Prokaryotic Cells Explained for NEET | Easy Biology Notes
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| Labeled diagram of a prokaryotic cell showing nucleoid, plasmids, cell wall, and mesosome structure for NEET revision. |
1. Prokaryotes have a cell wall surrounding the cell membrane except in Mycoplasma.
- Most prokaryotic cells (bacteria) have a cell wall outside the plasma membrane.
- The cell wall gives shape and protection.
- Exception: does not have a cell wall.
NEET Point: Mycoplasma is the smallest living cell and lacks a cell wall.
2. The semi-fluid matrix filling the cell is the cytoplasm.
- The inside of the cell contains a jelly-like substance called cytoplasm.
- It contains enzymes, nutrients, ribosomes, and other materials.
- Many metabolic activities occur here.
3. There is no well-defined nucleus.
- Prokaryotic cells do not have a true nucleus.
- Their genetic material is not enclosed inside a nuclear membrane.
NEET Point: Prokaryotes have a nucleoid, not a true nucleus.
4. The genetic material is basically naked, not enveloped by a nuclear membrane.
- DNA is directly present in the cytoplasm.
- It is called naked DNA because no nuclear membrane surrounds it.
5. In addition to genomic DNA, many bacteria have small circular DNA outside the genomic DNA.
- Bacteria usually have one main circular chromosome.
- Apart from this, extra small circular DNA molecules may be present.
6. These smaller DNA are called plasmids.
- Small circular DNA molecules are known as plasmids.
- They replicate independently of the bacterial chromosome.
Definition: Plasmid = Extra-chromosomal circular DNA.
7. The plasmid DNA confers certain unique phenotypic characters.
- Plasmids provide special characteristics to bacteria.
- These characteristics help bacteria survive in different environments.
8. One such character is resistance to antibiotics.
- Some plasmids carry genes that make bacteria resistant to antibiotics.
- These genes are called R-genes (Resistance genes).
NEET Point: Antibiotic resistance is often due to plasmids.
9. Plasmid DNA is used to monitor bacterial transformation with foreign DNA.
- Scientists use plasmids in genetic engineering.
- Foreign genes can be inserted into plasmids.
- Plasmids act as vectors to transfer genes into bacteria.
10. Nuclear membrane is found in eukaryotes.
- A nuclear membrane surrounds the nucleus in eukaryotic cells.
- It separates DNA from cytoplasm.
Examples of Eukaryotes:
- Plants
- Animals
- Fungi
- Protists
11. No organelles like those in eukaryotes are found in prokaryotes except ribosomes.
-
Prokaryotes lack membrane-bound organelles.
-
They do not have:
- Mitochondria
- Golgi apparatus
- Endoplasmic reticulum
- Lysosomes
- Chloroplasts
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Only ribosomes are present.
NEET Point: Prokaryotic ribosomes = 70S (50S + 30S)
12. Prokaryotes have something unique in the form of inclusions.
- Prokaryotic cells contain inclusion bodies.
- They store reserve materials.
Examples:
- Glycogen granules
- Phosphate granules
- Sulphur granules
13. Mesosome is a specialized differentiated form of cell membrane.
- Mesosomes are special structures found in prokaryotes.
- They are formed by folding of the plasma membrane inward.
14. They are essentially infoldings of cell membrane.
- Mesosomes are inward projections of the plasma membrane.
- They increase membrane surface area.
Cell Envelope and its Modifications
15. Most bacterial cells have a chemically complex cell envelope.
- The outer covering of bacteria is called the cell envelope.
- It protects the cell from damage.
16. The cell envelope consists of three layers.
Layers of Cell Envelope (Outside → Inside)
- Glycocalyx
- Cell Wall
- Plasma Membrane
NEET Diagram Order: Glycocalyx → Cell Wall → Plasma Membrane
17. These layers work together as a protective unit.
- Each layer has its own function.
- Together they protect the bacterial cell.
Gram Positive and Gram Negative Bacteria
18. Bacteria are classified based on Gram staining.
- A staining technique developed by is called Gram staining.
- It differentiates bacteria based on cell wall structure.
19. Gram-positive bacteria
- Retain the violet stain.
- Appear purple under microscope.
Examples:
- Bacillus
- Clostridium
20. Gram-negative bacteria
- Do not retain violet stain.
- Appear pink/red after counterstaining.
Examples:
- Escherichia coli
- Salmonella
Glycocalyx
21. Glycocalyx differs in composition and thickness.
- Different bacteria have different glycocalyx structures.
- Thickness and chemical composition vary.
22. Loose sheath is called slime layer.
- In some bacteria, glycocalyx is thin and loose.
- It is called the slime layer.
Function: Protection and attachment to surfaces.
23. Thick and tough glycocalyx is called capsule.
- Some bacteria possess a thick glycocalyx.
- This thick covering is called a capsule.
Function: Protects bacteria from host immune system.
Cell Wall
24. Cell wall determines cell shape.
- It gives definite shape to bacteria.
- Prevents deformation.
25. Cell wall provides strong structural support.
- It protects the bacterial cell from mechanical injury.
