churn in American English. churnverb [ I/T ] [ I ] The water was churning and the boat was rocking. [ M ] The fish churned up the water when we threw them some food. [ T ] fig. Seeing the car ahead flip over churned his stomach.
The nucleus controls everything that happens in the cell. This means that it controls the chemical reactions that take place in both and animal and plant cells. Some organelles in the cell have their own job like mitochondria control the respiratory (for example).
The cell membrane controls what enters and leaves the cell, allowing the cell to absorb the oxygen and nutrients it needs to function and also protects the cell from most dangerous chemicals.