Assertion Reason Questions for Biology Chapter 11 Transport in Plants

Directions: In the following questions, a statement of assertion is followed by a statement of reason.
Mark the correct choice as:
(a) If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) If Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.

Q.1. Assertion : No energy expenditure is observed in the process of diffusion.
Reason : Diffusion occurs along the concentration gradient, i.e., from a region of higher concentration to a region of lower concentration.

Answer Answer: (b) Process diffusion can be defined more meaningfully as the net transport of solute or solvent from a region of higher chemical potential or higher concentration to lower chemical potential or lower concentration area where ion, atoms or molecules moves randomly without the involvement of energy.

Q.2. Assertion : b -cyanine does not diffuse to the outside of the cell through washed beet root slices when kept in cold water.
Reason : Membrane is not permeable to pigment b -cyanine.

Answer Answer: (b) Process of diffusion can be summarised easily as the movement of uncharged ions, atoms or molecules through a biological membrane depends upon the permeability of biological membrane. Depending upon the permeability, the membrane may be semi permeable or differentially permeable, selectively permeable and impermeable. Here, the membrane is impermeable to pigment betacynin. That is why, pigment betacynin is unable to colourise the water.

Q.3. Assertion: A special type of diffusion of water through a semipermeable membrane is known as osmosis.
Reason: The net direction and rate of osmosis only depends on the pressure gradient.

Answer Answer: (c) Osmosis is diffusion of water from its pure state (or dilute solution) into a solution (or stronger solution) when the two are separated by a semi-permeable membrane. The direction and rate of osmosis depend upon the sum of two forces, pressure gradient (gradient of ψw) and concentration gradient (gradient of ψs). The difference in the water potentials of solutions separated by a semipermeable membrane determine the net force or gradient.

Q.4. Assertion: In symport transport both molecules cross the membrane at the same time in the same direction.
Reason: In antiport transport, both molecules move in opposite direction.

Answer Answer: (b) Some carrier proteins allow transport only if two types of molecules move together. This is known as co-transport. Symport and antiport are two types of co-transport. Symport allows both the molecules to move in same direction and antiport allows both the molecules to move in opposite direction.

Q.5. Assertion: In plant cells to counteract the increase in turgour pressure, the cell wall produces an equal and opposite pressure, i.e., wall pressure.
Reason: When plant cells undergo endosmosis, they swell but do not burst.

Answer Answer: (a) The pressure which develops in the confined part of an osmotic system due to osmotic entry of water into it is called turgor pressure. It is also called hydrostatic pressure or pressure potential. Wall pressure is the force exerted by the cell wall over the protoplast. Normally wall pressure is equal and opposite to turgor pressure except when the cell becomes flaccid.

Q.6. Assertion: If the process is in the order, limiting→ incipient → evident, plasmolysis will be severe.
Reason: Plasmolysis is exosmosis.

Answer Answer: (b) Under the influence of a hypertonic solution, shrinkage of the protoplast of a cell from its cell wall causes exosmosis or withdrawl of water from the central vacuole of cell. Simultaneously, the pressure on the wall is reduced and the elastic wall contracts causing a reduction in cell size. This first stage of plasmolysis is known as limiting plasmolysis. Initially the protoplast withdraws itself from the corners. This stage is known as incipient plasmolysis. Protoplast shrinks further and withdraws from the cell wall except at one or a few points due to continued exosmosis. It is known as evident plasmolysis. In such case, cells cannot survive.

Q.7. Assertion: In hypertonic solution, a plant cell shrinks.
Reason: Due to plasmolysis in hypertonic solution, water moves out of the cells.

Answer Answer: (a) With regard to water movement the behaviour of the plant cells or tissues depends on the surrounding solution. In a hypertonic solution, when the cell or tissue is placed water moves out; it is first lost from the cytoplasm and then from the vacuole. When water is drawn out of the cell through diffusion into the extracellular (outside cell) fluid, it causes the protoplast to shrink away from the walls. The cell is said to be plasmolysed.

Q.8. Assertion: Turgor pressure is the positive pressure that develops in the plant cell due to entry of water.
Reason: During growth of cells, the turgor pressure is responsible for enlargement and extension.

Answer Answer: (b) Due to entry of water into it, a positive pressure develops in a plant cell or system. This positive hydrostatic pressure is also known as turgor pressure. Turgor pressure keeps the cells and their organelles stretched, this is essential for proper functioning of a cell. It gives support to non-woody tissues like parenchyma. During growth, turgor pressure is essential for cell enlargement.

Q.9. Assertion: Osmotic pressure is equivalent numerically to the osmotic potential.
Reason: Osmotic pressure is the negative pressure applied, while osmotic potential is positive.

Answer Answer: (c)

Q.10. Assertion : Pure water has maximum water potential.
Reason : The osmotic potential is zero in pure water.

Answer Answer: (c) Water potential is the potential energy of water relative to pure water in reference conditions. Pure water has maximum water potential, whereas, addition of solutes to water lowers the water potential. Osmosis is a special type of diffusion in which water diffuses from its pure state i.e., higher water potential to concentrated solution i.e., lower chemical potential through a semipermeable membrane. Since pure water has no difference in chemical potential, it has zero osmotic potential.

Q.11. Assertion : Pure water is obtained by reverse osmosis from a solution through differentially permeable membrane.
Reason : Water obtained from reverse osmosis is devoid of impurities and is extra pure.

Answer Answer: (b) In pure water the impurities are negligible. Pure water is generally obtained by reverse osmosis but other sources like rain water, snow, etc., are also the source of pure water.

Q.12. Assertion : Water potential is new term for diffusion pressure deficit.
Reason : Both diffusion pressure deficit and water potential have a negative value.

Answer Answer: (c) The reduction in the diffusion pressure of water in a solution over its pure state is called diffusion pressure deficit or DPD. It is a term coined by Meyer (1938). It has positive value. Water potential is a modern term coined by Slatyer and Taylor (1960) which is equivalent to DPD, but it has a negative value.

Q.13. Assertion: By lowering O2 tension, water absorption is reduced.
Reason: Water absorption reduces due to the accumulation of CO2.

Answer Answer: (b) In the soil, the accumulation of CO2 appears to have a greater inhibitory effect on water absorption than do lowered oxygen tensions. An increase in CO2 causes an increase in the viscosity of protoplasm and a decrease in the roots permeability to water thereby, bringing about a retardation in water absorption.

Q.14. Assertion: The more number of solute molecules, the lower (more negative) is Yw
Reason: The free energy of water is reduced by the presence of solute particles and thus, decreases the water potential

Answer Answer: (a) Water molecules possess kinetic energy. Water molecules are in random motion in liquid and gaseous form. The greater the concentration of water in a system, greater is its kinetic energy or water potential. Pure water has greatest water potential i.e., zero. When a solute is added to pure water, it decreases the free energy of water and hence, decreases the water potential.

Q.15. Assertion :When the ambient temperature is high and soil contains excess of water, the plants tend to lose water in the form of droplets from lenticels.
Reason : Root pressure regulates the rate of loss of water form lenticels. [AIIMS 2006]

Answer Answer: (d) Root pressure is a pressure produced in the roots of plants, causing exudation of sap from cut stems and guttation of water from leaves. The pressure is generated by the concentration of solutes in the xylem of the root and stem which then causes water to move into the xylem by osmosis.

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