NCERT Solutions for Class 9 Science Exploration Chapter 2

Cell is the basic structural and functional unit of life because every living organism is made of one or more cells.
Class 9 Science Exploration Chapter 2 explains cell structure, organelles, osmosis, cell division, and cell theory for the 2026-27 syllabus.

NCERT Solutions for Class 9 Science Exploration Chapter 2 help students understand the chapter Cell: The Building Block of Life from the new Class 9 Science textbook. This chapter is important for CBSE students because it connects microscope-based observations with major Biology concepts like cell membrane, cell wall, osmosis, organelles, mitosis, meiosis, and cell theory. The chapter also introduces Indian scientific context through Puga Valley hot springs in Ladakh and explains how early cell-like structures may have formed in water-rich environments. These NCERT Class 9 Science Solutions cover in-text activities, Pause and Ponder questions, and the Revise, Reflect, Refine exercise questions in a clear answer-writing format.

Key Takeaways

• Basic unit: The cell is the structural and functional unit of all living organisms.
• Core Biology skill: Students learn to compare plant, animal, bacterial, prokaryotic, and eukaryotic cells.
• Major process: Osmosis explains water movement through a selectively permeable membrane.
• Exam relevance: CBSE and school exams can ask diagrams, differences, MCQs, reasoning questions, and activity-based answers from this chapter.

NCERT Solutions for Class 9 Science Exploration Chapter 2 Structure 2026

NCERT Solutions for Class 9 Science Exploration Chapter 2 In-Text Questions

The in-text questions in Chapter 2 test observation, reasoning, and experiment-based Biology understanding. These answers use the same concepts explained in the chapter.

Q1. Activity 2.1: Let Us Estimate the Size of a Cell

Question: Suppose the visible field diameter is 5 mm and 25 onion peel cells are seen along the diameter. Estimate the size of one onion peel cell.

Answer: The estimated size of one onion peel cell is $200 , \mu m$.

Explanation:
Convert the field diameter into micrometres.

$1 , mm = 1000 , \mu m$

$5 , mm = 5 \times 1000 = 5000 , \mu m$

Use the formula:

$Estimated , cell , size = \frac{Diameter , of , visible , field}{Number , of , cells , along , diameter}$

$Estimated , cell , size = \frac{5000}{25} = 200 , \mu m$

So, one onion peel cell is approximately $200 , \mu m$ in size.

Q2. Activity 2.2: Potato Pieces in Plain Water and Salt Solution

Question: What happens when one potato piece is placed in plain water and another in 20% salt or sugar solution?

Answer: The potato piece in plain water swells, while the potato piece in salt or sugar solution shrinks.

Explanation:
The potato piece in plain water gains water because water enters its cells through osmosis. The potato piece in concentrated salt or sugar solution loses water because water moves out of its cells.

In plain water:

1. Outside solution has more water.
2. Water enters potato cells.
3. Potato piece swells and gains weight.

In concentrated solution:

1. Outside solution has less water and more solute.
2. Water moves out of potato cells.
3. Potato piece shrinks and loses weight.

This experiment explains osmosis Class 9 Science through a real plant tissue example.

Q3. Activity 2.3: Onion Peel Cells and Cheek Cells

Question: Why are onion peel cells box-shaped, while human cheek cells are irregular in shape?

Answer: Onion peel cells are box-shaped because they have a rigid cell wall, while cheek cells are irregular because animal cells do not have a cell wall.

Explanation:
The plant cell wall gives onion cells a fixed and regular shape. Cheek cells have only a flexible cell membrane, so they can change shape more easily.

When placed in 20% sugar solution:

1. Plant cell contents shrink due to water loss.
2. The outer cell wall remains firm.
3. Cheek cells shrink because they lack a rigid wall.

This observation explains the difference between plant cell and animal cell Class 9.

Q4. Pause and Ponder: Why Do Plants Need Cell Walls?

Question: 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 need cell walls because they are fixed in one place and need rigid support against wind, rain, and water loss.

Explanation:
Plant cells have a rigid cell wall made mainly of cellulose. It supports leaves, flowers, and stems and helps plants remain upright.

