5 2 defence against disease

Physical defences are physical features of a plant that prevent invasion of pathogens, e.g.:

True. Bark is tough and so provides a barrier to pathogens and other threats.

False. A thick waxy cuticle is a physical defence designed to deter microorganisms.

Chemical defences in plants include:

True. Some chemical defences can be used to treat human diseases or relieve symptoms, e.g. aspirin from willow trees and digitalis from foxgloves.

Symptoms that indicate disease in plants might include:

Methods that can be used to identify and diagnose plant disease in the field include:

Lab procedures that can be used to detect and identify plant disease include:

Mucus traps pathogens, dirt and dust within airways. Cilia then beat/waft to move the mucus up and out of the trachea.

Skin is a physical barrier that prevents pathogens from entering the body.

True. The stomach contains hydrochloric acid which is a chemical defence mechanism that destroys many 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.

Hydrochloric acid protects the body from pathogens as it is a strong acid that can kill pathogens that have been swallowed.

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.

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.

During a specific immune response the following events occur:

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.

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.

Vaccination/immunisation introduces dead or inactive pathogens into the body to induce immunity.

The immune system recognises the antigens in a vaccine and produces specific antibodies, as well as memory lymphocytes.

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.

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.

Herd immunity is achieved when a large proportion of the population is vaccinated. When herd immunity is achieved:

Disadvantages of vaccination include: