Selina Concise Solutions for ICSE Class 10 Biology Chapter 3 Absorption By Roots The Process Involved

A. Multiple Choice Type:

Question 1. Absorption of water by the plant cells by surface attraction is called:
(a) Diffusion
(b) Osmosis
(c) Imbibition
(d) Endosmosis
Answer: (c) Imbibition
In simple words: Imbibition is like a dry sponge soaking up water — the plant cell walls attract and absorb water molecules directly onto their surface.

📝 Teacher's Note: Use the example of a dry seed swelling when soaked in water to demonstrate imbibition. Students often confuse this with osmosis, so emphasize that imbibition doesn't need a membrane.

🎯 Exam Tip: Remember "I" for Imbibition and "I" for Initial water absorption — it's the first step before osmosis can occur.

Question 2. A plant cell placed in a certain solution got plasmolysed. What was the kind of solution?
(a) Isotonic sugar solution
(b) Hypotonic salt solution
(c) Hypertonic salt solution
(d) Isotonic salt solution
Answer: (c) Hypertonic salt solution
In simple words: Plasmolysis happens when the cell is placed in a very concentrated solution that pulls water out of the cell, making it shrink.

📝 Teacher's Note: Show students onion peel cells under a microscope in salt water to visually demonstrate plasmolysis. This makes the concept memorable.

🎯 Exam Tip: Remember: Hypertonic = Higher concentration = cell shrinks (plasmolysis). The "hyper" means "more" concentrated than the cell.

Question 3. The state of a cell in which the cell wall is rigid and stretched by the increase in volume due to the absorption of water is called.
(a) Flaccidity
(b) Turgidity
(c) Capillarity
(d) Tonicity
Answer: (b) Turgidity
In simple words: Turgidity is when a plant cell becomes firm and swollen with water, like a fully inflated balloon that's stretched tight.

📝 Teacher's Note: Compare turgid cells to inflated balloons and flaccid cells to deflated ones. This analogy helps students understand turgor pressure easily.

🎯 Exam Tip: Key words for turgidity: "rigid," "stretched," "increased volume," "water absorption" — any of these indicate the answer is turgidity.

Question 4. Which one of the following is a characteristic NOT related with the suitability of the roots for absorbing water?
(a) Tremendous surface area
(b) contain cell sap at a higher concentration than the surrounding soil water
(c) Root hairs have thin cell walls
(d) Grow downward into the soil
Answer: (d) Grow downward into the soil
In simple words: Growing downward helps roots reach water, but it's not directly about the absorption process — it's about positioning, not the actual mechanism.

📝 Teacher's Note: Emphasize that this question asks for what is NOT suitable for absorption. Students often miss the "NOT" and choose a wrong answer.

🎯 Exam Tip: Read "NOT" questions twice and underline the word "NOT" to avoid confusion. Growing downward is about gravity response, not absorption efficiency.

Question 5. Movement of molecules of a substance from the region of their higher concentration to the region of their lower concentration without the involvement a separating membrane, is called
(a) Osmosis
(b) Diffusion
(c) active transport
(d) Capillarity
Answer: (b) Diffusion
In simple words: Diffusion is like perfume spreading in a room — molecules naturally move from crowded areas to less crowded areas without any barrier.

📝 Teacher's Note: Demonstrate with a drop of food coloring in water or perfume in the classroom. The key difference from osmosis is "no membrane required."

🎯 Exam Tip: Key phrase: "without membrane" = Diffusion. "With membrane" = Osmosis. This is the main distinguishing factor.

Question 6. Osmosis and diffusion are the same except that osmosis there is:
(a) a freely permeable membrane
(b) a cell wall in between
(c) a selectively permeable membrane in between
(d) an endless inflow of water into a cell
Answer: (c) a selectively permeable membrane in between
In simple words: Osmosis is diffusion with a special filter (membrane) that only lets certain molecules pass through, like water but not sugar.

📝 Teacher's Note: Use the analogy of a coffee filter — it lets water through but stops coffee grounds. Similarly, cell membranes are selective.

🎯 Exam Tip: "Selectively permeable" means choosy — the membrane selects what can pass through. This is osmosis's defining feature.

Question 7. The highest water potential (capacity to move out higher concentrated solution) is that of
(a) Pure water
(b) 10% salt solution
(c) Honey
(d) 50% sugar solution
Answer: (a) Pure water
In simple words: Pure water has the highest energy to move and mix with other solutions because it has no dissolved particles holding it back.

