Absorption of water and Ascent of sap Questions in English

(B) The conduction of sap (water and minerals) in plants occurs through the $Sapwood$ (also known as $Alburnum$).
$Sapwood$ is the outer,living,and functional part of the secondary xylem.
Unlike $Heartwood$ $(Duramen)$,which is dead and filled with tannins,resins,and gums,the cells of $Sapwood$ are alive and contain abundant pore spaces that facilitate the upward movement of sap.

(D) Wilting is the loss of turgidity in plant cells,which occurs when the rate of transpiration exceeds the rate of water absorption. The $Xylem$ is the specialized vascular tissue responsible for the upward conduction of water and dissolved minerals from the roots to the leaves. If the $Xylem$ is blocked,water cannot reach the aerial parts of the plant,leading to a loss of turgor pressure and subsequent wilting.

(A) The correct answer is $A$. The suction of water and minerals due to transpiration pull is a physical process driven by the cohesive and adhesive properties of water molecules.
Water molecules exhibit a high degree of mutual attraction,known as cohesive force,which can reach up to $350$ atmospheres.
This allows for a continuous water column to be pulled upward through the xylem vessels at a very high velocity compared to biological processes like cyclosis,phloem transport,or hormonal distribution,which rely on metabolic energy and diffusion/active transport mechanisms.

(C) In plants,the transport of water and minerals occurs through the xylem tissue. The xylem consists of tracheids and vessels,which are dead cells at maturity,meaning they lack protoplasts. The absence of protoplasts creates a hollow,tube-like structure that allows for the efficient,unobstructed movement of water and dissolved minerals from the roots to the aerial parts of the plant. Therefore,the death of protoplasts is essential for water transport.

(B) Suberized roots are covered with a layer of suberin,which is impermeable to water. Therefore,water cannot enter through the general surface of these roots.
Water entry in such roots occurs only through specific openings or areas where the suberin layer is absent or broken,such as lenticels,wounds,or breaks around branch roots.
Roots and root hairs are the primary sites of water absorption in young,non-suberized roots,but they are not involved in water entry through suberized roots as they are typically absent or non-functional in those regions.
The root cap is a protective structure at the tip of the root and is not involved in water absorption.

(A) The plasma membrane of a cell acts as a selectively permeable membrane.
When water and mineral salts move from the $Soil$ into the $root hair$, they must cross the plasma membrane of the root hair cells.
This process involves the selective uptake of specific ions and water molecules, demonstrating the property of selective permeability.
While other movements also involve membranes, the initial entry from the soil into the living root hair cell is the most classic example of this biological phenomenon.

(A) $Xylem$ is responsible for the transport of water from roots to the aerial parts of the plant.
If $Xylem$ is blocked,the water supply to the leaves and other tissues is interrupted.
Due to the lack of water,the turgor pressure in the cells decreases,which causes the plant to lose its rigidity and undergo wilting.

(D) As various ions from the soil are actively transported into the vascular tissues of the roots, water follows its potential gradient and increases the pressure inside the xylem. This positive pressure is known as $Root \text{ } pressure$. It is responsible for pushing water up to small heights in the stem and is observable during early morning or night when evaporation is low.

(A) The ascent of sap in plants is primarily driven by the transpiration pull,which creates a negative pressure (tension) in the xylem vessels.
Root pressure provides a positive push,which is significant in smaller plants or during specific conditions like high humidity,but the transpiration pull is the main force responsible for the long-distance transport of water in tall woody stems.

(D) The most widely accepted theory for the ascent of sap is the $Transpiration$ $Cohesion-Tension$ theory,proposed by $Dixon$ and $Joly$ in $1894$.
According to this theory,the ascent of sap is driven by the transpiration pull generated at the leaf surface due to the evaporation of water.
This pull is transmitted down the water column in the $Xylem$ due to the cohesive and adhesive properties of water molecules,which prevent the column from breaking under tension.

(C) The most important force responsible for the ascent of sap in tall trees is the cohesion-tension mechanism.
Cohesive force is the intermolecular force of attraction between $H_2O$ molecules,which allows them to form a continuous water column in the xylem.
This column is pulled upward by the transpiration pull generated at the leaf surface.

(D) The most widely accepted theory for the ascent of sap in tall trees is the $Cohesion-Tension-Transpiration$ pull model.
$1$. $Cohesion$: The mutual attraction between water molecules due to hydrogen bonding allows the water column to remain intact without breaking.
$2$. $Adhesion$: The attraction of water molecules to the polar surfaces of the xylem vessel walls.
$3$. $Transpiration$ $pull$: As water evaporates from the stomata of leaves,it creates a negative pressure (tension) in the xylem,which pulls the entire water column upwards from the roots to the leaves.
Therefore,the combination of cohesion and transpiration pull is the primary mechanism for water transport in tall trees.

