What system is made of the urchin's stomach and intestines that allow the urchin to absorb important nutrients?

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?

What tool do geneticists use to predict the outcome of genetic crosses? a.karyotype b.punnett square c.centrifuge

Everything in the universe originated from a single point. how was it possible for everything in the universe to have occupied a single point in space?