Transpiration (General) and Stomata Questions in English

(A) Water stomata,also known as hydathodes,are specialized structures involved in the process of guttation.
These structures are typically found in plants that inhabit humid regions where transpiration is reduced,leading to the exudation of water droplets from the leaf margins.
Therefore,the correct option is $A$.

(A) The guard cells of the stomata have a specialized structure to regulate the opening and closing of the pore. The inner walls of the guard cells (those facing the stomatal pore) are thick and inelastic,while the outer walls (away from the pore) are thin and elastic. This structural difference allows the guard cells to change shape and open the stoma when they become turgid.

(B) The exchange of gases like $O_2$ and $CO_2$ between the plant and the atmosphere occurs through the stomata and lenticels.
This process is primarily governed by the principle of diffusion.
Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration until equilibrium is reached.
Since gases move down their concentration gradient,no metabolic energy is required for this process.

(A) The phenomenon described is temporary wilting.
It is the temporary drooping down of leaves and young shoots due to the loss of turgidity during the noon hours.
At this time,the rate of transpiration is at its maximum.
Temporary wilting is corrected only after the rate of transpiration decreases in the afternoon,accompanied by the replenishment of water around the root hairs.

(D) Excessive transpiration leads to a rapid loss of water from the plant body,which exceeds the rate of water absorption by the roots.
This creates a water deficit in the leaf cells,leading to a loss of turgor pressure,which causes the plant to wilt.
Initially,this is known as temporary wilting,but if the condition persists,it can lead to permanent wilting and damage to the plant tissues.

(B) Transpiration is the process of water loss from the aerial parts of plants.
$90\%$ to $95\%$ of the total water loss occurs through the stomata,which are small pores present on the surface of leaves.
Cuticular transpiration accounts for a very small percentage,while lenticular transpiration and guttation (through hydathodes) contribute minimally to the total water loss.

(C) Transpiration is the process of loss of water in the form of water vapor from the aerial parts of the plant.
This loss of water creates a negative pressure or tension,known as transpiration pull,in the xylem vessels.
This pulling force is transmitted throughout the water column in the xylem,which is responsible for the ascent of sap from the roots to the top of the tree.

(D) Transpiration is the biological process by which water is lost in the form of water vapour from the aerial parts of the plant,such as leaves,stems,and flowers.
This process primarily occurs through the stomata present on the leaf surface.
It plays a crucial role in the upward movement of water and minerals from the roots to the leaves and helps in cooling the plant surface.

(A) Guard cells are specialized plant cells that surround the stomatal pore.
They regulate the opening and closing of the stomata to control gas exchange and transpiration.
In most dicot plants,these cells are kidney-shaped,while in monocots,they are dumbbell-shaped.
Therefore,guard cells are an integral part of the stomatal apparatus.

(D) Transpiration is a physiological process because it occurs in plants through living tissues (like stomata,cuticle,or lenticels) and is regulated by the plant's metabolic activities.
Evaporation is a purely physical process that occurs from any free surface (living or non-living) due to the conversion of liquid water into vapour by heat energy.
Therefore,the fundamental difference lies in the biological control involved in transpiration compared to the passive nature of evaporation.

(B) The correct answer is $B$.
Transpiration is the process of water loss from the aerial parts of plants.
There are three main types of transpiration:
$1$. $Stomatal$ $transpiration$: Occurs through stomata, accounting for $80-90\%$ of total water loss.
$2$. $Cuticular$ $transpiration$: Occurs through the cuticle, accounting for $5-10\%$ of water loss.
$3$. $Lenticular$ $transpiration$: Occurs through lenticels, accounting for less than $1\%$ of water loss.
Therefore, $Stomatal$ transpiration is the most common type.

(B) Wilting occurs during the hottest part of the day and is visible externally due to the drooping of leaves and young shoots.
At noon,the rate of transpiration is significantly higher than the rate of water absorption by the roots.
This imbalance leads to a loss of turgor pressure in the plant cells,causing the leaves to wilt.

(A) The process of transpiration involves the loss of water in the form of water vapor from the aerial parts of the plant,primarily through the stomata in the leaves.
This evaporation of water consumes heat energy,which leads to a cooling effect on the leaf surface and the surrounding air.
This mechanism is crucial for protecting plants from heat injury,especially during hot summer days with intense sunlight.

