Cell Theory and Overview of Cell – Easy NEET Notes (Line by Line)
Schwann’s Contribution (1839)
- Theodor Schwann (1839) was a German zoologist.
- He studied different types of animal cells.
- He observed that animal cells have a thin outer covering.
- This outer covering is now called the plasma membrane (cell membrane).
- Schwann also studied plant tissues.
- He found that plant cells possess a cell wall outside the plasma membrane.
- He concluded that the cell wall is a unique feature of plant cells.
- Based on his observations, Schwann proposed that:
- Plants and animals are made up of cells.
- Cells and their products form the body of organisms.
NEET Point
✅ Schwann discovered the importance of the plasma membrane and recognized the cell wall as a characteristic feature of plant cells.
Formation of Cell Theory
- Matthias Schleiden studied plant cells.
- Theodor Schwann studied animal cells.
- Together, Schleiden and Schwann formulated the Cell Theory.
Main Idea
- All plants and animals are made up of cells.
- Cells are the basic units of life.
Limitation
- Their theory did not explain how new cells are formed.
Virchow’s Contribution (1855)
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Rudolf Virchow explained the origin of new cells.
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He stated that:
"Omnis cellula e cellula"
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Meaning:
"Every cell arises from a pre-existing cell."
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He modified the Cell Theory and gave it its final form.
NEET Point
✅ Virchow (1855) → New cells come only from existing cells.
Modern Cell Theory
1. All living organisms are composed of cells and cell products.
- Every living organism is made up of one or more cells.
- Cell products include substances produced by cells.
2. All cells arise from pre-existing cells.
- New cells are formed by division of existing cells.
- No cell originates spontaneously.
NEET One-Liner
✅ Cell Theory = Schleiden + Schwann
✅ Modified by Virchow
Overview of Cell
Plant Cell (Onion Peel Cell)
- A typical plant cell has a cell wall as the outermost boundary.
- Just inside the cell wall is the plasma membrane.
- The cell wall provides:
- Protection
- Shape
- Mechanical support
NEET Point
✅ Cell wall is present only in plant cells (not in animal cells).
Animal Cell (Human Cheek Cell)
- Animal cells do not have a cell wall.
- The outer boundary is the plasma membrane.
- The plasma membrane controls the movement of substances in and out of the cell.
Nucleus
- Inside every eukaryotic cell is a dense structure called the nucleus.
- The nucleus is surrounded by a membrane called the nuclear membrane.
- It acts as the control center of the cell.
Functions
- Controls cellular activities.
- Stores genetic information.
Chromosomes and DNA
- The nucleus contains chromosomes.
- Chromosomes contain DNA (Deoxyribonucleic Acid).
- DNA is the genetic material.
- DNA carries hereditary information from parents to offspring.
NEET Point
✅ DNA → Genetic material
✅ Chromosomes are present inside the nucleus
Prokaryotic and Eukaryotic Cells
Eukaryotic Cells
- Cells having a membrane-bound nucleus.
- Contain membrane-bound organelles.
- Examples:
- Plant cells
- Animal cells
- Fungi
- Protists
Features
✅ True nucleus present
✅ Membrane-bound organelles present
Prokaryotic Cells
- Cells lacking a membrane-bound nucleus.
- Genetic material lies directly in the cytoplasm.
- Membrane-bound organelles are absent.
Examples
- Bacteria
- Mycoplasma
Features
✅ No true nucleus
✅ No membrane-bound organelles
Cytoplasm
- Cytoplasm is a semi-fluid matrix inside the cell.
- It occupies most of the cell volume.
- Present in both prokaryotic and eukaryotic cells.
Functions
- Site of many biochemical reactions.
- Keeps the cell alive and functional.
NEET Point
✅ Cytoplasm = Main arena of cellular activities.
Cell Organelles in Eukaryotic Cells
Eukaryotic cells contain several membrane-bound organelles:
1. Endoplasmic Reticulum (ER)
- Helps in synthesis and transport of materials.
2. Golgi Complex
- Modifies, packages and secretes substances.
3. Lysosomes
- Digest unwanted materials.
- Called "suicidal bags of the cell."
4. Mitochondria
- Site of cellular respiration.
- Produce ATP (energy).
5. Microbodies
- Perform specialized metabolic functions.
6. Vacuoles
- Storage of water, food and waste materials.
NEET Point
✅ Membrane-bound organelles are present only in eukaryotic cells.
Organelles Absent in Prokaryotes
Prokaryotic cells lack:
- ER
- Golgi body
- Lysosomes
- Mitochondria
- Vacuoles
NEET Point
✅ Prokaryotes have no membrane-bound organelles.
