B1.1.2 How our bodies defend themselves against infectious diseases

Question 1

What is a pathogen?

Answer 1

• A microorganism (bacteria/virus/fungus) that causes an infectious disease

Question 2

How do bacteria and viruses make us feel ill? (2 marks)

Answer 2

• They may produce poisons (toxins) that make us feel ill.

- Viruses damage the cells in which they reproduce.

Question 3

How do white blood cells help defend our bodies against pathogens? (3 marks)

Answer 3

• by ingesting pathogens
• by producing antibodies, which destroy particular bacteria or viruses
• by producing antitoxins, which counteract the toxins released by the pathogens

Question 4

Which cells defend us against pathogens?

Answer 4

White blood cells

Question 5

Why is it beneficial if a large proportion of the population is immune to a pathogen?

Answer 5

The spread of the pathogen is very much reduced.

Question 6

What did Semmelweiss suggest in hospitals?

What was the effect of his suggestion?

Answer 6

• Semmelweiss insisted that doctors washed their hands before examining patients
• the number of deaths from infectious diseases in his hospital was greatly reduced

Question 7

Why does washing hands between dealing with patients reduce the number of deaths caused by infectious diseases?

Answer 7

It kills the pathogens that cause the infectious disease.

Question 8

What do painkillers do?

What don’t they do?

Answer 8

• They help to relieve the symptoms of infectious disease

- They do not kill the pathogens.

Question 9

What is penicillin?

Answer 9

An antibiotic

Question 10

What are antibiotics?

Answer 10

Medicines that help to cure bacterial disease by killing infectious bacteria inside the body.

Question 11

Why can antibiotics not be used to kill viral pathogens?

Answer 11

Viruses live and reproduce inside cells so the antibiotics cannot reach them.

Question 12

Why can’t penicillin be used to treat ALL bacterial infections?

Answer 12

Specific bacteria should be treated by specific antibiotics, penicillin will only work against certain types of bacteria.

Question 13

What has caused an increase in the rate that antibiotic resistant strains of bacteria develop?

Answer 13

Overuse and inappropriate use of antibiotics

Question 14

What process has enabled many strains of bacteria, including MRSA, to develop resistance to antibiotics?

Answer 14

Natural selection.

Question 15

Describe how new strains of antibiotic resistant bacteria evolve. (4 marks)

Answer 15

• Mutations of pathogens produce new strains.
• Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen.
• Antibiotics however kill off other pathogens so the resistant strain has less competition
• With less competition the new strain is able to reproduce quickly

Question 16

Why are doctors so concerned about new strains of pathogens? (2 marks)

Answer 16

• The new strain will spread rapidly because people are not immune to it.
• There is no effective treatment.

Question 17

Why is it necessary to develop new antibiotics?

Answer 17

To counteract the emergence of new antibiotic-resistant strains of bacteria.

Question 18

Outline how a vaccine works using key terms. (4 marks)

Answer 18

• A small quantities of dead or inactive forms of the pathogen are injected into the body (vaccination).
• the vaccines stimulate the white blood cells to produce antibodies that destroy the pathogens.
• This makes the person immune to future infections by the microorganism.
• The body can respond by rapidly making the correct antibody, in the same way as if the person had previously had the disease.

Question 19

What does the MMR vaccine protect children against?

Answer 19

Measles, mumps and rubella.

Question 20

What are uncontaminated cultures of microorganisms needed for?

Answer 20

For investigating the action of disinfectants and antibiotics.

Question 21

Outline how uncontaminated cultures of microorganisms are produced. (3 marks)

Answer 21

• Petri dishes and culture media are sterilised before use to kill unwanted microorganisms
• Inoculating loops (used to transfer microorganisms to the media) are sterilised by passing them through a flame
• The lid of the Petri dish are secured with adhesive tape to prevent microorganisms from the air contaminating the culture

Question 22

In school and college laboratories what is the maximum temperature that cultures should be incubated at?

Answer 22

25 °C

Question 23

Why should cultures be incubated at 25 °C?

Answer 23

To reduce the likelihood of growth of pathogens that might be harmful to humans.

Question 24

Why in industry are cultures incubated at temperatures higher than 25 °C?

Answer 24

To produce more rapid growth.