(B) In hypostomatic leaves (Apple or mulberry type),stomata are present only on the lower (abaxial) surface of the leaves.
This adaptation helps in reducing water loss through transpiration.
Therefore,the correct answer is the under surface of the leaf.

(C) Loftfield $(1921)$ classified stomata into four types based on their daily periods of opening and closing:
$(1)$ Alfalfa type: Stomata remain open throughout the day and close at night.
$(2)$ Potato type: Stomata remain open throughout the day and night,except for a few hours in the evening.
$(3)$ Barley type: Stomata open only for a few hours during the day.
$(4)$ Equisetum type: Stomata remain open throughout the day and night.

(B) In scotoactive stomata,the stomatal pores open during the night and close during the day.
This mechanism is primarily observed in succulent plants (xerophytes) that perform Crassulacean Acid Metabolism $(CAM)$.
By opening stomata at night,these plants minimize water loss through transpiration,which is higher during the hot,dry day.

(A) In $Barley$ type plants,the stomata open only for a few hours during the day time.
These are also known as cereal-type stomata.
For the rest of the time,they remain closed.
This mechanism helps in reducing water loss through transpiration.

(A) Stomatal frequency is defined as the number of stomata present per unit area of the leaf surface.
It is typically expressed as the number of stomata per square millimeter $(mm^2)$ or square centimeter $(cm^2)$.
The number of stomata per square centimeter ranges from $1,000$ to $60,000$ in different plant species.
Generally,the stomatal frequency of trees and shrubs is higher than that of herbs.

(B) The stomatal index $(I)$ is defined as the percentage of the number of stomata to the total number of epidermal cells including the stomata in a given area of the leaf surface.
Mathematically,it is expressed as: $I = \frac{S}{E + S} \times 100$.
Here,$S$ represents the number of stomata per unit area,and $E$ represents the number of epidermal cells per unit area.
Therefore,the correct formula is $\frac{S}{E + S}$.

(C) Transpiration is called a necessary evil because it is both beneficial and harmful to the plant.
It is considered an 'evil' because it leads to significant water loss,which can cause water deficit in plants,potentially inhibiting photosynthesis,reducing growth,and affecting other metabolic processes.
It is considered 'necessary' because it facilitates the upward conduction of water and minerals from the roots to the leaves,helps in maintaining the turgidity of cells,and provides a cooling effect to the plant surface through evaporation.

(B) The number of stomata present per unit area of a leaf is known as stomatal frequency.
In most plants,the stomatal frequency typically ranges from $1000$ to $60000$ stomata per $cm^2$ of leaf surface.
This value varies significantly depending on the plant species,environmental conditions,and the side of the leaf (abaxial vs. adaxial surface).

(C) Transpiration is the process of loss of water in the form of water vapor from the aerial parts of the plant,primarily through the stomata in leaves.
As water evaporates from the surface of the mesophyll cells,it absorbs latent heat from the leaf tissue.
This dissipation of heat through the evaporation of water provides a significant cooling effect,which helps in maintaining the leaf temperature within a favorable range for metabolic activities.

(C) Herbaceous plants are known to lose a significant amount of the water they absorb through the process of transpiration.
Scientific studies indicate that more than $99\%$ of the water absorbed by the roots of these plants is lost to the atmosphere through transpiration from the aerial parts,primarily the leaves.
Only a very small fraction (less than $1\%$) is utilized for plant growth and metabolic activities like photosynthesis.

(C) Transpiration is defined as the loss of water in the form of water vapour from the aerial parts of a plant.
These aerial parts include leaves,stems,flowers,and fruits.
Therefore,transpiration occurs through all aerial parts of the plant.

(D) Guard cells are specialized cells that surround the stomatal pore.
Unlike typical epidermal cells,guard cells contain chloroplasts,which allow them to perform photosynthesis and regulate the opening and closing of stomata.
Epidermal cells generally lack chloroplasts as they are primarily protective in function.

(A) Transpiration is the process of water loss in the form of water vapor from the aerial parts of plants.
Most of the transpiration occurs through the stomata present in the leaf epidermis.
Therefore,the epidermis (specifically the leaf epidermis containing stomata) is the primary organ responsible for transpiration.

(B) The guard cells are specialized epidermal cells that surround the stomatal pore.
The inner walls of the guard cells,which face the stomatal aperture,are thick and inelastic.
The outer walls,which face away from the stomatal aperture,are thin and elastic.
This structural difference allows the guard cells to change shape and regulate the opening and closing of the stomata.

