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ICSE BIOLOGY ABSORPTION BY ROOTS NOTES

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Disha Educentre Exhaustive Notes ~1~ 3. Absorption by Roots ABSORPTION BY ROOTS Scope of Syllabus: Characteristics of roots which make them suitable for absorbing water should be discussed with the process of absorption. Structure of a full-grown root hair must be explained. Experiments to show conduction of water through the xylem should be discussed. Mention the causative forces must be made for better understanding as per syllabus. ~ Part A ~ ROOT HAIR AND INVOLVED PROCESSES I. Definitions and Explanations 1. Imbibition 2. Diffusion 3. Root Pressure 4. Guttation II. Imbibition is a process by which the living or dead plant cells absorb water by surface attraction. Diffusion is the free movement of molecules of a substance (solute or solvent, gas, liquid) from the region of higher concentration to the region of lower concentration where the two have a direct contact. Root pressure is the pressure developed in the roots due to the continued inward movement of water through cell-to-cell osmosis, which helps in the ascent of cell sap upward through the stem. The loss of excess water from plants in the form of tiny drops along the leaf margins is known as guttation. Questions-Answers 1. What are the processes for which plants need water? ANSWER Plants need water for four processes photosynthesis, transpiration, transportation and mechanical stiffness. (i) Photosynthesis Water is a raw material in the synthesis of carbohydrates by green plants. (ii) Transpiration Water lost by the plants through its leaves must be compensated for. (iii) Transportation Water is transported from the roots to the shoots and from leaves to other plants. Dissolved substances are also transported along with it. (iv) Mechanical Water provides turgidity to cells, which impart mechanical stiffness to it. Stiffness 2. Draw a neat, labelled diagram of a root hair showing its various parts. 3. What are the different adaptations of root hairs? hairs have the following adaptations:Their cell wall is freely permeable. Their cell membrane is semipermeable. The cell sap in them contains less water (solvent) as compared to water solution. Thus, it is hypotonic. It is unicellular; i.e. it has a large surface area. It is temporary; i.e. it is soon replaced by newer root hairs. ANSWER Root Notes Prepared by Neil Valentine D Silva Biology for X ICSE 4. ~2~ Disha Educentre Exhaustive Notes What are the different ways in which root hairs are suitable for absorbing water? hairs are suitable for absorbing water in the following ways:Unicellularity: Root hair are unicellular. This helps them to absorb and retain water. Large Surface Area: A large number of root hairs present in even the tiniest plant. This gives them a large surface area, which facilitates absorption of water. Lower Concentration: The cell sap inside the root hairs is of a higher concentration than the solution in the soil. Osmotic pressure always makes solvent move from low concentration to high concentration. Hence, surrounding water enters the root hairs. Permeable Cell Wall: Root hairs have a freely permeable cell wall. This allows the movement of all substances freely in and out of the root hairs. Semipermeable Cell Membrane: Root hairs have a semipermeable cell membrane. This selectively allows water to pass through but not the larger molecules of dissolved salts. Tubular Shape: Root hairs have a tubular shape. This elongated shape provides more surface area for absorption. ANSWER Root (i) (ii) (iii) (iv) (v) (vi) 5. What is the importance of root hairs to a plant? ANSWER The following are the ways in which root hairs are important to a plant:(i) Absorption of Water: Root hairs absorb water from the soil. They contain cell sap which is at a higher concentration than the surrounding soil medium. Hence water enters the root hairs through osmosis. (ii) Absorption of Mineral Elements: The active transport of minerals from the surrounding soil medium takes place first into the root hairs. 6. Explain imbibition. ANSWER Imbibition is a process by which the living or dead plant cells absorb water by surface attraction. Cell wall is made up of cellulose and proteins, which have an affinity for water (hydrophilic). It absorbs water from the surroundings and swells up. Example: When seeds are soaked in water overnight, they swell up because they absorb water. 7. Explain an experiment to demonstrate imbibition. ANSWER Take tightly packed dry seeds in a thin-walled test tube. Add water, cork the tube, seal it with wax and keep it overnight. Next morning, it will be seen that the tube is cracked or broken and all seeds are swollen. This happens because the seeds absorb the water, become turgid and then exert pressure on their surroundings. 8. Describe diffusion. Give an example of diffusion. is the transport of gases or dissolved substances in solution from a region of high concentration to a region of low concentration when the two are in direct contact. Molecules of gases are in a state of random motion, and hence they possess kinetic energy. Due to this kinetic energy, they occupy the maximum available space. If different gases are brought in contact, they will mix with each other so as to spread out as much as possible. Example: Smoke from a fireplace spreads out throughout the room. ANSWER Diffusion 9. What are the main characteristics of diffusion? main characteristics of diffusion are as follows:- ANSWER The Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes 10. ~3~ Absorption by Roots Diffusion always takes place from a region of higher concentration to a region of lower concentration. The rate of diffusion depends on the size, temperature and contraction of its molecules. The rate and direction of diffusion molecules are independent of the molecules of other substances that may be present. Give examples of diffusion in plants and in animals. of Diffusion in Plants Exchange of gases during photosynthesis, transpiration and respiration occurs by diffusion. It brings about the absorption of minerals in the roots. Examples of Diffusion in Animals In mammals, the exchange of gases during respiration takes place in lungs by diffusion. In eggs of hens, oxygen diffuses into the air spaces present in the egg shell. ANSWER Examples 11. Describe an experiment to show the process of diffusion in liquids. can be shown by the following experiment. Procedure: Take a beaker containing clean water and place a crystal of a coloured compound such as potassium permanganate (purple) in one corner. Observation: In some time, the crystal dissolves in the water and its colour starts spreading from the point where it is placed (high concentration) to other parts within the liquid (low concentration). Finally, the entire mixture becomes homogeneously coloured. Inferences: The crystal diffuses within the liquid. The diffusion takes place from the area of higher concentration to the area of lower concentration. The diffusion continues till the solution is homogeneously coloured; i.e. till it reaches a uniform concentration. ANSWER Diffusion ~ Part B ~ OSMOSIS AND ACTIVE TRANSPORT I. Definitions and Explanations 1. Osmosis 2. Endosmosis 3. Exosmosis 4. Semipermeable Membrane 5. Differently Permeable Membrane Osmotic Pressure 6. Osmosis is the diffusion of solvent (water) molecules across a semipermeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration). Endosmosis is the inward diffusion of water through a semipermeable membrane when the surrounding solution is less concentrated. This causes the cell to swell up. Exosmosis is the outward diffusion of water through a semipermeable membrane when the surrounding solution is more concentrated. This causes the cell to shrink. A semipermeable membrane is a membrane which allows the passage of molecules selectively; i.e. it only allows the passage of solvent molecules. Example: urinary bladder of goat, parchment paper A differently permeable membrane is a membrane that allows the passage of solvent molecules and also of some solute molecules. Example: plasma membrane of plant and animal cells Osmotic pressure is the minimum pressure that must be exerted to prevent the passage of the pure solvent into the solution, when the two are separated by a semipermeable membrane. Notes Prepared by Neil Valentine D Silva ~4~ Biology for X ICSE 7. Tonicity 8. Isotonic Solution Hypotonic Solution 9. 