3.2.4 - cell recognition and the immune system

Question 1

what are non-specific defences?

Answer 1

the bodies defence mechanisms (physical or chemical barriers) which target all pathogens in the same way

Question 2

non-specific defences - skin?

Answer 2

surface layer of dead cells - difficult to penetrate
surface covered with oily sebum - slightly acidic layer can prevent growth of harmful bacteria
healthy skin has harmless microorganisms which reduce pathogen growth by competing for resources
if there is a wound, blood clots to form a scab and stop pathogens getting in

Question 3

non-specific defences - eyes?

Answer 3

eyelashes prevent things getting in
tears contain lysosomes

Question 4

non-specific defences - nose?

Answer 4

contains mucus to trap pathogens
sneezing (expulsive reflex) expels pathogens

Question 5

non-specific defences - mouth?

Answer 5

saliva contains lysosomes
coughing and vomiting (expulsive reflexes) expel pathogens
trachea has goblet cells which produce mucus to trap pathogens and cilia which beat to push mucus out of trachea

Question 6

non-specific defences - stomach?

Answer 6

mucus contains hydrochloric acid which kills pathogens

Question 7

what are phagocytes?

Answer 7

white blood cells which carry out phagocytosis (neutrophils and macrophages)

Question 8

what is phagocytosis an example of?

Answer 8

a non-specific defence (phagocytes kill any pathogen)

Question 9

what happens during the process of phagocytosis?

Answer 9

1. the pathogen produces chemoattractants (toxins) which attract the phagocyte
2. the phagocyte binds to receptors on the pathogen cell
3. the phagocyte engulfs the pathogen by endocytosis, and the pathogen is contained in the cell within a phagosome
4. lysosomes fuse with the phagosome, forming a phagolysosome
5. the lysosomes release lysosymes into the phagolysosome, which hydrolyse the pathogen
6. the products of hydrolysis are egested from the phagocyte by exocytosis
   specific to macrophages:
7. the phagocyte presents the antigens from the pathogen on its surface, so it becomes an antigen presenting cell (APC)