Transport of mineral ions, water and sugars in plants is a complex process that sometimes requires energy. Here is a collection of all important questions related to direction, energy requirements and the distance of translocation between the plant parts that are crucial for NEET 2023.
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- Guttation is the process of exudation of water and minerals from plants through
(a) stomata
(b) hydathodes
(c) lenticel
(d) none of these
Answer: (b)
Explanation: Guttation is exudation or loss of xylem sap, i.e water and minerals from an uninjured leaf through the openings of structures known as hydathodes. Hydathodes are present at the terminal ends of the veins at the margins and apices of leaves. Root pressure is an important factor in guttation.
Refer: Difference Between Lenticels And Hydathodes
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- Pick out the wrong statement.
I. Guard cells expand on the inner side of the stoma, resulting in kidney-shaped cells.
II. The shape taken by the guard cells is independent of the cellulose microfibrils.
III. The unequal stretching of the guard cells allows the pore to form between the two guard cells.
(a) I and II
(b) Only II
(c) I and III
(d) I, II and III
Answer: (a)
Explanation: Guard cells expand on the outer edges of stoma, but not on the inner side. The shape taken by the guard cells is dependent on cellulose microfibrils that fan out radially from the pore, somewhat similar to radial tires. The cell walls surrounding the stomata opening are thickened, preventing that side of the guard cell from expanding.
Therefore, when pressure in the cell increases due to water entry, the guard cell does not widen, but rather the outer edge stretches disproportionately more than the inner edge. This unequal stretching allows the pore to form in between the two guard cells.
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- Casparian strips are present in the ______ of roots and are made of ________.
(a) endodermis, chitin
(b) endodermis, suberin
(c) pericycle, suberin
(d) epiblema, suberin
Answer: (b)
Explanation: The radial and tangential walls of endodermis have a deposition of suberin. These are called casparian strips. The suberin deposition is impervious to water.
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- Root pressure develops due to
(a) passive absorption
(b) active absorption
(c) increase in transpiration
(d) none of these
Answer: (b)
Explanation: Root pressure develops due to active absorption. Active absorption is the movement of ions against the concentration gradient utilising metabolic energy.
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- Which of the following criteria does not pertain to facilitated transport?
(a) Transport saturation
(b) Uphill transport
(c) Requirement of special membrane proteins
(d) High selectivity
Answer: (b)
Explanation: Facilitated transport or facilitated diffusion is the movement of molecules or ions across a biological membrane through the membrane proteins without expenditure of energy. It is downhill transport of molecules with the help of membrane proteins. Transport saturation can occur when all the proteins are occupied with molecules, also the proteins are highly selective in nature.
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- Choose the correct statement.
(a) The rate of diffusion increases with increasing size of molecules.
(b) Substances that have hydrophilic moiety can easily pass through the plasma membrane.
(c) Diffusion is an example of downhill transport.
(d) The transport of substances with the help of membrane proteins always require ATP.
Answer: (c)
Explanation: In diffusion, the movement of molecules occurs along the concentration gradient, that is from higher to lower concentration (downhill transport) until a level of equilibrium is reached. In simple diffusion, no transport proteins are required whereas facilitated diffusion takes place with a special set of membranous proteins where ATP is not required. The rate of diffusion is directly proportional to the membrane surface area, temperature, pressure, concentration gradient, and inversely proportional to the square root of density and size of molecules.
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- The movement of a single molecule across a membrane by carrier proteins is called:
(a) Symport
(b) Uniport
(c) Antiport
(d) All of these
Answer: (b)
Explanation: Uniport is the transfer of a specific molecule across the membrane in one direction. Symport is unidirectional coupled diffusion of two molecules. Lastly, antiport is bidirectional coupled diffusion of two molecules in opposite directions.
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- Which of the following is an example of imbibition?
(a) Swelling of wood during the rainy season.
(b) Shrinkage of the protoplasm of cells when placed in a hypertonic solution.
(c) Sodium-potassium pump.
(d) Exchange of gases through stomata.
Answer: (a)
Explanation: The swelling of wood during the rainy season is due to adsorption of moisture. Adsorption (surface attraction) of water by hydrophilic substances is called imbibition. Shrinkage of protoplasm of cells when placed in a hypertonic solution is called plasmolysis. Sodium-potassium pump is an example of active transport. Exchange of gases through stomata is by diffusion.
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- Which of the following is not an example for short distance transport?
(a) Diffusion
(b) Facilitated diffusion
(c) Translocation
(d) Active transport
Answer: (c)
Explanation: Simple diffusion, facilitated diffusion and active transport are means of short distance transport in plants. In short distance transport, the movement is within the cell, across the membranes and from cell to cell.
Translocation is a movement of substances in bulk over long distances through the vascular tissue. For example, the solutes that are synthesised in the chlorophyllous regions are transported to the various parts of the plant.
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- Osmotic potential of pure water under standard pressure and temperature is
(a) one
(b) zero
(c) less than zero
(d) between zero and one
Answer: (b)
Explanation: The magnitude of decrease of water potential with respect to that of pure water due to the dissolution of a solute is called osmotic potential or solute potential. Pure water contains no solutes and thus, there is no decrease in water potential. Therefore, the osmotic potential of pure water is zero.
