Question

If a cell divides once a day on average, what fraction of a confluent culture must be reseeded into a new culture vessel (same size) to achieve a confluent culture in 4 days.

Choices:

1/2 or

1/8 or

1/20

Answer 1

Answer - 1/20

Consider the cell occupy 100% confluency in the flask. And assume it is 100 cells in the flask to make 100% confluency.

If 1/2 confluency cells add to new flask 1/2 X 100 = 50 cells reseeded to the new flask. So doubling time 24 hr the next day itself it fully occupy the flask. 50 cells converted in to 100 cells. 1 day enough to acheive the confluency.

For 1/8 X 100 = 12.5 cells reseeded. After 1 day it becomes 25 cells. 2nd day become 50 cells and third day become 100 cells and acheive the confluency.

For 1/20X100 = 5 cells reseeded. First day 10 cells, 2nd day 20cells, 3rd day 40 cells and 4th day it becomes 80 cells to acheive the 80% of confluency in the flask.

So, the answer must be 1/20.