CBSE Board, Class 11 Biology
UNIT I : DIVERSITY IN THE LIVING WORLD
Chapter 2, Biological Classification
NCERT solutions of Biology Chapter 2 exercise questions
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Class 11 Biological Classification - CBSE Guide and Answers of NCERT Biology Chapter 2 Exercise Questions (1 - 6)
Question 7: Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Solution: Plants contain chlorophyll. But some plants show heterotrophic mode of nutrition. They are:
(a) Insectivorous Plants: Plants have specialised leaves to trap insects. The trapped insects are killed and digested by proteolytic enzymes secreted by the epidermis of the leaves. Example - Pitcher plant, Nepenthes, etc.
(b) Parasitic Form: Cuscutta develops haustoria, which penetrates into the vascular bundles of the host plant to absorb water and solutes.
Question 8: What do the terms phycobiant and mycobiant signify?
Solution: Lichens are the symbiotic association between algae and fungi. The algal partner is called phycobiant whereas mycobiant refers to fungal partner of lichen thallus. Phycobiant makes food while mycobiant provides protection and reproduction to lichen.
Question 9: Give a comparative account of the classes of Kingdom Fungi under the following:
(i) Modes of nutrition, (ii) Modes of reproduction
Mode of Nutrition
Saprophytic and Parasitic (obligats)
Saprophytic parasitic or coprophilous
Saprophytic and Parasitic
Mostly decomposes, some are Saprophytic and Parasitic
Mode of Reproduction
(a) Asexual Reprodn
(b) Sexual Reprodn
(a) Asexual reproduction through zoospores and aplanospores produced in sporangia
(b) By isogam or oogamy
(a) Asexual spore formed outside sporangium in chain called conidia.
(b) By fusion of compatible gametes or +ve & -ve strain hykhae.
(a) Basidiospore formed on a club shaped basidium exogeneously.
(b) Compatible nuclei fuse to form zygote.
Question 10: What are the characteristic features of Euglenoids?
Solution: Euglenoids show the following distinguishing characters:
1. Fresh water, free-living found in ponds and ditches.
2. Absence of cell-wall but contains flexible pellicle made up of protein.
3. All the euglenoids have one or two flagella which help in swimming.
4. Bear a red pigmented eye spot and a gullet near the base of flagellum.
5. Some are green and holophytic like other plants. Few are non-green and saprobic, some are like holotrophic animals.
6. Store carbohydrates in the form of paramylum.
7. The photosynthetic pigments are similar to green algae-chlorophyll a, chlorophyll b, and carotenoids.
Question 11: Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.
Solution: Viruses are ultramicroscopic infectious particles or smallest entities, composed of nucleoproteins. The structural components of viruses are - Nucleoid, Capsid, and Envelope.
Nucleoid: It represents the viral chromosome. Nucleoid or viral chromosome is made of a single molecule of nucleic acid which is either DNA or RNA but never both. DNA containing viruses are called deoxyviruses while RNA containing viruses are termed as riboviruses. It may be linear or circular with various degrees of coiling.
Capsid (Sheath, Coat): It is the proteinaceous covering around the virus which protects the nucleoid from damage from physical and chemical agents. It consists of a number of subunits called capsomeres or capsomers.
Envelope: It is a loose membranous converting that occurs in some animal viruses, rarely plant and bacterial viruses. Envelope consists of proteins from (virus), lipids and carbohydrates (from host). Examples are HIV, Herpes Virus, etc.
Enzymes: Enzyme lysozyme is present in the region that comes in contact with the host cell in bacteriophages. Other enzymes are neuraminidase in Influenza Virus, RNA polymerase, RNA transcriptase, reverse transcriptase.
The structural forms found in viruses are mainly three types - helical (elongate body, e.g., TMV), cuboidal (short broad body with rhombic, rounded, polyhedral shape, e.g., Polymyelitis virus) and binal (with both cuboidal and helical parts, e.g., many bacteriophages like T2).
Genetic Material: Nucleoid represents the genetic material of virus. It is also the infective part of virus. Genetic material can be double stranded DNA (e.g., T2, T4 bacteriophages, Herpes Virus, Hepatitis B), single stranded DNA (e.g., Coliphase MS 2), double stranded RNA (Reovirus, Tumour virus) and single stranded RNA (e.g., TMV, Polio Virus). Retroviruses synthesise complementary DNA through reverse transcriptase (e.g., HIV).Others have RNA---> RNA replication.
Common Viral Diseases: Dengue, Cough and Cold, Mumps, AIDS, Influenza, Small Pox, Potato Mosaic.
Question 12: Organise a discussion in your class on the topic - Are viruses living or non-living?
Solution: Viruses are considered as connecting links between living and non-living beings. They possess some living character and some non-living characters.
Characters of Living Beings:
1. Nucleic acids present in their body, are capable of synthesizing protein for their coat, although they use ribosomes of the host for this purpose.
2. Nucleic acids show similar gene mutations as chromosomes of the living organism.
3. Viruses replicate inside the living cells.
4. Daughter viruses resemble parent viruses.
5. Viruses are host specific.
6. They have antigenic properties.
7. They cause disease, like bacteria and fungi.
8. Ability to control cellular machinery of the host.
9. Viruses are obligate parasites.
10. Viruses are killed by UV radiations, autoclaving and many disinfectants.
11. They follow particular pattern of life cycle and reproduction.
Characters of Non-Living Beings:
1. Absence of cellular structure.
2. Metabolically inert when outside the host cell.
3. Absence of energy storing and energy liberating systems.
4. There is no growth.
5. A virus does not divide.
6. Multiplication occurs by synthesis of parts and then their assembly like those of machines.
7. Irritability is absent.
8. Movements are absent.
9. They can be crystallized.
10. Enzyme system absent.
11. They do not respire.
12. Culture of viruses in different types culture media (outside the cells) have failed.
Conclusions: Viruses are ultramicroscopic infectious particles composed of nucleoproteins and are obligate intracellular parasites where different cellular structures have degenerated due to overtaking of metabolic machinery of host.
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