NCERT Solutions for Class 9th Science Chapter 2 End-of-chapter questions — Revise, Reflect, Refine

Book page 24 Updated on2026-09-08

Q1.

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)

Answer

(i) Cell membrane and cell wall — permeability

	Cell membrane	Cell wall
Permeability	Selectively permeable — lets some substances through and blocks others	Freely permeable — water and dissolved minerals pass straight through
What that means	Water crosses; salt and sugar molecules are held back, which is what makes osmosis possible	Does no sorting at all; the selection is left to the membrane just inside it
Present in	Every living cell	Plants, fungi and bacteria only

(ii) RER and SER — structure

	Rough Endoplasmic Reticulum	Smooth Endoplasmic Reticulum
Surface	Ribosomes attached to its surface, so it looks rough under an electron microscope	No ribosomes on its surface, so it looks smooth
Main function	Protein synthesis and protein secretion (for example in gland cells such as pancreatic cells)	Synthesis and storage of fats and hormones

(iii) Chloroplasts and chromoplasts — pigments

	Chloroplast	Chromoplast
Pigment	Chlorophyll — a green pigment	Pigments other than chlorophyll — yellow, orange or red
Function of the pigment	Absorbs sunlight for photosynthesis	Gives bright colour, which attracts pollinators and fruit-eating animals
Found in	Leaves and other green parts	Flower petals and fruits

Why it happens: in each pair the two structures are close relatives, and one small difference decides the job. Membrane and wall are both boundaries, but only a selective boundary can control the cell's internal composition — a freely permeable wall could never do that, so the two are needed together. RER and SER are one continuous network; attaching ribosomes to part of it turns that part into a protein factory. Chloroplast and chromoplast are both plastids; swapping the pigment turns a food factory into a signal.

Q2.

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

The correct explanation is (iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.

Cell X in pure water: outside is hypotonic → water moves in → cell swells
Cell Y in concentrated salt: outside is hypertonic → water moves out → cell shrinks
In both cases the only substance crossing the membrane is water

Why the other options fail:

(i) is wrong because salt molecules do not cross the cell membrane — it is selectively permeable. And even if salt entered, it would make the inside more concentrated and draw water in, so the cell would swell, not shrink.
(ii) is wrong for the same reason: it assumes salt solution entered the cell. Nothing entered Cell Y.
(iv) is wrong because osmosis is by definition the movement of water, not of solute. Solute movement is diffusion, and here it does not happen at all.

Why it happens: the whole of osmosis rests on one asymmetry — the membrane is open to the solvent and closed to the solute. Because the salt cannot move to even out the concentrations, water has to move instead. Both cells in this question obey exactly the same rule; only the direction of the concentration difference is reversed. Note also what an animal cell risks: with no cell wall, Cell X in pure water can go on swelling until it bursts.

Q3.

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.

Answer

Fig. 2.20 is a plant cell — you can tell from the thick outer wall, the chloroplasts and the large vacuole.

Label	Part	Function
(a)	Mitochondrion	(ii) Site of cellular respiration
(b)	Nucleus	(i) Controlling all the activities of a 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 the cell contents from surroundings
(g)	Vacuole	(iii) Storage organelle that also provides rigidity to the cell

The seven labelled parts of Fig. 2.20 and what each of them does.

Why it happens: two clues separate the trickiest pair, (e) and (f). Both arrows point at the boundary, but (e) meets the thick outer orange layer and (f) meets the thin line just inside it. Match that to the wording of the functions: “provides structural rigidity” can only be the rigid cellulose wall, while “separates the cell contents from surroundings” describes a boundary that controls exchange, which is the membrane. Function (iii) is also worth noting — the vacuole is a storage organelle and a source of rigidity, because the water it stores keeps up the turgor pressure that makes the cell firm.

Q4.

Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories? (i) Leucoplast / Cell wall (ii) Mitochondria / Ribosome (iii) Cell wall / Golgi apparatus (iv) Lysosome / Endoplasmic reticulum — the first column being ‘Present in the plant cells’ and the second ‘Absent in the animal cells’.