(A) Each stoma is bordered by two specialized epidermal cells called $guard$ $cells$.
These cells are generally kidney-shaped or bean-shaped in dicots,while in grasses,they are dumb-bell-shaped.
These cells regulate the opening and closing of the stomatal pore.

(D) In most angiosperms,stomata are diurnal,meaning they open during the day to facilitate gas exchange for photosynthesis and close at night to prevent excessive water loss through transpiration. Therefore,stomata are typically closed at midnight.

(D) The correct answer is $D$. The leaves are the primary organs for transpiration in plants. The process of water loss through the leaves is known as foliar transpiration. While some transpiration can occur through the stem (lenticular transpiration) or cuticle,the majority of water loss occurs through the stomata present on the leaves.

(A) Transpiration is the process of loss of water in the form of water vapor from the aerial parts of the plant.
Mesophytic plants,which grow in environments with moderate water availability,typically exhibit the highest rates of transpiration because they possess well-developed stomata and sufficient water supply to support continuous evaporation.
In contrast,hydrophytes often have reduced transpiration due to high humidity or submerged conditions,and xerophytes have specialized adaptations (like sunken stomata or thick cuticles) to minimize water loss.
Therefore,mesophytic plants show the maximum transpiration rate.

(D) Transpiration is the process of loss of water in the form of water vapor from the aerial parts of the plant.
There are three main types of transpiration based on the site of water loss:
$1$. $Stomatal$ $transpiration$: Loss of water through stomata (accounts for $80-90\%$ of total transpiration).
$2$. $Cuticular$ $transpiration$: Loss of water through the cuticle (waxy layer on leaves).
$3$. $Lenticular$ $transpiration$: Loss of water through lenticels (small pores in woody stems).
$Endodermal$ $transpiration$ is not a recognized type of transpiration because the endodermis is an internal layer of the root that regulates water movement into the xylem and is not involved in the direct loss of water vapor to the atmosphere.

(D) Stomata are generally more abundant on the lower (abaxial) surface of a dorsiventral leaf compared to the upper (adaxial) surface.
Since transpiration is directly proportional to the number of stomata,the majority of water loss occurs through the lower surface.
In most plants,approximately $97$% of the total transpiration takes place through the abaxial surface.

(B) In $Anisostomatic$ (or $Potato$) type of stomata,the number of stomata is significantly higher on the lower surface of the leaf compared to the upper surface.
Such leaves are typically dorsiventral in nature.
$Pea$ ($Pisum$ $sativum$) and $Cabbage$ are classic examples of plants exhibiting the $Potato$ type of stomatal distribution.

(A) Stomata are microscopic pores found on the epidermis of leaves and stems that facilitate gas exchange and transpiration.
In submerged hydrophytes (plants that grow entirely underwater),stomata are completely absent because gas exchange occurs directly through the general body surface via diffusion.
In contrast,desert plants (xerophytes) have sunken stomata to reduce water loss,and floating plants have stomata present only on the upper surface of their leaves.

(B) Lenticels are small pores found in the bark of woody stems and branches.
These pores are filled with loosely arranged cells known as complementary cells.
Lenticular transpiration refers to the loss of water in the form of water vapour through these lenticels.
Therefore,lenticular transpiration occurs specifically in woody stems.

(D) The classification of stomatal distribution based on the location of stomata on the leaf surface includes the $Hypostomatic$ type.
In the $Hypostomatic$ type,stomata are restricted to the lower surface of the leaf.
Both $Apple$ $(Malus)$ and $Mulberry$ $(Morus)$ plants exhibit this $Hypostomatic$ distribution pattern.
Therefore,there is no difference between them as they both represent the same type of stomatal distribution.

(B) Transpiration is the process of water loss from the plant surface,primarily through stomata.
Most plants,especially dicots,have a significantly higher density of stomata on the lower surface (abaxial surface) compared to the upper surface (adaxial surface).
Greasing the surface blocks the stomata,thereby preventing transpiration.
Since the lower surface contains the majority of the stomata,greasing it will reduce the rate of water loss more significantly than greasing the upper surface.
Therefore,the leaf with the lower surface greased will retain water for the longest time and dry up last.