Animals move from place to place and need flexible cells for movement. Animal cells do not have cell walls, so their tissues can bend, contract, and change shape.

The cell wall is necessary for plants because it provides strength, shape, and protection.

Q5. Pause and Ponder: What If a Plant Cell Wall Became Flexible?

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

Answer: The plant cell would lose its fixed shape and would not support the plant properly.

Explanation:
A flexible cell wall would fail to resist pressure changes inside the cell. The plant cell may become weak, lose firmness, and collapse more easily during water loss.

The plant would also struggle to stay upright. Leaves and flowers would lose shape because the rigid support of the cell wall would be missing.

Q6. Pause and Ponder: Why Cut Potato Pieces in Equal Size?

Question: 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: Equal size and initial weight make the potato experiment fair and comparable.

Explanation:
If the two potato pieces are different in size, one piece may gain or lose more water only because it has more tissue. Measuring the initial weight helps calculate the actual change after osmosis.

A fair experiment changes only one factor. In this case, the changed factor is the surrounding liquid.

Q7. Activity 2.4: Prokaryotic and Eukaryotic Cells

Question: Which cells in Fig. 2.10 fall under prokaryotic and eukaryotic cells?

Answer: The bacterial cell is prokaryotic, while the plant cell and animal cell are eukaryotic.

Explanation:
A bacterial cell does not have a well-defined nucleus or membrane-bound organelles. Its genetic material is present in a nucleoid region.

Plant and animal cells have a well-defined nucleus and membrane-bound organelles. This makes them eukaryotic cells.

Q8. Pause and Ponder: Do White Flowers Contain Pigment?

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

Answer: White flowers may lack coloured pigments or may contain pigments that do not absorb visible light strongly.

Explanation:
Bright flower colours usually come from chromoplasts containing yellow, orange, or red pigments. White flowers appear white because most visible light is reflected rather than absorbed.

Some white flowers may also have air spaces that scatter light. Their colour is not due to chlorophyll or bright chromoplast pigments.

Q9. Pause and Ponder: Draw a Well-Labelled Plant or Animal Cell

Question: Draw a well-labelled schematic diagram of a plant or an animal cell using the given clues.

Answer: A plant cell diagram should show cell wall, cell membrane, cytoplasm, nucleus, ER, mitochondria, chloroplasts, and vacuole.

Explanation:
Use these labels in the diagram:

1. Cell wall as the outer rigid boundary
2. Cell membrane just inside the cell wall
3. Cytoplasm as the jelly-like internal material
4. Nucleus as a dark round body
5. ER as a network around the nucleus
6. Mitochondria as rod-shaped organelles
7. Chloroplasts as rod-shaped green plastids
8. Large central vacuole inside the plant cell

An animal cell diagram should not show cell wall or chloroplasts.

Q10. Pause and Ponder: Why Not One Giant Mitochondrion?

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

Answer: A cell has many small mitochondria because they provide more surface area for energy-producing reactions.

Explanation:
Mitochondria produce ATP on their inner membrane. Many small mitochondria provide more membrane surface area than one giant mitochondrion of similar total volume.

More surface area allows faster exchange of materials and more efficient energy production. This is why cells use many small mitochondria.

Q11. Pause and Ponder: What If Skin Cells Divide by Meiosis?

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

Answer: A skin cut would not heal properly if skin cells divided by meiosis instead of mitosis.

Explanation:
Skin repair needs mitosis because mitosis produces two identical daughter cells with the same chromosome number. These identical cells replace damaged skin cells.

Meiosis produces gametes with half the chromosome number. Such cells cannot replace normal skin cells properly.

NCERT Solutions for Class 9 Science Exploration Chapter 2 Exercise Questions

The Revise, Reflect, Refine section checks detailed understanding of the cell chapter. These Class 9 Science Chapter 2 exercise solutions cover all 16 textbook questions.

Q1. Differentiate between the following pairs of terms based on the clues given in parentheses.

Answer: The differences are based on permeability, structure, and pigments.

Explanation:
Cell membrane controls what enters and leaves the cell. Cell wall mainly gives shape, support, and protection.

RER helps in protein synthesis because ribosomes are attached to it. SER helps in lipid and hormone synthesis.