Answer

Only option (i) is correct: Leucoplast is present in plant cells and Cell wall is absent in animal cells.

Option	Present in the plant cells?	Absent in the animal cells?	Verdict
(i) Leucoplast / Cell wall	Yes — a colourless plastid that stores starch, oils or proteins	Yes — animal cells have only a membrane	Correct
(ii) Mitochondria / Ribosome	Yes	No — ribosomes are present in animal cells	Wrong
(iii) Cell wall / Golgi apparatus	Yes	No — the Golgi apparatus is present in animal cells	Wrong
(iv) Lysosome / Endoplasmic reticulum	Not shown in the plant cell of Fig. 2.10b; lysosomes are typical of animal cells	No — the ER is present in animal cells	Wrong

Why it happens: the question is really testing one idea — which structures are exclusive to plants. Only three things in this chapter are: the cell wall, the plastids (chloroplast, chromoplast, leucoplast) and the large central vacuole. Everything else — mitochondria, ribosomes, ER, Golgi apparatus, nucleus, cell membrane — is shared by plant and animal cells alike, because those are the general machinery of any eukaryotic cell. Once you hold that short list in mind, each option can be checked in a second.

Q5.

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

Renu is correct. Roots do contain plastids. Rohit has confused plastids with one particular kind of plastid, the chloroplast.

Plastids are a family of organelles with three members: chloroplasts (green, for photosynthesis), chromoplasts (yellow, orange or red) and leucoplasts (colourless, for storage).
Roots lack chloroplasts because there is no light underground and no photosynthesis to do — that part of Rohit's reasoning is right.
But roots are full of leucoplasts, which store starch, oils and proteins. Storing food is one of the main jobs of a root.
Some roots even have chromoplasts. A carrot is orange because of the pigment in the chromoplasts of its root; beetroot and sweet potato are coloured in the same underground way.

plastids = chloroplasts + chromoplasts + leucoplasts
root: chloroplasts absent, leucoplasts present, chromoplasts sometimes present
→ therefore plastids are present in roots

Why it happens: plastids are interconvertible — one type can turn into another when the cell's job changes. That is why a potato left in sunlight turns green (leucoplasts developing chlorophyll and becoming chloroplasts) and why a green tomato turns red as it ripens (chloroplasts becoming chromoplasts). Because the whole family shares one origin, a plant cell almost always has plastids of some kind; what varies is which type. Rohit's error is a useful one to remember: “no photosynthesis” proves only that chloroplasts are absent, not that plastids are.

Check it yourself: put a drop of iodine solution on a thin slice of raw potato or arbi (Colocasia). It turns blue-black, showing starch grains — starch stored inside leucoplasts.

Q6.

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

Similarities

Both are double-membrane-bound organelles.
Both have their own DNA and their own ribosomes, so both can make some of their own proteins.
Both share features with certain bacteria, which suggests both share an evolutionary history with single-celled organisms.
Both are energy organelles: one captures energy, the other releases it. Both increase their internal membrane surface — cristae in one, disc-shaped membranes in the other.
Both are found in plant cells.

Differences

	Mitochondrion	Chloroplast
Pigment	None	Chlorophyll, a green pigment
Inner structure	Inner membrane folded into finger-like cristae; an intermembrane space	Semi-fluid stroma containing disc-shaped membrane structures that hold chlorophyll
Process carried out	Cellular respiration — glucose and other molecules are broken down	Photosynthesis — light energy is absorbed and sugar is made
Energy	Releases stored chemical energy as ATP, the energy currency	Converts light energy into chemical energy in sugars
Occurrence	In all eukaryotic cells — plant and animal	Only in plants and some other photosynthetic organisms; only in the green parts
Storage	Does not store food	Sugars made are stored in the stroma along with starch granules

Chloroplast: light energy + CO₂ + H₂O → sugar + O₂ (energy stored)
Mitochondrion: sugar + O₂ → ATP + CO₂ + H₂O (energy released)

Why it happens: the two organelles are the opposite halves of one cycle, and their structures reflect that. Each folds its inner membrane because the reactions of both photosynthesis and respiration happen on membranes, so extra membrane area means a higher rate. The shared features — a double membrane, own DNA, own ribosomes — are the reason biologists think both were once free-living bacteria that came to live inside a larger cell. It also explains why a plant cell needs both: the chloroplast can only bank the energy of sunlight in sugar, and only the mitochondrion can withdraw it as ATP, which is the form every other part of the cell can actually spend.

