Preventing and identifying disease

Question 1

Describe the physical defence system within plants

Answer 1

● Waterproof waxy cuticle - surface barrier
preventing the entry of pathogens
● Cellulose cell wall - further barrier against
pathogens

Question 2

Give some examples of chemical barriers in plants

Answer 2

● Secretion of toxins to reduce damage by
pests e.g. stinging nettles
● Production of antibacterial chemicals that kill
bacterial pathogens

Question 3

Why are chemicals produced by plants useful?

Answer 3

They produce physiological effects on
the body so can be used in medicines to
treat disease.

Question 4

Give an example of a medicine derived from plants

Answer 4

● Quinine - antimalarial, bark of Cinchona sp.

● Aspirin - painkiller, bark/leaves of Salix alba

Question 5

Why are plant defence systems important?

Answer 5

● Plants are producers so all organisms higher
up in food chains rely upon their survival and
ability to fight disease
● Important in maintaining human food security

Question 6

How can plant diseases be detected and identified in

the field?

Answer 6

● Observation of symptoms e.g. Chalara ash dieback disease causes
bark lesions. Books and online resources aid identification
● Analysis of the distribution of infected plants can indicate the type of
pathogen involved and its mode of transmission e.g. airborne
● Changing environmental conditions to eliminate other causes such
as nutrient deficiencies or water-logged soils

Question 7

Why is it difficult to identify a disease

using symptoms alone?

Answer 7

Many diseases may have similar

symptoms

Question 8

How can plant diseases be detected

and identified in the lab?

Answer 8

● Detection of foreign antigens in a sample of
plant tissue using monoclonal antibodies
● Analysis of DNA to identify any pathogen DNA
in a tissue sample

Question 9

What is a non-specific defence?

Answer 9

● Always present
● Same for all organisms
● Prevents pathogens from entering the body

Question 10

Give some examples of the body’s physical defence

system

Answer 10

● Skin - protective surface barrier
● Blood clotting - platelets seal wounds preventing entry of
pathogens into the blood
● Respiratory tract - mucus traps pathogens, cilia waft
mucus to the back of the throat where it is swallowed

Question 11

Give some examples of the body’s chemical defence

system

Answer 11

● Tears - contain lysozyme which digests bacterial
cell walls, killing bacteria and protecting the eye
● Hydrochloric acid in stomach - acidic pH kills
pathogens that are swallowed

Question 12

What is the immune system?

Answer 12

● The body’s defence against pathogens
once they have entered the body
● Aims to prevent or minimise disease
caused by pathogens

Question 13

How do white blood cells detect pathogens in the

body?

Answer 13

Pathogens have unique antigens on their
surface which are detected by specialised
receptors on white blood cells.

Question 14

How does the immune system destroy pathogens?

Answer 14

● B-lymphocytes (type of WBC) produce antibodies in
response to a particular antigen
● Each antibody is specific to an antigen and binds to it
● Antibodies ‘tag’ pathogens or clump them together,
disabling them so that they can be killed by other WBCs.

Question 15

What are memory lymphocytes?

Answer 15

● WBCs produced in response to a foreign antigen that
remain in the body after a pathogen has been destroyed
● Provide immunity - if the body is re-infected, antibodies
are produced more rapidly and the pathogen is
destroyed before it can produce disease symptoms

Question 16

Compare the primary and secondary

immune responses

Answer 16

The secondary response produces
antibodies more rapidly and in higher
concentrations than in the primary
response. The pathogen is destroyed
before it can cause symptoms

Question 17

What is a vaccination?

Answer 17

● Deliberate exposure of an individual to foreign antigens
● Triggers an immune response (produces antibodies) and
provides immunity (due to memory cells)
● The individual does not contract the disease that they are
being immunised against

Question 18

Describe the components of a vaccine

Answer 18

Dead, weakened or inactivated
pathogens with their surface antigens
still present

Question 19

What are the benefits of vaccinations?

Answer 19

● Herd immunity - vaccination of a significant
proportion of the population gives some
protection to individuals who are not immune
● Helps to prevent epidemics and pandemics

Question 20

What are the drawbacks of vaccinations?

Answer 20

● High mutation rate of viruses changes the structure of viral antigens,
making vaccines that are already available ineffective
● Not guaranteed to work
● Inactivated pathogens may mutate and become pathogenic
● May cause an adverse reaction
● Vaccination programmes are costly