Cell: The Building Block of Life NCERT Solutions & Important Questions
Biology se darr lagta hai? Tension mat lo! Jab aap biology padhna shuru karte ho, toh sabse pehla aur sabse important topic aata hai—the Cell. Just like ek ghar ko banane ke liye bricks (eento) ki zaroorat hoti hai, waise hi har living organism cells se bana hota hai.
This is exactly what CBSE Class 9 Science Chapter 2: Cell: The building block of life is all about! Yeh chapter sirf aapke Class 9 school exams ke liye hi important nahi hai, balki agar aap aage chalkar NEET ya CUET (jaise aap SRCC target kar rahe ho, waise hi science wale bache top medical colleges target karte hain) dena chahte hain, toh yeh chapter aapka ultimate foundation hai.
In this ExamSpark special guide, we have provided the complete NCERT Solutions for Class 9 Science Chapter 2, handpicked Board Exam Questions 2026, and a free NCERT PDF Download link. Bina time waste kiye, chalo shuru karte hain!
Join TelegramLearning Objectives
- Understand why the cell is called the fundamental unit of life.
- Explain the historical discoveries related to cells (Robert Hooke, Leeuwenhoek).
- Differentiate clearly between Prokaryotic and Eukaryotic cells.
- Compare the structures and functions of Plant Cells and Animal Cells.
- Describe the functions of various cell organelles like Mitochondria, Nucleus, and Plastids.
- Understand the processes of diffusion and osmosis.
Key Concepts, Definitions and Formulas
Before jumping to the Class 9 Solutions, in basic terms ko samajhna bahut zaroori hai. Ratna nahi hai, bas samajhna hai!
- Cell: The structural and functional unit of all living organisms.
- Discovery of Cell (1665): Robert Hooke discovered the cell by observing a thin slice of cork under a primitive microscope.
- Cell Theory: Proposed by Schleiden and Schwann. It states that all plants and animals are composed of cells. Later expanded by Virchow ("Omnis cellula-e-cellula" - all cells arise from pre-existing cells).
- Plasma Membrane: The outermost covering of the cell that allows the entry and exit of selected materials. Therefore, it is called a selectively permeable membrane.
- Diffusion: Spontaneous movement of a substance from a region of high concentration to a region of low concentration.
- Osmosis: The passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration.
- Mitochondria: The "Powerhouse of the Cell". They release energy in the form of ATP (Adenosine Triphosphate).
- Lysosomes: Known as the "Suicide Bags" of the cell because they contain powerful digestive enzymes that can digest their own cell if it gets damaged.
- Ribosomes: The "Protein Factories" of the cell.
Full NCERT Solutions (Frequently Asked Questions)
Here are the detailed, step-by-step NCERT Solutions for Class 9 Science Chapter 2. Exam mein exactly aise hi likhna to get full marks! Click on the questions below to reveal the answers.
Question 1: Who discovered cells, and how?
Cells were discovered by the English scientist Robert Hooke in 1665.
- He examined a thin slice of cork (the bark of a tree) under a self-designed primitive microscope.
- He observed honeycomb-like structures consisting of small compartments.
- He called these tiny compartments "cells" (which means "little rooms" in Latin).
Question 2: Why is the cell called the structural and functional unit of life?
Structural Unit: All living organisms (plants and animals) are made up of cells. Just like bricks form a building, cells form the body of an organism.
Functional Unit: All the basic life functions taking place inside the body (like respiration, digestion, excretion) are actually performed by the individual cells. Hence, it is the functional unit.
Question 3: How do substances like CO2 and water move in and out of the cell? Discuss.
- Movement of CO2 (Gas): CO2 is a cellular waste that accumulates in high concentrations inside the cell. Outside the cell, the concentration is comparatively lower. So, CO2 moves out of the cell through the cell membrane by the process of diffusion (from high to low concentration).
- Movement of Water (Liquid): Water moves in and out of the cell through a selectively permeable membrane by a special type of diffusion called osmosis.
Question 4: Why is the plasma membrane called a selectively permeable membrane?
The plasma membrane is called a selectively permeable membrane because it permits the entry and exit of only some specific materials in and out of the cell, while it prevents the movement of other unwanted materials.
Question 5: Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.
(Standard NCERT Table Question)
| Feature | Prokaryotic Cells | Eukaryotic Cells |
|---|---|---|
| 1. Size | Generally small (1-10 µm) | Larger (5-100 µm) |
| 2. Nuclear Region | Poorly defined due to the absence of a nuclear membrane, and it is called a nucleoid. | Well-defined and surrounded by a nuclear membrane. |
| 3. Chromosome | Single chromosome. | More than one chromosome. |
| 4. Membrane-bound Cell Organelles | Absent (no mitochondria, plastids, etc.). | Present. |
Question 6: Make a comparison and write down ways in which plant cells are different from animal cells.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present (made of cellulose) | Absent |
| Plastids | Present (e.g., Chloroplasts) | Absent |
| Vacuoles | Very large, usually single and centrally located | Small in size or completely absent |
| Centrosome | Absent | Present (helps in cell division) |
Question 7: What would happen if the plasma membrane ruptures or breaks down?
