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Class 11 Biology Chapter 11 Transport in Plants
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Transport in Plants
Chapter – 11
VERY SHORT ANSWER TYPE QUESTIONS
Q.1. What part of root is actually involved in the absorption of water from soil ?
Ans :- Root hairs.
Q.2. What is translocation ?
Ans :- The movement of organs nutrients from the region of their synthesis or storage to the region of utilisation is called translocation of solute.
Q.3. What is the direction of transport of water and minerals in plants ?
Ans :- In rooted plant, transport of water and minerals is unidirectional i.e. in one direction.
Q.4. What is diffusion ?
Ans :- It is a phenomenon in which molecules or ions of solid, gas or liquid move from the zone of higher concentration towards zone of lower concentration.
Q.5. Is energy required in process of diffusion ?
Ans :- No, energy is not required in the process of diffusion.
Q.6. What is the only means for gaseous movement in plants ?
Ans :- Diffusion is the only means for gaseous movement in plants.
Q.7. Upon which factors does diffusion rate depends on ?
Ans :- The diffusion rate depends on the size of the substance, on solubility in lipids.
Q.8. Define facilitated diffusion ?
Ans :- A concentration gradient must already be present for molecule to diffuse even if facilitated diffusion.
Q.9. Why is facilitated diffusion is said to be specific ?
Ans :- Because it allows cell to select substances for uptake, hence facilitated diffusion is said specific.
Q.10. What are porins ?
Ans :- Porins are protein that form huge pores in the outer membrane of plastid, mitochondria and some bacteria.
Q.11. What are pumps ?
Ans :- Pumps are proteins that use energy to carry substances across the cell membrane.
Q.12. What is active transport ?
Ans :- When transport of molecules occur from lower concentration to higher concentration to higher concentration by using energy, it is called active transport.
Q.13. Name the components that determine the water potential ?
Ans :- Solute potential and pressure potential are the components that determine the water potential.
Q.14. What type of energy is present in water molecules ?
Ans :- Water molecules possess kinetic energy.
Q.15. What is the water potential of pure water at standard temperature ?
Ans :- Zero.
Q.16. What is solute potential ?
Ans :- The magnitude of lowering of water potential due to the dissolution of a solute is called solute potential.
Q.17. What will the solute potential if the amount of solute molecule is more ?
Ans :- The more the solute molecule, the lower is the solute potential.
Q.18. When can you increase the water potential ?
Ans :- If pressure greater than atmospheric pressure is applied to pure water or solution, its water potential increases.
Q.19. When does a cell become turgid ?
Ans :- When water enters a plant cell due to diffusion, a pressure is built up against the cell wall, making the cell turgid.
Q.20. Define osmosis ?
Ans :- Osmosis is defined as the diffusion of solvent molecules from a zone of higher concentration to its lower concentration through a semipermeable membrane.
Q.21. On what factors osmosis is depends on ?
Ans :- Osmosis depends upon pressure gradient and concentration gradient.
Q.22. What is an isotonic solution ?
Ans :- If the external solution balances the osmotic pressure of the cytoplasm, it is said to be isotonic.
Q.23. What is a hypotonic solution ?
Ans :- If the external solution is more dilute than the cytoplasm, it is hypotonic solution.
Q.24. Define imbibition ?
Ans :- Imbibition is a special type of diffusion when water is absorbed by solids-colloids-causing them to enormously increase in volume.
Q.25. Why are long distance transport systems necessary in plants ?
Ans :- Long distance transport system is necessary because the site of production or absorption and site of storage are too far from each other and diffusion or active transport would not suffice.
Q.26. How are water, minerals and food moved from one place to another ?
Ans :- Water, minerals and food generally move by mass or bulk flow system.
Q.27. What is mass flow ?
Ans :- Mass flow is the movement of substances in bulk or en mass from one point to another as a result of pressure difference between two points.
Q.28. Why do we apply water on the soil not on the leaves ?
Ans :- We apply water to the soil, not on the leaves, because water is absorbed by the roots.