10. Hypertonic Solution 11. Active Transport Disha Educentre Exhaustive Notes OR: Osmotic pressure of a solution is a measure of its tendency to take in water by osmosis. The relative concentrations of the solutions that determine the direction and extent of diffusion is known as tonicity. The solutions which have the same osmotic pressure or the same molecular concentration at the same temperature are said to be isotonic solutions. When two solutions of different concentrations are in contact, the solution that has a lesser concentration of solute molecules and lower osmotic pressure is said to be hypotonic solution. It has a higher water content. When two solutions of different concentrations are in contact, the solution that has a higher concentration of solute molecules and higher osmotic pressure is said to be hypertonic solution. It has a lower water content. Active transport is the passage of a substance (salt or ion) from its lower to higher concentration using energy from the cell, through a living cell membrane. 12. II. 1. Questions-Answers Describe osmosis. is the diffusion of water molecules across a semipermeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration). Osmosis is a movement of solvent only. In the case of absorption by roots, it is the water molecules that move, and not the dissolved salts and minerals. The movement of solvent is always from a point at lower concentration to that at higher concentration. The movement occurs through a semipermeable membrane. This membrane only allows solvent particles and not of solute particles. ANSWER Osmosis 2. What are the different kinds of osmosis? Explain. on the concentration of the cell with respect to the surrounding solution, there can be inward and outward osmosis. Endosmosis Occurs when the cell sap is less concentrated than the outside solution. Water moves from outside solution to the cell (inward). This leads to swelling up of cell. Exosmosis Occurs when the cell sap is more concentrated than the outside solution. Water moves from cell to outside solution (outward). This leads to shrinking of cell. ANSWER Depending 3. Draw a linear diagram to describe osmosis. ANSWER 4. Describe an experiment to demonstrate osmosis. ANSWER 5. What is the significance of osmosis? Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~5~ Absorption by Roots ANSWER Osmosis 6. is significant in the following ways:It helps in absorption of minerals and water by the plants. It develops turgidity and turgor pressure in plant cells. It leads to movement of water from one cell to another. The opening and closing of stomata are regulated by the osmotic entry and exit of water in the guard cells. When does osmosis stop? theory, osmosis stops when the concentrations of solvent becomes equal on both sides of the semipermeable membrane, i.e. when isotonic condition is reached. However, practically, osmosis continues in plants throughout their lives, because the leaves constantly lose water through transpiration. Due to this, the solvent concentration within the plant body is always lesser than the concentration outside. ANSWER According to 7. Explain osmotic pressure. ANSWER Osmotic pressure is the minimum pressure that must be exerted in order to prevent the passage of the pure solvent into the solution when the two are separated by a semipermeable membrane. It can also be explained as the pressure that must be exerted to the high concentration solution in order to stop osmosis. By knowing the osmotic pressure of a solution, we can determine how much water the solution will take in during osmosis. 8. What are the different cell conditions based on their tonicity? on tonicity, there are three different cell conditions. Isotonic Condition This is the condition when the cell solution has the same concentration as the outside medium. There is no movement of water molecules across the semipermeable cell membrane. This causes no change in the size of the cell. Hypotonic Condition This is the condition when the solution outside the cell has lower concentration than that inside the cell. Water molecules move from the outside medium to the inside. This causes swelling up (turgidity) of the cell. Hypertonic Condition This is the condition when the solution outside the cell has higher concentration than that inside the cell. Water molecules move from the inside medium to the outside. This causes shrinkage (flaccidity) of the cell. ANSWER Based (i) (ii) (iii) 9. Describe the concept of active transport. transport is the passage of a substance (salt or ion) from its lower to higher concentration using energy from the cell, through a living cell membrane. Certain nutrients such as nitrates and sulphates of K, Zn and Mn cannot pass through the cell membrane. This is because they have a high concentration inside the root cells to facilitate osmosis. Hence, in order to take more of these nutrients, it is necessary for the plant to use energy. The plant forcibly takes these minerals from their low concentration in the soil to the high concentration in the cell. This is known as active transport. The energy is provided by ATP. ANSWER Active Notes Prepared by Neil Valentine D Silva Biology for X ICSE III. 1. ~6~ Disha Educentre Exhaustive Notes Reasons and Justifications Raisins swell up when they are kept in water. solution within the raisins is hypotonic, i.e. it has lesser solute concentration than the surrounding medium. Due to this, endosmosis takes place, causing water from the surrounding medium to enter the raisins. This causes the raisins to swell up. ANSWER The IV. Distinctions and Comparisons 1. Hypotonic, Isotonic and Hypertonic Solutions (i) (ii) (iii) (iv) 2. (i) (ii) (iii) 3. Hypotonic Solution It has a lower concentration of solute molecules than the outside solution. It has more solvent (water) than the outside solution. Isotonic Solution It has the same concentration of solute molecules as the outside solution. It has the same amount of solvent (water) as the outside solution. It has low osmotic pressure. It has no osmotic pressure. Solvent (water) molecules There is no movement of move from outside to the cell. solvent (water) molecules. Hypertonic Solution It has a higher concentration of solute molecules than the outside solution. It has less solvent (water) than the outside solution. It has high osmotic pressure. Solvent (water) molecules move from the cell to the outside. Endosmosis and Exosmosis Endosmosis It is the movement of solvent (water) from the surroundings to the cell. It causes the cell to become turgid. It occurs when the cell solution is hypertonic. Exosmosis It is the movement of solvent (water) from the cell to the surroundings. It causes the cell to become flaccid. It occurs when the cell solution is hypotonic. Osmosis and Diffusion Osmosis Diffusion It is the movement of molecules from a region It is the movement of molecules from a region of low concentration to high concentration. of high concentration to a region of low concentration. (ii) It takes place across a living or non-living No such membrane is required. semipermeable membrane. (iii) Movement of only solvent molecules takes Movement