How heroin affects function of synapes

The oxidizing agent our bodies use to obtain energy from food is oxygen (from the air). if you breathe 15 times a minute (at rest), taking in and exhaling 0.5 l of air with each breath, what volume of air do you breathe each day? air is 21% oxygen by volume. what volume of oxygen do you breathe each day?

How can scientists test their ideas about the origin of the universe if they can't physically interact with or study?

What must be true for natural selection to heppen