Biological Classification - Class 11 Biology - Chapter 2 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Biological Classification | NCERT | Biology | Class 11
Which of the following is NOT true when comparing scientific names and common names?
A Scientific names vary from place to place.
B Common names vary from place to place.
C Scientific names are in Latin.
D There can be multiple common names for one organism.
The correct answer is Option A: Scientific names vary from place to place.
Organisms have two types of names: a common name and a scientific name. Common names vary widely due to linguistic differences in various places; hence, an organism can have multiple common names depending on local languages and customs.
Conversely, scientific names are formulated based on Latin, which is considered a 'dead' language and is no longer changing. This makes scientific names universal and consistent regardless of geographical location. Thus, each species has a unique and uniform scientific name globally.
Which of the following features is not present in the Phylum - Arthropoda?
A. Chitinous exoskeleton
B. Metameric segmentation
C. Parapodia
D. Jointed appendages
The correct option is C. Parapodia.
The Phylum Arthropoda is notable for being the largest phylum in the kingdom Animalia and includes various insects. Key characteristics of arthropods include:
Chitinous exoskeleton: A tough outer layer made of chitin that provides structural support and protection.
Jointed appendages: Specialized limbs that allow for a wide range of movements.
Metameric segmentation: The body is divided into segments, each with similar structures.
Parapodia, however, are not a feature of arthropods. They are primarily seen in polychaete annelids. Parapodia are paired, fleshy appendages used for gas exchange, locomotion, and anchorage, varying greatly in size and shape according to their functions. Thus, option C, Parapodia, is the feature not present in Phylum Arthropoda.
"Two areas of study, namely evolution and classification, are interlinked. Justify the statement."
Evolution and classification are deeply interconnected fields within biological sciences. The process of evolution drives the genetic variations in species, which is a critical factor in the formation of new species. This genetic variation and adaptation are the foundations of evolutionary theory.
As species evolve, they accumulate different genetic characteristics, which are inherited. The more characteristics two species share, the closer they are related, usually indicating a more recent common ancestor. This close relationship among species is demonstrated through similar physical and genetic traits.
Classification, on the other hand, involves organizing living organisms into groups based on their similarities and differences. This classification system reveals the hierarchical relationships among various organisms, effectively outlining a family tree that maps out the connections between different species.
A key aspect of classification is that it not only helps in understanding the similarities and differences among organisms but also in identifying their evolutionary relationships. This grouping of organisms in classification systems, like the Linnaean taxonomy, is primarily based on common characteristics derived from evolutionary backgrounds.
Therefore, classification is essentially a reflection of evolutionary history. The way we classify organisms today helps us in understanding their evolutionary paths, linking organisms to both their ancestors and their descendants.
In conclusion, studying evolution helps explain why organisms are the way they are, while classification arranges these organisms in a systematic order that reflects their evolutionary relationships. Thus, the study of evolution and classification are intrinsically interlinked.
Is a taxon that includes genera with similar characteristic features?
A) Species
B) Order
C) Phyla
D) Family
The correct option is D) Family
A family consists of a group of genera that exhibit similar characteristics. In the hierarchical system of biological classification, a family is ranked between order and genus. Families can also be subdivided into subfamilies, which are positioned above the rank of genus within the classification hierarchy.
For example, the family Blattidae includes the common household cockroaches, with *Blatta* being a well-known genus within this family.
If two organisms belong to the same order, they would also belong to the same ______ and ______ .
A. phylum
B. family
C. class
D. species
The correct answers are A. phylum and C. class.
In the taxonomic hierarchy, the ordering from broader to more specific categories is:
Kingdom
Phylum (or Division)
Class
Order
Family
Genus
Species
Thus, if two organisms are classified under the same order, they must necessarily belong to the same class and phylum as well. This is because each subsequent category in the hierarchy encompasses all the organisms in the preceding one. Given that the order is narrower than class and phylum, belonging to the same order implies they share the same higher taxonomic categories (phylum and class).
Choose the names of the organisms that fall under class 'Pisces':
A) Shark B) Pomfret C) Octopus D) Rohu
Solution:
The correct choices are:
A) Shark
B) Pomfret
D) Rohu
Members of the class Pisces are typically characterized as cold-blooded, aquatic animals. They have a streamlined body and are equipped with either paired or unpaired fins, which facilitate swimming. These organisms possess an exoskeleton made of scales and an endoskeleton that can either be cartilaginous or bony. Examples include shark, pomfret, and rohu.