(A) Water absorption in plants occurs through the root hairs by osmosis.
$1$. Water first enters the root hairs from the soil.
$2$. It then moves through the cortical cells (cortex).
$3$. From the cortex,it reaches the endodermis.
$4$. After crossing the endodermis,it enters the pericycle.
$5$. Finally,it reaches the xylem tissues,where it moves from protoxylem to metaxylem.
Therefore,the correct sequence is: Soil $\to$ Root hair $\to$ Cortex $\to$ Endodermis $\to$ Pericycle $\to$ Protoxylem $\to$ Metaxylem.

(D) Physical force theories,such as the Cohesion-Tension theory,propose that the ascent of sap is a purely physical process driven by transpiration pull and the cohesive properties of water molecules.
These theories suggest that living cells are not required for the movement of water through the xylem,as the xylem vessels themselves are dead at maturity.
Therefore,the ascent of sap can occur in both living and non-living systems,provided the physical conditions for water transport are met.
Thus,both statements $(b)$ and $(c)$ are correct interpretations of the physical force theory.

(B) Water absorption in plants occurs through the root hairs,which are extensions of the epidermal cells (living cells).
Once water enters the root,it moves through the cortex (living cells) and eventually reaches the xylem.
The xylem tissue itself consists of both living cells (xylem parenchyma) and non-living cells (tracheids,vessels,and xylem fibers).
Since the entire process of water uptake and transport involves the coordinated action of both living cells (for active transport and pathway) and non-living cells (for bulk flow in xylem),the correct answer is that it involves both living and non-living cells.

(B) Exudation (bleeding) of xylem sap occurs when a plant is cut or injured. This phenomenon is primarily caused by $Root \ pressure$. Root pressure is a positive pressure that develops in the xylem sap of roots due to the active absorption of mineral ions from the soil,which leads to water following by osmosis. This pressure is sufficient to push water and solutes up to small heights in the stem,resulting in exudation.

(A) The water present in the soil exists in various forms.
$1$. Gravitational water: This water moves deep into the soil due to gravity and is generally unavailable to plants.
$2$. Hygroscopic water: This water is held tightly by soil particles and is unavailable to plants.
$3$. Chemically bound water: This water is part of the chemical structure of soil minerals and is unavailable to plants.
$4$. Capillary water: This is the water held in the spaces between soil particles by capillary forces. It is the primary source of water that plants can absorb through their root hairs.

(A) The rise in the mercury level in a manometer attached to a cut stump is caused by $root \ pressure$.
Root pressure is the positive pressure that develops in the xylem sap of the roots of plants.
It occurs due to the active absorption of mineral ions from the soil into the root hairs,which is followed by the passive movement of water into the root cells by osmosis.
This accumulation of water creates a positive hydrostatic pressure,which pushes the sap upwards in the xylem,causing the mercury level in the manometer to rise.

(B) The correct answer is $B$.
Passive absorption is the most common and rapid method of water absorption in plants.
It accounts for approximately $98\%$ of the total water uptake by the plant.
According to this theory,the roots remain passive,and the driving force for water absorption is the transpiration pull generated in the leaves due to evaporation on a sunny day.

(C) Passive absorption of water is a process where the roots act merely as a passive channel for the movement of water.
In this process,the energy required for the movement of water is provided by the transpiration pull generated in the leaves.
As water evaporates from the stomata of the leaves,a negative pressure or tension is created in the xylem vessels,which pulls water from the roots upwards.
Therefore,passive absorption is primarily driven by transpirational tension.

(B) Under low transpiring conditions,the rate of transpiration is very low,which reduces the tension in the xylem vessels.
In such conditions,the plant absorbs water through active absorption.
Active absorption involves the expenditure of metabolic energy $(ATP)$ by the root cells to take up water against the concentration gradient.
Passive absorption,on the other hand,is driven by the transpiration pull,which is minimal when transpiration rates are low.

(C) The ascent of sap in plants is primarily driven by the transpiration pull.
Loss of water from the mesophyll cells of leaves due to transpiration decreases their turgor pressure $(T.P.)$ and increases their diffusion pressure deficit $(D.P.D.)$.
As a result of the increased suction pressure,these cells absorb water from the adjacent xylem vessels of the leaves.
This creates a negative pressure or tension in the xylem sap,which pulls the water column upwards from the roots to the leaves.

(B) The transport of water and dissolved minerals (salts) from the roots to the aerial parts of the plant occurs through the $Xylem$ tissue.
Specifically,sap moves upward through the lumen of $Xylem$ vessels and tracheids,which are the primary conducting elements of the $Xylem$.

