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Answer: The factors affecting the rate of diffusion are (1) the gradient of concentration, (2) permeability of the membrane separating them, (3) temperature and (4) pressure.
Question 2.
Answer: The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria. Function: It allows molecules up to the size of small proteins to pass through.
Question 3.
Answer: There are different proteins in the membrane, which play a major role in both active as well as passive transport. Active transport is carried out by membrane – protein. In protein pumps energy is used to carry substances across the cell membrane. These pumps can transport substances from a low concentration to a high concentration (‘uphill’ transport). 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. These proteins are sensitive to inhibitors that react with protein side chains
Question 4.
Answer: The water potential is greater if the concentration of the water is greater in the system. In pure water system the concentration of water is highest so the kinetic energy or water potential is maximum.
Question 5.
Answer: (a) Diffusion and Osmosis
(b) Transpiration and Evaporation
(c) Osmotic Pressure and Osmotic Potential
(d) Imbibition and Diffusion
(e) Apoplast and Symplast pathways of movement of water in plants.
(f) Guttation and Transpiration.
Question 6.
Answer: The fundamental concept of understanding the movement of water is called water potential. Water molecules possess kinetic energy and the greater the concentration of water greater the kinetic energy. This kinetic energy with which the movement of water takes place is called water potential. It is represented by the Greek symbol Psi or ψ w and is expressed in Pascals (pa). The factors affecting water potential is solute potential and pressure potential. The solute potential is the magnitude of lowering the water potential due to dissolution of solute in pure water it is represented by ψ s and it is always negative. The pressure potential is a pressure greater than the atmospheric pressure applied to pure water it is represented as ψ p andit is usually positive.
Question 7.
Answer: A pressure greater than atmospheric pressure when applied to pure water or a solution, its water potential increases. This pressure is called pressure potential and it is represented as ψ p it is usually positive.
Question 8.
Answer: The mycorrhizal association is a symbiotic association of a fungus with a root system. The fungal filaments 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 that perhaps a root cannot do. The fungus provides minerals and water to the roots, in turn the roots provide sugars and N-containing compounds to the mycorrhizae.
Question 9.
Answer: The positive pressure created by the flow of water, which increases the pressure inside the xylem is called root pressure. This root pressure only provides a modest push in the overall process of water transport. They obviously do not play a major role in water movement up tall trees. The greatest contribution of root pressure may be to re-establish the continuous chains of water molecules in the xylem, which often break under the enormous tensions created by transpiration. Root pressure does not account for the majority of water transport; most plants meet their need by transpiratory pull.
Question 10.
Answer: The circulation of water through the xylem vessels is achieved mainly through the transpiration pull. The driving force for this process is transpiration from the leaves. This is referred to as the cohesion-tension-transpiration pull model of water transport. Factors that influence transpiration are (1) Water is transient in plants. (2) Less than 1 per cent of the water reaching the leaves is used in photosynthesis and plant growth. (3) Most of it is lost through the stomata in the leaves. This water loss is known as transpiration. The transpiration pull helps in the upward intake of water through roots and circulation of water through the xylem vessels to all the parts of the plant.
Question 11.
Answer: The factors that responsible for the ascent of sap are 1.Cohesion – This is a mutual attraction between water molecules. 2.Adhesion – An attraction of water molecules to polar surfaces (such as the surface of tracheary elements) is known as adhesion. 3.Surface Tension – The water molecules are attracted to each other in the liquid phase more than to water in the gas phase.
Question 12.
Answer: The root endodermis has a layer of suberin in this layer which has the ability to actively transport ions only in one direction.
Question 13.
Answer: Xylem transports only inorganic nutrients like water and minerals. The source for water and minerals is soil; from the soil the inorganic nutrients move upward. Since this movement is in only one direction xylem transport is unidirectional. Phloem transports mainly organic substances like food. The source in this transport is understood to be that part of the plant which synthesises the food, i.e., the leaf and sink, the part that needs or stores the food. But, the source and sink may be reversed depending on the season, or the plant’s needs. Sugar stored in roots may be mobilised to become a source of food in the early spring when the buds of trees, act as sink; they need energy for growth and development of the photosynthetic apparatus. Since the source-sink relationship is variable, the direction of movement in the phloem can be upwards or downwards, i.e., bi-directional.
Question 14.