Octopus, on the other hand, belongs to the Phylum Mollusca and is not a fish but a cephalopod, which is why it does not fall under the class Pisces.
The scientific name of cockroach is:
A) Periplaneta indiana
B) Periplaneta americana
C) Periplaneta africana
D) Periplaneta asiana
The correct answer to the question is B) Periplaneta americana.
The scientific classification of organisms includes a binomial system of nomenclature, which comprises two main parts: the genus name and the species name. For the cockroach in question, the genus name is Periplaneta, and the species name is americana, making the full scientific name Periplaneta americana.
Given below is the representation of the extent of global diversity of vertebrates. What groups do the portions represent?
VERTEBRATES
A. Mammals B. Birds C. Fishes D. Amphibians E. Reptiles
B. Fishes B. Mammals C. Birds D. Reptiles E. Amphibians
C. Birds B. Reptiles C. Fishes D. Mammals E. Amphibians
D. Fishes B. Amphibians C. Mammals D. Birds E. Reptiles
The accurate classification for the diversity of vertebrate groups is Option B:
A. Fishes
B. Mammals
C. Birds
D. Reptiles
E. Amphibians
In terms of species diversity, fishes are known to have the highest variety, followed by birds.
A related group of species are put together to form a taxon called:
A. order
B. kingdom
C. genus
D. family
The correct answer is C. genus.
Genus is a taxonomic classification ranking between 'family' and 'species'. It's a level within the hierarchical organization of biological classification. Specifically, a genus comprises a group of closely related species. In the binomial nomenclature system, which is used to name various species, the genus name is always the first part of the species' two-part name.
For instance, in the name Felis leo, Felis represents the genus, which encompasses various species of cats and belongs to the family Felidae.
Which taxonomic category is less general in characters as compared to family?
The taxonomic hierarchy serves as a tool for classifying and identifying living organisms. The sequence from the most inclusive category to the most specific follows this mnemonic for easier recall: $$ \text{K P C O F G S} $$ where:
K = Kingdom
P = Phylum
C = Class
O = Order
F = Family
G = Genus
S = Species
The specificity of characteristics increases as you move down this hierarchy from Kingdom to Species. Comparatively, each level is more detailed and specific than the previous one.
Given the context of the question concerning a category less general than family, we focus on categories below Family in terms of generality. These categories, which exhibit more specific shared characteristics among organisms, include:
Genus
Species
Since Genus is directly below Family, it offers a more specific grouping compared to Family, sharing all the characteristics of a family but with added details that distinguish one genus from another within the same family. Thus, the correct answer to the question is Genus, as it is less general than Family.
Potato and tomato have many characteristics which are common to both. In which level of taxonomical organisation will they have maximum similarities?
A Order
B Genus
C Family
D Division
The correct answer is B) Genus.
Genus is a taxonomic category that ranks below the family and is used as the first part of the binomial nomenclature in species naming. It groups closely related species. For example, both the potato (Solanum tuberosum) and the tomato (Solanum lycopersicum) are part of the genus Solanum, indicating that they share a high level of similarity.
The category above genus is Family, which groups several related genera. Further up, Order encompasses a collection of closely related families. At a broader level, Division (or Phylum in animals) is below Kingdom and classifies organisms based on general features.
Since potatoes and tomatoes both belong to the genus Solanum, they have the maximum similarities at the genus level.
ICBN is connected with:
A) Correct nomenclature of animals
B) Correct nomenclature of plants
C) Correct nomenclature of biochemical
D) All of the above
Solution
The correct option is B) Correct nomenclature of plants.
ICBN stands for International Code of Botanical Nomenclature, which is specifically associated with the nomenclature rules for plants.
Periplaneta americana is the scientific name of a cockroach. The specific epithet here is:
A. americana
B. Periplaneta
C. Specific epithet is not mentioned in scientific names
D. Specific epithet follows the second component, and is not mentioned here.
The correct answer is A. americana.
In binomial nomenclature, which is the standard naming convention for species, a scientific name consists of two parts: the generic name followed by the specific epithet. In the given scientific name Periplaneta americana, Periplaneta is the generic name, and americana is the specific epithet. Therefore, option A is correct.
