Most cells have: 1  A nucleus – controlling the activity of the cell. 2  All cells have these at one point. 3  Cytoplasm – where chemical reactions occur. 4  Inside the cytoplasm are enzymes which speed up these reactions. 5  A cell membrane – to control the passage of substances in and out of the cell.ost cells have: 1  A nucleus – controlling the activity of the cell. 2  Cytoplasm – where chemical reactions occur. 3  A cell membrane – to control the passage of substances in and out of the cell. 4  A Mitochondria which is where the energy is released from.