3.1 Communicable Diseases

Question 1

what is a pathogen?

Answer 1

a disease-causing microorganism e.g. bacteria.

Question 2

what is a communicable disease?

Answer 2

a disease caused by a pathogen which can be passed between animals and plants e.g. flu.

Question 3

how do bacteria cause disease?

Answer 3

once inside the body, they divide rapidly by binary fission. they kill cells and produce harmful toxins.

Question 4

how do viruses cause disease?

Answer 4

they invade and reproduce inside living body cells, leading to cell damage.

Question 5

give three ways in which pathogens can be spread

Answer 5

• by air - flu, tuberculosis and the common cold are spread by droplet infection.
• by water - fungal spores in water spread plant diseases.
• by direct contant - common in plant diseases and sexually transmitted infections.

Question 6

give four ways in which the spread of pathogens can be reduced

Answer 6

• hygiene - handwashing, disinfectants, tissues.
• reducing contact with infected individuals - quarantine.
• removing vectors - use of pesticides and insecticides, removal of habitats.
• vaccination.

Question 7

why is it especially important to prevent the spread of viral diseases?

Answer 7

scientists have not yet developed cures for many viral diseases.

Question 8

what is measles?

Answer 8

measles is a serious viral disease that can cause blindness and brain damage. the main symptoms are a fever and a red skin rash.

Question 9

how is measles spread?

Answer 9

by air - through the inhalation of droplets from coughs and sneezes.

Question 10

what is HIV/AIDS?

Answer 10

HIV is a virus which attacks and damages the immune system until it can no longer function properly. AIDS is the condition resulting from a long-term HIV infection. there is no cure of vaccine for HIV/AIDS.

Question 11

how is HIV spread?

Answer 11

direct sexual contact and the exchange of bodily fluids e.g. blood, breastmilk.

Question 12

how can the spread of HIV/AIDS be prevented?

Answer 12

• use of condoms
• screening of blood for transfusions
• not sharing needles
• bottle-feeding by HIV-positive mothers
• use of antiretroviral drugs to prevent the development of AIDS

Question 13

what is tobacco mosaic virus?

Answer 13

a plant pathogen which causes leaf discolouration when cells are damaged. affected areas cannot photosynthesise, reducing the crop yield. as there is no treatment, farmers grow TMV-resistant crop strains to avoid infection.

Question 14

how is tobacco mosaic virus spread?

Answer 14

contact between infected and healthy plants. insects may act as vectors which transfer the virus between different plants.

Question 15

what is salmonella?

Answer 15

a type of bacteria found in raw meat, poulty and eggs. if they enter the body via food poisoning, they can affect natural gut bacteria.

Question 16

what are the symptoms of salmonella food poisoning?

Answer 16

• fever
• abdominal cramping
• vomiting
• diarrhoea
  may be fatal in be very young or elderly populations due the risk of dehydration.

Question 17

how can the spread of salmonella be limited?

Answer 17

• vaccinating animals inteded for consumption
• keep raw meat away from cooked meat
• disinfect hands and surfaces after contact with raw meat
• thorougly cook meat

Question 18

what is gonorrhoea?

Answer 18

a sexually transmitted bacterial infection caused by unprotected sex with an infected individuals. early symptoms include yellow/green dischange from genitals and painful urination, although it may be symptomless.
its spread can be controlled through the use of anitbiotics (no longer penicillin as many strains are resistant) and using condoms.

Question 19

what is rose black spot?

Answer 19

a fungal disease which causes purple or black spots to develop on rose leaves. it reduces the area of the leaf which is available for photosynthesis and causes leaves to turn yellow and drop prematurely.

Question 20

how is the rose black spot fungus spread?

Answer 20

fungal sports are spread by the wind and in water.

Question 21

how can the rose black spot fungus be treated?

Answer 21

• using fungicides
• destroying infected leaves

Question 22

what is malaria?

Answer 22

malaria is a disease caused by protist pathogens. the disease is carried from host to host by mosquitoes, and the protists enter the human bloodstream when they feed. symptoms include fever and shaking, and it may also be fatal in some cases.

Question 23

how can the spread of malaria be reduced?

Answer 23

• using insecticides
• using insect nets to avoid bites
• prevent mosquito breeding by removing stagnant water
• antimalarial drugs

Question 24

how does the skin prevent pathogens from entering the body?

Answer 24

• acts as a physical barrier.
• scab formation after skin is cut/wounded.
• antimicrobial secretions which can kill pathogens.
• healthy skin flora compete with pathogens and acts as an additional barrier.

