NCERT Solutions for Class 9 Science Chapter 2 Cell: The Building Block of Life (2026-27)

Revise, Reflect, Refine (NCERT Textbook Page No. 24)

Question 1: Differentiate between the following pairs of terms based on the clues given in parentheses:
(i) Cell membrane and cell wall (permeability)
(ii) RER and SER (structure)
(iii) Chioroplasts and chromoplasts (pigments)

Answer:
(i) Cell membrane and cell wall:
The cell membrane is selectively permeable, which means it allows only certain substances to enter or leave the cell. The cell wall is freely permeable, so it allows most substances to pass through it easily.

(ii) RER and SER:
RER, or Rough Endoplasmic Reticulum, has ribosomes attached to its surface, so it looks rough. SER, or Smooth Endoplasmic Reticulum, does not have ribosomes on its surface, so it appears smooth.

(iii) Chloroplasts and chromoplasts:
Chloroplasts contain the green pigment chlorophyll, which helps in photosynthesis. Chromoplasts contain coloured pigments such as yellow, orange, and red carotenoids, which give bright colours to flowers and fruits.

Question 2: Two similar animal cells are placed in two different solutions.
Cell X is placed in pure water.
Cell Y is placed in a concentrated salt solution.
Cells are observed after some time. Cell X swells, and Cell Y shrinks. Which statement provides the correct explanation for the above observations?
(i) Salt molecules moved into Cell Y, causing it to shrink.
(ii) Water moved into Cell X, and more water moved out of Cell Y than the salt solution entered in it.
(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
(iv) Solute movement caused osmosis in both cells.

Answer: The correct option is (iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.

Cell X swells because it is placed in pure water, so water enters the cell by osmosis. Cell Y shrinks because it is placed in a concentrated salt solution, so water moves out of the cell through the cell membrane.

Question 3: Look at the diagram of a cell in Fig. 2.20. Identify the parts labelled from (a) to (g) and correctly match them with their functions given below:
(i) Controlling all the activities of a cell.
(ii) Site of cellular respiration.
(iii) Storage organelle that also provides rigidity to the cell.
(iv) Separates the cell contents from surroundings.
(v) Provides structural rigidity to the cell.
(vi) Packs and stores materials received from ER.
(vii) Helps in manufacturing food.

Answer:
The labelled parts and their functions are:

(i) Controlling all the activities of a cell – (b) Nucleus
(ii) Site of cellular respiration – (a) Mitochondria
(iii) Storage organelle that also provides rigidity to the cell – (g) Vacuole
(iv) Separates the cell contents from surroundings – (f) Cell membrane
(v) Provides structural rigidity to the cell – (e) Cell wall
(vi) Packs and stores materials received from ER – (c) Golgi apparatus
(vii) Helps in manufacturing food – (d) Chloroplast

Question 4: Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories?

Answer: The correct option is (i) Leucoplast, Cell wall.

Leucoplasts and cell walls are present in plant cells. Animal cells do not have cell walls, and leucoplasts are also absent in animal cells.

Question 5: Two students, Renu and Rohit, were having a discussion on the plastids. Renu emphasised that all parts of the plants, even roots, contain plastids. However, Rohit did not agree with the statement and told her that plasrids are absent in plant roots since the roots are underground and do not need to perform photosynthesis. Who is correct? Justify your answer.

Answer:
Renu is correct.

All parts of plants, including roots, contain plastids. However, root cells do not usually contain chloroplasts because roots remain underground and do not receive sunlight for photosynthesis.

Instead, roots contain leucoplasts, which are colourless plastids. They help store food materials such as starch, oils, and proteins. Therefore, plastids are present in roots, but they are mainly storage plastids, not photosynthetic plastids.

Question 6: Mitochondria and chloroplasts are two important organelles in a plant cell. Discuss how these two Organalles are structurally and functionally similar to each other, and different from each other.

Answer:
Similarities:
Mitochondria and chloroplasts are both double-membrane cell organelles. Both have their own DNA and ribosomes, so they can make some of their own proteins. They are also involved in energy-related processes inside the cell and are called semi-autonomous organelles.

