Question 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?

Accepted Answer

- A cell wall is a support structure, and a plant that cannot walk away from trouble needs support far more than an animal does. - A plant is fixed in one place, so it cannot escape wind, rain or heat — it must stand up to them where it stands. The rigid cell wall gives each of its cells the strength to do that. - The wall also keeps leaves and flowers firm, holds their shape, and helps the whole plant stay upright. - That rigidity costs the plant nothing it needs, because the cell wall is permeable: water and dissolved minerals still pass straight through it, so roots go on absorbing water and nutrients from the soil. - The wall is what saves a plant cell in a concentrated solution — the contents shrink away inside, but the cell keeps its box shape (Fig. 2.9). - An animal moves, so its cells must bend, stretch and change shape. Animal cells have no cell wall, and this flexibility supports the movement and functioning of animal tissues. - A wall around animal cells would lock every tissue rigid, and the animal could not move at all.

Question 2

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)

Accepted Answer

(i) Cell membrane and cell wall — permeability - The cell membrane is selectively permeable: it lets some substances through and blocks others. In Activity 2.2 it let water move in and out of the potato cells but held back the salt and sugar molecules. - The cell wall is permeable: water and dissolved minerals pass straight through it. The two working together are what let a root absorb water and nutrients from the soil. (ii) RER and SER — structure - RER carries ribosomes on its surface, which is what makes it look rough under an electron microscope. - SER has no ribosomes on its surface, so it looks smooth. (iii) Chloroplasts and chromoplasts — pigments - Chloroplasts contain the green pigment chlorophyll, which absorbs sunlight for photosynthesis. - Chromoplasts contain pigments other than chlorophyll — yellow, orange or red — which colour flower petals and fruits and so attract pollinators and seed-dispersing animals.

Question 3

What consequences would you predict for a plant cell if its cell wall were to become as flexible as a cell membrane?

Accepted Answer

- The cell would lose its shape and its firmness, and the plant built from such cells would no longer stand up. - In a concentrated sugar or salt solution the whole cell would collapse inwards, like a cheek cell, instead of only its contents pulling away while the outline held (compare Fig. 2.9a and b). - In plain water the opposite failure: water would keep entering by osmosis with nothing rigid to push back, so the cell would swell and could burst. - Cells could no longer press firmly against one another, so stems would droop and leaves and flowers would go limp even when the plant had plenty of water. - The plant would have no defence left against wind and rain — which is exactly the stress the cell wall exists to resist. - Water and minerals would still get in, since the wall was already permeable; what would be lost is only the rigidity.

Question 4

Two 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.

Accepted Answer

(iii). - (iii) Water moved into Cell X and moved out of Cell Y through the cell membrane. - Cell X is in pure water. Outside there is more water and less solute than inside, so the surroundings are hypotonic; water enters by osmosis and the cell swells. - Cell Y is in concentrated salt solution. Outside there is less water and more solute, so the surroundings are hypertonic; water leaves by osmosis and the cell shrinks. - One fact explains both: the cell membrane is selectively permeable — water crosses it, salt does not. - (i) is wrong — salt molecules do not move into Cell Y. What leaves is water, and that is why it shrinks. - (ii) is wrong for the same reason: it assumes salt solution entered the cell, so there is nothing for the outgoing water to be "more than". - (iv) is wrong — osmosis is the diffusion of water across a selectively permeable membrane. Solute movement is not what caused it here, and the solute did not move at all.

Question 5

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? membrane, In addition to the nucleus, the cytoplasm contains several sub-cellular Vacuole Chloroplast Cell wall Ribosome cell (Fig. 2.10a, b and c). A bacterial cell lacks a well-defined nucleus and membrane-bound

Accepted Answer

- Because the two pieces must differ in only one thing — the liquid they are placed in. - Roughly equal size means roughly equal surface area of cell membrane exposed to the liquid, so water enters or leaves at comparable rates. A large piece and a small piece would change by different amounts for reasons that have nothing to do with the solution. - The initial weight is the baseline. The whole result of the activity is the change, change = final weight - initial weight, and with no initial value there is no change to calculate. - It turns "the potato looks a little swollen" into a measured number, so the gain in Beaker A and the loss in Beaker B can be shown rather than claimed. - This is what makes it a fair test: one variable changed, everything else held the same.

