BiologyICSE Class 10 · Absorption by Roots

Plasmolysis, Turgidity and Flaccidity (ICSE Class 10 Biology)

Updated 15 October 2026 · Fact-checked

A plant cell placed in a hypotonic solution gains water by endosmosis and becomes turgid; turgor pressure pushes the protoplast against the wall, which pushes back equally. In a hypertonic solution it loses water by exosmosis, becomes flaccid and then plasmolysed: the protoplast shrinks away from the cell wall. Placing it back in water reverses this (deplasmolysis).

Understand Plasmolysis, Turgidity and Flaccidity

Why this topic matters. Every idea in the chapter (osmosis, root hairs, wilting, fertiliser 'burning') depends on how a single plant cell gains or loses water. ICSE tests it through A-R items on turgor and labelled diagrams of a plasmolysed cell.

The plant cell as an osmotic system. The cell wall (cellulose) is freely permeable: water and dissolved substances pass through it. The plasma membrane (and the membrane round the vacuole) is selectively permeable: water passes, most solutes do not. The cell sap in the large central vacuole is a solution of sugars and salts. So the protoplast behaves like a bag of solution inside a strong, porous box.

Three kinds of outside solution (compared with the cell sap).

Outside solution	Water moves	Result
Hypotonic (more dilute, e.g. pure water)	into the cell (endosmosis)	cell becomes turgid
Isotonic (same concentration)	no net movement	cell unchanged
Hypertonic (more concentrated, e.g. strong salt or sugar solution)	out of the cell (exosmosis)	cell becomes flaccid, then plasmolysed

Turgidity. When water enters, the vacuole swells and the protoplast presses outward on the wall. This outward pressure is turgor pressure. The stretched wall presses back inward with an equal and opposite wall pressure. When the two balance, no more water can enter: the cell is fully turgid, firm but unburst. Turgidity keeps leaves spread out, keeps herbaceous stems upright, and helps guard cells open stomata.

Flaccidity. When a cell loses water, turgor pressure falls and the cell becomes soft and limp. Many flaccid cells together make the plant wilt. On a hot afternoon leaves may droop because they lose water faster than roots absorb it; they recover at night.

Plasmolysis. In a hypertonic solution water leaves the vacuole and cytoplasm by exosmosis. The vacuole shrinks and the protoplast pulls away from the cell wall, first at the corners (incipient plasmolysis) and then all round. Because the wall is freely permeable, the space between the wall and the shrunken protoplast fills with the outside hypertonic solution, not with air or cell sap.

Deplasmolysis. If a plasmolysed cell is placed in water (hypotonic) soon enough, water re-enters by endosmosis, the protoplast swells back and the cell becomes turgid again. If plasmolysis lasts too long the protoplast dies and the cell cannot recover.

Everyday examples.

Salting raw mango slices or cucumber draws water out (plasmolysis), so they go limp and release juice.
Heavy fertiliser round a plant makes the soil water hypertonic; root cells lose water and the plant wilts and 'burns'.
Salt and sugar preserve pickles and jams: microbes in them are plasmolysed and cannot grow.
Wilted spinach revives in a bowl of water (deplasmolysis and regained turgor).
Weeds on a path die when salt is sprinkled on them.

Flow chart. Turgid cell in hypertonic solution → exosmosis → turgor pressure falls → flaccid → protoplast shrinks from wall → plasmolysed; plasmolysed cell in water → endosmosis → deplasmolysis → turgid again.

Draw-and-label checklist: plasmolysed cell. Rectangular cell wall drawn as a double line, unchanged in size; shrunken, rounded protoplast in the centre with the plasma membrane as its outer boundary; cytoplasm as a thin layer inside that membrane; nucleus inside the cytoplasm; small shrunken vacuole with cell sap; the gap between wall and protoplast shaded and labelled hypertonic solution. Labels: cell wall, plasma membrane, cytoplasm, nucleus, vacuole (cell sap), hypertonic solution.

Draw-and-label checklist: turgid cell. Same wall; protoplast filling the cell and pressed against the wall; large central vacuole; thin cytoplasm lining the wall; arrows: turgor pressure outward, wall pressure inward.

