Transpiration (General) and Stomata Questions in English

(D) Transpiration is affected by several external and plant factors:
External factors include:
$(1)$ Temperature: Higher temperatures increase the rate of transpiration.
$(2)$ Light: Stomata open in light,increasing transpiration.
$(3)$ Humidity: High humidity decreases the rate of transpiration.
$(4)$ Wind speed: Higher wind speed increases the rate of transpiration.
Plant factors include:
- Number and distribution of stomata.
- Percentage of open stomata.
- Water status of the plant.
- Canopy structure.

(N/A) Transpiration is often described as a 'necessary evil' because it is an inevitable consequence of the physiological processes required for plant survival.
$1$. It creates a transpiration pull,which is essential for the absorption and upward transport of water and minerals from roots to leaves.
$2$. It provides the necessary water for photosynthesis.
$3$. It cools the leaf surfaces,sometimes by $10$ to $15$ $^{\circ}C$,through evaporative cooling.
$4$. It maintains the shape and structure of plants by keeping the cells turgid.
Therefore,while plants lose a significant amount of water through transpiration,it is an unavoidable process that supports vital functions.

(N/A)

Stomata of Monocot	Stomata of Dicot
$(1)$ Guard cells are dumbbell-shaped.	$(1)$ Guard cells are bean-shaped or kidney-shaped.
$(2)$ Subsidiary cells are present and often triangular.	$(2)$ Subsidiary cells may be present or absent; if present,they are not typically triangular.
$(3)$ Epidermal cells are generally rectangular and elongated.	$(3)$ Epidermal cells are irregular in shape.
$(4)$ Stomata are arranged in parallel vertical rows.	$(4)$ Stomata are scattered irregularly.
$(5)$ Stomata are distributed almost equally on both surfaces (isobilateral).	$(5)$ Stomata are more numerous on the lower epidermis than the upper epidermis (dorsiventral).

(N/A) $(1)$ Transpiration serves multiple essential functions for the plant:
$\Rightarrow$ It plays a crucial role in the ascent of sap by creating a transpiration pull.
$\Rightarrow$ It maintains the turgidity of cells,which is essential for structural support.
$\Rightarrow$ It provides the necessary water for photosynthesis in leaves.
$\Rightarrow$ It provides a cooling effect,thereby maintaining the leaf temperature.
$\Rightarrow$ It facilitates the absorption of mineral salts from the soil and their transport to various parts of the plant.
Because it is essential for these vital processes despite causing significant water loss,it is termed a 'necessary evil'.
$(2)$ Water is fundamental for plant life because:
$\Rightarrow$ It is the primary medium for all physiological processes.
$\Rightarrow$ It is a major component of the protoplasm.
$\Rightarrow$ It directly influences the growth and productivity of plants.
$\Rightarrow$ It acts as a solvent for various hormones,enzymes,mineral salts,and nutrients,facilitating their transport throughout the plant body.

(N/A) $(1)$ Guttation: When evaporation is low and excess water collects in the form of droplets around special openings of veins near the tip of grass blades,such water loss in its liquid phase is known as guttation.
$(2)$ Transpiration: Transpiration is the evaporative loss of water by the aerial organs of the plant.

(A) $(1)$ Location: Found on the epidermis of leaves.
Function: Facilitates the exchange of gases ($CO_2$ and $O_2$) and the process of transpiration.
$(2)$ Location: The inner space of the mitochondria,known as the mitochondrial matrix.
Function: It is the site where the enzymes for the Krebs' cycle ($TCA$ cycle) are located,and thus,the Krebs' cycle occurs here.

(N/A) No,different species of plants growing in the same area do not show the same rate of transpiration at a particular time.
Justification:
$1$. Transpiration is influenced by both external (environmental) and internal (plant-specific) factors.
$2$. Internal factors include the number and distribution of stomata,the percentage of open stomata,water status of the plant,and canopy structure.
$3$. Different species have different morphological and anatomical adaptations,such as the thickness of the cuticle,the presence of trichomes,or the depth of stomatal pits (e.g.,xerophytes vs. mesophytes).
$4$. Even if external factors like light intensity,temperature,humidity,and wind speed are identical for both plants,their physiological responses and structural traits lead to different rates of water loss.

