I think calcium but i could be wrong
Answer:
they give the lungs a really big surface area. they have moist, thin walls (just one cell thick) they have a lot of tiny blood vessels called capillaries.
The walls of the alveoli are only one cell thick. This makes the exchange surface very thin - shortening the diffusion distance across which gases have to move. Each alveolus is surrounded by blood capillaries which ensure a good blood supply.Adaptations of the alveoli:
Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance. Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface. Permeable walls - allow gases to pass through.
Explanation:
Have great day
Answer: Human evolution, the process by which human beings developed on Earth from now-extinct primates. Viewed biologically, we humans are Hono Sapines, a culture-bearing upright-walking species that lives on the ground and very likely first evolved in Africa about 315,000 years ago.
Support, Blood cell production, Protection
