NCERT Class 11 Biology Chapter 2 Notes Biological Classification- Download PDF Notes

Download PDF of Biological Classification Class 11 Notes

This chapter explains how living organisms are grouped into five kingdoms: Monera, Protista, Fungi, Plantae, and Animalia. It also covers topics about viruses, viroids, and lichens. Students can download the PDF of NCERT Class 11 Biology Chapter 2 Notes for offline study. Going through the NCERT Notes for Class 11 Biology helps students save time during the exam.

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Biological Classification Class 11 Notes

Biological classification is the method of arranging organisms based on morphological, physiological, genetic and evolutionary relationships. It helps in the systematic identification, study, and understanding of biodiversity. The NCERT Class 11 Biology Chapter 2 Notes cover the key concepts from the Biological Classification chapter.

Early Classification System

In the early stages, organisms were broadly classified into two kingdoms, Plantae and Animalia. However, the system had many limitations as it did not distinguish between prokaryotic and eukaryotic organisms or unicellular and multicellular forms.

Five Kingdom Classification

R.H. Whittaker, in 1969, proposed the five-kingdom classification, which is widely accepted.

The table compares and contrasts the five kingdoms' various qualities.

Kingdom Monera

Kingdom Monera includes prokaryotic unicellular organisms that lack a true nucleus and membrane-bound organelles. The genetic material is present as a nucleoid in the cytoplasm. The cell wall and bacteria are made of peptidoglycan. Archaebacteria have different cell wall compositions, making them resistant to extreme conditions. Monerans reproduce asexually through binary fission, budding, etc. Some bacteria are autotrophic(photosynthetic or chemosynthetic), while others are heterotrophic (parasitic, saprophytic, or symbiotic). They play an important role in decomposition, nitrogen fixation, and biotechnology. Examples include E.coli, Lactobacillus, Nostoc, and Anabaena.

Kingdom Protista

The protist kingdom consists of unicellular eukaryotic organisms that exhibit animal-like, plant-like or fungus-like characteristics. Protista are highly diverse and serve as a link between prokaryotes and multicellular eukaryotes. They reproduce asexually(binary fission, budding) and sexually(syngamy, conjugation). Some protists, like diatoms and dinoflagellates, are photosynthetic autotrophs, while others, like Amoeba and Paramecium, are heterotrophic and ingest food. Many protists, such as Plasmodium, Trypanosoma and Euglena, have complex lives. Protists are commonly found in aquatic environments and play a key role in nutrient cycling and the food chain.

Chrysophytes

Chrysophytes, including diatoms and golden algae, are microscopic photosynthetic protists found in freshwater. and marine environments. They have a silica-based cell wall known as the frustule, which forms diatomaceous earth over time. They reproduce both asexually and sexually and exhibit features of both plants and animals. Their ability to survive under extreme conditions makes them ecologically significant.

Dinoflagellates

Dinoflagellates are unicellular, mostly marine plankton that have two flagella, making them highly motile. Their cell walls contain cellulose and can be photosynthetic or heterotrophic. Some species also exhibit bioluminescence, producing a glow in the ocean at night. Examples include Gonyaulax, which causes red tides. They reproduce mainly by binary fission and are important in the marine food chain.

Euglenoids

Euglenoids, such as Euglena, are unicellular, flagellated protists found in freshwater. They are unique because they show both autotrophic and heterotrophic nutrition, depending on light availability. Instead of a cell wall, they have a protein-rich pellicle, giving them flexibility. They have an eye spot that helps them detect light for photosynthesis. They reproduce by binary fission and are important in aquatic ecosystems.

Slime Moulds

Slime moulds are fungus-like protists that exist as amoeboid single cells in favourable conditions but aggregate into a plasmodium under stress. They feed on organic matter, and bacteria play a role in decomposition. Slime moulds form fruiting bodies with spores during reproduction that are highly resistant to harsh conditions. They exhibit characteristics of both fungi and protists, making them an extraordinary link between the two groups.