(C) The active uptake of water is primarily influenced by the transpirational pull generated in the leaves.
Transpiration creates a negative pressure or tension in the xylem vessels,which is transmitted down to the roots.
This tension facilitates the movement of water from the soil into the root system.
Therefore,the rate of water absorption is directly proportional to the rate of transpiration.

(B) The continuity of the water column in the $xylem$ is primarily maintained by the cohesive and adhesive properties of water molecules.
Cohesion refers to the mutual attraction between water molecules due to hydrogen bonding.
Adhesion refers to the attraction of water molecules to the polar surfaces of the $xylem$ vessel walls.
Together,these forces create a high tensile strength that prevents the water column from breaking under the tension generated by transpiration.

(A) Root pressure is a positive pressure that develops in the roots of plants due to the active absorption of mineral ions from the soil,which is followed by the osmotic movement of water into the root xylem.
When root pressure is high,it indicates that the plant is actively absorbing water from the soil to maintain turgor and push sap upwards.
Therefore,the process of water absorption is rapid under conditions of high root pressure.

(C) The ascent of sap is primarily driven by the cohesion-tension theory.
Water molecules remain connected to each other in a continuous column within the xylem due to strong cohesive forces, which arise from hydrogen bonding between water molecules.
This cohesion provides high tensile strength to the water column, allowing it to withstand the gravitational pull and the tension generated by transpiration.
The cohesive force has a significant value, typically ranging from $(45-207) \text{ atm}$.

(C) The primary site for water absorption in young roots is the root hair zone.
This zone is located approximately $(2-10) \text{ cm}$ away from the root tip.
Root hairs are unicellular, tubular extensions of the epiblema (epidermal) cells that significantly increase the surface area for the absorption of water and dissolved minerals from the soil.

(A) When the shoot of a well-watered plant is cut off near the base, a positive hydrostatic pressure develops in the xylem of the roots due to the active absorption of mineral ions. This pressure is known as $Root \text{ pressure}$. It is responsible for pushing the xylem sap upwards, which manifests as the exudation of watery fluid from the cut stump.

(D) Active absorption of water refers to the process where the force for water absorption is generated within the root cells themselves.
This process requires metabolic energy,usually in the form of $ATP$,to move water against the concentration gradient.
Both osmotic and non-osmotic forces are involved in this mechanism,and the primary requirement is the availability of energy produced through cellular respiration.

(C) The primary driving force for the ascent of sap in plants is transpiration.
Transpiration creates a negative pressure (tension) in the xylem vessels due to the evaporation of water from the stomata in the leaves.
This tension pulls the water column upwards from the roots to the top of the plant,a process known as the cohesion-tension-transpiration pull model.

(A) The rate of water absorption by roots is directly proportional to the rate of transpiration.
When transpiration increases,it creates a higher transpiration pull (negative pressure) in the xylem vessels.
This pull draws more water from the roots into the stem and leaves to compensate for the water lost through the stomata.
Therefore,an increase in the rate of transpiration leads to an increase in the absorption of water by the roots.

(C) During the process of transplantation,the root system of the seedling is disturbed.
Most of the delicate root hairs,which are responsible for the absorption of water and mineral salts from the soil,are damaged or lost during the uprooting process.
As a result,the plant is unable to absorb sufficient water to maintain its physiological processes,leading to wilting and often the death of the seedling.

(B) When a potted plant is flooded with water,the soil becomes waterlogged,which leads to poor aeration (lack of oxygen) in the soil.
Root cells require oxygen for aerobic respiration to generate the energy $(ATP)$ needed for the active transport of mineral ions into the root xylem.
As the metabolic activities of root cells,such as respiration,are retarded due to the lack of oxygen,the active absorption of minerals and water is significantly reduced.
Consequently,the magnitude of root pressure decreases significantly.

(C) The cohesion-tension theory explains the ascent of sap in plants.
On a $Sunny day$, the rate of transpiration is very high due to high temperature and low humidity.
This high rate of transpiration creates a strong negative pressure (tension) in the xylem vessels, which pulls the water column upwards.
This tension force significantly exceeds the root pressure, which is generally low and insufficient to push water to the top of tall trees.

(B) During mid-day hours,the rate of transpiration is at its peak due to high solar radiation and temperature.
As water evaporates from the stomata of leaves,it creates a negative pressure potential (suction force) in the xylem vessels.
This negative pressure pulls the water column upwards from the roots to the leaves.
Because the water column is being pulled under this negative pressure,the xylem sap is said to be in a state of tension (or negative hydrostatic pressure).

(B) The absorption of water by plant roots is significantly influenced by soil temperature.
At very low temperatures (such as $1^o C$),the viscosity of water increases,making it harder for water to move through the soil and into the root cells.
Additionally,low temperatures reduce the permeability of the root cell membranes and decrease the metabolic activity of root cells,which inhibits active transport processes.
Therefore,as the soil temperature drops to $1^o C$,the rate of water absorption by the roots decreases significantly.

