For gas exchange to be efficient, the respiratory membrane must be a. at least 3 micrometers thick b.0.5 to 1 micrometer thick c. between 5 and 6 micrometers thick d. the thickness of the respiratory membrane is not important in the efficiency of gas exchange.

the correct answer is 4) heat and pressure

metamorphic rocks arise from transformation of existing rocks types, in a process called metamorphism. during metamorphism the original rock(prolith) change into metamorphic rock by heating (150-200c) and pressure of more than 1000 bar. the original rock can be sedimentary, igneous, or existing metamorphic rock.