Q7.

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

Answer

The correct pair is (ii) Mitochondria, Nucleus.

Organelle	Contains DNA?	What it contains instead / in addition
Nucleus	Yes	Chromosomes made of DNA and specific proteins; the functional segments of DNA are genes
Mitochondrion	Yes	Its own DNA and its own ribosomes — it makes some of its own proteins
Chloroplast	Yes	Also has its own DNA and ribosomes
Ribosome	No	It is the site where protein is synthesised, not a store of DNA
Golgi apparatus	No	Modifies, sorts and packs proteins and lipids into vesicles
Lysosome	No	A single membrane-bound sac full of digestive enzymes

Options (i), (iii) and (iv) each pair one DNA-containing organelle with one that has none, so all three are wrong. Note that chloroplasts do contain DNA — option (i) fails only because ribosomes do not.

Why it happens: DNA is needed wherever proteins have to be made locally. The nucleus holds the cell's master copy. Mitochondria and chloroplasts keep a small private set because they also keep their own ribosomes and build a few of their own proteins on the spot — the very feature that suggests they descend from ancient free-living bacteria. Everything else in the cell receives its proteins ready-made from the cytoplasm, so it has no use for DNA of its own.

Q8.

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?

Answer

(i) The hypothesis. That water moves into or out of plant cells by osmosis according to the concentration of the surrounding solution — so a carrot in a dilute (hypotonic) medium will gain water and remain firm, while a carrot in a concentrated (hypertonic) medium will lose water and become limp.

(ii) Improvements.

Match the two carrots properly: use pieces of the same mass and same length, cut from carrots of the same age and variety.
Weigh and measure each piece before and after the 24 hours, so the result is a number and not an impression. Record the change: final mass − initial mass.
State the salt concentration exactly (for example 20 per cent) and use the same volume of liquid in both beakers, with both carrots fully immersed.
Keep both beakers at the same temperature and cover them, so evaporation does not concentrate one solution.
Repeat with three or four carrots in each beaker and take an average — one carrot is not enough evidence.
Take readings at intervals (say every 4 hours) instead of only at the end, so the progress of the change is seen.
Blot both pieces dry the same way before weighing, so clinging surface water is not counted.

(iii) Why they feel different.

Plain water: solute concentration outside < inside (hypotonic)
→ water enters the carrot cells by osmosis → vacuoles fill → cells become turgid
→ each cell presses against its rigid cell wall → tissue is stiff and crunchy

Concentrated salt: solute concentration outside > inside (hypertonic)
→ water leaves the cells by osmosis → vacuoles empty → cells become flaccid
→ no pressure against the walls → tissue is soft, bendy and limp

Why it happens: crunchiness is a mechanical property produced by water pressure. A carrot snaps because millions of full, turgid cells push outwards against their walls, so the tissue behaves like a bundle of inflated tubes and breaks cleanly instead of bending. Draw the water out and the same walls are still there, but they are no longer under pressure, so the carrot bends like an empty tube. This is exactly the wilting of Question 4 on page 19, and it is exactly what happens when salt is rubbed on cut vegetables and water oozes out.

Q9.

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

Answer

Structures in a cell	Bacterial cell	Animal cell
Chromosome	Present	Present
Nucleus	Absent	Present
Mitochondria	Absent	Present
Golgi complex	Absent	Present
Chromoplasts	Absent	Absent

Two rows need a word of explanation.

Chromosome — bacterial cell. Genetic material is certainly present, but not as the rod-shaped chromosomes of a dividing eukaryotic cell. In a prokaryote the DNA is a single circular molecule associated with specific proteins, lying in a region called the nucleoid with no membrane around it. It is usually called the bacterial chromosome, so the entry is “Present”, but you should say what form it takes.
Chromoplasts. These are plastids, and plastids occur only in plant cells. They are therefore absent from both columns of this table.