📝 Teacher's Note: Explain water potential as the "eagerness" of water to move. Pure water is most eager, while solutions with dissolved particles are less eager.

🎯 Exam Tip: Higher water potential = less concentrated = more pure. Pure water always has the highest water potential (zero is the maximum).

Question 8. The space between the cell wall and plasma membrane in a plasmolysed cell is filled with.
(a) isotonic solution
(b) hypotonic solution
(c) Hypertonic solution
(d) water
Answer: (c) Hypertonic solution
In simple words: When a cell shrinks during plasmolysis, the concentrated salt solution from outside enters the space between the cell wall and the shrunken cell membrane.

📝 Teacher's Note: Draw a diagram showing the plasmolysed cell with the external solution filling the gap. This visual helps students understand the process.

🎯 Exam Tip: In plasmolysis, the external hypertonic solution enters the space created when the cell membrane pulls away from the cell wall.

Question 9. What is responsible for guttation?
(a) Osmotic pressure
(b) Root pressure
(c) suction pressure
(d) Capillarity
Answer: (b) Root pressure
In simple words: Root pressure pushes water up through the plant so forcefully that water droplets are squeezed out of leaf tips, like water being pushed out of a squeezed sponge.

📝 Teacher's Note: Point out guttation droplets on grass in early morning. Students often see this but don't know what causes it.

🎯 Exam Tip: Guttation = Root pressure. It's the force from roots pushing water up that creates those morning water droplets on leaves.

Question 10. The most appropriate characteristic of a semipermeable membrane is that
(a) it has minute pores
(b) it has no pores
(c) it allows the solute to pass through but not the solvent
(d) it allows a solvent to pass through freely but prevents the passage of the solute.
Answer: (d) it allows a solvent to pass through freely but prevents the passage of the solute
In simple words: A semipermeable membrane is like a very fine net that lets small fish (water) swim through but blocks big fish (dissolved substances).

📝 Teacher's Note: Clarify that solvent (usually water) passes through, while solute (dissolved particles like salt or sugar) cannot pass through.

🎯 Exam Tip: Remember: Semipermeable = Solvent yes, Solute no. Water molecules are small enough to pass, but dissolved particles are too big.

Very Short Answer Type:

Question. Name the following:
(a) The condition of a cell placed in a hypotonic solution.
(b) The process by which intact plants lose water in the form of droplets from leaf margins
(c) The process by which water enters root hairs.
(d) The term for the inward movement of solvent molecules through the plasma membrane of a cell.
(e) The process by which molecules distributes themselves evenly within the space they occupy
(f) The pressure which is responsible for the movement of water molecules across the cortical cells of the root.
(g) The pressure which is responsible for the movement of water molecules across the cortical cells of the root.
Answer:
(a) Turgidity
(b) Guttation
(c) Osmosis
(d) Endosmosis
(e) Diffusion
(f) Root pressure
(g) Root pressure

📝 Teacher's Note: Questions (f) and (g) appear to be duplicated in the source material. Focus on ensuring students understand each term's specific meaning.

🎯 Exam Tip: Learn these terms as pairs: Hypotonic→Turgidity, Leaf droplets→Guttation, Water entry→Osmosis. This helps in quick recall.

Question. Give the equivalent terms for the following:
(a) Pressure of the cell contents on the cell wall
(b) The condition in which the cell contents are shrunken
(c) Loss of water through a cut stem
Answer:
(a) Turgor pressure
(b) Flaccidity
(c) Bleeding

📝 Teacher's Note: Help students understand that turgor pressure and wall pressure are equal and opposite forces, like pushing against a wall.

🎯 Exam Tip: Remember: Turgor = pressure outward, Flaccidity = shrunken/limp, Bleeding = cut stem loses water.

Question. Complete the following statements:
(a) Hypotonic solution is one in which the solution kept outside the cell has lower solute concentration than ………………… the cell.
(b) Active transport is one in which the ions outside the roots are ……………
(c) The bending movements of certain flowers towards the sun and the sleep movements of certain plants at night are examples of…………
Answer:
(a) the fluids inside
(b) transported inside against their concentration gradient
(c) turgor movements

📝 Teacher's Note: Emphasize that active transport requires energy because it goes against the natural flow, like swimming upstream.

