f) Cellular Response
Viruses


Structure
o Very small
o Contain DNA or RNA
o Genetic material (nucleic acid) surrounded by protein coat
o Reproduce inside cells as cannot reproduce without host cell
o Alter host cell metabolism so they can replicate viral DNA/RNA
o Release in large numbers from host cell
Virus Production
o Virus attaches to host cell
o Viral nucleic acid enters cell and takes control of cell metabolism
o Copies of viral nucleic acid made using host cells nucleotides, enzymes and ATP
o Protein coat made
o Virus particles assembled
o Virus particles released
Animal Defences

Phagocytosis
o Carried out by phagocytes
o Non-specific defence
o Bacteria/virus engulfed by phagocyte into vesicle
o Lysosomes fuse to vesicle and release enzymes into vesicle
o Bacteria/virus digested by enzymes
Antigen
Phagocytotic WBC

WBC engulfs
antigen trapping
it in a vacuole
Lysosomes containing
powerful protein digesting
enzymes fuse with the vacuole
Enzymes
released into the
vacuole
Antigen digested
Digested parts diffuses
into cytoplasm
Antibody production
o antibodies are made of protein
o produced by lymphocytes
o production stimulated by non-self antigens/proteins
o antibodies are specific to the shape of antigens
o antibody renders bacteria/virus harmless by combining with antigen
o Antibodies are produced from first contact with bacteria/virus
 Production is slower and lower in volume
o Second contact is faster, higher in volume and lasts longer

Transplant surgery
o transplanted tissues have foreign antigens and are recognised as non-self
o antibodies made against transplant and tissue is rejected
o risk of rejection is reduced by suppressors/drugs which suppress immune system
Plant defences




Toxic chemicals
Give an unpleasant taste which discourages animals from eating the plant
o tannins
o cyanide
o nicotine
Barrier substances
Isolate injured area to prevent spread of disease
o Resins