Five kingdom classification was given by:
A. Huxley
B. Hooker
C. Whittaker
D. Linnaeus
The correct answer is C. Whittaker.
R.H Whittaker proposed the five kingdom classification in 1969.
Lamarckism cannot explain:
A) Webbed toes in aquatic birds
B) Weak muscles in the son of a wrestler
C) Long, narrow, and limbless body of snakes
D) Heterophylly
The correct answer is B) Weak muscles in the son of a wrestler.
The theory of Lamarckism, also referred to as the theory of inheritance of acquired characters or the theory of use and disuse of organs, postulates that traits developed during an organism's lifetime can be passed on to its offspring. However, this theory does not explain the occurrence of weak muscles in the son of a wrestler, since such acquired traits (like muscle strength from training) do not alter the genetic code and thus cannot be inherited directly.
Which criteria are used for classification of organisms?
Organisms are classified based on a system developed by Robert H. Whittaker in 1969, which differentiates them into five kingdoms. These kingdoms are organized based on specific criteria pertaining to the cells and nutrition modes of the organisms:
Kingdom Monera: Includes prokaryotic bacteria and blue-green algae.
Kingdom Protista: Consists of unicellular eukaryotic organisms like protozoans, fungi, and algae.
Kingdom Plantae: Comprises multicellular green plants and advanced algae.
Kingdom Fungi: Encompasses multinucleate higher fungi.
Kingdom Animalia: Consists of multicellular animals.
The primary criteria used by Whittaker for classification include:
Cellular structure: Distinguishing between prokaryotic (without a distinct nucleus, as in Monera) and eukaryotic (with a nucleus, as in Protista, Plantae, Fungi, and Animalia).
Nutrition type, which can be:
Photosynthesis (in plants),
Absorption from the environment (in fungi),
Ingestion (in animals).
Organizational structure: Differentiating between organisms that are unicellular, multicellular, or multinucleate.
These criteria provide a comprehensive way to classify and understand the vast diversity of life forms on Earth.
Define artificial system of classification.
Artificial system of classification refers to a method in which organisms are grouped based on one or a few superficial characteristics rather than considering a wider range of traits. This approach might focus on visible factors such as color, shape, or size of the organisms.
Interbreeding of two members of the same $\qquad$ produces fertile offspring.
A) Family B) Order C) Class D) Species
The correct answer is D) Species.
Species is the most fundamental level of biological classification. Members of the same species exhibit a high degree of similarity and are capable of interbreeding to produce fertile offspring. This capability to reproduce successfully is a distinguishing feature of organisms classified within the same species. Conversely, the interbreeding between organisms from different classes, families, or orders within the taxonomy generally does not result in fertile offspring, unless those organisms belong to the same species. Thus, the ability to produce fertile offspring is unique to members of the same species.
All fungi are:
A. Parasites
B. Saprophytes
C. Symbionts
D. Heterotrophs
Fungi, as a group, display varied nutritional strategies, but they are primarily categorized based on how they obtain their nutrition.
Fungi are heterotrophs, meaning they acquire their nutrients by consuming organic compounds. This characteristic distinguishes them from autotrophs like most plants, which use photosynthesis to create their own food from sunlight. Within the heterotrophic classification, fungi can further be divided based on their specific strategies:
Saprophytic - These fungi decompose dead organic material, absorbing nutrients in soluble form. This category represents a vital role in ecological nutrient cycling.
Parasitic - These fungi live at the expense of their hosts, obtaining nutrients directly from them, which can sometimes yield detrimental effects to the host.
Symbiotic - These fungi form mutually beneficial relationships with other organisms. A classic example is the mycorrhizal association between fungi and plant roots, where both parties benefit—fungi increase water and nutrient absorption for the plant, and in return, the plant supplies the fungi with carbohydrates produced via photosynthesis.
Given these possibilities, it's clear that not all fungi necessarily fall into one exclusive category such as only being parasites, saprophytes, or symbionts. Thus, the correct answer that universally applies to all fungi in terms of their nutrition mode is:
D. Heterotrophs
This option broadly covers the fact that all fungi depend on external organic sources for their nutritional requirements, irrespective of the method they employ (saprophytic, parasitic, or symbiotic) to obtain these nutrients.
