Identify the main gas that diffuses from the alveolus to the
capillary

In external respiration, oxygen diffuses across the respiratory membrane from the alveolus to the capillary, whereas carbon dioxide diffuses out of the capillary into the alveolus.

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.

when a reversible reaction is occurring in both directions at the same rate; the products and reactants do not change in concentration. a chemical reaction where the compound is broken into its constituent parts.