26. Prevents bursting or collapsing.
- Prevents osmotic bursting when water enters the cell.
- Maintains cell integrity.
Plasma Membrane
27. Plasma membrane is selectively permeable.
- Allows some substances to enter and leave.
- Blocks unwanted substances.
28. It interacts with the outside world.
- Exchange of nutrients, gases, and wastes occurs through it.
29. Structure is similar to eukaryotic plasma membrane.
- Both follow the fluid mosaic model.
- Made mainly of phospholipids and proteins.
Mesosome
30. Mesosome is formed by extensions of plasma membrane.
- Plasma membrane folds inward and forms mesosomes.
31. These extensions occur as:
- Vesicles
- Tubules
- Lamellae
32. Functions of Mesosomes
- Help in cell wall formation.
- Assist DNA replication.
- Help chromosome segregation during cell division.
- Aid respiration.
- Increase surface area of plasma membrane.
- Help secretion processes.
Quick NEET Revision Table
| Structure | Important Function |
|---|---|
| Cell Wall | Shape and protection |
| Cytoplasm | Site of metabolic reactions |
| Nucleoid | Contains naked DNA |
| Plasmid | Antibiotic resistance, genetic engineering |
| Ribosome (70S) | Protein synthesis |
| Inclusion Bodies | Storage of reserve food |
| Glycocalyx | Protection and adhesion |
| Capsule | Prevents phagocytosis |
| Slime Layer | Attachment and protection |
| Plasma Membrane | Selective transport |
| Mesosome | Respiration, cell wall formation, DNA replication |
NEET One-Liners
- Prokaryotes lack a true nucleus.
- DNA is naked and circular.
- Plasmids are extra-chromosomal circular DNA.
- Prokaryotes contain 70S ribosomes.
- Mycoplasma lacks a cell wall.
- Cell envelope = Glycocalyx + Cell Wall + Plasma Membrane.
- Glycocalyx may form slime layer or capsule.
- Mesosomes are infoldings of plasma membrane.
- Gram-positive bacteria retain Gram stain.
- Inclusion bodies store reserve materials.
Below are CBSE Class 11 Biology Exam-Oriented Questions and Answers from the topic "Prokaryotic Cell Structure, Cell Envelope and Mesosomes".
1. Multiple Choice Questions (MCQs)
Q1. Which organism lacks a cell wall?
a) Bacillus
b) E. coli
c) Mycoplasma
d) Cyanobacteria
Answer: c) Mycoplasma
Q2. The genetic material in prokaryotes is:
a) Enclosed in nucleus b) Naked DNA c) Linear DNA d) Histone-bound DNA
Answer: b) Naked DNA
Q3. Extra-chromosomal circular DNA in bacteria is called:
a) Chromosome b) Nucleoid c) Plasmid d) Mesosome
Answer: c) Plasmid
Q4. Ribosomes present in prokaryotes are:
a) 80S b) 70S c) 60S d) 50S
Answer: b) 70S
Q5. The outermost layer of bacterial cell envelope is:
a) Plasma membrane b) Cell wall c) Glycocalyx d) Mesosome
Answer: c) Glycocalyx
Q6. Thick and tough glycocalyx is called:
a) Slime layer b) Capsule c) Cell wall d) Lamella
Answer: b) Capsule
Q7. Mesosomes are formed by:
a) Cell wall b) Ribosomes c) Plasma membrane d) Cytoplasm
Answer: c) Plasma membrane
Q8. Gram-positive bacteria:
a) Do not retain Gram stain b) Retain Gram stain c) Lack cell wall d) Lack DNA
Answer: b) Retain Gram stain
2. Very Short Answer Questions (1 Mark)
Q1. What is a nucleoid?
Answer: The region containing naked DNA in a prokaryotic cell is called nucleoid.
Q2. Name the cell organelle present in prokaryotes.
Answer: Ribosomes.
Q3. What are plasmids?
Answer: Small circular extra-chromosomal DNA molecules present in bacteria.
Q4. Name the smallest living cell.
Answer: Mycoplasma.
Q5. What is glycocalyx?
Answer: The outermost covering of bacterial cell envelope.
Q6. Name two forms of glycocalyx.
Answer: Slime layer and capsule.
Q7. What is the function of cell wall?
Answer: It provides shape and protection.
Q8. What is mesosome?
Answer: Infolding of plasma membrane in prokaryotes.
3. Short Answer Questions (2–3 Marks)
Q1. Write any three characteristics of prokaryotic cells.
Answer:
- Lack true nucleus.
- Possess naked circular DNA.
- Lack membrane-bound organelles.
Q2. What are plasmids? Mention one importance.
Answer: Plasmids are small circular DNA molecules present outside bacterial chromosome.
Importance: They often carry antibiotic resistance genes.
Q3. Differentiate between capsule and slime layer.
| Capsule | Slime Layer |
|---|---|
| Thick and tough | Thin and loose |
| Well organized | Unorganized |
| Protects from phagocytosis | Helps in attachment |
Q4. Mention any three functions of mesosomes.