Which of the following is an example of insectivorous plant:
A) Amla
B) Baheda
C) Utricularia
D) Isoetes
Insectivorous plants, also known as carnivorous plants, are specialized plants that derive some or most of their nutrients by trapping and consuming insects and other small organisms. These plants are often found in nutrient-poor environments, such as boggy or acidic soils, where they have evolved this unique feeding strategy to compensate for the lack of essential nutrients in the soil.
From the provided question options—Amla, Baheda, Utricularia, and Isoetes—the correct choice identifying an insectivorous plant is:
C) Utricularia
Explanation:
Amla and Baheda are known for their medicinal properties and are not insectivorous. They primarily rely on photosynthesis for food production and do not consume insects.
Isoetes, commonly referred to as quillworts, are not carnivorous but rather are water-dwelling or terrestrial plants that also rely on traditional means of nutrition through photosynthesis.
Utricularia, also known as bladderworts, are indeed insectivorous plants. They capture prey primarily in their aquatic or moist soil habitats using small bladder-like traps that suck in tiny organisms from the surrounding water or air.
Utricularia can be found in various regions, except Antarctica, adapting to diverse ecological niches. These plants attract and digest insects to supplement their nutritional intake, particularly capturing prey rich in nutrients which are deficient in their native soils. Hence, the correct answer to the question is Utricularia.
Which among the following is an example of fungi?
A. Anabaena
B. Euglena
C. Mycoplasma
D. Agaricus
Anabaena: This is a type of blue-green algae and belongs to the category of autotrophs, meaning it can synthesize its own food through photosynthesis. Therefore, it is not a fungus.
Euglena: This organism belongs to the kingdom Protista. Like Anabaena, Euglena is also capable of photosynthesis and therefore is an autotroph, not a fungus.
Mycoplasma: This is a type of bacteria, and it belongs to the kingdom Monera. As bacteria, Mycoplasma is fundamentally different from fungi.
Agaricus: This is indeed a genus that includes various species of mushrooms. Fungi, including those in the Agaricus genus, are characterized as heterotrophs that acquire nutrients by absorbing from dead and decaying material.
Thus, the correct answer is: D. Agaricus
Agaricus is a genus of mushrooms which includes both edible and poisonous species. This genus falls under the Fungi kingdom, meeting the criterion of the question.
Classification based on features like chromosome number, structure, and behavior is called:
chemotaxonomy
numerical taxonomy
phylogeny
cytotaxonomy
The correct option is D. cytotaxonomy
Cytotaxonomy is the branch of biology focused on the relationships and classification of organisms by comparing features like chromosome number, structure, and behavior, particularly during meiosis.
In contrast:
Chemotaxonomy involves the classification of plants and animals based on similarities and differences in their biochemical composition.
Numerical taxonomy utilizes numerical methods to study and classify organisms, emphasizing quantitative analysis.
Phylogeny examines the evolutionary relationships of organisms and employs this information in their classification.
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Discuss how classification systems have undergone several changes over a period of time?
Classification Systems Evolution
Classification systems have indeed undergone significant changes over time, influenced by improved understanding and the discovery of new species and characteristics. Here's a brief history highlighting the key changes:
Aristotle's Classification:
Aristotle was one of the earliest to propose a more scientific basis for classification.
Classified organisms based on simple morphological characters.
Divided plants into trees, shrubs, and herbs.
Divided animals into those with red blood and those without.
Linnaean Two-Kingdom System:
Carolus Linnaeus introduced a Two-Kingdom system of classification.
Divided life forms into Kingdom Plantae and Kingdom Animalia.
Limitations: Did not distinguish between prokaryotes and eukaryotes, unicellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms.
Five Kingdom Classification by Whittaker (1969):
Proposed by R.H. Whittaker.
Divided life forms into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia.
Main criteria: Cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships.
Three-Domain System:
Further modified the classification system, splitting the Kingdom Monera into two domains: Archaea and Bacteria, while the remaining eukaryotic kingdoms were placed in the third domain, Eukarya.
Introduced by Carl Woese and colleagues, based on molecular analyses, particularly rRNA sequences.
State two economically important uses of:
(a) heterotrophic bacteria
(b) archaebacteria
(a) Heterotrophic Bacteria
Production of Antibiotics: Many heterotrophic bacteria are utilized in the production of antibiotics. For example, the genus *Streptomyces* is a significant source of antibiotics used to treat various bacterial infections.