Question 6

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.

Accepted Answer

- The cell in Fig. 2.20 is a plant cell — the functions listed include a cell wall, a large storage vacuole and food manufacture, and an animal cell has none of these. - (i) Controlling all the activities of a cell — nucleus, the house of coded instructions, holding the chromosomes. - (ii) Site of cellular respiration — mitochondrion, where glucose is broken down and the energy stored as ATP. - (iii) Storage organelle that also provides rigidity to the cell — vacuole; the water it stores keeps up the pressure inside the cell, which keeps the cell firm. - (iv) Separates the cell contents from surroundings — cell membrane. - (v) Provides structural rigidity to the cell — cell wall. - (vi) Packs and stores materials received from ER — Golgi apparatus. - (vii) Helps in manufacturing food — chloroplast, whose chlorophyll absorbs sunlight for photosynthesis. - Now read the seven labels off Fig. 2.20 in your book and write the matching letter beside each part named above.

Question 7

Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories? Option (i) (ii) (iii) (iv)

Accepted Answer

(i). - (i) — Leucoplast (present in the plant cells) and Cell wall (absent in the animal cells). - Leucoplast is a colourless plastid that stores starch, oils or proteins, and plastids of every kind occur only in plant cells — so it belongs under "present in the plant cells". ✔ - Cell wall lies outside the cell membrane in plants, fungi and bacteria; animal cells have none, which is why they change shape so easily. ✔ - (ii) fails on Ribosome — ribosomes are present in animal cells, and indeed in every cell including bacteria, so they cannot be listed as absent. - (iii) fails on Golgi apparatus — it is present in animal cells; Camillo Golgi first saw it in the nerve cells of a barn owl. - (iv) fails on Endoplasmic reticulum — the ER is present in animal cells too. - So only option (i) has both cells of the pair in the right column.

Question 8

material enclosed by a membrane) Primitive nucleus or nucleoid (genetic

Accepted Answer

- No — a white petal contains no pigment at all. - Its plastids are leucoplasts, the plastids that lack pigments and are therefore colourless; their job is storing food such as starch, oils or proteins. - Colour in petals and fruits comes from chromoplasts, whose pigments are yellow, orange or red; green comes from chlorophyll inside chloroplasts. - With no pigment to absorb any part of the light falling on it, the petal throws nearly all of that light back, and what reaches our eyes is white. - The chapter's point about bright colours also fits: pigments exist to attract pollinators and fruit-eating animals, so a flower that attracts by scent or shape has no need to make one.

Question 9

material without membrane around it)

Accepted Answer

- Draw the plant cell — it is the one that shows every clue, including the rod-shaped chloroplasts. - Outline, two lines and not one: a thick outer rectangle with rounded corners for the cell wall, and a thinner line drawn just inside it, following it the whole way round, for the cell membrane. - Vacuole: one large central space filling most of the cell, bounded by a single line and labelled vacuole (cell sap). Everything else goes in the narrow band of cytoplasm between it and the membrane. - Nucleus (clue i): a dark round body pushed to one side. Draw its boundary as two closely spaced lines — the double-layered nuclear membrane — leave two or three gaps in it for the nuclear pores, and put a small solid circle inside for the nucleolus. - Endoplasmic reticulum (clue ii): begin it at the nuclear membrane, so it clearly runs out of the nuclear envelope, and let it spread through the cytoplasm as a branching network of long flattened tubes. Dot one stretch with tiny beads and label it rough ER (ribosomes attached); leave another stretch undotted and label it smooth ER. - Mitochondria (clue iii): two or three rod-shaped bodies, each with a smooth outer line and an inner line thrown into finger-like folds — label those folds cristae. - Chloroplasts (clue iii): three or four rod-shaped bodies with a double boundary, a few small discs drawn inside them, and the space around the discs labelled stroma. - Golgi apparatus: a stack of four or five flattened, slightly curved sacs, with tiny circles budding off the ends as vesicles. - Ribosomes: scatter a few free dots in the cytoplasm as well as the ones sitting on the rough ER. - Label the remaining space cytoplasm, run a ruled label line from every single part to its name written outside the cell, and title the figure "A typical plant cell". - If you pick the animal cell instead: no cell wall and no chloroplasts, an irregular rounded outline, only small scattered vacuoles, and add lysosomes as small single-membrane sacs.