Plasmolysis, Turgidity and Flaccidity: key facts

Tonicity and the plant cell: Hypotonic outside endosmosis, turgid
Isotonic outside no net change
Hypertonic outside exosmosis, flaccid then plasmolysed; Always compare the outside solution with the cell sap.
Turgor and wall pressure: Turgor pressure exerted by the protoplast on the wall, acts outward
Wall pressure exerted by the wall on the protoplast, acts inward
Fully turgid cell the two are equal and opposite; Equal and opposite, never 'in the same direction'.
Parts of a plasmolysed cell: Cell wall unchanged, freely permeable
Plasma membrane boundary of the shrunken protoplast
Cytoplasm inside the membrane
Gap between wall and protoplast outside hypertonic solution; The commonest diagram trap in ICSE.
Plasmolysis versus deplasmolysis: Plasmolysis: in hypertonic solution, exosmosis, protoplast shrinks from wall | Deplasmolysis: in water, endosmosis, protoplast regains its shape; Deplasmolysis works only if the cell is still alive.

Hypotonic outside	endosmosis, turgid
Isotonic outside	no net change
Hypertonic outside	exosmosis, flaccid then plasmolysed

Turgor pressure	exerted by the protoplast on the wall, acts outward
Wall pressure	exerted by the wall on the protoplast, acts inward
Fully turgid cell	the two are equal and opposite

Cell wall	unchanged, freely permeable
Plasma membrane	boundary of the shrunken protoplast
Cytoplasm	inside the membrane
Gap between wall and protoplast	outside hypertonic solution

How to answer Plasmolysis, Turgidity and Flaccidity questions

ICSE asks you to identify a cell's state from a diagram or situation, explain it with osmosis, label a plasmolysed cell, or judge A-R statements on turgor.

1Compare the outside solution with the cell sap and name it hypotonic, isotonic or hypertonic.
2State the direction of water movement and name it: endosmosis (in) or exosmosis (out).
3Name the end state: turgid, flaccid, plasmolysed or deplasmolysed.
4Give the visible result for the plant: firm, wilted, limp slices, recovered leaves.
5In a diagram, label the gap between wall and protoplast as hypertonic solution and keep cytoplasm inside the membrane.
6For turgor questions, write 'equal and opposite' and say which way each pressure acts.

Plasmolysis, Turgidity and Flaccidity in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Fertiliser burn

Suppose a gardener, wanting quick growth, pours a large handful of urea fertiliser round a young tomato plant and waters it lightly. By the next afternoon the leaves hang limp even though the soil is wet.

Explain why the plant wilted although there was water in the soil, and what the gardener should do.

Try it first, then show the solutionSolution

The dissolved fertiliser makes the soil water more concentrated than the cell sap of root hairs: the soil solution is hypertonic.
Water now moves out of the root cells by exosmosis instead of in; root cells become flaccid and may plasmolyse.
With no water entering, leaf cells lose turgor through transpiration and the plant wilts.
Flooding the soil with plenty of water dilutes the solution, making it hypotonic again so that the root cells can recover by deplasmolysis.

Answer: Excess fertiliser made the soil solution hypertonic, so root cells lost water by exosmosis; heavy watering dilutes it and lets the cells recover.

Memory hook: Too much salt round the root pulls water out of the root.

Crisping wilted vegetables

Suppose a vendor sprinkles water on drooping coriander and keeps lettuce leaves in a bowl of cold water for half an hour before selling them.

Why do the leaves become crisp again?

Try it first, then show the solutionSolution

Wilted leaves have flaccid cells that have lost water.
Plain water is hypotonic to their cell sap, so water enters by endosmosis.
The vacuoles swell and turgor pressure rises until it is balanced by wall pressure.
Turgid cells make the leaf firm and crisp.

Answer: Endosmosis restores turgor, so flaccid cells become turgid and the leaves stiffen.

Memory hook: Water in, wall tight, leaf upright.

Tricks to remember Plasmolysis, Turgidity and Flaccidity

Short memory aids. Say each one aloud once, then use it on a question the same day.

HYPER makes it shrink
HYPERtonic: water hurries out and the protoplast shrinks; HYPOtonic: water goes in and the cell swells like a HIPPO.
Use it when: Choosing the right solution in MCQs.
Balloon in a basket
The protoplast is a balloon blown up inside a cane basket: the balloon pushes out (turgor), the basket pushes back (wall pressure).
Use it when: Turgor and wall pressure act in opposite directions.
The gap holds the outside
Whatever is outside the wall flows into the gap, because the wall lets everything through.
Use it when: Labelling the hypertonic solution in a plasmolysed cell.

Plasmolysis, Turgidity and Flaccidity: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: State of a cell from the solution · 2 marks · Short answerBoard level

A peeled strip of Rhoeo leaf is placed in a 10% salt solution. (a) Is the solution hypotonic or hypertonic to the cell sap? (b) Name the process by which water moves and the condition the cells reach.

Try it first, then show the solutionSolution

(a) Hypertonic: it is more concentrated than the cell sap (1 mark).
(b) Exosmosis; the cells become plasmolysed, the protoplast shrinking away from the cell wall (1 mark).