🎯 Exam Tip: Hypotonic = lower concentration outside than inside. Active transport = against the gradient (needs energy). Turgor movements = plant movements due to pressure changes.

Question. When placed in a more concentrated solution, the cell contents will………… (shrink / swell up). The pressure by which the ………… molecules tend to cross the semi-permeable membrane is called osmotic pressure. (salt / water). Active transport is in a direction ………….. to that of diffusion. (opposite / Same)
Answer:
(a) Shrink
(b) Water
(c) opposite

📝 Teacher's Note: Make sure students understand that osmotic pressure is about water movement, not salt movement, even though salt concentration drives the process.

🎯 Exam Tip: Concentrated solution → cell shrinks. Osmotic pressure = water pressure. Active transport = opposite to natural diffusion.

Question. Match the items in column I with those in column II

📝 Teacher's Note: Use the analogy of pipes in a building: xylem pipes carry water up, phloem pipes carry food down. Cell walls are like open doors, cell membranes are like selective doors.

🎯 Exam Tip: Remember: Xylem = water up, Phloem = food down. Cell membrane = selective, Cell wall = fully open. Root pressure causes guttation.

Short Answer Type:

Question. Differentiate between the following:
(a) Plasmolysis and deplasmolysis
(b) Turgor pressure and wall pressure
(c) Guttation and bleeding
(d) Turgidity and Flaccidity
Answer:

(a) Plasmolysis vs Deplasmolysis:

(b) Turgor pressure vs Wall pressure:

(c) Guttation vs Bleeding:

(d) Turgidity vs Flaccidity:

📝 Teacher's Note: Use visual aids to show these processes. Students learn better when they can see the cell changes happening step by step.

🎯 Exam Tip: For comparison questions, always mention both the process and the resulting state of the cell. This ensures complete answers and full marks.

Class X Chapter 4 – Absorption Of Roots Biology

Question. It is the state of a cell in which the cell cannot accommodate any more water and it is fully distended.
Answer: It is the state of a cell in which the cell cannot accommodate any more water and it is fully distended.
In simple words: This describes turgidity - when a plant cell is completely full of water and becomes rigid like a fully inflated balloon.

📝 Teacher's Note: Use the balloon analogy to help students visualize turgidity. Demonstrate with a balloon being filled with water until it becomes rigid and cannot hold any more.

🎯 Exam Tip: Keywords to mention are "turgid state", "fully distended", "maximum water absorption" and "rigid cell wall" to score full marks.

Question. It is the condition in which the cell content is shrunken and the cell is not tight.
Answer: It is the condition in which the cell content is shrunken and the cell is not tight.
In simple words: This describes flaccidity - when a plant cell loses water and becomes limp, like a deflated balloon.

📝 Teacher's Note: Contrast this with turgidity using the same balloon analogy. Show how a deflated balloon represents flaccid cells - soft and not rigid.

🎯 Exam Tip: Key terms to include are "flaccid condition", "cell contents shrunken", "loss of water" and "not tight" for complete answers.

Question 2. (a) Mention whether the following statements are true (T) or false (F)
(i) A plant cell placed in hypotonic solution gets Plasmolysed.
(ii) Addition of salt to pickles prevents growth of bacteria because they turn turgid.
(iii) Cells that have lost their water content are said to be deplasmolysed.
(iv) Xylem is the water conducting tissue in plants.
(v) The shrinkage of protoplasm, when a cell is kept in hypotonic solution.
(vi) The cell wall of the root cell is a differentially permeable membrane.

(b) Correct the false statements by altering the last word only.
Answer: (a) (i) False (ii) False (iii) False (iv) True (v) False (vi) False

(b) (i) A plant cell placed in hypotonic solution gets turgid.
(ii) Addition of salt to pickles prevents growth of bacteria because they turn flaccid.
(iii) Cells that have lost their water content are said to be plasmolysed.
(iv) The shrinkage of protoplasm, when a cell is kept in hypertonic solution.
In simple words: These corrections show that hypotonic solutions make cells swell (turgid), while hypertonic solutions make them shrink (flaccid/plasmolysed).

📝 Teacher's Note: Create a simple chart showing hypotonic = cell swells, hypertonic = cell shrinks. Use examples like raisins in water (swell) vs grapes in salt water (shrink).