of both solute and solvent takes place in one direction. place in both directions. (iv) It occurs in liquids only. It occurs in all fluids (liquids and gases). (v) It is a slow process. It is rapid in gases. (vi) The movement of solvent takes place over a The molecules of liquids and gases diffuse over short distance. large distances. (vii) It takes place against the concentration gradient It takes place along the concentration gradient (from low concentration to high concentration). (from high concentration to low concentration). (i) 4. Active Transport and Passive Transport Active Transport Passive Transport Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~7~ (i) Living cells of the root play an active role. (ii) Metabolic energy is used to bring about active transport. It cannot occur in the absence of root as the force needed to cause active transport is developed in the root. It takes place osmotically, from low concentration surrounding solution to high concentration cell solution. (iii) (iv) Absorption by Roots Living cells of the root do not play an active role; they only carry water passively. Metabolic energy is not used to bring about passive energy. It can take place even without the root as the force needed for passive transport is developed in the shoot. It takes place due to the tension created in the xylem sap by the transpiration pull of the shoot. V. Diagram-based Questions 1. (i) The following is a diagram of an experiment at its beginning. What phenomenon is shown by the experiment? Which limb of the U-tube contains more concentrated sucrose A or B? Why have the two kinds of molecules been shown in different sizes? Why is the membrane separating the two solutions labelled as semipermeable membrane? Which limb of the U-tube (A or B) is functions like the root hair of a plant? (ii) (iii) (iv) (v) ANSWERS (i) (ii) (iii) (iv) (v) 2. (i) (ii) (iii) Osmosis Limb A of the U-tube contain more concentrated sugar solution. To represent solute and solvent molecules. Semipermeable membrane allows only solvent or water molecules to pass through it. It does not allow the solute particles to pass through. Limb A of the U-tube functions like the root hair of a plant. The given figure represents two solutions separated by a semipermeable membrane. The large particles are the solute and the small particles are the solvent. If the membrane is to behave as a semipermeable membrane, what can be stated about the size of pores? Will the solvent molecules pass through the membrane from left to right, from right to left or not at all? In which direction will there be a net movement of solvent molecules? ANSWERS (i) The pores must be smaller than the solute molecules but larger than the solvent molecules. Notes Prepared by Neil Valentine D Silva Biology for X ICSE (ii) (iii) 3. (i) (ii) (iii) (iv) (v) ~8~ Disha Educentre Exhaustive Notes Solvent molecules will pass through the membrane in both directions. Since the solvent molecules are present on both sides, they will strike the semipermeable membrane and pass through it. There is a net movement of solvent molecules from the lower concentration to higher concentration; i.e.. from right to left. The apparatus given below was set up for an experiment. After some time, the level of the liquid in the vertical section increased. What process does the experiment demonstrate? Name two liquids that could be used in this experiment. Why did the level of liquid in the vertical tube rise? Explain how this process affects an organism such as amoeba. Give one example of this process in plants and state its benefit to them. ANSWERS (i) (ii) (iii) (iv) (v) 4. (i) (ii) (iii) (iv) Osmosis Distilled water or concentrated sugar solution The liquid rises in the tube because it enters into it through the goat s bladder. This is how osmosis takes place. In amoeba, osmosis helps in maintaining its water balance. In plants this occurs in root hairs. It helps water to enter the plants from the surrounding soil. The apparatus arranged in the figure signifies an important process. Name the process. Where does the process occur in plants? What solution is placed inside the dialysis tubing? What happens to the level of solution in the capillary tube? ANSWERS (i) (ii) (iii) (iv) Osmosis Root hair Sugar solution The level of liquid in the capillary rises. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~9~ Absorption by Roots ~ Part C ~ TURGIDITY AND FLACCIDITY I. Definitions and Explanations 1. Turgidity 2. 3. Turgor Pressure Wall Pressure 4. Diffusion Pressure Deficit 5. Plasmolysis 6. Flaccidity II. The condition where a cell cannot accommodate any more water in it is known as turgidity, and the cell in this condition is said to be turgid. The pressure of the cell contents on the cell wall is known as turgor pressure. The pressure exerted by the cell wall on the contents of the cell is known as wall pressure. The difference between the diffusion pressure of a pure solvent and the diffusion pressure of a solvent in solution is known as the diffusion pressure deficit or suction pressure. The contraction of the cytoplasm from the cell wall caused due to the withdrawal of water when placed in a hypertonic solution is known as plasmolysis. The condition in which the plasma membrane shrinks and withdraws from the cell wall is known as flaccidity and the cell in this condition is said to be flaccid. Questions-Answers 1. When does a cell become turgid? What are the characteristics of the cell at this stage? ANSWER A cell becomes turgid when it cannot accommodate any more water; i.e. when it has swollen up to the maximum extent by absorbing water from the surroundings. The following are the characteristics of a turgid cell: It has the maximum volume. Its wall is stretched to the maximum. Due to wall pressure, the cell contents are forced towards the centre of the cell. The cell contents also exert pressure on the cell wall known as turgor pressure. Turgor pressure is high in a turgid cell. The cell wall may also rupture due to high turgor pressure. The cell is in a stage of equilibrium, because no water enters or exits the cell when it is turgid. 2. When is a cell said to be flaccid? What are the characteristics of the cell at this stage? ANSWER If a cell is placed in a high concentration solution, then water molecules move outwards from the cell. Due to this, the cell shrinks. At this stage, the cell is said to be a flaccid cell. The following are the characteristics of a flaccid cell: The cell has a shrunken appearance. The plasma membrane is separated from the cell wall. If the cell continues to lose water, its flaccidity increases. This may cause cell death. Flaccidity is reversible. If the cell is again put in low concentration solution, water molecules will move within the cell and it will begin to swell up again. 