Protozoans

Protozoans are unicellular heterotrophic protists found in water, soil, and as parasites in animals. They are classified into amoeboid, flagellated, ciliated and sporozoans based on locomotion. Ameoboids-like Amoeba, move using pseudopodia, while flagellates, like Trypanosoma, use flagella. Ciliates such as Paramecium, which have cilia for movement and feeding, and sporozoans, like Plasmodium, cause diseases like Malaria.

Kingdom Fungi

Fungi has eukaryotic, multicellular, heterotrophic organisms with chitinous cell walls. Unlike plants, fungi do not perform photosynthesis. Instead, they obtain nutrients through saprophytic, paracytic or symbiotic relationships. Kingdom fungi reproduce asexually via spores, budding and fragmentation and sexually through plasmogamy, karyogamy and meiosis. They are important in decomposition, nutrient cycling and medicine. Some fungi cause diseases in plants and animals. Common examples include mushrooms, Yeast, Rhizopus and Aspergillus.

Based on the mycelium mode of spore generation and fruiting bodies, fungi are categorised into distinct classes.

Phycomycetes

These are also called lower fungi, which include species like Rhizopus and Mucor. Phycomycetes are mostly aquatic or grow on decaying matter and reproduce through asexual(sporangiospores) and sexual(zygospores) methods that help in rapid growth. They play a role in decomposition and industrial processes like alcohol fermentation.

Ascomycetes

They are also known as sac fungi, including Penicillium, Saccharomyces and Aspergillus. Ascomycetes reproduce asexually by conidia and sexually by forming ascospores in sac-like asci. They are decomposers and pathogens and are used in fermentation. They are important in baking and alcohol production, while Penicillium produces the antibiotic penicillin.

Basidiomycetes

Basidiomycetes, or club fungi, include mushrooms, puffballs, and rust fungi. Their characteristic feature is the basidium, where sexual spores, called Basidiospores, are produced. They are mostly saprophytic or parasitic, decomposing organic matter or infecting plants. Many basidiomycetes like Agaricus(mushrooms) are edible, while others cause plant diseases like rust or smuts.

Deuteromycetes

Deuteromycetes, or imperfect fungi, include species like Alternaria and Trichoderma. They reproduce only asexually by conidia, and the sexual stages are unknown. Many are pathogenic or decomposers, while some are beneficial in biocontrol and enzyme production. Trichoderma is used in agriculture for pest control, and Alternaria causes plant diseases like leaf spots.

Kingdom Plantae

Kingdom Plantae includes multicellular eukaryotic autotrophic organisms that perform photosynthesis using chlorophyll pigments. They have a cell wall made of cellulose and store food as starch. They play a fundamental role in oxygen production, carbon dioxide absorption and food chains. They reproduce through seeds, spores and vegetative propagation. They are the primary producers in the ecosystem and provide food, oxygen, medicine and raw materials for human use. The kingdom is divided into major groups:

• Algae, which include simple aquatic photosynthetic organisms. Example- Chlamydomonas, Spirogyra
• Bryophytes, which include the first land plants which lack vascular tissue. Example- Moss, Liverworts
• Pteridophytes, which are the first vascular plants and reproduce through spores. Example- Ferns, Horsetails
• Gymnosperms are naked-seed plants with cones. Example- Pines, Cycads
• Angiosperms, include flowering plants with fruits and seeds. Example- Mango, Rose, Wheat

Kingdom Animalia

Kingdom Animalia consists of multicellular eukaryotic heterotrophic organisms that lack cell walls. Animals are classified based on body symmetry, germ layers, body cavities, and embryonic development. They reproduce asexually, with some species showing asexual reproduction (e.g., budding in Hydra). Animals are crucial for pollination, ecosystem, stability, and human economy through domestication, food production, and companionship. The kingdom is divided into invertebrates(without a backbone) and vertebrates(with a backbone). Examples of animal groups:

• Invertebrates, which include Porifera and Arthropoda
• Vertebrates that include Pisces and mammals