Ribosomes
- Ribosomes are non-membrane-bound organelles.
- Present in both:
- Prokaryotic cells
- Eukaryotic cells
- Site of protein synthesis.
Location
- Free in cytoplasm.
- Attached to Rough ER.
- Present inside mitochondria.
- Present inside chloroplasts.
NEET Point
✅ Ribosomes are found in all living cells.
Centrosome
- Present mainly in animal cells.
- Non-membrane-bound organelle.
- Helps in cell division.
NEET Point
✅ Centrosome is usually absent in higher plant cells.
Cell Size
- Cells vary greatly in size, shape and function.
- Mycoplasma is the smallest known cell.
- Size of Mycoplasma ≈ 0.3 µm.
NEET Point
✅ Smallest cell → Mycoplasma
✅ Largest cell (commonly asked) → Ostrich egg
Quick Revision (NEET)
| Scientist | Contribution |
|---|---|
| Schleiden | Plants are made of cells |
| Schwann | Animals are made of cells; plasma membrane described |
| Virchow | New cells arise from pre-existing cells |
Cell Theory
- All living organisms are made of cells and cell products.
- All cells arise from pre-existing cells.
Important Facts
- Cell wall → Plant cells only.
- Plasma membrane → Present in all cells.
- DNA → Genetic material.
- Ribosomes → Present in all cells.
- Mitochondria → Powerhouse of cell.
- Centrosome → Helps in cell division.
- Prokaryotes → No true nucleus, no membrane-bound organelles.
- Eukaryotes → True nucleus and membrane-bound organelles present.
 |
| Cell Theory Explained: From Schwann to Virchow and the structure of plant and animal cells |
Class 11 Biology (CBSE) – Cell Theory & Overview of Cell
Question Bank with Answers
A. MCQs (1 Mark Each)
1. Who first explained that new cells arise from pre-existing cells?
a) Schleiden b) Schwann c) Virchow d) Hooke
Answer: c) Virchow
2. The statement "Omnis cellula e cellula" was given by:
a) Schwann b) Virchow c) Schleiden d) Brown
Answer: b) Virchow
3. Cell wall is a characteristic feature of:
a) Animal cells b) Plant cells c) Bacterial cells only d) Human cells
Answer: b) Plant cells
4. Which organelle is present in both prokaryotic and eukaryotic cells?
a) Golgi body b) Mitochondria c) Ribosome d) ER
Answer: c) Ribosome
5. DNA is present in:
a) Cytoplasm only b) Cell wall c) Chromosomes d) Vacuole
Answer: c) Chromosomes
6. Prokaryotic cells lack:
a) Cytoplasm b) Plasma membrane c) Ribosomes d) Membrane-bound organelles
Answer: d) Membrane-bound organelles
7. The powerhouse of the cell is:
a) Golgi body b) Lysosome c) Mitochondria d) Ribosome
Answer: c) Mitochondria
8. Centrosome is generally found in:
a) Plant cells b) Animal cells c) Fungi d) Bacteria
Answer: b) Animal cells
9. The smallest known cell is:
a) Amoeba b) Bacteria c) Mycoplasma d) Paramecium
Answer: c) Mycoplasma
10. Cell theory was proposed by:
a) Schleiden and Schwann b) Virchow and Brown c) Hooke and Leeuwenhoek d) Brown and Virchow
Answer: a) Schleiden and Schwann
B. Very Short Answer Questions (1 Mark)
1. Who proposed Cell Theory?
Answer: Schleiden and Schwann.
2. What is the meaning of "Omnis cellula e cellula"?
Answer: Every cell arises from a pre-existing cell.
3. What is the genetic material of the cell?
Answer: DNA.
4. Name the outermost layer of plant cells.
Answer: Cell wall.
5. Name the site of protein synthesis.
Answer: Ribosomes.
6. What is the living matrix of the cell called?
Answer: Cytoplasm.
7. Which organelle controls cell activities?
Answer: Nucleus.
8. Give one example of a prokaryote.
Answer: Bacteria.
C. Short Answer Questions (2–3 Marks)
1. State the modern Cell Theory.
Answer:
- All living organisms are composed of cells and cell products.
- All cells arise from pre-existing cells.
2. Differentiate between Prokaryotic and Eukaryotic cells.
| Prokaryotic Cells | Eukaryotic Cells |
|---|---|
| No true nucleus | True nucleus present |
| No membrane-bound organelles | Membrane-bound organelles present |
| Smaller in size | Larger in size |
3. Why are ribosomes called universal organelles?
Answer:
- Ribosomes are present in both prokaryotic and eukaryotic cells.
- They are the sites of protein synthesis.
4. What are the functions of cytoplasm?
Answer:
- It is the site of various metabolic reactions.