(N/A) In the diagram,$(i)$ shows dumbbell-shaped guard cells,while $(ii)$ shows bean-shaped (or kidney-shaped) guard cells.
$(b)$ Dumbbell-shaped guard cells $(i)$ are characteristic of monocot plants (e.g.,grasses). Bean-shaped guard cells $(ii)$ are characteristic of dicot plants.

(A) In $(i)$,the guard cells are turgid. Their outer walls are extended outward,indicating a high water content.
In $(ii)$,the cell is flaccid (shrunken) because it has lost water,which causes the stomatal pore to close.

(C) The element that plays an important role in the opening and closing of stomata is Potassium $(K^+)$.
$1$. During the opening of stomata,$K^+$ ions are actively transported from the surrounding subsidiary cells into the guard cells.
$2$. This accumulation of $K^+$ ions lowers the water potential inside the guard cells.
$3$. Due to the lower water potential,water moves from the surrounding cells into the guard cells via osmosis.
$4$. As water enters,the guard cells become turgid and expand,causing the stomatal pore to open.
$5$. Conversely,the exit of $K^+$ ions leads to the loss of water from the guard cells,making them flaccid and causing the stomata to close.

(A) $\Rightarrow$ The transpiration pull (or suction force) is the primary physiological phenomenon responsible for the upward movement of water in plants, allowing it to reach heights of up to $130 \,m$ through the xylem.
$\Rightarrow$ As water molecules evaporate from the stomata of the leaves, a negative pressure or tension is created in the xylem vessels.
$\Rightarrow$ This tension pulls the continuous column of water upwards from the roots to the leaves due to the cohesive and adhesive properties of water molecules.
$\Rightarrow$ This process effectively overcomes the force of gravity, enabling water to reach the tips of tall trees within a short period.

(B) The process of loss of water in liquid form from the tips of grass leaves or margins of leaves in some herbaceous plants is known as $Guttation$.
This phenomenon usually occurs at night or early morning when the rate of transpiration is very low and root pressure is high.
$Transpiration$ is the loss of water in the form of water vapor.
$Imbibition$ is the absorption of water by solid particles (colloids) causing them to increase in volume.
$Plasmolysis$ is the shrinkage of the protoplast from the cell wall due to water loss in a hypertonic solution.

(D) The stomatal apparatus is a complex structure that includes the stomatal aperture,the two guard cells that regulate its opening and closing,and the surrounding specialized epidermal cells known as subsidiary cells. Together,these components facilitate gas exchange and transpiration in plants.

(A) Stomata $(A)$ are specialized structures present in the epidermis of leaves.
They regulate the process of transpiration (loss of water) and gaseous $(B)$ exchange (oxygen and carbon dioxide).
Each stoma is composed of two bean-shaped cells known as guard $(C)$ cells,which control the opening and closing of the stomatal pore.
Therefore,the correct combination is $A-$ Stomata,$B-$ gaseous,$C-$ guard.

(A) Guttation refers to the exudation of water droplets (in the form of a dilute salt solution) from the margins and tips of leaves.
Guttation water is exuded from a group of leaf cells through specialized openings or pores called hydathodes.
It occurs in some angiosperms like garden nasturtium $(Tropaeolum)$,$Colocasia$,tomato,etc.
It is most noticeable when transpiration is suppressed and relative humidity is high,such as during the night or early morning when root pressure is high.

(D) Transpiration is the process of water loss from the aerial parts of plants in the form of water vapor.
While several environmental factors such as $Temperature$, $Light$, and $Wind$ influence the rate of transpiration, $Relative \text{ } humidity$ is considered the most critical factor.
$Relative \text{ } humidity$ determines the water vapor pressure gradient between the leaf interior (sub-stomatal cavity) and the external atmosphere.
When the $Relative \text{ } humidity$ is low, the air is dry, creating a steep diffusion gradient that facilitates rapid water loss.
Conversely, high $Relative \text{ } humidity$ reduces this gradient, thereby significantly slowing down the rate of transpiration.