3. Describe plasmolysis and deplasmolysis. is the shrinkage of the cell, which causes the plasma membrane to withdraw from the cell wall. This is the same as flaccidity. It occurs when the cell is placed in a solution of high concentration, due to which water molecules move outwards from the cell. The opposite of plasmolysis is deplasmolysis. If a plasmolysed (flaccid) cell is placed in a solution of low concentration, then water molecules will move from the outside medium to the cell. It will begin to swell up again and the plasma membrane will be brought closer to the cell wall. ANSWER Plasmolysis 4. With the help of an illustration, describe the different stages of plasmolysis. are four main stages in plasmolysis. Stage 1 The cell wall and plasma membrane are pressed against each other. ANSWER There Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 10 ~ Disha Educentre Exhaustive Notes The vacuole size is the largest at this stage. Stage 2 The plasma membrane begins to withdraw from the cell wall. All the cell contents begin to shrink. Stage 3 The plasma membrane and the cell wall become distinct from each other. At the same time, the space between the plasma membrane and cell wall starts getting filled up with the hypertonic solution from the outside environment that causes the plasmolysis. Stage 4 The cytoplasmic contents form a rounded mass. The content of hypertonic solution increases within the cell. 5. What is turgor pressure? How is it useful to the plants? pressure is the pressure exerted by the cell contents on the cell wall. Turgor pressure is useful in the following ways: It provides rigidity to the plant. It helps the plant to push up through the hard ground. It builds up root pressure in the plant. ANSWER Turgor 6. Explain the significance of turgidity. ANSWER Turgidity is significant to the plant in the following ways: It helps in maintaining the shape and form of the plants. The turgidity of the guard cells regulates the opening and closing of the stomata. It is due to turgidity and its loss that seismonastic (touch) movements in plants such as Mimosa pudica are brought about. If a cell loses its turgidity below a certain extent, it causes cell death. Loss of turgidity leads to wilting of leaves and drooping of shoots. 7. Which pressure is responsible for the movement of leaves of the Mimosa pudica plant? Explain how this movement takes place. OR: Give an example of turgor movements in plants and explain how it occurs. ANSWER The movement of the Mimosa pudica plant takes place due to turgor pressure within its cells. In the Mimosa pudica, the base of the leaves called as the pulvinus is responsible for holding the leaves erect. The cells of the pulvinus have turgor pressure within them. When the leaves are touched, the stimulus causes the pulvinus cells to lose their turgor pressure. On losing this pressure, the cells inside the pulvinus becomes flaccid. This makes them lose their rigidity and they droop. This makes the leaf droop as well. If the touch stimulus is strong enough, it can cause several leaves to droop all at once. However, the change is temporary, because the turgor pressure rebuilds within the pulvinus cells within a few seconds and the leaves are back in their initial position. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes 8. ~ 11 ~ Absorption by Roots Explain the significance of plasmolysis. is significant to the plant in the following ways: It proves that the cell wall is permeable and the protoplasm is semipermeable. It helps in determining whether a cell is alive or dead. Plasmolysis stops when cells are dead. It is used in determining the osmotic pressure of a cell. ANSWER Plasmolysis 9. Under what conditions will water not enter the cell? ANSWER Water will not enter the cell if: The turgor pressure becomes equal to the wall pressure. The cell sap and the outside solution have equal concentrations. III. 1. Reasons and Justifications Jams and jellies do not get spoiled for a long period of time. and jellies have highly concentrated solution of sugars in them. If any bacterium or fungus enters jams or jellies, osmosis takes place, drawing the water content from the bacterial or fungal cell. This leads to plasmolysis of the cell and it shrinks. Continued plasmolysis causes cell death. Hence, jams and jellies remain fresh for long periods of time. ANSWER Jams 2. Saltwater gargle provides relief for throat infection. infection is caused due to bacteria. When saltwater solution is brought into contact with them, osmosis takes place, drawing the water content from the bacterial cell. This leads to the plasmolysis of the bacterial cell and it shrinks. Continued plasmolysis causes cell death. Hence, saltwater gargle is recommended in cases of throat infection. ANSWER Throat 3. Seedlings are preferably transplanted in the evenings and not in the mornings. the evenings, the guard cells of the stomatal openings of leaves are closed. No transpiration takes place. Due to this, no root pressure is developed in the roots as there is no loss of water from the plant body. The roots get ample time to fix themselves in the soil. In the mornings, the open stomata will cause transpiration from the leaves, leading to continuous movement of water from the roots. This does not allow the roots to fix themselves properly in the surrounding soil. ANSWER In 4. Plants sometimes wilt when excess fertiliser is added. ANSWER Excess fertiliser introduces solute into the soil, which makes the soil solution of a high concentration than the cells of the plant roots. Due to this, exosmosis takes place in the root hairs and the cells become flaccid. Beyond a condition, this can lead to extreme wilting of the plant and even plant death. 5. Meat and fish are salted to preserve them. meat and fish makes their cells gain a high concentration. If any bacterial or fungal attack takes place on these foods, they undergo exosmosis. This plasmolyses their cells; i.e. makes them flaccid, and causes their death. ANSWER Salting 6. We can find out whether seeds are dead or alive by soaking them in water. Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 12 ~ Disha Educentre Exhaustive Notes ANSWER Only living cells undergo plasmolysis; dead cells do not. When live seeds are soaked in water, the water enters them by plasmolysis. This makes the density of seeds lesser and they float on the water surface. Dead seeds do not undergo plasmolysis and they remain at the bottom of the vessel. IV. Distinctions and Comparisons 1. Turgidity and Flaccidity (Plasmolysis) (i) (ii) (iii) (iv) (v) (vi) 2. (i) (ii) (iii) 3. (i) (ii) (iii) 4. Turgidity When a cell cannot accommodate any more water; i.e. when it is in its fully distended state, it is said to be turgid. It occurs due to the entry of water into the cell by endosmosis. A cell becomes turgid when its turgor pressure becomes higher than its wall pressure. At this state, the plasma membrane is in contact with the cell wall. At this state, the cell wall is non-rigid. Turgid cells give mechanical strength to the plant. Flaccidity (Plasmolysis) When a cell is not fully distended; i.e. when it can accommodate more water, it is said to be flaccid. It occurs due to the exit of water from the cell by exosmosis. A cell becomes flaccid when its wall pressure becomes higher than its turgor pressure. At this state, the plasma membrane is withdrawn from the cell wall. At this state, the cell wall is soft. Flaccid cells do not give any mechanical strength to the plant. Plasmolysis and Deplasmolysis Plasmolysis It takes place when a plant cell is placed in hypertonic solution (i.e. the concentration of the cell solution is lesser than the concentration of the surrounding soil). The plasma membrane of the cell is withdrawn from the cell wall. It causes the cell to become flaccid. Deplasmolysis It takes place when a plant cell is placed in hypotonic solution (i.e. the concentration of the cell solution is higher than the concentration of the surrounding soil). The plasma membrane of the cell touches the cell wall. It causes the cell to become turgid. Turgor Pressure and Osmotic Pressure Turgor Pressure Osmotic Pressure It is the pressure of the cell contents on the cell It is the pressure by which the water molecules wall. tend to cross the semipermeable membrane and enter from the low concentration region to the high concentration region. It is not equal to the weight needed to nullify It is equal to the weight needed to nullify turgidity. osmosis. It helps in keeping the cell turgid or distended. It helps in the absorption of water from the soil. Turgor Pressure and Wall Pressure ANSWER (i) (ii) Turgor Pressure It is the pressure exerted by the cell contents on the cell wall. When turgor pressure is higher than wall pressure, it causes the cell to become turgid. Wall