- It supports and suspends cell organelles.
5. Mention any three membrane-bound organelles.
Answer:
- Endoplasmic reticulum
- Golgi apparatus
- Mitochondria
D. Long Answer Questions (5 Marks)
1. Explain the contributions of Schleiden, Schwann and Virchow in the development of Cell Theory.
Answer:
Schleiden (1838):
- Studied plant tissues.
- Concluded that plants are made of cells.
Schwann (1839):
- Studied animal tissues.
- Concluded that animals are composed of cells.
- Recognized plasma membrane and cell wall.
Virchow (1855):
- Proposed "Omnis cellula e cellula".
- Explained that new cells arise from pre-existing cells.
Modern Cell Theory:
- All organisms are made of cells and cell products.
- All cells arise from pre-existing cells.
2. Describe the structure of a typical eukaryotic cell.
Answer:
- Cell membrane forms the boundary.
- Cytoplasm fills the interior.
- Nucleus contains chromosomes and DNA.
- Membrane-bound organelles include ER, Golgi apparatus, mitochondria, lysosomes and vacuoles.
- Ribosomes help in protein synthesis.
E. Assertion and Reason Questions
1.
Assertion (A): Ribosomes are found in both prokaryotic and eukaryotic cells.
Reason (R): Ribosomes are non-membrane-bound organelles.
Answer: Both A and R are true, and R is the correct explanation.
2.
Assertion (A): Prokaryotic cells contain membrane-bound organelles.
Reason (R): Prokaryotic cells lack a true nucleus.
Answer: Assertion is false, Reason is true.
3.
Assertion (A): Cell wall is present in plant cells.
Reason (R): Cell wall provides protection and support.
Answer: Both A and R are true, and R is the correct explanation.
4.
Assertion (A): Virchow modified Cell Theory.
Reason (R): He stated that all cells arise from pre-existing cells.
Answer: Both A and R are true, and R is the correct explanation.
F. Fill in the Blanks
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_________ and Schwann formulated Cell Theory. Answer: Schleiden
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New cells arise from _________ cells. Answer: pre-existing
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The genetic material is called _________. Answer: DNA
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The outer boundary of animal cells is the _________. Answer: plasma membrane
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_________ are the sites of protein synthesis. Answer: Ribosomes
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_________ is the smallest known cell. Answer: Mycoplasma
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The control center of the cell is the _________. Answer: nucleus
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Plant cells possess a rigid _________. Answer: cell wall
G. Match the Columns
| Column A | Column B |
|---|---|
| A. Virchow | 1. Protein synthesis |
| B. Ribosome | 2. Omnis cellula e cellula |
| C. DNA | 3. Genetic material |
| D. Mitochondria | 4. Powerhouse of cell |
Answers
A → 2
B → 1
C → 3
D → 4
H. Statement-Based Questions
1. Identify the incorrect statement.
a) Ribosomes are present in all cells.
b) Prokaryotes have membrane-bound organelles.
c) DNA is genetic material.
d) Cell wall is present in plant cells.
Answer: b) Prokaryotes have membrane-bound organelles.
2. Which statement is correct?
a) Animal cells have cell wall.
b) Mitochondria synthesize proteins.
c) Cytoplasm is the site of cellular activities.
d) Ribosomes are membrane-bound.
Answer: c) Cytoplasm is the site of cellular activities.
I. Case Study Questions
Case Study 1
A student observed onion peel cells under a microscope. He found a rigid outer covering and a nucleus inside the cell.
Questions
1. What is the rigid outer covering called?
Answer: Cell wall
2. Is it a plant cell or animal cell?
Answer: Plant cell
3. What is the function of the nucleus?
Answer: Controls cellular activities and contains genetic material.
4. Which genetic material is present in the nucleus?
Answer: DNA
Case Study 2
A scientist studied a cell that lacked a membrane-bound nucleus and membrane-bound organelles.
Questions
1. What type of cell is this?
Answer: Prokaryotic cell
2. Give one example.
Answer: Bacteria
3. Which organelle is still present in this cell?
Answer: Ribosome
4. Does it contain mitochondria?
Answer: No
Important CBSE Exam Questions
Most Repeated 1 Mark
- Who proposed Cell Theory?
- What is Omnis cellula e cellula?
- What is DNA?
- Name the smallest cell.
- What is the function of ribosomes?
Most Repeated 3 Mark
- Differentiate between prokaryotic and eukaryotic cells.
- Explain Cell Theory.
- Write functions of cytoplasm.
Most Repeated 5 Mark
- Explain contributions of Schleiden, Schwann and Virchow.
- Describe the structure of a eukaryotic cell.
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