B6.3 (2) Flashcards
b6.3.6 onwards
what is the purpose of the leaf cuticle?
waxy outer layer which prevents pathogens passing through, and water from collecting on the leaf surface
why is it important that leaf cuticle prevents pathogens passing through?
- so pathogens cannot have direct contact with epidermal cells
- less chance of infection
how does the leaf cuticle prevent water collecting on the surface? (and why is that important)
- is hydrophobic
- as fungal pathogens need standing water for spore germination
define a cell wall (in terms of plant defenses)
structural barrier made of cellulose, which gives strength and flexibility
cell walls ….. …. with other …. which forms a type of …. that helps ……. neighbouring ……. together
cross link
fibres (eg. peptin)
gel
cement
cells
cell walls cross link with other fibres which forms a type of gell that helps cement neighbouring cells together
what does the cell wall contain?
a variety of chemical defences which activate rapidly when the cell detects pathogens
give 4 examples of physical plant defences
- spike
- thorn
- stinging cells
- bark
difference between chemical and physical defences?
physical defences prevent microorganisms from entering
chemical defences are substances secreted by the plant that kill microorganisms
how does bark act as a physical defence?
external layer of dead cells that forms a barrier against infection
give 5 examples of chemical defences in plants
- insect repellants
(repel insect vectors that carry disease) - insecticides (kill insects)
- antibacterial compounds
(kill bacteria) - antifungal compounds
(kill fungi) - cyanide (some plants make chemicals which break down to form cyanide when attacked) - TOXIC
describe two antibacterial compounds in more detail
- phenols (distrupt bacterium cell wall)
- defensins (distrupt cell membrane)
describe two antifungal compounds in more detail
- chitinases
(enzymes which break down chitin in fungal cell walls) - caffeine
(toxic to fungi and insects)
give two examples of insect repellants
- citronella
- pine resin
give an example of an insecticide
pyrethrins
what are the 4 main ways plant diseases can be detected and identified?
- observation
- microscopy
- DNA analysis
- identification of antigens
define the term diagnosis
correctly identifying the existence of a plant disease
how is observation used to identify plant diseases?
(give advantages and disadvantages)
- finding visual symptoms
adv - quick, cheap, easy
dis - similar symptoms for different diseases
(not accurate)
how is microscopy used to identify plant diseases?
identifying pathogen by looking at its shape
- electron gives better diagnosis than light
advantages and disadvantages of usinig microscopy to identify plant diseases?
adv - much more accurate
dis
- may be slower (sample must be given to lab)
- require equipment
downside of identifying plant diseases in the field?
only identified once symptoms are apparent (so plant is infected)
how is DNA analysis used to identify plant diseases?
idea that…
- each plant has a unique genome
- and a map of the genome is produced
- and then compared to known DNA profiles (to identify individual strains of the microorganism)
how is antigen identification used to identify plant diseases?
- detect antigens (proteins) found on the surface of pathogens
- through chemical analysis
- as specific antigens are found on specific pathogens
why are plant lab tests useful?
(and give one disadvantage)
can identify the pathogen before it causes significant damage to the crop
- but can be slow
what have scientists developed so that farmers can identify common pathogens?
diagnostic kits
give 5 non-specific defence systems of the human body against pathogens
- and briefly describe what each of them do
1) skin (a physical barrier)
- dry, dead outer cells are difficult for pathogens to penetrate
2) acid in stomach
- contains strong HCL acid (kills almost all pathogens - ie. from food/drink/mucus)
3) cilia and mucus in airways
- mucus trap smaller microorganisms
- cilia moves up to throat + swallowed
4) nasal hairs
- keep out dust + larger micro-organisms
5) tears
- contain lysozymes (destroy bacteria cell wall)
what are non-specific defense mechanisms in the body?
responses that prevent the entry of all microorganisms (and preventing them from causing disease)
what key feature does the skin have to kill pathogens?
produces antimicrobial secretions
what are platelets (and where are they made)?
- small fragementsof cells
- made in the bone marrow
- which help blood to clot
what do platelets do?