Question 10

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.

Accepted Answer

- Renu is correct — plastids are found in all parts of a plant, roots included. - Plastids are not only chloroplasts. The chapter names three kinds: chloroplasts (green, for photosynthesis), chromoplasts (yellow, orange or red, in petals and fruits) and leucoplasts (colourless, for storage). - Non-green parts carry leucoplasts, which store food material such as starch, oils or proteins. The chapter's own examples are the starch-storing cells of potato and taro (Colocasia) — underground parts that never see sunlight. - So a root does not photosynthesise, yet it still needs plastids, because storing the food that the leaves send down is itself a plastid's job. - Rohit's error is treating "plastid" and "chloroplast" as the same word. His reasoning correctly explains why roots have few or no chloroplasts — it does not show that they have no plastids.

Question 11

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.

Accepted Answer

Structurally similar - Both are double-membrane-bound organelles, with an outer and an inner membrane. - Both carry their own DNA and their own ribosomes, so both can make some of their own proteins. - Both therefore appear to share an evolutionary history with certain single-celled bacteria. Functionally similar - Both are the plant cell's energy organelles — one captures energy, the other releases it, and between them they run the cell's whole energy budget. Structurally different - In a mitochondrion the inner membrane is folded into cristae, finger-like projections that increase the surface area for the reactions. - In a chloroplast the inner space holds a semi-fluid stroma containing disc-shaped membrane structures; there are no cristae. - A chloroplast holds the green pigment chlorophyll; a mitochondrion holds no pigment at all. Functionally different - Mitochondria break glucose down during cellular respiration and store the released energy as ATP, the energy currency of the cell. - Chloroplasts build glucose up: chlorophyll absorbs sunlight for photosynthesis, and the sugars made are stored in the stroma along with starch granules. - Mitochondria are present in plant and animal cells alike; chloroplasts are present only in plant cells.

Question 12

Membrane-bound organelles Ready to Go Beyond In eukaryotic cells, a network of fine fibres forms the cytoskeleton, which provides structural support, maintains cell shape, and enables cell movement and internal transport. It is visible only under an electron microscope as a separate entity. The cytoplasm may also store starch (in plant cells), or crystals of calcium oxalate or silica (in some plant cells). These are known as cell inclusions.

Accepted Answer

- Because surface area is what a mitochondrion works with, and many small ones carry far more of it than one giant one of the same volume. - Cellular respiration happens on the inner membrane. That is precisely why the inner membrane is thrown into cristae, finger-like projections that increase the surface area for the chemical reactions and so make more energy available. More membrane means more sites where ATP can be made. - Surface area grows as the square of the size while volume grows as the cube, so anything larger has less surface per unit of volume: - one cube of side 2: surface = 6 × 2^2 = 24, volume = 2^3 = 8, ratio = 24 / 8 = 3 - eight cubes of side 1: surface = 8 × 6 × 1^2 = 48, volume = 8 × 1 = 8, ratio = 48 / 8 = 6 - the same total volume, but twice the working surface once it is split up. - Small mitochondria can also be spread right through the cytoplasm and sit next to whatever needs ATP; one giant mitochondrion would leave the far corners of the cell short. - And a cell can build, repair or dispose of them one at a time as its energy demand changes — losing one of many is not losing everything. Also in the supplied text — Activity 2.4, Table 2.1 Cell structure Bacterial cell Plant cell Animal cell --- --- --- --- Cell membrane Present Present Present Cell wall Present Present Absent Cytoplasm Present Present Present Well-defined nucleus Absent Present Present Primitive nucleus (nucleoid) Present Absent Absent Membrane-bound organelles Absent Present Present Also in the supplied text — "Which cells in Fig. 2.10 are prokaryotic and eukaryotic?" - Fig. 2.10(a), the bacterial cell, is prokaryotic — no well-defined nucleus (a nucleoid instead) and no membrane-bound organelles. - Fig. 2.10(b) the plant cell and Fig. 2.10(c) the animal cell are eukaryotic — each has a membrane-bound nucleus and several membrane-bound organelles.

