Download Cellular Defence Mechanisms

Cellular Defence Mechanisms
Chapter 11
Immune Response







Immunity – ability to resist infectious disease
Non-specific
e.g. phagocytosis
- provides a general protection
Specific
- specialised response against an infectious
agent
E.g. antibody production
Phagocytosis








‘Cell Eating’
Foreign bodies engulfed and destroyed
Carried out by phagocytes (white blood cells)
Phagocyte detects & moves towards chemicals released
by foreign body (e.g. bacteria)
Phagocyte adheres to bacterium & engulfs it into a
vacuole
Lysosomes fuse with this vacuole
Digestive enzymes released into vacuole – bacterium
digested
Dead bacteria & phagocytes often form pus
Specific immune response








Antigen – complex molecule (e.g. protein)
recognised as foreign
Recognised by lymphocytes
Lymphocytes stimulated to produce antibodies
- Y-shaped molecules
- each arm has receptor site specific to an
antigen
- when an antigen is recognised, it is locked
onto by an antibody
- receptor site & antigen fit like a ‘lock & key’
- antigen is rendered harmless
Immunological Memory











Primary Response
On first infection by a disease-causing organism
Body produces antibodies
Production is slow – illness usually occurs
Secondary Response
Re-exposure to an antigen
Antibody production is more rapid
Higher concentration of antibodies produced
High concentration maintained
Controlled by memory cells – specific to antigens from initial
exposure
- clone antibody forming lymphocytes
Types of specific immunity








Active Immunity
Organism produces it’s own antibodies
(i) Naturally acquired
- person is exposed to an antigen, suffers the
disease, & makes antibodies
- person is immune to future attacks
(ii) Artificially acquired
- person recieves a vaccine (e.g. polio vaccine)
- vaccines induce antibody production, but don’t
cause disease
Types of specific immunity









Passive Immunity
Ready-made antibodies passed into someone’s body
(i) Natural
- antibodies cross placenta/ in milk from mother to child
- provides short term protection
(ii) Artificial
- extracting antibodies from one organism, inserting into
another
E.g. horse to human
- short term effects
Transplant rejection






Recipient’s immune system often regards
transplanted tissue as foreign
Will try to destroy the tissue – tissue rejection
Chance of success increased by:
- tissue typing
- immunosuppressor drugs
Drugs can leave recipient succeptible to other
infections
Cellular Defence in plants




Plants attacked by micro-organisms &
herbivores
2 methods of defence:
- production of toxic compounds
- isolation of the problem
Plant defence – toxic compounds









Tannins
Acidic substances
Common in leaves, unripe fruit, seed coats etc.
Toxic by acting as enzyme inhibitors
Cyanide
- poison – blocks cytochrome system
- some plants (e.g. white clover) convert
glycoside (harmless) into cyanide
- these are cyanogenic plants
- not always effective
Plant defence – toxic compounds








Nicotine
- produced by root cells of tobacco plant
- then transported to leaves
- poisons herbivorous insects
- used as an insecticide
Phytoalexins
- released in response to fungal infections
- plant cell genes stimulated to synthesise
phytoalexins
Isolation of the problem












Insect galls
- swelling of plant tissue after parasite infection
- tannins often also produced
- extra layers and tannins form a protective barrier to isolate the
parasite
Resin
- sticky, acidic substance
- common in trees/shrubs (have resin canals)
- on infection, resin secretion increased
- resin flows through canals to site of injury
- resin floods spaces around area under attack
- can also block xylem/phloem
- pathogen is then isolated