Water relation Questions in English

(B) Cohesion refers to the mutual attraction between water molecules.
This attraction is primarily caused by hydrogen bonding ($H$-bonds) between the oxygen atom of one water molecule and the hydrogen atom of another water molecule.
These $H$-bonds create a strong cohesive force that allows water to move in a continuous column through the xylem vessels of plants.

(C) Echards refers to the specific portion of soil water that is held by soil particles with such high tension that it cannot be absorbed by plant roots.
Therefore,it represents the amount of water that is not available to the plant.
In contrast,the water that is available for absorption by plants is known as chresard.

(C) Permanent wilting percentage or coefficient $(PWC)$ is the minimum amount of water in the soil at which the plant can no longer extract sufficient water to maintain its turgor pressure.
At this stage,the plant remains permanently wilted even if placed in a saturated atmosphere.
If water is not added to the soil at this point,the plant will eventually die.

(D) The wilting coefficient is defined as the percentage of water content in the soil at which the plants growing in that soil begin to wilt and fail to recover their turgidity even when placed in a saturated atmosphere.
It represents the lower limit of available water for plant growth.
Therefore,the correct option is $D$.

(B) The storage capacity of soil,often referred to as field capacity,is primarily defined by the amount of water it can retain against the force of gravity.
Capillary water is the water held in the soil pores by capillary forces.
It is the only form of water available to plants for absorption and is often called growth water.
Gravitational water drains away,and hygroscopic water is held too tightly by soil particles for plants to absorb.

(D) Soil is considered physiologically dry when plants are unable to absorb water from the soil even if water is present.
This occurs in two main scenarios:
$1$. When the concentration of the soil solution is higher than the concentration inside the root cells (high salinity),which prevents water uptake via osmosis.
$2$. When the soil temperature is $0^{\circ}C$,which reduces the permeability of root cell membranes and increases the viscosity of water,making absorption difficult.
Therefore,both $(b)$ and $(c)$ lead to physiological dryness.

(C) The amount of water retained by a unit weight of undisturbed soil after complete drainage under gravity is known as $Field \ capacity$.
When soil is thoroughly wetted and allowed to drain,the water that moves downward due to gravity is called $Gravitational \ water$.
Once the downward movement stops,the water held in the soil pores against gravity by capillary forces is known as $Capillary \ water$.
The total water content remaining in the soil at this point is defined as the $Field \ capacity$ of the soil.

(A) hypotonic solution is defined as a solution that has a lower solute concentration compared to another solution or the cytoplasm of a cell. When a cell is placed in a hypotonic solution,water moves into the cell due to osmosis,causing the cell to swell. Therefore,the correct option is $A$.

(D) The density of water is primarily influenced by two main factors:
$1$. $\text{Temperature}$: As water cools, its density increases until it reaches $4^{\circ}C$. Below $4^{\circ}C$, the hydrogen bonding structure causes it to expand, decreasing its density.
$2$. $\text{Dissolved salts}$ $(\text{Salinity})$: The presence of dissolved salts increases the mass of a given volume of water, thereby increasing its density.
Therefore, the correct answer is $D$.

(D) Water possesses a high specific heat and high latent heat of vaporization due to hydrogen bonding between its molecules. This property helps organisms maintain a stable internal temperature. Therefore,statement $A$ is false.
Water molecules exhibit strong cohesive forces (attraction between similar molecules) due to hydrogen bonding,which is essential for the ascent of sap in plants. Therefore,statement $R$ is true.
Thus,$A$ is false and $R$ is true.

(B) The osmotic pressure $(OP)$ of a solution is the pressure that must be applied to prevent the movement of water into the solution across a semi-permeable membrane.
Osmotic potential $(\Psi_s)$ is the negative value of osmotic pressure, i.e., $\Psi_s = -OP$.
Therefore, numerically, osmotic pressure and osmotic potential are equal, although they have opposite signs.
In a flaccid cell, the turgor pressure $(TP)$ is zero, and the osmotic pressure equals the diffusion pressure deficit $(DPD)$.
However, the most direct numerical similarity defined in plant physiology is between osmotic pressure and osmotic potential (ignoring the sign).
Thus, option $B$ is the most accurate representation of numerical similarity.