Dairy Products: Heterotrophic bacteria like *Lactobacillus* are essential in the dairy industry for the production of yogurt and cheese. They help in fermenting milk and giving these products their distinct flavors and textures.
(b) Archaebacteria
Biogas Production: Methanogens, a type of archaebacteria, are used in biogas production. They break down organic matter in anaerobic conditions to produce methane, which can be used as a renewable source of energy.
Bioremediation: Archaebacteria, such as those found to thrive in extreme conditions, can be utilized in bioremediation to clean up environments contaminated with hazardous substances by breaking them down into less harmful compounds.
What is the nature of cell-walls in diatoms?
In diatoms, the cell walls form two thin overlapping shells, which fit together like a soap box. The walls are embedded with silica and thus are indestructible.
Find out what do the terms 'algal bloom' and 'red-tides' signify.
Algal Bloom
Algal blooms refer to the rapid increase or accumulation of algae in water systems, typically in freshwater or marine environments. These blooms can be identified by the discoloration of the water due to the high density of pigmented cells. Algal blooms can be harmful as they may produce toxins that affect both aquatic life and human health and can lead to the depletion of oxygen in the water, causing dead zones.
Red Tides
Red tides are a specific type of algal bloom caused by the rapid multiplication of certain species of dinoflagellates, which are a type of microscopic algae. These organisms produce distinct pigments (often red, but can be brown or green) that color the water red. The term "red tide" is somewhat misleading because such occurrences are not necessarily associated with tidal movements. Red tides can be harmful and may release toxins that are dangerous to marine life and humans, leading to the death of fish and shellfish and posing health risks from contaminated seafood.
How are viroids different from viruses?
Viroids differ from viruses in the following ways:
Nature of Genetic Material:
Viroids: Consist solely of a short strand of circular, single-stranded RNA.
Viruses: Have genetic material that could be either RNA or DNA, which can be single-stranded or double-stranded.
Protein Coat:
Viroids: Lack a protein coat.
Viruses: Have a protein coat called a capsid made up of capsomeres, which protects their genetic material.
Infectious Agent:
Viroids: Typically cause diseases in plants.
Viruses: Can infect a wide variety of hosts, including plants, animals, and bacteria.
Size:
Viroids: Generally smaller than viruses.
In summary, viroids are much simpler than viruses, being just free RNA molecules without any protein components, while viruses are more complex, containing both nucleic acid and a protective protein coat.
Describe briefly the four major groups of Protozoa.
The four major groups of Protozoa are:
Amoeboid Protozoans:
Habitat: Found in fresh water, sea water, or moist soil.
Movement: Move and capture prey using pseudopodia (false feet), as in Amoeba.
Special Features: Marine forms may have silica shells; some, like Entamoeba, are parasites.
Flagellated Protozoans:
Habitat: Can be free-living or parasitic.
Movement: Possess flagella.
Special Features: Parasitic forms, such as Trypanosoma, can cause diseases like sleeping sickness.
Ciliated Protozoans:
Habitat: Aquatic.
Movement: Use thousands of cilia for movement.
Feeding: Have a cavity (gullet) that opens to the outside of the cell surface, steering food-laden water into the gullet. Example: Paramoecium.
Sporozoans:
Habitat: Diverse environments.
Reproduction: Characterised by having an infectious spore-like stage in their life cycle.
Special Features: Notable example is Plasmodium, the malarial parasite, which causes malaria.
Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Yes, certain plants are partially heterotrophic. Examples include:
Insectivorous Plants: These plants derive some nutrients by consuming insects. Examples are:
Bladderwort
Venus Flytrap
Parasitic Plants: These plants partially obtain nutrients by parasitizing other plants. An example is:
Cuscuta
What do the terms phycobiont and mycobiont signify?
The terms phycobiont and mycobiont refer to the components of lichens, which are symbiotic associations between algae and fungi:
Phycobiont: This is the algal component of the lichen. It is autotrophic and responsible for preparing food through photosynthesis.
Mycobiont: This is the fungal component of the lichen. It is heterotrophic and provides shelter and absorbs mineral nutrients and water for the algae.
These terms highlight the mutual relationship between the algae and fungi in lichens.