Q.29. What are root hairs ?
Ans :- Root hairs are thin walled slender extensions of root epidermal cells that greatly increase the surface area of absorption.
Q.30. Name the pathways through which water enters deeper in the roots ?
Ans :- Apoplast and symplast pathway.
Q.31. What is apoplast system ?
Ans :- The apoplast is the system of adjacent cell wells that is continuous throughout the plant, except at the casparian strips of the endodermis.
Q.32. What is symplast system ?
Ans :- The symplastic system is the system of interconnected protoplast. During symplastic movements, the water travels through the cells – their cytoplasm.
Q.33. Why is the endodermis impervious to water ?
Ans :- The endodermis is impervious to water because of a bond of suberised matrix called the casparian strip.
Q.34. How does water enters the young roots ?
Ans :- In young roots, water enters into the xylem vessels and / or tracheids.
Q.35. What is mycorrhiza ?
Ans :- A mycorrhiza is a symbiotic association of a fungus with a root system.
Q.36. What percent of water is used in photosynthesis ?
Ans :- Less than 1% of water reaching the leaf is used in photosynthesis.
Q.37. What is transpiration ?
Ans :- Then loss of water from the aerial parts of a plant in the form of water vapour is called transpiration.
Q.38. What is stomata ?
Ans :- The minute pores present at the base of leaf through which exchange of oxygen and carbon-di-oxide takes place is called stomata.
Q.39. What is the immediate cause of opening and closing of stomata ?
Ans :- The immediate cause of opening and closing of stomata is a change in the turgidity of the guard cells.
Q.40. On what factors does transpiration depends ?
Ans :- Transpiration depends on temperature, light, humidity and wind speed.
Q.41. In terms of fixing carbon which plants are more efficient C3 or C4 ?
Ans :- C4 plants are twice as efficient as C3 plants in terms of fixing carbon.
Q.42. Name the elements which are most readily mobilised ?
Ans :- Ans :- The elements which are most readily mobilised are phosphorous, sulphur and nitrogen.
Q.43. What is the direction of movement in phloem ?
Ans :- The direction of movement in phloem is bi-directional.
Q.44. What is pressure flow hypothesis ?
Ans :- The mechanism used for the translocation of sugars from source to sink is called pressure flow hypothesis.
Q.45. Name the experiment used to identify the tissues through which food is transported ?
Ans :- Girdling experiment.
SHORT ANSWER TYPE QUESTIONS
Q.1. Write a note on diffusion ?
Ans :- In diffusion, molecules move in a random fashion, the net result being substances moving form region of higher concentration to the region of lower concentration. Diffusion is very important to plants since it is the only means for gaseous movement within the plant body.
The rate of diffusion is affected by the gradient of concentration, permeability of the membrane temperature and pressure.
Q.2. What are porins ? What role of they play in diffusion ?
Ans :- The porins are proteins that form huge pres in the outer membranes of the plastid, mitochondria and some bacteria allowing molecules up to the size of small proteins to pass through.
The porins form channels in the membrane for molecules to pass through by the process of diffusion.
Q.3. Describe the role played by protein pumps during active transport in plants.
Ans :- Protein pump use energy to carry substances across the cell membrane. These pumps transport substances from a low concentration to a high concentration. Transport rate reaches a maximum when all the protein transporters are being used or are saturated. The carrier protein is very specific in what it carries across the membrane.
Q.4. Water is needed for all physiological activities Justify ?
Ans :- Water plays a very important role in all living organisms. It provides a medium in which most substances are dissolved. The protoplasm of the cell is nothing but water in which different molecules are dissolved. The distribution of water within a plant varies woody parts have very little water, soft part mostly contain water.
Q.5. Describe briefly water potential ?
Ans :- Water molecules possesses kinetic energy, this energy is referred as water in a system, greater is its kinetic energy or water potential. Hence, pure water will have the greatest water potential. So all solutions have a lower water potential than pure water.
