Notes on 2.2 Bacterial Cells
Bacterial Cell Structure:
• Bacterial cells, or prokaryotic cells, are distinct from animal and plant cells (eukaryotic
cells).
• Cell Wall: Unlike plant cell walls which are made of cellulose, bacterial cell walls serve
a similar function in providing support and preventing the cell from bursting under
osmotic pressure but are made from different materials (like peptidoglycan in many
bacteria).
• Cell Membrane: Just like in other cells, the bacterial cell membrane is partially
permeable, controlling the influx and efflux of substances.
• Cytoplasm: Contains all the enzymes and substances necessary for metabolic
reactions, excluding mitochondria or chloroplasts.
• Ribosomes: Present for protein synthesis, similar to those in eukaryotic cells but
slightly smaller (70S ribosomes).
Genetic Material:
• Nucleoid: Bacteria do not have a nucleus; instead, their DNA is organized in a circular
chromosome located in a region called the nucleoid.
• Plasmids: Bacteria may also contain plasmids, which are small rings of DNA that can
be used in genetic engineering.
Reproduction:
• Bacteria reproduce through binary fission, a form of asexual reproduction where one
cell divides into two identical cells, as seen in the electron microscope image of
Enterococcus faecalis.
Comparison with Eukaryotic Cells:
• Nucleus: Absent in bacteria, which distinguishes them fundamentally from plant and
animal cells.
• Organelles: Lack membrane-bound organelles like mitochondria and chloroplasts.
• Size: Generally smaller than eukaryotic cells.
Multiple Choice Questions
1. Which component is unique to bacterial cells compared to plant and animal cells?
• A) Nucleus
• B) Cell wall made of cellulose
• C) Cell membrane
• D) Circular DNA
2. What is the function of the cell wall in bacterial cells?
• A) Photosynthesis
• B) Protein synthesis
• C) Protecting the cell and preventing bursting
• D) Storing genetic information
3. Which of the following best describes bacterial ribosomes?
• A) They are larger than those in eukaryotic cells.
• B) They are the same as in plant cells.
•
C) They are smaller than those in eukaryotic cells.
• D) They do not exist in bacterial cells.
4. Bacterial cells reproduce by:
• A) Sexual reproduction
• B) Binary fission
• C) Budding
• D) Spore formation
5. What are plasmids?
• A) The main chromosomes of bacteria
• B) Small, circular pieces of DNA used in genetic engineering
• C) Organelles that produce energy
• D) Structures that store nutrients
True or False
6. Bacterial cells have a nucleus. (True/False)
7. Bacterial cell walls are made of cellulose. (True/False)
8. Cytoplasm in bacterial cells contains mitochondria. (True/False)
9. All bacteria have the same shape and size. (True/False)
10. Bacterial cells can contain more than one circular DNA molecule. (True/False)
Short Answer Questions
11. Explain how the absence of a nucleus in bacterial cells affects their function and
structure.
12. Describe the role of plasmids in bacterial cells and their importance in
biotechnology.
13. Compare and contrast the cell walls of bacterial cells and plant cells.
Diagram Labeling
14. Label the parts of a bacterial cell on a provided diagram. Include the cell wall,
cell membrane, cytoplasm, ribosomes, and DNA.
Answers to Exercises on Bacterial Cells
Multiple Choice Questions
1. Which component is unique to bacterial cells compared to plant and animal cells?
• D) Circular DNA
2. What is the function of the cell wall in bacterial cells?
• C) Protecting the cell and preventing bursting
3. Which of the following best describes bacterial ribosomes?
• C) They are smaller than those in eukaryotic cells.
4. Bacterial cells reproduce by:
• B) Binary fission
5. What are plasmids?
• B) Small, circular pieces of DNA used in genetic engineering
True or False
6. Bacterial cells have a nucleus. (False)
7. Bacterial cell walls are made of cellulose. (False)
8. Cytoplasm in bacterial cells contains mitochondria. (False)
9. All bacteria have the same shape and size. (False)
10. Bacterial cells can contain more than one circular DNA molecule. (True)
Short Answer Questions
11. Explain how the absence of a nucleus in bacterial cells affects their function and
structure.
• Bacterial cells lack a nucleus, meaning their DNA is not enclosed within a membrane
but rather is free in the cytoplasm. This setup, termed prokaryotic, allows for quicker
transcription and translation processes as there is no nuclear barrier. However, it also
exposes the genetic material to more potential damage from environmental factors.
12. Describe the role of plasmids in bacterial cells and their importance in
biotechnology.
• Plasmids are small, circular DNA molecules that exist independently of the main
bacterial chromosome. They often contain genes that can confer advantageous traits
such as antibiotic resistance. In biotechnology, plasmids are used as vectors to insert
new genes into bacteria, facilitating the production of proteins, vaccines, and other
useful substances.
13. Compare and contrast the cell walls of bacterial cells and plant cells.
• Bacterial cell walls are primarily composed of peptidoglycan, which is different from
the cellulose-based cell walls of plant cells. While both provide structural support and
protection, the chemical differences make bacterial walls a target for antibiotics, which
disrupt wall synthesis.
Diagram Labeling
14. Label the parts of a bacterial cell on a provided diagram.
• Cell wall: Surrounds the cell, providing structural support and protection.
• Cell membrane: Located just inside the cell wall, controls the passage of substances
in and out of the cell.
• Cytoplasm: The gel-like substance inside the cell containing all cell components and
molecules.
• Ribosomes: Tiny structures in the cytoplasm where proteins are synthesized.
• DNA: Typically a single circular chromosome located in the cytoplasm, contains
genetic information.