Absorption By Roots 1. Name the following : (i) The fraction of soil water readily available to plants. (ii) The process by which plants lose water. (iii) The pressure exerted by the cell wall to balance the turgor pressure. (iv) The process that occurs in plants when the root pressure is high and transpiration is low. (v) The tissue through which the ascent of sap takes place in plants and plants lose water in the form of water droplets. (vi) The condition of cell placed in a hypotonic solution. (vii) The process by which water enters root hairs. (viii) The process by which molecules evenly distribute themselves within the space they occupy. Ans. (i) Capillary water (iii) Wall pressure (v) Xylem (vii) Endosmosis (ii) Transpiration (iv) Guttation (vi) Turgid (viii) Diffusion 1
2. Write the correct answers from the given options : (i) Osmosis involves the diffusion of : (a) Suspended particles from lower to higher concentration. (b) Suspended particles from higher to lower concentration. (c) Water from more concentrated solution to less concentrated solution. (d) Water from less concentrated solution to more concentrated solution. (ii) 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. (iii) What is responsible for guttation? (a) Osmotic pressure. (b) Root pressure. (c) Suction pressure. (d) Capillarity. (iv) Active salt absorption by the roots depends on : (a) Active water absorption. (b) Activity of xylem cells. (c) Expenditure of energy. (d) Breaking up of water molecule. 2
Ans.(i) (d) Water from less concentrated solution to the more concentrated solution. (ii) (c) Hypertonic solution. (iii) (b) Root pressure. (iv) (c) Expenditure of energy. 3. Mention if the following statements are true/false. If false, rewrite the wrong ones by changing only the words printed in bold face. (i) Osmosis regulates the opening and closing of stomata. (ii) Guttation occurs when the loss of water by transpiration exceeds the rate of uptake by roots. (iii) In endosmosis, movement of water molecules takes place from the outside into the cell, when it is placed in a hypertonic solution. (iv) Cells that have lost their water content are said to be deplasmolysed. (v) Xylem is the water conducting tissue in plants. Ans.(i) True (ii) False (Wilting) (iii) True (iv) False (Plasmolysed) (v) True 4. Match the items of column I with those in column II. Column I (1) Xylem (2) Phloem (3) Cell membrane (4) Root pressure (5) Cell wall Column II (a) semi-permeable (b) permeable (c) downward flow of sap (d) upward flow of water (e) guttation. 3
Ans.(1) d, (2) c, (3) a, (4) e, (5) b 5. What is the difference between plasmolysis and deplasmolysis? Ans. Plasmolysis is the shrinkage of cytoplasm from a living cell under the influence of the surrounding strong solution (hypertonic solution). When a plasmolysed cell becomes fully turgid, when it is placed in a hypotonic solution, the process is called deplasmolysis. 6. What forces are involved in the absorption of water from the soil by root hair? Ans. Transpiration pull of the aerial parts of the plants, cohesive forces between water molecules, adhesive forces between water and xylem vessels, and root pressure are the various forces. 7. Why do aquatic plants growing in fresh water become flaccid when put into saline water? Ans. Saline water being hypertonic brings about exosmosis, causing plasmolysis and flaccidity. 8. State three ways in which roots are suited for absorbing water. Ans. In land plants most of the water is absorbed through the roots. Roots are suited for absorbing water in the following ways : 4
(i) Surface area of roots : Roots are branched extensively ending in millions of root tips. Numerous root hairs are present in the root hair zone of the root tip. Therefore, all together the roots of plants provide tremendous surface area which facilitates absorption of water. (ii) Root hair contains cell sap of a concentration higher than that of the surrounding water. This characteristic is an important requirement to draw in the water from outside. (iii) Root hairs have thin walls : Root hairs are an extension of the epidermal cell of the root. The cell wall is thin and allows the movement of water molecules and dissolved substances freely in and out. The cell membrane is thin but semi-permeable, i.e., it allows water molecules to pass through but not the larger molecules of the dissolved salts. 5
9. What is the difference between a flaccid cell and a turgid cell? Ans. Turgidity is a condition when a cell is fully stretched with water and all its walls are in a state of tension. e.g. when stomata is open. When a cell loses water from its cytoplasm and the plasma membrane is withdrawn, it is said to be flaccid, e.g., when stomata closes. 10. Give any two examples of turgor movements in plants. Ans. (i) Turgor pressure helps to push through the hard ground as in mushrooms and in a seedling. (ii) Sometimes, the roots of certain trees have been seen to crack the walls or a concrete floor of an adjoining building. This again is due to turgor pressure. 11. What is the difference between flaccid and turgid? Give one example of flaccid condition in plants. Ans. When a cell is put in a hypertonic solution, the cell content becomes shrunken and the cell is no more tight. This condition of the cell is called flaccid. If the cell is kept in hypotonic solution, the cell wall becomes rigid and stretched by the increase in volume of vacuoles due to absorption of water. The cell is then said to be turgid. 6