Question 13

Which of the following pairs of cell organelles contains DNA? (i) Chloroplasts, Ribosomes (ii) Mitochondria, Nucleus (iii) Golgi bodies, Ribosomes (iv) Nucleus, Lysosomes

Accepted Answer

(ii). - (ii) Mitochondria, Nucleus. - Nucleus — it contains chromosomes, and chromosomes are composed of DNA and specific proteins; the functional segments of that DNA are the genes. - Mitochondria — they have their own DNA and their own ribosomes, which is exactly why they can make some of their own proteins. - (i) fails on the ribosome. A chloroplast does contain DNA, but a ribosome does not — it is the site where protein is assembled, not where genetic information is kept. One member of the pair is enough to spoil it. - (iii) fails on both members: neither Golgi bodies nor ribosomes contain DNA. - (iv) fails on the lysosome — it is a single membrane-bound sac of digestive enzymes, with no DNA.

Question 14

Cut the tip portion of the root on the slide and put a coverslip. Gently squash the coverslip with your thumb to spread the cells on the slide.

Accepted Answer

- The cut would not heal. - Skin repairs itself by mitosis, the division that gives two daughter cells with the same DNA and the same number of chromosomes as the parent — so the new skin is an exact replacement for the skin that was lost. - Meiosis halves the chromosome number. Each new cell would carry only half the DNA of the skin cell it came from, and a cell holding half a set of instructions cannot work as a skin cell. - Meiosis also stops after making four cells; its products are gametes, not cells that go on dividing. The wound would get one round of unusable cells and then nothing, whereas mitosis repeats again and again until the gap is filled. - Meiosis deliberately creates variation, so even the few cells formed would differ genetically from the skin around them instead of matching it. - On top of all this the body would be making gamete-like cells in entirely the wrong place: the chapter is explicit that meiosis occurs only in the cells of reproductive organs — testes and ovaries.

Question 15

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?

Accepted Answer

(i) The hypothesis being tested - That water moves into or out of a plant tissue by osmosis, in the direction set by the concentration of the solution around it. - Stated so it can be tested: a carrot in plain water will take in water and stay firm, while an identical carrot in a concentrated salt solution will lose water and go limp. (ii) How to improve the experiment - Weigh both carrots before and after, as in Activity 2.2, so the result is a measured change = final weight - initial weight instead of an impression of how they look. - Match the carrots properly — same variety, same length and thickness, cut and trimmed at the same time. - Hold everything but the solution identical: same volume of liquid, same size of beaker, same temperature, same 24 hours. - State the salt concentration used, for example 20 per cent, so that someone else can repeat the experiment exactly. - Use two or three carrots in each beaker rather than one, so a single odd carrot cannot decide the result. (iii) Why the two carrots end up different - Plain water is hypotonic to the cell sap inside the carrot cells, so water enters them by osmosis. The vacuoles fill, the pressure inside each cell rises and the cells press outwards against their cell walls — the carrot stays stiff and crunchy. - Concentrated salt solution is hypertonic, so water leaves the cells by osmosis. The vacuoles lose water, the cells go slack and the tissue loses its firmness — the carrot turns rubbery and limp. - It is the same thing that happens to a whole plant short of water: the vacuoles empty, the cells stop being firm, and the plant wilts.

Question 16

Observe the slide under a microscope.

Accepted Answer

- Yes, the squashed and stained root tip shows the cells clearly — and they are not all alike. - Aceto-carmine stains the genetic material, so in some cells you see an ordinary nucleus, in others darkly stained thread-like or rod-shaped bodies instead, and in a few the stained material appears drawn towards opposite ends of the cell. - Why they differ: the cells at a growing root tip divide continuously, so at the moment the root was fixed in aceto-alcohol every cell had been caught at a different point in cell division. The slide is a set of snapshots of different stages, which is exactly what Fig. 2.17 shows. - Which stage comes first cannot be settled from this chapter — it names neither the stages nor their order, and says the stages of cell division are taken up in higher grades. All that can be said here is that the differences are stages of one continuous process, not different kinds of cell.

