Chapter 12- communicable diseases

Question 1

What are physical plant defences against pathogens

Answer 1

-callose is deposited in cell wall and membrane including plasmodesmata. Acting as a barrier and prevents pathogen from spreading
- calloseblocks sieve plates in phloem preventing spread of pathogens
- login added to callose/cell wall making the barrier thicker and stronger
- callose seals off infected cells fro, healthy cells to to prevent prevent the pathogens from spreading

Question 2

What are 5 chemical plant defences against pathogens?

Answer 2

-insect repellent e.g. citronella
- insecticides e.g. caffeine which is toxic to insects and fungi
- antibacterial compounds e..g antibiotics (contains lysosomes, especially which contains enzymes that break down bacterial cell walls )
- antifungal compounds e.g. phenol and chitanasws (enzymes that break down chitin in fungal cell walls)
- toxins e.g. cyanide which is toxic to most living things

Question 3

What are the 4 non specific animal defences for keeping pathogens out.

Answer 3

• Skin= covers the body and prevents entry of pathogens. It has microorganisms that outcompete pathogens for space on the body’s surface. The skin also produces sebum (an oily substance which inhibits growth of pathogens)
• Mucous membranes= line many of the body tracts e.g. airways, they secrete sticky mucus. This traps microorganisms and contains lysosomes which destroy pathogens
• Lysosomes= in tears, urine and acid in our stomach prevents pathogens getting into our bodies
• blood clotting
• inflammatory response

Question 4

describe blood clotting and wound repair. (non- specific response)

Answer 4

If you cut yourself, pathogens can easily enter the body so blood clots rapidly seal the wound.
When platelets come into contact with collagen in skin they secrete several substances:

Thromboplastin= an enzyme that triggers a reaction chain resulting in a formation of a blood clot

Serotonin= makes smooth muscle in walls of blood vessels contract so they narrow and reduce the supply of blood to the area.

After the scab has formed, epidermal cells below the scab start to grow sealing the wound permanently, damaged blood vessels regrow.

Question 5

describe the inflammatory response. (non- specific response)

Answer 5

There is inflammation at the site of wound, it is characterized by pain, heat, redness and swelling.

Mast cells are activated in damaged tissue and release chemical called histamines and cytokines.

Histamines make the blood vessels dilate, causing heat and redness preventing pathogens from reproducing

Histamines do this by making blood vessel walls leakier so blood plamas is forced out, this become tissue fluid which causes swelling and pain. This delivers immune cells in blood to site of infection, fluid dilutes toxins

Cytokines attract white blood cells. They dispose of pathogens by phagocytosis.

Question 6

Complete the following sequence (5 steps) to outline how a vaccine gives an individual immunity. The
first two steps have been completed for you.
Step 1: A vaccine is produced that is a safe form of an antigen.
Step 2: A small amount of vaccine is injected into blood of the individual to be vaccinated

Answer 6

step 3
antigen presentation /
antigen binds to specific, B / T, lymphocyte / cell ✓
steps 3 or 4
clonal selection /
clonal expansion /
plasma cells produced /
produce antibodies
primary immune response ✓
step 5
ref. memory cells /
secondary immune response ✓

Question 7

what is meant by the term autoimmune disease?

Answer 7

abnormal immune response ✓
against tissues normally in the body ✓