NCERT Class XI: Biological Classification

What was the initial purpose of classification systems?

What was the initial purpose of classification systems?

Early classifications were based on the need for food, shelter, and clothing, rather than scientific criteria.

What kingdoms have remained constant across all classification systems?

What were Aristotle’s contributions to early classification?

Aristotle classified plants into trees, shrubs, and herbs and animals into those with red blood and those without.

Who is Theophrastus, and what is his contribution?

Theophrastus is known as the father of botany. He wrote Historia Plantarum and classified plants into herbs, shrubs, undershrubs, and trees.

What was Linnaeus’s major contribution to taxonomy?

Linnaeus created the two-kingdom classification and introduced binomial nomenclature in his book Species Plantarum

What were the limitations of the two-kingdom system?

The two-kingdom system grouped prokaryotes and eukaryotes together and didn’t account for heterotrophic fungi versus autotrophic plants .

What classification system did George Bentham and Joseph Dalton Hooker propose?

They proposed a natural classification system of spermatophytes (seed plants), based primarily on floral characters .

What did R.H. Whittaker’s five-kingdom classification introduce?

Whittaker’s system classified organisms into Monera, Protista, Fungi, Plantae, and Animalia, based on factors such as cell structure and nutrition .

 What are some organisms that are not included in Whittaker’s five-kingdom classification?

Viruses, viroids, prions, and lichens are not included .

What is the primary mode of nutrition for organisms in Kingdom Monera?

 Organisms in Monera can be autotrophic (photosynthetic or chemosynthetic) or heterotrophic (saprophytic or parasitic) .

What is the key feature distinguishing Protista from other kingdoms?

Protista consists of unicellular eukaryotic organisms, while other kingdoms contain multicellular organisms .

What is the characteristic cell structure of organisms in Kingdom Fungi?

Fungi have a cell wall made of chitin, and they lack chlorophyll, making them heterotrophic .

How do organisms in Kingdom Plantae obtain nutrition?

Organisms in Plantae are autotrophic and perform photosynthesis to obtain their food .

What type of reproduction is most common in the Animalia kingdom?

Animals reproduce sexually, with the production of specialized reproductive cells (gametes).

What is the structural difference between Gram-positive and Gram-negative bacteria?

Gram-positive bacteria have a thick, single-layered cell wall made of peptidoglycan, while Gram-negative bacteria have a double-layered cell wall .

What is the role of the glycocalyx in bacteria?

The glycocalyx forms a protective layer around bacteria, helping them avoid detection by white blood cells and aiding in colony formation .

What is a plasmid, and what is its function in bacteria?

 A plasmid is a small, circular piece of DNA found in bacteria that can replicate independently and often carries genes for antibiotic resistance .

How does bacterial conjugation work?

In conjugation, a donor bacterium (F+) transfers genetic material to a recipient (F-) through a sex pilus, resulting in the recipient becoming F+ .

What is the economic importance of heterotrophic bacteria?

Heterotrophic bacteria are used in the production of dairy products like curd and cheese, and some are involved in nitrogen fixation, enhancing soil fertility .

What is the primary habitat of organisms in Kingdom Protista?

Protists are primarily aquatic, living in freshwater or marine environments .

What is the composition of a diatom’s cell wall?

Diatom cell walls are made of silica embedded in cellulose, forming a structure called a frustule .

 What is the significance of Euglena in classification?

Euglena is mixotrophic, performing photosynthesis in the presence of light and acting as a heterotroph in its absence, making it difficult to classify .

What causes red tides?

Red tides are caused by rapid multiplication of dinoflagellates like Gonyaulax, which give the water a red appearance due to their pigments.

How do slime molds survive during unfavorable conditions?

Slime molds form resistant spores during unfavorable conditions, allowing them to survive until the environment becomes favorable again .

What is the structural unit of a fungus?

The structural unit of a fungus is the hypha, which forms a network called the mycelium.

How do fungi reproduce asexually?