Chloroplasts help in photosynthesis. Chromoplasts give colours to flowers, fruits, and vegetables.

Q2. Two animal cells are placed in pure water and concentrated salt solution. Which statement correctly explains why Cell X swells and Cell Y shrinks?

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

Explanation:
Cell X is placed in pure water, so water enters the cell through osmosis. This makes Cell X swell.

Cell Y is placed in concentrated salt solution, so water moves out of the cell. This makes Cell Y shrink.

Salt molecules do not directly cause the shrinkage by entering the cell. The movement of water through the cell membrane causes the change.

Q3. Identify the labelled parts of the cell and match them with their functions.

Answer: The labelled parts in a typical plant cell can be matched with common organelle functions.

Explanation:
The exact letters depend on the labels shown in Fig. 2.20. Match the visible structures by shape and position.

Cell wall is the outer rigid layer. Cell membrane lies inside it. Nucleus is usually round and dark. Chloroplasts are present only in plant cells.

Q4. Which pairs of cell organelles are correctly placed under the given categories?

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

Explanation:
Leucoplasts are present in plant cells and are absent in animal cells. Cell wall is also absent in animal cells.

The other options are incorrect because mitochondria, ribosomes, Golgi apparatus, lysosomes, and endoplasmic reticulum are not exclusive in the way shown.

Q5. Renu says all plant parts, even roots, contain plastids. Rohit says plastids are absent in roots. Who is correct?

Answer: Renu is correct because roots can contain plastids in the form of leucoplasts.

Explanation:
Roots do not usually perform photosynthesis because they are underground and do not receive sunlight. So, they may not have chloroplasts in large numbers.

However, roots can contain leucoplasts. Leucoplasts store food materials like starch, oils, or proteins.

Potato and taro cells contain leucoplasts that store starch. This supports Renu’s statement.

Q6. Discuss similarities and differences between mitochondria and chloroplasts.

Answer: Mitochondria and chloroplasts are similar because both are double-membrane organelles and contain their own DNA and ribosomes.

Explanation:

Both organelles are linked to energy processes. Mitochondria release energy from food, while chloroplasts help make food using sunlight.

Q7. Which pair of organelles contains DNA?

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

Explanation:
The nucleus contains DNA in chromosomes. Mitochondria also have their own DNA and ribosomes.

Chloroplasts also contain DNA, but the pair “chloroplasts, ribosomes” is incorrect because ribosomes do not contain DNA.

Q8. Carrot Experiment in Plain Water and Salt Solution

Question: A researcher places one carrot in plain water and another in concentrated salt solution. Answer the sub-parts.

Answer: The experiment tests osmosis in plant cells.

(i) Hypothesis:
The researcher wants to test whether water enters or leaves carrot cells depending on the concentration of the surrounding solution.

(ii) Improvement:
She should use carrots of equal size and weight, measure initial and final mass, use equal volumes of solution, and keep both carrots for the same time.

(iii) Explanation:
The carrot in plain water stays stiff because water enters its cells by osmosis. This keeps the cells turgid.

The carrot in concentrated salt solution becomes rubbery because water moves out of its cells. The cells lose firmness and become flaccid.

Q9. Indicate the presence or absence of structures in bacterial and animal cells.

Answer: The structures differ because bacterial cells are prokaryotic and animal cells are eukaryotic.

Explanation:
Bacteria have genetic material, but it is not enclosed in a membrane-bound nucleus. Animal cells have nucleus and membrane-bound organelles.

Chromoplasts are plastids, so they are found in plant cells, not animal or bacterial cells.

Q10. Potato Cup Experiment

Question: Explain why water gathers in Cups B and C, why Cup A is necessary, and why water does not gather in Cups A and D.

Answer: Water gathers in Cups B and C because sugar and salt create concentrated solutions that draw water through living potato tissue by osmosis.

(i) Why water gathers in Cups B and C:
Sugar in Cup B and salt in Cup C make the hollow region concentrated. Water moves from the beaker through potato cells into the hollow region by osmosis.

(ii) Why Cup A is necessary:
Cup A acts as a control. It shows that water does not gather in the hollow portion without sugar or salt.

