Unit of Life: Cell Shape, Cell Size and Prokaryotic Cells NEET Notes

 Cell Shape and Size Explained | Prokaryotic Cells NEET Biology

Different cell shapes, cell sizes and prokaryotic cell types explained for NEET Biology preparation.

- Dr.Sanjaykumar Pawar 

UNIT OF LIFE – Cell Size, Shape and Prokaryotic Cells (Easy NEET Notes)

1. Different Shapes of Cells

Red Blood Cells (RBCs)

• Shape: Round and biconcave disc.
• Biconcave means depressed in the center on both sides.
• This shape increases surface area for oxygen transport.
• RBCs carry oxygen to all parts of the body.
• Average diameter = about 7 µm.

White Blood Cells (WBCs)

• Shape: Irregular and amoeboid.
• Amoeboid means they can change their shape.
• They move from blood vessels into tissues.
• WBCs help in body defense and immunity.

Columnar Epithelial Cells

• Shape: Long, narrow and column-like.
• Found in the lining of stomach and intestine.
• Help in absorption and secretion of substances.

Nerve Cell (Neuron)

• Shape: Branched and long.
• Consists of cell body, dendrites and axon.
• Nerve cells transmit impulses throughout the body.
• They are among the longest cells in the human body.

Mesophyll Cells

• Shape: Round or oval.
• Found in leaves of plants.
• Contain chloroplasts.
• Perform photosynthesis.

Tracheid

• Shape: Elongated and tube-like.
• Found in xylem tissue of plants.
• Help in water and mineral transport.

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Cell Size

Important Facts

• Cells vary greatly in size.
• Size depends on the function performed by the cell.

Smallest Cells

• Mycoplasma cells are the smallest known living cells.
• Size = about 0.3 µm.

Largest Single Cell

• Ostrich egg is the largest isolated single cell.

Human Red Blood Cell

• Diameter = approximately 7.0 µm.

Longest Cells

• Nerve cells are among the longest cells in animals.

NEET Point

Cell size is not related to the size of the organism.

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Cell Shape

Cells may be:

• Disc-like
• Polygonal
• Columnar
• Cuboidal
• Thread-like
• Irregular

Important Concept

The shape of a cell is related to the function it performs.

Examples:

• RBC → Oxygen transport.
• Neuron → Transmission of nerve impulses.
• WBC → Body defense.
• Tracheid → Water conduction.

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8.4 Prokaryotic Cells

Definition

• Prokaryotic cells are primitive and simple cells.
• They do not have a true nucleus.
• Membrane-bound organelles are absent.

Examples

• Bacteria
• Blue-green algae (Cyanobacteria)
• Mycoplasma
• PPLO (Pleuro Pneumonia Like Organisms)

Characteristics

• Smaller than eukaryotic cells.
• Multiply rapidly.
• Show great variation in size and shape.
• Genetic material is not enclosed by a nuclear membrane.

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Basic Shapes of Bacteria

1. Bacillus

• Rod-shaped bacteria.
• Example: Bacillus species.

2. Coccus

• Spherical or round bacteria.
• Example: Streptococcus.

3. Vibrio

• Comma-shaped bacteria.
• Example: Vibrio cholerae.

4. Spirillum

• Spiral-shaped bacteria.
• Example: Spirillum species.

Easy Trick

"BCVS"

• B → Bacillus = Rod
• C → Coccus = Round
• V → Vibrio = Comma
• S → Spirillum = Spiral

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NEET Quick Revision

Cell Shapes

Cell	Shape	Function
RBC	Round, biconcave	Oxygen transport
WBC	Amoeboid	Defense
Columnar cell	Long, narrow	Absorption
Neuron	Branched, long	Impulse transmission
Mesophyll cell	Round/Oval	Photosynthesis
Tracheid	Elongated	Water transport

Important Values

• Smallest living cell = Mycoplasma (0.3 µm)
• Largest single cell = Ostrich egg
• Human RBC diameter = 7 µm
• Longest cells = Nerve cells

Bacterial Shapes

• Bacillus → Rod
• Coccus → Spherical
• Vibrio → Comma
• Spirillum → Spiral

NEET One-Liner:
👉 "Cell shape and size vary according to the function performed by the cell." 

