1Revise, Reflect, Refine16 questions
Q.1Differentiate 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)v
Answer:Cell membrane is selectively permeable, while cell wall is freely permeable and rigid. RER has ribosomes on its surface, while SER lacks ribosomes. Chloroplasts contain chlorophyll; chromoplasts contain other coloured pigments.
Q.2Two similar animal cells are placed in two different solutions: y Cell X is placed in pure water. y 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.v
Answer:(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
Q.3Look 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. (d) (iii) Storage organelle that also provides rigidity to the (a) (e) cell. (b) (iv) Separates the cell contents from surroundings. (c) (f) (v) Provides structural rigidity to the cell. (vi) Packs and stores materials received from ER. (g) (vii) Helps in manufacturing food.v
Answer:Match each labelled part to its function as follows: (i) controlling all the activities of the cell — nucleus; (ii) site of cellular respiration — mitochondrion; (iii) storage organelle that also gives the cell rigidity — vacuole; (iv) separates the cell contents from the surroundings — cell membrane (plasma membrane); (v) provides structural rigidity to the cell — cell wall; (vi) packs and stores materials received from the endoplasmic reticulum — Golgi apparatus; (vii) helps in manufacturing food — chloroplast.
Q.4Which of the following option(s) of the pairs of cell Fig. 2.20 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 reticulumv
Answer:Option (i) is correctly placed: leucoplast is present in plant cells and the cell wall is absent in animal cells, so both entries in the pair are right. The other options are wrong because the second structure in each is actually present in animal cells — (ii) ribosomes occur in animal cells, (iii) the Golgi apparatus occurs in animal cells, and (iv) the endoplasmic reticulum occurs in animal cells — so they are not absent there.
Q.5Two 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.v
Answer:Renu is correct. Roots may not have green chloroplasts, but they can contain colourless plastids called leucoplasts for storage.
Q.6Mitochondria 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.v
Answer:Both mitochondria and chloroplasts are double-membrane organelles with their own DNA and ribosomes. Mitochondria release energy during respiration, while chloroplasts trap light energy for photosynthesis.
Q.7Which of the following pairs of cell organelles contains DNA? (i) Chloroplasts, Ribosomes (ii) Mitochondria, Nucleus (iii) Golgi bodies, Ribosomes (iv) Nucleus, Lysosomesv
Answer:(ii) Mitochondria, Nucleus.
Q.8A 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). hours she recorded her observations. (i) What hypothesis does she want to test through this experiment? A B (ii) What would you suggest for the improvement of this experiment? Fig. 2.21: Experimental (iii) Why does the carrot in plain water stay stiff and crunchy, but the set-up having carrot (a) in plain water, and carrot in concentrated salt solution become rubbery and limp? (b) in salt solutionv
Answer:The hypothesis is that osmosis changes plant tissue firmness in different solutions. Use equal-sized carrots, equal volumes and fixed time. Plain water makes cells turgid; concentrated salt solution draws water out, making cells limp.
Q.9Indicate the presence or absence of following structures in bacterial and animal cells: Structures in a cell Bacterial cell Animal cell Chromosome Nucleus Mitochondria Golgi complex Chromoplastsv
Answer:Bacterial cell: chromosome present; nucleus, mitochondria, Golgi complex and chromoplasts absent. Animal cell: chromosome, nucleus, mitochondria and Golgi complex present; chromoplasts absent.
Q.10Carry 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. Fig. 2.22: Experimentalv
Answer:Water gathers in Cups B and C because sugar/salt creates a hypertonic solution and water enters by osmosis through living potato cells. Cup A is the control. Cup D is boiled, so membranes are damaged and osmosis does not occur.
Q.11Identify the pair that incorrectly matches the cell organelle with set-up its function. (i) Ribosome — Protein synthesis (ii) SER — Lipid and cellulose synthesis (iii) Lysosome — Digestion of foreign agentsv
Answer:Ribosome—protein synthesis is correct; lysosome—digestion of foreign agents is correct. SER helps in lipid synthesis, but cellulose synthesis is not its usual function, so the SER—lipid and cellulose synthesis pair is the inaccurate match.
Q.12What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?v
Answer:The cell would lose its main site of ATP production; energy-dependent activities would fail and the cell would eventually die.
Q.13Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain.v
Answer:Apoptosis, or programmed cell death, helps remove abnormal cells and inhibits tumour formation. Plants can also develop tumour-like abnormal growths, such as galls, when cell division is disturbed by pathogens or hormones.
Q.14The 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.v
Answer:Ribosomes on rough ER make membrane proteins and smooth ER makes lipids. These products move from ER to the Golgi apparatus, are modified and packed into vesicles, and the vesicles fuse with the cell membrane. Path: RER/SER → Golgi apparatus → vesicles → cell membrane.
Q.15What would happen if gametes are formed by mitotic divisions?v
Answer:Gametes would retain the diploid chromosome number; after fertilisation the zygote would have double the normal chromosome number, causing serious developmental problems.
Q.16A 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? (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?v
Answer:The farmer used osmosis-based preservation. High salt or sugar makes the surroundings hypertonic, so water leaves spoilage-causing microbes and their growth is inhibited. Amla pickle or lemon preserve with salt/sugar is an example. The values shown are scientific thinking, waste reduction, food security, sustainability and value addition.