🎯 Exam Tip: Remember the rule: "hypo = swell, hyper = shrink" and always check if the solution type matches the described cell condition.

Question 3. What is the difference between 'flaccid' and 'turgid'? Give one example of flaccid condition in plants.
Answer: The cell is said to be turgid when the plant cell wall becomes rigid and stretched by an increase in the volume of vacuoles due to the absorption of water when placed in hypotonic solution. On the other hand, the cell is said to be flaccid when the cell contents get shrunken when the cell is placed in hypertonic solution and the cell is no more tight. Flaccidity is the reverse of turgidity.

Example: Weeds can be killed in a playground by sprinkling excessive salts around their base. Or A plant cell when immersed in hypertonic solution like salt solution for about 30 minutes will become flaccid or limp.
In simple words: Turgid cells are like firm, inflated balloons (full of water), while flaccid cells are like deflated balloons (lost water and become soft).

📝 Teacher's Note: Demonstrate by showing fresh vs wilted lettuce leaves. Fresh leaves are turgid (crisp), wilted leaves are flaccid (limp).

🎯 Exam Tip: Always provide a practical example like wilting plants or salt on weeds to demonstrate flaccidity for full marks.

Question 4. Give reasons for the following:
(a) If you sprinkle some common salt on grass growing on a lawn, it is killed at that spot.
(b) If you uproot a plant from the soil, its leaves soon wilt.
(c) It is better to transplant seedlings in a flower-bed in the evening and not in the morning.
(d) A plant cell when kept in a hypertonic salt solution for about 30 minutes turns flaccid.
(e) Potato cubes when placed in water become firm and increase in size.
Answer: (a) Common salt when sprinkled on the grass causes the Plasmolysis of grass cell ultimately leading them to death. Hence, if we sprinkle some common salt on grass growing on a lawn, it is killed at the spot.

(b) If a plant is uprooted, the leaves continue losing water by transpiration, but there is no more water absorbed the roots. This does not allow the compensation for the loss of water by transpiration; hence the leaves of the uprooted plant wilt soon.

(c) Transplantation causes stress to the seedlings. If the seedlings are transplanted in the morning, they would have to immediately bear the additional stress of excessive transpiration occurring during the hot afternoon. Transplantation in the evening helps the seedlings to adjust for a longer time during the night (cooler temperatures) because the quantity of water absorbed exceeds the loss of water through transpiration. Therefore, it is better to transplant seedling in a flower bed in the evening and not in the morning.

(d) In a hypertonic solution, the solution outside the cell has higher solute concentration than the fluids inside the cell. Therefore, water flows out from the plant cell due to exosmosis. The cytoplasm shrinks and the plasma membrane withdraws away from the cell wall and this the cell becomes flaccid. Hence a plant cell when kept in a hypertonic salt solution for about 30 minutes turns flaccid.

Potato cubes contain excess of salts and sugars as compared to the water in which the cubes are placed. Hence, due to endosmosis, water from the surrounding enters the potato cubes making them firm and increasing their size.
In simple words: These examples show how water movement affects plants - salt causes water loss (killing grass), uprooted plants can't replace lost water (wilting), evening transplants face less water stress, and potato cubes absorb water to become firm.

📝 Teacher's Note: Use practical demonstrations like placing potato in salt water vs plain water, or showing students wilted vs fresh plants to illustrate these concepts clearly.

🎯 Exam Tip: For each part, mention the key process (plasmolysis, transpiration, osmosis) and explain the water movement direction to score full marks.

Question 5. Mention whether the following statements are true (T) or false (F) and give explanation in support of your answer.
Answer: (a) True.
Plasmolysis occurs due to outflow of water from the cell when placed in hypertonic solution due to which the cytoplasm shrinks away from the cell wall. On the other hand, deplasmolysis is the result of the re-entry of water into the plasmolysed cell when placed in hypotonic solution due to which the protoplasm again swells up pressing tight against the cell wall.

(b) False.
Guttation is the process by which drops of water appear along leaf margins due to excessive root pressure whereas bleeding is the loss of cell sap through a cut stem.

(c) False.
There is only one seed coat in a seed.

(d) False.
The leaves of the twig remain turgid since its xylem is intact and xylem is responsible for water conduction in plants.

(e) False.
Guttation occurs due to excessive root pressure. It is maximum when root pressure is maximum which occurs in the early mornings or at night. This is because during these times, transpiration is very low and water absorption is very high.

