B6.3 (2) Flashcards
b6.3.6 onwards
what is the purpose of the leaf cuticle? (3)
- prevents uncontrolled water loss
- ensures water does not collect on the leaf so that microbes do not collect there (as it will be damp)
- physical barrier to prevent pathogens from entering leaf
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 and shape
- physical barrier preventing pathogens from entering
what does the cell wall contain?
a variety of chemical defences which activate rapidly when the cell detects pathogens
cellulose
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 types of chemical defences in plants
- insect repellants
(repel insect vectors that carry disease) - insecticides (kill insects)
- antibacterial compounds
(kill bacteria) - antifungal compounds
(kill fungi) - poisons
how do anti microbial substances protect a plant from pathogens?
may kill the pathogen or prevent it from reproducing
can plants produce anti-microbial substances?
yes
what are the 4 main ways plant diseases can be detected and identified?
- observation
- microscopy
- DNA analysis
- identification of antigens, using monoclonal antibodies
define the term diagnosis
correctly identifying the existence of disease in an organism
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? (in comparison to observation with naked eye)
adv - much more accurate
dis
- may be slower (sample must be given to lab)
- require equipment
downside of identifying plant diseases in the field?(visually/microscope)
only identified once symptoms are apparent (so plant is infected + may have spread)
how is DNA analysis used to identify plant diseases?
idea that…
- a map of the genome of the plant is produced
- can identify DNA of pathogen
- therefore can diagnose plant
how is antigen identification used to identify plant diseases?
- detect antigens (proteins) found on the surface of pathogens
- through chemical analysis which may use monoclonal antibodies
- 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 + expensive
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 features does the skin have to kill pathogens? (2)
- produces antimicrobial secretions (sweat)
- natural (not harmful) microorganisms which outcompete pathogens for resources
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? (and how do they do it) (4)
- 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 = clot
- clot hardens to form a scab
what is the role of the immune system when defending the human body against disease? (2)
- 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
- engulfs pathogen
- and enzymes within it digest the micro-organism
IS NON-SPECIFIC (destroys all pathogens)
describe what a lymphocyte does in more detail
Don’t need to know: HAS 2 types of cells
- T cells and B cells
Need to know: B CELLS - make antibodies and antitoxins
- remember the correct antiBODY for the specific anitgen
Don’t need to know: 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 in the immune system response
secrete large quantities of antibodies
- from B lymphocyte cells
Explain why there are so many different kinds of lymphocyte cells. (3)
- 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 cell found on the cell surface/membrane
- which allows the body to recognise the cell
what is the key-word to describe lymphocytes?
SPECIFIC (responds to one pathogen only)
what is a primary response to a pathogen? (definition)
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? (to the same pathogen)
- 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
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
