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SLC SCIENCE VIRUS NOTE

 Virus is a very tiny, infections and highly pathogenic organisms, which can multiply only within the living host. They don't have cellular structure. They contain hereditary material in the form of DNA or RNA enclosed in a protein coat called capsid. A mature virus is called a viron.
They exhibit properties of both living and non-living things, as Virus has no metabolic activity of its own.
They are smallest living organism with the size of about 20nm to 300 nm. Based on the host they attack, viruses are of 3 types.
·    Animal Virus
·    Plant Virus
·         Bacteriophages
They are also classified into RNA virus and DNA virus on the basis of nucleic acid present in them.
Q. Why is a virus considered as the boarder line between living and non living things?
Virus is a living thing only inside a cell and nonliving thing outside a cell so it is considered as a chain between living and non living things.
Q. Why are viruses called obligatory parasite?
                   Viruses are called obligatory parasite because they are fully dependent on the other organisms.
Characteristics/ Nature of Virus
·         They don't show respiration & metabolism
·         They can reproduce only inside living cell.
·         They don't show cellular structure.
·         They are like molecules.
·         They show host specificity i.e. particular virus can attack only a particular host
Transmission of Virus:
Virus transmits by means of air, water and food particles. When an infected person sneezes, virus from the water droplets enter the near by healthy person. Viruses also transmit by blood and body fluids. Some common viral diseases, organs affected medium & control measures are shown in the table below.
Name of the disease
Name of Virus
Organs effected
Medium
Control Measures
Common cold
Rhino virus
Upper respiratory tract
Saliva
Control of infection
Mumps
Parmyxo virus
Respiratory tract
Saliva
Control of infection
Measles
Parmyxo virus
Mouth, Skin, Instestine and Respiratory tract
Saliva
Control of infection
Polio
Polio virus
Pharynx, Intestine, Blood and Brain
Feaces, Saliva
Polio drops
Rabies
Rabies virus
Spinal cord, brain
Saliva
Anti rabies vaccine
AIDS
Retro virus
Skin, Blood and Brain
Unsafe sex, Blood
Avoid sex with multiple partners, Use condoms
Q. Culture of virus is impossible, why?
            Culture of virus is impossible because it is very minute and it is alive inside host only.
Exercise for Practice
1.      Identify the two diseases caused by virus regarding the parts affected.      
a.       
                                                              i.      High fever
                                                            ii.      Respiratory tract becomes affected.
                                                          iii.      Eyes become sensitive to sunlight
                                                          iv.      Skin rashes
b.       
                                                              i.      Respiratory system,
                                                            ii.      fever is intermittent
                                                          iii.      parotid gland
                                                          iv.      Testes.
2.      Write two characters of virus.                              
3.      Why virus is called obligate parasite?
5.       
a.      Why are virus known as obligatory parasites?
b.      AIDS virus doesn't kill a human being but it helps other diseases. Justify this statement.
6.      What is the reason for transmitting HIV virus causing cold through blood and air media    respectively?  
7.      What causes polio?                                                    
8.      Which virus causes common cold? What happens if a person suffering from AIDS catches common cold
9.      Are viruses living or non-living objects? Explain.                             
10.  Give full form of AIDS and TMV.   
11.  Write the full form of AIDS. State four main methods by which the virus that causes AIDS gets transmitted from one person to another
12.  How does individual suffer from AIDS? Give a way of transmission of this disease. What symptoms is seen in the victim?
13.  Give Characteristics of Virus
14.  What is virus  

15.  Why do polio victims become paralyzed?
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