(f) False.
Dry seeds when submerged in water swell up due to imbibitions. On contact with water dry seeds imbibe water and swell up.
In simple words: These answers clarify common misconceptions about plant processes like plasmolysis/deplasmolysis being opposite processes, and guttation occurring when plants absorb more water than they lose.

📝 Teacher's Note: Create comparison charts for students showing opposite processes like plasmolysis vs deplasmolysis, and explain timing of guttation using real examples.

🎯 Exam Tip: For true/false questions, always provide scientific reasoning with correct terminology to justify your answer for full marks.

Long Answer Type:

Question 1. Give two examples of turgor movements in plants.
Answer: Examples of turgor movements in plants:
(i) In Mimosa pudica, a sensitive plant, the stimulus of touch leads to loss of turgor at the base of the leaflets and at the base of the petioles called pulvinus. This causes the folding and drooping of leaves of the plant.
(ii) The leaves of insectivorous plants close up to entrap a living prey. When the insect come in contact with the leaf, it loses it turgor hence closing the leaves of the plant.
(iii) The bending movements of certain flowers towards the sun.
(Any two)
In simple words: Turgor movements happen when plant parts move by gaining or losing water pressure, like the sensitive plant closing its leaves when touched.

📝 Teacher's Note: Demonstrate with a real Mimosa pudica plant if available, or show videos of these movements to help students understand the rapid response.

🎯 Exam Tip: Mention the mechanism (loss/gain of turgor) and provide specific examples like Mimosa pudica or Venus flytrap for complete answers.

Question 2. Explain the mechanism of closing and opening of the stomata.
Answer: The closing and opening of the stomata depends on the turgidity of the guard cells. Each guard cell has a thicker wall on the side facing the stoma and a thin wall on the opposite side. Guard cells contain chloroplasts. As a result of the synthesis of glucose during photosynthesis and some other chemical changes, the osmotic pressure of the contents of the guard cells increases and they absorb more water from the neighbouring cells, thus becoming turgid. Due to turgor, the guard cells become more arched outwards and the aperture between them widens, thereby opening the stoma.

At night or when there is shortage of water in the leaf, the guard cells turn flaccid and their inner rigid walls become straight, thus closing the stomatal aperture.
In simple words: Stomata open when guard cells absorb water and swell up like balloons, creating a gap between them. They close when guard cells lose water and deflate.

📝 Teacher's Note: Use a diagram showing guard cell shape changes and relate it to a zipper opening and closing mechanism for better understanding.

🎯 Exam Tip: Describe both opening (turgid guard cells) and closing (flaccid guard cells) mechanisms with reference to cell wall structure for full marks.

Question 3. Concentration of mineral nutrient elements is higher inside the root hairs than in the surrounding soil. How do roots take them in from the soil?
Answer: If the concentration of mineral nutrient elements is higher inside the root-hairs than in the surrounding soil, then roots take them in from the soil by 'active transport'. In active transport, the mineral ions are forcibly carried from the surrounding soil i.e. the region of their lower concentration into the roots i.e. the region of their higher concentration through the cell membrane by expenditure of energy. This energy is supplied by the cell in the form of ATP.
In simple words: Plants use energy (like electricity) to pump minerals from soil into roots, even when there are already more minerals inside the roots than in the soil.

📝 Teacher's Note: Compare active transport to pumping water uphill - it requires energy to move against the natural flow direction.

🎯 Exam Tip: Mention "active transport", "ATP energy", and "against concentration gradient" as key terms for scoring full marks.

Question 4. Explain how soaked seeds swell up and burst their seed coats.
Answer: When soaked in water, the seeds swell up due to imbibition and endosmosis. During these two processes water enters the cell. Due to endosmosis, at some point, the seed coat is unable to bear the turgor pressure and hence, the seed coat bursts.
In simple words: Seeds absorb water like sponges and swell up so much that their outer covering (seed coat) bursts open due to the pressure.

📝 Teacher's Note: Demonstrate by soaking different seeds (beans, peas) overnight and showing the swollen seeds with split coats to students.

🎯 Exam Tip: Mention both "imbibition" and "endosmosis" as water absorption processes, and "turgor pressure" causing seed coat bursting.

