5.4 physical, chemical & microbiota barriers

examples of physical, chemical & microbiological factors

physical factors: intact skin, mucous membranes, ear wax (cerumen)

chemical factors: sweat, tears, stomach acid

microbiological factors: normal flora (e. coli, lactobacillus acidophilus)

physical barriers in animals

intact skin

• epidermis of the skin consists of many layers of cells

• the outer layer is constantly being shed, preventing the entry of pathogens

mucous membranes

• consists of epithelial cells

• secrete mucous which can trap pathogens

ear wax (cerumen)

• reduced pathogenic access to the ear drum and ear canal

• protects ear from dust and other foreign particles

chemical barriers in animals

sweat, mucus, tears & saliva

• contains the enzyme lysozyme which kills pathogens

stomach acid

• contains digestive enzymes which kills pathogens that enter the digestive tract in food or water

microbiological barriers in animals

normal flora

• non-pathogenic bacteria found in particular regions of the body and inhibits the growth of pathogenic microbes

gut

• e. coli competes with pathogenic bacteria for resources

vagina

• lactobacillus acidophilus produces lactic acid inhibiting pathogenic microbes

physical barriers in plants

cuticle

• waxy covering on leaves reduces water accumulation and helps prevent cells becoming infected

stomata

•  can be closed to prevent pathogens entering

• may be sunken and sit lower down, to further protect the plant

cell wall

• cellulose cell wall can help protect cells from infection from viruses

chemical barriers in plants

saponin

• plant proteins that disrupt bacterial and fungal cell membranes

caffeine

• toxic to fungi and insects

the secretion of a toxin or an odour that is harmful or unfavourable to pathogens

the production of enzymes that affect pathogen functioning