CBSE Class 11 Biology Question Bank

Cell: The Unit of Life (Cell Shape, Size and Prokaryotic Cells)

A. Multiple Choice Questions (MCQs)

1. Which is the smallest living cell?

a) Bacterium b) Mycoplasma c) Amoeba d) RBC

Answer: b) Mycoplasma

2. The largest isolated single cell is:

a) Human egg b) Nerve cell c) Ostrich egg d) Amoeba

Answer: c) Ostrich egg

3. Human RBC is approximately:

a) 0.7 µm b) 7 µm c) 70 µm d) 700 µm

Answer: b) 7 µm

4. Which bacterial shape is comma-shaped?

a) Bacillus b) Spirillum c) Vibrio d) Coccus

Answer: c) Vibrio

5. Which cells are amoeboid in shape?

a) RBC b) WBC c) Mesophyll cells d) Tracheids

Answer: b) WBC

6. Which cells are among the longest cells in the body?

a) RBC b) Epithelial cells c) Nerve cells d) WBC

Answer: c) Nerve cells

7. Rod-shaped bacteria are called:

a) Cocci b) Vibrios c) Spirilla d) Bacilli

Answer: d) Bacilli

8. Prokaryotic cells lack:

a) Cell membrane b) Cytoplasm c) True nucleus d) Ribosomes

Answer: c) True nucleus

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B. Very Short Answer Questions (1 Mark)

1. Name the smallest living cell.

Answer: Mycoplasma.

2. What is the diameter of human RBC?

Answer: About 7 µm.

3. Name the largest isolated cell.

Answer: Ostrich egg.

4. What is the shape of coccus bacteria?

Answer: Spherical.

5. Give one example of a prokaryotic organism.

Answer: Bacteria.

6. Which cell performs photosynthesis in leaves?

Answer: Mesophyll cells.

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C. Short Answer Questions (2–3 Marks)

1. Why are RBCs biconcave in shape?

Answer:

• Biconcave shape increases surface area.
• It helps in efficient exchange of oxygen and carbon dioxide.
• It allows flexibility while moving through capillaries.

2. Mention any three characteristics of prokaryotic cells.

Answer:

1. Small in size.
2. Lack true nucleus.
3. Membrane-bound organelles are absent.

3. Why do cells differ in shape?

Answer: Cells differ in shape because their structure is related to the function they perform. Different functions require different shapes.

4. Write any four bacterial shapes.

Answer:

• Bacillus (rod-shaped)
• Coccus (spherical)
• Vibrio (comma-shaped)
• Spirillum (spiral-shaped)

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D. Long Answer Questions (5 Marks)

1. Explain different shapes of cells with their functions.

Answer:

• RBCs: Biconcave and round; transport oxygen.
• WBCs: Amoeboid; provide defense.
• Columnar epithelial cells: Long and narrow; absorption and secretion.
• Nerve cells: Long and branched; conduct nerve impulses.
• Mesophyll cells: Oval; perform photosynthesis.
• Tracheids: Elongated; transport water.

The shape of a cell is related to the function it performs.

2. Describe the major features of prokaryotic cells.

Answer:

• Small and simple cells.
• Represented by bacteria, cyanobacteria and mycoplasma.
• Lack membrane-bound nucleus.
• DNA lies in nucleoid region.
• Membrane-bound organelles absent.
• Reproduce rapidly by binary fission.
• Show different shapes such as bacillus, coccus, vibrio and spirillum.

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E. Assertion and Reason Questions

1.

Assertion (A): Nerve cells are among the longest cells in the body.

Reason (R): They transmit impulses over long distances.

Answer: Both A and R are true and R is the correct explanation of A.

2.

Assertion (A): RBCs are biconcave.

Reason (R): Biconcave shape increases surface area for gas exchange.

Answer: Both A and R are true and R is the correct explanation of A.

3.

Assertion (A): Prokaryotic cells possess membrane-bound organelles.

Reason (R): They have a simple organization.

Answer: Assertion is false but Reason is true.

4.

Assertion (A): Vibrio bacteria are spherical.

Reason (R): Vibrio bacteria are comma-shaped.

Answer: Assertion is false but Reason is true.

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F. Fill in the Blanks

1. The smallest living cell is __________. Answer: Mycoplasma

2. Human RBC measures about __________ µm in diameter. Answer: 7

3. Rod-shaped bacteria are called __________. Answer: Bacilli

4. Spiral-shaped bacteria are called __________. Answer: Spirilla

5. The largest isolated cell is the __________ egg. Answer: Ostrich

6. White blood cells show __________ movement. Answer: Amoeboid

7. Prokaryotic cells lack a true __________. Answer: Nucleus

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G. Statement-Based Questions

Identify whether the statements are True or False.