If the selectively permeable plasma membrane ruptures, the cell will lose its ability to regulate the internal environment. The cellular contents will leak out, and chemical substances will move in and out freely. As a result, basic cellular functions will stop, and the cell will ultimately die.
Question 8: What would happen to the life of a cell if there was no Golgi apparatus?
The Golgi apparatus performs the functions of storage, modification, and packaging of products manufactured in the ER (Endoplasmic Reticulum). If there is no Golgi apparatus:
- Packaging and dispatching of materials synthesized by the cell will be stopped.
- Lysosomes will not be formed.
- Complex sugars will not be made from simple sugars.
Question 9: Which organelle is known as the powerhouse of the cell? Why?
The Mitochondria is known as the powerhouse of the cell.
Reason: The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine Triphosphate) molecules. Since they generate energy for the cell, they are the powerhouses.
Question 10: Where do the lipids and proteins constituting the cell membrane get synthesized?
- Proteins: Synthesized by the Rough Endoplasmic Reticulum (RER) because it has ribosomes attached to its surface.
- Lipids: Synthesized by the Smooth Endoplasmic Reticulum (SER).
Question 11: How does an Amoeba obtain its food?
Amoeba obtains its food through a process called endocytosis. The plasma membrane of Amoeba is highly flexible. It forms finger-like extensions called pseudopodia to engulf the food particle along with a drop of water, forming a food vacuole inside the cell.
Question 12: What is osmosis?
Osmosis is the spontaneous movement of water molecules from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane.
EXTRA IMPORTANT QUESTIONS (BOARD STYLE 2026)
Exam preparation strong karne ke liye, yahan ExamSpark ke top 15 handpicked questions hain from all difficulty levels.
Multiple Choice Questions (MCQs)
1. The colored plastids present in plant cells are called:
a) Leucoplasts
b) Chloroplasts
c) Chromoplasts
d) Amyloplasts
Answer: (c) Chromoplasts (Difficulty: Medium)
2. Which of the following is an example of a single-celled organism?
a) Fungi
b) Amoeba
c) Earthworm
d) Rose plant
Answer: (b) Amoeba (Difficulty: Easy)
3. Plasmolysis in a plant cell is defined as:
a) Breakdown of plasma membrane in hypotonic medium
b) Shrinkage of cytoplasm in hypertonic medium
c) Shrinkage of nucleoplasm
d) None of the above
Answer: (b) (Difficulty: Hard)
4. The undefined nuclear region of prokaryotes is known as:
a) Nucleus
b) Nucleolus
c) Nucleic acid
d) Nucleoid
Answer: (d) Nucleoid (Difficulty: Medium)
5. Ribosomes are the site of:
a) Fat synthesis
b) Respiration
c) Protein synthesis
d) Photosynthesis
Answer: (c) Protein synthesis (Difficulty: Easy)
Short Answer Questions (2-3 Marks)
6. Write the full form of ATP and DNA.
Answer:
ATP: Adenosine Triphosphate.
DNA: Deoxyribonucleic Acid. (Difficulty: Easy)
7. Why do plant cells have large vacuoles compared to animal cells?
Answer: Plant cells need to store a lot of water, nutrients, and waste products. The large central vacuole also provides turgidity and rigidity to the plant cell, allowing plants to stand upright. (Difficulty: Medium)
8. What is the difference between hypertonic and hypotonic solutions?
Answer:
- Hypertonic Solution: The surrounding solution has a lower concentration of water than the cell. (Cell shrinks).
- Hypotonic Solution: The surrounding solution has a higher concentration of water than the cell. (Cell swells up). (Difficulty: Hard)
9. State the function of chromosomes.
Answer: Chromosomes contain information for the inheritance of features from parents to the next generation in the form of DNA molecules. (Difficulty: Medium)
Long Answer Questions (5 Marks)
10. Draw a neat, labelled diagram of an Animal Cell and explain the function of the Nucleus.
Answer: (Students must practice drawing the cell diagram from NCERT).
Functions of Nucleus:
- It controls all metabolic activities of the cell (Brain of the cell).
- It contains genetic material (DNA) which transfers traits from parents to offspring.
- It plays a central role in cellular reproduction (cell division). (Difficulty: Hard)
11. Explain the different types of plastids present in plant cells.
Answer: Plastids are of three types:
- Chloroplasts: Green plastids containing chlorophyll. They are responsible for photosynthesis.
- Chromoplasts: Coloured plastids (red, yellow, orange). They give colour to flowers and fruits to attract insects for pollination.