(A) Guttation is the process of exudation of liquid droplets from the margins of leaves. This process takes place through specialized pores known as hydathodes. Since these pores remain permanently open and are involved in the release of water,they are also referred to as water stomata.

(B) The processes of water absorption and transpiration occur continuously in plants.
However,approximately $98-99 \%$ of the water absorbed by the plant is lost through the process of transpiration.

(A) The opening and closing of stomata are primarily regulated by the concentration of $K^{+}$ ions in guard cells,the conversion of starch to sugar (and vice versa),and environmental factors like light and $CO_{2}$ concentration.
$N_{2}$ (nitrogen) is an inert gas present in the atmosphere. While it is essential for biological nitrogen fixation by specific bacteria,it does not play a direct role in the physiological mechanism of stomatal movement.
Therefore,the opening of stomata is not affected by $N_{2}$.

(D) According to the active $K^{+}$ transport theory proposed by Levitt,the opening of stomata is primarily driven by the influx of $K^{+}$ ions into the guard cells.
These $K^{+}$ ions are sourced from the adjacent subsidiary and epidermal cells.
Conversely,the closure of stomata is facilitated by the efflux (exertion) of $K^{+}$ and $Cl^{-}$ ions from the guard cells back into the surrounding epidermal tissue,which leads to a decrease in turgor pressure within the guard cells.

(D) Transpiration is categorized based on the plant surface into stomatal,cuticular,lenticular,and bark transpiration.
Stomatal transpiration depends on the opening of stomata,which typically occurs during the day.
In contrast,cuticular transpiration (through the waxy cuticle),lenticular transpiration (through lenticels),and bark transpiration (through the bark) are passive processes that continue throughout both day and night.
Therefore,all the options provided represent types of transpiration that occur continuously.

(A) The loss of water from aerial parts of living plants is known as transpiration.
Transpiration may be stomatal $(80-90\%)$,cuticular $(3-9\%)$,and lenticular $(0.1\%)$.
Transpiration is absent in submerged hydrophytic plants because stomata are completely absent in the leaves of these plants.
Examples of such plants include $Anacharis$ and $Potamogeton$.

(A) Wilting occurs when the rate of transpiration is higher than the rate of water absorption by the roots.
This imbalance leads to a net loss of water from the plant tissues,causing a decrease in turgor pressure within the cells.
As turgor pressure drops,the plant cells lose their rigidity,resulting in the drooping or wilting of leaves and stems.
Transpiration is the evaporative loss of water from the aerial parts of the plant,which can occur through stomata,the cuticle,or lenticels.

(D) The proton $(H^{+}-K^{+})$ transport theory was proposed by Levitt $(1974)$. According to this theory,there is an accumulation of $K^{+}$ ions in the guard cells during the daytime. This accumulation leads to a decrease in the water potential of the guard cells. Consequently,water enters the guard cells via endosmosis,causing them to become turgid,which results in the opening of the stomata.

(A) The $ABA$ (Abscisic Acid) theory is considered the most recent explanation for the mechanism of stomatal closure,proposed by Cowan et al. in $1982$.
According to this theory,the synthesis of abscisic acid during water stress (drought) or mid-day conditions promotes the reversal of the $H^+ \rightleftharpoons K^+$ pump.
This leads to an increase in the concentration of $H^+$ ions within the guard cell cytoplasm,causing the efflux of $K^+$ ions and water,which results in the closure of the stomata.
The active $K^+$ transport theory,which explains the opening and closing of stomata,was initially proposed by Imamura $(1943)$ and Fujino $(1967)$,while the Proton $(H^+-K^+)$ transport theory was proposed by Levitt $(1974)$.

(C) The diagram depicts the demonstration of transpiration using a bell jar experiment.
In this experiment,a potted plant is placed on a slab,and a dry bell jar is inverted over it.
After sealing the edges of the jar with wax or petroleum jelly,the apparatus is left undisturbed.
After some time,the inner surface of the bell jar becomes misty due to the water vapor released by the plant through the process of transpiration.

