The Defence System & Viruses (chpt. 37 & 38)

Question 1

Immunity

Answer 1

The ability to resist infection

Question 2

Pathogen

Answer 2

Disease causing organism

Question 3

How does the general defence system work?

Answer 3

Acts as a barrier to all pathogens attempting to enter the human body

Question 4

How does the specific defence system work?

Answer 4

Attacks particular pathogens

Question 5

Antigen

Answer 5

A foreign molecule that stimulates the production of antibodies

Question 6

Antibody

Answer 6

A protein produced by lymphocytes (WBC) in response to a specific antigen

Question 7

Two types of immunity

Answer 7

Natural

Induced

Question 8

What is active immunity

Answer 8

Antibodies produced in a persons body

Question 9

Examples of active immunity x2

Answer 9

Natural: pathogens enter body through broken skin etc.

Artificial: vaccine

Question 10

What is passive immunity?

Answer 10

Antibodies from another organism enter person’s body

Question 11

Passive immunity examples x2

Answer 11

Natural: e.g breastfeeding

Artificial: injections of ready-made antibodies e.g.tetanus

Question 12

Vaccination

Answer 12

Administration of a non-disease causing dose of the pathogen

Question 13

Purpose of vaccination?

Answer 13

Stimulates antibodies and active immunity

Question 14

How can you view viruses?

Answer 14

Using an electron microscope

Question 15

Describe the structure of a virus

Answer 15

Nuclei acid (DNA or RNA), surrounded by a protein coat, capsid

Question 16

Why are viruses described as obligate parasites?

Answer 16

Use host ribosomes, mitochondria etc. to make copies for replication so are always ‘obliged’ to be parasites

Question 17

How are viruses classified?

Answer 17

By their shapes

Question 18

Rod-shaped / helical virus

Answer 18

Spiral

Eg. tobacco mosaic virus

Question 19

Round / polyhedral virus

Answer 19

Many faces

Eg. Polio, herpes

Question 20

Complex virus

Answer 20

Combination of helical and polyhedral

Eg. HIV, rabies

Question 21

Steps in viral replication

Answer 21

1. Attachment - attaches to receptor sites on host cell
2. Entry - nucleic acid is squeezed out of protein coat and into host
3. Synthesis - host nucleic acid is made inactive, new viral nucleic acid and protein coats are produced
4. Assembly - new viruses assembled inside host
5. Release - released by lysis (burst out)

Question 22

Disadvantages of viruses

Answer 22

Human diseases → mumps, warts, chicken pox

Animal diseases → foot & mouth, rabies

Question 23

Advantages of viruses

Answer 23

Genetic engineering → transfer of genes using viruses e.g - vectors

Question 24

Bacteriophage

Answer 24

A virus that infects bacteria

Example of a positive virus

Question 25

Asepsis vs sterility

Answer 25

Asepsis: free from pathogens
Sterility: free from microorganisms

Question 26

Explain the difficulty in describing viruses as living

Answer 26

Non-cellular

No metabolism

Question 27

Give two ways in which the general defence system works to defend against viruses

Answer 27

Skin acts as a barrier
Mucus traps pathogens
HCl in stomach kills pathogens
Blood clotting prevent entry

Question 28

Give two ways in which the specific defence system works to defend against viruses

Answer 28

Produce antibodies
Memory cells recognise virus
T cells coordinate immune response
Killer T cells kill infected cells

Question 29

True or false:
A virus particles contains both DNA and RNA

Answer 29

False

Question 30

Name any two shapes of viruses

Answer 30

Round
Rod
Complex

Question 31

Name one organ specific to the immune system

Answer 31

Spleen
Thymus
Lymph node

Question 32

Which part of the virus is recognised by antibodies?

Answer 32

Protein coat
Antigen
Capsid