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

These Class 9 Science Exploration Chapter 2 solutions cover Cell: The Building Block of Life from the new NCF-2023 textbook (2026–27).

Class: 9 Subject: Science Book: Exploration Chapter: 2 Exercise: Revise, Reflect, Refine (16 Qs) Session: 2026–27
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Class 9 Science Exploration Chapter 2 Solutions – Overview

Chapter 2 of Exploration, Cell: The Building Block of Life, establishes the cell as the basic structural and functional unit of all living things. It covers how cells are studied with light and electron microscopes, the cell membrane (selectively permeable) and cell wall, the nucleus and the main organelles (mitochondria, endoplasmic reticulum, Golgi apparatus, ribosomes, plastids, vacuoles, lysosomes), the processes of diffusion and osmosis, and cell division (mitosis and meiosis). These Class 9 Science Exploration Chapter 2 solutions answer every textbook question step by step.

Key Concepts & Definitions

Cell: the basic structural and functional unit of life; every cell arises from a pre-existing cell.

Cell membrane: the selectively permeable boundary controlling what enters and leaves the cell. Cell wall: a rigid, freely permeable outer layer in plant (and bacterial) cells.

Nucleus: controls all cell activities and holds the DNA. Prokaryotic cells (bacteria) have no true nucleus; eukaryotic cells do.

Key organelles: mitochondria (respiration/energy), ribosomes (protein synthesis), ER (transport; RER has ribosomes, SER does not), Golgi apparatus (packaging), plastids (chloroplasts, leucoplasts, chromoplasts), vacuole (storage/rigidity), lysosome (digestion).

Diffusion: net movement of particles from higher to lower concentration (no membrane needed). Osmosis: movement of water across a selectively permeable membrane.

Cell division: mitosis (growth and repair) and meiosis (forms gametes; halves the chromosome number).

“Think It Over” — Answers

Where does a cell come from?

ANSWEREvery cell arises from a pre-existing cell by cell division — a central idea of the cell theory.

How have technological interventions facilitated the creation of new knowledge in understanding the world beyond the naked eye?

ANSWERInstruments like the light microscope and the more powerful electron microscope let us see cells and tiny organelles that are invisible to the naked eye, revealing their detailed structure and how they work.

How is the cell the structural and functional unit of life?

ANSWERIt is structural because all living organisms are built from cells, and functional because every life process (nutrition, respiration, growth, reproduction) is carried out within cells.

Class 9 Science Exploration Chapter 2 Solutions — Revise, Reflect, Refine

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) Chloroplasts and chromoplasts (pigments)

ANSWER (i) The cell membrane is selectively (partially) permeable — it controls what passes through; the cell wall is freely permeable — most substances pass through it. (ii) RER (rough ER) has ribosomes on its surface, so it looks rough; SER (smooth ER) has no ribosomes and looks smooth. (iii) Chloroplasts contain the green pigment chlorophyll (for photosynthesis); chromoplasts contain other pigments (red, orange, yellow), as in flowers and fruits.

2. Two similar animal cells are placed in two different solutions — Cell X in pure water, Cell Y in concentrated salt solution. Cell X swells and Cell Y shrinks. Which statement correctly explains this? (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.  (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 (iii) — by osmosis, water moves into Cell X (surrounded by pure water, so it swells) and out of Cell Y (surrounded by concentrated salt solution, so it shrinks), across the selectively permeable cell membrane.

3. Look at the diagram of a cell in Fig. 2.20. Identify the parts labelled (a) to (g) and match them with their functions: (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 Match each function to its organelle (then read the matching labels off Fig. 2.20): (i) Controls all activities → Nucleus.(ii) Site of cellular respiration → Mitochondrion.(iii) Storage + rigidity → Vacuole.(iv) Separates contents from surroundings → Cell membrane.(v) Structural rigidity → Cell wall.(vi) Packs/stores materials from ER → Golgi apparatus.(vii) Manufactures food → Chloroplast.