(iii) Why water does not gather in Cups A and D:
Cup A has no solute, so no concentration gradient is created.

Cup D is made from boiled potato. Boiling kills the potato cells and damages selectively permeable membranes, so osmosis does not occur.

Q11. Identify the incorrect match between cell organelle and function.

Answer: The incorrect match is (ii) SER — Lipid and cellulose synthesis.

Explanation:
SER helps in lipid synthesis and storage of fats and some hormones. It does not synthesise cellulose.

Cellulose is mainly associated with the plant cell wall. Ribosomes synthesise proteins, and lysosomes digest foreign agents and waste materials.

Q12. What happens if all mitochondria are removed from a eukaryotic cell?

Answer: The cell would not produce enough ATP for its activities and may die.

Explanation:
Mitochondria release energy during cellular respiration. This energy is stored as ATP.

Without mitochondria, the cell cannot meet its energy needs for transport, repair, synthesis, and division. A eukaryotic cell cannot function normally without mitochondria.

Q13. Which phenomenon inhibits tumour formation in the human body? Can plants also develop tumours?

Answer: Contact inhibition helps inhibit tumour formation in the human body.

Explanation:
Normal animal cells usually stop dividing when they touch neighbouring cells. This control prevents unnecessary cell growth.

Cancer cells lose contact inhibition and divide uncontrollably, forming tumours.

Plants can also develop tumour-like growths. However, plant cells have rigid cell walls and different growth patterns, so their tumour development differs from animal cancer.

Q14. Which organelles help in the synthesis of cell membrane? Write the path of these compounds.

Answer: Endoplasmic reticulum and Golgi apparatus help in the synthesis and transport of cell membrane components.

Explanation:
The cell membrane is made of proteins and lipids. Ribosomes on RER help make proteins, while SER helps make lipids.

Pathway:

1. Ribosomes on RER synthesise proteins.
2. SER synthesises lipids.
3. ER transports proteins and lipids to the Golgi apparatus.
4. Golgi apparatus modifies, sorts, and packages them into vesicles.
5. Vesicles move to the plasma membrane.
6. Vesicles fuse with the cell membrane and add new components.

Labelled pathway:

$RER , / , SER \rightarrow Golgi , apparatus \rightarrow Vesicles \rightarrow Cell , membrane$

Q15. What would happen if gametes are formed by mitotic divisions?

Answer: Gametes would not have half the chromosome number if they were formed by mitosis.

Explanation:
Mitosis produces daughter cells with the same chromosome number as the parent cell. If gametes formed by mitosis, sperm and egg would each carry the full chromosome number.

After fertilisation, the zygote would have double the normal chromosome number. This would disturb normal development and chromosome balance.

Meiosis is necessary because it reduces the chromosome number by half in gametes.

Q16. Farmer Deepa Preserves Amla and Lemons Using Salt and Sugar

Question: Answer the questions based on the passage about preserving amla and lemons.

Answer: Farmer Deepa applied osmosis and food preservation by using high concentrations of salt and sugar.

(i) Scientific concept applied:
The main concept is osmosis. High salt or sugar concentration removes water from microbial cells.

(ii) How salt and sugar prevent spoilage:
High concentrations of salt and sugar create a hypertonic solution around bacteria and fungi. Water moves out of their cells by osmosis.

When microbes lose water, they cannot grow and multiply properly. This slows spoilage and increases shelf life.

(iii) Healthy recipe:
A healthy recipe can be lemon pickle with lemon pieces, salt, turmeric, mustard seeds, and a small amount of oil. Another option is amla murabba made with reduced jaggery and clean storage methods.

(iv) Scientific values addressed:
The case shows scientific food preservation, waste reduction, value addition, food security, local income generation, and sustainable agro-processing.

Cell Membrane and Cell Wall Class 9

Cell membrane and cell wall Class 9 questions often test permeability and shape. The cell membrane is present in all cells, but the cell wall is present in plants, fungi, and bacteria.

The cell membrane is selectively permeable. It allows some substances to pass through and blocks others.

The cell wall is rigid and permeable. It gives support, shape, and protection to plant cells.