Why it happens: read the first two rows together and the whole prokaryote–eukaryote distinction appears. A bacterium has the genetic material but not the genetic compartment — DNA without a nuclear membrane. Rows 3 and 4 follow from the same limitation: mitochondria and the Golgi complex are membrane-bound organelles, and a cell that cannot build internal membranes cannot have them. A bacterium still respires and still makes and exports proteins; it simply does all of it in the cytoplasm and at the cell membrane instead of in separate organelles.

Q10.

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). Keep Cup A empty; add one teaspoon sugar in Cup B; add one teaspoon salt in Cup C; 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.

Answer

(i) Why water collects in Cups B and C.

sugar (B) or salt (C) in the hollow + the potato's own moisture → a strongly concentrated solution
water in the beaker = dilute
living potato cells between them = a selectively permeable barrier
→ water moves from the beaker, through the potato tissue, into the hollow by osmosis
→ the hollow slowly fills up

The potato wall of the cup behaves like one thick membrane. Water moves down the concentration gradient — from the dilute side to the concentrated side — and the sugar or salt cannot come the other way, so the level in the hollow rises.

(ii) Why Cup A is necessary. Cup A is the control. It is identical to B and C in every way except that its hollow is empty, so there is no concentration gradient. If water gathered in A as well, it would prove that water was simply seeping through the potato because of gravity or a leak, and the experiment would tell us nothing about osmosis. Because A stays dry, we can be sure that it is the concentration difference — and nothing else — that drives the water in B and C.

(iii) Why the hollows of A and D stay dry.

Cup	Condition	Reason no water gathers
A	Raw potato, hollow empty	Both sides are equally dilute — no concentration gradient, so there is no net movement of water
D	Boiled potato, sugar in the hollow	Boiling kills the cells and destroys the cell membranes, so the tissue is no longer selectively permeable. Osmosis needs a living membrane; without it, sugar simply diffuses out and no water accumulates

Why it happens: the experiment is designed so that each cup removes one possible explanation. B and C show the effect; A shows that a concentration gradient is needed; D shows that living, intact membranes are needed. D is the more powerful of the two controls, because a boiled potato still has cell walls and still has the same shape and thickness — the only thing that has changed is that the membranes are dead. Heat denatures the proteins and disorganises the lipid bilayer, and with the gatekeepers gone the tissue leaks in both directions.

Tip: use B with sugar and C with salt for a reason. If both fill up, you have shown that the effect depends on concentration, not on which particular substance was used.

Q11.

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

The incorrectly matched pair is (ii) SER — Lipid and cellulose synthesis.

Pair	Correct?	Reason
(i) Ribosome — Protein synthesis	Correct	Ribosomes are the sites of protein synthesis, whether free in the cytoplasm or attached to the ER
(ii) SER — Lipid and cellulose synthesis	Incorrect	The SER is involved in the synthesis and storage of fats and hormones. Cellulose is not made there — it is a cell wall carbohydrate assembled at the cell membrane from glucose units
(iii) Lysosome — Digestion of foreign agents	Correct	Lysosomes are enzyme-filled sacs that break down unwanted proteins, carbohydrates, fats and damaged organelles

Why it happens: the trap in option (ii) is that half of it is true. The SER really does make lipids, so a quick reader accepts the whole statement. But cellulose belongs outside the membrane, in the cell wall, and it is built from many glucose units linked together — a job that has nothing to do with the smooth ER. It is also a useful reminder that the SER exists in animal cells too, where there is no cellulose at all.

Q12.