4. Which of the following option(s) of pairs of cell organelles are correctly placed under the categories “Present in plant cells” and “Absent in animal cells”? (i) Leucoplast / Cell wall (ii) Mitochondria / Ribosome (iii) Cell wall / Golgi apparatus (iv) Lysosome / Endoplasmic reticulum

ANSWER (i) — a leucoplast is present in plant cells, and a cell wall is absent in animal cells, so both entries are correct. The others fail (mitochondria, ribosomes, Golgi and ER are present in animal cells too).

5. Renu says all parts of plants, even roots, contain plastids; Rohit says plastids are absent in roots because roots do not perform photosynthesis. Who is correct? Justify.

ANSWER Renu is correct. Roots do contain plastids — in the form of leucoplasts (colourless plastids that store starch). Rohit confuses “plastids” with “chloroplasts”: roots lack chloroplasts (no photosynthesis), but they still have plastids.

6. Discuss how mitochondria and chloroplasts are structurally and functionally similar to, and different from, each other.

ANSWER Similar: both are double-membraned organelles, both have their own DNA and ribosomes (semi-autonomous), and both are involved in energy transformations. Different: mitochondria carry out cellular respiration (release energy/ATP from food) and occur in all eukaryotic cells; chloroplasts carry out photosynthesis (trap light to make food), contain chlorophyll, and occur only in green plant cells.

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 (ii) Mitochondria, Nucleus — both contain DNA. (Chloroplasts also have DNA, but ribosomes, Golgi bodies and lysosomes do not.)

8. A researcher placed one carrot in plain water and another in concentrated salt solution (Fig. 2.21) and recorded observations after 24 hours. (i) What hypothesis does she want to test?(ii) What would you suggest to improve the experiment?(iii) Why does the carrot in plain water stay stiff and crunchy, but the one in salt solution become rubbery and limp?

ANSWER (i) Hypothesis: water moves into or out of the carrot’s cells by osmosis depending on the surrounding solution’s concentration. (ii) Improvements: use carrots of equal size/mass; measure and record mass and length before and after; keep the same volume of solution and the same temperature; repeat the trial for reliability. (iii) In plain water, water enters the carrot cells by osmosis, making them turgid → stiff and crunchy. In concentrated salt solution, water leaves the cells by osmosis, making them flaccid → rubbery and limp.

9. Indicate the presence or absence of the following structures in bacterial and animal cells: Chromosome, Nucleus, Mitochondria, Golgi complex, Chromoplasts.

ANSWER
StructureBacterial cellAnimal cell
ChromosomePresent (single, circular)Present
Nucleus (true)AbsentPresent
MitochondriaAbsentPresent
Golgi complexAbsentPresent
ChromoplastsAbsentAbsent

10. Four peeled potato cups are placed in water: Cup A empty; Cup B + 1 tsp sugar; Cup C + 1 tsp salt; Cup D (boiled potato) + 1 tsp sugar. (i) Why does water gather in Cup B and Cup C?(ii) Why is Cup A necessary?(iii) Why does water not gather in Cups A and D?

ANSWER (i) The sugar/salt makes the contents of Cups B and C more concentrated than the surrounding water, so water moves into the cups by osmosis through the living potato cells and gathers there. (ii) Cup A (empty) is the control — it shows that without sugar or salt no water gathers, proving the effect is due to the solute (osmosis). (iii) Cup A has no concentration difference, so no net osmosis. Cup D’s potato is boiled, which kills the cells and destroys their selectively permeable membranes, so osmosis cannot occur even though sugar is added.

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 (ii) is incorrect. The SER does synthesise lipids, but it does not synthesise cellulose, so this match is wrong. (Ribosome–protein synthesis and lysosome–digestion are correct.)

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

ANSWER Without mitochondria there is no cellular respiration, so the cell cannot produce ATP (energy). It would be unable to carry out its energy-requiring activities and would soon die.

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

ANSWER Contact inhibition — normal animal cells stop dividing when they touch neighbouring cells — inhibits tumour formation. When this fails, uncontrolled division leads to tumours. Plants generally do not show contact inhibition and grow differently because of their rigid cell walls; however, tumour-like growths (e.g. crown-gall caused by a bacterial infection) can still occur in plants.

