First line of defence (component of the innate immune system, consisting of physical, chemical, and microbiological barriers to keep pathogens out of an organism)

Physical barriers

barriers that prevent or impede entry of pathogens

Chemical

barriers that inhibit the growth or development of pathogens and/or act to destroy pathogens

Microbiological

the presence of normal flora (non-pathogenic bacteria) in the body that can prevent the growth of pathogen microorganisms as they compete for space and resources

Physical Barriers in Plants

• thick bark

• maxy cuticles of leaves

• formation of galls to prevent spread of infection

• presence of thorns to deter insects and grazers

• closing of stomata to prevent pathogen invasion during CO2 uptake

Chemical Barriers in Plants

• defensins; peptides that are toxic to microbes and fungi

• oxalic acid; a substance that is toxic if ingested

• glucanases; defend plants against fungi

Physical barriers in Animals

• intact skin and surfaces between external and internal environments

• mucous secretions and/or hairs in the respiratory tract that trap organisms

• cilia that sweep organisms away from airways and into the throat where they are swallowed and destroyed by the gastrointestinal tract

Chemical barriers in Animals

• presence of lysozyme enzymes in tears and saliva that destroy bacterial cell walls

• acidic sweat that destroys pathogens growing on the surface of the body

• stomach acid that destroys pathogens that have been swallowed

• antibacterial compounds in earwax

Microbiological barriers in Animals

• presence of bacteria on skin, lower gastrointestinal tract, and vagina