NCERT Class 9 Science Chapter 2 Solutions – Cell
Are you looking for accurate and complete ncert class 9 science chapter 2 solutions for the new CBSE curriculum (2026-27)? You are in the right place! In this guide, we provide step-by-step, direct, and easy-to-understand solutions for all exercise questions from NCERT Exploration Class 9 Science Chapter 2: Cell: The Building Block of Life.
These answers are crafted specifically to help students write clean, exam-ready answers in their notebooks without extra confusion or lengthy fluff.
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) Chloroplasts and chromoplasts (pigments)
(i) Cell membrane vs Cell wall (permeability):
- Cell membrane: Selectively permeable; it controls the entry and exit of specific substances.
- Cell wall: Fully permeable; it allows water and dissolved substances to pass through without restriction.
(ii) RER vs SER (structure):
- Rough Endoplasmic Reticulum (RER): Has ribosomes attached to its outer membrane surface, giving it a rough appearance.
- Smooth Endoplasmic Reticulum (SER): Lacks ribosomes on its surface, making it smooth in structure.
(iii) Chloroplasts vs Chromoplasts (pigments):
- Chloroplasts: Contain green photosynthetic pigments called chlorophyll.
- Chromoplasts: Contain non-green pigments (like yellow, orange, or red carotenoids).
Question 2
Two similar animal cells are placed in two different solutions: Cell X is placed in pure water, and 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 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.
(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
Reason: Cell X is in a hypotonic solution (pure water), so water enters by endosmosis causing it to swell. Cell Y is in a hypertonic solution (salt water), so water leaves by exosmosis through the cell membrane, causing it to shrink.
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.
- (a) Nucleus: (i) Controlling all the activities of a cell.
- (b) Golgi apparatus: (vi) Packs and stores materials received from ER.
- (c) Chloroplast: (vii) Helps in manufacturing food.
- (d) Mitochondria: (ii) Site of cellular respiration.
- (e) Cell wall: (v) Provides structural rigidity to the cell.
- (f) Cell membrane: (iv) Separates the cell contents from surroundings.
- (g) Vacuole: (iii) Storage organelle that also provides rigidity to the cell.
Question 4
Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories?
Correct Option: (iii) Cell wall (Present in plant cells) | Golgi apparatus (Absent in animal cells / strictly plant cell wall presence).
Note: The primary structure present in plant cells and completely absent in animal cells is the Cell wall.
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 plastids are absent in plant roots since the roots are underground and do not need to perform photosynthesis. Who is correct? Justify your answer.
Renu is correct.
Justification: Plastids are not restricted only to green leaves. Underground roots contain non-green plastids known as leucoplasts. Leucoplasts do not carry out photosynthesis, but their main function is to store nutrients such as starch, oils, and proteins in root cells.
Question 6
Mitochondria and chloroplasts are two important organelles in a plant cell. Discuss how these two organelles are structurally and functionally similar to each other, and different from each other.
Structural & Functional Similarities:
- Both are double-membrane bound organelles.
- Both possess their own DNA and ribosomes, enabling them to make some of their own proteins.
- Both are involved in cellular energy conversions.
Differences:
- Chloroplasts: Contain chlorophyll pigment, synthesize sugar via photosynthesis, and convert solar energy into chemical energy.
- Mitochondria: Lack chlorophyll, perform cellular respiration to break down glucose, and synthesize ATP (energy currency).
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
(ii) Mitochondria, Nucleus
Explanation: The nucleus contains nuclear DNA, while mitochondria (and chloroplasts) contain their own extranuclear circular DNA.
Question 8
A researcher carried out an 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 her observations.
(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?
(i) Hypothesis: Water moves into or out of plant cells by osmosis depending on whether the surrounding fluid is hypotonic or hypertonic.
(ii) Improvement Suggestion: Take quantitative measurements of the initial and final weight and length of both carrots using a balance and ruler.
