Class 11 Biological Classification - CBSE Biology Answers of NCERT Textbook Exercise



Chapter 2. Biological Classification

NCERT (CBSE) Solutions - NCERT Answers - Chapter Exercise Questions

Question 1: Discuss how classification systems have undergone several changes over a period of time.
Answer: Classification systems are procedures of arranging organisms into groups and subgroups on the basis of similarities and dissimilariries of certain characters. The earliest systems were artificial. Then came natural systems, phylogenetic and now phenetic systems.
Artificial System of Classification: It is a system of classification which uses one or two morphological characters for grouping of organisms. Theophrastus first proposed Artificial System of Classification.
Natural System of Classification: This system is based on the natural affinities among organisms. These systems used as many taxonomic characters as possible to group organisms. In these systems organisms are classified on the basis of mainly morphological, reproductive, anatomical but cytological, physiological, embryological features, biochemistry etc. John Ray was first to propose a natural system of classification.
Phylogenetic System of Classification: Classification based on evolutionary relationships of organisms is called phylogenetic system of classification. It is based on the Darwin's evolutionary concept. First, Eichler and Endlicher proposed a phylogenetic classification system which was later on developed by others.
Phenetic Classification: It is a system of phylogenetic classification which is based on affinities, similarities, and dissimilariries of characteristics present in the present day organisms without searching for the evolution and diversification of these traits in their fossil ancestors.
Then depending upon the type of system of classification, organisms were also classified into Two Kingdom or Three Kingdom, Four Kingdom, Five Kingdom and now into Six Kingdom System.
Five Kingdom System: On the basis of cell-structure, mode of nutrition, reproduction, and phylogenetic relationship Whittaker proposed Five Kingdom Classification. The five kingdoms were named as - Monera, Protista, Fungi, Plantae and Animalia. But Whittaker’s Five Kingdom System of classification has also some demerits such as, the position of viruses is not clear, algae is placed into monera, protista and plantae.     
Six Kingdom System: On the basis of gene sequences, this system of classification was proposed by Gray and Doolittie.
Thus, classification systems have undergone several changes over a period of time and are still changing.
Question 2: State two economically important uses of:
(a) Heterotrophic bacteria
(b) Archaebacteria
(a) Two economically important uses of heterotrophic bacteria are:
1. Nitrogen fixation in roots of legumimous plants.
2. Being decomposers, used in production of antibiotics.
(b) Two economically important uses of archaebacteria are:
1. Production of bio-gas from cow-dung.
2. Lives in guts of ruminant animals & help them in digestion of starch.
Question 3: What is the nature of cell-wall in diatoms?
Answer: The cell wall in diatoms is very tough because it is impregnated with silica which makes characteristic patterns on the cell. The cell wall consists of two overlapping halves like a soap-case, the upper one is called epitheca while the lower or inner one hypotheca. The cell wall is almost indestructible and forms diatomaceous earth.
Question 4: Find out what do the terms "algal bloom" and "red-tides" signify.
Algal bloom: It refers to the excess growth of algae especially blue green algae, in polluted waters.
Red-tides: Red-tides refer to the red colour imparted to the sea water by the rapid multiplication of dinoflagellates like Gonyaulax. These marine organisms make a red sheet over seas because of red pigment in their cell.
Question 5: How are viroids different from viruses?
1. Larger than viroids.
2. Nucleic acid can be DNA or RNA.
3. A protein covering or coats called capsomeres are present.
4. Virus is known to infect all types of organisms.
5. Cause diseases like - Mumps, AIDS.
6. It is a nucleoprotein particle.
1. Smaller than viruses.
2. Viroid is formed of only RNA.
3. It is an RNA particle.
4. A protein coat is absent.
5. Viroid is known to infect only plants.
6. Cause diseases like - Potato spindle tuber, chrysanthemum stunt.

Question 6: Describe briefly the four major groups of Protozoa.
Answer: The four major groups of protozoa are:
1. Amoeboid protozoans: They move and capture their prey by pseudopodia as in Amoeba. Many forms have silica shells on their surface. Some of them such as Entamoeba are parasites.
2. Flagellated Protozoans: They have flagella. The parasitic form such as Trypanosoma, cause disease.
3. Ciliated Protozoans: They have cilia. They also have a cavity (gullet) that opens to the outside of cell surface. Food is carried into the gullet as in Paramoecium.
4. Sporozoans: They have an infectious spore-like stage in their life cycle. The most important example is Plasmodium (malarial parasite).

To see answers of remaining questions (7 - 12) please visit: 
NCERT Solutions of CBSE Class XI Biology - Chapter 2, Biological Classification

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