Plant cells remain firm in a concentrated solution because the cell wall keeps the outer shape. Animal cells shrink more because they lack a cell wall.

Osmosis Class 9 Science

Osmosis Class 9 Science means diffusion of water through a selectively permeable membrane. Water moves from a dilute solution to a concentrated solution.

In plain water, potato or carrot cells gain water and become firm. In concentrated salt or sugar solution, they lose water and become soft or shrunken.

Important terms:

1. Hypotonic solution: Outside solution has lower solute concentration.
2. Hypertonic solution: Outside solution has higher solute concentration.
3. Isotonic solution: Inside and outside solute concentrations are equal.

Osmosis is important in root water absorption and food preservation.

Prokaryotic and Eukaryotic Cells Class 9

Prokaryotic and eukaryotic cells Class 9 questions usually ask about nucleus and organelles. Bacterial cells are prokaryotic, while plant and animal cells are eukaryotic.

Prokaryotic cells carry out most activities directly in the cytoplasm. Eukaryotic cells use specialised organelles for different functions.

Plant Cell and Animal Cell Class 9

Plant cell and animal cell Class 9 differences are commonly asked in school exams. Students should focus on cell wall, chloroplasts, vacuoles, and shape.

Plant cells have rigid support because of the cell wall. Animal cells are more flexible because they lack a cell wall.

Mitosis and Meiosis Class 9

Mitosis and meiosis Class 9 questions test growth, repair, reproduction, and chromosome number. Mitosis is used for body growth and repair, while meiosis forms gametes.

Mitosis helps a skin cut heal. Meiosis helps form sperm, eggs, pollen grains, and egg cells.

Cell Theory Class 9 Science

Cell theory Class 9 Science explains the common cellular basis of all living organisms. It connects bacteria, plants, animals, and humans through the same basic unit of life.

Classical cell theory states:

1. All living organisms are made up of one or more cells.
2. The cell is the basic unit of structure and function in living beings.
3. All cells arise from pre-existing cells.

Matthias Schleiden stated that plants are made of cells. Theodor Schwann stated that animals are made of cells. Rudolf Virchow added that new cells arise from pre-existing cells.

Topics Covered in NCERT Solutions for Class 9 Science Exploration Chapter 2

Class 9 Science Exploration Chapter 2 covers the cell as the basic unit of life. The chapter moves from observing cells under microscopes to understanding how cells grow, divide, and maintain life.

• Origin of life in water
• Puga Valley hot springs in Ladakh
• Thermophiles and unicellular organisms
• Cell as the basic unit of life
• Unicellular and multicellular organisms
• Tissues, organs, and organ systems
• Limit of resolution of the human eye
• Light microscope and electron microscope
• Magnification, resolution, and contrast
• Estimating size of onion peel cells
• Cell membrane and selective permeability
• Osmosis Class 9 Science
• Diffusion and concentration gradient
• Isotonic, hypotonic, and hypertonic solutions
• Cell wall in plants, fungi, and bacteria
• Plant cell and animal cell Class 9
• Prokaryotic and eukaryotic cells Class 9
• Cell organelles Class 9 Science
• Nucleus, DNA, chromatin, chromosomes, and genes
• Ribosomes, ER, Golgi apparatus, lysosomes, and mitochondria
• Plastids, chloroplasts, chromoplasts, and leucoplasts
• Vacuoles and cell sap
• Cell division, mitosis, and meiosis
• Cell theory Class 9 Science
• Contact inhibition, tumours, and cancer cells
• Synthetic biology and ethical questions

Important Concepts in NCERT Solutions for Class 9 Science Exploration Chapter 2

Class 9 Science Chapter 2 solutions require clear understanding of cell parts and their functions. These concepts are often tested through diagrams, tables, MCQs, and reason-based questions.

Important Cell Organelles in Class 9 Science Exploration Chapter 2

Cell organelles Class 9 Science questions usually ask students to match organelles with functions. Students should learn both the structure and the function of each organelle.

Important Differences in NCERT Solutions for Class 9 Science Exploration Chapter 2

Cell The Building Block of Life Class 9 includes many comparison-based questions. These differences help students answer school exam questions in a compact format.

NCERT Solutions for Class 9 Science Exploration