- change blood protein fibrinogen into fibrin
- to form a network of fibres in the cut
- which causes red blood cells to be trapped in fibres = this forms a blood clot
- clot hardens to form a scab - keeps skin clean and gives time to heal; in time, scab falls off
what is the role of the immune system when defending the human body against disease?
- destroys pathogens when they gain entry + the toxins they produce
- protect in case the same type of pathogen invades in future
what is the immune system’s main form of defence?
white blood cells
what are the two types of white blood cells and what does each one do?
Phagocytes - engulf micro-organisms
Lymphocytes - produces antitoxins and and antibodies
describe what a phagocyte does in more detail
- ingests pathogen
- and enzymes within it digest the micro-organism
IS NON-SPECIFIC (destroys all pathogens)
describe what a lymphocyte does in more detail
HAS 2 types of cells
- T cells and B cells
B CELLS - make antibodies and antitoxins
- remember the correct antiBODY for the specific anitgen
T CELLS - remember the antigen (act as memory cells)
what can antibodies do?
- bind to pathogen’s antigen on surface
- ‘mark’ pathogen
- or make pathogen burst
- or make pathogens clump together (easier for phagocyte to find them)
what do antitoxins do?
bind to toxins released by the pathogen + neutralise it
what is the role of plasma cells? (and what kind of cells are they)
secrete large quantities of antibodies
- from B lymphocyte cells
why are there so many different kinds of T and B lymphocyte cells?
- each antibody binds to only one type of antigen (and one microorganism/pathogen)
- so every time a new type of pathogen enters, a different lymphocyte makes a new antibody to fight it
- so a new B cell is needed to make the antibody
what does it mean if the body is immune to a disease?
- body has antibodies to that disease
- and so if pathogen detected, it produces many antibodies fast enough that it kills pathogen before has time to develop unto an illness
define an antigen
a protein unique to a pathogen found on the cell surface/membrane
- which allows the body to recognise the pathogen
what is the key-word to describe lymphocytes?
SPECIFIC (responds to one pathogen only)
what is a primary response to a pathogen?
the reaction of the immune system when it first detects an antigen (antibody concentration rises slowly)
why is the secondary response different to the primary response?
- as the body still remembers the last
infection - so some antibodies may still be present
- memory cells are present from the last infection (can make antibodies fast)
what feature of platelets allow them to carry out their defence functions?
- proteins on surface that help them clump together to heal a would
- secrete proteins that result in a clotting cascade
if …. ….. defence systems do not work …… defence systems are used
such as ….. blood cells, ie. …. and …. cells
non-specific
specific
white
T and B
or lymphocyte/phagocyte
how are lymphocytes and phagocytes adapted to their function?
lymphocyte = large nucleus (to remember antibody to make)
phagocyte = small nucleus (large area to engulf pathogens)
- contain enzymes
- can change shape easily
how does a body clot using platelets
- clotting factors cause platelets to become sticky + adhere to the damaged region to form a plug
- clotting factors cause localised vasoconstriction to reduce blood flow
- clotting factors trigger the conversion of the inactive prothrombin into the activated thrombin
- thrombin then catalyses the conversion of the protein fibrinogen into an insoluble fibrous form called fibrin
- fibrin strands form a mesh of fibres around the platelet plug and trap cells = form a clot
- when the damaged areas is completely repaired = an enzyme PLASMIN is activated to dissolve the clot
physical features of a phagocyte
- multi-lobed nucleus
- granular cytoplasm
features of lymphocytes
- large round nucleus
- clear cytoplasm
how does lymphocytes work
- lymphocytes produce antibodies = which is y shaped proteins that is specific to antigens on the surface of the pathogen
- antibodies attach to the antigens + cause AGGLUTINATION = clumping together to prevent pathogenic cells from moving easily
- this secrets chemicals that signals to phagocytes that there are cells present and need to be destroyed
- lymphocytes also produce antitoxins to neutralise toxins released by pathogens
how does phagocytosis work
engulfing pathogens + and then making enzymes that digest them
what are antibodies
proteins found on the surface of lymphocytes
what are monoclonal antibodies
laboratory generated antibodies used in diagnostics and treatment