12. 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? Ans. Absorption of water by the root is by means of root hair. A root hair contains cell sap which has a higher concentration of salts as compared to the outside soil water. This difference sets off osmosis and the outside water diffuses into the root hair. From the cell bearing root hair, water continues to pass to adjoining cells are one after another to finally enter the xylem vessels. The turgidity acquired by the cells in the process also helps to push the water upwards through the xylem vessels. Absorption of mineral elements from the soil involves active transport by the cells. 13. Explain why : (i) Grass is killed if salt is sprinkled on it. (ii) Jams and pickles do not spoil easily. (iii) A closed can of dried seeds bursts open if some water enters it by accident. (iv) Freshwater fish cannot survive in sea water. (v) The roots of some plants are seen growing through walls and crevices. (vi) Root hairs become flaccid when too much chemical fertiliser is added to the moist soil around it Ans.(i) Living cells of grass roots occur in turgid condition when salt is sprinkled on it, plasmolysis occurs and the cells die. 7
(ii) Jams and pickles do not spoil easily because sugaring and salting of these foodstuffs raises the osmotic pressure of the medium thus killing the bacteria and fungi due to plasmolysis. (iii) The seeds imbibe water and swell up. The attraction of the dry cell walls and protoplasm for water causes an imbibitional pressure to develop within the plant body. It is this imbibition pressure that causes the can to burst open. (iv) Freshwater fish cannot survive in sea water as in this hypertonic environment the fish lose water from their body to the surrounding and get dehydrated. (v) Roots of some plants are seen growing through walls and crevices because turgidity caused by turgor pressure aids the thin-walled tissues of the root tips to crack the walls. (vi) Addition of too much of fertilizer to the moist soil results in flaccidity of root hair, because the concentration of soil solution increases and water starts coming out of the root hair cells leading to flaccidity. 14. What is meant by ascent of sap? List three factors that are responsible for this. Ans. The upward conduction of water from the roots to the shoot apex is called ascent of sap. The three factors that are responsible for ascent of sap are: (i) Root pressure (ii) Transpiration pull (iii) Forces of cohesion and adhesion. Loss of water from the aerial surfaces through transpiration causes a transpiration pull. This leads to absorption of water from soil. Because of cohesive forces among water molecules and adhesive forces between water and xylem vessels, a water column is maintained from the base of the plant to its top. 8
15. Leaves of a sensitive plant wilt and droop down on a slight touch. What mechanism brings about this change? Ans. Drooping of the leaflets of sensitive plant : If any leaf of Mimosa (Touch-me-not) is touched, it will fold up and within 2-3 seconds the entire leaf droops. Slowly the leaf recovers. Stimulus of touch leads to loss of turgor pressure at the base of leaflets and base of petioles causing the leaf to wilt temporarily. 16. Explain two manifestations of root pressure. Ans. The two manifestations of root pressure are : (i) Exudation or Bleeding : Sometimes sap (water with dissolved inorganic and organic substances) exudes from the injured part of the plant. Exudation of milky latex from Calotropis is an example. (ii) Guttation : When root pressure is high and transpiration is low, water drops ooze out through special structures called hydathodes. It can be seen in garden nasturtium. 9
17. The leaves of a well-watered potted plant were found wilted during a hot sunny day. (i) Suggest two reasons which could have caused the wilting of the leaves. (ii) Would the cells of the leaves in the wilted state be flaccid or turgid? (iii) Explain briefly the meaning of the term mentioned in your answer to (ii) above. (iv) What advantage would the plant have derived from wilting? (v) What explanation would you suggest if the wilted leaves did not recover even during the night? Ans. (i) Wilting of leaves can be due to excessive loss of water, due to transpiration and low root pressure. (ii) Cells of the leaves in wilted state would be flaccid. (iii) A cell which loses its distended state due to the shrinkage of protoplasm and withdrawal of plasma membrane from cell wall is called a flaccid cell. (iv) As the water evaporates from the leaf surface, it leaves behind hygroscopic salts which absorb moisture from the atmosphere and do not allow the plant to dry up. (v) If the wilted leaves do not recover at night it is because of water deficiency in the soil. 10