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

Answer

The cell would run out of usable energy and die, because nothing else in it can release the energy stored in glucose and package it as ATP.

no mitochondria → no cellular respiration
→ no ATP, the energy currency of the cell
→ every energy-requiring activity stops

Specifically, the following would fail:

Transport across the membrane that needs energy would stop, so the cell could no longer keep its internal composition different from its surroundings.
Protein synthesis on the ribosomes, and the packing and transport of those proteins by the ER and Golgi apparatus, would stop.
Cell division would stop, so there would be no growth and no repair.
Movement — muscle contraction in an animal, the beating of cilia — would stop at once. A sperm cell, whose tail is packed with mitochondria, would be motionless.
Cells with the highest energy demand — heart muscle, nerve cells, kidney cells — would fail first.

Why it happens: a plant cell in this situation would be no better off, and that point is worth thinking about. Its chloroplasts could still capture sunlight and make sugar, but sugar is only stored energy; the cell cannot spend it directly. Only the mitochondrion converts it into ATP, the small, ready-to-use packet that every other process accepts. So a plant cell without mitochondria would starve in the middle of its own food supply. A few specialised cells manage without — a mature red blood cell has no mitochondria and gets by on a much less efficient pathway in the cytoplasm — but no ordinary cell could keep working for long.

Q13.

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

Answer

The phenomenon is contact inhibition — in many animal cells, cell division stops when a cell comes into contact with its neighbouring cells.

healthy tissue: cell divides → daughter cells fill the gap → cells touch neighbours → division stops
cancer: contact inhibition lost → cells keep dividing with no room → tumour

Can plants develop tumours? Plants can form abnormal, uncontrolled swellings of tissue — but they are not tumours in the human sense, and here is the difference.

	Animal (human) tumour	Abnormal growth in a plant
Contact inhibition	Normally present; lost in cancer	Not shown at all — plant cells never had it, because their rigid cell walls hold them apart
Can cells move?	Yes — malignant cells invade nearby tissue and spread to other organs	No — each cell is cemented in place by its cell wall, so the growth stays local
Result	May become life-threatening when it spreads	A localised lump or gall; the plant usually survives

Why it happens: the cell wall is the key to the whole comparison. Because plant cells do not show contact inhibition, they follow a different pattern of growth and are controlled by other means — chiefly by chemical signals that decide where a plant grows. And because those same rigid walls glue every cell to its neighbours, a plant cell physically cannot break loose and travel to another organ. That is why the most dangerous feature of a human cancer, its ability to spread, has no counterpart in a plant. In humans, keeping tumours away depends on two safeguards working together: contact inhibition, which stops division when there is no room, and programmed cell death, which removes damaged cells before they can become cancerous.

Q14.

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

Four organelles are involved: ribosomes, the Rough ER, the Smooth ER and the Golgi apparatus.

Organelle	What it contributes
Ribosomes (on the RER)	Synthesise the membrane proteins
Rough ER	Receives those proteins and transports them onwards
Smooth ER	Synthesises the lipids (fats) of the bilayer
Golgi apparatus	Modifies, sorts and packages the proteins and lipids into vesicles

The path:

ribosome on RER (protein) + SER (lipid)
→ transport vesicle buds off the ER
→ Golgi apparatus — modified, sorted, packed
→ secretory vesicle buds off the Golgi
→ vesicle travels to the surface and fuses with the cell membrane
→ its own membrane becomes part of the cell membrane

Membrane proteins are made on the RER, membrane lipids on the SER; both travel in vesicles to the Golgi apparatus, are packed there, and are finally delivered to the cell membrane by vesicles that fuse with it.

Why it happens: the elegant part of this route is the last step. The vesicle does not push its contents through the membrane — it is a small closed bag of membrane, so when it fuses with the cell membrane its own lipid bilayer simply joins the bilayer of the cell surface, and the proteins it carries end up embedded there facing the right way. That is how a membrane grows without ever being broken open. It also explains why the ER is described as continuous with the outer membrane of the nuclear envelope: the whole system — nuclear envelope, ER, Golgi, vesicles, cell membrane — is one connected membrane network with material flowing through it in one direction.

Q15.

What would happen if gametes are formed by mitotic divisions?

Answer

The chromosome number would double in every generation, and the species could not survive.

