Biological Classification Class 11 Science Biology NCERT Solutions

Biological Classification Class 11 Science Biology NCERT Solutions: Biological Classification is the chapter 2 from class 11 Science Biology. Here you'll get Biological Classification class 11 Science/Biological Classification class 11 Science Biology NCERT Solutions.

Biological Classification Class 11 Biology chapter 2 Main Points / Summary / Notes

Biological classification of plants and animals was first proposed by Aristotle on the basis of simple morphological characters. Linnaeus later classified all living organisms into two kingdoms – Plantae and Animalia. Whittaker proposed an elaborate five kingdom classification – Monera, Protista, Fungi, Plantae and Animalia.

The main criteria of the five kingdom classification were cell structure, body organisation, mode of nutrition and reproduction, and phylogenetic relationships.

In the five kingdom classification, bacteria are included in Kingdom Monera. Bacteria are cosmopolitan in distribution. These organisms show the most extensive metabolic diversity. Bacteria may be autotrophic or heterotrophic in their mode of nutrition.

Kingdom Protista includes all single-celled eukaryotes such as Chrysophytes, Dinoflagellates, Euglenoids, Slime-moulds and Protozoans. Protists have defined nucleus and other membrane bound organelles. They reproduce both asexually and sexually. Members of Kingdom Fungi show a great diversity in structures and habitat. Most fungi are saprophytic in their mode of nutrition.

They show asexual and sexual reproduction. Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes are the four classes under this kingdom.

The plantae includes all eukaryotic chlorophyll-containing organisms. Algae, bryophytes, pteridophytes, gymnosperms and angiosperms are included in this group.

The life cycle of plants exhibit alternation of generations – gametophytic and sporophytic generations. The heterotrophic eukaryotic, multicellular organisms lacking a cell wall are included in the Kingdom Animalia.

The mode of nutrition of these organisms is holozoic. They reproduce mostly by the sexual mode. Some acellular organisms like viruses and viroids as well as the lichens are not included in the five kingdom system of classification.

NCERT Solutions for Class 11 Biology Chapter 2 Biological Classification

1. Discuss how classification systems have undergone several changes over a period of time ?

Ans: The classification systems have undergone several changes with time. The first attempt of classification was made by Aristotle. He classified plants as herbs, shrubs, and trees. Animals, on the other hand, were classified on the basis of presence or absence of red blood cells. This system of classification failed to classify all the known organisms.

Therefore, Linnaeus gave a two kingdom system of classification. It consists of kingdom Plantae and kingdom Animalia. However, this system did not differentiate between unicellular and multicellular organisms and between eukaryotes and prokaryotes. Therefore, there were large numbers of organisms that could not be classified under the two kingdoms.

To solve these problems, a five kingdom system of classification was proposed by R.H Whittaker in 1969. On the basis of characteristics, such as cell structure, mode of nutrition, presence of cell wall, etc., five kingdoms, Monera, Protista, Fungi, Plantae, and Animalia were formed.

2. State two economically important uses of:

(a) heterotrophic bacteria

(b) archaebacteria

Ans:

(a) Heterotrophic bacteria: Some heterotrophic bacteria are decomposers and they help in humus formation. Heterotrophic bacteria like Rhizobium also aid in fixing of nitrogen for plants. Heterotropic bacteria like Lactobacillus help in the formation of curd

(b) Archaebacteria: Archaebacteria such as Methanobacterium and some others are used in the production of gobar gas which is used as fuel. Ceratin archaebacteria are used in bioleaching of minerals also. Archaebacteria such as Thermus aquaticus i s used to obtain Taq polymerase enzyme which is used in recombinant DNA technology.

3. What is the nature of cell-walls in diatoms ?

Ans: The cell wall of diatoms is composed of two, thin overlapping shells which fit together in such a way that they look like a soap case. The cell wall is impregnated with silica in characteristic patterns. Diatom cell walls are almost indestructible and on accumulation, they form diatomaceous earth.

NCERT Solutions of Class 11 Biology Chapter 2 Biological Classification

4. Find out what do the terms ‘algal bloom’ and ‘red-tides’ signify.

Ans: Algal bloom: 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 tides: Red tide is the red colouration of sea water due to the presence of dinoflagellate Gonyaulax. This dinoflagellate produces toxins that lead to the death of fishes.

5. How are viroids different from viruses ?

Ans: Viroids are smaller in size than viruses. Viruses are made up of protein encapsulating the genetic material whereas viroids are free RNA particles. Viroids cause diseases in plants whereas viruses infect both plants and animals.

6. Describe briefly the four major groups of Protozoa.

Ans: Protozoa are microscopic unicellular protists with heterotrophic mode of nutrition. They may be holozoic, saprobic, or parasitic. These are divided into four major groups.

(i) Amoeboid protozoa: This type of protozoa are found in fresh water, sea water or moist soil. They can move and capture their prey with the help of pseudopodia. The pseudopodia are the extensions of the cell membrane. eg. Amoeba.

(ii) Flagellated protozoa: These protozoa can be parasitic or free-living. They use their flagella for movement. e.g. Trypanosoma causing sleeping sickness.

(iii) Ciliated protozoa: These protozoa possess a number of cilia all over their bodies for movement. Ciliated protozoa are characterised by the presence of two nuclei. eg. macronuclei and micronuclei.