Question 17

Indicate the presence or absence of following structures in bacterial and animal cells: Structures in a cell Chromosome Nucleus Mitochondria Golgi complex Chromoplasts

Accepted Answer

Structure in a cell Bacterial cell Animal cell --- --- --- Chromosome Present (a single circular DNA molecule with proteins, lying in the nucleoid) Present Nucleus Absent Present Mitochondria Absent Present Golgi complex Absent Present Chromoplasts Absent Absent - A bacterial cell is prokaryotic: no membrane-bound nucleus and no membrane-bound organelles at all. That single fact removes the nucleus, the mitochondria and the Golgi complex together; its cellular activities take place directly in the cytoplasm. - Chromosome in a bacterium — present. The chapter defines a chromosome as being "composed of DNA and specific proteins", and it describes a prokaryote's genetic material as "a single circular molecule associated with specific proteins". That is DNA plus specific proteins, so the structure itself is there; what the bacterium lacks is the membrane around it. The region holding this single circular chromosome is called the nucleoid, which is why the chromosome row and the nucleus row differ. - An animal cell is eukaryotic, so the nucleus with its chromosomes, the mitochondria and the Golgi complex are all present. Its chromosomes are visible as rod-shaped bodies only when the cell is about to divide; at other times the same DNA is present as chromatin. - Chromoplasts are absent from both. Plastids of every kind — chloroplasts, chromoplasts and leucoplasts — occur only in plant cells.

Question 18

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.

Accepted Answer

(i) Why water gathers in Cup B and Cup C - The sugar in Cup B and the salt in Cup C dissolve in the trace of moisture in the hollow, making the fluid there far more concentrated than the plain water in the beaker. - The potato between them is living tissue: its cell walls are permeable and its cell membranes are selectively permeable, so water can cross but sugar and salt cannot. - Water therefore moves by osmosis from the beaker (more water, less solute) through the potato wall into the hollow (less water, more solute), and collects there as a visible pool. (ii) Why Cup A is necessary - Cup A is the control. It is set up in exactly the same way as the others except that nothing is added, so the only difference between A and B or C is the solute. - Without it you could not rule out the alternatives — that the potato simply leaks, or that water splashed in. Because A stays dry, the sugar and salt must be what causes the pools in B and C. (iii) Why no water gathers in Cups A and D - Cup A — plain water on both sides. There is no concentration difference, so there is no net movement of water in either direction. - Cup D — the potato was boiled, and boiling kills the cells and destroys their selectively permeable cell membranes. The sugar creates a concentration difference, but there is no longer a living selectively permeable membrane for osmosis to work across, so no water is drawn through. - Cup D is the second control, and it makes the sharper point of the two: osmosis needs a living membrane, not merely a difference in concentration.

Question 19

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

Accepted Answer

- The incorrectly matched pair is (ii) SER — Lipid and cellulose synthesis. NCERT's printed key gives (iii); that disagreement is set out in the last bullet rather than hidden. - (i) is correctly matched: ribosomes are the sites of protein synthesis. - (ii) is half right and half wrong. The SER is indeed "involved in the synthesis, and storage of fats and hormones" — but the chapter gives it no role whatever in cellulose. Cellulose is the material of the plant cell wall, a carbohydrate of many glucose units linked together, laid down outside the cell membrane. A pair that carries a false claim is not a correct match. - (iii) is correctly matched. Lysosomes are "single membrane-bound sacs filled with enzymes" that break down proteins, carbohydrates and fats, and the chapter's own example has the lysosomal enzymes of a sperm breaking down the outer layer of the egg — material that is not the cell's own worn-out waste. Digesting foreign agents is those same enzymes doing that same job, so nothing in the chapter marks this pair as false. - Weigh the two in the same terms and the choice is forced: the chapter is merely silent about lysosomes and foreign agents, whereas it directly contradicts an SER that makes cellulose. Silence is not a mismatch; a contradiction is. (ii) is therefore the pair to name.

