Cells are ok in liquid cultures, as long as the amount is right. The majority grows fine at 5% carbondioxide and for some types, 20% oxygen. Typicalls the cells are kept in wide surface containers instead of tubes, so there can be some gas exchange passively. If the volume is too large, it may be insufficient. But also if there's too little liquid medium, the nutrients get exhausted faster and cell waste piles up faster, which is toxic and will kill cells again. And one of the main wastes is carbondioxide again.