Differences:
Mitochondria are present in both plant and animal cells. They carry out cellular respiration and release energy in the form of ATP. Chloroplasts are mainly present in green plant cells and help in photosynthesis by using sunlight to prepare food.

Structurally, mitochondria have folded inner membranes called cristae, which increase the surface area for respiration. Chloroplasts contain a fluid-filled space called the stroma and disc-like structures that contain chlorophyll for photosynthesis.

Question 7: Which of the following pairs of cell organelles contains DNA?
(i) Chloroplasts, Ribosomes
(ii) Mitochondria, Nucleus
(iii) Golgi bodies, Ribosomes
(iv) Nucleus, Lysosomes

Answer: The correct option is (ii) Mitochondria, Nucleus.

The nucleus contains the main genetic material of the cell. Mitochondria also have their own DNA, which allows them to make some of their own proteins.

Question 8: A researcher conducted an art experiment in which she took two carrots of similar size. She placed one carrot in plain water and the other carrot in concentrated salt solution (Fig. 2 .21). After 24 hours, she recorded hr obserrations

(i) What hypothesis does she want to test through this experiment?
(ii) What would you suggest for the Improvement of this experiment?
(iii) Why does the carrot in plain water stay stiff and crunchy, but the carrot in concentrated salt solution become rubbery and limp?

Answer:
(i) The researcher wants to test the effect of osmosis on plant tissues. She wants to observe how carrots behave when placed in plain water and in a concentrated salt solution.

(ii) The experiment can be improved in the following ways:

• Use carrots of the same size and thickness for fair comparison.

• Measure the initial and final weight of both carrots using a digital balance.

• Keep both carrots in the solutions for the same duration.

• Use a fixed concentration of salt solution.

• Repeat the experiment to get more accurate results.

(iii) The carrot kept in plain water remains stiff and crunchy because water enters the carrot cells by osmosis. This makes the cells turgid.

The carrot kept in a concentrated salt solution becomes rubbery and limp because water moves out of the carrot cells into the salt solution. This causes loss of turgidity, making the carrot soft and flexible.

Question 9: Indicate the presence or absence of following structures in bactenal and animal cells:

Answer:

Bacterial cells do not have a well-defined nucleus or membrane-bound organelles. Animal cells are eukaryotic, so they contain a nucleus, mitochondria, and a Golgi complex.

Question 10: Carry out the following experiment:
Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Place each of the potato cups in a beaker containing water (Fig. 2.22).

Now, set up the experiment as follows:
(a) Keep Cup A empty.
(b) Add one teaspoon sugar in Cup B.
(c) Add one teaspoon salt in Cup C.
(d) Add one teaspoon sugar in the boiled potato in Cup D.

Observe the four potato cups at least two hours and answer the following questions:
(i) Explain why water gathers in the hollowed portion of Cup B and Cup C.
(ii) Why is Cup A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed portions of Cups A and D.

Answer:
(i) Water gathers in the hollowed portions of Cup B and Cup C due to osmosis. Sugar and salt make the solution inside the potato cups more concentrated than the water outside. So, water moves from the beaker into the potato cups through the semipermeable membranes of the potato cells.

(ii) Cup A is necessary because it acts as a control. It helps us compare the results and shows that water does not collect in the potato cup when no solute, like sugar or salt, is added.

(iii) Water does not gather in Cup A because there is no concentration difference between the inside and outside of the potato cup.

Water does not gather in Cup D because it is made from a boiled potato. Boiling destroys the semipermeable membranes of the potato cells, so osmosis cannot take place.

Question 11: Identify the pair that incorrectly matches the cell organelle with its function.
(i) Ribosome – Protein synthesis
(ii) SER – Lipid and cellulose synthesis
(iii) Lysosome – Digestion of foreign agents

Answer: The incorrectly matched pair is (ii) SER – Lipid and cellulose synthesis.

SER helps in the synthesis of lipids. However, cellulose synthesis is not done by SER. In plant cells, cellulose is mainly formed near the cell membrane and becomes a major part of the cell wall.