Question 25

how does the respiratory system prevent pathogens from entering the body?

Answer 25

• nose - has hairs and mucus which trap pathogens.
• trachae and bronchi - have musuc that traps pathogens. ciliated cells move mucus to the mouth so it can be swallowed.

Question 26

how does the stomach prevent pathnogens infecting the body?

Answer 26

• secretes hydrochloric acid - kills any pathogens present.

Question 27

how does phagocytosis protect us against disease?

Answer 27

white blood cells (phagocytes) ingest and destroy pathogens so they cannot infect more cells.

Question 28

how does antibody protection protect us against disease?

Answer 28

white blood cells produce antibodies which are complementary to a specific antigen on a pathogen. the binding of antibodies to antigens causes pathogens to clump together, making them easier to destroy. in the case of a seconf infection, the correct antibodies can be produced rapidly, preventing the person getting the same disease again.

Question 29

how does antitoxin production protect us against disease?

Answer 29

antitoxins bind to toxins released by pathogens and neutralise them.

Question 30

what is a vaccination?

Answer 30

contains a dead or inactivated form of the pathogen which stimulates white blood cells to produce complementary antibodies to the pathogen. in the case of a second infection, memory cells can rapidly produce the correct antibodies and prevent illness.

Question 31

what is herd immunity?

Answer 31

if a sufficiently high proportion of a population are immune to a disease (especially through vaccination), the spread of this disease will be limited.

Question 32

what are the advantages of vaccinaations?

Answer 32

• they have eradicated many deadly diseases e.g. smallpox
• many epidemics can be prevented by vaccinations.
• herd immunity protects those who cannot have vaccinations.

Question 33

what are the disadvantages of vaccinations?

Answer 33

• not guaranteed to work - might not protect against multiple strains of a pathogen.
• may be side effects or adverse reactions.

Question 34

what drugs are used to cure some bacterial diseases?

Answer 34

antibiotics - they can kill bacterial pathogens inside the body.

Question 35

how do antibiotics work?

Answer 35

antibiotivs e.g. penicillin kill bacterial pathogens inside the body, but do not kill human cells. whilst some antibiotics kill a wide range of bacteria, it is important that the right antibiotic is used for specific bacteria.

Question 36

why can antibiotics not be used to treat viral diseases?

Answer 36

antibiotics have no effect on viral pathogens as they live inside the host’s (human) cells. therefore, it is difficult to design drugs that would kill the virus and not destroy human cells at the same time.

Question 37

what is antibiotic resistance?

Answer 37

antibiotic resistance occurs when mutations lead to individual bacteria being resistant to an antibiotic. these bacteria are able to survive, reproduce and pass on their alleles, leading to a greater proportion of antibiotic-resistant bacteria. this is concerning as some type of bacteria are becoming resistant to all known antibiotics, so the diseases that they cause cannot be cured.

Question 38

how can we prevent antiobiotic resistance?

Answer 38

• avoid overuse and unnecessary use of antibiotics - e.g. antibiotics are often used for viral infections.
• finish antibiotic courses - to ensure all bacteria is killed.

Question 39

what effect do painkillers have on infectious diseases?

Answer 39

painkillers can only treat the symptoms but do not kill pathogens.

Question 40

what plant is the heart drug digitalis extracted from?

Answer 40

foxgloves

Question 41

what painkiller originates from a compound found in willow bark?

Answer 41

aspirin

Question 42

what antibiotic was discovered by Alexander Fleming from a type of mould?

Answer 42

penicillin

Question 43

what are the four qualities of a good medicine?

Answer 43

• effective
• safe
• stable
• able to be taken in and removed easily

Question 44

what three main factors are tested for when developing new drugs?

Answer 44

• toxicity
• efficacy
• dose

Question 45

how is preclinical testing carried out?

Answer 45

in a laboratory - uses cells, tissues and live animals

Question 46

how is clinical testing carried out?

Answer 46

uses healthy volunteers and patients. firstly, the drug is tested at a low dose on healthy people - then tested on patients and on a large scale to find the optimum dose. often, one group receive a placebo (not the test drug) and the other group receive the actual drug, in order to assess its efficacy.

Question 47

what is the difference between a single-blind and a double-blind trial?

Answer 47

in a single-blind trial, only the doctor knowns whether the patient is receiving the drug or the placebo. in a double-blind trial, neither the patient nor the doctor knowns. double-blind trails help remove bias on the part of the doctor.

Question 48

what is a peer review?

Answer 48

where the results of drug trials are checked over by scientists knowledgeable in this field.