Preventing and Identifying Disease (2)

Describe the physical defence system within plants (biology only)

● Waterproof waxy cuticle - surface barrier preventing the entry of pathogens;

● Cellulose cell wall - further barrier against pathogens

Give some examples of chemical barriers in plants (biology only)

● Secretion of toxins to reduce damage by pests e.g. stinging nettles;

● Production of antibacterial chemicals that kill bacterial pathogens

Why are chemicals produced by plants useful? (biology only)

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

Give an example of a medicine derived from plants (biology only)

● Quinine - antimalarial, bark of Cinchona sp.;

● Aspirin - painkiller, bark/leaves of Salix alba

Why are plant defence systems important? (biology only)

● 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

How can plant diseases be detected and identified in the field? (biology only/higher)

● 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

Why is it difficult to identify a disease using symptoms alone? (biology only/higher)

Many diseases may have similar symptoms

How can plant diseases be detected and identified in the lab? (biology only/higher)

● 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

What is a non-specific defence?

● Always present;

● Same for all organisms;

● Prevents pathogens from entering the body

Give some examples of the body's physical defence system (3)

● 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

Give some examples of the body's chemical defence system (2)

● 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

What is the immune system?

● The body's defence against pathogens once they have entered the body;

● Aims to prevent or minimise disease caused by pathogens

How do white blood cells detect pathogens in the body?

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

How does the immune system destroy pathogens?

● 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.

What are memory lymphocytes?

● 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

Compare the primary and secondary immune responses.

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.

What is a vaccination?

● 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

Describe the components of a vaccine.

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

What are the benefits of vaccinations? (biology only)

● 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

What are the drawbacks of vaccinations? (biology only)

● 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