Answer: The mechanism used for the translocation of sugars from source to sink is called the pressure flow hypothesis. As glucose is prepared at the source, which is the leaf, by the processes of photosynthesis it 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. This process of loading at the source produces a hypertonic condition in the phloem. Water in the adjacent xylem moves into the phloem by osmosis. As osmotic pressure builds up the phloem sap will move to areas of lower pressure. At the sink osmotic pressure must be reduced. 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. As sugars are removed, the osmotic pressure decreases and water moves out of the phloem. This mechanism used for the translocation of sugar from source to sink is called pressure flow hypothesis.
Question 15.
Answer: The opening or closing of the stomata by the guard cell is due to a change in the turgidity of the guard cells. The inner wall of each guard cell, towards the pore or stomatal aperture, is thick and elastic. When turgidity increases within the two guard cells flanking each stomatal aperture or pore, the thin outer walls bulge out and force the inner walls into a crescent shape. The opening of the stoma is also aided due to the orientation of the microfibrils in the cell walls of the guard cells. Cellulose microfibrils are oriented radially rather than longitudinally making it easier for the stoma to open. When the guard cells lose turgor, due to water loss (or water stress) the elastic inner walls regain their original shape, the guard cells become flaccid and the stoma closes.
Transport In Plants
Class 11th Biology CBSE Solution
Ncert Questions
- What are the factors affecting the rate of diffusion?
- What are porins? What role do they play in diffusion?
- Describe the role played by protein pumps during active transport in plants.…
- Explain why pure water has the maximum water potential.
- Differentiate between the following: (a) Diffusion and Osmosis(b) Transpiration and…
- Briefly describe water potential. What are the factors affecting it?…
- What happens when a pressure greater than the atmospheric pressure is applied to pure…
- How is the mycorrhizal association helpful in absorption of water and minerals in plants?…
- What role does root pressure play in water movement in plants?
- Describe transpiration pull model of water transport in plants. What are the factors…
- Discuss the factors responsible for ascent of xylem sap in plants.…
- What is the essential role the root endodermis plays during mineral absorption in plants?…
- Explain why xylem transport is unidirectional and phloem transport bi-directional.…
- Explain pressure flow hypothesis of translocation of sugars in plants.…
- What causes the opening and closing of guard cells of stomata duringtranspiration?…
Ncert Questions
Question 1.What are the factors affecting the rate of diffusion?
Answer: The factors affecting the rate of diffusion are (1) the gradient of concentration, (2) permeability of the membrane separating them, (3) temperature and (4) pressure.
Question 2.
What are porins? What role do they play in diffusion?
Answer: The porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria. Function: It allows molecules up to the size of small proteins to pass through.
Question 3.
Describe the role played by protein pumps during active transport in plants.
Answer: There are different proteins in the membrane, which play a major role in both active as well as passive transport. Active transport is carried out by membrane – protein. In protein pumps energy is used to carry substances across the cell membrane. These pumps can transport substances from a low concentration to a high concentration (‘uphill’ transport). 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. These proteins are sensitive to inhibitors that react with protein side chains
Question 4.
Explain why pure water has the maximum water potential.
Answer: The water potential is greater if the concentration of the water is greater in the system. In pure water system the concentration of water is highest so the kinetic energy or water potential is maximum.
Question 5.
Differentiate between the following: (a) Diffusion and Osmosis(b) Transpiration and Evaporation(c) Osmotic Pressure and Osmotic Potential(d) Imbibition and Diffusion(e) Apoplast and Symplast pathways of movement of water in plants.(f) Guttation and Transpiration.
Answer: (a) Diffusion and Osmosis
(b) Transpiration and Evaporation (c) Osmotic Pressure and Osmotic Potential (d) Imbibition and Diffusion (e) Apoplast and Symplast pathways of movement of water in plants. (f) Guttation and Transpiration.
Question 6.
Briefly describe water potential. What are the factors affecting it?
Answer: The fundamental concept of understanding the movement of water is called water potential. Water molecules possess kinetic energy and the greater the concentration of water greater the kinetic energy. This kinetic energy with which the movement of water takes place is called water potential. It is represented by the Greek symbol Psi or ψ w and is expressed in Pascals (pa). The factors affecting water potential is solute potential and pressure potential. The solute potential is the magnitude of lowering the water potential due to dissolution of solute in pure water it is represented by ψ s and it is always negative. The pressure potential is a pressure greater than the atmospheric pressure applied to pure water it is represented as ψ p andit is usually positive.
Question 7.
What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?