Question 12: What outcome do you expect if all the mitochondria are removed from a eukaryotic cell?

Answer: If all mitochondria are removed from a eukaryotic cell, the cell will not be able to produce enough ATP through cellular respiration. ATP is the main energy source required for cellular activities.

Without mitochondria, important processes such as metabolism, active transport, growth, repair, and cell division will be affected. Eventually, the cell may stop functioning and die.

Question 13: Which phenomenon inhibits the formation of tumours in the human body? Can plants also develop tumours? Explain.

Answer: The phenomenon that inhibits tumour formation in the human body is contact inhibition.

In normal cells, contact inhibition stops cells from dividing when they come in contact with nearby cells. This prevents uncontrolled cell growth.

Yes, plants can also develop tumour-like growths. These are often caused by infections or abnormal cell division. However, plant tumours usually do not spread like animal cancers because plant cells have rigid cell walls, which restrict the movement of abnormal cells.

Question 14: The cell membrane of a cell is made up of proteins and lipids. Which cell organelles help in the synthesis of cell membrane? Write the path of these compounds from their site of synthesis to the cell membrane and show this through a labelled diagram.

Answer: The endoplasmic reticulum and Golgi apparatus help in the formation of the cell membrane.

The Rough Endoplasmic Reticulum (RER) helps in protein synthesis because it has ribosomes attached to it. The Smooth Endoplasmic Reticulum (SER) helps in lipid synthesis. These proteins and lipids are then sent to the Golgi apparatus, where they are modified, packed, and transported to the cell membrane through vesicles.

Pathway:

Nucleus → SER/RER (Synthesis of lipids/proteins) → Transport Vesicle – Golgi Apparatus (Modification and packaging)

Secretory Vesicles → Cell/Plasma Membrane Endoplasmic Reticulum and Golgi apparatus – pathway for protein processing and secretion.

Question 15: Which would happen if gametes are formed by mitotic divisions?

Answer: If gametes are formed by mitotic divisions, they will have the same number of chromosomes as the parent cell. This means they will be diploid instead of haploid.

During fertilisation, two diploid gametes would fuse and form a zygote with double the normal chromosome number. This would disturb the chromosome balance in the next generation. If this continued, the chromosome number would keep increasing in every generation.

Such changes can make cells abnormal and may affect the survival of the organism. Also, mitosis does not bring genetic variation the way meiosis does, so diversity among offspring would be reduced.

Question 16: A farmer, Deepa, was very happy with the harvest of amia (Indian Gooseberry) and lemons on her farm. However, she could sell only one-fourth of the produce in the local market. Recognising that a significant amount of produce may be lost post-harvest, she employed a traditional yet scientifically sound method to extend the shelf life of amla and lemons. She turned perishable produce into profitable products, such as pickles and sharbat. She used the excess produce to prepare pickles, mura bbas, and sharhat by adding appropriate amounts of salt, sugar, or jaggery to small pieces of fruit and their juices.

These were then stored in small glass bottles for sale, helping her prevent the wastage of post-harvest produce. This shift from farming to agro-processing would strengthen food security and boost the local economy, creating a sustainable model that cuts waste while increasing her income. Based on the above passage, answer the following questions:
(i) Which scientific concept has the farmer applied in the preservation of the farm produce?
(ii) How does the addition of high concentrations of salt and sugar create an environment that prevents the growth of spoilage-causing bacteria and fungi?
(iii) Suggest a healthy recipe of this kind for food preservation.
(iv) What are the scientific values addressed in this case?

Answer:
(i) The farmer has applied the scientific concept of osmosis in food preservation.

(ii) High concentrations of salt and sugar create a hypertonic environment around bacteria and fungi. Due to osmosis, water moves out of the cells of these microorganisms. This causes dehydration and prevents their growth, thereby reducing spoilage.

(iii) A healthy recipe for food preservation is amla pickle with less oil and jaggery.

