Communicable Diseases

Question 1

How do pathogens cause disease?

Answer 1

Bacteria - they reproduce rapidly and can affect the host by releasing toxins, these damage tissues and make us feel unwell
Viruses - they invade and reproduce inside living body cells, which causes cell damage.
Fungi - grow on living tissue, some are single-celled and others have a body made of hyphae
Protists - eukaryotic organisms some of them are parasitic, that live on or inside the host organism. They are often transferred by vectors.

Question 2

How can pathogens be spread?

Answer 2

By air
By water
By direct contact

Question 3

What are the optimum conditions for bacterial growth?

Answer 3

warm, moist and contains a supply of nutrients

Question 4

Measles

Answer 4

Pathogen:
- virus
Symptoms:
- Fever
- Red skin rash
Spread:
- In the air, by the inhalation of droplets
- from the coughs and sneezes of an infected person
Treatment & Prevention:
- No treatment - therefore must isolate the infected person
- MMR vaccine - childhood vaccination programme
Long term effects:
- Blindness
- Brain damage

Question 5

HIV

Answer 5

pathogen:
Virus
Symptoms:
Flu-like illness
Diarrhoea
Weight loss
Swollen glands (lymph glands in the armpit)
Spread: exchange of body fluids:
Direct sexual contact
Contaminated blood transfusions
Drug users sharing infected needles
Infected mother to child during birth or in breast milk
Treatment & Prevention:
No treatment
Use of condoms
Screening of blood for transfusions
Not sharing needles

Question 6

Tobacco Mosaic

Answer 6

pathogen:
Tobamovirus
Symptoms:
Stunted plant growth - due to lack of photosynthesis, reducing the yields of crops
Mosaic pattern on leaves - virus infects the chloroplasts
Leaf discolouration
Spread:
Plants in direct contact with infected plants
Insects may act as vectors - transfer the virus between plants
Prevention & Treatment:
No treatment
Good field hygiene to prevent the spread
Use of tobacco mosaic virus-resistant strains of crop plants

Question 7

Salmonella

Answer 7

Pathogen
Bacteria
Symptoms
Fever 
Abdominal cramps
Vomiting
Diarrhoea
Why do these symptoms occur?
The body is trying to remove the infection from the gut
May be fatal in very young or elderly people due to the risk of dehydration
Spread:
Contaminated water
Food that has not been cooked properly
Prevention & Treatment:
Vaccinate animals intended for consumption
Disinfect hands and surfaces after contact with raw meat
Keep raw meat away from cooked meat
Thoroughly cook meat

Question 8

Gonorrhoea (STD)

Answer 8

Pathogen:
Gonnoccus (bacteria)
Symptoms:
Thick, yellow or green discharge from genitals
Painful urination
Some people may be asymptomatic
Spread:
Unprotected sexual contact
Treatment & Prevention:
Use of contraception (condoms)
Antibiotics (no longer penicillin as many strains are resistant)
Long term effects:
Infertility
Ectopic pregnancies
Pelvic Pain
Babies born (to infected mothers) can get eye infections and be born blind

Question 9

Rose black Spot

Answer 9

Pathogen:
Fungus
Symptoms:
Purple or black spot on rose leaves - reducing area of leaf for photosynthesis
Leaves can turn yellow and drop off - loss of leaves means less chloroplast for photosynthesis, and reduction in photosynthesis means the plant has less energy to make flowers
Spread:
Spores from the fungus are carried in the wind or water
Treatment & Prevention:
Fungicide chemicals
Destroy infected leaves (by removing or burning)
Breeding plants resistant to the disease

Question 10

Malaria

Answer 10

Pathogen:
Plasmodium parasite (protist)
Spread:
By a female anopheles mosquito- which acts as a vector
Symptoms:
Recurrent fever and shaking when the protists are bursting out of the red blood cells
These episodes can weaken the host
Treatment & Prevention:
Use of insecticides
Mosquito nets
Antimalarial drugs
Prevent mosquito breeding by removing stagnant water

Question 11

Examples of primary defences:

Answer 11

Nose
Hair and mucus trap pathogens
Enzymes digest pathogens
Trachea & bronchi
Cilia waft pathogens - they are then swallowed and broken down by the acid in the stomach
Goblet cells produce mucus
Tar in cigarettes can coat cilia, this makes it unable to waft causing a build-up of excess mucus - this causes a smoker’s cough
Skin
Extra natural layer of protection from pathogens
Good bacteria fight off pathogens/bad bacteria
Haemophiliacs are prone to infections - they cannot cote their blood and produce scabs when wounds arise
Stomach
Glands in the stomach produce hydrochloric acid in the stomach lining - kills bacteria and causes their enzymes to denature so they can’t function