Answer: (a) Hypertonic. (b) Exosmosis; plasmolysis.

Example 2: Turgor A-R item · 1 mark · Assertion-reasonHarder board level

Assertion (A): A fully turgid cell does not take in any more water.
Reason (R): In a fully turgid cell, turgor pressure and wall pressure are equal and act in opposite directions.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).

Try it first, then show the solutionSolution

Both statements are true, and the balance of the two opposite pressures is why no further water enters.

Answer: (c).

Example 3: Label the plasmolysed cell · 3 marks · Short answerHarder board level

Draw a neat labelled diagram of a plasmolysed cell from the cortex of a root and label: cell wall, plasma membrane, cytoplasm, hypertonic solution. (A labelling question on a plasmolysed root cell was asked in 2025.)

Try it first, then show the solutionSolution

Draw the cell wall as an unchanged rectangle and a shrunken protoplast in the middle (1 mark).
Label the plasma membrane at the edge of the protoplast and the cytoplasm just inside it, round the vacuole (1 mark).
Label the space between the wall and the protoplast as hypertonic solution, and the cell wall (1 mark).

Answer: Correct diagram with the gap as hypertonic solution and cytoplasm inside the plasma membrane.

Example 4: Plasmolysis and deplasmolysis · 3 marks · Short answerHarder board level

Define plasmolysis and deplasmolysis. Why can a cell that has been plasmolysed for a long time not be deplasmolysed?

Try it first, then show the solutionSolution

Plasmolysis: shrinkage of the protoplast away from the cell wall due to exosmosis when the cell is kept in a hypertonic solution (1 mark).
Deplasmolysis: recovery of a plasmolysed cell to the turgid state by endosmosis when placed in water (1 mark).
Prolonged loss of water kills the protoplasm; the dead plasma membrane is no longer selectively permeable, so osmosis cannot restore the cell (1 mark).

Answer: Definitions as above; prolonged plasmolysis kills the protoplast, so it cannot recover.

Example 5: Salt on a lawn · 3 marks · Case-basedHOTS / competency

Suppose a family uses common salt to clear snow from a footpath every winter. In spring the grass along the path edges is brown and dead while the rest of the lawn is green. Explain this using the terms hypertonic, exosmosis and plasmolysis, and suggest how the grass could be saved next year.

Try it first, then show the solutionSolution

Melted salt water runs into the soil at the edges, making the soil solution hypertonic to the root-hair cell sap (1 mark).
Water leaves root cells by exosmosis; cells plasmolyse and die, so roots cannot absorb water and the grass dries out (1 mark).
Use sand or grit instead of salt, or flush the edges with plenty of water so the soil solution becomes hypotonic again (1 mark).

Answer: Salty soil water is hypertonic, causing exosmosis and plasmolysis of root cells; avoid salt or flush the soil.

Example 6: Why plant cells do not burst · 2 marks · Short answerHOTS / competency

A red blood cell bursts in distilled water but a plant cell does not. Explain.

Try it first, then show the solutionSolution

Both gain water by endosmosis in distilled water (½ mark).
The plant cell has a strong cellulose wall that exerts an inward wall pressure equal to the turgor pressure, so water stops entering before the cell bursts (1 mark).
The red blood cell has only a thin membrane with no wall, so it keeps swelling and bursts (½ mark).

Answer: The cell wall's wall pressure balances turgor pressure in the plant cell; the red blood cell has no wall.

Where students lose marks in Plasmolysis, Turgidity and Flaccidity

The slips examiners see most often, and what to write instead.

Mistake: Wrong labels on the plasmolysed cell
CISCE examiners' comments (2025): candidates misplaced labels, labelled the nucleus as cytoplasm, showed cytoplasm between the cell wall and the membrane, marked the vacuole sap as the hypertonic solution, and marked the cell wall as the plasma membrane.
Wrong working
Hypertonic solution arrow pointing to the vacuole; cytoplasm label in the gap.
Right working
Hypertonic solution in the gap between wall and protoplast; cytoplasm inside the plasma membrane round the vacuole.
Do this: Practise the diagram until the gap, membrane and cytoplasm are automatic.
Usually costs: 1-3 marks.
Mistake: Saying turgor and wall pressure act in the same direction
CISCE examiners' comments (2025): in an A-R item on a turgid cell, candidates did not realise that turgor pressure and wall pressure act in opposite directions, and so judged the Reason true.
Do this: Write 'equal in magnitude and opposite in direction' every time.
Usually costs: 1 mark.
Mistake: Using 'hypotonic' and 'hypertonic' for the cell instead of the outside solution
The terms describe the outside solution compared with the cell sap. Mixing them up reverses the direction of water movement.
Do this: Say 'the solution is hypertonic to the cell sap'.
Usually costs: 1 mark.
Mistake: Writing 'the cell wall shrinks'
In plasmolysis only the protoplast shrinks; the rigid wall keeps its shape.
Do this: Write 'the protoplast shrinks away from the cell wall'.
Usually costs: 1 mark.

