CBSE Chapter 2 Biological Classification Class 11 Notes

Section–A (1 Mark Questions)

1. Who proposed the five-kingdom classification?

Ans. Robert Whittaker proposed the five-kingdom classification. This classification includes Kingdom Monera, Protista, Fungi, Plantae, and Animalia.

2. Which group comprises of single celled eukaryotes only?

Ans. Kingdom Protista comprises of single celled eukaryotes only. Unicellular eukaryotes are single-celled microorganisms with a defined nucleus, mitochondria, and other organelles.

3. What is the difference between a virus and a viroid?

Ans. The main difference between virus and viroid is that the virus is a nucleoprotein particle whose nucleic acid can be either DNA or RNA while viroid are RNA particles. Moreover, the virus consists of a protein coat known as the capsid while viroids lack a protein coat.

4. What is the nature of the cell wall in diatoms?

Ans. The cell wall of diatoms is siliceous and indestructible. The cell wall is composed of two thin overlapping walls which fit together like a soap box.

5. Why are cyanobacteria used in agricultural fields for crop improvement?

Ans. Cyanobacteria are used in. agricultural crop improvement because of their ability to fix atmospheric nitrogen and make it available to the plants. This improves the yield of the crops and reduces the cost of application of nitrogen fertilizers.

6. Define ciliated protozoans.

Ans. Ciliated protozoans are aquatic, actively moving organisms because of the presence of thousands of cilia. They have a cavity (gullet) that opens to the outside of the cell surface. The coordinated movement of rows of cilia causes the water laden with food to be steered into the gullet. Example: Paramoecium.

7. Define plasmodium of slime molds.

Ans. Slime molds are saprophytic protists. The body moves along decaying twigs and leaves engulfingorganic material. Under suitable conditions, they form an aggregation called plasmodium which may grow and spread over several feet.

Section–B (2 Mark Questions)

8. How are all bacteria classified based on their shapes?

Ans. Bacteria are classified into five groups according to their basic shapes: spherical (cocci), rod (bacilli), spiral (spirilla), or comma (vibrio). They can exist as single cells, in pairs, chains or clusters. Bacteria are found in every habitat on Earth: soil, rock, oceans, and even arctic snow.

9. What do the terms “algal bloom” & “red tides” signify?

Ans.An algal bloom is a term used for excessive growth of algae over a water body causing discolouration of the water body. Algal blooms result in the death of fishes and other aquatic organisms.

Red tide is the red colouration of sea water due to the presence and rapid reproduction of dinoflagellates like Gonyaulax, Ceratium. The dinoflagellates produce toxins that kill fishes and other marine animals.

10. What are the demerits of five kingdom classification?

Ans. The demerits of five kingdom classification are:

• Unicellular algae are kept in kingdom Protista, whereas algae like multicellular organisms are kept in kingdom Plantae. But similar organisms must be put together.

• There is diversity in the kingdom Protista. Dissimilar organisms must not be kept in the same group.

• All organisms other than those in kingdom Monera show that they are polyphyletic in origin. It is a great shortcoming of five kingdom classification.

• There is no place for viruses in the five kingdom classification.

• Similar organisms are kept far from each other. For example, unicellular and multicellular algae.

11. What is the basis of Whittaker’s system of classification?

Ans. R.H. Whittaker (1969) proposed a Five Kingdom Classification. The kingdoms defined by him were named Monera, Protista, Fungi, Plantae, and Animalia. The main criteria for classification used by him include cell structure, thallus organisation, mode of nutrition, reproduction and phylogenetic relationships.

12. Why is Neurospora an important genetic tool?

Ans. Neurospora can be grown easily under laboratory conditions by providing organic salts, carbohydrates, and vitamins. Under X-ray treatments, mutations can be introduced easily in the Neurospora cells and meiotic division is easily visible.

13. Why are some fungi grouped under “fungi imperfecti”?

Ans. Some fungi such as Deuteromycota are fallen under fungi imperfecti because these fungi do not fit into the commonly established taxonomic classifications of fungi that are based on biological species concepts or morphological characteristics of sexual structures because their sexual form of reproduction has never been observed only their asexual form of reproduction is known, which is by sporogenesis.

14. Cyanobacteria and heterotrophic bacteria are very different from each other in terms of nutrition but fall under eubacteria of the kingdom Monera. Is this type of grouping justified?

