16. The main difference between normal and transformed cells
    (1) immortality and contact inhibition
    (2) shorter generation time and cell mobility
    (3) apoptosis and tumour suppressor gene hyper- function.
    (4) inactivation of oncogenes and shorter cell cycle duration

The main difference between normal and transformed cells is best described as:

(1) immortality and contact inhibition

Explanation:

• Immortality: Transformed (cancer) cells can divide indefinitely, escaping the normal cellular limits on division. Normal cells have a finite number of divisions before undergoing senescence.

• Contact inhibition: Normal cells exhibit contact inhibition, meaning they stop dividing when they come into contact with neighboring cells, maintaining tissue architecture. Transformed cells lose contact inhibition and continue to proliferate even when densely packed, leading to uncontrolled growth and tumor formation.

• Other aspects such as shorter generation time and increased mobility can be features of transformed cells but are not the primary defining difference in comparison to normal cells.

• Apoptosis and tumor suppressor gene hyper-function are typically reduced or lost in transformed cells, not increased.

• Inactivation of oncogenes is generally not seen in transformed cells; rather, oncogenes are often activated.