5. Strategies of Defence against Pathogens Part 1

Question 1

What is a disease?

Answer 1

Any condition that interferes with how an organism, or any part of it, functions.

Question 2

What is a pathogen?

Answer 2

An infectious agent that causes disease.

Question 3

What is the host? Give an example:

Answer 3

The organism that is infected (Eg. You are the host of the rhinovirus when you have a cold)

Question 4

What is immunology?

Answer 4

The study of disease and how organisms defend against pathogens.

Question 5

List the 5 types of pathogens:

Answer 5

• Viruses
• Prions
• Bacteria
• Fungi
• Protists

Question 6

What are viruses?

Answer 6

Are non-living, and contain either DNA or RNA (but never both), and are surrounded by either a protein coat or phospholipid bilayer acquired from the host cell membrane.

Question 7

List the steps of how viruses can act:

Answer 7

1. Injecting nucleic acid into the host cell
2. Multiple copies of viral nucleic acid and protein coat components are made by the host cell
3. New virus particles are released by causing the cell to undergo lysis (burst)

Question 8

List the 2 non-cellular causes of disease (non-living):

Answer 8

• Viruses

- Prions

Question 9

List the 3 cellular causes of disease (living):

Answer 9

• Bacteria
• Fungi
• Protists

Question 10

Describe some ‘different’ ways viruses can act:

Answer 10

• In some cases, the virus will not kill the host cell but use it to continually pump out new viral particles until the cell dies of ‘exhaustion’
• Some viruses, such as HIV, integrate their DNA into the host genome and can remain dormant to hide from the immune system (temperate viruses)

Question 11

How are viruses very specific? Give some examples:

Answer 11

Each virus only infects particular species and only particular host cells within that species.
Eg. Bacteriophage only infect bacteria, rhinovirus only infects epithelial cells in the upper respiratory tract

Question 12

Describe why viruses cause illness:

Answer 12

• Enter the host cell (either the whole virus or just the genetic data)
• Hijack the host cell machinery to make many more copies
• Either causes lysis (bursting) of the cell to release thousands of new viral particles to infect more cells or continually produce viral particles as they are made until the cell dies (depleted resources).

Question 13

What are prions and how do they act? Give an example:

Answer 13

Are non-living infectious proteins (no nucleic acid present), which cause degenerative neurological diseases.
-Act by altering the shape of normal prion proteins, where these abnormal prions then alter other normal proteins
-Abnormal prions in one place cause damage to tissue leading to degeneration
Eg. Mad cow disease, where cows become edgy, irritable with a funny gait and their brains become a spongy clump.

Question 14

What are bacteria, are they pathogenic, and describe their structure:

Answer 14

Are prokaryotes, and are the most abundant and diverse group of organisms on Earth, where only a relatively small number cause disease.

• Most are not pathogenic (infectious) and many are beneficial
• Most have a cell wall made of peptidoglycan
• DNA is in a circular chromosome, and may also contain small extra pieces of DNA called plasmids

Question 15

List some examples of what bacteria can be transmitted by?

Answer 15

• Direct contact
• Food and water
• Droplets of moisture in the air
• Wounds or bites

Question 16

Describe why bacteria cause illness:

Answer 16

• Once inside the host, bacteria rapidly replicates
• Some damage host tissues directly, and others produce toxins (their metabolic waste) that disrupt host cells either nearby or throughout the body via the bloodstream
• Many parts of bacteria can stimulate such strong host immune responses it causes harm
• Some bacteria interfere with the host immune system making them susceptible to other pathogens

Question 17

What are fungi and what is its most common type of infection? Give some examples:

Answer 17

Are eukaryotes with a cell made of chitin, and are larger than bacteria.
-Most common type of infection is external
Eg. Athletes foot, ringworm

Question 18

What are protists?

Answer 18

Are unicellular eukaryotic organisms, where less than 24 of its species cause disease in humans.
Eg. Giardia lamblia, amoebic dysentery, and malaria

Question 19

What is the aim of the first level of preventing disease (non-specific)? List 4 ways it does this:

Answer 19

To stop the pathogen entering the body in the first place.

• Skin
• Mucus membranes (flush away pathogens)
• Chemical defenses
• Normal flora

Question 20

What is skin and what happens if it is cut and blood vessels are damaged?

Answer 20

Is the tough physical barrier, consisting of epithelial cells, between the outside and the inside of the body, and is the largest organ in the body.
-If cut and blood vessels are damaged, platelets become sticky and form a clot to plug the wound

Question 21

What are mucous membranes (flush away pathogens)?

Answer 21

Line the respiratory, urinary, reproductive, and IG tract, trapping pathogens and dirt.
-In the respiratory tract, the mucus is expelled by the cilia, which is then swallowed, causing pathogens to be destroyed by stomach acids.

Question 22

Describe chemical defenses and gives some examples:

Answer 22

Skin releases chemicals that destroy or inhibit the growth of micro-organisms.

• Sweat and oil give skin a low pH (3-5)
• Stomach acid has a very low pH that kills most micro-organisms
• Tears, saliva, and mucus contain lysosome that break down certain bacterial cell walls

Question 23

What is normal flora?

Answer 23

Bacteria, fungi, and protozoa, which don’t harm the host, but prevent the growth of pathogens through competition for nutrients and space.

Question 24

What are viroids?

Answer 24

Tiny loops of RNA, which cause diseases in plants.

Question 25

List 2 physical barriers that are present in plants that increase the resistance of a plant to pathogenetic infection:

Answer 25

• Thick bark

- Waxy cuticle on leaves