Question 5. Leaves of the sensitive plant wilt and droop down on a slight touch. What mechanism brings about this change?
Answer: Leaves of the sensitive plant wilt and droop down on a slight touch due to turgor movement. Petiole of sensitive plant is held up by turgid pulvinus tissue. The stimulus of touch leads to loss of turgor at the base of the leaflets and at the base of the petioles i.e. pulvinus. The cells of the lower side of pulvinus lose water and the petiole collapses. This causes the wilting and drooping of the leaves
In simple words: When you touch a sensitive plant, special cells at the base of leaves quickly lose water and become deflated, causing the leaves to fold and droop instantly.

📝 Teacher's Note: Emphasize the speed of this response and compare it to how quickly we pull our hand away from something hot - both are protective mechanisms.

🎯 Exam Tip: Focus on "pulvinus tissue", "loss of turgor", and "turgor movement" as key concepts for a complete answer.

Question 6. What is transpiration pull? How is it caused?
Answer: As water is lost from the leaf surface by transpiration, more water molecules are pulled up due to the tendency of water molecules to remain joined i.e. cohesion. This produces a continuous column of water throughout the stem which is known as 'transpiration pull'. A negative pressure or tension is produced in the xylem that pulls the water from the roots and soil. Transpirational pull is an important force which causes the ascent of sap.
In simple words: When leaves lose water, they create a pulling force like a straw sucking up water, which draws more water up from the roots through the plant stem.

📝 Teacher's Note: Use the analogy of drinking through a straw - when you suck, you create negative pressure that pulls the liquid up the straw.

🎯 Exam Tip: Include terms "cohesion", "negative pressure", "continuous water column", and "ascent of sap" for a complete scientific explanation.

Structured/ Application/ Skill Type:

Question 1. The following diagram represents a plant cell after being placed in a strong sugar solution.
Answer: This diagram shows a plasmolysed plant cell where the cytoplasm has shrunk away from the cell wall due to water loss when placed in a hypertonic sugar solution. The cell membrane has pulled away from the rigid cell wall, creating spaces between them.
In simple words: The diagram shows what happens when a plant cell loses too much water - the inside part shrinks away from the outer wall, like a deflated balloon inside a rigid box.

📝 Teacher's Note: Use this diagram to explain plasmolysis visually and ask students to identify the cell wall, cell membrane, and cytoplasm in the diagram.

🎯 Exam Tip: When describing diagrams, always identify the condition shown (plasmolysis) and explain what caused it (hypertonic solution) for full marks.

Question 1. Guidelines 1 to 5 indicate the following:
(1) Cell wall, (2) Strong sugar solution, (3) Protoplasm (4) Large vacuole, (5) Nucleus
(a) What is the state of the cell shown in the cell shown in the diagram?
(b) Name the structure which acts as a selectively permeable membrane.
(c) If the cell had been placed in distilled water instead of strong sugar solution, which feature would not have been seen?
(d) Name any one feature of this plant cell which is not present in an animal cell.
Answer:
(a) The cell is flaccid i.e. it is plasmolysed.
(b) Plasma Membrane
(c) Plasmolysis would not occur and flaccidity would not be seen i.e. the protoplasm would not have shrunken away from the cell wall.
(d) Cell Wall is absent in animal cell.
In simple words: When a plant cell loses water and shrinks away from its cell wall, it becomes flaccid. The plasma membrane acts like a selective door that controls what enters and exits the cell.

📝 Teacher's Note: Use a raisin in salt water as an analogy - students can observe the shriveling effect firsthand. Emphasize that animal cells would burst in the same conditions since they lack protective cell walls.

🎯 Exam Tip: Always mention "plasma membrane" for selective permeability questions, not cell wall. Remember that plasmolysis only occurs in plant cells due to the rigid cell wall structure.

Question 2. A leaf cell of a water plant was placed in a liquid other than pond water. After sometime, it assumed a shape as shown below:
(a) Give the term for the state of the cell it has acquired.
(b) Comment on the nature (tonicity) of the liquid surrounding the cell.
(c) Redraw in the space provided, the diagram of the cell is it is soon placed in ordinary water for some time.
Answer:
(a) Flaccid Cell
(b) The liquid is hypertonic solution. It has higher solute concentration outside the cell than the fluids inside the cell.
(c) [Diagram showing turgid cell with expanded cytoplasm filling the cell wall]
In simple words: The cell became soft and shrunken because it was placed in a very salty solution that pulled water out of it, like a sponge drying up.