Answer: A pressure greater than atmospheric pressure when applied to pure water or a solution, its water potential increases. This pressure is called pressure potential and it is represented as ψ p it is usually positive.
Question 8.
How is the mycorrhizal association helpful in absorption of water and minerals in plants?
Answer: The mycorrhizal association is a symbiotic association of a fungus with a root system. The fungal filaments 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 that perhaps a root cannot do. The fungus provides minerals and water to the roots, in turn the roots provide sugars and N-containing compounds to the mycorrhizae.
Question 9.
What role does root pressure play in water movement in plants?
Answer: The positive pressure created by the flow of water, which increases the pressure inside the xylem is called root pressure. This root pressure only provides a modest push in the overall process of water transport. They obviously do not play a major role in water movement up tall trees. The greatest contribution of root pressure may be to re-establish the continuous chains of water molecules in the xylem, which often break under the enormous tensions created by transpiration. Root pressure does not account for the majority of water transport; most plants meet their need by transpiratory pull.
Question 10.
Describe transpiration pull model of water transport in plants. What are the factors influencing transpiration? How is it useful to plants?
Answer: The circulation of water through the xylem vessels is achieved mainly through the transpiration pull. The driving force for this process is transpiration from the leaves. This is referred to as the cohesion-tension-transpiration pull model of water transport. Factors that influence transpiration are (1) Water is transient in plants. (2) Less than 1 per cent of the water reaching the leaves is used in photosynthesis and plant growth. (3) Most of it is lost through the stomata in the leaves. This water loss is known as transpiration. The transpiration pull helps in the upward intake of water through roots and circulation of water through the xylem vessels to all the parts of the plant.
Question 11.
Discuss the factors responsible for ascent of xylem sap in plants.
Answer: The factors that responsible for the ascent of sap are 1.Cohesion – This is a mutual attraction between water molecules. 2.Adhesion – An attraction of water molecules to polar surfaces (such as the surface of tracheary elements) is known as adhesion. 3.Surface Tension – The water molecules are attracted to each other in the liquid phase more than to water in the gas phase.
Question 12.
What is the essential role the root endodermis plays during mineral absorption in plants?
Answer: The root endodermis has a layer of suberin in this layer which has the ability to actively transport ions only in one direction.
Question 13.
Explain why xylem transport is unidirectional and phloem transport bi-directional.
Answer: Xylem transports only inorganic nutrients like water and minerals. The source for water and minerals is soil; from the soil the inorganic nutrients move upward. Since this movement is in only one direction xylem transport is unidirectional. Phloem transports mainly organic substances like food. The source in this transport is understood to be that part of the plant which synthesises the food, i.e., the leaf and sink, the part that needs or stores the food. But, the source and sink may be reversed depending on the season, or the plant’s needs. Sugar stored in roots may be mobilised to become a source of food in the early spring when the buds of trees, act as sink; they need energy for growth and development of the photosynthetic apparatus. Since the source-sink relationship is variable, the direction of movement in the phloem can be upwards or downwards, i.e., bi-directional.
Question 14.
Explain pressure flow hypothesis of translocation of sugars in plants.
Answer: The mechanism used for the translocation of sugars from source to sink is called the pressure flow hypothesis. As glucose is prepared at the source, which is the leaf, by the processes of photosynthesis it 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. This process of loading at the source produces a hypertonic condition in the phloem. Water in the adjacent xylem moves into the phloem by osmosis. As osmotic pressure builds up the phloem sap will move to areas of lower pressure. At the sink osmotic pressure must be reduced. 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. As sugars are removed, the osmotic pressure decreases and water moves out of the phloem. This mechanism used for the translocation of sugar from source to sink is called pressure flow hypothesis.
Question 15.
What causes the opening and closing of guard cells of stomata duringtranspiration?
Answer: The opening or closing of the stomata by the guard cell is due to a change in the turgidity of the guard cells. The inner wall of each guard cell, towards the pore or stomatal aperture, is thick and elastic. When turgidity increases within the two guard cells flanking each stomatal aperture or pore, the thin outer walls bulge out and force the inner walls into a crescent shape. The opening of the stoma is also aided due to the orientation of the microfibrils in the cell walls of the guard cells. Cellulose microfibrils are oriented radially rather than longitudinally making it easier for the stoma to open. When the guard cells lose turgor, due to water loss (or water stress) the elastic inner walls regain their original shape, the guard cells become flaccid and the stoma closes.