4.1 Flashcards
What is a pathogen?
a microorganism that causes disease
What kingdom do bacteria belong to?
prokaryotae
How do fungi reproduce (general)
Fungus lives on skin and forms mycelium which grow under skin and form hyphae. These hyphae grow to the surface of the skin and release spores
What are the two main types of pathogen transmission?
direct and indirect
Define direct transmission
When a host transmits a pathogen to a new host with no intermediate.
Define indirect transmission
When a pathogen is transmitted from a host to a new host via a vector
What is a vector?
an organism that carries a pathogen from one host to another
What are the types of direct transmission?
- physical
- faecal-oral
- droplet infection
- transmission by spores
What is a passive plant defense?
Defences present before infection, role is to prevent entry and spread of pathogen. Passive defenses are chemical or physical barriers.
Name the physical defences
- Cellulose cell wall
- Lignin thickening of walls (waterproof and completely indigestible)
- waxy cuticle (stops water collecting on leaves as pathogens collect in water)
- Bark
- Stomatal closure when pathogens are detected
- Callose (large polysaccharide deposited in sieve tubes at the end of growing season. It’s deposited around the seive plates, blocking flow, stops transport of pathogens)
- Tylose (balloon-like swelling in xylem vessels- plugs it)
Name the passive chemical defenses
Terpenes and tannins
Why don’t plants produce loads of chemicals prior to an infection?
Requires a lot of energy
Name the active defenses in plants
- Thicken cell walls with additional cellulose
- Deposit callose between cell wall and cell membrane (callose is a polysaccharide that stop pathogens invading cells) strengthens cell walls and blocks plasmodesmata
- Oxidative bursts produce highly reactive oxygen that can kill cells of invading organisms
Name the chemicals produced in the active plant defence
- Terpenoids
- Phenols
- alkaloids
- defensive proteins
- hydrolytic enzymes
What is the acronym to remeber the chemical defences of plants?
Terrible (terpenoids)
Feelings (phenol)
Always (alkaloids
Dampen (defensive proteins)
Hope (hydrolytic enzymes)
What is necrosis?
Deliberate cell suicide where a few cells are sacrificed to save the plant as dead cells will limit pathogens access to water.
What is a canker?
A sunken necrotic lesion in trees that kills cambium tissue
Are primary defences specific or non-specific? Why?
non-specific because they prevent the entry of pathogens
Name the primary defences
Skin
Blood clotting
Mucous membranes
Coughing and sneezing
Inflammation
How does skin act as a primary defence?
keratinisation:
- Keratinocytes (produced by mitosis of basal epidermis) on epidermis migrate up to surface
- As they migrate and dry out, cytoplasm is replaced by keratin.
- Keratin acts as barrier to pathogens
how does blood clotting act as a primary defence?
- Platelets release substances that trigger an enzyme cascade
- This results in the production of fribrin
- Fibrin forms a mesh and traps platelets, forming a clot
- The clot dries and forms a scab
- Stem cells divide via mitosis and new cells go to edges of scab and draw it inwards
How do mucous membranes act as a primary defence?
- Goblet cells secrete mucous
- Musous traps pathogens
- Cilliated epithelial cells waft pathogen to top of trachea where it enters oesophagus
- Swallowed and digested
How is coughing and sneezing a primary defence?
Expulsive reflex
How does inflammation work?
- Pathogen invasion detected by mast cels
- Release histamines (cell signalling substances)
- Histamines cause vasodilation, more blood (oxygen and white blood cells to site)
- ## Causes excess tissue fluid (swelling)
What is an antigen-presenting cell?
A cell that isolates the antigen from the pathogen and places it onto its own plasma membrane to become recognisable to other immune cells
What is clonal selection?
A selection of B and T cells that are specific to the antigen
What are cytokines?
Cell signalling molecules that stimulate an immune response
What is a neutrophil?
WBC that engulfs foreign matter and traps it in a phagosome and fuses with a lysosome
What are opsonins?
Proteins that bind to antigens so that phagocytes can bind.
What does a neutrophil look like? How does it work?
multi-lobed nucleus
they bind to opsonins, engulf pathogens by trapping them in a phagosome, lysosomes fuse with the phagosomes and the pathogen is digested.
Where a macrophages made and stored?
Made: Bone marrow
Stored: lymph nodes
What do macrophages do?
Ingest pathogens and become antigen presenting cells
What is the point of antigen presenting cells?
They move round the body where they can come into contact with T and B lymphocytes.
There may only be one B or T lymphocyte that can recognise the specific ntigen so increasing the number of antigens can increase chances of coming into contact
What is the activation of B and T lymphocytes called?
Clonal selection
List three types of cell signalling in the specific immune response
macrophages: release monokines that attract neurtophils and cause B cells to differentiate and release antibodies
t cells and macrophages release interleukins: stimulate clonal expansion
Many cells release interferon: Inhibits virus replication
Describe the process of the specific immune response:
- Pathogen invates
- Macrophage ingests pathogen to become APC
- Helper T cell releases interleukins to trigger B cells
- Clonal expansion (stimulates by interleukins): mitosis to form plasma and memory cells
- Plasma cells: secrete specific antibodies, transported by the lymph, and form antigen-antibody complexes
- Meomry B cells: stay in body for years constantly secreteing antibodies
Role of T memory cells?
Provide long term immunity
Role of T regulator cells?
Shut down immune response after pathogen successfully removed, also involved in creating autoimmunity
Role of T helper cells?
release cytokines, stimulating B cells to develop and stimulating phagocytosis in phagocytes
Role of T killer cells?
Attack and kill host cells that display foreign antigens
Role of plasma cells?
Circulate in blood, manufacturing and releasing antibodies
Role of B memory cells?
Remain in the body for multiple years and act as immunological memory
Role of opsonins?
bind to pathogens and allow anitibodies to bind (act as binding site to phagocytic cells)
Role of agglutinins?
Can bind to 2 pathogens and agglutinate them, its third site allows the stimulation of phagocytosis
Role of antitoxins?
Bind to toxins and render them harmless
Describing those primary/secondary response graphs…
- takes a few days to produce enough antibodies to kill infection successfully
- seconday immune response is faster next time as B and T memory cells recognise pathogen and can act much more quickly to produce antibodies (faster and higher concentration)
What is active immunity?
When the immune system is activated and manufactures its own antibodies
What is artificial immunity?
immunity achieved as a result of medical intervention
What is an epidemic?
Rapid spread of disease across high population
What is natural immunity?
Immunity achieved through normal life processes
What is passive immunity?
When antibodies are passed to an individual through breastfeeding or innoculation
