Life is based on carbon; substances in organic chemistry where carbon is a key element is the organic chemistry analysis. The characteristics of carbon make it the cornerstone of organic molecules that make up living substances. Carbon can create really lengthy interlocking chains of C-C bonds. It helps carbon to form the foundation of carbon-containing organic compounds, the base of all established organic livelihoods.
When you heat something of cool it down you don't change the substance you might change the why is looks, but it is still the same substance. For example you cool water to 0 degrees Celsius it turns into ice but it still is two parts hydrogen and one part oxygen H2O. Physical changes will change state and/or form but it will still be what it originally was on the molecular level. Hope that helped.