Viruses,viriods, lichens, prions

Question 1

shapes of viruses

Answer 1

-circle-hiv
-rod shape-tmv
- tadpole like-bacteriophage

Question 2

explain symmetry of viruses

Answer 2

(i) Helical symmetry :
Capsomeres arranged in
are helical manner in the capsid
e.g. TMV and Mumps virus
etc.

(ii)It is a type of polyhedral e.g. Herpes virus, Adeno virus, phi × 174
bacteriophage

Question 3

describe tmv

Answer 3

 It is the most thoroughly studied virus and was
discovered by the Russian worker D. Ivanowsky
(1892).
 It has helical symmetry.
 Having single stranded RNA
 In its capsid, number of capsomeres is 2130.
 5% RNA and 95% protein are present in TMV.

Question 4

what is the function of tail fibres and tail pins in bacteriophages

Answer 4

tail pins are for piercing through the subtratu,

tail fbres are for attaching to the subtratum

Question 5

describe bacteriophage

Answer 5

Bacteriophage was discovered by F.W.
Twort and Named by Felix d’ Herelle
Bacteriophages are generally double
stranded DNA virus.
In QB - bacteriophage - ss RNA is
present.


In ɸ × 174 bacteriophage - ss DNA is
present.

Question 6

in which plant affecting virus ds rna/dna is found

Answer 6

in Cauliflower mosaic virus dsDNA is present
and in Gemini virus ss-DNA is present.

Question 7

what is the hbitat of lichens

Answer 7

Lichens are found at those places where normal plants do not grow such as on
rocks, cold Arctic regions, on walls etc. Lichens are also found on dead and decaying
wooden pieces, leaves, soil etc.
(ii)
Lichens are not found in polluted areas.

Question 8

importance of lichens

Answer 8

The lichens grow on rocks and secrete different types of
acids. These acids break the rocks. In this way, these lichens help in soil formation.

Indicator of air pollution - Lichens are sensitive towards
concentration of
where concentration of SO2.They die in more
SO2.Therefore they are not found in those areas (polluted areas) SO2 is high. So they are used as pollution indicators.

(iii) Forest fire :
 Usnea, popularly known as old man’s beard, is of inflammable nature.
 It sometimes causes forest fire in summer season.

Question 9

explain symbiosis of mycorrhiza

Answer 9

The symbiotic association of fungus and the roots of higher plants is known as mycorrhiza.
Mycorrhiza means - fungus root.
 This symbiotic association is beneficial for both of them because fungus absorbs minerals
like P, Cu, Zn, K, N and water from soil and provide them to higher plants while higher
plants provide food and habitat to fungus. Fungus protects the roots from many diseases
also.

Question 10

explain mycorrhiza in pinus plant

Answer 10

it is obligatory relationship in pinus plant, the pinus seed cannot germinate w/o this association