Take washed and chopped amla pieces. Add a small amount of mustard oil, turmeric, salt, chilli powder, and a little jaggery. Mix well and store the pickle in a clean and dry glass jar. Keep it in sunlight for a few days. This helps preserve amla while maintaining its taste and nutritional value.

(iv) The scientific values addressed in this case are:

• Use of scientific knowledge in daily life

• Prevention of food wastage

• Resource conservation

• Traditional knowledge with scientific understanding

• Food preservation and sustainability

• Entrepreneurship and economic awareness

Think it Over (NCERT Textbook Page No. 8)

Question 1: Where does a cell come from?

Answer: A cell comes from a pre-existing cell through the process of cell division. New cells do not form on their own. They arise only from cells that already exist.

Question 2: How have technological interventions facilitated the creation of rich knowledge in understanding the world beyond the naked eye?

Answer: Technological interventions such as microscopes, electron microscopes, and advanced imaging tools have helped scientists study things that cannot be seen with the naked eye.

Simple microscopes first helped scientists discover cells. Later, powerful microscopes made it possible to observe tiny cell structures such as the nucleus, mitochondria, and other organelles. These tools expanded our understanding of cells, microorganisms, and the microscopic world.

Question 3: ‘How’ is the cell structural and functional unit of life’

Answer: The cell is called the structural unit of life because all living organisms are made up of cells.

It is called the functional unit of life because all important life processes, such as nutrition, respiration, growth, excretion, response to surroundings, and reproduction, take place inside cells. In multicellular organisms, cells also combine to form tissues, organs, and organ systems.

Question 4: How does a cell multiply?

Answer: A cell multiplies through the process of cell division. During cell division, one parent cell divides to form new daughter cells.

Cell division helps living organisms grow, repair damaged tissues, replace old cells, and reproduce.

Think it Over (NCERT Textbook Page No. 11)

Question 5: How does the structure of the cell membrane in the cells of alveoli control the movement of substances across it?

Answer: The cell membrane in the cells of alveoli is very thin and selectively permeable. This structure allows gases such as oxygen and carbon dioxide to pass through easily by diffusion.

Oxygen moves from the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli. The thin membrane and large surface area of alveoli make gas exchange quick and efficient.

What If. (NCERT Textbook Page No. 12)

Question 1: Mung bean seeds are kept in a concentrated solution after soaking in water for 12 hours? What will happen to them?

Answer: If soaked mung bean seeds are kept in a concentrated solution, water will move out of the seed cells by osmosis.

As a result, the seeds may shrink, lose water, and fail to swell properly. Their germination may slow down or stop because the cells do not get enough water for growth.

Pause and Ponder (NCERT Textbook Page No. 14)

Question 1: What argument would you give for the necessity of a cell wall in plants, usually fixed in one place, versus in animals usually moving from one place to the other?

Answer: Plants are usually fixed in one place, so they need strong support and protection. The cell wall gives plant cells a definite shape, rigidity, and strength. It also helps the plant remain upright and protects cells from bursting when water enters them.

Animals move from one place to another, so their cells need flexibility. Therefore, animal cells do not have a rigid cell wall.

Question 2: What consequences would you predict for a plant cell if its cell wall were to become as flexible as a cell membrane?

Answer: If the plant cell wall became as flexible as the cell membrane, the plant cell would lose its fixed shape and support. The plant would become weak and may not remain upright.

The cell wall also prevents the cell from bursting when excess water enters. If it became too flexible, the cell would not be able to withstand pressure changes properly, and the plant could wilt or collapse easily.

Question 3: Why is it important to cut the two potato pieces in roughly equal size and measure their initial weight before placing them in different liquids?

Answer: It is important to cut the two potato pieces in roughly equal size and measure their initial weight to make the experiment fair.

If the pieces are of different sizes or weights, the change observed after placing them in different liquids may not be due only to osmosis. Equal size and initial weight help compare the effect of different solutions accurately.

Pause and Ponder (NCERT Textbook Page No. 19)

Question 4: Do white flowers contain any pigment? Give reasons.

Answer: Yes, white flowers may contain pigments, but they do not have strong coloured pigments in visible amounts.