Pressure It is the pressure exerted by the cell wall on the cell contents. When wall pressure is higher than turgor pressure, it causes the cell to become flaccid. Notes Prepared by Neil Valentine D Silva ~ 13 ~ Disha Educentre Exhaustive Notes Absorption by Roots V. Diagram-based Questions 1. The diagram shows a plant cell after being placed in a sugar (strong) solution. Study the diagram and answer the questions:What is the state of the cell shown in the diagram? Name the structure which acts as a selectively permeable membrane. If the cell had been placed in distilled water instead of a strong sugar solution, which feature would not have been present? If the cell possessed chloroplasts, where would they be present? Name any one feature of this plant cell which is not present in animal cells. (i) (ii) (iii) (iv) (v) ANSWERS (i) (ii) (iii) (iv) (v) Flaccid condition Plasma membrane The shrunken protoplast would not have been present. The chloroplast would be present in the shrunken protoplast. The presence of cell wall ~ Part D ~ ROOT PRESSURE I. Definitions and Explanations 1. Root Pressure 2. Guttation 3. Ascent of Sap Capillarity 4. Root pressure is the pressure developed in the roots due to the continued inward movement of water through cell-to-cell osmosis, which helps in the ascent of cell sap upward through the stem. The loss of excess water from plants in the form of tiny drops along the leaf margins is known as guttation. The upward movement of water along with the minerals present in it from the root to the leaves of the plant is known as ascent of sap. When a narrow tube is inserted in water, then water rises in it. This is known as capillarity. II. Questions-Answers 1. Define root pressure. Explain its movement in the plant. Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 14 ~ Disha Educentre Exhaustive Notes ANSWER Root pressure is the pressure developed in the roots due to the continued inward movement of water through cell-to-cell osmosis, which helps in the ascent of cell sap upward through the stem. Root pressure occurs due to cell-to-cell osmosis, beginning from the root hair. The root hair absorbs water from the surrounding soil due to osmosis. Due to this, root pressure in the root hair increases. It presses against the next cell and water enters into it. This cell presses into the next cell and so on, creating a cell-to-cell movement of water. The water moves from the root hair to the cortical cells to the xylem cells. In the xylem cells, the water enters with considerable force because the root pressure builds up to a considerable amount by this stage. 2. Describe an experiment to demonstrate root pressure in plants. ANSWER Root pressure is not a very strong force. It acts only up to a height of 18 cm. Hence, it is able to take water up to a short height, but it cannot take water up to the shoot system in tall plants. 3. What is the limitation of root pressure? pressure is not a very strong force. It acts only up to a height of 18 cm. Hence, it is able to take water up to a short height, but it cannot take water up to the shoot system in tall plants. ANSWER Root 4. What is guttation and bleeding? ANSWER Guttation In some plants such as tomatoes, grasses, bananas and ferns, the root pressure is enough to bring the water all the way to the stem. It then comes out through the ends of the leaf veins. This water appears as tiny drops along the margins of the tips of leaves. This is known as guttation. Bleeding Sometimes, when parts of plants such as leaves are accidentally cut, water oozes out of them. This water is brought to the leaf due to root pressure. This is known as bleeding. 5. What are the forces contributing to the ascent of sap? ANSWER The following are the four main forces contributing to the ascent of sap:(i) Root Pressure: This force pushes the sap in the xylem plants to a certain height. (ii) Capillarity: Xylem vessels have narrow diameter that makes water from a low level rise up and fill the vacuum created due to water loss by transpiration. (iii) Transpiration: Water is lost from the top leaves, and that makes more water to be pulled from downwards. Water molecules remain attached together due to cohesive forces. (iv) Adhesion: Water sticks to the surface of cells, which pulls more water from the lower areas. 6. How do cohesive and adhesive forces bring about ascent of sap? ANSWER Cohesive Forces: Cohesion is the attractive force that exists between similar molecules. The water molecules that have already ascended upwards in the narrow capillaries of the xylem vessels attract the water molecules below them by cohesive forces. As the top water molecules are given out by transpiration, the lower molecules are pulled upwards. Thus, cohesion helps in ascent of sap. Adhesive Forces: Adhesion is the attractive force that exists between dissimilar molecules. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes 7. ~ 15 ~ Absorption by Roots Water molecules stick to the surface of the cells. This creates more space within the capillaries of the xylem, and a partial vacuum is created. This pulls up more water molecules from below to fill up the empty space. Thus, adhesion helps in ascent of sap. What downward motion takes place in plants? How does it happen? food formed by the leaves moves downwards in the plants through the phloem cells. This movement happens under the influence of gravity. ANSWER The ~ Part E ~ EXPERIMENTS ON CONDUCTION AND ABSORPTION OF WATER IN PLANTS I. Questions-Answers 1. Demonstrate an experiment to show that roots absorb water. ANSWER Aim: To show that roots absorb water. Procedure: Fill a test tube with water. Take a plant like balsam with its roots intact and put it into the test tube. Put a few drops of oil on the surface of water in the test tube so that it does not evaporate. Mark the level of water. Prepare a similar second test tube but do not put the plant inside it. Mark the level of water as before. Observe the water level after a few days. Observation: The level of water with the test tube having the balsam plant goes down. Inference: Roots absorb water from the surrounding medium. 2. Demonstrate an experiment to show that water is conducted upwards through xylem. ANSWER Aim: To show that water is conducted upwards through xylem. Procedure: Uproot a medium-sized balsam plant and place it in a beaker containing pink stain eosin solution. The roots must be completely submerged. Keep the setup aside for 3-4 hours. Then take the plant out and wash it in tap water. Take a transverse section of the roots, stems and leaves and observe it under a microscope. Observation: The xylem vessels will appear distinct because they will be stained red. Inference: Water is conducted upwards through the xylem. Notes Prepared by Neil Valentine D Silva ~ 16 ~ Biology for X ICSE 3. Disha Educentre Exhaustive Notes Demonstrate an experiment to show that food from leaves is conducted downwards through the phloem in the stem. ANSWER Aim: To show that food from leaves is conducted downwards through the phloem in the stem. Procedure: Girdle the stem of a guava plant. The girdling should be done deep enough to penetrate the phloem and cambium but not the xylem. Sap oozes out of the girdle and flows in a downward direction. Keep this aside for a few weeks. Observation: The part of the plant above the girdle grows in diameter, whereas the part below it stops growing and begins to die. Inference: Food is conducted downwards through the phloem in the stem. BOARD EXAMINATION QUESTIONS 2002 1. Choose the correct answer for the following:Marine fish when thrown under tap water bursts because of ________________. (a) Endosmosis (b) Exosmosis (c) Diffusion (d) Plasmolysis ANSWER Endosmosis 2. Name the following:Condition of a cell placed in a hypotonic solution. ANSWER Turgid or deplasmolysed Define the term diffusion . ANSWER Diffusion is the free movement of molecules of a substance (solute or solvent, gas, liquid) from the region of higher concentration to the region of lower concentration where the two have a direct contact. 