Normal (meiosis):
parent cell 46 → gamete 23 ; 23 (sperm) + 23 (egg) = 46 — number restored

If gametes were formed by mitosis:
gamete = 46 (same as the parent cell)
46 + 46 = 92 in the child
next generation: 92 + 92 = 184
then 368, 736, … the number doubles every generation

Meiosis halves the chromosome number before fertilisation, so the number of the species stays constant. Mitotic gametes would double it each time.

The consequences would be:

No constant chromosome number. Each species has a fixed number that its cells are built to handle. A doubling would break the machinery of cell division, and most such embryos would not survive.
Severe abnormalities and infertility. Extra sets of chromosomes mean extra copies of every gene, and the balance between gene products would be destroyed.
Far less variation. Meiosis mixes the parents' chromosomes; that is why children resemble their parents but are not exactly the same. Mitotic gametes would pass on the parent's combinations unchanged, so the diversity that lets a population adapt would be lost.

Why it happens: meiosis exists precisely to solve this problem. Sexual reproduction joins two cells, so the number carried by each must first be halved, otherwise addition alone would run away. That is why the first division of meiosis reduces the chromosome number to half, and why the second is simply mitosis-like — one halving is all that is needed, and it must happen exactly once.

Q16.

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?

Answer

(i) The scientific concept. Osmosis — and with it the idea of a hypertonic medium. Deepa surrounds the fruit with a solution far more concentrated than the contents of any microbial cell, so water is drawn out of the microbes and they cannot grow.

(ii) How salt and sugar stop bacteria and fungi.

salt or sugar added in high concentration
→ the solution around the food becomes strongly hypertonic
→ water moves out of the bacterial and fungal cells by osmosis, across their selectively permeable membranes
→ the cells shrink and plasmolyse; the membrane pulls away from the wall
→ almost no free water is left inside for enzyme reactions
→ the microbes cannot grow, multiply or spoil the food

The same drawing-out also removes free water from the food itself, and microorganisms cannot grow in food that has little available water — this is why a well-made pickle or murabba keeps for months.
Note that the microbes are usually not killed outright; they are simply held in a state where they cannot function. Dilute the pickle brine and spoilage begins again.

(iii) A healthy recipe of this kind.

Sample answer — Amla murabba with jaggery (a low-refined-sugar version)

Wash 500 g fresh amla, prick each fruit all over with a fork and steam or blanch for 4–5 minutes so it softens.
Dissolve about 400 g jaggery in 250 mL water, boil, and strain out the impurities.
Add the amla and simmer until the syrup is thick and coats the fruit. The concentration must be high enough to keep the medium hypertonic.
Add a pinch of cardamom, a few strands of saffron and a small piece of dry ginger for flavour, and a squeeze of lemon juice, whose acidity gives a second barrier to microbes.
Cool completely, fill into a clean, dry, sterilised glass jar, and keep the fruit fully covered by syrup. Always use a dry spoon.

Why it is healthier: jaggery instead of refined sugar keeps some iron and minerals, amla is one of the richest natural sources of vitamin C, and no chemical preservative or artificial colour is used. A low-salt lemon pickle preserved with lemon juice, turmeric and mustard oil, and sun-dried, works on the same principle.

(iv) The scientific values addressed.

Applying scientific knowledge to real life — using osmosis to solve a farming problem.
Respect for traditional knowledge, tested by science — pickling and murabba are old Indian practices, and the chapter's science explains exactly why they work.
Sustainability and prevention of waste — produce that would have rotted is turned into a product.
Food security — seasonal fruit is made available through the year.
Enterprise and self-reliance — value addition raises a farmer's income and supports the local economy.
Hygiene and safety — clean, dry, sterilised bottles and correct concentrations; a careless job would let mould grow.
Observation and reasoning — recognising the post-harvest loss and acting on the reason for it.

Why it happens: this is the same physics as the potato in Beaker B on page 11 and the shrivelled carrot in Question 8 — only the cell losing water is now a bacterium or a fungal spore instead of a potato cell. Preservation by salt or sugar therefore needs no electricity and no chemicals; it simply keeps the surroundings so concentrated that no microbe can hold on to its own water.

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