Binary fission in bacteria

In a nutshell

Prokaryotic cells can reproduce using binary fission, which is a type of simple cell division. This summary explores binary fission and how to calculate the mean division time.

Binary fission

Binary fission enables prokaryotic cells to replicate.

Biology; Cell biology; KS4 Year 10; Binary fission in bacteria

1.	The circular DNA and plasmids inside the cell replicate.
2.	The cell increases in size and the circular DNA strands move to opposite sides (poles) of the cell.
3.	The cytoplasm of the cell starts to divide into two and new cell walls start to form.
4.	The cytoplasm fully divides and two new daughter cells are produced.

In each of the new daughter cells, there is one copy of the circular DNA and a variable number of copies of the plasmids.

Conditions for replication

The best conditions for replication involve a warm environment and plenty of nutrients. If bacteria are in their ideal conditions, they can divide very quickly. However, if the conditions become less ideal, the cells will not be able to divide and eventually begin to die.

Mean division time

Definition

The mean division time is the average amount of time taken for one bacterial cell to divide into two.

In order to calculate the total number of bacteria in a population, the mean division time should be used. By knowing the mean division time of a cell, the number of times the cell has divided in a certain amount of time can be calculated. Therefore, one can work out the number of cells that have been produced in that specific time.

Procedure

1.	Convert all times into the same units.
2.	Divide the total time by the mean division time to get the number of divisions.
3.	Calculate $2^x$ , $x$ being the total number of divisions.
4.	This is the total number of cells in the population.

Example

A bacterial cell has a mean division time of $40\space minutes$ . How many cells will it have produced after $2\space hours$ ?

Convert $2\ hours$ into $minutes$ :

$2\ hrs \times 60 = 120\space minutes$

Calculate the amount of divisions that occur in $120\ minutes$ if the division time is $40\ minutes$ :

$\frac{120}{40} = 3\space divisions$

Calculate the number of cells following the calculated number of divisions:

$2^3 = 2 \times 2 \times 2 = \underline{8\space cells}$

$\underline{Therefore,\ after\ 2\ hours\, there\ will\ be\ 8\ cells.}$