CBSE Board, Class 11 Biology
UNIT I : DIVERSITY IN THE LIVING WORLD
Chapter 2, Biological Classification
NCERT solutions of Biology Chapter 2 exercise questions
To
see answers of previous questions (1 - 6) visit:
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
Solution:
|
Characters
|
Phycomycetes
|
Ascomycetes
|
Basidiomycetes
|
Deuteromycetes
|
|
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.
|
By conidia.
Absent.
|
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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