(iv) Sporozoa: These protozoa include organisms that have an infectious spore-like stage in their life cycle. Sporozoans do not possess cilia or flagella. They are mostly endoparasites. eg. Plasmodium.

7. Plants are autotrophic. Can you think of some plants that are partially heterotrophic ?

Ans: Plants have autotrophic mode of nutrition as they contain chlorophyll pigment. Thus, they have the ability to prepare their own food by the process of photosynthesis. However, some insectivorous plants are partially heterotrophic. They have various means of capturing insects so as to supplement their diet with required nutrients derived from insects, causing proliferation of growth. The examples include pitcher plant (Nepenthes), Venus fly trap, bladderwort, and sundew plant.

8. What do the terms phycobiont and mycobiont signify ?

Ans: Phycobiont and mycobiont are parts of a lichen. A lichen refers to a symbiotic association of algae and fungi. In this association, fungi derive nutrition from algae while provides shelter to algae. The term phycobiont signifies the algal component of a lichen whereas mycobiont signifies the fungal component of lichen.

9. Give a comparative account of the classes of Kingdom Fungi under the following:

(i) mode of nutrition

(ii) mode of reproduction

Ans:

(A) Phycomycetes: This group of fungi includes members such as Rhizopus, Albugo, etc.

(i) Mode of nutrition: They are obligate parasites on plants or are found on decaying matter such as wood.

(ii) Mode of reproduction: Asexual reproduction takes place through motile zoospores or non-motile aplanospores that are produced endogenously in sporangium.

Sexual reproduction may be of isogamous, anisogamous, or oogamous type. It results in the formation of thick-walled zygospore.

(B) Ascomycetes: This group of fungi includes members such as Penicillium, Aspergillus, Claviceps, and Neurospora.

(i) Mode of nutrition: They are sporophytic, decomposers, parasitic or coprophilous (growing on dung).

(ii) Mode of reproduction: Asexual reproduction occurs through asexual spores produced exogenously, such as conidia produced on conidiophores.

Sexual reproduction takes place through ascospores produced endogenously in sac-like asci and arranged inside ascocarps.

(C) Basidiomycetes: This group of fungi includes members such as Ustilago, Agaricus and Puccinia.

(i) Mode of nutrition: They grow as decomposers in soil or on logs and tree stumps. They also occur as parasites in plants causing diseases such as rusts and smuts.

(ii) Mode of reproduction: Asexual reproduction takes place commonly through fragmentation. Asexual spores are absent.

Sex organs are absent but sexual reproduction takes place through plasmogamy. It involves fusion of two different strains of hyphae. The resulting dikaryon gives rise to a basidium. Four basidiospores are produced inside a basidium.

(D) Deuteromycetes: This group of fungi includes members such as Alternaria, Trichoderma, and Colletotrichum.

(i) Mode of nutrition: Some members are saprophytes while others are parasites. However, a large number act as decomposers of leaf litter.

(ii) Mode of reproduction: Asexual reproduction is the only way of reproduction in deuteromycetes. It occurs through asexual spores called conidia.

Biological Classification Class 11 Biology Chapter 2 Questions Answers

10. What are the characteristic features of Euglenoids ?

Ans: Characteristic features of Euglenoids are

i. Euglenoid is a group of unicellular protists with mixotrophic nutrition (both autotrophic and heterotrophic).

ii. Euglenoids lack a cell wall. Their bodies are covered by a proteinaceous membrane called pellicle.

iii. Euglenoids contain chlorophyll pigment, so they are photoautotrophic. However, in the absence of light, they behave like heterotrophs. Thus, they have mixotrophic nutrition.

iv. Euglenoids possess two flagella at the anterior surface.

v. Euglenoids have both plant-like and animal-like characters. For example, the presence of chlorophyll is a plant character while the absence of a cell wall is animals character.

11. Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Ans: Viruses are sub-microscopic infectious agents that can infect all living organisms. A virus consists of genetic material surrounded by a protein coat. The genetic material may be present in the form of DNA or RNA.

Most of the viruses, infecting plants, have single stranded RNA as genetic material. On the other hand, the viruses infecting animals have single or double stranded RNA or double stranded DNA.

Bacteriophages or viruses infecting bacteria mostly have double stranded DNA. Their protein coat called capsid is made up of capsomere subunits. These capsomeres are arranged in helical or polyhedral geometric forms.

Some common viral diseases are common cold, AIDS, swine flu, hepatitis.

12. Organise a discussion in your class on the topic – Are viruses living or non-living ?

Ans: Viruses are considered to be intermediates between living and non-living entities. They resemble living beings in the following aspects:

i. Viruses are made up of organic macromolecules which is a characteristic of only living beings.

ii. Viruses possess genetic material.

iii. In the presence of a suitable host, viruses reproduce or multiply.

iv. Viruses show the presence of enzymes like transcriptase, vitamins like riboflavin etc.

v. Viruses can show mutations, antigenic properties, infectivity, host specificity etc.

Thus, on the basis of these features, viruses must be categorised as living. However, viruses also resemble non-living things in the following aspects:

i. Viruses lack protoplast

ii. Viruses are unable to live independently as a living cell.

iii. Viruses do not show respiration, energy storing system, growth, division etc.

iv. Viruses can be crystallized.

Thus, based on these features viruses can be classified as non-living things. Hence, the status of the virus as living or non-living is controversial.

Class 11 / HS 1st Year Science Biology English Medium