By convention, the water potential of pure water at standard temperature, which is not under pressure is taken to be zero.
Q.6. What is solute potential ?
Ans :- If some solute is dissolved in pure water, the solution has fewer free water and the concentration of water decreases, reducing its water potential. Hence, all solutions have a lower water potential than pure water, the magnitude of this lowering due to the dissolution of a solute is called solute potential or Ys • Ys is always negative the more the solute molecule, the lower is the solute potential.
Q.7. What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution ?
Ans :- If a pressure greater than atmospheric pressure is applied to pure water or a solution, its water potential increase. Pressure can build up in a plant system when water enters a plant cell due to diffusion causing a pressure built up against the cell wall, it makes the cell turgid.
Q.8. Distinguish between diffusion and osmosis.
Ans :- Diffusion :-
(i) It is a phenomenon is which molecules or ions move from zone of higher to lower concentration zone.
(ii) All diffusion are not osmosis.
(iii) Diffusion takes place between different types of solvent.
(iv) Diffusion takes place between gas and gas, liquid and gas, solid and gas.
(i) It is an act of diffusion of solvent molecules from the area of higher concentration towards area of lower concentration when separated by a semipermeable membranes.
(ii) Osmosis is always diffusion.
(iii) Osmosis takes place between similar type of solvent.
(iv) Osmosis takes place between liquid and liquid only.
Q.9. State the significance of osmosis in plant life ?
Ans :- Significance of osmosis in plant life :-
(i) Osmosis helps in the absorption of water by plants.
(ii) Cell to cell movement of water takes place through osmosis.
(iii) The turgidity of the cell are maintained by osmosis which provide turgidity to the plant part.
(iv) It is responsible for maintaining water balance of the plant.
(v) Opening and closing of stomata, flower are all due to osmosis.
Q.10. Explain the process of plasmolysis ?
Ans :- The contraction and separation of protoplasm from the cell walls due to exosmosis is called plasmolysis. Plasmolysis occurs when water moves out of the cell and the cell membrane of a plant cell shrinks away from its cell wall. This occurs when the cell is placed in a solution that is hypertonic to the protoplasm. Water moves out it is first lost from the cytoplasm and then from the vacuole. The movement of water occurred across the membrane moving from an area of high water potential to an area of lower water potential.
Q.11. What a note on imbibition ?
Ans :- Imbibition is a special type of diffusion when water is absorbed by solid colloids causing them to increase in volume. e.g. absorption of water by seeds and dry wood.
Imbibition is also diffusion since water movement is along a concentration gradient, the seeds and other such material have almost no water hence they absorb water easily water potential gradient between the absorbent and the liquid imbibed is essential for imbibition. For any substance to imbibe any liquid, affinity between the adsorbent and the liquid is a prerequisite.
Q.12. With the help of well-labelled diagram, show the process of plasmolysis.
Q.13. Mention the significance of transpiration ?
Ans :- Significance of transpiration :-
a) It creates a suction force for absent of sap and help in absorption of water and minerals.
b) Transpiration helps to absorb excess of water to neet the mineral requirement of plants.
c) Keeps the leaf surface cool.
Q.14. Differentiate between transpiration and evaporation.
Ans :- Transpiration :-
i) Loss of water from the aerial parts of plants in the form of water vapour is called transpiration.
ii) Transpiration keeps the leaf surface cool.
iii) It is a physiological process.
iv) Excessive transpiration causes wilting.
i) Loss of water in the form of water vapour from any surface containing any surface containing water is called evaporation.
ii) Evaporations causes dryness.
iii) It is a physical process.
iv) Excessive evaporation causes rapid dryness.
Q.15. Differentiate between transpiration and guttation.
Ans :- Transpiration :-
i) The loss of water from the aerial parts of a plant in the form of water vapour is called transpiration.
ii) It occurs through stomata.
iii) Water is lost in the form of water vapour.
iv) Occurs during day-time.
i) The loss of water from the tip and margin of the leaf in the from of water droplet is called guttation.
ii) It occurs through hydathode .
iii) Water is lost in the form of water droplets.
iv) Occurs during night.
