02 Barriers 2025

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What is the first line of defence?

Non-specific barriers that prevent pathogens from entering the body.

What are physical barriers in animals?

Structures that block pathogen entry, like skin, mucus, and cilia.

What are chemical barriers in animals?

Substances that destroy or inhibit pathogens, e.g. stomach acid, sweat, tears, and lysozymes.

What are microbiological barriers in animals?

Non-pathogenic microbes (normal flora) that outcompete pathogens for space and nutrients.

Give three examples of physical barriers in animals

Skin, mucous membranes, cilia in respiratory tract.

Give three examples of chemical barriers in animals

Stomach acid, lysozymes in tears/saliva, acidic vaginal secretions.

Give two examples of microbiota barriers

Gut bacteria, skin bacteria.

What is the role of normal flora in immunity?

They prevent the growth of harmful microbes by competing for space and resources.

What are physical barriers in plants?

Thick cell walls, waxy cuticle, bark, closing stomata.

What are chemical barriers in plants?

Toxins, enzymes, and antimicrobial compounds that kill or inhibit pathogens.

Example of a plant physical barrier

Waxy cuticle prevents waterborne pathogens entering leaves.

Example of a plant chemical defence

Saponins or defensins that disrupt pathogen cell membranes.

How do plants defend against pathogens?

Through pre-existing structural barriers (physical) and reactive chemicals (chemical).

Why are these barriers called non-specific?

They protect against all pathogens, not just specific ones.

What is the purpose of the first line of defence?

To stop pathogens before they can enter and infect the body or plant.