Fungi reproduce asexually through spore formation, including sporangiospores (inside sporangia) and conidia (formed at the tips of hyphae) .

What is the role of mycorrhiza in plant-fungal symbiosis?

Mycorrhiza is a symbiotic association between fungi and plant roots, where fungi enhance water and nutrient absorption for the plant in exchange for carbohydrates .

What is the difference between zoospores and aplanospores?

Zoospores are motile, flagellated spores formed in zoosporangia, while aplanospores are non-motile and formed in regular sporangia

What is plasmogamy in fungi?

Plasmogamy is the fusion of two fungal cells without the fusion of their nuclei, leading to a dikaryotic phase (two nuclei per cell) .

How are bacteria used in the dairy industry?

Bacteria like Lactobacillus are used in the fermentation of milk to produce dairy products like curd and cheese .

What role do fungi play in the production of antibiotics?

Fungi like Penicillium are used to produce antibiotics such as penicillin, which are crucial in treating bacterial infections .

What is the significance of Rhizobium bacteria in agriculture?

Rhizobium forms symbiotic relationships with leguminous plants, fixing atmospheric nitrogen into ammonia, which enhances soil fertility .

How are cyanobacteria used to increase rice production?

Cyanobacteria like Anabaena in symbiosis with Azolla enhance nitrogen fixation, which increases the yield of rice crops .

Why are viruses not classified under the five-kingdom system?

Viruses are not classified under any kingdom because they are not considered living organisms outside a host and lack cellular structure .

What is a viroid, and how is it different from a virus?

A viroid is a smaller infectious agent composed only of a short strand of circular RNA without a protein coat, unlike viruses which have DNA or RNA encased in a protein shell .

What are prions, and what diseases do they cause?

Prions are infectious proteins that cause neurodegenerative diseases, such as Creutzfeldt-Jakob disease in humans and mad cow disease in cattle .

What are the main components of a bacterial cell wall?

The bacterial cell wall is primarily made of peptidoglycan, a complex polymer of sugars and amino acids.

What are ribosomes like in prokaryotic cells?

Prokaryotic cells, like bacteria, have 70S ribosomes, which are smaller than the 80S ribosomes found in eukaryotes .

What is the role of mesosomes in bacterial cells?

Mesosomes are infoldings of the bacterial cell membrane that are involved in cell respiration, DNA replication, and distribution to daughter cells during division .

How do endospores help bacteria survive extreme conditions?

Endospores are highly resistant structures formed by some bacteria that can survive extreme temperatures, radiation, and chemical damage

What is the significance of dinoflagellates like Noctiluca?

Noctiluca is a bioluminescent dinoflagellate, meaning it produces light through a chemical reaction, contributing to phenomena like glowing oceans .

What is mixotrophic nutrition in Euglena?

Euglena is mixotrophic because it can photosynthesize in the presence of sunlight and switch to heterotrophic nutrition when light is unavailable .

How do slime molds form spores?

Slime molds form fruiting bodies that release spores during unfavorable conditions. These spores are resistant and dispersed by air .

What are the main types of hyphae in fungi?

Fungal hyphae can be coenocytic (aseptate) without cross-walls or septate with cross-walls that divide the hyphae into cells .

What are conidia, and how do they form?

Conidia are asexual, non-motile spores that form externally at the tips of fungal hyphae, commonly in fungi like Aspergillus .

What is dikaryophase in fungi?

Dikaryophase is a stage in fungal sexual reproduction where cells have two genetically distinct nuclei (n + n) before nuclear fusion (karyogamy) occurs .

What is zygospore formation in fungi?

Zygospores are formed during sexual reproduction in zygomycetes when two compatible hyphae fuse and undergo plasmogamy and karyogamy .

What is a mycorrhizal association, and why is it beneficial?

Mycorrhiza is a mutualistic association between fungi and plant roots. Fungi provide plants with increased nutrient absorption while receiving carbohydrates in return

 How is yeast used in commercial industries?

