immunity and infection

Question 1

examples of physical barriers

Answer 1

keratin in skin

Question 2

example of chemical barrier

Answer 2

lysozyme in mucus
hydrochloric acid in the stomach

Question 3

describe infection control practices hospitals have introduced

Answer 3

hand wash stations
testing patients for presence of antibiotic resistant bacteria before admission
increased washing of bedding/ disinfection

Question 4

Explain how changes in the blood vessels result in the redness and swelling seen at the site
of inflammation

Answer 4

histamine is released
- causes vasodilation
increases blood flow to affected area
- also increases permeability of capillaries to increase
allows blood plasma to leave the capillary

Question 5

describe how HIV particles are able to enter t helper cells

Answer 5

glycoproteins on the surface of the virus (GP120)
bind to CD4 receptors on the surface of T helper cells
viral envelope fuses with the cell membrane of T helper cells
viral RNA enters the cell

Question 6

Explain why the destruction of T helper cells causes the symptoms of AIDS.

Answer 6

lack of T helper cells reduces cytokine production
- reduces activation of B cells
reduces antibody production
increased risk of opportunistic infections

Question 7

how to bacteriostatic antibiotics work

Answer 7

preventing multiplication of bacteria

Question 8

which cell produces antibodies

Answer 8

plasma cell

Question 9

Explain why the presence of microorganisms on the skin and in the gut helps to
prevent pathogenic organisms multiplying in the body.

Answer 9

flora in the gut and skin are better adapted to conditions in body
so they can outcompete pathogenic organisms
bacteria in the gut secrete chemicals which help destroy pathogens

Question 10

Explain why these antibiotics could affect the production of proteins in bacteria.

Answer 10

ribosome shape is altered
mRNA prevented from binding to ribosome
translation can not occur
protein is not synthesised

Question 11

Devise a laboratory procedure to compare the effectiveness of penicillin with one of the
new antibiotics.
(6)

Answer 11

prepare agar plates seeded with bacteria- that is resistant to other antibiotics
prepare solutions of new antibiotic and penicillin
place solution onto paper discs
control time and temp of incubation and conc of antibiotic
measure zone of inhibition
repeat for effective antibiotics
repeat with different strains of resistant bacteria

Question 12

A person who has been vaccinated becomes infected with HPV-16. Explain the role of the T
cells in the body of this person.

Answer 12

vaccinated person will have t memory cells
- these recognise antigens specific to virus
- t helper cells activate b cells/ t killer cells
t killer cells destroy cells infected with virus

Question 13

Explain why there are relatively few species of bacteria in the stomach

Answer 13

pH in stomach is too low for enzymes of most bacteria to function
any enzymes in the stomach have adaptations that allow them to survive

Question 14

what is meant by term bacteriostatic antibiotic

Answer 14

substance which can inhibit the growth of bacteria

Question 15

structure of HIV

Answer 15

contains two strands of RNA
have glycoproteins
HIV is spherical