Defence Against Disease Flashcards
All 29 cards in this deck
What is the leaf cuticle and how does it defend a plant?
A waxy layer covering the leaf surface; it is a physical barrier that stops pathogens reaching the cells underneath.
How does the plant cell wall act as a defence against pathogens?
It is a tough cellulose layer around each cell that pathogens cannot easily penetrate.
Name two types of chemical that plants produce to defend themselves.
Antibacterial (antimicrobial) chemicals, and poisons/toxins that deter herbivores and pests.
Give two plant chemicals used as human medicines and what they are used for.
Aspirin (from willow bark) to relieve pain and fever; quinine (from cinchona bark) to treat malaria.
True or false? The waxy cuticle defends a leaf by killing pathogens that land on it.
False. It is a physical barrier — it stops pathogens entering, it does not kill them.
True or false? Some chemicals plants make to defend themselves are used to treat human diseases.
True. e.g. aspirin from willow bark relieves pain.
Name three ways a plant disease can be detected and identified in the field.
Observing visible symptoms, distribution analysis of affected plants, and eliminating possible environmental causes.
What is distribution analysis in the detection of plant disease?
Looking at where the affected plants are: spread outwards from one point suggests an infectious pathogen, while even damage across a whole area suggests an environmental cause.
Give three visible symptoms that suggest a plant is diseased.
Stunted growth, spots or discolouration on leaves, rotting/malformed stems or leaves (also visible pests).
Name two laboratory diagnostic tests used to identify a plant pathogen.
DNA analysis (e.g. PCR) of the pathogen's genetic material, and antibody test kits (monoclonal antibodies) that detect the pathogen's antigens.
True or false? Yellow leaves on a plant always mean it has been infected by a pathogen.
False. Environmental causes such as mineral deficiency or lack of water must be eliminated first.
What are the steps to work out the cause of disease in a crop in the field?
e.g. patches of wheat with yellow, spotted leaves
- Observe the visible symptoms: yellowing and leaf spots.
- Eliminate environmental causes: check minerals and water supply.
- Analyse the distribution and send a sample for lab diagnostic testing: spreading patches suggest a pathogen.
How does the skin prevent pathogens entering the body?
It is a physical barrier of tough, dead keratinised cells covering the body surface.
What is the role of mucus in the airways?
It is sticky and traps pathogens and dust before they reach the lungs.
What is the role of cilia in the trachea and bronchi?
Tiny hairs that beat to waft mucus (with trapped pathogens) up to the throat, where it is swallowed.
Where are lysozymes found in the body and what do they do?
In tears, saliva and mucus; they are enzymes that break down bacterial cell walls, killing the bacteria.
How does hydrochloric acid in the stomach defend against disease?
Its very low pH kills pathogens in food and in swallowed mucus by denaturing their enzymes and proteins.
What is an antigen?
A molecule (usually a protein) on the surface of a pathogen or cell that is recognised as foreign by the immune system.
What is an antibody and which cells produce it?
A protein that binds to a specific antigen, marking the pathogen for destruction; produced by lymphocytes (white blood cells).
True or false? One type of antibody can bind to any type of antigen.
False. Each antibody is specific — its shape is complementary to one antigen only.
What are memory lymphocytes and what do they do?
Lymphocytes that stay in the blood after an infection; if the same antigen returns they rapidly produce large amounts of antibody.
On a graph of antibody concentration against time, what two features show the secondary response to the same antigen?
Antibodies are produced sooner (shorter delay) and reach a much higher concentration than in the primary response.
What are the steps of the specific immune response?
e.g. a bacterium enters the blood
- Exposure to the pathogen: lymphocytes recognise its antigens as foreign.
- The antigens trigger an immune response: lymphocytes divide and produce antibodies specific to that antigen.
- Memory lymphocytes are also produced and remain in the blood.
What does a vaccine contain?
An inactive (dead or weakened) form of the pathogen, or its antigens.
How does immunisation make a person immune?
e.g. a measles vaccination
- The inactive pathogen carrying antigens is injected.
- The antigens trigger an immune response: lymphocytes produce antibodies.
- Memory lymphocytes remain, so a real infection gives a fast, large secondary response and the person does not become ill.
What is herd immunity?
When enough of a population is vaccinated that the pathogen cannot spread easily, so unvaccinated people are also protected.
Give two advantages of immunisation.
It prevents epidemics/can eradicate a disease, and it protects individuals (and vulnerable people) from serious illness through herd immunity.
Give two disadvantages of immunisation.
It does not always give immunity, and it can cause side effects such as swelling, or very rarely a severe reaction.
True or false? A vaccine can give you the disease it protects against.
False. The pathogen in the vaccine is inactive or weakened, so it cannot cause the disease.