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NCERT Solutions for Class 9 Science Chapter 2 Cell: The Building Blocks of Life
Achieve better learning outcomes with Chapter-wise NCERT Solutions for Class 9 Science, created in accordance with the latest NCERT syllabus and fully CBSE aligned. These expert-created solutions feature detailed, step-by-step answers that help students understand textbook concepts, solve questions accurately, and build confidence for examinations.
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1.0Download NCERT Class 9 Science Chapter 2 Cell: The Building Blocks of Life
Chapter 2: Cell: The Building Blocks of Life explains the structure, organization, and functions of cells, helping students understand the fundamental units of life. It lays the groundwork for studying more advanced topics in biology.
2.0Learning Outcomes – NCERT Class 9 Science Chapter 2: Cell: The Building Blocks of Life
- Explain why the cell is the basic structural and functional unit of life.
- Differentiate between plant and animal cells as well as prokaryotic and eukaryotic cells.
- Describe the structure and functions of major cell organelles, including the nucleus, mitochondria, chloroplast, endoplasmic reticulum, Golgi apparatus, ribosomes, vacuoles, plasma membrane, and cell wall.
- Explain the processes of diffusion and osmosis and their importance in cells.
- Understand the role of the plasma membrane as a selectively permeable barrier.
- Describe the significance of cell division (mitosis and meiosis) in growth, repair, reproduction, and variation.
- Prepare and observe simple cell slides to identify the basic structure of cells.
- Apply knowledge of cell structure and function to explain biological processes and real-life examples.
3.0Detailed NCERT Solutions for Class 9 Science Chapter 2: Cell: The Building Blocks of Life Solutions
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)
Ans.
(i) Cell membrane and Cell wall (Permeability)
- Cell membrane: Selectively permeable; allows some substances to pass while blocking others.
- Cell wall: Freely permeable; allows water and dissolved substances to pass through.
(ii) RER and SER (Structure)
- RER (Rough Endoplasmic Reticulum): Ribosomes are attached on its surface, so it looks rough.
- SER (Smooth Endoplasmic Reticulum): Ribosomes are absent, so it looks smooth.
(iii) Chloroplasts and Chromoplasts (Pigments)
- Chloroplasts: Contain green pigment chlorophyll.
- Chromoplasts: Contain coloured pigments like yellow, orange, or red.
2. Two similar animal cells are placed in two different solutions:
- Cell X is placed in pure water.
- Cell 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.
Ans. (iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
Explanation:
- Cell X is in pure water (hypotonic solution), so water enters the cell by osmosis, causing it to swell.
- Cell Y is in concentrated salt solution (hypertonic solution), so water moves out through the cell membrane by osmosis, causing it to shrink.
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:
Ans. (a) Mitochondria → (ii) Site of cellular respiration (b) Nucleus → (i) Controls all activities of the cell (c) Golgi apparatus → (vi) Packs and stores materials received from ER (d) Chloroplast → (vii) Helps in manufacturing food (e) Cell wall → (v) Provides structural rigidity to the cell (f) Cell membrane → (iv) Separates cell contents from surroundings (g) Vacuole → (iii) Storage organelle that also provides rigidity to the cell
4. Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories?
Ans. Option (i) Present in plant cells: Leucoplast Absent in animal cells: cell wall
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.
Ans. Renu is correct. Justification: Plastids are present in all parts of plants, including roots. Roots do not perform photosynthesis because they are underground and usually lack chloroplasts (green plastids containing chlorophyll). However, roots contain leucoplasts, which are colourless plastids that store food materials such as starch, oils, or proteins. For example, leucoplasts in potato and taro cells store starch. Therefore, plastids are not absent in roots; they are present in the form of leucoplasts, not chloroplasts.
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.
Ans. Similarities between Mitochondria and Chloroplasts:
- Double membrane-bound organelles
- Both are surrounded by an outer and an inner membrane.
- Have their own DNA and ribosomes
- Both can make some of their own proteins.
- Similar to certain bacteria - These features suggest that both share an evolutionary history with singlecelled organisms.
- Energy-related functions - Both are involved in energy conversion processes inside the cell.
Differences between Mitochondria and Chloroplasts:
- Which of the following pairs of cell organelles contains DNA? (i) Chloroplasts, Ribosomes (ii) Mitochondria, Nucleus (iii) Golgi bodies, Ribosomes (iv) Nucleus, Lysosomes
Ans. (ii) Mitochondria and Nucleus
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?
Ans. (i) Hypothesis tested through the experiment: The researcher wants to test that water moves in and out of cells through a selectively permeable membrane by osmosis depending on the concentration of the surrounding solution. (ii) Suggestion for improvement of the experiment:
The experiment can be improved by: Measuring and recording the initial and final weight of both carrots. Taking carrots of similar size for accurate comparison. (iii) Reason for the observations:
The carrot kept in plain water stays stiff and crunchy because water enters the carrot cells by osmosis. The carrot kept in concentrated salt solution becomes rubbery and limp because water moves out of the carrot cells into the concentrated solution, causing the cells to lose water and firmness.