(C) When a twig is placed in water containing salt,the surrounding solution becomes hypertonic relative to the plant cells.
This hypertonic environment reduces the rate of water loss from the twig through transpiration because the water potential gradient is minimized.
Additionally,the presence of salt creates an environment that inhibits the growth of bacteria,which would otherwise cause the twig to decay or wilt prematurely.
Therefore,the twig remains fresh for a longer period primarily due to the decrease in the rate of transpiration and the inhibition of bacterial activity.

(A) The most significant physiological feature of stomata is their response to light.
Generally,stomata open in the daytime (i.e.,in the presence of light) and close at night or in darkness. These are called photoactive stomata.
However,in succulent plants like $Kalanchoe$ of the family $Crassulaceae$,the stomata open at night and close during the daytime.
Such stomata are called scotoactive stomata.
Since light is the primary environmental factor influencing the opening and closing mechanism in most plants,it is the main regulator.

(B) Transpiration is the manifestation of turgor pressure.
More than $95 \%$ of the total water loss occurs through the stomata of leaves.
The mechanism of opening and closing of stomata is regulated by the turgidity of the guard cells,which is a direct result of changes in turgor pressure.

(D) According to the proton transport theory proposed by Levitt $(1974)$,the opening of stomata is driven by the active uptake of potassium ions $(K^+)$ into the guard cells.
To maintain electrical neutrality,the uptake of $K^+$ ions is balanced by the uptake of chloride ions $(Cl^-)$.
Additionally,starch is converted into malic acid,which dissociates into hydrogen ions $(H^+)$ and malate ions.
The accumulation of these solutes (malate,$K^+$,and $Cl^-$) in the vacuoles decreases the water potential of the guard cells,leading to the influx of water via osmosis,which causes the stomata to open.

(C) The opening of stomata is primarily explained by the active $K^+$ transport theory. The sequence of events for stomatal opening is as follows:
$1$. $III.$ Rise of potassium ion $(K^+)$ level in guard cells: During the day,$K^+$ ions are actively transported into the guard cells.
$2$. $I.$ Lowering of osmotic potential of guard cells: The accumulation of $K^+$ ions increases the solute concentration,thereby lowering the osmotic potential of the guard cells.
$3$. $IV.$ Guard cells absorb water from neighbouring epidermal cells: Due to the lower osmotic potential,water enters the guard cells via endosmosis.
$4$. $VI.$ Guard cells swell and create a pore between them: The influx of water increases the turgor pressure,causing the guard cells to swell and open the stomatal pore.
Therefore,the correct sequence is $III, I, IV, VI$.

(B) Statement $I$ is correct: $PMA$ (Phenylmercuric acetate) and low-viscosity silicon oils act as antitranspirants.
Statement $II$ is correct: $BAP$ (Benzylaminopurine),$NAA$ (Naphthalene acetic acid),and cobalt chloride are known to act as antitranspirants.
Statement $III$ is correct: Abscisic acid $(ABA)$ induces stomatal closure.
Statement $IV$ is incorrect: Starch in guard cells is converted into sugar (glucose) or organic acids,not directly into $PEP$ ions via simple hydrolysis.
Statement $V$ is incorrect: $A$ potometer works on the principle that the amount of water absorbed by the plant is approximately equal to the amount of water transpired.
Statement $VI$ is incorrect: Transpiration rate is inversely proportional to relative humidity. High humidity reduces the water potential gradient,thereby decreasing the rate of transpiration.

(B) Hydathodes are specialized pores or openings found at the vein endings of leaves. They facilitate the exudation of water in the form of liquid droplets from the interior of the plant to its surface,a process known as $Guttation$.

(D) When stomata are open,they facilitate several physiological processes:
$1$. Exchange of gases: $O_2$ is released and $CO_2$ is taken in during photosynthesis.
$2$. Evaporation of water: This process,known as transpiration,allows water vapor to escape from the leaf surface.
$3$. Uptake of carbon dioxide: $CO_2$ enters the leaf through the stomata to be used in the Calvin cycle.
Therefore,all the listed options are correct.

