The exchange takes place in the millions of alveoli in the lungs and the capillaries that envelope them.
Answer: A community is all of the populations of different species that live in the same area and interact with one another. A community is composed of all of the biotic factors of an area. An ecosystem includes the living organisms (all the populations) in an area and the non-living aspects of the environment.
The work done is 137 joules.
Lifting opposes the acceleration of gravity, which is 9.8 m/sec/sec.
20 x 0.7 x 9.8 = 137 J (kg-m2/sec2)