9. Indicate the presence or absence of following structures in bacterial and animal cells:
Ans. Presence or absence of structures
- 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.
Ans. (i) Water gathers in the hollowed portions of Cup B and Cup C because the sugar in Cup B and the salt in Cup C create a concentrated solution. Water moves from the surrounding water into the potato cells and then into the hollowed portion through the selectively permeable cell membrane by osmosis. (ii) Cup A acts as a control setup. It shows that without sugar or salt, water does not collect in the hollowed portion. (iii) In , there is no sugar or salt to create a concentration difference, so osmosis does not occur.
In Cup D, the potato is boiled, so the cells are dead and the selectively permeable cell membrane is damaged. Therefore, osmosis does not take place and water does not collect.
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 Ans. The incorrectly matched pair is: (ii) SER - Lipid and cellulose synthesis
Explanation:
- Ribosome: Protein synthesisCorrect (ribosomes are the site of protein synthesis).
- SER: Lipid and cellulose synthesis, Incorrect because SER synthesises lipids and hormones, not cellulose.
- Lysosome: Digestion of foreign agents Correct (lysosomes contain enzymes that digest foreign substances and damaged cell parts).
12. What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?
Ans. If all the mitochondria are removed from a eukaryotic cell, the cell will not be able to carry out cellular respiration properly and will not produce enough ATP (energy currency). Since ATP is needed for most cellular activities, the cell will stop functioning and eventually die.
13. Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain.
Ans. The phenomenon that inhibits the formation of tumours in the human body is contact inhibition. In this process, normal animal cells stop dividing when they come in contact with neighbouring cells, which prevents uncontrolled growth.
Yes, plants can also develop tumours, but plant cells do not show contact inhibition because of their rigid cell walls and follow a different pattern of growth. If cell division becomes abnormal, tumours may form in plants too.
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.
Ans. The cell organelles involved in the synthesis of the cell membrane are:
- Ribosomes → synthesize proteins
- Rough Endoplasmic Reticulum (RER) → helps in protein synthesis and transport
- Smooth Endoplasmic Reticulum (SER) → synthesizes lipids (fats)
- Golgi apparatus → modifies, packages, and transports proteins and lipids to the cell membrane
Path of cell membrane formation
- Proteins are made by ribosomes attached to the RER.
- Lipids are synthesized by the SER.
- These materials move to the Golgi apparatus for modification and packaging.
- The Golgi packs them into vesicles.
- Vesicles fuse with the cell membrane, adding proteins and lipids to it.
Ribosomes
↓ RER → Protein synthesis ↓ SER → Lipid synthesis ↓ Golgi Apparatus (modifies and packages) ↓ Vesicles ↓ Cell Membrane (formed by proteins + lipids) Thus, RER, SER, ribosomes, and Golgi apparatus work together in the synthesis of the cell membrane.
15. What would happen if gametes are formed by mitotic divisions?
Ans. If gametes were formed by mitotic division instead of meiosis, they would have the same number of chromosomes as the parent cell instead of half. During fertilisation, when two such gametes combine, the new cell would have double the normal number of chromosomes. This chromosome number would keep increasing in every generation, causing abnormalities and disturbing the normal chromosome number of the species. Also, genetic variation would not be produced, because mitosis forms genetically identical cells.
16. A farmer, Deepa, was very happy with the harvest of amla (Indian Gooseberry) and lemons on her farm. However, she could sell only onefourth 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, murabbas, and sharbat 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 agroprocessing 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?
Ans. (i) The farmer applied the concept of osmosis for food preservation. (ii) High concentrations of salt and sugar create a hypertonic environment. Water moves out of bacteria and fungi by osmosis, causing their cells to shrink and preventing their growth and spoilage. (iii) A healthy recipe is amla murabba. Fresh amla is preserved by adding sugar or jaggery and storing it in clean glass bottles. (iv) The scientific values are:
- Scientific application of knowledge
- Resource conservation
- Prevention of food wastage
- Sustainability
- Innovation and problem-solving
- Economic development and food security
4.0Important Key Concepts of NCERT Solutions for Class 9 Science Chapter 2: Cell: The Building Blocks of Life
5.0 Quick Revision on Class 9 Science Chapter 2: Cell: The Building Blocks of Life
6.0Related Study Materials Class 9 Science
Download ALLEN's complete study material prepared as per the latest NCERT syllabus and enhance your Class 9 Science understanding. e along with NCERT Solutions, NCERT books, Revision Notes, Sample Papers & Previous Years Questions Papers to build conceptual clarity, revise effectively & prepare confidently for school & CBSE exams.
7.0Advantages of Chapter 2 Science Class 9 NCERT Solutions
- Explains Cell Structure: Develops a clear understanding of the structure and organisation of cells.
- Strengthens Organelle Concepts: Simplifies the functions of major cell organelles.
- Improves Microscope Understanding: Helps students understand how cells are observed using microscopes.
- Clarifies Cell Processes: Explains concepts like osmosis and cell division in an easy-to-understand manner.
- Builds Conceptual Clarity: Helps students differentiate between plant and animal cells.
- Creates a Strong Foundation: Prepares students for advanced topics in biology and life sciences.