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- Solute potential is
(a) decrease in magnitude of Ψw due to the dissolution of solute
(b) magnitude of change in the Ψw due to the mechanical pressure.
(c) component of Ψw contributed by the application of pressure by the solution
(d) pressure exerted by the protoplast due to the entry of water into the cell
Answer: (a) Ψw=Ψs + Ψp
Explanation:
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- Water Potential: The measure of concentration and free energy of water in a system per unit volume is called water potential (Ψw). It can be zero or negative.
- Solute Potential: The magnitude of decrease of water potential due to the dissolution of a solute is called solute potential (Ψs). It is always negative.
- Pressure Potential: The magnitude of change of water potential due to the mechanical pressure is called pressure potential (Ψp). It can be positive or negative.
- If a cell swells after being placed in a solution, the solution is
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(a) hypertonic
(b) hypotonic
(c) isotonic
(d) none of the above
Answer: (b)
Explanation: The cell swells due to the movement of solvent into the cell from the solution, this is called endosmosis. If the concentration of solute is low in the solution when compared to the cell sap, such a solution is called hypotonic.
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- When a cell is placed in 0.5M concentrated sugar solution, there is no change in its volume. But the same cell is placed in 0.5M concentrated solution of sodium chloride there will be
(a) decrease in volume
(b) increase in volume
(c) no change in volume
(d) none of the above
Answer: (a)
Explanation: The cell placed in a sodium chloride solution will undergo exosmosis and this results in the decrease in volume of the cell.
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- Transpiration and root pressure cause water to rise in plants by
(a) pushing it upward
(b) pushing and pulling it, respectively
(c) pulling it upward
(d) pulling and pushing it, respectively
Answer: (d)
Explanation: Transpiration is the loss of water from the aerial parts of the plants mainly through the stomata. This water loss creates a tension and pulls the water column up. This is called transpirational pull, a major force responsible for the ascent of sap. The positive hydrostatic pressure developed in the xylem of the root due to the entry of water is called root pressure. Root pressure pushes the water column up and causes ascent of sap.
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- The conduction of water from root hair to xylem of root is
(a) symplastic
(b) apoplastic
(c) both apoplastic and symplastic
(d) none of these
Answer: (c)
Explanation: Apoplast is the space outside the plasma membrane within which the materials can diffuse freely. Symplast, on the other hand, is the inner side of the plasma membrane through which low-weight materials can diffuse freely. The transport of water from root hair to root xylem makes use of both symplastic and apoplastic pathways.
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- Adhesion is one of the physical properties of water that refers to
(a) mutual attraction between water molecules
(b) attraction of water molecules to other substances
(c) strong affinity of water molecules in the liquid phase
(d) repulsion between water molecules
Answer: (b)
Explanation: Adhesion is the attraction of water molecules to other polar substances. Cohesion is the mutual attraction between water molecules. Water has high surface tension due to hydrogen bonding in water molecules, and in the liquid phase, there is greater attraction between water molecules than in the gaseous phase.
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- Ascent of sap through xylem due to transpirational pull depends upon
(a) mutual attraction between water molecules
(b) attraction of water molecules to other polar molecules
(c) surface tension
(d) all of these
Answer: (d)
Explanation: The major force responsible for the ascent of sap is transpirational pull. Cohesion-tension transpiration pull theory was put forward by Dixon and Jolly to explain the ascent of sap. The theory states that the upward movement of water driven by transpiration depends on certain physical properties of water like: cohesion, adhesion and surface tension.
Refer: Difference Between Ascent Of Sap And Translocation
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- Statement 1: The translocation of food is always from source to sink.
Statement 2: Translocation in phloem is bidirectional
(a) Statement 1 and statement 2 are correct
(b) Statement 1 and statement 2 are wrong
(c) Statement 1 is correct and statement 2 is wrong
(d) Statement 1 is wrong and statement 2 is correct
Answer: (a)
Explanation: In favourable conditions, the leaves are the source of food and roots are the sink to which food is translocated. But when unfavourable conditions arise, the roots become the source of food and leaves become the sink to which food is translocated. Hence, translocation of food is always from the source to the sink and it is bidirectional in nature.
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- Unidirectional movement of substance occurs through
(a) xylem
(b) xylem and phloem
(c) phloem
(d) none of these
Answer: (a)
Explanation: The plants absorb water and minerals from the soil through the roots. These substances enter the xylem of the root and are conducted to different parts of the plant. Hence the movement of substances in xylem is unidirectional from roots to stems and leaves.
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- Consider the following statements regarding the fate of a ring girdled plant and choose the most appropriate answer.
(a) Both the shoot and root of a ring girdled plant die together
(b) The shoot of the plant dies first followed by the root
(c) The root of the plant dies first followed by the shoot
(d) Neither the root nor the shoot will die
Answer: (c)
Explanation: During the girdling experiment, a portion of the bark was removed. It was observed that the portion of the bark above the extracted ring was swollen. The swelling was due to accumulation of sugar due to lack of downward movement of sugar in the absence of phloem. Although the bark above the ring looked healthy, the tissue below the ring stopped growing and began to shrivel. The roots eventually died first due to lack of sugar followed by the shoot.
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