18. (i) Name one chemical substance which is transported from the roots to the shoot and one which is transported from the leaves to the lower parts of the plant. (ii) Suggest one simple experiment to show that water absorbed by the roots of a plant travels upward through the conducting tissues of the stem. Ans. (i) Ammonium nitrate is transported from roots to the shoot and sugar is transported from leaves to the lower parts of the plant. (ii) Water rises in the stem through xylem : To demonstrate the movement of water through xylem strand, a simple experiment can be performed. Take two balsam plants. Put them under water (as shown in the diagram) to prevent air bubbles from getting in. Name them as A and B. The shoots are then fixed to the stands and allowed to remain for about two days with lower ends in the water. After two days, we will observe: Plant A Leaves remain turgid and appear normal. Plant B Leaves wilt and droop down. The experiment shows that water moves upwards through xylem. 11
19. Given below are diagrams of a certain structure in plants in two conditions. (i) Name the structure shown. (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 structure depicted in A and B. Ans.(i) Stoma (ii) 1 Guard cell 2 Cell wall towards the stomatal opening 3 Nucleus 4 Adjoining cell 5 Stomatal opening. 12
(iii) A shows an open stomata. B shows a closed stomata. (iv) The mechanism of opening and closing of stomata : The opening and closing of stomata is regulated by the amount of water and solute present in the guard cells. The guard cells have thick inner wall facing the opening and thin outer wall on the opposite side. Their cytoplasm contains chloroplasts. During the day, the guard cells begin photosynthesis and the sugar produced during the process increases the osmotic pressure, causing water to move in from the adjoining cells. Thus, the guard cells become turgid and bulge outwards due to their thin outer walls, thus widening the stomatal opening lying in between. 20. Explain how soaked seeds swell up and burst their seed coats. Ans. If you soak some seeds, it will swell up after few hours and ultimately burst their seed coats. In this case, the water continues to diffuse in through the membranous cover of seed coat. This influx of water builds up an internal pressure that may reach a limit, which the seed coat no longer can bear and they burst. 13
21. What is transpiration pull? How is it caused? Ans. As the 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 (cohesion), and thus to produce a continuous column of water through the stem. 22. What is root pressure? How would you demonstrate it? Ans. 1. Root pressure is the pressure exerted by the cortical cells of the root upon their liquid contents, under fully turgid condition, forcing water into the xylem vessels and through them up the stem. 2. Turgor builds Root Pressure in Root Cells : Take a potted plant of Tomato or Balsam. Cut its main stem a few centimetres above the soil level. Fix a long narrow glass tube to the cut stump with the help of a rubber tubing. Put some coloured water in the glass tubing. Add a drop of oil at the top to check evaporation. Clamp the glass tubing. Mark the initial level of water. Observe after two hours. The water level in the tube will rise due to root pressure. Root pressure is sufficient to raise the water level up to a few feet. 14
Water passes from one cell to another due to the root pressure. One turgid cell presses the other cell, the force of flow of water increases inward. When the water reaches xylem vessel, it enters with force. However, this force alone cannot push water in tall trees. Exudation or Bleeding : Sometimes sap (water with dissolved inorganic and organic substances) exudes from the injured part of the plant, a manifestation of root pressure. Exudation of milky latex from Calotropis and Euphorbia are examples of exudation. Guttation : When the root pressure is high and transpiration is low, water drops ooze out through special structures called hydathodes. It can be seen early morning in banana, garden nasturtrium, colocasia, tomato, grass, etc. 23. The following diagram represents a plant cell after being placed in a strong sugar solution. Guidelines 1 to 5 indicate the following : Ans. 1. Cell wall 2. Large vacuole 3. Strong sugar solution 4. Protoplasm 5. Nucleus 15
24. What is the difference between diffusion and osmosis? State the significance of osmosis in plant physiology. Ans. Diffusion 1. It is the movement of substances from the region of their higher concentration to that of lower concentration. 2. No membrane is required. Osmosis It is the movement of water molecules from a solution of lower concentration to that of higher concentration across a semi-permeable membrane. It occurs through a semi-permeable membrane. Significance of Osmosis : Osmosis is mainly responsible for the movement of water from non-living xylem elements into living cells. Osmosis depends on the stretched and rigid condition of cells which makes growth possible and which is responsible for keeping the young stem erect and leaves extended. 25. The figure below shows a diagrammatic representation of the movement of certain substances inside the stem of a certain plant. 16