Exam tips

Name the process and the result together: 'exosmosis, so the cell is plasmolysed'.
In any diagram keep the wall the same size and shrink only the protoplast.
For A-R items, test each statement separately before checking the link.
Link wilting to flaccid cells and revival to regained turgor.

Practice questions on Plasmolysis, Turgidity and Flaccidity

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
A cell placed in a solution shows no change in size. The solution is:
(a) hypotonic (b) hypertonic (c) isotonic (d) pure water
Hint
Equal concentration.
Answer
(c) isotonic.
Q2 · 1 mark · Very short answerBoard level
Name the pressure exerted by the cell wall on the protoplast of a turgid cell.
Hint
It opposes turgor pressure.
Answer
Wall pressure.
Q3 · 2 marks · Short answerHarder board level
An onion peel is mounted in a strong sugar solution coloured with a red dye. Under the microscope, the gaps that open between the cell walls and the shrunken protoplasts look red. Explain why.
Hint
Think about the permeability of the wall.
Answer
The cells are plasmolysed and the gaps are filled with the coloured outside (hypertonic) solution, because the cell wall is freely permeable and lets it in; the selectively permeable plasma membrane keeps the dye out of the protoplast.
Q4 · 2 marks · Short answerHarder board level
Distinguish between turgidity and flaccidity (two points).
Hint
Water content and firmness.
Answer
Turgidity: the cell is full of water, the protoplast presses on the wall, the cell is firm. Flaccidity: the cell has lost water, turgor pressure is low, the cell is soft and limp (the plant wilts).
Q5 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Pickles kept in strong brine do not easily rot.
Reason (R): Microbes falling into the brine lose water by exosmosis and cannot grow.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Brine is hypertonic.
Answer
(c).
Q6 · 2 marks · Short answerHarder board level
Give two roles of turgidity in plants.
Hint
Support and stomata.
Answer
Any two: keeps leaves expanded and herbaceous stems erect; opens stomata by making guard cells turgid; helps young roots push through soil; keeps cells in shape for normal functioning.
Q7 · 2 marks · Short answerHarder board level
Why do raw mango slices become limp and release juice when salt is sprinkled on them? Name the process involved.
Hint
Salt dissolves in surface moisture.
Answer
The salt forms a hypertonic solution on the slices; water leaves the cells by exosmosis, the cells become flaccid and plasmolysed, and the juice collects outside. Process: plasmolysis (by exosmosis).
Q8 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose three equal potato strips, each 5 cm long, are kept for an hour in liquids P, Q and R. Afterwards the strip in P is 5.4 cm and stiff, the strip in Q is 5 cm, and the strip in R is 4.6 cm and bendy.
(a) Which liquid is hypertonic to the potato cells? (1)
(b) Which liquid could be distilled water? Give a reason. (1)
(c) What is the condition of the cells in R, and how could they be restored? (1)
Hint
Longer and stiffer means water went in.
Answer
(a) R. (b) P: the strip gained water by endosmosis and became turgid, so P is hypotonic. (c) Flaccid or plasmolysed; place the strip in distilled water for deplasmolysis, if the cells are still alive.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which part of a plant cell is freely permeable?Show answer
The cell wall.
2.What is the term for the recovery of a plasmolysed cell in water?Show answer
Deplasmolysis.
3.In which kind of solution does a plant cell become turgid?Show answer
A hypotonic solution (such as pure water).
4.What makes a plant wilt?Show answer
Loss of turgor: its cells become flaccid.
5.Which pressure acts outward on the cell wall?Show answer
Turgor pressure.

Plasmolysis, Turgidity and Flaccidity: frequently asked questions

What is plasmolysis in simple words?

It is the shrinking of a plant cell's living contents away from its wall when the cell loses water to a stronger solution around it.

Is plasmolysis harmful?

Brief plasmolysis can be reversed by deplasmolysis, but long plasmolysis kills the cell. It is useful in preserving food, because it stops microbes from growing.

Is a turgid cell in a balanced state?

Yes. Turgor pressure pushing out and wall pressure pushing in are equal and opposite, so no more water enters.

Why do animal cells not show plasmolysis?

Plasmolysis means the protoplast pulling away from a cell wall. Animal cells have no wall; in a hypertonic solution they simply shrink and crinkle.