1. Nerve cells are among the shortest cells. Answer: False

2. Cell shape depends on function. Answer: True

3. Bacillus bacteria are rod-shaped. Answer: True

4. Mycoplasma is the largest living cell. Answer: False

5. Tracheids help in water transport. Answer: True

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H. Match the Columns

Column A	Column B
1. Bacillus	a. Comma-shaped
2. Coccus	b. Spiral
3. Vibrio	c. Rod-shaped
4. Spirillum	d. Spherical

Answers

1 → c

2 → d

3 → a

4 → b

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I. Case Study Questions

Case Study

A student observed different cells under a microscope. Some cells were round and biconcave, some were long and branched, while others were elongated tube-like structures.

Questions

1. Identify the round and biconcave cells. Answer: Red Blood Cells.

2. Which cells are long and branched? Answer: Nerve cells.

3. Which elongated cells help in water transport in plants? Answer: Tracheids.

4. Why do these cells differ in shape? Answer: Because cell shape is related to the function performed.

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J. Competency-Based Questions

1.

A scientist discovers a cell without a true nucleus and membrane-bound organelles.

a) What type of cell is it? Answer: Prokaryotic cell.

b) Give one example. Answer: Bacterium.

2.

A blood sample contains cells with a biconcave shape.

a) Identify the cells. Answer: RBCs.

b) State one advantage of this shape. Answer: Increased surface area for gas exchange.

UNIT OF LIFE

│

├── Cell Shape

│   │

│   ├── Red Blood Cell (RBC)

│   │   ├── Round

│   │   ├── Biconcave

│   │   └── Oxygen transport

│   │

│   ├── White Blood Cell (WBC)

│   │   ├── Amoeboid

│   │   ├── Irregular shape

│   │   └── Body defense

│   │

│   ├── Columnar Epithelial Cell

│   │   ├── Long

│   │   ├── Narrow

│   │   └── Absorption & secretion

│   │

│   ├── Nerve Cell (Neuron)

│   │   ├── Branched

│   │   ├── Long

│   │   └── Impulse transmission

│   │

│   ├── Mesophyll Cell

│   │   ├── Round/Oval

│   │   └── Photosynthesis

│   │

│   └── Tracheid

│       ├── Elongated

│       └── Water transport

│

├── Cell Size

│   │

│   ├── Smallest Cell

│   │   └── Mycoplasma (0.3 µm)

│   │

│   ├── Largest Single Cell

│   │   └── Ostrich Egg

│   │

│   ├── Human RBC

│   │   └── 7 µm diameter

│   │

│   └── Longest Cells

│       └── Nerve Cells

│

├── Cell Shape Variation

│   │

│   ├── Disc-like

│   ├── Polygonal

│   ├── Columnar

│   ├── Cuboidal

│   ├── Thread-like

│   └── Irregular

│

├── Important Concept

│   └── Shape depends on function

│

└── Prokaryotic Cells

    │

    ├── Characteristics

    │   ├── Small size

    │   ├── Primitive cells

    │   ├── No true nucleus

    │   ├── No membrane-bound organelles

    │   └── Rapid multiplication

    │

    ├── Examples

    │   ├── Bacteria

    │   ├── Blue-green algae

    │   ├── Mycoplasma

    │   └── PPLO

    │

    └── Bacterial Shapes

        │

        ├── Bacillus

        │   └── Rod-shaped

        │

        ├── Coccus

        │   └── Spherical

        │

        ├── Vibrio

        │   └── Comma-shaped

        │

        └── Spirillum

            └── Spiral-shaped

NEET TRICK

BCVS

B → Bacillus → Rod

C → Coccus → Round

V → Vibrio → Comma

S → Spirillum → Spiral

INTERNAL LINKS

• Cell Theory and Cell Discovery 

• Structure of Cell Membrane 

• Prokaryotic vs Eukaryotic Cells

 • Cell Organelles Complete Notes 

• Plasma Membrane and Cell Wall 

• Nucleus Structure and Functions

 • Biomolecules NEET Notes

 • Transport in Cells 

• Cell Cycle and Cell Division

 • NCERT Biology Chapter-wise Revision Notes