Class 9 › Science › Exploration Cell: The Building Block of Life Class 9 Science · Exploration · Chapter 2
Summary Questions & answers Practise this chapter → This chapter establishes the cell as the basic structural and functional unit of life. Some organisms are unicellular (a single cell, like bacteria or yeast) while others are multicellular; in the latter, similar cells form tissues, tissues build organs, and organs form organ systems, yet the cell stays the fundamental unit throughout. Because cells are smaller than the eye’s limit of resolution (about 0.1 mm at the near point of 25 cm), we study them with microscopes — Robert Hooke first saw cork "cells" in 1665, and modern light and electron microscopes reveal ever finer detail. Every cell is bounded by a selectively permeable cell (plasma) membrane, described by the fluid-mosaic model as a lipid bilayer with embedded proteins; substances cross it by diffusion and water by osmosis. Plant, fungal and bacterial cells add a rigid cellulose cell wall. Cells are classed as prokaryotic (no membrane-bound nucleus or organelles; genetic material in a nucleoid) or eukaryotic (true nucleus plus organelles). Key organelles include the nucleus (holding DNA-bearing chromosomes), ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, mitochondria (the ATP-producing "powerhouse"), plastids in plants (chloroplast, chromoplast, leucoplast) and vacuoles. Cells multiply by division — mitosis (two identical daughter cells for growth and repair) and meiosis (four cells with half the chromosomes, for reproduction). The cell theory of Schleiden, Schwann and Virchow unifies all of this: all organisms are made of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.
Cell membrane (plasma membrane)
The selectively permeable boundary of every cell, described by the fluid-mosaic model as a lipid bilayer with embedded proteins.
Osmosis
The movement of water across a selectively permeable membrane from a dilute (more water) to a concentrated (less water) region.
Prokaryotic cell
A cell without a membrane-bound nucleus or organelles; its genetic material lies in a region called the nucleoid (e.g. bacteria).
Eukaryotic cell
A cell with a true, membrane-bound nucleus and several membrane-bound organelles (e.g. plant and animal cells).
Mitochondria
Double-membraned organelles, the "powerhouse" of the cell, that release energy as ATP during cellular respiration.
Cell theory
The unifying idea that all organisms are made of cells, the cell is the basic unit of life, and all cells come from pre-existing cells.
Q1 What is the limit of resolution of the human eye, and why does it matter for studying cells? Answer Q2 Who first observed cells, and how? Answer Q3 Differentiate between diffusion and osmosis. Answer Q4 What does the fluid-mosaic model say about the cell membrane? Answer Q5 Why do plant cells have a cell wall while animal cells do not? Answer Q6 Distinguish prokaryotic from eukaryotic cells. Answer Q7 Why are mitochondria called the powerhouse of the cell? Answer Q8 Name the three types of plastids and their roles. Answer Q9 Compare mitosis and meiosis. Answer Q10 State the cell theory and name the scientists who developed it. Answer Q1 Where does a cell come from? Answer Q2 How have technological interventions facilitated the creation of new knowledge in understanding the world beyond the naked eye? Answer Q3 How is the cell structural and functional unit of life? Answer Q4 How does a cell multiply? Answer Q1 What will happen if mung bean seeds are kept in a concentrated solution after soaking in water for 12 hours? What will happen to them? Answer Q1 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 Q2 2. What consequences would you predict for a plant cell if its cell wall were to become as flexible as a cell membrane? Answer Q3 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 Q1 4. Do white flowers contain any pigment? Give reasons. Answer Q2 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. Answer Q3 5. Draw a well-labelled schematic diagram of a plant or an animal cell using these clues — (ii) ER spreads like a network of extended nuclear envelope. Answer Q4 5. Draw a well-labelled schematic diagram of a plant or an animal cell using these clues — (iii) Mitochondria and chloroplasts are rod shaped. Answer Q1 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 Q2 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 Q1 1. Differentiate between the following pairs of terms based on the clues given in parentheses: (i) Cell membrane and cell wall (permeability) Answer Q2 1. Differentiate between the following pairs of terms based on the clues given in parentheses: (ii) RER and SER (structure) Answer Q3 1. Differentiate between the following pairs of terms based on the clues given in parentheses: (iii) Chloroplasts and chromoplasts (pigments) Answer Q4 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 Q5 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. Answer Q6 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: (ii) Site of cellular respiration. Answer Q7 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: (iii) Storage organelle that also provides rigidity to the cell. Answer Q8 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: (iv) Separates the cell contents from surroundings. Answer Q9 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: (v) Provides structural rigidity to the cell. Answer Q10 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: (vi) Packs and stores materials received from ER. Answer Q11 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: (vii) Helps in manufacturing food. Answer Q12 4. Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories? Option Present in the plant cells Absent in the animal cells (i) Leucoplast Cell wall (ii) Mitochondria Ribosome (iii) Cell wall Golgi apparatus (iv) Lysosome Endoplasmic reticulum Answer Q13 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. Answer Q14 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. Answer Q15 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 Q16 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? Answer Q17 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. (ii) What would you suggest for the improvement of this experiment? Answer Q18 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. (iii) Why does the carrot in plain water stay stiff and crunchy, but the carrot in concentrated salt solution become rubbery and limp? Answer Q19 9. Indicate the presence or absence of following structures in bacterial and animal cells: Chromosome Answer Q20 9. Indicate the presence or absence of following structures in bacterial and animal cells: Nucleus Answer Q21 9. Indicate the presence or absence of following structures in bacterial and animal cells: Mitochondria Answer Q22 9. Indicate the presence or absence of following structures in bacterial and animal cells: Golgi complex Answer Q23 9. Indicate the presence or absence of following structures in bacterial and animal cells: Chromoplasts Answer Q24 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. Answer Q25 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: (ii) Why is Cup A necessary for this experiment? Answer Q26 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: (iii) Explain why water does not gather in the hollowed portions of Cups A and D. Answer Q27 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 Q28 12. What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell? Answer Q29 13. Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain. Answer Q30 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 Q31 15. What would happen if gametes are formed by mitotic divisions? Answer Q32 16. A farmer, Deepa, was very happy with the harvest of amla (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, 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 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? Answer Q33 16. A farmer, Deepa, was very happy with the harvest of amla (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, 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 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: (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? Answer Q34 16. A farmer, Deepa, was very happy with the harvest of amla (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, 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 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: (iii) Suggest a healthy recipe of this kind for food preservation. Answer Q35 16. A farmer, Deepa, was very happy with the harvest of amla (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, 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 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: (iv) What are the scientific values addressed in this case? Answer
Who first observed and named "cells" while looking at a slice of cork in 1665?
A Robert Brown B Robert Hooke C Rudolf Virchow D Theodor Schwann
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