(iii) Explanation:
- Carrot in plain water: Takes in water via endosmosis because plain water is hypotonic, making cells turgid, stiff, and crunchy.
- Carrot in salt solution: Loses water via exosmosis because salt water is hypertonic, causing cell plasmolysis and making it rubbery and limp.
Question 9
Indicate the presence or absence of following structures in bacterial and animal cells:
| Structures in a cell | Bacterial cell | Animal cell |
|---|---|---|
| Chromosome | Present (Single circular DNA / Nucleoid) | Present (Multiple linear chromosomes) |
| Nucleus | Absent | Present |
| Mitochondria | Absent | Present |
| Golgi complex | Absent | Present |
| Chromoplasts | Absent | Absent |
Question 10
Carry out the following experiment (Fig. 2.22): Four peeled potato halves were prepared as cups (Cup A empty, Cup B with sugar, Cup C with salt, Cup D with boiled potato + sugar). Answer the following:
(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.
(i) Water in Cup B & C: Sugar and salt create a hypertonic solution inside the hollow cavity. Water moves from the trough into the potato cup through the living cell membrane by osmosis.
(ii) Role of Cup A: Cup A acts as a control setup to demonstrate that water does not enter the cavity simply due to physical suction or empty space, but strictly due to the solute concentration gradient.
(iii) No water in Cup A & D:
- Cup A: It is empty, so there is no osmotic gradient created.
- Cup D: Boiling kills the potato cells and destroys the selectively permeable cell membrane, making osmosis impossible.
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
(ii) SER — Lipid and cellulose synthesis
Reason for incorrect pair: SER synthesizes lipids, but cellulose is synthesized at the plasma membrane by cellulose synthase enzymes, not inside the SER.
Question 12
What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?
Mitochondria are the "powerhouses of the cell" that produce ATP through cellular respiration. If all mitochondria are removed:
- ATP generation will stop completely.
- Active transport and essential metabolic functions will cease.
- The cell will eventually starve and die due to energy failure.
Question 13
Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain.
In Humans: Tumor formation is inhibited by contact inhibition and programmed cell death (apoptosis).
In Plants: Yes, plants can also develop tumors, commonly called galls or crown galls. For example, infection by the soil bacterium Agrobacterium tumefaciens transfers bacterial genes into plant cells, inducing uncontrolled cell division and tumor formation.
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.
Organelles involved:
- Proteins: Synthesized by Ribosomes on the Rough Endoplasmic Reticulum (RER).
- Lipids: Synthesized by the Smooth Endoplasmic Reticulum (SER).
Path of Transport (Membrane Biogenesis):
Endoplasmic Reticulum (RER/SER) → Transport Vesicles → Golgi Apparatus (Processing & Packaging) → Secretory Vesicles → Cell Membrane
Question 15
What would happen if gametes are formed by mitotic divisions?
Mitosis produces daughter cells with the same chromosome number ($2n$) as the parent cell. If gametes were formed by mitosis:
- Gametes would be diploid ($2n$) instead of haploid ($n$).
- During fertilization, two diploid gametes would fuse to create a tetraploid ($4n$) offspring.
- The chromosome number would double with every generation ($2n \rightarrow 4n \rightarrow 8n$), disrupting normal organism survival.
Question 16
Based on the passage about Deepa preserving amla and lemons:
(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?
(i) Scientific Concept: Plasmolysis and Osmosis (Hypertonic preservation).
(ii) Mechanism: High concentrations of salt or sugar create a hypertonic environment outside bacterial and fungal cells. Water is drawn out of microbial cells by exosmosis, causing them to shrink and die.
(iii) Healthy Recipe Suggestion: Homemade Sun-Dried Lemon Pickles: Fresh sliced lemons stored with coarse rock salt, turmeric, and black pepper, cured naturally in glass jars under sunlight.
(iv) Scientific Values Addressed: Resource management, sustainable agro-processing, food preservation awareness, waste reduction, and applying science to boost rural income.
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Based on latest NCERT class 9 book.