Q.16. How is water absorbed in plants ?
Ans :- Several theories have been forwarded by scientist to explain the process of upward movement of water.
(i) Root pressure theory :- A pressure is developed by the cortical cells of the root farce water into stem of the root (root pressure).
(ii) Imbibition theory :- Imbibition of water through the walls of xylem is responsible for ascent of sap.
(iii) Capillary theory :- Xylem vessels act as capillary tube and water moves up due to capillary action.
(iv) Transpiration pull :- Cohesive and adhesive property of water molecule form an unbroken continuous. Water column in the xylem. Transpiration current creates a suction force at the top of the column.
Q.17. How is mycorrhizal association helpful in absorption of water and minerals in plants ?
Ans :- A mycorrhiza is a symbiotic association of a fungus with the root system. The fungal filament form a network around the young root or they penetrate the root cells. The hyphae have a very large surface area that absorb mineral ions and water from the soil from a much larger volume of soil. The fungus provides minerals and water to the roots. In turn the root provide sugar and N – containing compounds to the mycorrhizae. e.g. pinus seed cannot germinate without the presence of mycorrhiza.
Q.18. Root pressure is responsible for pushing up the water. Justify with example.
Ans :- Take a small soft stemmed plant. On a day when there is plenty of atmospheric moisture cut the stem near the base with sharp blade. Drops of solution ooze out of the cut stem this comes out due to positive root pressure. Effects of root pressure is also observable at night and early in the morning when evaporation is low, and excess of water collects in the form of droplets around special opening of veins near the tip of grass blade and leaves of herbaceous parts. Such water loss in liquid phase is known as guttation.
The greatest contribution of root pressure is to re-establish the continuous chain of water molecules in xylem which often break under the enormous tension created by transpiration.
LONG ANSWER TYPE QUESTIONS
Q.1. Describe transpiration pull model of water transport in plants. What are the factors influencing transportation ? How is it useful to plants ?
Ans :- Due to transpiration the mesophyll cells of leaves continuously lose water from the leaf surface for which they absorb water continuously from xylem of petiole. Due to this, a tension is created in the xylem of petiole which is extended downward to the xylem of roots and the water is pulled upward in the form of continuous unbroken water column to reach up to the top of plant.
The cohesion of water molecule and adhesion of water molecules and the walls of xylem vessels form a continuous unbreakable water column from root to the leaves. Due to transpiration, the mesophyll cells are filled up by water from the xylem vessels. Thus a suction force is created which continuously pull the water column upward.
Q.2. Explain the mechanism of opening and closing of stomata with a well-labelled diagram.
Ans :- The opening and closing of stomata is brought about by change in turgidity of the guard cells which is mainly influenced by photosynthesis.
Several hypothesis has been proposed from time to describe of opening and closing of stomata. However, it is established that following sequence of events take place during opening and closing of stomata.
Opening of stomata :-
During day time photosynthesis takes place. Co2 is consumed during photosynthesis due to which the concentration of Co2 in the intercellular space decreases. This results in increase of pH level. Increase in pH favours hydrolysis of starch into glucose. As a result the concentration of the cell sap inside the guard cells increases. The wall of the guard cells being permeable to water, water moves into it and the guard cells become turgid. When the guard cells become turgid, a pore in formed in between them and the stomata in called open.
Closing of stomata :-
During dark photosynthesis does not occur as a result of which Co2 accumulates in the intercellular space. As a result pH of the guard cells decreases. Decrease in pH favours conversion of glucose into starch. Starch being insoluble decreases the conc of the cell sap of the guard cells. Therefore, water moves in to the neighbouring cells and Guard cells become flaccid and closes the stomata pore.
Q.3. Explain the translocation of sugar in plant.
