Cell Chapter Study Notes for RRB, SSC & Competitive Exams

These Cell Biology study notes are designed for RRB, SSC, NTPC, Group D, SSC CGL, SSC CHSL and other competitive examinations. These notes focus on frequently asked facts, important concepts and exam-oriented questions.

1. Basic Facts About the Cell

Topic	Important Fact
Cell	Basic structural and functional unit of life
Cell Theory	Proposed by Schleiden and Schwann
Term "Cell"	Coined by Robert Hooke in 1665
First Observed Cell	Cork cells observed by Robert Hooke
Cell Theory Modified By	Rudolf Virchow
Virchow's Statement	Every cell arises from a pre-existing cell
Smallest Known Living Cell	Mycoplasma
Largest Single Cell	Ostrich egg
Longest Cell	Neuron
Powerhouse of Cell	Mitochondria
Protein Factory	Ribosome
Suicidal Bag	Lysosome
Control Centre	Nucleus
Kitchen of Cell	Chloroplast
Packaging Centre	Golgi Apparatus

2. Prokaryotic and Eukaryotic Cells

Prokaryotic Cell

• Examples include bacteria and cyanobacteria.
• True nucleus is absent.
• Nuclear membrane is absent.
• Membrane-bound organelles are absent.
• Ribosomes are generally 70S.
• DNA is generally circular.
• They are usually smaller and simpler.

Eukaryotic Cell

• Examples include plants, animals, fungi and protozoa.
• True nucleus is present.
• Nuclear membrane is present.
• Membrane-bound organelles are present.
• Cytoplasmic ribosomes are generally 80S.
• They are generally larger and more complex.

Exam Trick: Mitochondria and chloroplasts contain 70S ribosomes, while the cytoplasm of eukaryotic cells generally contains 80S ribosomes.

3. Cell Membrane

The cell membrane, also called the plasma membrane, is mainly composed of lipids and proteins. It is selectively permeable and regulates the movement of substances into and out of the cell.

Fluid Mosaic Model

The Fluid Mosaic Model was proposed by Singer and Nicolson in 1972.

Types of Transport

• Diffusion: Movement of substances from higher concentration to lower concentration.
• Osmosis: Movement of water through a selectively permeable membrane.
• Active Transport: Movement of substances using energy, usually ATP.

Tonicity

• Hypotonic: Cell gains water.
• Hypertonic: Cell loses water.
• Isotonic: No net movement of water.

Important: A plant cell placed in a hypertonic solution undergoes plasmolysis.

4. Cell Wall

Organism	Main Cell Wall Material
Plants	Cellulose
Fungi	Chitin
Bacteria	Peptidoglycan

Exam Point: Animal cells do not have a cell wall.

5. Nucleus

The nucleus is the major control and genetic centre of a eukaryotic cell. It contains most of the cell's genetic material.

Main Parts of Nucleus

• Nuclear membrane
• Nucleoplasm
• Nucleolus
• Chromatin

The nucleolus is mainly involved in ribosomal RNA production and ribosome assembly.

6. Mitochondria

Mitochondria are known as the powerhouse of the cell. They are the major site of aerobic respiration and ATP production.

• Mitochondria have a double membrane.
• The inner membrane forms folds called cristae.
• The internal region is called the matrix.
• They contain their own DNA.
• They contain 70S ribosomes.
• They are considered semi-autonomous organelles.

Frequently Asked: Cristae are folds of the inner mitochondrial membrane.

7. Ribosomes

Ribosomes are non-membranous organelles and are known as the protein factories of the cell.

Cell / Location	Ribosome
Prokaryotes	70S
Eukaryotic Cytoplasm	80S
Mitochondria	70S
Chloroplasts	70S

Note: The S in 70S and 80S refers to the Svedberg sedimentation coefficient.

8. Endoplasmic Reticulum

Rough Endoplasmic Reticulum

• Contains ribosomes on its surface.
• Important for protein synthesis and transport.

Smooth Endoplasmic Reticulum

• Does not contain ribosomes.
• Important in lipid synthesis.
• Helps in detoxification.
• In certain cells, it is involved in calcium storage.

Memory Trick: Rough ER = Protein | Smooth ER = Lipid

9. Golgi Apparatus

The Golgi apparatus is involved in modification, sorting, packaging and secretion of proteins and lipids.

• Associated with the work of Camillo Golgi.
• Involved in packaging and dispatching cellular products.
• Helps in formation of lysosomes.

Exam Keyword: Packaging and dispatching centre of the cell = Golgi apparatus.

10. Lysosomes

Lysosomes are commonly called suicidal bags of the cell because they contain powerful hydrolytic enzymes.

• Contain digestive enzymes.
• Help digest cellular waste.
• Help break down worn-out organelles.
• Are surrounded by a single membrane.
• Are associated with the Golgi apparatus.

11. Chloroplast

Chloroplasts are the major sites of photosynthesis in plants and algae.