Give a comparative account of the classes of Kingdom Fungi under the following:
(i) mode of nutrition
(ii) mode of reproduction
Here's a comparative account of the classes of Kingdom Fungi under the given headings:
(i) Mode of Nutrition
Phycomycetes (e.g., Mucor, Rhizopus): Mostly saprophytic, sometimes parasitic.
Ascomycetes (e.g., Aspergillus, Penicillium): Saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
Basidiomycetes (e.g., Agaricus, Ustilago): Saprophytic, parasitic, or decomposers.
Deuteromycetes (e.g., Alternaria, Colletotrichum): Saprophytic, parasitic, and decomposers.
(ii) Mode of Reproduction
Phycomycetes:
Asexual Reproduction: By zoospores (motile) or by aplanospores (non-motile), produced endogenously in sporangium.
Sexual Reproduction: By fusion of gametes forming zygospore (isogamous or anisogamous).
Ascomycetes:
Asexual Reproduction: By conidia produced exogenously on special mycelium called conidiophores.
Sexual Reproduction: By ascospores produced endogenously in sac-like asci (singular ascus).
Basidiomycetes:
Asexual Reproduction: Generally absent, but vegetative reproduction by fragmentation is common.
Sexual Reproduction: By basidiospores produced exogenously on basidium after karyogamy and meiosis, without distinct sex organs.
Deuteromycetes:
Asexual Reproduction: By conidia.
Sexual Reproduction: Only known for some and placed in appropriate classes once identified.
Table
Class | Mode of Nutrition | Asexual Reproduction | Sexual Reproduction |
---|---|---|---|
Phycomycetes | Saprophytic, Parasitic | Zoospores, Aplanospores | Zygospore |
Ascomycetes | Saprophytic, Decomposers, Parasitic, Coprophilous | Conidia | Ascospores |
Basidiomycetes | Saprophytic, Parasitic, Decomposers | Rare, usually by Fragmentation | Basidiospores |
Deuteromycetes | Saprophytic, Parasitic, Decomposers | Conidia | Unknown, classified when discovered |
What are the characteristic features of Euglenoids?
The characteristic features of Euglenoids are:
Habitat: Majority are freshwater organisms found in stagnant water.
Cell Wall: They lack a traditional cell wall; instead, they have a protein-rich layer called pellicle, which provides flexibility to their body.
Locomotion: They have two flagella; one is short and the other is long.
Photosynthesis and Heterotrophy: They are photosynthetic in the presence of sunlight. When deprived of sunlight, they can become heterotrophic by preying on other smaller organisms.
Pigments: The pigments in euglenoids are identical to those found in higher plants.
Example: Euglena.
Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
Structure and Nature of Genetic Material of Viruses
Viruses are non-cellular organisms characterized by an inert crystalline structure outside the living cell. Their structure consists of a protein coat called capsid, made up of smaller subunits called capsomeres. This capsid protects the genetic material, which can be either RNA or DNA, but not both.
Plant viruses typically have single-stranded RNA.
Animal viruses may have single- or double-stranded RNA or double-stranded DNA.
Bacterial viruses (bacteriophages) usually have double-stranded DNA.
Common Viral Diseases
Mumps
Smallpox
Herpes
Influenza
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Comprehensive Class 11 Notes on Biological Classification
Introduction to Biological Classification
Definition and Importance
Biological classification is the scientific process of categorising living organisms into hierarchical groups based on their shared characteristics and evolutionary history. This system helps in the systematic study of the vast diversity of life forms and their complex relationships.
Historical Background
Aristotle's Contribution
Aristotle was one of the earliest scientists to attempt a scientific categorisation of living organisms. He used simple morphological characteristics to classify plants into trees, shrubs, and herbs and animals into two groups: those with red blood and those without.
Linnaeus' Two Kingdom Classification
In the 18th century, Carl Linnaeus proposed a two-kingdom system, which included all plants in Kingdom Plantae and all animals in Kingdom Animalia. Although simplifying classification, this system was inadequate as it did not account for differences between unicellular and multicellular organisms, nor between eukaryotes and prokaryotes.
Five Kingdom Classification
Overview of Whittaker's System
In 1969, R.H. Whittaker proposed a more comprehensive classification system dividing organisms into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. His criteria for classification included cell structure, body organisation, mode of nutrition, and phylogenetic relationships.