Write five sentences on the process of the arrangement of structures indicated in the diagram. [Each statement must include one or more of the following four words xylem, phloem, roots, leaves]. Ans. (i) Water is absorbed by the plant through the roots. (ii) Water travels up from roots through xylem. (iii) The continuity in xylem column is maintained by transpiration pull and root pressure. (iv) Leaves are the site of manufacture of food. (v) Food is translocated to various parts of the plant through phloem. 26. (i) What is the state of cell shown in the diagram? (ii) Name the structure which acts as a selectively permeable membrane. (iii) If the cell had been placed in distilled water instead of strong sugar solution, which feature would not have been seen? (iv) Name any one feature of this plant cell which is not present in animal cell. Ans. (i) Flaccid (ii) Plasma membrane (iii) Flaccidity (iv) A big vacuole 17
27. A ring of bark was removed from a tree in spring. The tree continued to live through summer but a swelling appeared on the bark above the ring while the bark below shrivelled up. (i) Account for the swelling in the bark above the ring. (ii) Account for the shrivelling of the bark below the ring. (iii) Name the tissue through which food is conducted in plants. (iv)name the tissue through which water is conducted in plants. Ans. (i)girdling the bark results in accumulation of the food material which is synthesised in the leaves and translocated through the phloem downwards. This causes swelling in the bark above the ring. (ii) The bark below the ring shrivels because the phloem column has been cut and the stored organic content of the lower part is ultimately exhausted. (iii) Phloem (iv) Xylem 18
28. The skin of a raw potato was removed and slices were taken off from all sides giving it the shape of a square block. The centre was scooped out to form a cup. Strong sugar solution was put in the cup and the level of solution was marked by inserting a pin. The potato block was put in a dish containing water coloured with a drop of ink. (i) What is the aim of the experiment? (ii) What change would you expect in the cavity of the potato after one hour? (iii) Give an explanation for this change. (iv) If the raw potato is replaced by a boiled potato and treated in the same way, what difference would you note in the result? (v) Give an explanation for this change. Ans.(i) The aim of the experiment is to demonstrate the process of osmosis. (ii) After an hour, the level of the solution increases in the cavity of potato. (iii) Since the solution in the potato is hypertonic, the cell sap from the potato cells move outward causing exosmosis. This causes an increase in the volume of the fluid inside the potato. (iv) The level of the solution will not rise. (v) Since boiling damages the cells of the potato and its cell sap would have exuded out earlier itself, the water level remains the same. 19
29. Two potato cubes each 1 cm3 in size, were placed separately in two containers (A and 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 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 sugar solution. (iii) Name and define the physical process being investigated in the experiment. Ans.(i) As the cubes were put in water (hypotonic) the water started entering into the cube as the concentration inside the cell (cell sap) is higher. Due to the entery of water inside the cubes, they became bigger and firm as compared to the earlier condition. (ii) In sugar solution, the water from the cell sap starts going out due to higher concentration outside and thereby becoming soft and smaller in size. (iii) Osmosis is the diffusion of water molecules through a semi-permeable membrane from a dilute to a concentrated solution. 20
30. Study the diagram given below and answer the questions that follow : (i) Explain the physiological process being studied. (ii) What will be observed in the two test-tubes after two to three days? (iii) Give a reason for your answer in (ii) above. (iv) Why is the surface of water covered with oil? (v) State the purpose of setting up test tube B. Ans.(i) The physiological process of absorption of water by plants is being demonstrated in the above experiment. In terrestrial plants the roots are water absorbing organs. The plant absorbs water through root hair due to the difference in the concentration (potential) of soil solution and the cell sap. It can be active or passive. Passive absorption can occur independently without any activity of root whereas, active absorption depends directly on the activity of the root. 21