- Leucoplasts: Colourless plastids. Their main function is to store starch, oils, and protein granules. (Difficulty: Hard)
Case-Based Questions
12. Rahul placed some dried raisins (kismis) in a bowl of plain water. After a few hours, he noticed the raisins had swollen up.
a) Which biological process caused the raisins to swell? (Ans: Endosmosis).
b) Was the plain water a hypertonic or hypotonic solution? (Ans: Hypotonic solution).
c) What would happen if he placed the swollen raisins back into highly concentrated salt water? (Ans: They would shrink due to exosmosis). (Difficulty: Medium)
13. A biology teacher was observing a cell under a microscope. She noted the presence of a rigid outer wall, green colored organelles, and a large central empty-looking space.
a) Identify whether it is a plant cell or an animal cell. (Ans: Plant Cell).
b) Name the green-colored organelles. (Ans: Chloroplasts).
c) Name the rigid outer wall and state what it is made of. (Ans: Cell Wall, made of cellulose). (Difficulty: Medium)
Assertion-Reason Questions
(Options: A- Both A & R are true and R is correct explanation. B- Both A & R are true but R is NOT correct explanation. C- A is true, R is false. D- A is false, R is true.)
14. Assertion (A): Lysosomes are known as the suicide bags of a cell.
Reason (R): Lysosomes contain powerful enzymes capable of breaking down all organic material and can digest their own cell if it gets damaged.
Answer: (A) Both are true, and R is the exact reason for A. (Difficulty: Medium)
15. Assertion (A): Animal cells can withstand very dilute external media without bursting, better than plant cells.
Reason (R): Plant cells have a rigid cell wall that prevents bursting.
Answer: (D) A is false, R is true. Plant cells can withstand dilute media better because their rigid cell wall pushes back against the swelling (turgor pressure). Animal cells lack this wall and will burst. (Difficulty: Hard)
COMMON MISTAKES STUDENTS MAKE
Exam checker teachers ke according, Class 9 students usually yeh galti karte hain:
- Cell Wall vs. Plasma Membrane: Bacche confuse ho jate hain. Yaad rakho, Cell Wall sirf plants, fungi, aur bacteria mein hoti hai. Plasma membrane dono (plants aur animals) mein hoti hai.
- Mitochondria vs. Chloroplasts: Mitochondria = Energy (Powerhouse). Chloroplasts = Food making (Kitchen of the cell). Don't mix their functions!
- Prokaryotic cell structure: Hamesha yaad rakho, "Pro" means primitive. They do not have a well-defined nucleus or membrane-bound organelles.
- Spelling Mistakes: Vacuole, Mitochondria, Lysosome jaise words ki spelling bar-bar likh kar practice karo.
EXAM PREPARATION TIPS
- Diagrams are your best friends: Plant cell, Animal cell, aur Prokaryotic cell ke diagrams ki labeling kam se kam 3 baar draw karke practice karo.
- Learn the 'Nicknames': Match the following ke liye cell organelle nicknames zaroor yaad karo (Suicide bag, Powerhouse, Kitchen, Protein factory).
- Tabular Differences: Plant vs Animal cell aur Prokaryote vs Eukaryote hamesha table format mein likho. Examiner ko check karne mein aasaani hoti hai, aur aapko full marks milte hain.
FAQ SECTION
Q1: Is Chapter 2 Cell important for Class 9 Science boards?
Yes! This chapter carries high weightage (around 6-8 marks) and is the absolute foundation for Class 10 Life Processes and future Class 11-12 Biology.
Q2: Where can I get the NCERT PDF Download for Chapter 2 Class 9 Science?
You can download the official NCERT book PDF from the government site (ncert.nic.in) or simply download our complete ExamSpark annotated PDF at the bottom of this page.
Q3: What are the most important questions from the Cell chapter?
The differences between Plant and Animal cells, Prokaryotic vs Eukaryotic cells, and the specific functions of Mitochondria, Lysosomes, and the Plasma Membrane are repeatedly asked in exams.
Q4: Who discovered the living cell first?
While Robert Hooke discovered dead cells in 1665, Anton Von Leeuwenhoek was the first to discover free-living cells in pond water in 1674.
Q5: Why does a plant cell not burst in a hypotonic solution?
Because of the rigid Cell Wall! When the cell swells up with water, the cell wall exerts an equal opposing pressure, preventing the cell from bursting.
CONCLUSION
Class 9 biology ka safar yahin se shuru hota hai. Agar aapne "Cell: The building block of life" acche se samajh liya, toh aage aane wale chapters (Tissues, Diversity) aapke liye bahut easy ho jayenge. Concepts ko ratne ki bajaye unhe daily life aur logic se connect karo.
Make sure to revise these NCERT Solutions for Class 9 Science Chapter 2 thoroughly. Practice the PYQs (Past Year Questions) we provided, draw those diagrams, and download our ExamSpark notes. Study smart, prepare confidently, and 2026 board exams mein top karo!