Compare the movement of oxygen and carbon dioxide across the cell membrane

"As oxygen-rich (and carbon dioxide-poor) blood travels by a cell the oxygen diffuses through the cell membrane to the area of lower concentration inside the cell. ... Because the CO2 is of a higher concentration in the cell than in the blood passing by, this gas continually diffuses out of the cell."

the unequal cytoplasmic division that  results  in  one egg  and three polar bodies ensures that a fertilized  egg has  ample nutrients  forits journey  to  the uterus.