Defend the following stetement: all compounds are substances, but not all substances are compounds

A compound is always a substance because it's made out of two or more atoms bonded together. Now a substance isn't always a compound because it takes two or more elements to create a compound in a chemical reaction, ans substances can contain only one element. In other words a substance can be constructed of one type of atom. Some substances that aren't compounds are: gold and baking soda.

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.