📝 Teacher's Note: Demonstrate with salt and fresh vegetables - show how salt makes cucumbers release water. This visual helps students understand hypertonic solutions practically.

🎯 Exam Tip: For tonicity questions, always relate concentration to water movement direction. Higher solute concentration = lower water concentration = water moves out.

Question 3. The diagram given below represents an experimental set-up to demonstrate a certain process. Study the same and answer the questions that follow:
(a) Name the process.
(b) Define the above named process.
(c) What would you observe in the experimental set-up after an hour or so?
(d) What control experiment can be set up for comparison?
(e) Keeping in mind the root-hair, cell and its surroundings, name the parts that correspond to (1) concentrated sugar solution (2) parchment paper and (3) water in the beaker.
(f) Name any other substance that can be used instead of parchment paper in the above experiment.
(g) Mention two advantages of the process to the plants.
Answer:
(a) Osmosis
(b) Osmosis is the diffusion of water molecules across a semi-permeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration).
(c) After an hour or so, the level of sugar solution in the thistle funnel will rise and the level of water in the beaker will drop slightly.
(d) For control experiment, the beaker will contain the water. At the same time, instead of the sugar solution; the thistle funnel with the cellophane paper tied on its mouth and inverted in the beaker will also contain water.
(e)
(1) concentrated sugar solution Cell sap (of higher concentration than that of the surrounding water) within the root hair.
(2) parchment paper cell membrane of root hair.
(3) water in the beaker water in soil.
(f) cellophane paper, egg membrane, animal bladder (any one)
(g) (i) The roots of plants absorb water and minerals from surrounding soil due to osmosis.
(ii) Osmosis allows plants to absorb water from the soil which helps plants to keep cells alive in roots, stems and leaves.
(iii) Osmosis is also important in the opening and closing of stomata which is an important feature for the processes like transpiration and photosynthesis. (Any two)
In simple words: This experiment shows how water naturally moves through a barrier from where there's more water to where there's less water, just like how plant roots drink water from soil.

📝 Teacher's Note: Set up this experiment in class and check after 2-3 hours for visible results. Students often forget that osmosis needs time to show measurable effects.

🎯 Exam Tip: For the definition, always mention "semi-permeable membrane" and specify the direction of movement from dilute to concentrated solution. This gets full marks.

Question 4. The diagram below represents a layer of epidermal cells showing a fully grown root hair. Study the diagram and answer the questions that follow:
(a) Name the parts labelled A, B, C and D.
(b) The root hair cell is in a turgid state. Name and explain the process that caused this state.
(c) Mention one distinct difference between the parts labelled A and B.
(d) Draw a diagram of the above root hair cell as it would appear when a concentrated solution of fertilizers is added near it.
Answer:
(a)
A - Cell wall
B - Cell membrane
C - Cytoplasm
D - Nucleus
(b) A root hair gets turgid because of the absorption of water from the surrounding. Absorption of water by root hair is achieved by the process of osmosis. The concentration of water in the surrounding is more than that of the interior of the cell; this causes the water from the surrounding to move in because of endosmosis.
(c)

(d) [Diagram would show plasmolysed cell with shrunken cytoplasm separated from cell wall]
In simple words: The root hair cell swells up with water like a water balloon because water moves in from the soil where there's more water available than inside the cell.

📝 Teacher's Note: Use the analogy of a rigid box (cell wall) with a flexible bag inside (cell membrane). Students can visualize how the bag can shrink but the box stays the same shape.

🎯 Exam Tip: Always distinguish between "freely permeable" for cell wall and "semi-permeable" for cell membrane. This distinction is frequently tested.

