Causes of disease

Question 1

Define health

Answer 1

Astate of complete physical, mental and
social well-being (as defined by the
World Health Organization, WHO)

Question 2

Define disease

Answer 2

A disorder of the body or mind that

negatively affects an individual’s health

Question 3

What are the two types of disease?

Answer 3

● Communicable

● Non-communicable

Question 4

What is a communicable disease?

Answer 4

● A disease that is passed directly
between individuals
● Caused by a pathogen

Question 5

Define pathogen

Answer 5

A disease-causing organism e.g. virus,

fungi, bacteria, protists

Question 6

What is a non-communicable disease?

Answer 6

● A disease that cannot be transmitted between
individuals
● Generally long lasting with a slow-onset
● Caused by lifestyle, environmental conditions, genetic
mutations etc.

Question 7

What is a symptom?

Answer 7

A change experienced by an organism

that indicates disease

Question 8

Why does having an illness make an individual more

likely to contract another disease?

Answer 8

A disease may weaken an individual’s
immune system making them increasingly
susceptible to other infections.

Question 9

Describe cholera

Answer 9

● Caused by Vibrio cholerae bacterium
● Spread by drinking water or washing in water that has
been contaminated with infectious faeces
● Symptoms: diarrhoea, vomiting

Question 10

How can the incidence of cholera be reduced?

Answer 10

● Access to clean water

● Improved sanitation (sewage disposal etc.)

Question 11

Describe tuberculosis (TB)

Answer 11

● Caused by Mycobacterium tuberculosis bacterium
● It is an airborne bacteria spread by droplet infection
● Symptoms: lung damage, chesty cough, wheezing

Question 12

How can the transmission of TB be

reduced?

Answer 12

● Improved hygiene (washing hands, sneezing into
tissues etc.)
● Infected individuals should avoid crowded areas
● Increased ventilation in the individual’s home

Question 13

Describe Chalara ash dieback

Answer 13

● Caused by a fungus that infects ash trees
● Spread via airborne spores which are carried by the wind
● Causes dark lesions on bark and blackened leaves which
wilt and eventually die

Question 14

How can the transmission of Chalara ash

dieback disease be reduced?

Answer 14

● Control the movement of ash trees
● Kill infected plants
● Replant with a different species

Question 15

Describe malaria

Answer 15

● Caused by plasmodium protist
● Spread by mosquito vectors which pick up the plasmodium
protist when feeding on the blood of an infected organism and
transmit malaria to other organisms during feeding
● Flu-like symptoms, damage to red blood cells, liver damage

Question 16

How can the incidence of malaria be

reduced?

Answer 16

● Mosquito nets
● Insect repellant
● Cover arms and legs

Question 17

Describe stomach ulcers

Answer 17

● Caused by Helicobacter pylori bacterium
● Transmitted orally by eating infected foods or drinking
infected water
● Symptoms: stomach pain, vomiting, nausea

Question 18

How can the transmission of Helicobacter pylori be

reduced?

Answer 18

● Access to clean water
● Improved hygiene
● Improved sanitation (sewage disposal etc.)

Question 19

Describe Ebola

Answer 19

● Caused by Ebola virus
● Spread by direct contact with infected body fluids e.g.
blood, semen, saliva, mucus, vomit
● Symptoms: fever, diarrhoea, vomiting, internal bleeding

Question 20

How can the transmission of Ebola be reduced?

Answer 20

● Improved hygiene
● Isolating infected individuals
● Sterilisation of outbreak areas

Question 21

Describe simply how viruses cause disease

Answer 21

They enter host cells and replicate inside
of them. The host cells rupture, releasing
new viruses.

Question 22

How do viruses differ from other microorganisms e.g.

bacteria, fungi?

Answer 22

Viruses are not living organisms. They
do not reproduce and can only replicate
inside a host cell.

Question 23

By what two pathways do viruses replicate inside

living cells?

Answer 23

● Lytic pathway

● Lysogenic pathway

Question 24

Describe the lytic pathway

Answer 24

1. Virus binds to specific receptors on host cell
2. Virus injects its DNAinto host cell and replicates its DNA
   using host cell machinery
3. New viral structures are produced and assembled
4. Host cell ruptures, releasing new viruses

Question 25

Describe the lysogenic pathway

Answer 25

1. Virus binds to specific receptors on host cell
2. Viral DNA injected into host cell and becomes integrated into host cell
   genome
3. Viral DNA replicates each time the host cell divides. However, the cell
   remains normal.
4. Trigger causes the activation of viral DNA. It enters lytic pathway

Question 26

Describe HIV

Answer 26

● Caused by human immunodeficiency virus
● Spread by direct contact with infected body fluids e.g. blood,
semen, breast milk.
● Destroys white blood cells making the individual
immunodeficient and increasingly susceptible to other diseases.
Leads to AIDS.

Question 27

How can the spread of HIV be reduced?

Answer 27

● Use of condoms and protected sex
● No needle exchange
● Screening blood for HIV
● Deterring infected mothers from breastfeeding

Question 28

Describe Chlamydia

Answer 28

● Caused by Chlamydia bacterium
● Spread through sexual contact or direct contact with
infected genital fluids
● Can result in infertility

Question 29

How can the transmission of Chlamydia

be reduced?

Answer 29

● Use of condoms and protected sex

● Screening