3. 4. (i) (ii) The figure given below is a diagrammatic representation of a part of the cross-section of the root in the root hair zone. Study the figure and answer the questions that follow:Name the parts labelled from 1 to 5. Is the root hair unicellular or multicellular? Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes (iii) (iv) (v) ~ 17 ~ Absorption by Roots Name the process responsible for the entry of water molecules from the soil inward. What pressure is responsible for the movement of water from the soil inward? How is this pressure set up? ANSWERS (i) (ii) (iii) (iv) (v) The labelled parts are:1. Root hair 2. Soil particles 3. Xylem vessels 4. Cortex cells 5. Vacuoles Root hair is unicellular. Osmosis Osmotic pressure The pressure is set up due to difference in the osmotic gradient. This makes the root hair and cortical cells to become alternately turgid and flaccid. 2003 5. Name the following:The pressure which is responsible for the movement of water molecules across cortical cells of the root. ANSWER Root pressure 6. Give reason:- Wilted lettuce leaves if kept in cold water become crisp. is due to movement of water from the surroundings to the inside of the leaves due to plasmolysis. Wilted lettuce leaves are plasmolysed. When they are kept in cold water, the water enters the cells of the leaves. Thus, the leaves becomes deplasmolysed, i.e. turgid. This makes the leaves stiff and crisp once again. ANSWER This 2004 7. Rewrite the terms in the correct order so as to be in a logical sequence:Cortical cell, root hair, xylem, water, veins ANSWER Water root hair cortical cells xylem veins 8. Give reasons for the following:(i) Salt and sugar are used in preserving food. (ii) Some plants show wilting of their leaves during midday even when they are wellwatered. (iii) On sprinkling common salt on grass growing in a lawn, the grass is killed. ANSWER (i) Salt and sugar can be used in preserving food. The principle used here is exosmosis. When salt and sugar are added in food, their cells gain a high concentration. This makes their cell solution hypertonic. Now if any bacterial or fungal attack takes place, exosmosis occurs in them. The solvent moves from the low concentration (microorganism) to the high concentration (food). The organisms thus become plasmolysed and they die. (ii) At midday, the rate of transpiration from the leaves is higher than the rate of absorption from the roots. Thus, plants lose water faster than they can take up. Hence, some plants show wilting of leaves at midday. Notes Prepared by Neil Valentine D Silva Biology for X ICSE (iii) ~ 18 ~ Disha Educentre Exhaustive Notes When salt is sprinkled on a lawn, the water present in the soil gains high concentration and becomes a hypertonic solution. Now, the cells within the root hairs of the grasses in the lawn are at a low concentration. Exosmosis occurs from the cells of the root hairs. Water moves from low concentration (root hair cells) to high concentration (solution in the lawn soil). The root hairs thus lose water and get plasmolysed and die. 2005 9. Explain the term plasmolysis. Give one application of this phenomenon in our daily lives. ANSWER Plasmolysis is the shrinkage of the cell, which causes the plasma membrane to withdraw from the cell wall. This is the same as flaccidity. It occurs when the cell is placed in a solution of high concentration, due to which water molecules move outwards from the cell. Application: Salt and sugar are added as preservatives to food. They make the solution hypertonic. When any microorganism comes in contact with food, exosmosis occurs and they get plasmolysed and die. 10. Given below is the diagrammatic representation of the transverse section of a part of a plant. Study the same and answer the questions that follow:(i) Name the part of the plant that is shown. (ii) Label the parts 1 to 6 indicated in the diagram. (iii) Write the functions of parts 3 and 5. ANSWER (i) (ii) (iii) Root 1: root hair 2: epiblema 3: cortex cells 4: endodermis 5: phloem 6: xylem Function of part 3 (cortex cells): The cells of the cortex store starch. Function of part 5 (phloem): Phloem translocates food from the leaves to all the other parts of the plant body. 11. Give reason:- Marine fish bursts when thrown under tap water. ANSWER The bodies of marine fish contain a high salt concentration. Tap water in comparison has a low concentration. Thus, it is a hypotonic solution. When the marine fish is thrown under tap water, endosmosis occurs. Water enters from the outside to the inside of the body of the fish. This causes the fish to burst. 2006 12. Define hypotonic solution. two solutions of different concentrations are in contact, the solution that has a lesser concentration of solute molecules and lower osmotic pressure is said to be hypotonic solution. It has a higher water content. ANSWER When 2007 13. Name the following:Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes (i) (ii) ANSWER (i) (ii) 14. ~ 19 ~ Absorption by Roots A solution whose concentration is greater than that of the cell sap. Transports water from the soil to the other parts of the plant. Hypertonic solution Root hairs Explain the term osmosis. is the diffusion of solvent (water) molecules across a semipermeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration). ANSWER Osmosis 15. Identify the incorrect term and replace it with the correct term:Soil water root hair cell of cortex epidermis xylem ANSWER The incorrect term is epidermis. It should be endodermis. Soil water root hair cell of cortex endodermis xylem 16. Give reason:- Plants begin to die when excess of soluble fertiliser is added to the soil. fertiliser increases the concentration of the soil water. This makes the soil water hypertonic. The soil water is at high concentration and cell sap of the plants is at low concentration. This causes exosmosis to occur from the plant cells. Water moves from the plant cells to the surroundings. Due to this, plasmolysis occurs in the plant parts, and they wilt and die. ANSWER Soluble 2008 17. The following paragraph is related to absorption of water from the soil. Copy and complete the following paragraph by selecting the correct word from those given in the box. You may use any term only once. Exosmosis / hypertonic / osmosis / isotonic / hypotonic / cortical / endosmosis Water enters the root hair from the soil by the process of _____________. This is because the solution in the soil is _______________ whereas the cell sap in the root hair cell is ____________. The water then passes through the ______________ cells by cell to cell ____________ and reaches the xylem of the root. ANSWER Endosmosis, hypotonic, hypertonic, cortical, osmosis 18. Rearrange the terms so that they are in a logical sequence as directed:Soil water, xylem, cortex, endodermis, root hair (conduction of water) ANSWER Soil water root hair cortex endodermis xylem 19. Given below is an example of a particular structure and its special functional activity. Example: Glomerulus and ultrafiltration On a similar pattern complete: Phloem and ______________. ANSWER Conduction of food 20. Given below is an incomplete explanation of a certain biological process/term where a key word has been left out. Rewrite the completed explanation by inserting the key word in the space indicated by ^ . Osmosis is the movement of water molecules from its region of high concentration to its region of low concentration through a ^ membrane. ANSWER ^ = semipermeable 21. Give the technical/biological term for the following:The process of mixing two different substances/molecules. ANSWER Diffusion Notes Prepared by Neil Valentine D Silva Biology for X ICSE 22. ~ 20 ~ Disha Educentre Exhaustive Notes Differentiate between the following on the basis of what is given in brackets. Wall Pressure and Turgor Pressure (explain briefly). ANSWER (i) (ii) Turgor Pressure It is the pressure exerted by the cell contents on the cell wall. When turgor pressure is higher than wall pressure, it causes the cell to become turgid. Wall Pressure It is the pressure exerted by the cell wall on the cell contents. When wall pressure is higher than turgor pressure, it causes the cell to become flaccid. 