Question: which stage of the cell cycle is variable

title: Cell cycle
text: The first phase within interphase , from the end of the previous M phase until the beginning of DNA synthesis , is called G ( G indicating gap ) . It is also called the growth phase . During this phase , the biosynthetic activities of the cell , which are considerably slowed down during M phase , resume at a high rate . The duration of G is highly variable , even among different cells of the same species . In this phase , the cell increases its supply of proteins , increases the number of organelles ( such as mitochondria , ribosomes ) , and grows in size . In G phase , a cell has three options . ( 1 ) To continue cell cycle and enter S phase ( 2 ) Stop cell cycle and enter G phase for undergoing differentiation. ( 3 ) Get arrested in G phase hence it may enter G phase or re-enter cell cycle . The deciding factor is availability of nitrogens and storage of energy rich compounds at the deciding point called check point . This check point is called the restriction point or START and is regulated by G / S cyclins , which cause transition from G to S phase . Passage through the G check point commits the cell to division . S 

Answer: answer: The first phase within interphase , from the end of the previous M phase until the beginning of DNA synthesis , is called G ( G indicating gap ) .
The duration of G is highly variable , even among different cells of the same species .
answer: The duration of G (G indicating gap), the first phase within interphase, is highly variable, even among different cells of the same species.