Ans :- The translocation of sugar can be explained by mass Flow or pressure flow hypothesis. Glucose prepared at the source is converted to sucrose. The sugar is then moved in the form of sucrose into the companion cells and then into the living phloem sieve tube cells by active transport. Water in the adjacent xylem moves into phloem by osmosis. As osmotic pressure builds up the phloem sap will move to areas of lower pressure. Again active transport is necessary to move the sucrose out of the phloem sap and into the cells which will use the sugar converting it into energy, starch or cellulose. When sugar is removed, the osmotic pressure decreases and water moves out of the phloem.
So, the movement of sugar in the phloem begins at the source, where sugars are loaded into the sieve tube Loading of the phloem sets up a water potential gradient that facilitates the mass movement in the phloem.
Q.4. Explain why xylem transport is unidirectional and phloem transport bidirectional.
Ans :- As it is will known, source is a part of the plant which synthesises the food. i.e. the leaf, and sink is the part that needs or stores the food. But, the source and sink may be reversed, depending on the plants need, depending on the season. Sugar stored in the roots may be mobilised to become a source of food in the early spring. When the bud of the tree act as sink, because they need energy for growth and development of the photosynthetic apparatus. Since the source sink relationship changes, the direction of movement in the phloem also changes ie upward or downwards ie bi-directional whereas in xylem, the movement is always unidirectional ie upwards because water and mineral are absorbed only through roots and the flow is towards one direction. Hence, xylem transport is unidirectional and phloem transport is bi-directional.
Q.5. Explain the mechanism of translocation of mineral ions ?
Ans :- lons are first taken up by xylem then transported to all parts of the plant through transpiration stream.
The chief sink for mineral elements are the growing regions of the plant, such as apical and lateral meristem, young leaves, developing flowers, fruits and seeds, and the storage organs. The mineral ions are unloaded at the vein-ending through diffusion and active uptake by these cells. When a leaf is on the verge of dying, the mineral content are moved to younger leaves. Similarly before leaf fall in deciduous plants, minerals are removed to other parts.
Elements most readily mobilised are phosphorus, sulphur, nitrogen and potassium. Calcium is not remobilized.
Q.6. a) What are the factors affecting ascent of sap ?
b) What are the factors affecting absorptive by roots ?
Ans :- a) The factors affecting ascent of sap are as follows :-
(i) Water absorption Ascent of sap depends on the amount of water absorbed by the roots. The absorption depends on factors like availability of water, temperature, concentration of soil solution etc.
(ii) Transpiration :- Transportation is responsible for creating a suction force in the xylem vessel. This in turn pulls up the water column formed in the vessel. More the rate of transpiration more is the movement of water upward. Transpiration again depends on factory like number and distribution of stomata, wind, humidity, availability of water in the soil, temperature of air etc.
b) The factors affecting rate of absorption are :-
(i) Soil water :- Availability of water in the soil directly influences the rate of absorption by the root.
(ii) Transpiration :- More the rate of transpiration, more is the rate of absorption. Transpiration directly influences the passive absorption process. Because it creates a suction force in the xylem vessel which extends upto root hairs.
(iii) Soil solution :- If the soil solution becomes more concentrated due to presence of soluble minerals, the rate of absorption become slow. This is because the OP of soil solution become more than the OP of the cell sap.
(iv) Root growth :- Absorption of water also depends upon the growth of root system. Root which can penetrate more deeper can absorbs more water.
Q.7. Explain the mechanism of water movement in the leaf with the help of diagram ?
Ans :- The process of photosynthesis requires water. The system of xylem vessels from the root to the leaf vein can supply the needed water. As water evaporates through the stomata, since the thin film of water over the cell is continuous, it results in the placed end to end having perforation at the point of contact, thus forming a continuous column. The cohesion among water molecules and adhesion between water molecules and wall of the xylem vessels forms an unbreakable continuous column from root to the leaves.
As the xylem is filled up with and unbroken column of water extending from roots the leaves, a tension or pull if generated at the top of the column due to loss of water by transpiration, suction force develops which pulls the column continuously upward.
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