23. Given below are diagrams of plant cells as seen under the microscope after having been placed in two different solutions. (i) What is the technical term for the condition of:a) Cell A b) Cell B? (ii) From the solutions given in brackets (water, strong sugar solution, 1% salt solution), name the solution into which:a) Cell A b) Cell B was placed before being viewed under the microscope? (iii) Under what conditions in the soil will the root hair cell resemble:a) Cell A b) Cell B? (iv) Name the pressure responsible for the movement of water from the hair cell to the xylem of the root. How is it set up? (v) Name the pressure that helps in the movement of water up the xylem of the root. ANSWER (i) Cell A: turgid or deplasmolysed Cell B: flaccid or plasmolysed (ii) Cell A: water Cell B: 1% salt solution (iii) Cell A: hypotonic condition Cell B: hypertonic condition (iv) Root pressure. Root pressure is set up due to the alternate turgidity and flaccidity of the root hair cells and the cortical cells. (v) Turgor pressure 24. Account for the following briefly:Herbaceous plants growing in well-watered soils are found to wilt on a hot day. ANSWER On a hot day, there is a high transpiration rate and low root pressure. This makes the plants wilt. The plants lose more water through the stomatal openings in their leaves. Also, since evaporation of water from the soil also takes place, low root pressure is developed for water uptake. 25. Distinguish between:Tonoplast and plasma membrane (location). ANSWER Tonoplast: It is located around the vacuoles. Plasma membrane: It is located around each cell. 2009 26. Give the specific function of the following structure found in the body of plants/animals:Xylem ANSWER Xylem is a vascular plant tissue that performs the upward conduction of water. 27. Identify and name the following process/term from the statement given below:Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~ 21 ~ Absorption by Roots Movement of molecules from a region of high concentration to a region of low concentration. ANSWER Diffusion 28. Explain the following terms:- Root pressure. pressure is the pressure developed in the roots due to the continued inward movement of water through cell-to-cell osmosis, which helps in the ascent of cell sap upward through the stem. ANSWER Root 2010 29. Rewrite each term in a logical sequence as directed:Cortical cells, root hair, soil water, endodermis, xylem (entry of water into the plant from the soil). ANSWER Soil water root hair cortical cells endodermis xylem 30. Given below is a diagram of an apparatus set up to study a very important physiological process. (i) Name the process being studied. (ii) Explain the process. (iii) What change would you observe in the thistle funnel containing sugar solution after about 10 minutes? (iv) Is sugar solution hypertonic or hypotonic? (v) Name the part of the plant which is represented by the sugar solution. (vi) Explain why much salt is added to pickles. ANSWER (i) Osmosis (ii) Osmosis is the diffusion of solvent (water) molecules across a semipermeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration). (iii) The level of water will rise in the thistle funnel after 10 minutes. (iv) Hypertonic (v) Root hair (vi) When salt is added to pickles, it becomes a hypertonic solution due to high concentration. Now, if any microorganism lands in the pickle, it will undergo exosmosis, i.e. the solvent from the body of the microorganism will move out of it. Due to this, the microorganism will get plasmolysed and die. Hence, salt added to pickle acts as a natural preservative. 31. Explain the term:- Turgidity. condition where a cell cannot accommodate any more water in it is known as turgidity, and the cell in this condition is said to be turgid. ANSWER The 2011 32. Rewrite and complete the following sentences by inserting the correct word:(i) Wooden doors swell up in the rainy season due to _____________. (ii) ____________ is the phenomenon of contraction of the cytoplasm from the cell wall. ANSWER (i) Wooden doors swell up in the rainy season due to imbibition. (ii) Plasmolysis is the phenomenon of contraction of the cytoplasm from the cell wall. 33. Give reasons:- Potato cubes when placed in water become firm and increase in size. Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 22 ~ Disha Educentre Exhaustive Notes ANSWER The concentration of the cytoplasm in the potato cells is higher than that of the surrounding water. Hence, when potato cubes are placed in water, they are in a hypotonic solution. This causes endosmosis, i.e. water enters from outside (low concentration) into the potato cells (high concentration). Due to this, potato cells become turgid and the cubes become firm and increase in size. 34. The diagram given alongside represents a layer of epidermal cells showing a fully grown root hair. Study the diagram and answer the questions that follow:(i) Name the parts labelled A, B, C and D. (ii) The root hair cell is in a turgid state. Name and explain the process that causes this state. (iii) Mention one distinct difference between the parts labelled A and B. (iv) Draw a diagram of the above cell as it would appear if a concentrated solution of fertiliser is added to it. ANSWER (i) A: cell wall B: cell membrane C: cytoplasm D: nucleus (ii) The process is osmosis. The cell sap inside the root hairs is at a higher concentration than the surrounding water. Hence, endosmosis occurs and the root hair cell becomes turgid. (iii) The difference between cell wall and cell membrane is:Cell Wall Cell Membrane It is present only in plant cells. It is present in both plant and animal cells. (iv) Concentration solution of fertiliser will increase the concentration outside and make it a hypertonic solution. This would lead to exosmosis. Hence, the root hair cell would become plasmolysed (lose its turgidity). It will appear as follows:2012 35. Rewrite each term in a logical sequence as directed:Cortical cells, root hair, xylem, soil water, endodermis (absorption of water by the plants). ANSWER Soil water root hair cortical cells endodermis xylem 36. Given alongside is a diagram of a cell as seen under a microscope after having been placed in a solution. (i) What is the technical term used for the state/condition of the cell given above? (ii) Give the technical term for the solution in which the cell was placed. (iii) Name the parts numbered 1 to 4. (iv) Is the cell given above a plant cell or an animal cell? Give two reasons in support of your answer as evident from the diagram. (v) What would you do to bring this cell back to its original condition? ANSWER (i) The cell is plasmolysed; i.e. it has undergone plasmolysis. (ii) The solution in which the cell was placed is hypertonic; i.e. having a higher concentration than the cell. (iii) 1: nucleus 2: chloroplast 3: vacuole 4: empty space of plasmolysed cell (iv) The cell is a plant cell because:a) Chloroplast is present. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes (v) ~ 23 ~ Absorption by Roots b) Vacuole is of a large size. We could put this cell in a solution of low concentration or water to bring it back to its original concentration. 