NCERT Solutions for Class 11 Biology Chapter 11
Transport in Plants Class 11
Chapter 11 Transport in Plants Exercise Solutions
Exercise : Solutions of Questions on Page Number : 193
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:
(b) Transpiration and Evaporation
(d) Imbibition and Diffusion
(f) Guttation and Transpiration.
(a) Diffusion and osmosis
Diffusion |
Osmosis |
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1. |
Diffusion is the passive movement of particles, ions, and molecules along the concentration gradient. |
1. |
Osmosis is the process in which the diffusion of a solvent (water) occurs across a semi-permeable membrane. |
2. |
It can occur in solids, liquids, and gases. |
2. |
It occurs in the liquid medium. |
3. |
It does not require a semi-permeable membrane. |
3. |
It requires a semi-permeable membrane. |
(b) Transpiration and evaporation
Transpiration |
Evaporation |
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1. |
It occurs in plants. |
1. |
It occurs from any free surface and involves living and non-living surfaces. |
2. |
It is a physiological process. |
2. |
It is a physical process. |
3. |
It occurs mainly through the stomatal pores on plant leaves. |
3. |
It is occurs through any free surface. |
4. |
It is controlled by environmental factors as well as physiological factors of plants such as root-shoot ratio and number of stomata. |
4. |
It is entirely driven by environmental factors. |
(c) Osmotic pressure and osmotic potential
Osmotic pressure |
Osmotic potential |
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1. |
It is expressed in bars with a positive sign. |
1. |
It is expressed in bars with a negative sign. |
2. |
It is a positive pressure. |
2. |
It is a negative pressure. |
3. |
Its value increases with an increase in the concentration of solute particles. |
3. |
Its value decreases with an increase in the concentration of solute particles. |
(d) Imbibition and diffusion
Imbibition |
Diffusion |
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1. |
Imbibition is a special type of diffusion. In this process, water is absorbed by solids and colloids, causing an enormous increase in volume. |
1. |
Diffusion is the passive movement of particles, ions, and molecules along the concentration gradient. |
2. |
It usually involves water. |
2. |
It involves solids, liquids, and gases. |
(e) Apoplast and symplast pathways of movement of water in plants
Apoplast pathway |
Symplast pathway |
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1. |
The apoplast pathway involves the movement of water through the adjacent cell walls of the epidermis and cortex. The movement of water is restricted at the casparian strips of the root endodermis. |
1. |
The symplast pathway involves the movement of water through the interconnected protoplasts of the epidermis, cortex, endodermis, and root pericycle. |
2. |
It is a faster process of water movement and water moves through mass flow. |
2. |
It is a slower process of water movement. |
(f) Guttation and transpiration
Guttation |
Transpiration |
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1. |
It occurs usually at night. |
1. |
It occurs usually during the day. |
2. |
Water is lost from the leaves in the form of liquid droplets. |
2. |
Water is lost from the leaves in the form of water vapour. |
3. |
It occurs through the vein endings of leaves. |
3. |
It occurs through the stomata. |
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4. |
It is an uncontrolled process. |
4. |
It is a controlled process. |
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Briefly describe water potential. What are the factors affecting it?
Water potential quantifies the tendency of water to move from one part to the other during various cellular processes such as diffusion, osmosis, etc. It is denoted by the Greek letter Psi or Ψ and is expressed in Pascals (Pa). The water potential of pure water is always taken as zero at standard temperature and pressure.
Water potential (Ψw) is expressed as the sum of solute potential (Ψs) and pressure potential (Ψp). Ψw = Ψs + Ψp
When some solute is dissolved in water, the water potential of pure water decreases. This is termed as solute potential (Ψs), which is always negative. For a solution at atmospheric pressure, Ψw = Ψs.
What happens when a pressure greater than the atmospheric pressure is applied to pure water or a solution?
(a) With the help of well-labelled diagrams, describe the process of plasmolysis in plants, giving appropriate examples.
