What are some examples of physical defences against disease in plants?
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What are some examples of physical defences against disease in plants?
Physical defences are physical features of a plant that prevent invasion of pathogens, e.g.:
cellulose cell walls
a tough waxy cuticle on leaves
dead cells that form a layer around the outside of stems
True or False?
Bark provides a physical defence to protect trees from pathogens.
True.
Bark is tough and so provides a barrier to pathogens and other threats.
True or False?
A tough waxy cuticle acts as a chemical defence in plants.
False.
A thick waxy cuticle is a physical defence designed to deter microorganisms.
What is an example of a chemical defence in plants?
Chemical defences in plants include:
antibacterial chemicals
poisons or chemicals that taste unpleasant to deter herbivores
True or False?
Some plant defences can be utilised by humans.
True.
Some chemical defences can be used to treat human diseases or relieve symptoms, e.g. aspirin from willow trees and digitalis from foxgloves.
What are symptoms that may indicate disease in plants? (Higher Tier Only)
Symptoms that indicate disease in plants might include:
stunted growth
spots on leaves
areas of decay (rot)
growths
malformed stems or leaves
discolouration
the presence of pests
What methods can be used to detect and identify plant disease in the field? (Higher Tier Only)
Methods that can be used to identify and diagnose plant disease in the field include:
observation of visible symptoms, e.g. stunted growth and discolouration of leaves
eliminating other possible causes of observed symptoms, e.g. grazing, pollution or drought
carry out a distribution analysis; the location of infected plants may indicate the type of pathogen involved
What lab procedures can be used to detect and identify plant disease? (Higher Tier Only)
Lab procedures that can be used to detect and identify plant disease include:
microscope analysis
culturing/growing microorganisms found on plant samples
use of antibodies to identify pathogenic antigens
DNA testing to check for presence of pathogens
soil tests
How do cilia and mucus provide a physical defence against disease?
Mucus traps pathogens, dirt and dust within airways. Cilia then beat/waft to move the mucus up and out of the trachea.
What is the role of skin in disease defence?
Skin is a physical barrier that prevents pathogens from entering the body.
True or False?
Stomach acid is a chemical defence against disease.
True.
The stomach contains hydrochloric acid which is a chemical defence mechanism that destroys many pathogens.
How does lysozyme provide protection from pathogens?
Lysozyme is an enzyme that is secreted by the eyes and released in tears. Lysozyme breaks down and kills bacteria that might otherwise cause eye infection.
How does hydrochloric acid provide protection from pathogens?
Hydrochloric acid protects the body from pathogens as it is a strong acid that can kill pathogens that have been swallowed.
Define the term specific immune response.
A specific immune response is a response that is specific to one type of pathogen and its antigens. The same response is likely to be ineffective against another type of pathogen.
Define the term antigen.
An antigen is a molecule on the surface of a cell or virus that allows it to be identified. Pathogens have antigens that are recognised as foreign by the immune system.
What happens in the body in response to a pathogen during a specific immune response?
During a specific immune response the following events occur:
the body is exposed to a pathogen
the antigens of the pathogen trigger an immune response
antibodies are produced in response to the antigens
memory lymphocytes are also produced
memory lymphocytes provide future immunity to the pathogen
What is the role of a memory lymphocyte?
The role of a memory lymphocyte is to provide immunity if an individual comes into contact with the same pathogen again in the future. The presence of memory lymphocytes allows faster production of more antibodies after reinfection.
What is the role of antibodies in the immune response?
Antibodies attach to antigens on pathogens. This can prevent the pathogens from infecting host cells, and can make it easier for the immune system to destroy the pathogens.
What is vaccination?
Vaccination/immunisation introduces dead or inactive pathogens into the body to induce immunity.
What role does the immune system play in vaccination?
The immune system recognises the antigens in a vaccine and produces specific antibodies, as well as memory lymphocytes.
How does vaccination lead to long-term immunity?
Vaccination leads to long-term immunity because when someone is infected again by the same pathogen, memory lymphocytes are activated and the immune system quickly produces the correct antibodies.
True or False?
Vaccines increase the likelihood that a pathogen will spread.
False.
Vaccinating a large proportion of a population reduces the likelihood that a pathogen will spread; this is because most people in the population will be immune.
How does herd immunity help to prevent the spready of disease?
Herd immunity is achieved when a large proportion of the population is vaccinated. When herd immunity is achieved:
vaccinated people cannot spread the disease
the disease cannot spread to vaccinated people
levels of disease will be low enough in a vaccinated population to protect those who cannot be vaccinated
What are some disadvantages of vaccination?
Disadvantages of vaccination include:
pathogenic mutations can change the antigens, meaning that the immune system no longer recognises the pathogen and a new vaccine is needed
vaccination doesn't always give full immunity
side-effects of vaccinations can reduce the uptake in the population