Ans. Though the mode of nutrition is the major difference between Cyanobacteria and heterotrophic bacteria, they are kept under eubacteria of kingdom Monera due to a following similarities they share:

• Both of them do not possess a well-defined nucleus.

• Their DNA lies freely in the cytoplasm.

• The ribosomes are 70S type.

• The nucleus does not have a nucleolus and a nuclear membrane.

Topics Covered in Class 11 Bio Ch 2 Notes

• Animal Kingdom

• Monera, Protista, and Fungi salient features and classification into major groups

• Lichens

• Viruses

• Viroid

Access class 11 Biology Chapter 2- Biological Classification Notes

Biological classification is defined as the process of grouping organisms according to certain similarities.

Linnaeus proposed the two kingdoms of classification, He classified organisms in the animal kingdom which is called Animalia and in the plant kingdom which is called Plantae. There were certain limitations with the classification of two kingdoms as it does not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms, and photosynthetic and non-photosynthetic organisms.

Five Kingdoms Classification

RH Whittaker suggested the five-kingdom classification. The classification of these five kingdoms is as follows: Monera, Protista, Fungi, Plantae, and Animalia. The classification was based on the organization of the thallus, the cell structure, mode of nutrition, the phylogenetic relationship, and the mode of reproduction.

(Image will  be uploaded soon)

Kingdom Monera

The bacteria are one of the main members of Monera.

All organisms found in this kingdom are prokaryotes, It includes blue-green algae together with bacterium. They can be found in terribly extreme habitats such as hot springs, deserts, snow, and deep oceans., All monerans are prokaryotes, i.e., do not have a definite nucleus. They can be autotrophs, heterotrophs moreover as parasites. Cell wall is present.

(Image will  be uploaded soon)

Archaebacteria

Archaebacteria can be thermoacidophilic (can survive in hot springs), halophilic (survive in high salt concentrations), and methanogenic (Live in swampy areas). Their cell wall structure differs from other monerans. Methanogens are found in the intestines of some ruminants such as buffalo and cows and help to produce biogas from animal dung.

Eubacteria

They are called "true bacteria". They are characterized by the presence of a mobile flagellum and a rigid cell wall. Contains cyanobacteria (blue-green algae). They are similar to plants as they contain chlorophyll a. For this reason, they are called photosynthetic autotrophs.

Cyanobacteria are unicellular, filamentous algae that form colonies which are surrounded by a gelatinous sheath. Some have special structures known as heterocysts that help in nitrogen fixation in place. For example Nostoc.

(Image will  be uploaded soon)

Chemosynthetic Autotrophs - These bacteria can oxidize certain inorganic substances such as nitrites, nitrates. The energy which is released during the process of oxidation is used in the production of ATP.

Bacteria can reproduce asexually by a process called the binary fission. They can also reproduce through spores if the situation is not favorable. Mycoplasma is also classified found under Monera. They have no cell wall and can easily survive under anaerobic conditions. Mycoplasmas are known to be the smallest living organism.

Kingdom Protista

Single-celled eukaryotes placed under the kingdom Protista. They are mostly aquatic in nature. They are found to be unicellular, eukaryotic organisms. They have a well-defined nucleus that is surrounded by the nuclear membrane. They can move through both cilia and flagella, respiration can be both aerobic and anaerobic, the mode of reproduction can be both sexual and asexual.

They are divided into Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds, and Protozoans.

1. Chrysophytes

It consists of both diatoms and golden algae. They live in both fresh and marine water. They are mostly photosynthetic. Silica is found in their cell wall and this is the reason that their cell wall is indestructible and is responsible for the formation of diatomaceous earth. They are the main producers found in the oceans. They are mostly unicellular flagellates. they are amoeboid.

(Image will  be uploaded soon)

2. Dinoflagellates

These types of organisms are marine and perform photosynthesis. They can be of different colours, for example, yellow, brown, red, or blue. The appearance of colour is due to the presence of different coloured pigments present in the cells of the dinoflagellates. The cell wall is made up of cellulose. They have 2 flagella, with one flagellum placed longitudinally and the other flagella placed transversely. Some of the examples are- Gonyaulax catenella, Noctiluca scintillans.

