How are arteries and veins different

The main difference between arteries and veins is the job that they do. 

Arteries carry oxygenated blood away from the heart to the body, and veins carry oxygen-poor blood back from the body to the heart. Your body also contains other, smaller blood vessels.

The chief difference between arteries and veins is the job that they do. Arteries carry oxygenated blood away from the heart to the body, and veins carry oxygen-poor blood back from the body to the heart. Your body also contains other, smaller blood vessels.

In a forest, there would probably be a deer, and a deer tick. The tick will latch onto the deer's skin, bury its head in the flesh and suck its blood. This would be an example of parasitism because one is benefiting (the tick) and the other is harmed (the deer).
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