(A) Transpiration is the process of water loss from the aerial parts of plants.
$A$. Sunlight: Increases temperature and triggers stomatal opening,which increases transpiration.
$B$. Darkness: Causes stomata to close,which decreases transpiration.
$C$. High humidity: Reduces the water potential gradient between the leaf interior and the atmosphere,decreasing transpiration.
$D$. High speed winds: While wind can increase transpiration by removing the boundary layer,sunlight is the primary factor that directly influences the physiological opening of stomata. However,in the context of standard biology questions,sunlight is the most significant factor that promotes transpiration by opening stomata.

(B) The guard cells of stomata possess cellulose microfibrils that are oriented radially rather than longitudinally. This specific radial orientation is crucial because it allows the guard cells to expand more in length than in width when they become turgid,which pulls the inner walls apart and opens the stomatal pore.

(C) According to Levitt's potassium pump theory:
- During the day,starch is incompletely oxidized to $PEP$ (Phosphoenolpyruvate) in the guard cells.
- $PEP$ is then converted into malic acid,which dissociates into malate ions and protons $(H^+)$ within the guard cells.
- Protons $(H^+)$ are actively pumped out of the guard cells into the subsidiary cells,while $K^+$ ions are taken up into the guard cells.
- The accumulation of potassium malate increases the osmotic pressure $(OP)$ of the guard cells,leading to water influx and stomatal opening.

(D) - In a dry atmosphere,the relative humidity is low,which increases the water potential gradient between the leaf interior and the atmosphere,thereby increasing the rate of transpiration.
- $A$ slow breeze removes the humid air surrounding the leaf surface,replacing it with drier air,which promotes the rate of transpiration.
- $ABA$ (Abscisic acid) inhibits transpiration by inducing stomatal closure; therefore,it is known as a stress hormone.
- $A$ high salt concentration in soil water lowers the water potential of the soil,making it difficult for plants to absorb water,which decreases the rate of transpiration.

(B) Transpiration is the process of water loss from plants in the form of water vapor.
It is most rapid under conditions that favor evaporation.
High temperature increases the kinetic energy of water molecules,facilitating their escape into the atmosphere.
Low humidity creates a steep water potential gradient between the leaf interior and the surrounding air,promoting faster diffusion.
Turgid guard cells ensure that the stomata remain open,allowing for the exit of water vapor.
Moist soil ensures that the plant has an adequate supply of water to maintain this process without wilting.

(C) The correct answer is $C$. During the process of stomatal opening (photoactive),the following events occur:
$1$. The $pH$ of guard cells increases due to the dissociation of malic acid into malate ions and $H^+$ ions.
$2$. Starch in the guard cells undergoes hydrolysis to form phosphoenolpyruvate $(PEP)$.
$3$. Malic acid dissociates into malate ions and $H^+$ ions.
$4$. As a result of these processes,the osmotic potential of the guard cells decreases,causing water to enter the guard cells from the subsidiary cells via osmosis. This increases the turgor pressure $(TP)$ of the guard cells,not the subsidiary cells,leading to the opening of the stomata.
Therefore,an increase in the $TP$ of subsidiary cells does not occur; instead,their $TP$ decreases as they lose water to the guard cells.

(A) In the guard cells of the stomata,the cellulose microfibrils are arranged radially rather than longitudinally. This radial arrangement is crucial for the opening and closing mechanism of the stomata. Therefore,the statement that they are arranged longitudinally is incorrect.

(A) During stomatal opening,potassium ions $(K^+)$ accumulate in the guard cells,which lowers their water potential. As a result,water enters the guard cells from the surrounding subsidiary cells via osmosis. This influx of water increases the Turgor Pressure $(TP)$ of the guard cells,causing them to swell and open the stoma. Conversely,the loss of water from the subsidiary cells leads to a decrease in their $TP$. Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the change in $TP$ leading to stomatal opening.