(Image will  be uploaded soon)

3. Euglenoids

Euglenoids are freshwater organisms found in stagnant water; They are surrounded by a protein-rich layer called pellicle. They have one short flagellum and one long flagellum; they can behave as both autotrophic and heterotrophic organisms; for example Euglena.

Most euglenoids have chloroplasts so that they can synthesize their own food. The food reserves found in the euglenoids are the paramylon (carbohydrate).

(Image will  be uploaded soon)

4. Slime moulds

They are saprophytic in nature, and under favourable conditions form aggregates known as plasmodium.

They form fruiting bodies with spores under unfavourable conditions, they have true cell walls and are extremely resistant to adverse conditions.

5. Protozoan like Protists

They are known to be heterotrophs. They can live as both predators as well as parasites. Protozoans are of four types-

• Amoeboid protozoa are found in freshwater, moist soil, or seawater and have pseudopodia to ingest food particles such as in Amoeba.

• Flagellate protozoa can be of both types i.e free-living or parasitic. This group of organisms is responsible for various parasitic diseases. For example; Trypanosoma causes sleeping sickness.

• Ciliated protozoa have thousands of cilia. The movement of the cilia helps them to move forward or backwards. It also helps in getting nourishment from the outside. For example; Paramecium.

(Image will  be uploaded soon)

• Sporozoa forms reproductive cells known as spores. They are pathogenic and parasitic. For example, the Plasmodium species causes malaria. Reproduction can be of both types i.e asexual or sexual.

(Image will  be uploaded soon)

Kingdom Fungi

Fungi are naturally heterotrophic; some feed on dead organic matter and are called saprophytes, and some can feed on living organisms known as parasites. Some fungi can live in mutual relationships with other organisms such as algae, they are called lichens. These types of fungi are called symbionts.

Lichens are symbiotic relationship between fungi and algae and mycorrhiza is the symbiotic relationship between fungi and the roots of higher plants.

Reproduction in fungi can occur by many methods such as budding, fragmentation, and fission. Asexual reproduction occurs by means of spores, which are known as conidia, zoospores, or sporangiospores.

Sexual reproduction takes place through different spores known as oospores, ascospores, and basidiospores.

In fungi, there are three steps in a sexual cycle:

The first step is protoplasmic fusion, known as plasmogamy, then the fusion of nuclei occurs known as karyogamy which leads to the formation of the zygote. Then finally, the meiosis of the zygote leads to the formation of the spores.

The Mycelium is known as the vegetative part of the fungus. The hypha network is called the mycelium. During the sexual cycle of fungi, two haploid hyphae fuse to form diploid cells. The kingdom fungi are divided into different classes.-

• Phycomycetes (Lower Fungi) - Asexual reproduction occurs through motile spores known as zoospores, and immobile spores are known as aplanospores. The spores are produced within the sporangium. The zygospore is formed by the fusion of the gametes. The mycelium is coenocytic (several nuclei) and multicellular. For example, Mucor, Rhizopus, Albugo.

(Image will  be uploaded soon)

• Ascomycetes (SAC Fungi) - They can be both saprophytic and parasitic. Asexual reproduction occurs through conidia. Sexual reproduction occurs through ascospores; branched and septate mycelium is found in Ascomycetes; for example Penicillium, Aspergillus, Claviceps, etc.

(Image will  be uploaded soon)

• Basidiomycetes (Club Fungi) - Vegetative reproduction takes place through the process of fragmentation. Sexual organs are absent. Plasmogamy between two vegetative or somatic cells leads to the formation of the basidium.  The basidium undergoes karyogamy and meiosis to form four basidiospores, for example, Agaricus (mushrooms), Ustilago (fire rot), etc.

• Deuteromycetes are commonly known as imperfect fungi because they do not reproduce sexually at any stage of their life cycle. Sexual reproduction occurs through conidia. The mycelium is septate and branched; for example Alternaria, Trichoderma, etc.

• Zygomycetes (conjugation fungi) are a primitive group of fungi. Asexual reproduction takes place by non-motile sporangiospores. For example, Rhizopus.

Kingdom Plantae

It includes all eukaryotic, multicellular, and photosynthetic plants.

The characteristics of the members of Plantae are as follows:

• Most of them are eukaryotic in nature.

• The main pigment present is chlorophyll.

• Its cell wall is made up of cellulose.

• Photosynthesis helps in the synthesis of food. 

