Question
The process responsible for facilitating loss of water in liquid form from the tip of grass blades at night and in early morning is [NEET (Sep.) 2020]
(a) root pressure
(b) imbibition
(c) plasmolysis
(d) transpiration
Answer/Explanation
Ans. (a)
Root pressure is positive hydrostatic pressure. It develops in tracheary element at night and in early morning. Which results loss of water in liquid form from tip of grass blades. Imbibition is the process by which colloidal soild particles absorb water and swell without being dissolved. Which results loss ofwater in liquid form from tip of grass blades. Plasmolysis is the process in which cells lose water in a hypertonic solution. Transpiration is the loss of water from a plant in the form of water vapour.
Question
Xylem translocates [NEET (National) 2019]
(a) water and mineral salts only
(b) water, mineral salts and some organic nitrogen only
(c) water, mineral salts, some organic nitrogen and hormones
(d) water only
Answer/Explanation
Ans. (c)
Xylem in plants helps in the translocation of water, mineral salts, some organic nitrogen and hormones from the soil to the aerial parts of the plant. This process is known as the ascent of sap and it involves four major forces namely root pressure, capillarity. transpirational pull and cohesion and adhesion of water molecule and cell wall.
Question
The water potential of pure water is [NEET 2017]
(a) zero
(b) less than zero
(c) more than zero, but less than one
(d) more than one
Answer/Explanation
Ans. (a)
The value of water potential of pure water is highest and it is zero. Water molecules possess kinetic energy. Greater the concentration of water in a system, greater is its kinetic energy or its water potential. If we add solute in water, the solution has fewer free water molecule and concentration of water decreases thus reducing its water potential.
Question
Two cells $A$ and $B$ are contiguous. Cell $A$ has osmotic pressure 10 atm, turgor pressure 7 atm and diffusion pressure deficit 3 atm. Cell $B$ has osmotic pressure 8 atm, turgor pressure 3 atm and diffusion pressure deficit 5 atm. The result will be [CBSE AIPMT 2007]
(a) movement of water from cell B-A
(b) no movement of water
(c) equilibrium between the two
(d) movement of water from cell A-B
Answer/Explanation
Ans. (d)
The water moves from lower DPD to higher $D P D$, i.e. from cell A to cell B. This is because when a cell is placed in pure water, the water enters into the cell as a result of the diffusion pressure deficient (QPO) of cell sap. $D P D=O P-T P$.
Question
Water enters a cell due to [CBSE AIPMT 2001]
(a) $O P$
(b) SP
(c) TP
(d) WP
Answer/Explanation
Ans. (b)
Suction pressure (also called DPD) is believed to suck water (cause movement of water molecule]from pure solvent/hypotonic solution. It is a measure of the ability of the cells to absorb water. BS Meyer (1938) coined the term suction pressure or $\mathrm{DPD}$.
Question
In soil, water available for roots (to plants) is [CBSE AIPMT 1999, 91]
(a) capillary water
(b) hygroscopic water
(c) gravitational water
(d) chemically bound water
Answer/Explanation
Ans. (a)
Water is present in the space between the soil particles. A large proportion of water is retained between the soil particles against the gravitational force. This is called capillary water. It is readily available to plants for absorption by roots.
Question
The water potential and osmotic potential of pure water are [CBSE AIPMT 1998]
(a) 100 and zero
(b) zero and zero
(c) 100 and 200
(d) zero and 100
Answer/Explanation
Ans. (b)
The term water potential indicates the net tendency of any system to donate water to its surroundings. The water potential of pure water at atmospheric pressure is zero. Any addition of solute to this water reduces its water potential and makes its value negative. The osmotic potential of pure water also would be zero.
Question
If turgidity of a cell surrounded by water increases, the wall pressure will [CBSE AIPMT 1997]
(a) increase
(b) decrease
(c) fluctuate
(d) remain unchanged
Answer/Explanation
Ans. (a)
If a plant cell is placed in a hypotonic solution/pure water, water starts moving in by endosmosis. As the volume of the protoplast increases, it begins to exert pressure against the cell wall (turgor pressure). The cell wall exerts equal and opposite pressure (wall pressure) on the protoplast.
Question
Osmotic pressure in the leaf cells is positive during [CBSE AIPMT 1997]
(a) excessive transpiration
(b) low transpiration
(c) excessive absorption
(d) guttation
Answer/Explanation
Ans. (a)
Osmotic pressure in the leaf cells is positive during excessive transpiration. Transpiration is a physical and physiological process in which aerial parts of a living plant remove water in the form of vapours. As the water is lost from the leaf surface by transpiration, osmotic pressure of the leaf cells increases.
Question
The movement of water from one cell of the cortex to the adjacent one in roots is due to
(a) accumulation of inorganic salts in the cells
(b) accumulation of organic compounds in the cells
(c) chemical potential gradient
(d) water potential gradient
Answer/Explanation
Ans. (d)
Water potential is the difference in the chemical potential per unit molal volume of water in a system and that of pure water at the same temperature and pressure. Water always moves from the area of high water potential to the area of low water potential.
Question
The direction and rate of water movement from cell to cell is based on [CBSE AIPMT 1992]
(a) WP
(b) TP
(c) DPD
(d) incipient plasmolysis
Answer/Explanation
Ans. (c)
The difference between the diffusion pressure of the solution and its solvents at a particular temperature and atmospheric condition is called DPD. The direction and rate of water movement from cell to cell is based on DPD(Diffusion Pressure Deficit).
Question
Water potential can be obtained by [CBSE AIPMT 1991]
(a) $O P+T P$
(b) $O P=W P$
(c) $\Psi_{\mathrm{S}}+\Psi_{\mathrm{p}}$
(d) $O P-D P D$
Answer/Explanation
Ans. (c)
Water potential is the difference between the free energy of water in a system and free energy of pure water. It can be obtained by $\Psi_{\mathrm{w}}=\Psi_s+\Psi_{\mathrm{b}}$. It is a function of solute potential and pressure potential.
Question
Mainly conduction of water in an angiosperm occurs through [CBSE AIPMT 1990]
(a) tracheids
(b) xylem vessels
(c) sieve tubes
(d) All of these
Answer/Explanation
Ans. (b)
The water absorbed by roots has to be conducted upward so as to meet the needs of tissues there. Water moves up through the lumen of xylem vessels.
Question
Root system in a plant is well developed [CBSE AIPMT 1990]
(a) due to deficiency of auxins
(b) due to deficiency of cytokinins
(c)due to deficiency of minerals
(d) for increased absorption of water
Answer/Explanation
Ans. (d)
Water in land plants is mainly absorbed through the roots, especially at the tips in the region of root hairs. Therefore, root system in a plant is well developed, for increasing absorption of water.