14. The cell membrane is made of proteins and lipids. Which organelles help synthesise it? Write the path of these compounds from their site of synthesis to the cell membrane (with a labelled diagram).

ANSWER Proteins are made by ribosomes on the rough ER (RER); lipids are made by the smooth ER (SER). Path: Ribosome (on RER) → endoplasmic reticulum → Golgi apparatus (modifies and packs them into vesicles) → vesicles fuse with the cell membrane. (Draw this as a labelled flow: Ribosome/RER → ER → Golgi → vesicle → cell membrane.)

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

ANSWER Mitosis keeps the chromosome number the same, so gametes would be diploid instead of haploid. On fertilisation the chromosome number would double in every generation, which would disturb the species’ fixed chromosome number. That is why gametes are formed by meiosis, which halves the chromosome number.

16. Farmer Deepa preserved amla and lemons by making pickles, murabbas and sharbat with salt, sugar or jaggery. Based on the passage: (i) Which scientific concept did she apply?(ii) How does adding high concentrations of salt and sugar prevent the growth of spoilage bacteria and fungi?(iii) Suggest a healthy recipe of this kind.(iv) What scientific values are addressed?

ANSWER (i) Food preservation by osmosis — using a high concentration of salt/sugar. (ii) The high salt/sugar makes the surroundings hypertonic, so water is drawn out of the microbial cells by osmosis (plasmolysis). Dehydrated bacteria and fungi cannot grow or multiply, so the food does not spoil. (iii) For example, amla murabba (amla cooked in sugar syrup) or a salt-preserved lemon pickle. (Reasonable answers accepted.) (iv) Reducing waste and promoting sustainability, ensuring food security, applying science to daily life and livelihood, resourcefulness and economic self-reliance.

Common Misconceptions to Avoid

Watch out for these

  • Treating the cell wall and cell membrane as the same — the wall is rigid and freely permeable; the membrane is selectively permeable.
  • Calling osmosis the same as diffusion — osmosis is specifically the movement of water across a selectively permeable membrane.
  • Thinking plastids occur only in leaves — roots have colourless plastids (leucoplasts).
  • Believing only the nucleus has DNA — mitochondria and chloroplasts have their own DNA too.
  • Assuming chloroplasts are in animal cells — they are found only in green plant cells.
  • Confusing mitosis with meiosis — mitosis is for growth/repair; meiosis forms gametes and halves the chromosome number.

Extra Practice Questions

Very Short Answer Type Questions

Q1. Which organelle is called the “powerhouse of the cell”?

ANSWERThe mitochondrion (it releases energy as ATP through respiration).

Q2. Name the organelle that controls all the activities of the cell.

ANSWERThe nucleus.

Q3. What is the green pigment present in chloroplasts called?

ANSWERChlorophyll.

Short Answer Type Questions

Q1. Differentiate between diffusion and osmosis.

ANSWERDiffusion is the net movement of any particles from a higher to a lower concentration and needs no membrane. Osmosis is the movement of water across a selectively permeable membrane from a more dilute to a more concentrated solution.

Q2. Why is the cell membrane called selectively permeable?

ANSWERBecause it allows only certain substances to pass through while restricting others, thus controlling what enters and leaves the cell.

Long Answer Type Question

Q1. Compare mitosis and meiosis on the basis of where they occur, the number of divisions, and the daughter cells produced.

ANSWER Mitosis occurs in body (somatic) cells, involves one division, and produces two daughter cells that are genetically identical to the parent with the same chromosome number — used for growth and repair. Meiosis occurs in reproductive cells, involves two successive divisions, and produces four daughter cells with half the chromosome number and genetic variation — used to form gametes.

