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Flashcards in B6.3 (2) Deck (46)
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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)


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



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

- 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 = clot

- clot hardens to form a scab


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

- 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


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