Lungs serve the purpose of gas exchange. we inhale air, drawing in oxygen (o2) and exhale air, expelling carbon dioxide (co2). this is done across thin-walled pockets of cells called alveoli. because body cells consume o2 and generate co2, concentrations of co2 and o2 are higher and lower, respectively, at alveoli surfaces than they are in adjacent capillaries. both of these molecules are small, and freely pass through membrane bilayers. based on this information, the movement of o2 from the alveoli of the lungs into the bloodstream is an example of

This is referred to as gas exchange. The alveolar-capillary CO2 and O2 gradient drive diffusion of gasses across the alveoli membrane. Oxygen in the alveoli diffuses into capillaries where its concentration is low while carbon dioxide from the capillaries diffuse into the alveoli where its concentration is low.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.