Question 5. Two potato cubes each 1 cm³ in size, were placed separately in two containers (A&B), the container (A) having water and the other (B) containing concentrated sugar solution. After 24 hours when the cubes were examined, those placed in water were found to be firm and had increased slightly in size and those placed in concentrated sugar solution were found to be soft and had somewhat decreased in size. Use the above information to answer the questions that follow:
(a) Account for the firmness and increase in the size of the potato cubes placed in water.
(b) Account for the softness and decrease in size of the potato cubes which were places in sugar solution.
(c) Name and define the physical process being investigated in this experiment.
Answer:
(a) Water is hypotonic to the potato cells, due to which endosmosis occurs and water enters the potato cells. The protoplasm swells up pressing tight against the cell wall. The cells are fully distended i.e. turgid. This causes the firmness and increase in the size of the potato cubes when placed in water.
(b) Sugar solution is hypertonic to the potato cells, due to which exosmosis occurs and water flows out of the potato cells. The potato cell loses its distended appearance, the cytoplasm shrinks and the plasma membrane withdraws from the cell wall. The cells become limp or flaccid. This causes the softness and decrease in size of the potato cubes when placed in sugar solution.
(c) The process being investigated is osmosis. Osmosis is the diffusion of water molecules across a semi-permeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration).
In simple words: The potato in water became firm because water entered its cells like filling balloons, while the potato in sugar solution became soft because water left its cells like deflating balloons.

📝 Teacher's Note: This is an excellent hands-on experiment students can do at home. Encourage them to measure and record size changes every few hours to see the process in action.

🎯 Exam Tip: Use the terms "endosmosis" (water in) and "exosmosis" (water out) to show deep understanding. Also mention "turgid" and "flaccid" states for full marks.

Question 6. Given below is the diagrammatic representation of the transverse section of a part of a plant. Study it and answer the questions that follow:
(a) Name the part of the plant that is shown
(b) Label the parts 1 to 6
(c) Write the functions of parts 3 and 5
Answer:
(a) It is the diagrammatic cross-section of a part of a root.
(b)
1 - Root hair
2 - Epidermis
3 - Cortex
4 - Endodermis
5 - Phloem
6 – Xylem
(c) Cortex (label 3) is the ground tissue and is active in the uptake of water and minerals. It also helps in storage of photosynthetic products.
Phloem (label 5) helps in transporting the prepared food from leaves to different parts of the plant.
In simple words: The diagram shows a cross-section of a root with its different layers - the outer root hairs absorb water, the cortex helps store food and nutrients, while the xylem and phloem transport water and food respectively throughout the plant.

📝 Teacher's Note: Use a microscope or prepared slides to show actual root cross-sections. Students often confuse xylem and phloem functions - emphasize that xylem carries water UP from roots, while phloem carries food DOWN from leaves.

🎯 Exam Tip: Always mention both functions of cortex (water/mineral uptake AND storage) to get full marks. Draw clear, labeled diagrams showing the arrangement of tissues from outside to inside.

Question 7. Study the diagram given below and answer the questions that follows:
(a) Name the process being studied in the above experiment
(b) Explain the process mentioned in (a) above
(c) why is oil placed over water?
Answer:
(a) The process of water absorption by plant roots through osmosis is being studied here.
(b) A root-hair contains cell sap which contains higher concentration of salts as compared to outside soil water. This difference sets off osmosis and outside water diffuses into the root-hair. From the cell bearing root-hair, water passes into adjoining cells one after another to finally the xylem vessels.
(c) The surface of water was covered with oil to prevent any loss of water by evaporation.
In simple words: This experiment shows how plant roots absorb water - the root has more salt inside than the water outside, so water naturally moves in through osmosis. Oil is used to stop water from evaporating so we can see the true absorption.

📝 Teacher's Note: Demonstrate this experiment live in class. Students can observe water level changes over 24-48 hours. Emphasize that osmosis is a passive process requiring no energy from the plant.

🎯 Exam Tip: Always mention "concentration gradient" and "from low to high concentration" when explaining osmosis. The oil layer detail shows you understand experimental controls.

Question 8. Show by a series of diagrams, the change which a plant cell will undergo when placed in
(a) Hypertonic salt solution and
(b) Hypotonic salt solution
Answer:
(a) [Diagram showing plasmolysis stages - cell membrane shrinking away from cell wall as water leaves the cell]
(b) [Diagram showing cell becoming turgid - cell membrane pressing against cell wall as water enters the cell]
In simple words: In salty water (hypertonic), the plant cell loses water and shrinks away from its wall (plasmolysis). In less salty water (hypotonic), the cell gains water and becomes swollen and firm (turgid).

📝 Teacher's Note: Use the analogy of a balloon - in salty water it deflates, in pure water it inflates. Show students actual plasmolysis using onion cells under a microscope with salt solution.

🎯 Exam Tip: Draw clear before-and-after diagrams showing cell membrane position. Label "plasmolysis" for hypertonic and "turgid" for hypotonic solutions. Show water movement direction with arrows.