(C) Active absorption of water is an energy-dependent process that requires metabolic energy in the form of $ATP$.
This process is mediated by the metabolic activity of root cells,specifically the root hairs.
Since metabolic activities like respiration are enzyme-controlled,they are highly sensitive to temperature.
The optimal temperature range for most metabolic processes in plants,including active water absorption,is between $20^{\circ}C$ and $35^{\circ}C$.
Temperatures below or above this range significantly reduce the rate of respiration and,consequently,the rate of active water absorption.

(C) Transpiration creates a negative pressure potential (transpiration pull) in the xylem vessels.
This pull is responsible for the rapid ascent of sap (water and dissolved minerals) from the roots to the aerial parts of the plant.
While transpiration also results in water loss and cooling,the primary physiological role in the context of plant transport is facilitating the upward movement of water.

(B) When a plant undergoes rapid transpiration,water is lost from the leaves in the form of water vapor. This creates a negative pressure or tension in the xylem vessels,known as the transpiration pull. This tension is transmitted down to the roots,which pulls water from the soil into the plant. Since this process is driven by the physical force of transpiration and does not require the expenditure of metabolic energy $(ATP)$ by the root cells,it is termed as passive absorption. Therefore,rapid transpiration is primarily associated with passive water absorption.

(B) Transpiration creates a negative pressure potential (transpiration pull) in the xylem vessels,which is essential for the upward movement of water from the roots to the leaves. Therefore,transpiration directly facilitates the conduction of water through the plant. While it is linked to stomatal function,the primary physiological process it drives is the ascent of sap.

(D) The movement of water against gravity in plants is primarily explained by the Cohesion-Tension-Transpiration Pull theory.
$1$. Cohesion: The strong attraction between water molecules due to hydrogen bonding creates a continuous water column in the xylem.
$2$. Adhesion: The attraction between water molecules and the xylem vessel walls prevents the column from breaking.
$3$. Transpiration Pull: As water evaporates from the stomata in leaves,it creates a negative pressure (tension) that pulls the entire water column upward from the roots.
Therefore,both transpiration pull and the cohesive properties of water are essential for this process.

(C) The process of guttation involves the exudation of liquid water from the tips or margins of leaves through specialized structures called hydathodes.
This phenomenon occurs due to the development of a positive hydrostatic pressure,known as $root \ pressure$,in the xylem vessels at the vein endings.
This $root \ pressure$ forces the liquid water out through the hydathodes,especially when transpiration is low and water absorption is high.

(A) During the night,the rate of transpiration is negligible or zero because the stomata are closed and there is no sunlight.
As a result,the water absorbed by the roots is not lost through transpiration,leading to an accumulation of water in the xylem vessels.
This accumulation creates a positive hydrostatic pressure known as root pressure.
Therefore,root pressure is more pronounced during the night compared to the day.

(B) When a cut shoot is placed in a potometer,the water absorption is primarily driven by the transpiration pull generated by the leaves.
Since the shoot is detached from the roots,it cannot perform active water absorption.
The water is pulled up through the xylem due to the evaporation of water from the stomata,which creates a negative pressure or tension.
This process is known as passive water absorption,as it does not require metabolic energy from the plant to move the water.

(C) The "Relay pump theory" of ascent of sap was proposed by Godlewski in $1884$.
According to this theory, the ascent of sap occurs due to rhythmic changes in the osmotic pressure of the living cells of xylem parenchyma and medullary rays.
These living cells act as pumps, relaying water upwards through the xylem.

(A) The Pulsation Theory of ascent of sap was proposed by Sir $J. C. Bose$ in $1923$. According to this theory,the living cells of the innermost layer of the cortex,which is the endodermis,exhibit rhythmic pulsations. These pulsations create a pumping action that helps in the upward movement of water (ascent of sap) through the xylem vessels. This is considered a vital force theory because it relies on the metabolic activity of living cells.

(C) Dixon and Jolly proposed the $Cohesion-Tension$ theory in $1894$ to explain the mechanism of water transport in plants.
This theory states that the transpiration pull,combined with the cohesive and adhesive properties of water molecules,creates a continuous column of water that is pulled upward through the xylem from the roots to the leaves.

(A) The Vital Force Theory suggests that the ascent of sap is due to the activity of living cells. Among the various theories proposed,the Relay Pump Theory,which is a type of vital force theory,was proposed by Godlewsky in $1884$. This theory suggests that the living cells of the xylem parenchyma and medullary rays act as pumps to push water upwards. Therefore,the correct option is $A$.