Fish poop.
Tropical white beaches get their pearly white color from the excrement of fish far off of the coast which eat coral and other things that reside on the ocean floor. When they eat they swallow some sand into their mouths as well, and process it with the food they just ate. Their stomachs can't really digest the sand, tiny minute rocks essentially, and thus turn their color white. Or the rock forming the sand can be naturally pigmented a whitish tone as well.
A double helix is <span>a pair of parallel helices intertwined about a common axis, especially that in the structure of the DNA molecule. or in other words a double spiral.</span>
Answer:
Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface. Permeable walls - allow gases to pass through. Extensive blood supply - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.
I believe the inability to make saliva would affect digestion drastically. The first phase in the process of digestion comes with saliva - it breaks down some substances in your mouth, because it contains amylase which helps during this process. If it weren't for saliva, you probably wouldn't even be able to swallow food - and even if you did, it would be almost impossible to break it down in your body.