Yeast, particularly Saccharomyces cerevisiae, is used in baking and brewing industries for fermentation to produce bread, beer, and wine .

What are the harmful effects of fungi on crops?

Fungi can cause plant diseases such as rusts, smuts, and blights, leading to significant crop damage. For example, Phytophthora infestans causes potato blight

How does nitrogen fixation benefit agriculture?

Nitrogen fixation by bacteria like Rhizobium converts atmospheric nitrogen into ammonia, enriching soil fertility and reducing the need for synthetic fertilizers .

What is the role of cyanobacteria in nitrogen fixation?

Cyanobacteria like Anabaena and Nostoc fix atmospheric nitrogen in specialized cells called heterocysts, contributing to soil fertility in paddy fields

What are the two main modes of reproduction in Protista?

Protists reproduce both asexually, primarily through binary fission, and sexually, through gamete fusion and zygote formation

What is the role of gametic meiosis in diatoms?

 In diatoms, sexual reproduction involves gametic meiosis where the diploid nucleus divides to produce haploid gametes, which then fuse to form a diploid zygote.

How does Plasmodium cause malaria in humans?

Plasmodium, a sporozoan, infects human red blood cells and liver cells, causing cycles of fever and anemia associated with malaria .

What is the significance of Trypanosoma in human health?

Trypanosoma is a flagellated protozoan that causes African sleeping sickness, a disease transmitted by the tsetse fly

What are the major divisions in Kingdom Plantae?

The major divisions of Plantae include Bryophyta (mosses), Pteridophyta (ferns), Gymnosperms (non-flowering plants), and Angiosperms (flowering plants) .

How do gymnosperms differ from angiosperms?

 Gymnosperms produce seeds that are exposed on cones, while angiosperms produce seeds enclosed within a fruit (ovary) .

What is the main mode of nutrition in Kingdom Animalia?

Animals are heterotrophic, obtaining food by ingestion, followed by digestion and absorption of nutrients .

What are the basic levels of body organization in animals?

Animals exhibit various levels of organization: cellular level (sponges), tissue level (cnidarians), organ level (flatworms), and organ-system level (vertebrates)

What is the biological definition of species?

A species is the smallest taxonomic category, defined as a group of individuals that can interbreed and produce fertile offspring .

What is a taxon?

A taxon is a taxonomic group or category, such as a species, genus, or family, representing a unit in biological classification .

What is binomial nomenclature?

Binomial nomenclature is a system of naming organisms using two terms: the genus name (capitalized) and the species name (lowercase), e.g., Homo sapiens .

What are the main differences between asexual and sexual reproduction in fungi?

Asexual reproduction involves the formation of spores like sporangiospores or conidia, while sexual reproduction involves plasmogamy (fusion of cytoplasm), karyogamy (fusion of nuclei), and meiosis .

What are zygomycetes, and how do they reproduce?

Zygomycetes are a class of fungi that reproduce asexually through the formation of sporangiospores and sexually via zygospores during gametangial copulation .

What is an ascus, and why is it important in Ascomycetes?

An ascus is a sac-like structure in which sexual spores (ascospores) are produced during sexual reproduction in Ascomycetes, giving them the name “sac fungi” .

What are basidiospores, and how are they formed?

Basidiospores are sexual spores formed on basidia (club-shaped structures) in Basidiomycetes during sexual reproduction

What are dinoflagellates, and what makes them unique?

Dinoflagellates are unicellular protists that often possess two flagella, and some species like Noctiluca are bioluminescent. They are also responsible for harmful algal blooms like red tides .

What is the role of heterocysts in cyanobacteria?

Heterocysts are specialized cells in some cyanobacteria like Anabaena that are involved in nitrogen fixation by converting atmospheric nitrogen into usable forms.

How do protozoans move?

Protozoans use different structures for movement, such as pseudopodia (Amoeba), flagella (Trypanosoma), or cilia (Paramecium) .

What is binary fission in protozoans?