(N/A) Osmotic Pressure and Osmotic Potential are related concepts in plant physiology, often used to describe the movement of water across semi-permeable membranes.

Osmotic Pressure	Osmotic Potential
$(1)$ 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 (becomes more negative) with an increase in the concentration of solute particles.

(N/A) $\Rightarrow$ Water is essential for all physiological activities of the plant.
$\Rightarrow$ Water plays a very important role in all living organisms.
$\Rightarrow$ It provides the medium in which most substances are dissolved.
$\Rightarrow$ The protoplasm of the cells is essentially water in which different molecules are dissolved and suspended.
$\Rightarrow$ $A$ watermelon has over $92\%$ water.
$\Rightarrow$ Most herbaceous plants have only about $10\%$ to $15\%$ of their fresh weight as dry matter.
$\Rightarrow$ Woody plants have relatively very little water,while soft parts of plants mostly contain water.
$\Rightarrow$ $A$ seed may appear dry,but it still contains water; otherwise,it would not be alive and respiring.
$\Rightarrow$ Terrestrial plants take up a huge amount of water daily,but most of it is lost to the air through evaporation from the leaves.
$\Rightarrow$ $A$ mature corn plant absorbs almost $3$ litres of water in a day,while a mustard plant absorbs water equal to its own weight in about $5$ hours.
$\Rightarrow$ Because of this high demand for water,it is not surprising that water is often the limiting factor for plant growth and productivity in both agricultural and natural environments.

(D) Turgor pressure,denoted as $\Psi_{P}$,is the pressure exerted by the protoplast against the cell wall due to the entry of water.
$1$. Structural Support: It provides rigidity to soft tissues and helps herbaceous plants remain upright.
$2$. Cell Growth: The turgor pressure is responsible for cell enlargement and extension growth.
$3$. Protection: Due to the rigidity of the cell wall,the cell does not burst even when water enters,maintaining the cell's integrity.

(B) Halophytes grow in saline environments where the water potential of the soil is very low.
To absorb water from such hypertonic soil,these plants accumulate high concentrations of inorganic ions and organic solutes within their vacuoles.
This accumulation significantly lowers the osmotic potential of the cell sap,allowing water to enter the cells via osmosis.
As water enters,it exerts a high turgor pressure (cell pressure) against the cell wall,which is essential for maintaining the structural integrity and metabolic activity of the plant in saline conditions.
While salt glands help in removing excess salt,the high internal cell pressure is primarily a result of the high solute concentration maintained to facilitate water uptake.

(C) Two solutions are said to be isotonic when they have the same osmotic concentration or osmolarity.
In an isotonic solution,there is no net movement of water across the semi-permeable membrane because the solute concentration is equal on both sides.

(D) Casparian strips are located in the radial and tangential walls of the endodermal cells.
They are composed of water-impermeable,waxy material called suberin (often associated with lignin).
Statement $I$ is incorrect because Casparian strips are found in the endodermis,not surrounding the pericycle.
Statement $II$ is correct as they are made of lignosuberin.
Statement $III$ is correct because by blocking the apoplastic pathway,they force water and solutes to enter the symplast to cross the endodermis.
Therefore,statements $II$ and $III$ are correct,but since this combination is not provided in the options,the most appropriate choice based on the provided options is $D$ (None of these).

(C) Osmosis is the spontaneous diffusion of water across a semi-permeable membrane. The movement of water molecules is influenced by both the chemical potential gradient (concentration gradient) and the pressure gradient. The net direction of water movement is determined by the water potential,which is the sum of solute potential (related to concentration) and pressure potential. Therefore,both the net direction and the rate at which osmosis occurs are dependent on these two factors.

(C) The turgidity and shape of plant cells are primarily maintained by the presence of water within the cell,specifically within the large central vacuole.
When water enters the cell through osmosis,it exerts pressure against the cell wall,known as turgor pressure.
This turgor pressure pushes the plasma membrane against the rigid cell wall,which provides structural support and maintains the cell's shape.
Without sufficient water,the cell loses its turgor pressure,leading to wilting or plasmolysis.