White flowers appear white because their petals reflect most wavelengths of light. They usually lack pigments such as anthocyanins that give red, blue, or purple colour. Some white flowers may contain colourless or very light pigments that are not clearly visible.

Question 5: Draw a well-labelled schematic diagram of a plant or an animal cell using these clues –
(i) Nucleus appears as a dark and round body inside the cell.
(ii) ER spreads like a network of extended nuclear envelope.
(iii) Mitochondria and chloroplasts are rod-shaped.
You may refer to Fig. 2.10.

Answer:

Pause and Ponder (NCERT Textbook Page No. 21)

Question 6: Can you identify which stage comes first during cell division?

Answer: The first stage of cell division is prophase.

During prophase, chromosomes become short, thick, and visible. The nuclear membrane starts disappearing, and the cell prepares for the next stages of division.

Pause and Ponder (NCERT Textbook Page No. 22)

Question 6: Instead of many small ones, why does a cell not have a single giant mitochondrion? How does this relate to the concept of surface area?

Answer: A cell has many small mitochondria instead of one giant mitochondrion because many small mitochondria provide a larger total surface area.

A larger surface area helps carry out respiration and energy production more efficiently. If there were only one large mitochondrion, the surface area available for energy-producing reactions would be less effective. Therefore, many small mitochondria help the cell produce energy faster and more efficiently.

Question 7: If the skin cells start dividing by meiosis instead of mitosis, what do you think will happen to a cut on the skin?

Answer: If skin cells start dividing by meiosis instead of mitosis, the cut on the skin will not heal properly.

Mitosis produces identical body cells needed for growth and repair. Meiosis produces cells with half the chromosome number, which are not suitable for replacing damaged skin cells. Therefore, wound healing would be affected.

Ready to Go Beyond (NCERT Textbook Page No. 23)

Question 1: Explore different ways by which cells maintain themselves.

Answer: Cells maintain themselves through many important processes. They take in nutrients, produce energy, remove waste materials, repair damaged parts, and respond to changes in their surroundings.

Cells also control what enters and leaves through the cell membrane. Organelles such as mitochondria, ribosomes, lysosomes, endoplasmic reticulum, and Golgi apparatus help the cell perform different functions. These activities allow the cell to stay alive and work properly.

Activity 2.1: Let Us Estimate The Size Of a Cell (NCERT Textbook Page No. 10)

Aim: To estimate the size of an onion peel cell using Estimated size of the onion peel cell a microscope by measuring the field of view and counting the number of cells across it.

Estimation: The estimated size of one onion peel cell can be calculated by dividing the diameter of the field of view by the number of cells seen across that diameter.

Observation: The diameter of the field of view is first measured. For example, if the diameter is 5 mm, it is equal to 5000 μm. Then the number of onion peel cells lying across this diameter is counted. If 10 cells are seen across the diameter, the approximate size of one cell can be estimated.

Conclusion: The size of one onion peel cell can be estimated by using this formula:

Estimated size of the onion peel cell  = Diameter of the visible field in micrometre ÷ Number of cells along the diameter

For example, 5000 μm ÷ 10 = 500 μm. This shows that cells are very small and need a microscope for observation.

Activity 2.2: Let Us Experiment (NCERT Textbook Page No. 11)

Aim: To observe the effect of osmosis by studying the change in weight of potato pieces placed in plain water and concentrated salt/sugar solution.

Observation: The potato piece kept in plain water absorbs water and becomes firm. Its weight increases because water enters the potato cells by osmosis.

The potato piece kept in concentrated salt or sugar solution loses water and becomes soft. Its weight decreases because water moves out of the potato cells into the concentrated solution.

Conclusion: This activity shows the process of osmosis. Water moves from a region of higher water concentration to a region of lower water concentration through a semipermeable membrane.

In plain water, water enters the potato cells and makes them turgid. In a concentrated salt or sugar solution, water leaves the potato cells and makes them flaccid.

