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1. “
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DEPARTMENT OF BOTANY
SEMINAR TOPIC- “VIRUS”
PRESENTED BY –BIBHUDATTA PANDA

2. WHAT IS A VIRUS÷
 A virus is an infectious microbe consisting of
a segment of nucleic acid (Either RNA or
DNA) surrounded by a protein coat.
 It is non-cellular,Because it is only
composed of protein coat,nucleic acid and
rarely lipid envelope

4. SIZE:
 Generally viruses size range from 20-
200nm in diameter.
 Can undergo mutation.
 So small and change so often, that
scientist don’t know exactly how many
type exist.
 These property make us difficult to fight
against viruses

6. DISCOVERY OF VIRUS:
 In 1892 Dmitri ivanovsky discovered
virus,But in 1898 Beijerink first named
it virus

7. ARE VIRUSES LIVING?
 Like living thing,Viruses contain protein and genetic material.
 But viruses don’t act like living things.
 Can‘t eat,grow or breakdown food when it outside the host.
 Lack of respiratory system.
 Can’t function on it’s own.
 Can only reproduce inside a living cell that serves as a host

8. CLASSIFICATION OF VIRUSES:
 We can classify viruses by
following factors.
 (1)Their shape
 (2)Their host
 (3)Life cycle

9. (1)SHAPE:
There are 4 main shape of viruses
 (a)Crystals
 The polio virus is shaped like
crystals shown below
 (b)Cylinder
 The tobacco mosaic Virus is
cylindrical shape Shown below

10.  (c)Spheres:
 SARS-COV-2(covid-19) look like
sphere. Also influenza and HIV
virus has this structure.
 (d)Spacecraft:
 One group of viruses attacks only
bacteria. Many of these look
almost like spacecraft (also called
bacteriophage virus)

11. (2)HOST:
 Based on their host viruses can be classified into three
type.
 (a) Animal viruses ÷Viruses that infect only animal.
(example-covid-19)
 (b) plant viruses ÷Viruses that infect only plant.
(example-cucumber mosaic virus)
 (c)Bacteriophage virus÷Virus that infect only
bacteria.(example-T4 virus

12. VIRUS AFFECTS WHICH ORGANISMS
Tobacco mosaic virus Plant Tobacco,Tomato,peppers
PotatoX Plant Patatoes
Cauliflower mosaic virus Plant Cauliflower plant
SARS-COV-2(covid-19) Animal Only human
HIV Animal Human
Adenovirus Animal Human and other
vertebrates
H1N1(swine flu) Animal Human and pets
Bacteriophage Bacteria E.Coli and other bacteria

13. (3)LIFE CYCLE:
 Virus can multiply their genetic material in two ways. (a)lytic (b)lysogenic
(a) Lytic life cycle:
Lytic or virulent phages are the phages which can only multiplay on bacteria and kill
the cell by lysis at the end of the life cycle.
Lytic life cycle complete in 5 diffrent steps.
Step-1 Attachment
Step-2. Penetration
Step-3. Biosynthesis
Step-4. Maturation
Step-5. Lysis

15. (b)Lysogenic life cycle:
 Step-1 Attachment
 Step-2 penetration
 Step-3 integration
 Step-4 Binary fission

17. BENEFICIAL USES OF VIRUSES:
(1)Gene therpy
(2)Vaccines production
(3)Cancer therapy
(4)Disease diagnosis
(5)Evidence of evolution
(6)Controlling harmfull animal and insects

18. HARMFUL USES OF VIRUSES:
(1)Biological weapons
(2)Cause of reducing population
(3)Poultry disease
(4)Cause plant disease
(5)Cause animal disease
(6)Reduce soil fertility

19. VIRAL EPIDEMICS AND PANDEMICS:
(1)Severe acute respiratory syndrome (SARS)Year-2003
(2)ZIKA-2007,2013
(3)Swine flu-2009
(4)MERS-2012
(5)Ebola-1976,2016
(6)SARS-COV-2(covid-19) 2019-2022

20. CONCLUSION:
Virus is an infectious particle and when enter the living host,It
starts it’s replication process.Till date many viral outbreak occurred
throughout the global. The recent pandamic covid-19 is still
threating us.I request all the member present here to use mask and
sanitize your hand properly