(C) The Assertion is correct because water is constantly absorbed by roots and lost through transpiration,making its presence in the plant transient.
The Reason is incorrect because less than $1\%$ of the water reaching the leaves is used in photosynthesis and plant growth,not more than $1\%$.
Therefore,the correct option is $C$.

(B) According to the proton transport theory,proposed by Levitt $(1974)$,the regulation of stomata (i.e.,opening and closing) depends upon the active entry and exit of potassium ions $(K^+)$ in the guard cells.
During the day,starch is converted into malic acid in the guard cells,which dissociates into malate ions and protons $(H^+)$.
The protons are pumped out of the guard cells,and in exchange,potassium ions $(K^+)$ are taken up from the surrounding subsidiary cells.
This accumulation of $K^+$ ions decreases the water potential of the guard cells,leading to the influx of water,which causes the stomata to open.

(N/A) The stomata are structures present in the epidermis of leaves. They consist of a stomatal pore,guard cells,and surrounding subsidiary cells.
$1$. Dicot Stomata: These possess bean-shaped or kidney-shaped guard cells. The guard cells contain chloroplasts and regulate the opening and closing of the stomatal pore.
$2$. Monocot Stomata: These possess dumb-bell shaped guard cells. The outer walls of these guard cells are thin,while the inner walls are thick.
Refer to the provided image for the detailed labelling of both types of stomata.

(D) The differences between guttation and transpiration are as follows:
$1$. Definition: Guttation is the loss of water in the form of liquid droplets from the margins of leaves through specialized pores called hydathodes. Transpiration is the evaporative loss of water from the aerial parts of the plant,primarily through stomata.
$2$. State of Water: In guttation,water is lost in liquid form. In transpiration,water is lost in the form of water vapor.
$3$. Site of Loss: Guttation occurs through hydathodes (water pores). Transpiration occurs mainly through stomata,and to a lesser extent through cuticles and lenticels.
$4$. Timing: Guttation typically occurs during the night or early morning when root pressure is high and transpiration is low. Transpiration occurs primarily during the day when stomata are open.
$5$. Solutes: The liquid lost during guttation contains various dissolved salts and organic substances. The water vapor lost during transpiration is pure water.

(N/A) Transpiration is considered a 'necessary evil' because it is an inevitable process that has both advantages and disadvantages for the plant.
$1$. Necessity: It is essential for the absorption and upward movement of water and minerals from the soil to the leaves (transpiration pull). It also helps in cooling the leaf surface and maintaining the turgidity of plant cells.
$2$. Evil: It leads to a significant loss of water. If the rate of transpiration exceeds the rate of water absorption by the roots,it causes water stress,leading to wilting,physiological damage,and potentially the death of the plant.

(B) $\Rightarrow$ When evaporation is low and excess water collects in the form of droplets around special openings of veins near the tip of grass blades and leaves of many herbaceous plants,this water loss in its liquid phase is known as guttation.
$\Rightarrow$ Guttation occurs due to high root pressure,which pushes water out through specialized pores called hydathodes.
$\Rightarrow$ Root pressure can at best,only provide a modest push in the overall process of water transport.

(B) The stomatal apparatus is a specialized structure found in the epidermis of leaves.
It is composed of three main parts:
$1$. The stomatal aperture (the central pore).
$2$. The guard cells (two specialized kidney-shaped or dumbbell-shaped cells surrounding the pore).
$3$. The subsidiary cells (specialized epidermal cells surrounding the guard cells).
Therefore,the correct composition is Stomatal aperture + Guard cells + Subsidiary cells.

(D) In the provided diagram of a stoma:
$1$. $R$ represents the bean-shaped cells that regulate the opening and closing of the stoma,known as Guard cells.
$2$. $Q$ represents the specialized cells surrounding the guard cells,known as Subsidiary cells.
$3$. $P$ represents the ordinary cells of the epidermis,known as Epidermal cells.
Therefore,the correct identification is $P=$ Epidermal cell,$Q=$ Subsidiary cell,$R=$ Guard cell.