2013 37. The figure given below shows the epidermal cells of an onion bulb. This cell was then transferred to a drop of sugar solution. (i) Draw a well labelled diagram of the epidermal cell as it would appear after immersion in a strong sugar solution. (ii) What scientific term is used for the changes as shown in (i) above? (iii) What should be done to restore the cell to its original condition? (iv) Give the scientific term for the recovery of cell as a result of the step taken in (iii) above. (v) Define the term osmosis. ANSWER (i) (ii) (iii) (iv) (v) The changes occurring are plasmolysis. The cell can be restored to original condition by placing it in water or dilute solution. The recovery is termed as deplasmolysis or turgidity or endosmosis. Osmosis is the diffusion of solvent (water) molecules across a semipermeable membrane from a more dilute solution (with a lower solute concentration) to a less dilute solution (with a higher solute concentration). Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 24 ~ Disha Educentre Exhaustive Notes Question .1. Name the following : (i) The tissue that transports manufactured starch from the leaves to all parts of plants. (ii) The tissue responsible for the ascent of sap in plants. (iii) The pressure responsible for the movement of water molecules across the cortical cells of the root. (iv) Condition of a cell placed in hypotonic solution. (v) The process by which water enters the root hair cell. (vi) The pressure exerted by cell contents on a plant cell wall. (vii) Tissue concerned with upward conduction of water in plants. (viii) Condition of cell in which the cell contents are shrunken. (ix) The inward movement of solvent molecules through the plasma membrane of a cell. (x) The process by which raisin swell up when placed in a beaker of water. (xi) Marine fish when thrown under tap water bursts because of : (a) Endosmosis (b) Exosmosis (c) Diffusion (d) Plasmolysis. (xii) Name the structure which transports manufactured food from leaves to other parts of the plant. (xiii) Name the kind of cells that constitute the cortex of a root. (xiv) Name the process by which intact plants lose water in the form of droplets. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~ 25 ~ Absorption by Roots Answer : Click Here Question .2. State true or false : (i) Cells that have lost their water content are said to be deplasmolysed. (ii) Xylem is the water conducting tissue in plants. (iii) Spreading of particles by mixing is called diffusion. (iv) Root hairs are extension of epidermal cells. Answer : Click Here Question . 3. Arrange the following in correct order so as to be in a logical sequence: (i) Endodermis, root hair, xylem, soil water, cells of cortex. (ii) Cortical cell, root hair, xylem, water, veins. Answer : Click Here Question .4. Define the following : (i) Hypotonic solution. (ii) Active transport. (iii) Diffusion. Answer : Click Here Question .5. Explain the term plasmolysis. Give one application of this phenomenon in our daily life. Answer : Click Here Question .6. Differentiate between : (i) Cobalt chloride paper and goats bladder. (ii) Osmosis and diffusion. Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 26 ~ Disha Educentre Exhaustive Notes Answer : Click Here Question .7. Choose the correct alternative : (i) Marine fish when thrown under tap water bursts because of (endosmosis, exosmosis, diffusion, plasmolysis). (ii) The space between the cell wall and plasma membrane in plasmolysed cell is filled with (isotonic solution, hypotonic solution, hypertonic solution, water). (iii) Osmosis involves diffusion of (suspended particles from lower to higher concentration, suspended particles from higher to lower concentration, water from the more concentrated solution to the less concentrated solution, water from the less concentrated solution to the more concentrated solution). (iv) The process by which molecules distribute themselves evenly with in the space they occupy is termed as (osmosis, diffusion, active transport, imbibition). (v) Synthesized food in green leaves is transported through (phloem, xylem, pith). Answer : Click Here Question .8. Give biological reasons for : (i) Salt and sugar are used in preserving food. (ii) Some plants show wilting of their leaves during mid day even when the soil is well watered. (iii) On sprinkling common salt on grass growing in a lawn, the grass is killed. (iv) Wilted lettuce leaves if kept in cold water become crisp. (v) Plants growing in fertilized soil are often found to wilt if the soil is not adequately watered. (vi) Grapes shrink when immersed in a very strong sugar solution. (vii) Root hairs become flaccid, when fertilizers are added to the moist soil around it. (viii) Transplanting of seedling to a flower bed in the evening is better than doing so in the evening. (ix) Strips of potato placed in 50% sucrose solution appear soft and shriveled. Answer : Click Here Question .9. Potato cubes 1 cm in size were placed in two containers, one containing water, the other containing concentrated sugar solution. After about 24 hours when the cubes were examined, then those placed in water were found to be firm and had increased in size by a few millimeters. Those placed in concentrated sugar solution were found to be soft and had decreased in size. Use the above information to answer the questions that follow : (i) Account for the firmness and increase in size of the potato cubes which were placed in water. (ii) Account for the softness and decrease in size of the potato cubes which were placed in the sugar solution. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~ 27 ~ Absorption by Roots (iii) Name and define the physical process being investigated in this experiment. Answer : Click Here Question .10. The diagram below represents an experimental set up to demonstrate a vital process. Study the same and then answer the questions that follow : Fig. (i) Name the above process. (ii) Define the above named process. (iii) Mention two advantages of this process to the plant. (iv) Name two liquids that could be used in this experiment. (v) Why did the level of the liquid in the vertical tube rise ? Answer : Click Here Question .11. The figure given below is a diagrammatic representation of a part of cross section of the root in the root hair zone. Study the same and then answer the question that follow: (i) Name the parts indicated by guidelines 1 to 5 . (ii) Is the root hair cell unicellular or multi-cellular ? (iii) Draw a labelled diagram of the root hair cell as it would appear if some fertilizer is added to the soil close to it. (iv) Name the process responsible for the entry of water molecules from the soil into A1 and then A2. (v) What pressure is responsible for the movement of water in the direction indicated by arrows ? Notes Prepared by Neil Valentine D Silva Biology for X ICSE ~ 28 ~ Disha Educentre Exhaustive Notes (vi) How is this pressure set up ? Answer : Click Here Question .12. Given below is the diagrammatic representation of the transverse section of a part of a plant. Study the same and answer the questions that follow : Fig. (i) Name the part of the plant that is shown. (ii) Label the parts 1 to 6, indicated in the diagram. (iii) Write the functions of parts 3 and 5. Answer : Click Here Question .13. Given below are the diagrams of a certain structure in plants in two conditions : Fig. (i) Name the structure shown. Notes Prepared by Neil Valentine D Silva Disha Educentre Exhaustive Notes ~ 29 ~ Absorption by Roots (ii) Name the parts numbered 1 5. (iii) What is the most apparent difference between A and B in the structure shown ? (iv) Describe the mechanism which brings about the change in the structures depicted in A and B. Answer : Click Here Notes Prepared by Neil Valentine D Silva

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