Binary Fission
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of prokaryotic cell structure and mitosis. You can test your knowledge on these below.
What are two structural differences between prokaryotic and eukaryotic cells?
- Prokaryotic cells lack a nucleus / mitochondria while eukaryotic cells have a nucleus / mitochondria.
- Prokaryotic cells have only smaller (70S) ribosomes, whereas eukaryotic cells have larger (80S) ribosomes (and 70S ribosomes in mitochondria/ chloroplasts).
State the four stages of mitosis?
Prophase - Metaphase - Anaphase - Telophase
What are three structural differences between prokaryotic and eukaryotic DNA?
- Prokaryotic DNA is circular whereas eukaryotic DNA is linear.
- Prokaryotic DNA is not associated with histone proteins whereas eukaryotic DNA is.
- Prokaryotic DNA does not contain introns (non-coding sections of DNA), whereas eukaryotic DNA does
Topic Explainer Video
Check out this @LauraDoesBiology video that explains binary fission or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Binary Fission in Bacteria
Definition:
Binary fission is the process by which prokaryotic cells, such as bacteria, divide to produce two genetically identical daughter cells.
Stages of Binary Fission
Replication of DNA
- The bacterial DNA (a single circular DNA molecule- called the nucleoid) is replicated.
- Any plasmids present also replicate.
Cell Growth
- The cell increases in size as the cytoplasm volume increases and ribosomes duplicate.
Separation of DNA
- The two copies of circular DNA move to opposite poles of the cell.
- The plasmids are separated between the two cells.
Cytokinesis (Cell Division)
- The cell membrane pinches inward, and a new cell wall forms between the two copies of DNA, producing two identical daughter cells.
Conditions Affecting the Rate of Binary Fission
- Temperature: Optimal temperature ensures rapid enzyme activity and division.
- Nutrient Availability: Sufficient resources (e.g., glucose, amino acids) are necessary for bacterial growth.
- pH: Extreme pH levels can denature bacterial enzymes, slowing division.
- Oxygen Availability: Aerobic bacteria require oxygen, while anaerobic bacteria do not.
Key Terms
- Binary Fission: A method of asexual reproduction in prokaryotic cells where one cell divides into two identical daughter cells.
- Plasmid: A small, circular piece of DNA found in bacteria that can carry additional genes (e.g., antibiotic resistance).
- Cytokinesis: The division of the cytoplasm to form two separate daughter cells.
- Generation Time: The time required for a bacterial population to double.
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Exam Tip
Do not confuse binary fission with mitosis-binary fission does not involve a spindle apparatus.
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A student is investigating bacterial growth. The bacteria have a mean division time of 20 minutes. If the student starts with 50 bacteria, how many will be present after 3 hours? (3 marks)
Step 1: Calculate the number of divisions:
- 3 hours = 180 minutes
- Number of divisions = 180 ÷ 20 = 9 divisions
Step 2: Use the formula:
- Final number of bacteria = Initial number × 2 number of divisions
- Final number = 50 × 29
- Final number = 50 × 512
- Final answer = 25,600 bacteria
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!