MCQs & Assertion–Reason

1. The basic structural and functional unit of life is the:

(a) tissue    (b) cell    (c) organ    (d) molecule

2. Which organelle is known as the “powerhouse of the cell”?

(a) nucleus    (b) ribosome    (c) mitochondrion    (d) Golgi apparatus

3. A cell wall is present in:

(a) animal cells only    (b) plant (and bacterial) cells    (c) no cells    (d) only nerve cells

4. The movement of water across a selectively permeable membrane is called:

(a) diffusion    (b) osmosis    (c) respiration    (d) transpiration

5. Which organelle controls all the activities of the cell?

(a) vacuole    (b) nucleus    (c) lysosome    (d) ribosome

6. Chlorophyll is found in:

(a) mitochondria    (b) chloroplasts    (c) ribosomes    (d) lysosomes

7. Which cell does NOT have a true nucleus?

(a) plant cell    (b) animal cell    (c) bacterial cell    (d) muscle cell

8. Cell division for growth and repair is:

(a) meiosis    (b) mitosis    (c) osmosis    (d) diffusion

9. Which organelle packs and dispatches materials received from the ER?

(a) ribosome    (b) Golgi apparatus    (c) mitochondrion    (d) vacuole

10. Ribosomes are the site of:

(a) respiration    (b) photosynthesis    (c) protein synthesis    (d) digestion

Answer key: 1-(b), 2-(c), 3-(b), 4-(b), 5-(b), 6-(b), 7-(c), 8-(b), 9-(b), 10-(c).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Mitochondria are called the powerhouse of the cell.

Reason: They release energy in the form of ATP through cellular respiration.

A-R 2. Assertion: The cell membrane is selectively permeable.

Reason: It controls the movement of substances into and out of the cell.

A-R 3. Assertion: A bacterial cell has no true nucleus.

Reason: Bacteria are prokaryotes whose genetic material is not enclosed in a nuclear membrane.

A-R 4. Assertion: Osmosis is the movement of any particles from a higher to a lower concentration.

Reason: Osmosis is the movement of water across a selectively permeable membrane.

A-R 5. Assertion: Chloroplasts are found in animal cells.

Reason: Chloroplasts contain chlorophyll for photosynthesis.

Answer key: 1-(A), 2-(A), 3-(A), 4-(D), 5-(D).

Quick Revision Summary

  • The cell is the basic structural and functional unit of life; new cells come from existing cells.
  • Cell membrane = selectively permeable; cell wall = rigid and freely permeable (plants/bacteria).
  • Nucleus controls activities; prokaryotes (bacteria) lack a true nucleus.
  • Organelles: mitochondria (respiration), ribosomes (protein), ER & Golgi (synthesis/packing), plastids, vacuole, lysosome.
  • Diffusion = particles high→low; osmosis = water across a selectively permeable membrane.
  • Mitosis = growth/repair (identical cells); meiosis = gametes (half the chromosomes).

Real-life Applications

Osmosis explains everyday preservation: salting fish or making fruit pickles, murabbas and jams draws water out of spoilage microbes so food lasts longer. It also explains why vegetables become crisp in plain water and limp in salty water, why over-watering or salty soil harms plants, and why a saline drip must match the concentration of body fluids.

How to score full marks in this chapter

Learn the organelles with one function each and be able to draw a labelled plant and animal cell. State the exact difference between diffusion and osmosis, and between mitosis and meiosis. For experiment questions, always identify the hypothesis, the control and the role of the selectively permeable membrane.

Frequently Asked Questions

What is Class 9 Science Exploration Chapter 2 about?

The cell as the unit of life — its structure, the membrane and wall, the nucleus and organelles, diffusion and osmosis, and cell division (mitosis and meiosis).

What is the difference between diffusion and osmosis?

Diffusion is the movement of particles from higher to lower concentration (no membrane needed); osmosis is the movement of water across a selectively permeable membrane.

How many questions are in the Revise, Reflect, Refine exercise?

16 questions, all solved on this page along with the “Think It Over” prompts.

Are these Class 9 Science Exploration Chapter 2 solutions free?

Yes. All solutions are free and follow the official NCERT Exploration textbook for 2026–27.

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