placed under Deuteromycetes) and the sexual stage another (placed under another class). Later, as linkages were established, these fungi were correctly identified and moved out of Deuteromycetes.
• Reproduction: Deuteromycetes reproduce only by asexual spores known as conidia.
• Mycelium: The mycelium of Deuteromycetes is septate and branched.
• Ecological Roles: Some members of Deuteromycetes are saprophytes or parasites, while a significant number of them are decomposers, helping in the decomposition of litter and contributing to mineral cycling.
• Examples: Common examples of Deuteromycetes include Alternaria, Colletotrichum, and Trichoderma.

Deuteromycetes represent a group of fungi that are primarily characterized by their asexual or vegetative phases. They are important in various ecological processes, including decomposition and nutrient cycling. When the sexual stages of these fungi are discovered, they are often reclassified into other fungal groups like ascomycetes and basidiomycetes.

Kingdom Plantae

• Definition: Kingdom Plantae comprises all eukaryotic chlorophyll-containing organisms, commonly referred to as plants. A few members within this kingdom exhibit partial heterotrophy, such as insectivorous plants or parasites (e.g., Bladderwort, Venus flytrap, and Cuscuta).
• Cell Structure: Plant cells possess a eukaryotic structure, with prominent chloroplasts and a cell wall primarily composed of cellulose.
• Plant Groups: Kingdom Plantae encompasses various plant groups, including algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
• Life Cycle: The life cycle of plants features two distinct phases: the diploid sporophytic phase and the haploid gametophytic phase, which alternate with each other. The lengths of these phases and whether they are free-living or dependent on other organisms can vary among different plant groups. This alternating phenomenon is known as the alternation of generations.

Kingdom Plantae includes a wide range of plant species with diverse characteristics and life cycle patterns, reflecting the vast variety of plant life on Earth.

Kingdom Animalia

• Characteristics: Kingdom Animalia is characterized by heterotrophic eukaryotic organisms that are multicellular, and their cells lack cell walls. These organisms directly or indirectly depend on plants for food.
• Digestion: Animals within this kingdom digest their food in an internal cavity and store food reserves as glycogen or fat. Their mode of nutrition is holozoic, achieved through the ingestion of food.
• Growth Pattern: Animals exhibit a definite growth pattern and grow into adults with a specific shape and size.
• Sensory and Neuromotor Mechanism: Higher forms of animals within this kingdom display elaborate sensory and neuromotor mechanisms. They often have well-developed sensory organs and nervous systems.
• Locomotion: Most animals in this kingdom are capable of locomotion, enabling them to move from one place to another.
• Reproduction: Sexual reproduction in animals involves copulation of male and female, followed by embryological development.

Kingdom Animalia encompasses a vast diversity of multicellular, heterotrophic organisms, each adapted to their specific ecological niches. These organisms exhibit complex behaviors, structures, and reproductive strategies.

Viruses

• Characteristics: Viruses are non-cellular organisms characterized by an inert crystalline structure outside a living cell. They are obligate parasites, meaning they require a host cell to replicate.
• Genetic Material: Viruses contain genetic material, which can be either RNA or DNA, but not both in the same virus. They are nucleoproteins.
• Infectious Nature: Viruses infect specific host cells and take over the host’s machinery for replication. They are considered neither truly living nor non-living.
• Examples: Viruses can cause various diseases in both plants and animals, such as mumps, smallpox, herpes, influenza, and AIDS.

Viroids:

• Discovery: Viroids were discovered in 1971 when T.O. Diener found an infectious agent smaller than viruses that caused potato spindle tuber disease.
• Composition: Viroids consist of free RNA, lacking the protein coat found in viruses.
• Symptoms: Viroids can cause diseases in plants, and their RNA is of low molecular weight.

Prions:

• Characteristics: Prions are infectious agents consisting of abnormally folded proteins. They are similar in size to viruses and are associated with certain neurological diseases, such as bovine spongiform encephalopathy (mad cow disease) and Creutzfeldt-Jakob disease (CJD) in humans.

Lichens:

• Definition: Lichens are symbiotic associations between algae and fungi. The algal component (phycobiont) is autotrophic, while the fungal component (mycobiont) is heterotrophic.
• Mutually Useful Association: Lichens form mutually beneficial associations where algae produce food for fungi, and fungi provide shelter while absorbing mineral nutrients and water for their algal partner.
• Indicators: Lichens are excellent indicators of pollution and do not grow in polluted areas. Their close association often conceals the fact that they consist of two different organisms.

While viruses, viroids, and prions are not included in the traditional five-kingdom classification, they represent unique and important components of the microbial world. Lichens, on the other hand, are fascinating examples of symbiotic relationships in the natural world.