Hydrogen,ammonia,methane,water
Elements in the first row (hydrogen and helium) will have outer electrons in the first energy level. Their principal quantum number is 1. Elements in the second row (lithium through neon) will have valence electrons in the second energy level with a principal quantum number of 2.
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:
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