Why must all living things carry on respiration

To break down food molecules and turn it into energy.

Explanation:

All living organisms must carry on releasing the energy stored in food molecules through a chemical process known as the respiration.

The main purpose of respiration by the living things is to break down the sugar (glucose) and turn it into energy, in the form of ATP (adenosine triphosphate), which is then used to perform some essential activities of life.

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.