Binary fission is an asexual reproduction process in which a protozoan divides into two genetically identical daughter cells

What are the major differences between bryophytes and pteridophytes?

Bryophytes (mosses) are non-vascular plants that reproduce via spores and rely on water for fertilization, while pteridophytes (ferns) have vascular tissues (xylem and phloem) and also reproduce via spores.

What are gymnosperms, and how do they reproduce?

Gymnosperms are seed-producing plants like pines that reproduce through exposed seeds on cones, without flowers.

How do angiosperms differ from gymnosperms?

Angiosperms are flowering plants that produce seeds enclosed within a fruit, whereas gymnosperms produce exposed seeds without flowers.

What is the difference between radial and bilateral symmetry in animals?

Radial symmetry, found in animals like jellyfish, means the body can be divided into similar halves along multiple planes, while bilateral symmetry, found in most animals, means the body has a distinct left and right side .

What are the main characteristics of chordates?

Chordates are animals that possess a notochord, a dorsal nerve cord, pharyngeal slits, and a post-anal tail at some stage in their life cycle .

How do invertebrates differ from vertebrates?

Invertebrates lack a vertebral column (backbone), while vertebrates have a well-developed backbone or spine .

What is the main difference between prokaryotic and eukaryotic cells?

Prokaryotic cells (e.g., bacteria) lack a true nucleus and membrane-bound organelles, while eukaryotic cells (e.g., plants, animals) have a defined nucleus and complex organelles

What are ribosomes, and how do they differ in prokaryotes and eukaryotes?

Ribosomes are cellular structures responsible for protein synthesis. In prokaryotes, ribosomes are 70S, while in eukaryotes, they are 80S .

How do prokaryotes reproduce?

 Prokaryotes reproduce asexually, mainly through binary fission, where the cell divides into two genetically identical cells .

What is the difference between photosynthetic and chemosynthetic bacteria?

Photosynthetic bacteria use sunlight to produce food, while chemosynthetic bacteria obtain energy by oxidizing inorganic compounds such as ammonia or sulfur .

What is bacterial photosynthesis, and how does it differ from plant photosynthesis?

Bacterial photosynthesis in organisms like purple and green sulfur bacteria uses light energy but does not produce oxygen (anoxygenic), whereas plant photosynthesis produces oxygen (oxygenic) .

What structures are involved in bacterial motility?

Bacteria move using flagella, which are tail-like structures that rotate to propel the cell. The arrangement and number of flagella can vary .

What is the role of pili in bacteria?

Pili are hair-like structures on the surface of bacteria that help in attachment to surfaces or host cells, and sex pili are involved in genetic exchange during conjugation .

What is the process of bacterial conjugation?

Conjugation is a form of horizontal gene transfer in bacteria where a donor cell transfers genetic material to a recipient cell through a sex pilus .

How do bacteria reproduce asexually?

Bacteria reproduce asexually through binary fission, where the bacterial DNA is replicated, and the cell divides into two identical daughter cells .

What is the role of nitrifying bacteria in the nitrogen cycle?

Nitrifying bacteria, such as Nitrosomonas and Nitrobacter, convert ammonia into nitrites and then into nitrates, which plants can use .

How do symbiotic bacteria help in nitrogen fixation?

Symbiotic bacteria like Rhizobium live in the root nodules of legumes and convert atmospheric nitrogen into ammonia, benefiting plant growth .

What are some common diseases caused by bacteria in humans?

Common bacterial diseases include tuberculosis (caused by Mycobacterium tuberculosis), typhoid (caused by Salmonella typhi), and cholera (caused by Vibrio cholerae) .

What is antibiotic resistance, and how does it occur?

Antibiotic resistance occurs when bacteria acquire genes (e.g., through plasmids) that enable them to survive exposure to antibiotics, making infections harder to treat .

What are mycoplasmas, and why are they unique?

Mycoplasmas are the smallest known free-living prokaryotes that lack a cell wall, giving them flexibility and making them resistant to antibiotics that target cell walls .