• The process of reproduction can be both sexual and asexual.

• They represent the phenomenon of alternation of generations, i.e., diploid sporophytes, and haploid gametophytes.

Kingdom Animalia

These types of organisms are heterotrophic and eukaryotic. Some of the characteristics of the members of Animalia are as follows:

• They are multicellular organisms of various size.

• The organ systems are well developed such as the skeletal system, circulatory system, respiratory system, etc.

• They are found to be bilaterally symmetrical.

• They also have well-developed locomotory organs. 

•  Breathing takes place through gills, book lungs, book gills, skin, lungs, etc. 

•  Membrane-bound cell organelles are present and nucleus is bounded by a nuclear membrane.

•  The circulation takes place through the blood, blood vessels, and the heart. 

• Reproduction takes place through the formation of haploid gametes. The fusion of the gametes forms a diploid zygote that divides to form a new diploid organism. 

•  The kidneys are the most important excretory organ.

Viruses

The viruses are acellular structures and therefore do not find a place in Whittaker’s five kingdom classification. They consist of nucleic acid (either DNA or RNA) that is surrounded by a protein coat. These viruses can grow and multiply only within a host cell. Viruses exist as crystals outside the host cell. They cause disease and severely damage the host. For example; variola causes smallpox, HIV (human immunodeficiency virus) causes AIDS, etc.

Viroids

They are the smallest known infectious structures and consist only of nucleic acid without a protein shell. 

Lichens

They are known to be the symbiotic associations of algae and fungi. The algal component are autotrophic and synthesize and provide food. The fungal component offers protection and shelter.

Important Questions for Practice

Very Short Answer Type Questions

1.  What is the nature of the cell wall in diatoms?

2. Is chemosynthetic bacteria autotrophic or heterotrophic?

3. Who proposed the five-kingdom classification?

4. Give any two examples of parasitic plants.

5. Give any two examples of insectivorous plants.

Short Answer Type Questions

1. What is the difference between a virus and a viroid?

2. What are insectivorous plants?

3. What are parasitic plants?

4.  Why does trypanosoma fall under the kingdom Protista?

5. Are viruses living or nonliving?

Long Answer Type Questions

1. What are the characteristic features of euglenoids?

2. Discuss the salient features of viruses with the help of a diagram.

3. What are the advantages of the five kingdom classification?

Benefits of Referring to the Class 11 Bio Ch 2 Notes

You can find below the benefits of the revision notes for CBSE Class 11  Biology  Chapter 2 Biological Classifications

• These revision notes will clear students'  concepts related to the Biological Classification chapter. 

• By referring to these notes, students will be able to solve all questions based on this asked in the exam confidently.

• The experts explain the topics in precise and easy-to-understand language. 

• The notes are well-structured and also comprise bullet points.

• The subject matter experts create these notes with a detailed analysis  of the topics covered.

• These revision notes are error-free and prepared by keeping in mind the student’s need for faster and more efficient revision of chapters without leaving any vital chapter topic.

• It enables students to effectively prepare their topics in less time and even the night before the exam.

Studying the textbook is immensely important, but referring to Class 11 Biology Chapter 2 notes is also beneficial. You can use this as a last-minute revision aid before exams. Therefore, download Chapter 2 Class 11  Biology notes curated by subject experts from Vedantu today!

Download CBSE Class 11 Biology Revision Notes 2024-25 PDF

Also, check CBSE Class 11 Biology revision notes for other chapters:

Biological Classification Chapter Related Important Links

It is a curated compilation of relevant online resources that complement and expand upon the content covered in a specific chapter. Explore these links to access additional readings, explanatory videos, practice exercises, and other valuable materials that enhance your understanding of the chapter's subject matter.

Conclusion

The revision notes for Class 11 Biology Biological Classification provided by Vedantu are an excellent resource for students to revise the important concepts covered in the chapter. The notes cover all the important topics in the chapter, including the basis of classification, different systems of classification, and the characteristics of different kingdoms. The revision notes are presented in a concise and easy-to-understand manner, making it easier for students to retain the information. They also include diagrams and illustrations to help students visualise the different concepts and processes. Vedantu provides additional study materials, such as sample papers and solutions to previous year question papers, to help students prepare for their exams. By using these resources, students can revise the important concepts covered in the chapter and perform well in their exams.