Viruses, Viroids, Prions and Lichens

Viruses are non-cellular infectious agents that exist at the boundary of living and nonliving. Viruses consist of a protein coat called the capsid and genetic material, either DNA or RNA, but lack cellular structures like cytoplasm and organelles. They cannot reproduce independently and require a host to multiply, making them obligate parasites. Some common viral diseases include AIDS, influenza, hepatitis, and COVID-19 in humans. They reproduce through the lytic and lysogenic cycles using the host cellular machinery to generate new virus particles. Due to the ability to mutate rapidly, viruses are challenging to control and can cause Pandemics.

Viroids

Viroids are simple infectious agents consisting of a single-stranded circular RNA molecule without a protein coat.

• They are much smaller than viruses and were first discovered by T.O. Diener in 1971.
• Unlike viruses, viroids do not encode proteins and rely entirely on the host enzymes for replication.
• They mainly infect plants, causing severe agricultural diseases such as potato spindle tuber disease.
• Their exact mechanism of pathogenicity is still under research, but they interfere with normal RNA processing in the host.
• Since viroids lack a protective capsid, they are more susceptible to environmental conditions than viruses.

Lichens

Lichens are a symbiotic association between a fungus and algae, where the fungus provides structure and water, while the alga performs photosynthesis. They are found in extreme habitats such as rocks, tree trunks, and Arctic regions, playing an important role in soil formation and ecological balance. The lichens are classified into crustose, foliose and fruticose lichens. They are bio-indicators of air pollution as they are highly sensitive to sulphur dioxide. Additionally, they are used in the production of perfumes and antibiotics due to their unique chemical properties.

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Biological Classification Previous Year Questions and Answers

Some of the questions which have come in past years from the chapter are given below. For better revision, students can also go through the Biological Classification Class 11 Notes to strengthen their concepts.

Question 1. Members of Phycomycetes are found in

i) Aquatic habitats

ii) On decaying wood

iii) Moist and damp places

iv) As obligate parasites on plants

Choose from the following options

Option 1. None of the above

Option 2. (i) and (iv)

Option 3. (ii) and (iii)

Option 4. All of the above

Answer :

Bread moulds belong to a class of fungi called phycomycetes. They can infect both humans and animals and are present in fruits, soil, and animal dung. Both sexual and asexual reproduction are possible in phycomycetes. Conidia or sporangia are formed during asexual reproduction, whereas an egg and sperm unite during sexual reproduction.

Hence, the correct answer is option (4) All of the above.

Question 2. Concerning the fungal sexual cycle, choose the correct sequence of events

Option 1. Karyogamy, plasmogamy, meiosis

Option 2. Meiosis, plasmogamy, karyogamy

Option 3. Plasmogamy, karyogamy, and Meiosis

Option 4. Meiosis, karyogamy, and plasmogamy

Answer :

In the sexual cycle of fungi, the first event is plasmogamy, where the cytoplasm of two parent cells fuses. Next comes karyogamy, where their nuclei fuse to form a diploid nucleus. Finally, meiosis takes place to restore the haploid condition and form spores. This is the standard and correct sequence of fungal sexual reproduction.

Hence, the correct answer is option (3) Plasmogamy, karyogamy, meiosis.

Question 3. Viruses are non-cellular organisms, but replicate themselves once they infect the host cell. To which of the following kingdom do viruses belong

Option 1. Monera

Option 2. Protista

Option 3. Fungi

Option 4. None of the above

Answer :

This is because viruses are considered to be living as well as non-living and therefore are not classified under any particular kingdom. Viruses exhibit characteristics of life, such as the ability to replicate, but they cannot carry out metabolic processes independently, which classifies them as non-living when outside a host. This dual nature complicates their classification in biological taxonomy.

Hence, the correct answer is option (4) none of the above.

Also Read:

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Chapter-Wise NCERT Class 11 Notes Biology

The chapter-wise Notes for class 11 biology are given below: