The endocrine system is responsible for communication in the body using - electrical signals

chemical hormones.

soluble gases

digestive enzymes

What material does not melt at any temperature

You exhale co2 which is produced during cellular respiration.  co2 combines with the water in your blood's plasma to make up one half of the body's most important buffer pair, carbonic acid.  the more physical activity you engage in, the more co2 your body is producing.  you can see this by putting some of the cabbage indicator in a glass and then blowing bubbles into it through a straw.  can you see a change in the color of the indicator?

What is the value of the standard enthalpy of formation of an element in its most stable form?