(C) The rate of transpiration is primarily driven by solar radiation and atmospheric humidity,reaching its peak around mid-day. This high rate of water loss creates a temporary water deficit within the plant tissues. As the plant loses water,the leaf cell sap concentration increases (osmotic potential decreases),which enhances the water-absorbing capacity of the roots. This physiological response leads to a delayed peak in water absorption,typically occurring about $2$ hours after the peak of transpiration.

(A) The correct answer is $A$. Transpiration is the process by which water is lost from the aerial parts of plants in the form of water vapor. This process consumes heat energy from the surrounding environment,which leads to a cooling effect on the plant surface and the immediate atmosphere,thereby helping to maintain the atmospheric temperature.

(D) The correct answer is $D$.
$1$. Algae and fungi lack a differentiated plant body (root,stem,and leaves),which are the primary sites for transpiration.
$2$. Submerged hydrophytes live entirely underwater and possess vestigial or non-functional stomata,which prevents the process of transpiration.
Therefore,all the mentioned organisms do not exhibit transpiration.

(C) Transpiration efficiency is defined as the amount of dry matter produced per unit of water transpired by the plant.
It is expressed as the ratio of $ \text{Dry matter produced} (\text{kg}) $ to $ \text{Water transpired} (\text{kg}) $.
Therefore, the correct ratio is $ \text{Dry matter produced} / \text{kg of transpired water} $.

(B) The correct answer is $B$.
Transpiration occurs through stomata,cuticle,and lenticels.
Stomatal transpiration accounts for the majority of water loss because stomata are specialized pores that can open and close.
Cuticular transpiration involves the loss of water through the cuticle,which is a waxy,hydrophobic layer covering the epidermis of leaves and stems.
Because the cuticle is a thick,waxy,and relatively impermeable layer,it offers much greater resistance to the diffusion of water vapor compared to the open stomatal pores.
Therefore,the cuticular path provides the greatest resistance to transpiration.

(C) In plant physiology,the movement of water vapor from the leaf to the atmosphere occurs through two parallel pathways: the cuticle and the stomata.
Since these pathways operate in parallel,the total resistance $(R)$ to water vapor diffusion is calculated using the reciprocal sum formula for parallel resistances.
Therefore,the relationship is given by $\frac{1}{R} = \frac{1}{rc} + \frac{1}{rs}$,where $rc$ is the cuticular resistance and $rs$ is the stomatal resistance.

(C) Cobalt chloride paper is blue when dry and turns pink in the presence of moisture.
Since dorsiventral leaves typically have a higher density of stomata on the lower surface (abaxial surface) compared to the upper surface (adaxial surface),the rate of transpiration is significantly higher on the lower side.
Consequently,more water vapor is released from the lower surface,causing the cobalt chloride paper to absorb moisture and turn pink more rapidly.

(B) During the day,the rate of transpiration is high due to sunlight and temperature.
Transpiration creates a negative pressure or tension in the xylem vessels,known as transpiration pull.
This tension causes the xylem vessels to contract slightly,which leads to a measurable shrinkage in the diameter of the tree trunk during the day.

(B) The Cohesion-Tension theory explains the ascent of sap in plants.
According to this theory, the loss of water from the leaves through transpiration creates a negative pressure or tension in the xylem vessels.
This tension pulls the water column upwards from the roots to the leaves due to the cohesive and adhesive properties of water molecules.
Therefore, this theory is directly related to transpiration, and it is also commonly referred to as the $Transpiration \text{ } Pull \text{ } Theory$.

(C) The movement of water through the xylem is primarily driven by the transpiration pull.
As water evaporates from the stomata of leaves (transpiration),it creates a negative pressure or tension in the xylem vessels.
This tension,known as transpiration pull,is strong enough to pull water columns upward against the force of gravity from the roots to the highest points of the plant.

(C) Transpiration is the evaporative loss of water by plants,which occurs primarily through the stomata in the leaves.
This process involves the movement of water vapor from the intercellular spaces of the leaf to the external atmosphere.
Since this movement of water vapor occurs from a region of higher concentration to a region of lower concentration,it is essentially a process of diffusion.

(C) The rate of transpiration is inversely proportional to atmospheric pressure. When atmospheric pressure is low,such as at high altitudes,the air density decreases,which facilitates the diffusion of water vapor from the leaf surface into the surrounding atmosphere. Therefore,the rate of transpiration increases.