Question 20

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

Accepted Answer

- The cell would run out of usable energy and die. - Mitochondria are the site of cellular respiration, where glucose and other molecules are broken down to release energy. Remove them and the cell has no way to get at the energy held in its food. - Nothing would then be left to store that energy as ATP, the energy currency that pays for almost everything a cell does. - Without ATP the cell cannot drive substances across its membrane, build proteins and lipids, run its clean-up, or divide. Its activities would slow, then stop altogether. - A plant cell would be no better off. Its chloroplasts could still trap sunlight and make sugar, but with no mitochondria it could not release the energy locked inside that sugar.

Question 21

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

Accepted Answer

- Contact inhibition. In many animal cells, division stops as soon as a cell comes into contact with its neighbouring cells, so cells do not pile up and no tumour forms. - Cancer cells lose this control and go on dividing uncontrollably, and that is what builds a tumour; cancerous tumours can then invade nearby tissues and even spread to other parts of the body to form new tumours. - Programmed Cell Death (PCD) works alongside it, a genetically regulated removal of cells that are no longer needed, keeping cell numbers in balance. - Yes, plants can form tumour-like growths. Because of their rigid cell walls, plant cells do not show contact inhibition at all and follow a different pattern of growth, so nothing switches division off when cells touch, and abnormal swellings can build up. - But such a growth cannot behave like a malignant animal tumour. The rigid cell wall fixes every plant cell in place, so cells cannot break away, push into neighbouring tissue, or travel to another part of the plant — a plant growth stays where it started.

Question 22

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.

Accepted Answer

- The ribosomes, the endoplasmic reticulum and the Golgi apparatus, working as a single pathway. - Proteins are made by ribosomes attached to the Rough ER — the RER's stated job is protein synthesis and protein secretion. - Lipids are made by the Smooth ER, which synthesises and stores fats. - Both are passed to the Golgi apparatus, which modifies, sorts and packages proteins and lipids into vesicles — the cell's post office. - The vesicles travel to the cell membrane and fuse with it, delivering their protein and lipid into the membrane itself. The path, in order - Ribosome on RER (protein) and SER (lipid) → transport vesicle → Golgi apparatus (modify, sort, package) → vesicle → cell membrane. What your labelled diagram must contain - The nucleus at one end, with its outer nuclear membrane running straight into the Rough ER — draw them joined, not separate. - The Rough ER as flattened sheets dotted along the outside with tiny beads; label the beads ribosomes. - The Smooth ER continuous with it, drawn as smooth undotted tubes. - Small circles budding off the ER, labelled vesicles, with an arrow pointing to the Golgi. - The Golgi apparatus as a stack of four or five flattened sacs, receiving on the face nearer the ER and releasing on the face nearer the membrane. - Further vesicles budding off that far face, with arrows to the plasma membrane and one vesicle drawn part-way through fusing with it. - A single long arrow running the length of the sequence to show the direction of travel, and a ruled label line to every part named above.

Question 23

What would happen if gametes are formed by mitotic divisions?

Accepted Answer

- The chromosome number would double in every generation, and sexual reproduction would stop producing any variation. - Mitosis gives each daughter cell the same number of chromosomes as the parent cell. A gamete made that way would carry the full number, not half. - At fertilisation two such gametes would fuse, so the zygote would have twice the parent's chromosome number; its own offspring would have twice that again, and so on without limit. - Meiosis exists to prevent exactly this. It reduces the number to half in the first of its two divisions, so that when gametes from two individuals combine, the original chromosome number is restored. - Mitosis also produces genetically identical daughter cells. Every gamete an individual made would then be an exact copy of the parent cell, carrying no new combinations, so the variation and diversity that sexual reproduction depends on would be lost — all the children of one couple would be genetically alike, each holding both parents' complete sets, instead of each being a fresh combination.

Question 24

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? (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? y Use selected software or digital tools to create animations or simulations of cell division and share them in the class. y Create a model of any type of a ‘synthetic cell’ using low-cost eco-friendly material. y Build a mitosis or meiosis model with your classmates for your science project or exhibition. How did teamwork contribute to the success of the activity? Did this activity change your perspective or understanding of the cell division topic in any way? If so, explain how? y Develop a nukkad natak for community awareness in simple dialogues about the different functions of cell organelles. The Quest Continues … What is the future of the development of synthetic cells using non-living chemicals? If a synthetic cell is developed, what may be the related ethical issues?