• Have a double membrane.
• Contain stroma and thylakoids.
• Stacks of thylakoids are called grana.
• Contain chlorophyll.
• Contain their own DNA and 70S ribosomes.

Light reactions: Mainly associated with thylakoid membranes.

Calvin Cycle: Occurs in the stroma.

12. Vacuole

• Acts mainly as a storage organelle.
• Plant cells generally have a large central vacuole.
• Contains cell sap.
• Helps maintain turgor pressure.
• The vacuole membrane is called the tonoplast.

13. Centrosome and Centrioles

• Centrosomes are commonly associated with animal cells.
• A centrosome generally contains a pair of centrioles.
• Centrioles help in spindle formation during cell division.
• Centrioles typically show a 9+0 arrangement.
• Cilia and flagella typically show a 9+2 arrangement.

14. Cytoskeleton

The cytoskeleton provides structural support, maintains cell shape and assists in movement and intracellular transport.

• Microtubules
• Microfilaments
• Intermediate filaments

15. Cell Division

Mitosis

• Usually produces two daughter cells.
• Chromosome number is generally maintained.
• Important for growth and repair.
• Daughter cells are generally genetically similar to the parent cell.

Meiosis

• Produces four haploid daughter cells.
• Chromosome number is reduced by half.
• Important for sexual reproduction.
• Produces genetic variation.

Feature	Mitosis	Meiosis
Daughter Cells	2	4
Chromosome Number	Maintained	Halved
Genetic Variation	Usually absent	Present
Main Role	Growth and repair	Gamete formation
Number of Divisions	1	2

16. Stages of Mitosis

Memory Trick: PMAT

Prophase

Chromosomes become visible and the spindle begins to form.

Metaphase

Chromosomes arrange themselves at the equatorial plate.

Exam Point: Chromosomes are arranged at the equator during metaphase.

Anaphase

Sister chromatids separate and move toward opposite poles.

Telophase

Two new nuclei form around the separated chromosomes.

Cytokinesis divides the cytoplasm.

17. Cell Cycle

G₁ → S → G₂ → M

• G₁ Phase: Cell growth.
• S Phase: DNA replication occurs.
• G₂ Phase: Preparation for cell division.
• M Phase: Mitosis and cytokinesis.

Most Asked Cell One-Liners for RRB and SSC

1. Basic unit of life? — Cell
2. Who coined the term cell? — Robert Hooke
3. Who proposed the cell theory? — Schleiden and Schwann
4. Who stated that every cell comes from a pre-existing cell? — Rudolf Virchow
5. Powerhouse of the cell? — Mitochondria
6. Protein factory? — Ribosome
7. Suicidal bag? — Lysosome
8. Packaging centre? — Golgi apparatus
9. Control centre? — Nucleus
10. Site of photosynthesis? — Chloroplast
11. Largest single cell? — Ostrich egg
12. Longest cell? — Neuron
13. Smallest known living cell? — Mycoplasma
14. Human cell without a nucleus? — Mature RBC
15. Plant cell wall is mainly made of? — Cellulose
16. Fungal cell wall contains? — Chitin
17. Bacterial cell wall contains? — Peptidoglycan
18. Fluid Mosaic Model was proposed by? — Singer and Nicolson
19. Cristae are found in? — Mitochondria
20. Grana are found in? — Chloroplast
21. DNA replication occurs during? — S phase
22. Chromosomes align at the equator during? — Metaphase
23. Sister chromatids separate during? — Anaphase
24. Mitosis produces how many daughter cells? — Two
25. Meiosis produces how many daughter cells? — Four
26. Vacuole membrane is called? — Tonoplast
27. 70S ribosomes occur in? — Prokaryotes, mitochondria and chloroplasts
28. 80S ribosomes occur where? — Eukaryotic cytoplasm
29. Centrioles generally show which arrangement? — 9+0
30. Cilia and flagella generally show which arrangement? — 9+2

High-Priority Topics for RRB and SSC Exams

Must Study

• Cell theory and scientists
• Prokaryotic vs eukaryotic cells
• Cell organelles and their functions
• Mitochondria
• Ribosomes and 70S/80S differences
• Lysosomes
• Golgi apparatus
• Chloroplast
• Cell membrane
• Osmosis and diffusion
• Mitosis and meiosis
• Stages of mitosis
• DNA and chromosome basics

Important Topics

• Cell wall composition
• Endoplasmic reticulum
• Vacuoles
• Centrosome and centrioles
• Cell cycle
• Cilia and flagella

Quick Revision

Cell → Nucleus → DNA → Chromosome → Gene

Mitochondria → ATP | Ribosome → Protein | Golgi → Packaging | Lysosome → Digestion | Chloroplast → Photosynthesis

Mitosis → 2 cells | Meiosis → 4 cells | S phase → DNA replication | Metaphase → Chromosomes at equator

---

Also Read: More Biology notes, General Science notes and previous-year questions for RRB and SSC competitive exams.