Activity 2.3: Let Us Investigate (NCERT Textbook Page No. 13)

Aim: To prepare and observe temporary slides of plant cells (onion/ Rhoeo leaf) and human cheek cells, compare their structures, and study the effect of a concentrated sugar solution on them.

Observation:

Onion/Rhoeo leaf cells:
The plant cells appear rectangular or brick-shaped. They have a clear cell wall, cell membrane, cytoplasm, and nucleus. The cells are arranged closely and regularly.

Human cheek cells:
The cheek cells appear irregular or rounded in shape. They do not have a cell wall. They have a cell membrane, cytoplasm, and a visible nucleus. These cells are loosely arranged.

Effect of concentrated sugar solution:

• In plant cells, water moves out of the cells by osmosis. The cytoplasm shrinks away from the cell wall, showing plasmolysis.

• In human cheek cells, water also moves out due to osmosis, and the cells shrink because they do not have a rigid cell wall.

Conclusion: Plant and animal cells differ mainly because plant cells have a cell wall, while animal cells do not. Both plant and animal cells lose water when placed in a concentrated sugar solution. Plant cells show plasmolysis, while animal cells shrink and become distorted.

Activity 2.4: Let Us Study (NCERT Textbook Page No. 14-15)

Aim: To study and compare the structures of bacterial, plant, and animal cells using diagrams and record the observations.

Table 2.1: Comparison of Different Kinds of Cells Based on Their Structure

Observation:

Table 2.1: Comparison of different kinds of cells based on their structure

Conclusion: Bacterial cells are prokaryotic cells. They do not have a well-defined nucleus or membrane-bound organelles. Plant and animal cells are eukaryotic cells and have a well-defined nucleus and membrane-bound organelles.

Plant cells are different from animal cells because they have a cell wall, plastids, and a large central vacuole. Animal cells do not have a cell wall or plastids.

Activity 2.5: Let Us Enhance Our Skills (NCERT Textbook Page No. 20)

Aim: To study the structure of actively dividing cells in the onion root tip and observe different stages of mitosis under a microscope.

Observation: The onion root tip contains many actively dividing cells. These cells are small, closely packed, and found in the meristematic region.

The following stages of mitosis can be observed:

Interphase: The nucleus is visible, and chromatin is present inside it.
Prophase: Chromosomes become short, thick, and clearly visible.
Metaphase: Chromosomes arrange themselves at the centre of the cell.
Anaphase: Sister chromatids separate and move towards opposite poles.
Telophase: Two new nuclei begin to form, and the cell prepares to divide.

The chromosomes appear dark because they absorb the stain, making them easy to observe under the microscope.

Conclusion: The onion root tip is a good region to study mitosis because it contains actively dividing cells. Mitosis produces two identical daughter cells with the same chromosome number as the parent cell. This process helps in the growth, repair, and replacement of cells.

Class 9 Science Chapter 2 Cell: The Building Block of Life Solutions

Vedantu provides NCERT Solutions for Class 9 Science Chapter 2, Cell: The Building Block of Life, from the Exploration textbook for the 2026-27 academic session. This chapter helps students understand cells as the basic structural and functional units of life. It explains important concepts such as cell membrane, cell wall, nucleus, cytoplasm, plastids, mitochondria, vacuoles, osmosis, and cell division.

The solutions include clear answers for exercise questions, in-text questions, activity-based questions, diagram-based questions, comparison tables, and application-based questions. Students can use these solutions for homework, revision, classroom learning, and exam preparation. The downloadable FREE PDF also helps students revise the complete chapter offline whenever needed.

CBSE Class 9 Science Chapter 2 Study Materials

Students can use the Chapter 2 study materials below to revise important concepts, practise extra questions, and strengthen their understanding of cells, cell organelles, osmosis, and cell division.

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The chapter-wise NCERT Solutions for Class 9 Science help students understand concepts from different areas of science in a simple and organised way. These resources provide clear explanations, textbook answers, activity-based solutions, diagrams, examples, and revision support for each chapter.

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The following Class 9 Science study materials support concept learning, practice, revision, and exam preparation. Students can use them along with the Exploration textbook solutions for better understanding and regular study.