Answer :
(a) Plasmolysis can be defined as the shrinkage of the cytoplasm of a plant cell, away from its cell wall and toward the centre. It occurs because of the movement of water from the intracellular space to the outer-cellular space. This happens when the plant cell is placed in a hypertonic solution (i.e., a solution having more solute concentration than the cell cytoplasm). This causes the water to move out of the cell and toward the solution. The cytoplasm of the cell
shrinks and the cell is said to be plasmolysed. This process can be observed in an onion peel kept in a highly concentrated salt solution.
(b)
How is the mycorrhizal association helpful in absorption of water and minerals in plants?
Mycorrhiza is a symbiotic association of fungi with the root systems of some plants. The fungal hyphae either form a dense network around the young roots or they penetrate the cells of the roots. The large surface area of the fungal hyphae is helpful in increasing the absorption of water and minerals from the soil. In return, they get sugar and nitrogenous compounds from the host plants. The mycorrhizal association is obligate in some plants. For
What role does root pressure play in water movement in plants?
Root pressure is the positive pressure that develops in the roots of plants by the active absorption of nutrients from the soil. When the nutrients are actively absorbed by root hairs, water (along with minerals) increases the pressure in the xylem. This pressure pushes the water up to small heights. Root pressure can be observed experimentally by cutting the stem of a well-watered plant on a humid day. When the stem is cut, the solution oozes from the cut end.
Root pressure is also linked to the phenomenon of guttation, i.e., the loss of water in the form of liquid droplets from the vein endings of certain herbaceous plants.
Describe transpiration pull model of water transport in plants. What are the factors influencing transpiration? How is it useful to plants?
In tall trees, water rises with the help of the transpirational pull generated by transpiration or loss of water from the stomatal pores of leaves. This is called the cohesion-tension model of water transport. During daytime, the water lost through transpiration (by the leaves to the surroundings) causes the guard cells and other epidermal cells to become flaccid. They in turn take water from the xylem. This creates a negative pressure or tension in the xylem vessels, from the surfaces of the leaves to the tips of the roots, through the stem. As a result, the water present in the xylem is pulled as a single column from the stem. The cohesion and adhesion forces of the water molecules and the cell walls of the xylem vessels prevent the water column from splitting.
Discuss the factors responsible for ascent of xylem sap in plants.
Transpirational pull is responsible for the ascent of water in the xylem. This ascent of water is dependent on the following physical factors:
· Cohesion - Mutual attraction between water molecules
· Surface tension - Responsible for the greater attraction between water molecules in liquid phase than in gaseous phase
· Adhesion - Attraction of water molecules to polar surfaces
· Capillarity -Ability of water to rise in thin tubes
What essential role does the root endodermis play during mineral absorption in plants?
Explain why xylem transport is unidirectional and phloem transport bi-directional.
During the growth of a plant, its leaves act as the source of food as they carry out photosynthesis. The phloem conducts the food from the source to the sink (the part of the plant requiring or storing food). During spring, this process is reversed as the food stored in the sink is mobilised toward the growing buds of the plant, through the phloem. Thus, the movement of food in the phloem is bidirectional (i.e., upward and downward).
Explain pressure flow hypothesis of translocation of sugars in plants.
What causes the opening and closing of guard cells of stomata during transpiration?
The tiny pores present on the surfaces of leaves, called stomata, help in the exchange of gases. Each stoma consists of bean-shaped or dumbbell-shaped guard cells. The epidermal cells surrounding the guard cells are modified to form subsidiary cells. The opening and closing of the guard cells is caused by a change in their turgidity. The inner walls of the guard cells are thick and elastic, while the outer walls are thin. The numerous microfibrils present in the guard cells facilitate the opening and closing of the guard cells.
At the time of the opening of the stomata, the turgidity of the guard cells increases. As a result, the outer walls bulge and the inner walls become crescent-shaped. The stomatal opening is facilitated by the radial arrangement of the microfibrils.
At the time of the closing of the stomata, the guard cells lose their turgidity, the outer and inner walls retain their original shapes, and the microfibrils get arranged longitudinally.