(ii) The water level will fall in test tube A whereas it will remain the same in B after two to three days. (iii) The water is being absorbed in test tube A by the roots of the plant in it, which results in lowering of water level. In B there is no plant, therefore, water level remains the same as it is not consumed. (iv) The oil prevents the physical evaporation of water from the surface thus, not affecting the experimental results. (v) Test tube B is acting as a control experiment to find the difference with a changed condition (In this case, the plant is not present.) 31. Explain the term Plasmolysis. Give one application of this phenomenon in our daily lives. Ans. Plasmolysis : Living cells of leaf of aquatic plants remain in turgid condition, but when they are kept in salt or sugar solution, they lose their distended form, protoplasm shrinks and plasma membrane is withdrawn. This shrinkage of protoplasm is called plasmolysis and cell is said to be plasmolysed. Application of plasmolysis in our daily life : In preserving food items in highly concentrated sugar solution as in the case of jams and jellies. 22
32. The figure given below is a diagramatic representation of a part of the cross section of the root in the root hair zone. Study the same and answer the questions that follow : (a) Name the parts indicated by guidelines 1 to 5. (b) Name the process responsible for the passage of water molecules from soil into A 1 and then into A 2. (c) What pressure is responsible for the movement of water in the direction indicated by arrows? (d) How is this pressure set up? Ans. (a) 1. Film of water around soil particles 2. Soil particles 3. Xylem vessel 4. Cortex 5. Vacuole (b) Osmosis (c) Root pressure (d) Due to difference in the concentration of salts in the cells. 23
33. Differentiate between the following : Ans. (a) Plasmolysis and deplasmolysis? (b) Turgor pressure and wall pressure (c) Guttation and bleeding Plasmolysis Shrinkage of cytoplasm from the cell wall is called plasmolysis. Turgor pressure The pressure of the cell contents on the cell wall is called turgor pressure. Guttation When root pressure is high and transpiration is low. Water drops ooze out through hydathodes. This is called guttation. Deplasmolysis The recovery or reversal of plasmolysis is called deplasmolysis. Wall pressure Pressure exerted by the cell wall on the cell content is called wall pressure. Bleeding Loss of water through a cut on stem is called bleeding. 34. Tick-mark the correct option (out of the given four) in each case : (a) Which of the following is a characteristic NOT related with the suitability of the roots for absorbing water? (i) Tremendous surface area (ii) Contain cell sap at a higher concentration than the surrounding soil water (iii) Root hairs have thin cell walls (iv) Grow downward into the soil 24
(b) Movement of molecules of a substance from the region of higher concentration to their lower concentration without the involvement of a separating membrane is called (i) Osmosis (ii) Diffusion (iii) Active transport (iv) Capillarity (c) Osmosis and capillarity are the same except that in osmosis there is (i) a freely permeable membrane (ii) a cell wall in between (iii) a selectively permeable membrane in between (iv) an endless inflow of water into a cell (d) The highest water potential (capacity to move out to higher concentrated solution) is that of (i) Pure water (ii) 10% salt solution (iii) Honey (iv) 50% sugar solution (e) The space between the cell wall and plasma membrane in a plasmolysed cell is filled with (i) isotonic solution (ii) hypotonic solution 25
(iii) hypertonic solution (iv) water (f) What is responsible for guttation? (i) Osmotic pressure (ii) Root pressure (iii) Suction pressure (iv) Capillarity Ans. (a) (iv) (b) (ii) (c) (iiii) (d) (i) (e) (ii) (f) (ii) 35. Which one of the following is the most appropriate characteristic of a Ans. (d) semi-permeable membrane? (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. 26
36. A leaf cell of a water plant was placed in a liquid other than pond water. After some time is 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 if it is soon placed in ordinary water for some time. Ans.(a) Plasmolysis (b) Hypertonic solution 37. Fill in the blanks by choosing the correct alternative from those given in brackets. (a) When placed in a more concentrated solution the cell contents will... (shrink/swell up) (b) The pressure by which the... molecules tend to cross the semi-permeable membrane is called osmotic pressure. (salt/water) (c) Active transport is in a direction... to that of diffusion. (opposite/same). 27
Ans.(a) shrink (b) water (c) opposite 38. Given below is the diagramatic representation of the transverse section of a part of a plant. Study it and answer the question that follow : (i) Name the part of the plant that is shown. (ii) Label the parts 1 to 6. (iii) Write the functions of parts 3 and 5. Ans.(i) Cross section of root (ii) 1. Root hair, 2. Epidermis, 3. Cortex, 4. Endodermis, 5. Phloem, 6. Xylem (iii) 3.Build up root pressure for osmosis for transport of water 5.Transport of organic substance 28
39. 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? Ans.(a) Osmotic pressure (b) Osmotic pressure is the minimum pressure that must be exerted to prevent the passage of pure solvent into the solution when the two are separated by a semi-permeable membrane. (c) Rise in the level of solution inside the thistle funnel. (d) Thistle funnel with plain water can be taken. 29