Answer:
Mechanical barriers — which include the skin , mucous membranes , and fluids such as tears and urine — physically block pathogens from entering the body. Chemical barriers — such as enzymes in sweat , saliva , and semen — kill pathogens on body surfaces.
I believe the answer is fish vertebrates. i hope this helped
To be honest, since we live on Earth (assuming you do as well), Earth is the easiest planet to study. We don't know much about the other planets because we've never been to any of them. I believe that the second easiest planet to study is either Uranus or Saturn.
Answer:Conservation biologists, philosophers, environmental ethicists, and others offer several key reasons to conserve biodiversity. One argument is that organisms have direct economic value for humans. We use plants and animals for medicines, food, clothes, building materials, recreation, and other luxuries and necessities. But what if an organism that is of no use to us for food or hides is screened for useful medicinal compounds and found to have none? Do we sanction its extermination? Why must a plant or animal be of direct economic benefit to humans to have worth? Economic value alone is not the only reason to preserve biodiversity.
Another reason often given…to conserve biodiversity is that organisms, as components of ecosystems, provide services, and their interactions with other organisms contribute to the overall healthy functioning of ecosystems… On a practical level, biologists want to know just how much the loss of a few species will reduce the quality of services within a specific ecosystem. Two schools of thought prevail.
