Not sure if I'm correct but my best guess is the cell membrane seeing as it surrounds the cell itself and is responsible for allowing certain molecules to diffuse in or out of the cell. Good Luck! :)
Answer:
B) cAMP
Explanation:
Phosphodiesterase is an enzyme that breaks a phosphodiester bond, for example in molecules such as cAMP and cGMP. So, phosphodiestarases are are regulators of signal transduction: regulate the duration of signaling pathway.
Caffeine is central-nervous-system stimulant and the mechanisms of its action usually are: mobilization of intracellular calcium or inhibition of specific phosphodiesterases.
Gas exchange occurs in the alveoli of the lungs and each is made from a single layer of flat cells, Many alveoli in the lungs, so a large surface area for exchangement of C02 and O2. They are surrounded by a network of capillaries and oxygen diffuses out of them via the alveolar epithelium to the hemoglobin.
Hope this helps
This indicator is an estimate of the amount of space on the earth that an individual uses in order to survive using existing technology. This space includes the biologically productive land and water area that produces the resources consumed by that individual such as food, water, energy, clothing, and building materials. It also includes the amount of land and water required to assimilate the wastes generated by that person. In other words, the ecological footprint measures a person's demand on the bio-capacity of the Earth.
