Why is saliva a physiological barrier

Saliva provides an effective barrier against drying and helps limit the penetration of physical irritants, toxins and carcinogens in foods, beverages and tobacco. Saliva contains buffering systems that help neutralize acidic foods and drinks to protect teeth and soft oral tissues from acid attacks.

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I hope this helps!

not meh

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i don't believe the ocean is purple, but it might once have been:

as for the sky, according to nasa:

"sunlight reaches earth's atmosphere and is scattered in all directions by all the gases and particles in the air. blue light is scattered more than the other colors because it travels as shorter, smaller waves. this is why we see a blue sky most of the time."