Kingdom Monera
Introduction to Monera
Bacteria are the sole members of Kingdom Monera. They are the most abundant microorganisms, found in almost every habitat imaginable, including extreme environments like hot springs and deep oceans.
Characteristics of Bacteria
Bacteria are categorised based on their shape into the following types:
- Coccus (spherical)
- Bacillus (rod-shaped)
- Vibrio (comma-shaped)
- Spirillum (spiral)
Archaebacteria and Their Habitats
Archaebacteria are a group of bacteria known for surviving in extreme conditions such as salty areas (halophiles), hot springs (thermoacidophiles), and marshy areas (methanogens). They have a unique cell wall structure that helps them endure these harsh environments.
Eubacteria and Cyanobacteria
Eubacteria, also known as true bacteria, have a rigid cell wall. Cyanobacteria, a subgroup of eubacteria, are photosynthetic and often found in freshwater or marine environments.
Kingdom Protista
Introduction to Protista
Kingdom Protista includes all single-celled eukaryotes. Though primarily aquatic, members of this kingdom show a wide range of diversity in both structure and function. This kingdom serves as a link between plants, animals, and fungi.
Different Groups in Protista
- Chrysophytes: Includes diatoms and golden algae, predominately found as plankton.
- Dinoflagellates: Marine organisms known for causing red tides.
- Euglenoids: Freshwater organisms that exhibit both autotrophic and heterotrophic modes of nutrition.
- Slime Moulds: Exhibit saprophytic nutrition and form spores under harsh conditions.
- Protozoans: Heterotrophic organisms classified into amoeboid, flagellated, ciliated, and sporozoans.
flowchart TD Protista --> Chrysophytes Protista --> Dinoflagellates Protista --> Euglenoids Protista --> SlimeMoulds Protista --> Protozoans
Kingdom Fungi
General Characteristics
Fungi are unique in their heterotrophic mode of nutrition, relying on absorbing organic material from their surroundings. They show great diversity in form and habitat.
Classification of Fungi
- Phycomycetes: Found in moist environments and known for both sexual and asexual reproduction.
- Ascomycetes: Known as sac fungi, includes multicellular forms like Penicillium.
- Basidiomycetes: Includes mushrooms and puffballs, primarily reproduces through basidiospores.
- Deuteromycetes: Imperfect fungi known only for their asexual stages.
Kingdom Plantae
Characteristics of Plantae
Kingdom Plantae encompasses all eukaryotic, chlorophyll-containing organisms. Members include algae, bryophytes, pteridophytes, gymnosperms, and angiosperms.
Alternation of Generations
Plants exhibit alternation of generations, alternating between diploid sporophytic and haploid gametophytic phases.
Kingdom Animalia
Characteristics of Animalia
Kingdom Animalia includes multicellular, eukaryotic organisms lacking cell walls. They exhibit heterotrophic nutrition and reproduce primarily via sexual reproduction.
Viruses, Viroids, Prions, and Lichens
Overview of Acellular Organisms
Although not included in the five kingdom classification, viruses, viroids, prions, and lichens play significant roles in biological studies.
Characteristics of Viruses
Viruses are acellular entities that can only replicate inside host cells. They consist of genetic material (either RNA or DNA) surrounded by a protein coat.
Viroids and Their Effects
Viroids are simpler than viruses, consisting solely of a short strand of RNA. They are known to cause diseases in plants.
Prions and Related Diseases
Prions are infectious proteins causing neurological diseases like mad cow disease in cattle and Creutzfeldt-Jakob disease in humans.
Lichens as Symbiotic Organisms
Lichens are symbiotic associations between fungi and algae. The algae provide food through photosynthesis, while the fungi offer protection and absorb nutrients.
- Components of Lichens:
- Phycobiont (Algal)
- Mycobiont (Fungal)
Conclusion
Summary of Biological Classification
Biological classification has evolved over centuries, starting with simple morphological classification to more complex systems like the five kingdom classification by Whittaker. While plant and animal kingdoms have been constants, evolving criteria have allowed for a more nuanced understanding of life's diversity.
Future Perspectives and Advances in Classification
As scientific understanding advances, classification systems are likely to continue evolving, incorporating more genetic and molecular data to better represent the complexities of life.
By exploring the characteristics and classifications within the biological world, students can better appreciate the incredible diversity of life on Earth.
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