Accepted Answer

(i) Osmosis (ii) Concentration of salt or sugar is higher than the cell sap of bacterial or fungal cell, and therefore, water inside the cell comes out due to osmosis.. - (i) Osmosis. Deepa is using the movement of water across the selectively permeable membranes of microbial cells to keep her produce from spoiling. (ii) How high concentrations of salt and sugar stop spoilage - The salt, sugar or jaggery makes the liquid around the fruit far more concentrated than the cell sap inside a bacterial or fungal cell — the surroundings become hypertonic. - Water therefore moves out of those microbial cells, through their selectively permeable membranes, by osmosis, from the dilute inside to the concentrated outside. - Stripped of water the cells shrink and cannot carry on their activities, grow or multiply, so the spoilage organisms never take hold and the pickle, murabba or sharbat keeps for months. - The fruit's own cells lose water in the same way, which is why the pieces in a murabba turn firm and translucent. (iii) A healthy recipe of the same kind - Amla murabba with jaggery: prick washed amla all over, steam or boil until just soft, then simmer in a thick jaggery syrup with a little cardamom until the fruit turns translucent; cool completely and bottle in a clean, dry glass jar. - Jaggery replaces refined sugar and still gives the concentrated syrup that osmosis needs, while keeping the iron and minerals. A salt-and-lemon-juice pickle dried in the sun works the same way with no oil at all. (iv) Scientific values addressed - Applying a scientific principle — osmosis — to solve a real problem instead of accepting the loss. - Observing carefully and drawing the right inference: three-quarters of the harvest was going to waste, and the cause was perishability, not the market. - Respecting traditional knowledge while checking that it is scientifically sound. - Sustainability — cutting waste rather than producing it. - Contributing to food security and to the local economy. - Self-reliance and enterprise: acting on what she understood, and turning a loss into an income.

NCERT Solutions · Class 9 Science Cell: The Building Block of Life

Pause and Ponder 2.1 (part 1 of 14)

Exercise 2.1

Revise, Reflect, Refine 2.1 (part 2 of 14)

Exercise 2.1

Pause and Ponder 2.2 (part 3 of 14)

Exercise 2.2

Revise, Reflect, Refine 2.2 (part 4 of 14)

Exercise 2.2

Pause and Ponder 2.3 (part 5 of 14)

Exercise 2.3

Revise, Reflect, Refine 2.3–2.4 (part 6 of 14)

Exercise 2.3

Exercise 2.4

Pause and Ponder 2.4–2.5 (part 7 of 14)

Exercise 2.4

Exercise 2.5

Revise, Reflect, Refine 2.5–2.6 (part 8 of 14)

Exercise 2.5

Exercise 2.6

Pause and Ponder 2.6 (part 9 of 14)

Exercise 2.6

Revise, Reflect, Refine 2.7 (part 10 of 14)

Exercise 2.7

Pause and Ponder 2.7 (part 11 of 14)

Exercise 2.7

Revise, Reflect, Refine 2.8 (part 12 of 14)

Exercise 2.8

Pause and Ponder 2.8 (part 13 of 14)

Exercise 2.8

Revise, Reflect, Refine 2.9–2.16 (part 14 of 14)

Exercise 2.9

Exercise 2.10

Exercise 2.11

Exercise 2.12

Exercise 2.13

Exercise 2.14

Exercise 2.15

Exercise 2.16

Cell structure	Bacterial cell	Plant cell	Animal cell
Cell membrane	Present	Present	Present
Cell wall	Present	Present	Absent
Cytoplasm	Present	Present	Present
Well-defined nucleus	Absent	Present	Present
Primitive nucleus (nucleoid)	Present	Absent	Absent
Membrane-bound organelles	Absent	Present	Present

Structure in a cell	Bacterial cell	Animal cell
Chromosome	Present (a single circular DNA molecule with proteins, lying in the nucleoid)	Present
Nucleus	Absent	Present
Mitochondria	Absent	Present
Golgi complex	Absent	Present
Chromoplasts	Absent	Absent