12. Binary Fission

Binary fission is the process by which prokaryotic organisms, such as bacteria, divide and reproduce. Because bacteria are single-celled, this process serves as both cell division and asexual reproduction.

1. How Binary Fission Works

Before a bacterial cell can divide, it must prepare by growing in size and replicating its genetic material.

1. Replication: The cell replicates its large circular strand of DNA and its smaller plasmids.

2. Migration: The two large circular DNA strands move to opposite ends (poles) of the cell.

3. Plasmid Distribution: Plasmids are distributed randomly; one daughter cell may end up with more than the other.

4. Division: The cytoplasm begins to divide, and a new cell wall forms down the middle.

5. Separation: The two halves pull apart, resulting in two new bacterial cells.

2. Conditions for Growth

The speed of division depends on the environment. Bacteria divide most rapidly in "optimal" conditions, which include:

• Warm temperatures

• Moist environments

• Plenty of available nutrients

If these conditions are not met, bacteria will divide much more slowly or stop dividing entirely.

3. Calculating Bacterial Growth

Bacterial populations grow exponentially because the number of cells doubles with every division cycle.

Key Terms

• Mean Division Time: The average time it takes for one bacterial cell to divide into two.

The Calculation Process

1. Find the number of divisions: Divide the total time by the mean division time. (Ensure both are in the same units, usually minutes).

2. Calculate the total cells: Use the formula:

   $\text{Starting number of cells} \times 2^{n}$

   (where n is the number of division cycles).

Example Calculation

Question: A cell divides every 30 minutes. How many cells are produced after 3 hours?

• Step 1: 3 hours = 180 minutes.

• Step 2: 180\30 = 6 divisions.

• Step 3: 1 x 2⁶ = 64 cells.

4. Summary: Binary Fission vs. Mitosis