Why does our body need a defense system ?

Explanation:

You have external defense systems, which include your skin, tears, mucus, saliva, stomach acid, cilia (small hairs) and helpful bacteria. ... The skin stops pathogens from entering the blood, at least when you're not bleeding. The tears, mucus, and cilia trap them and help push them back out of your body.

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above statement is not a true statement about the open ocean because the open ocean has low levels of nutrients. most of the photosynthetic activity on earth occurs in the open ocean within the photic zone. organisms in the deep ocean are exposed to frigid temperatures and total darkness but it does not begin at the low-tide mark.