Answer:
- Cell wall formation.
- DNA replication.
- Respiration.
Q5. What is the cell envelope?
Answer: The cell envelope is the protective covering of bacterial cells consisting of:
- Glycocalyx
- Cell wall
- Plasma membrane
4. Long Answer Questions (5 Marks)
Q1. Describe the structure of a typical prokaryotic cell.
Answer:
A typical prokaryotic cell consists of:
-
Cell Envelope
- Glycocalyx
- Cell wall
- Plasma membrane
-
Cytoplasm
- Semi-fluid matrix containing enzymes and ribosomes.
-
Genetic Material
- Naked circular DNA present in nucleoid.
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Plasmids
- Extra-chromosomal circular DNA.
-
Ribosomes
- 70S ribosomes for protein synthesis.
-
Mesosomes
- Infoldings of plasma membrane helping in respiration and DNA replication.
-
Inclusion Bodies
- Storage granules for reserve food.
Q2. Explain the structure and functions of bacterial cell envelope.
Answer:
The bacterial cell envelope has three layers:
1. Glycocalyx
- Outermost layer.
- May form slime layer or capsule.
2. Cell Wall
- Provides shape.
- Prevents bursting and collapsing.
3. Plasma Membrane
- Selectively permeable.
- Regulates movement of substances.
Functions:
- Protection
- Structural support
- Selective transport
- Prevention of osmotic damage
5. Assertion and Reason Questions
Q1.
Assertion (A): Prokaryotes lack a true nucleus.
Reason (R): Their DNA is not enclosed by a nuclear membrane.
a) Both A and R are true and R is correct explanation of A.
b) Both A and R are true but R is not correct explanation.
c) A is true but R is false.
d) A is false but R is true.
Answer: a)
Q2.
Assertion (A): Plasmids are important in genetic engineering.
Reason (R): They can carry foreign DNA into bacteria.
Answer: a)
Q3.
Assertion (A): Mesosomes are formed by plasma membrane.
Reason (R): Mesosomes help in cell wall formation and respiration.
Answer: a)
6. Fill in the Blanks
-
The DNA of prokaryotes is __________. Answer: Naked
-
Extra-chromosomal DNA is called __________. Answer: Plasmid
-
Prokaryotic ribosomes are __________ type. Answer: 70S
-
The outermost layer of bacterial cell envelope is __________. Answer: Glycocalyx
-
Thick glycocalyx is called __________. Answer: Capsule
-
Loose glycocalyx is called __________. Answer: Slime layer
-
Mesosomes are infoldings of __________ membrane. Answer: Plasma
-
The DNA-containing region of bacteria is called __________. Answer: Nucleoid
7. Match the Columns
Question
| Column A | Column B |
|---|---|
| A. Plasmid | 1. Protein synthesis |
| B. Ribosome | 2. Antibiotic resistance |
| C. Capsule | 3. Protection |
| D. Mesosome | 4. Respiration |
Answer
A → 2
B → 1
C → 3
D → 4
8. Statement-Based Questions
Q1. Read the statements carefully:
I. Prokaryotes have a true nucleus.
II. Prokaryotes possess 70S ribosomes.
Choose the correct option:
a) Both statements are true
b) Both statements are false
c) I is false but II is true
d) I is true but II is false
Answer: c)
Q2.
I. Plasmids are extra-chromosomal DNA.
II. Plasmids are useful in genetic engineering.
a) Both true
b) Both false
c) Only I true
d) Only II true
Answer: a)
9. Case Study Questions
Case Study 1
A scientist isolated a bacterium containing a circular chromosome and small circular DNA molecules. The bacterium had a capsule and 70S ribosomes.
Questions
Q1. What are the small circular DNA molecules called?
Answer: Plasmids
Q2. What is the function of plasmids?
Answer: They carry special traits such as antibiotic resistance.
Q3. Which type of ribosomes are present?
Answer: 70S ribosomes
Q4. What is the function of capsule?
Answer: Protection from adverse conditions and phagocytosis.
Case Study 2
A bacterial cell possesses glycocalyx, cell wall and plasma membrane. It also contains mesosomes.
Questions
Q1. Name the three layers of cell envelope.
Answer:
- Glycocalyx
- Cell wall
- Plasma membrane
Q2. Which structure regulates movement of substances?
Answer: Plasma membrane
Q3. What are mesosomes?
Answer: Infoldings of plasma membrane.
Q4. Mention one function of mesosomes.
Answer: Respiration or DNA replication.
Important CBSE Board Questions
Frequently Asked 1-Mark Questions
- Define plasmid.
- What is nucleoid?
- Name the smallest living cell.
- What is glycocalyx?
- What are inclusion bodies?
Frequently Asked 3-Mark Questions
- Explain plasmids and their significance.
- Differentiate capsule and slime layer.
- Write functions of mesosomes.
Frequently Asked 5-Mark Questions
- Describe the structure of a prokaryotic cell.
- Explain bacterial cell envelope with diagram.
- Differentiate Gram-positive and Gram-negative bacteria.
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